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  • 1.
    Andersson, David C.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Martinez, N.
    Zeller, D.
    Rondahl, S. H.
    Koza, M. M.
    Frick, B.
    Ekstrom, F.
    Peters, J.
    Linusson, Anna
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Changes in dynamics of alpha-chymotrypsin due to covalent inhibitors investigated by elastic incoherent neutron scattering2017Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, nr 37, s. 25369-25379Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An essential role of enzymes is to catalyze various chemical reactions in the human body and inhibition of the enzymatic activity by small molecules is the mechanism of action of many drugs or tool compounds used to study biological processes. Here, we investigate the effect on the dynamics of the serine protease alpha-chymotrypsin when in complex with two different covalently bound inhibitors using elastic incoherent neutron scattering. The results show that the inhibited enzyme displays enhanced dynamics compared to the free form. The difference was prominent at higher temperatures (240-310 K) and the type of motions that differ include both small amplitude motions, such as hydrogen atom rotations around a methyl group, and large amplitude motions, such as amino acid side chain movements. The measurements were analyzed with multivariate methods in addition to the standard univariate methods, allowing for a more in-depth analysis of the types of motions that differ between the two forms. The binding strength of an inhibitor is linked to the changes in dynamics occurring during the inhibitor-enzyme binding event and thus these results may aid in the deconvolution of this fundamental event and in the design of new inhibitors.

  • 2.
    Andersson, Ove
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Brant Carvalho, Paulo H. B.
    Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, Sweden.
    Häussermann, Ulrich
    Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, Sweden.
    Hsu, Ying-Jui
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Evidence suggesting kinetic unfreezing of water mobility in two distinct processes in pressure-amorphized clathrate hydrates2022Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 24, nr 34, s. 20064-20072Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Type II clathrate hydrates (CHs) with tetrahydrofuran (THF), cyclobutanone (CB) or 1,3-dioxolane (DXL) guest molecules collapse to an amorphous state near 1 GPa on pressurization below 140 K. On subsequent heating in the 0.2-0.7 GPa range, thermal conductivity and heat capacity results of the homogeneous amorphous solid show two glass transitions, first a thermally weak glass transition, GT1, near 130 K; thereafter a thermally strong glass transition, GT2, which implies a transformation to an ultraviscous liquid on heating. Here we compare the GTs of normal and deuterated samples and samples with different guest molecules. The results show that GT1 and GT2 are unaffected by deuteration of the THF guest and exchange of THF with CB or DXL, whereas the glass transition temperatures (Tgs) shift to higher temperatures on deuteration of water; Tg of GT2 increases by 2.5 K. These results imply that both GTs are associated with the water network. This is corroborated by the fact that GT2 is detected only in the state which is the amorphized CH's counterpart of expanded high density amorphous ice. The results suggest a rare transition sequence of an orientational glass transition followed by a glass to liquid transition, i.e., kinetic unfreezing of H2O reorientational and translational mobility in two distinct processes.

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  • 3. Arafa, Wael A. A.
    et al.
    Kärkäs, Markus D.
    Lee, Bao-Lin
    Åkermark, Torbjörn
    Liao, Rong-Zhen
    Berends, Hans-Martin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Messinger, Johannes
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Siegbahn, Per E. M.
    Åkermark, Björn
    Dinuclear manganese complexes for water oxidation: evaluation of electronic effects and catalytic activity2014Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, nr 24, s. 11950-11964Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During recent years significant progress has been made towards the realization of a sustainable and carbon-neutral energy economy. One promising approach is photochemical splitting of H2O into O-2 and solar fuels, such as H-2. However, the bottleneck in such artificial photosynthetic schemes is the H2O oxidation half reaction where more efficient catalysts are required that lower the kinetic barrier for this process. In particular catalysts based on earth-abundant metals are highly attractive compared to catalysts comprised of noble metals. We have now synthesized a library of dinuclear Mn-2 (II,III) catalysts for H2O oxidation and studied how the incorporation of different substituents affected the electronics and catalytic efficiency. It was found that the incorporation of a distal carboxyl group into the ligand scaffold resulted in a catalyst with increased catalytic activity, most likely because of the fact that the distal group is able to promote proton-coupled electron transfer (PCET) from the high-valent Mn species, thus facilitating O-O bond formation.

  • 4. Beranová, Lenka
    et al.
    Humpolíčková, Jana
    Sýkora, Jan
    Benda, Aleš
    Cwiklik, Lukasz
    Jurkiewicz, Piotr
    Gröbner, Gerhard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Hof, Martin
    Effect of heavy water on phospholipid membranes: experimental confirmation of molecular dynamics simulations2012Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 14, nr 42, s. 14516-14522Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Although there were experimental indications that phospholipid bilayers hydrated with D(2)O express different biophysical properties compared with hydration by ordinary H(2)O, a molecular concept for this behavior difference was only recently proposed by a molecular dynamics simulations study [T. Róg et al., J. Phys. Chem. B, 2009, 113, 2378-2387]. Here we attempt to verify those theoretical predictions by fluorescence measurements on 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membranes. Specifically, we determine the water isotope effect on headgroup hydration and mobility, lateral lipid diffusion and lipid backbone packing. Time-dependent fluorescence shift experiments show significantly slower dynamics and lower hydration of the headgroup region for a bilayer hydrated with D(2)O, an observation in good agreement with the calculated predicted differences in duration of lipid-lipid and lipid-water bridges and extent of water penetration into the bilayer, respectively. The water isotope effect on the lipid order parameter of the bilayer core (measured by fluorescence anisotropy) and lateral diffusion of lipid molecules (determined by two-focus fluorescence correlation spectroscopy) is close to the experimental errors of the experiments, however also refers to slightly more rigid organization of phospholipid bilayers in heavy water. This study confirms the view that the water isotope effect can be particularly found in time-resolved physicochemical properties of the membrane. Together with the simulations our experiments provide a comprehensive, molecular view on the effect of D(2)O on phospholipid bilayers.

  • 5.
    Boily, Jean-François
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Elucidation of oxyanion coordination geometries at solid surfaces of varied electric field strengths2009Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 11, nr 37, s. 8133-5Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Density functional theory calculations of oxyanions exposed to external electric fields revealed systematic variations in molecular geometries and vibration stretching frequencies. These variations can be used in laboratory studies to determine coordination geometries of oxyanions adsorbed on solid surfaces using infrared spectroscopy.

  • 6.
    Boily, Jean-François
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Rosso, Kevin M
    Crystallographic controls on uranyl binding at the quartz/water interface2011Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, nr 17, s. 7845-7851Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Molecular dynamics methods were used to simulate UO(2)(OH)(2)(0) binding to pairs of oxo sites (O(S)) on three low-index planes of α-SiO(2) in contact with water. Differences in binding site distributions on the (001), (010) and (101) planes produced distinct sets of stable U inner-sphere species. Steric constraints prevented bidentate coordination to the (001) surface, resulting in a mononuclear monodentate complex, [UO(2)(OH)(2)(H(2)O)(n)O(S)] (90% for n = 1 and 10% for n = 2 over 5 ns production runs). Binuclear bidentate coordination, [UO(2)(OH)(2)(H(2)O)(n)(O(S))(2)], was however favored on the (010) (99% for n = 0 and 1% for n = 1) and the (101) (72% for n = 0 and 28% for n = 1) planes. These results underscore a predominant four-coordinated equatorial shell for U when complexed to the quartz/water interface. Potential of mean force calculations uncovered a diversity of metastable outer- and inner-sphere complexes at local energy minima up to ∼0.4 nm from the surface. These calculations point to important differences in both energetic requirements and mechanisms for the approach of UO(2)(OH)(2)(0) to different quartz surfaces. Binding strengths are affected by binding site distribution, steric freedom, U hydration and OH orientation, and increase in the order (001) (3.7 kJ mol(-1)) < (101) (5.6 kJ mol(-1)) < (010) (6.5 kJ mol(-1)). A general binding mechanism involves (1) formation of monodentate outer-sphere complexes, (2) removal of oxo-bound waters, (3) formation of one (monodentate), then two (bidentate) direct U-O(S) bonds (inner-sphere), and (4) expulsion of excessive waters from the equatorial shell of U.

  • 7. Bonev, Boyan
    et al.
    Watts, Anthony
    Bokvist, Marcus
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Gröbner, Gerhard
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Electrostatic peptide-lipid interactions of amyloid-β peptide and pentalysine with membrane surfaces monitored by 31P MAS NMR2001Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 3, nr 14, s. 2904-2910Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High-resolution 31P magic angle spinning (MAS) NMR spectroscopy is presented as a direct and non-perturbing method for measuring changes in surface charge density occurring in mixed phospholipid membranes upon binding of charged surface-active peptides. 31P MAS NMR was used to investigate mixed lipid membranes of neutral phosphatidylcholine and negatively charged phosphatidylglycerol where the molar fraction of the charged lipid was varied from 0 to 1. The chemical shifts of the  individual membrane lipids showed a simple variation in response to changes in the fraction of the negatively charged component phosphatidylglycerol. Addition of the positively charged amyloid-β1-40 peptide, a key substance in Alzheimer's disease, resulted in changes in the isotropic chemical shifts of the membrane lipid phosphates in a way consistent with reduction in the negative surface charge of the mixed lipid bilayers. Binding of different amounts of the positively charged peptide pentalysine to L-α-dioleoylphosphatidylcholine/L-α-dioleoylphosphatidylglycerol(DOPC/DOPG) vesicles (2 : 1 molar ratio) also showed a systematic variation of both chemical shift values. These changes were described by a simple two-site model and indicate purely electrostatic binding of pentalysine.

  • 8.
    Boulanger, Nicolas
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Yu, Victor
    Hilke, Michael
    Toney, Michael F.
    Barbero, David R.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Graphene induced electrical percolation enables more efficient charge transport at a hybrid organic semiconductor/graphene interface2018Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, nr 6, s. 4422-4428Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Self-assembly of semiconducting polymer chains during crystallization from a liquid or melt dictates to a large degree the electronic properties of the resulting solid film. However, it is still unclear how charge transport pathways are created during crystallization. Here, we performed complementary in situ electrical measurements and synchrotron grazing incidence X-ray diffraction (GIXD), during slow cooling from the melt of highly regio-regular poly(3-hexylthiophene) (P3HT) films deposited on both graphene and on silicon. Two different charge transport mechanisms were identified, and were correlated to the difference in crystallites' orientations and overall amount of crystallites in the films on each surface as molecular self-assembly proceeded. On silicon, a weak charge transport was enabled as soon as the first edge-on lamellae formed, and further increased with the higher amount of crystallites (predominantly edge-on and randomly oriented lamellae) during cooling. On graphene however, the current remained low until a minimum amount of crystallites was reached, at which point interconnection of conducting units (face-on, randomly oriented lamellae and tie-chains) formed percolated conducting pathways across the film. This lead to a sudden rapid increase in current by approximate to 10 fold, and strongly enhanced charge transport, despite a much lower amount of crystallites than on silicon.

  • 9.
    Boulanger, Nicolas
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. Nano-Engineered Materials and Organic Electronics Laboratory.
    Yu, Victor
    Hilke, Michael
    Toney, Michael F.
    Barbero, David R.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. Nano-Engineered Materials and Organic Electronics Laboratory.
    In situ probing of the crystallization kinetics of rr-P3HT on single layer graphene as a function of temperature2017Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, nr 12, s. 8496-8503Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We studied the molecular packing and crystallization of a highly regio-regular semiconducting polymer poly(3-hexylthiophene) (P3HT) on both single layer graphene and silicon as a function of temperature, during cooling from the melt. The onset of crystallization, crystallites' size, orientation, and kinetics of formation were measured in situ by synchrotron grazing incidence X-ray diffraction (GIXD) during cooling and revealed a very different crystallization process on each surface. A favored crystalline orientation with out of plane pi-pi stacking formed at a temperature of 200 degrees C on graphene, whereas the first crystallites formed with an edge-on orientation at 185 degrees C on silicon. The crystallization of face-on lamellae revealed two surprising effects during cooling: (a) a constant low value of the pi-pi spacing below 60 degrees C; and (b) a reduction by half in the coherence length of face-on lamellae from 100 to 30 degrees C, which corresponded with the weakening of the 2nd or 3rd order of the in-plane (k00) diffraction peak. The final ratio of face-on to edge-on orientations was 40% on graphene, and 2% on silicon, revealing the very different crystallization mechanisms. These results provide a better understanding of how surfaces with different chemistries and intermolecular interactions with the polythiophene polymer chains lead to different crystallization processes and crystallites orientations for specific electronic applications.

  • 10.
    Brant Carvalho, Paulo H. B.
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, Sweden.
    Ivanov, Mikhail
    Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, Sweden.
    Andersson, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Loerting, Thomas
    Institute of Physical Chemistry, University of Innsbruck, Innsbruck, Austria.
    Bauer, Marion
    Institute of Physical Chemistry, University of Innsbruck, Innsbruck, Austria.
    Tulk, Chris A.
    Oak Ridge National Laboratory, Oak Ridge, TN, USA.
    Haberl, Bianca
    Oak Ridge National Laboratory, Oak Ridge, TN, USA.
    Daemen, Luke L.
    Oak Ridge National Laboratory, Oak Ridge, TN, USA.
    Molaison, Jamie J.
    Oak Ridge National Laboratory, Oak Ridge, TN, USA.
    Amann-Winkel, Katrin
    Institute of Physical Chemistry, University of Innsbruck, Innsbruck, Austria.
    Lyubartsev, Alexander P.
    Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, Sweden.
    Bull, Craig L.
    ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Oxon, Didcot, United Kingdom; School of Chemistry, University of Edinburgh, David Brewster Road, Edinburgh, UK.
    Funnell, Nicholas P.
    ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Oxon, Didcot, UK.
    Häussermann, Ulrich
    Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, Sweden.
    Neutron scattering study of polyamorphic THF·17(H2O): toward a generalized picture of amorphous states and structures derived from clathrate hydrates2023Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 25, nr 21, s. 14981-14991Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    From crystalline tetrahydrofuran clathrate hydrate, THF-CH (THF·17H2O, cubic structure II), three distinct polyamorphs can be derived. First, THF-CH undergoes pressure-induced amorphization when pressurized to 1.3 GPa in the temperature range 77-140 K to a form which, in analogy to pure ice, may be called high-density amorphous (HDA). Second, HDA can be converted to a densified form, VHDA, upon heat-cycling at 1.8 GPa to 180 K. Decompression of VHDA to atmospheric pressure below 130 K produces the third form, recovered amorphous (RA). Results from neutron scattering experiments and molecular dynamics simulations provide a generalized picture of the structure of amorphous THF hydrates with respect to crystalline THF-CH and liquid THF·17H2O solution (∼2.5 M). Although fully amorphous, HDA is heterogeneous with two length scales for water-water correlations (less dense local water structure) and guest-water correlations (denser THF hydration structure). The hydration structure of THF is influenced by guest-host hydrogen bonding. THF molecules maintain a quasiregular array, reminiscent of the crystalline state, and their hydration structure (out to 5 Å) constitutes ∼23H2O. The local water structure in HDA is reminiscent of pure HDA-ice featuring 5-coordinated H2O. In VHDA, the hydration structure of HDA is maintained but the local water structure is densified and resembles pure VHDA-ice with 6-coordinated H2O. The hydration structure of THF in RA constitutes ∼18 H2O molecules and the water structure corresponds to a strictly 4-coordinated network, as in the liquid. Both VHDA and RA can be considered as homogeneous.

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  • 11.
    de Lichtenberg, Casper
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Messinger, Johannes
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. Molecular Biomimetics, Department of Chemistry – Ångström, Uppsala University, Uppsala, Sweden.
    Substrate water exchange in the S2 state of photosystem II is dependent on the conformation of the Mn4Ca cluster2020Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 22, nr 23, s. 12894-12908Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In photosynthesis, dioxygen formation from water is catalyzed by the oxygen evolving complex (OEC) in Photosystem II (PSII) that harbours the Mn4Ca cluster. During catalysis, the OEC cycles through five redox states, S0 to S4. In the Sstate, the Mn4Ca cluster can exist in two conformations, which are signified by the low-spin (LS) g = 2 EPR multiline signal and the high-spin (HS) g = 4.1 EPR signal. Here, we employed time-resolved membrane inlet mass spectrometry to measure the kinetics of H218O/H216O exchange between bulk water and the two substrate waters bound at the Mn4Ca cluster in the SLS2, SHS2, and the S3 states in both Ca-PSII and Sr-PSII core complexes from T. elongatus. We found that the slowly exchanging substrate water exchanges 10 times faster in the SHS2 than in the SLS2 state, and that the SLS2 → SHS2 conversion has at physiological temperature an activation barrier of 17 ± 1 kcal mol−1. Of the presently suggested SHS2 models, our findings are best in agreement with a water exchange pathway involving a SHS2state that has an open cubane structure with a hydroxide bound between Ca and Mn1. We also show that water exchange in the S3 state is governed by a different equilibrium than in S2, and that the exchange of the fast substrate water in the Sstate is unaffected by Ca/Sr substitution. These findings support that (i) O5 is the slowly exchanging substrate water, with W2 being the only other option, and (ii) either W2 or W3 is the fast exchanging substrate. The three remaining possibilities for O–O bond formation in PSII are discussed.

    Fulltekst (pdf)
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  • 12.
    Driver, Gordon W.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Huang, Yang
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Laaksonen, Aatto
    Sparrman, Tobias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Wang, Yonglei
    Westlund, Per-Olof
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Correlated/non-correlated ion dynamics of charge-neutral ion couples: the origin of ionicity in ionic liquids2017Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, nr 7, s. 4975-4988Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Proton/Fluoride spin-lattice ($T_1$) nuclear magnetic relaxation dispersion (NMRD) measurements of 1-butyl-3-methyl-$1H$-imidazolium hexa-fluorophosphate, [$C_4mim][PF_6]$, have been carried out using high field spectrometers and fast-field-cycling instrument at proton Larmor frequencies ranging from 10kHz to 40 MHz, at different temperatures. The NMRD profiles are interpreted by means of a simple relaxation model based on the inter- and intra-ionic dipole-dipole relaxation mechanism. Using an atomic molecular-ion dynamic simulation at 323 K the relevant spin dipole-dipole(DD) correlation functions are calculated. The results indicate the NMRD profiles can be rationalized using intra- and inter-ionic spin DD interactions, however, both are mainly modulated by ionic reorientation because of temporary correlations with cations, where modulation by translational diffusion plays a minor role. Reorientational dynamics of charge-neutral ion couples (i.e. $[C_4mim]^{...}[PF_6]$) and $[C_4mim]^{+}$ ions are in the nano-second (ns) time range whereas the reorientation of $[PF_6]{^-}$ is characterized by a reorientational correlation time in the pico-second (ps) regime. Based on the NMRD profiles we conclude the main relaxation mechanism for $[PF_6]{^-}$ is, due to fast internal reorientational motion, a partially averaged F-F intra and a F-H inter-ionic DD coupling as the anion resides in close proximity to its temporary oppositely charged cation partner. The F-$T_1$- NMRD data display a ns dispersions which is interpreted as being due to correlated reorientational modulations resultant from H-containing charge-neutral ion couple $[C_4mim]^{...}[PF_6]$. The analysis of ionicity is based on the free anion fraction, $f$ and it increase with temperature with $f$ $\rightarrow$ 1 at the highest temperatures investigated. The fraction is obtained from the H-F NMRD profiles as correlated-non-correlated dynamics of the ions. The analysis of $T_1$ relaxation rates of C, H, F and P at high fields cannot generally give the fraction of ion but are consistent with the interpretation based on the NMRD profiles with relaxation contributions due to DD-intra and -inter, CSA-intra (and -inter for C), including spin rotation for P. The investigation has led to a description of the mechanics governing ion transport in the title ionic liquid via identification of transient correlated/non-correlated ion dynamics.

    Fulltekst (pdf)
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  • 13.
    Han, Guangye
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, USA .
    Huang, Yang
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Koua, Faisal Hammad Mekky
    Graduate School of Natural Science and Technology, Department of Biology, Faculty of Science, Okayama University, Tsushima, Japan .
    Shen, Jian-Ren
    Graduate School of Natural Science and Technology, Department of Biology, Faculty of Science, Okayama University, Tsushima, Japan.
    Westlund, Per-Olof
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Messinger, Johannes
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Hydration of the oxygen-evolving complex of photosystem II probed in the dark-stable S1 state using proton NMR dispersion profiles2014Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, nr 16, s. 11924-11935Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The hydration of the oxygen-evolving complex (OEC) was characterized in the dark stable S1 state of photosystem II using water R1(ω) NMR dispersion (NMRD) profiles. The R1(ω) NMRD profiles were recorded over a frequency range from 0.01 MHz to 40 MHz for both intact and Mn-depleted photosystem II core complexes from Thermosynechococcus vulcanus (T. vulcanus). The intact-minus-(Mn)-depleted difference NMRD profiles show a characteristic dispersion from approximately 0.03 MHz to 1 MHz, which is interpreted on the basis of the Solomon-Bloembergen-Morgan (SBM) and the slow motion theories as being due to a paramagnetic enhanced relaxation (PRE) of water protons. Both theories are qualitatively consistent with the ST = 1, g = 4.9 paramagnetic state previously described for the S1 state of the OEC; however, an alternative explanation involving the loss of a separate class of long-lived internal waters due to the Mn-depletion procedure can presently not be ruled out. Using a point-dipole approximation the PRE-NMRD effect can be described as being caused by 1-2 water molecules that are located about 10 Å away from the spin center of the Mn4CaO5 cluster in the OEC. The application of the SBM theory to the dispersion observed for PSII in the S1 state is questionable, because the parameters extracted do not fulfil the presupposed perturbation criterion. In contrast, the slow motion theory gives a consistent picture indicating that the water molecules are in fast chemical exchange with the bulk (τw < 1 μs). The modulation of the zero-field splitting (ZFS) interaction suggests a (restricted) reorientation/structural equilibrium of the Mn4CaO5 cluster with a characteristic time constant of τZFS = 0.6-0.9 μs.

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  • 14.
    Huang, Yang
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Nam, Kwangho
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Westlund, Per-Olof
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    The water R1(ω) NMRD profiles of a hydrated protein from molecular dynamics simulation2013Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, nr 33, s. 14089-14097Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

     The hydration of a protein, peroxiredoxin 5, is obtained from a molecular dynamics simulation and compared with the picture of hydration which is obtained by analysing the water proton R1 NMRD profiles using a generally accepted relaxation model [K. Venu, V.P. Denisov and B. Halle, J. Am. Chem. Soc. 119,3122(1997)]. The discrepancy between the hydration pictures derived from the water R1 0)-NMRD profiles and MD is relevant in a discussion of the factors behind the stretched NMRD profile, the distribution of orientationalorder parameters and residence times of buried water used in the NMRD model.

    Fulltekst (pdf)
    fulltext
  • 15.
    Håkansson, Pär
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Westlund, Per-Olof
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Nuclear magnetic relaxation study of the microstructure of a bicontinuous cubic phase2004Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, nr 6, s. 4321-4329Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A NMR relaxation and NMR translational diffusion study is performed on a bicontinuous cubic phase of the dodecyltrimethylammonium chloride/2H2O system with low water content. It is demonstrated how NMR relaxation measurements are combined with structural investigations of X-ray and NMR molecular diffusion measurements to create a consistent picture of the mesoscopic structure of the cubic phase. The 14N, spin-lattice (R1) and spin-spin relaxation rates (R2), were measured for the surfactant at two different field strengths and at four temperatures. The water and the surfactant translational diffusion coefficients were measured by NMR field gradient technique. The experimental spin relaxation rates, and translation diffusion coefficients were interpreted in a model based on a Brownian dynamics (BD) simulation of translational diffusion along curved interfaces (P. Håkansson, L. Persson and P.-O. Westlund, J. Chem. Phys., 2002,117(19), 8634-8643, ). The model surfaces used in our BD relaxation model are also frequently used in interpretations of X-ray crystallography and in free energy calculations on bicontinuous phases. One of our BD-models was able to quantify the influence of the water/lipid interface on the NMR relaxation and diffusion data. Together with X-ray data, a consistent picture of the microstructure for this system was obtained.

  • 16.
    Håkansson, Pär
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Westlund, Per-Olof
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Lindahl, Erik
    Edholm, Olle
    A direct simulation of EPR slow-motion spectra of spin labelled phospholipids in liquid crystalline bilayers based on a molecular dynamics simulation of the lipid dynamics2001Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 3, nr 23, s. 5311-5319Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    EPR line shapes can be calculated from the stochastic Liouville equation assuming a stochastic model for the reorientation of the spin probe. Here we use instead and for the first time a detailed molecular dynamics (MD) simulation to generate the stochastic input to the Langevin form of the Liouville equation. A 0.1 μs MD simulation at T = 50°C of a small lipid bilayer formed by 64 dipalmitoylphosphatidylcholine (DPPC) molecules at the water content of 23 water molecules per lipid was used. In addition, a 10 ns simulation of a 16 times larger system consisting of 32 DPPC molecules with a nitroxide spin moiety attached at the sixth position of the sn2 chain and 992 ordinary DPPC molecules, was used to investigate the extent of the perturbation caused by the spin probe. Order parameters, reorientational dynamics and the EPR FID curve were calculated for spin probe molecules and ordinary DPPC molecules. The timescale of the electron spin relaxation for a spin-moiety attached at the sixth carbon position of a DPPC lipid molecule is 11.9 × 107 rad s−1 and for an unperturbed DPPC molecule it is 3.5 × 107 rad s−1.

  • 17.
    Iakunkov, Artem
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Klechikov, Alexey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sun, Jinhua
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Steenhaut, Timothy
    Hermans, Sophie
    Filinchuk, Yaroslav
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Gravimetric tank method to evaluate material-enhanced hydrogen storage by physisorbing materials2018Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, nr 44, s. 27983-27991Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The most common methods to evaluate hydrogen sorption (volumetric and gravimetric) require significant experience and expensive equipment for providing reproducible results. Both methods allow one to measure excess uptake values which are used to calculate the total amount of hydrogen stored inside of a tank as required for applications. Here we propose an easy to use and inexpensive alternative approach which allows one to evaluate directly the weight of hydrogen inside a material-filled test tank. The weight of the same tank filled with compressed hydrogen in the absence of loaded material is used as a reference. We argue that the only parameter which is of importance for hydrogen storage applications is by how much the material improves the total weight of hydrogen inside of the given volume compared to compressed gas. This parameter which we propose to name Gain includes both volumetric and gravimetric characterization of the material; it can be determined directly without knowing the skeletal volume of the material or excess sorption. The feasibility of the Gravimetric Tank (GT) method was tested using several common carbon and Metal Organic Framework (MOF) materials. The best Gain value of ∼12% was found for the Cu-BTC MOF which means that the tank completely filled with this material stores a 12% higher amount of hydrogen compared to H2 gas at the same PTconditions. The advantages of the GT method are its inexpensive design, extremely simple procedures and direct results in terms of tank capacity as required for industrial applications. The GT method could be proposed as a standard check for verification of the high hydrogen storage capacity of new materials. The GT method is expected to provide even better accuracy for evaluation of a material's performance for storage of denser gases like e.g. CO2 and CH4.

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  • 18.
    Iakunkov, Artem
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Skrypnychuk, Vasyl
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nordenström, Andreas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Shilayeva, Elizaveta A.
    Korobov, Mikhail
    Prodana, Mariana
    Enachescu, Marius
    Larsson, Sylvia H.
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Activated graphene as a material for supercapacitor electrodes: effects of surface area, pore size distribution and hydrophilicity2019Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, nr 32, s. 17901-17912Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Activated reduced graphene oxide (a-rGO) is a material with a rigid 3D porous structure and high specific surface area (SSA). Using variation of activation parameters and post-synthesis mechanical treatment we prepared two sets of materials with a broad range of BET (N2) SSA ∼1000–3000 m2 g−1, and significant differences in pore size distribution and oxygen content. The performance of activated graphene as an electrode in a supercapacitor with KOH electrolyte was correlated with the structural parameters of the materials and water sorption properties. a-rGO is a hydrophobic material as evidenced by the negligibly small BET (H2O) SSA determined using analysis of water vapor sorption isotherms. However, the total pore volume determined using water vapor sorption and sorption of liquid water is almost the same as the one found by analysis of nitrogen sorption isotherms. Ball milling is found to provide an improved bulk density of activated graphene and collapse of all pores except the smallest ones (<2 nm). A decrease in the activation temperature from 850 °C to 550 °C is found to result in materials with a narrow micropore size distribution and increased oxygen content. Elimination of mesopores using ball milling or a lower activation temperature provided materials with better specific capacitance despite a significant decrease (by ∼30%) of the BET (N2) SSA. The best gravimetric and volumetric capacitances in KOH electrolyte were achieved not for samples with the highest value of the BET (N2) SSA but for materials with 80–90% of the total pore volume in micropores and an increased BET (H2O) SSA. Comparing the performance of electrodes prepared using rGO and a-rGO shows that a more hydrophilic surface is favorable for charge storage in supercapacitors with KOH electrolyte.

    Fulltekst (pdf)
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  • 19. Ingman, Petri
    et al.
    Driver, Gordon W
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    A quantitative ionicity scale for liquid chloride salts2012Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 14, nr 37, s. 13053-13057Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Knowledge of ionicity is requisite for successful identification of those salt qualities required to design and couple the most appropriate fluid for performance of an intended chemical function. We report on utilisation of 35Cl quadrupolar coupling constants (CQ) to quantitatively assess the ionicities of given chloride salts, by exploiting the electronic response of the quadrupolar chlorine atom as a function of its immediate chemical environment. We find that protic salts in particular, like their aprotic analogues, are highly ionised, while at the same time being highly associated, in stark contrast to literature reports claiming in general that they are of sub-ionic origin.

  • 20.
    Isaksson, Mikael
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Hägglöf, Peter
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Håkansson, Pär
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Ny, Tor
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Johansson, Lennart B-Å
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Extentded Förster theory for determining intraprotein distances: 2. An accurate analysis of fluorescence depolarisation experiments2007Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 9, nr 29, s. 3914-3922Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The extended Förster theory (EFT) is for the first time applied to the quantitative determination of the intramolecular distances in proteins. It is shown how the EFT (J. Chem. Phys., 1996, 105, 10896) can be adapted to the analyses of fluorescence depolarisation experiments based on the time-correlated single photon counting technique (TCSPC). The protein system studied was the latent form of plasminogen activator inhibitor type I (PAI-1), which was mutated and labelled by the thiol reactive BODIPY® derivative {N-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-yl)methyl iodoacetamide}. The energy migration occurs within pairs of photophysically identical donor groups that undergo reorientational motions on the timescales of energy migration and fluorescence relaxation. Unlike all models currently used for analysing fluorescence TCSPC data, the EFT explicitly accounts for the time-dependent reorientations that influence the rate of electronic energy transfer/migration in a complex manner. The complexity is related to the “κ2 problem”, which has been discussed for years. The EFT brings the analyses of DDEM data to the same level of molecular description as in ESR and NMR spectroscopy, i.e. it yields microscopic information about the reorientation correlation times, the order parameters, as well as inter-chromophoric distances.

  • 21.
    Isaksson, Mikael
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Kalinin, Stanislav
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Lobov, Sergei
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Wang, Shouye
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Ny, Tor
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Johansson, Lennart B-Å
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Partial donor-donor energy migration (PDDEM): a novel fluorescence method for internal protein distance measurements2004Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 6, nr 11, s. 3001-3008Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We show that the photophysics of chemically identical but photophysically non-identical fluorescent pairs can be used for measuring distances within proteins. For this purpose, the theory of partial donor-donor energy migration (PDDEM, S. Kalinin, J. G. Molotkovsky and L. B.-Angstrom. Johansson, Spectrochim. Acta, Part A, 2002, 58, 1057-1097) was applied for distance measurements between BODIPY groups covalently linked to cystein residues in plasminogen activator inhibitor of type 2 (PAI-2). Two sulfhydryl specific derivatives of BODIPY were used namely: N-(4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene-2-yl) iodoacetamide and N-(4.4-difluoro-5.7-ditriethyl-4-bona-3a,4a-diaza-s-indacene-3-yl) methyl iodoacetamide. To determine distances, the time-resolved fluorescence relaxation for two singly labelled forms of PAI-2, as well as the corresponding doubly labelled protein were combined and analysed in a global manner. Fluorescence depolarisation experiments on the labelled mutants were also analysed. The distances determined by PDDEM were in good agreement to those obtained from donor-donor energy migration (DDEM) experiments and structural data on PAI-2. The PDDEM approach allows for the use of very different fluorescent probes, which enables wide range of distances to be measured. The PDDEM model also provides a rational explanation to why previous observations of polyfluorophore-labelled proteins exhibit a shorter average fluorescence lifetime compared to the arithmetic average of lifetimes obtained for the corresponding single labelled proteins.

  • 22.
    Isaksson, Mikael
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Norlin, Nils
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Westlund, Per-Olof
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Johansson, Lennart B-Å
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    On the quantitative molecular analysis of electronic energy transfer within donor–acceptor pairs2007Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 9, s. 1941-51Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An extended Förster theory (EFT) on electronic energy transfer is presented for the quantitative analysis of time-resolved fluorescence lifetime and depolarisation experiments. The EFT, which was derived from the stochastic Liouville equation, yields microscopic information concerning the reorientation correlation times, the order parameters, as well as inter chromophoric distances. Weakly interacting donor and acceptor groups, which reorient and interact in a pair wise fashion, are considered, under isotropic and anisotropic conditions. For the analysis of experiments it is shown that not only do we need to consider the orientational distributions of the transition dipoles, but the internal reorienting molecular dynamics within the pair which is of even greater importance. The latter determines the shape as well as the rate of the observed donor fluorescence and depolarisation decays, which are most often not mono-exponential functions. It is shown that the commonly used Förster theory is a special case of the EFT. Strategies are presented for applying the EFT, which makes use of Brownian dynamics simulation.

  • 23.
    Kawde, Anurag
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. European Synchrotron Radiation Facility, Grenoble, France; Lund Institute of advanced Neutron and X-Ray Science, Lund University, Sweden; NanoLund and Chemical Physics, Department of Chemistry, Lund University,Sweden .
    Annamalai, Alagappan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sellstedt, Anita
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysiologisk botanik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå Plant Science Centre (UPSC).
    Uhlig, Jens
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Glatzel, Pieter
    Messinger, Johannes
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. Molecular Biomimetics, Department of Chemistry – Ångström Laboratory, Uppsala University, Sweden.
    More than protection: the function of TiO2 interlayers in hematite functionalized Si photoanodes2020Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 22, nr 48, s. 28459-28467Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Worldwide significant efforts are ongoing to develop devices that store solar energy as fuels. In one such approach, solar energy is absorbed by semiconductors and utilized directly by catalysts at their surfaces to split water into H2 and O2. To protect the semiconductors in these photo-electrochemical cells (PEC) from corrosion, frequently thin TiO2 interlayers are applied. Employing a well-performing photoanode comprised of 1-D n-Si microwires (MWs) covered with a mesoporous (mp) TiO2 interlayer fabricated by solution processing and functionalized with α-Fe2O3 nanorods, we studied here the function of this TiO2 interlayer by high-energy resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) spectroscopy, along with X-ray emission spectroscopy (XES) and standard characterization techniques. Our data reveal that the TiO2 interlayer not only protects the n-Si MW surface from corrosion, but that it also acts as a template for the hydrothermal growth of α-Fe2O3 nanorods and improves the photocatalytic efficiency. We show that the latter effect correlates with the presence of stable oxygen vacancies at the interface between mp-TiO2 and α-Fe2O3, which act as electron traps and thereby substantially reduce the charge recombination rate at the hematite surface.

    Fulltekst (pdf)
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  • 24. Kazemi, Mehdi Mohammad
    et al.
    Namboodiri, Mahesh
    Umeå universitet, Medicinska fakulteten, Institutionen för integrativ medicinsk biologi (IMB).
    Donfack, Patrice
    Materny, Arnulf
    Kerle, Daniela
    Rathke, Bernd
    Kiefer, Johannes
    Influence of the alkyl side-chain length on the ultrafast vibrational dynamics of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide (C(n)mimNTf(2)) ionic liquids2017Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, nr 24, s. 15988-15995Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Probing the vibrational dynamics of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (CnmimNTf2) ionic liquids (ILs) using femtosecond time-resolved coherent anti-Stokes Raman scattering (fs-CARS) has indicated the ultrafast vibrational energy transfer between counter ions which is governed by interionic interactions and facilitated by hydrogen bonds. In this study, fs-CARS is used to investigate the ultrafast dynamics of the vibrational modes of the CnmimNTf2 ILs with n = 6, 8, 10, and 12 in a spectral region, which involves the imidazolium ring and the alkyl side-chain vibrations. The vibrational Raman modes with wavenumbers around 1418 cm−1 are excited through the CARS process and the ultrafast time evolution of the consequently excited vibrational modes is monitored. The investigation of the life times of the fs-CARS transient signals indicates that the time scale of the dynamics becomes much faster when the alkyl side-chain length of the CnmimNTf2 is longer than n = 8. This observation suggests an increase in the hydrogen bonding interactions due to the nano-structuring of the ionic liquids, which became evident with an increasing length of the alkyl side-chain. This behavior is also found in molecular dynamics simulations. There, an increase of the oxygen density around the C(2)–H moiety of the imidazolium ring, which is the predominant site for hydrogen bond formation, is observed. In other words, the longer the alkyl side-chain, the more reorganization of the ionic liquid into polar and non-polar domains occurs and the higher the probability of finding interionic hydrogen bonds at the C(2)–H position becomes.

  • 25. Langhals, Heinz
    et al.
    Walter, Andreas
    Rosenbaum, Erik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Johansson, Lennart B-Å
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    A versatile standard for bathochromic fluorescence based on intramolecular FRET2011Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, nr 23, s. 11055-11059Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A perylene and a terrylene tetracarboxylic bisimide dyad was prepared in which an efficient energy transfer from the former to the latter is observed. The absorption spectrum of this compound covers a broad range. Bathochromic fluorescence with a high quantum yield was obtained independent of excitation wavelengths (λ < 655 nm). The dyad can be recommended for the use of calibrating fluorescence spectrometers, as well as a fluorescence standard in the bathochromic region.

  • 26.
    Liang, Yongqi
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Messinger, Johannes
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Improving BiVO4 photoanodes for solar water splitting through surface passivation2014Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, nr 24, s. 12014-12020Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    BiVO4 has shown great potential as a semiconductor photoanode for solar water splitting. Significant improvements made during recent years allowed researchers to obtain a photocurrent density of up to 4.0 mA cm(-2) (AM1.5 sunlight illumination, 1.23 V-RHE bias). For further improvements of the BiVO4 photoelectrodes, a deep understanding of the processes occurring at the BiVO4-H2O interface is crucial. Employing an electrochemical loading and removal process of NiOx, we show here that carrier recombination at this interface strongly affects the photocurrents. The removal of NiOx species by electrochemical treatment in a phosphate electrolyte leads to significantly increased photocurrents for BiVO4 photoelectrodes. At a bias of 1.23 V-RHE, the Incident Photon-to-Current Efficiency (IPCE) at 450 nm reaches 43% for the passivated BiVO4 electrode under back side illumination. A model incorporating heterogeneity of NiOx centers on the BiVO4 surface (OER catalytic centers, recombination centers, and passivation centers) is proposed to explain this improved performance.

  • 27.
    Lindgren, Matteus
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Laaksonen, Aatto
    Stockholms universitet, Avdelningen för fysikalisk kemi.
    Westlund, Per-Olof
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    A theoretical spin relaxation and molecular dynamics simulation study of the Gd(H2O)93+ complex2009Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 11, s. 10368-76Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A theoretical analysis of the paramagnetically enhanced water proton spin–lattice relaxation of a hydrated Gd3+ ion is combined with Molecular Dynamics (MD) simulations. The electron–proton dipole–dipole correlation function, CDDp(), as well as the pseudo-rotation (PR) model of the transient zero-field splitting (ZFS) are evaluated with the help of the data from MD simulations. The fast local water motion in the first hydration shell, i.e. the wagging and rocking motions, is found not to change the mono exponential character of the dipole correlation function CDDp(), but is important in the time dependence of the transient ZFS interaction.The dynamics of the transient ZFS interaction is modeled as the water-induced electric field gradient tensor at the site of the metal ion. This approach follows the ideas of the pseudo-rotation model, describing the fluctuating zero-field interaction as a constant amplitude in the principal frame but reorienting according to a rotational diffusion equation of motion. The MD results indicate that the pseudo-rotation model gives a multi-exponential correlation function which oscillates at short times and is described by three exponential terms. The time scale is shorter than previously assumed but contain an intermediate time constant (1–2 ps). The electron spin resonance (ESR) spectral width at half height at frequencies of X-band, Q-band, 75 MHz, 150 MHz and 225 MHz can be reproduced at 320 K without any contributions from 4th or 6th rank ZFS interactions. Consequently, there are two mutually inconsistent dynamic models of the ZFS interaction which can describe the water proton T1-NMRD (nuclear magnetic resonance dispersion) profile and the field dependent ESR spectra of the hydrated Gd(III) complex equally well.

     

  • 28.
    Lindgren, Matteus
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Westlund, Per-Olof
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    On the stability of chymotrypsin inhibitor 2 in a 10 M urea solution: the role of interaction energies for urea-induced protein denaturation2010Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, nr 32, s. 9358-9366Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Molecular dynamics simulations of chymotrypsin inhibitor 2 in both water and in 10 M urea have been compared with respect to the energies of interaction between protein and solvent. The analysis yield clear and detailed information regarding the enthalpic driving force of urea-induced protein denaturation. The protein is kept in the folded structure by applying positional restraints on the alpha-carbons, thereby creating an equilibrium system from which appropriate driving forces for denaturation can be obtained. All protein atoms are classified as belonging to the backbone, the polar side chains or to the hydrophobic side chains. The interaction energies are extracted for each class separately. The commonly proposed mechanisms of urea denaturation, i.e. that urea interacts mainly with the backbone or with the hydrophobic side chains, can then be tested. The results show that urea decreases the Lennard-Jones interaction energies between protein and solvent by a large amount. The electrostatic energies are almost unaffected by the switch of solvent. The energetically favorable interaction between CI2 and the urea solvent will function as a driving force for the protein to increase its solvent accessible surface area as compared to the folded protein in water. The magnitude of the decrease in the Lennard-Jones energies for the hydrophobic and the hydrophilic side chains and for the backbone were similar. We therefore conclude that urea interacts favorably with the whole protein surface and that all parts of the protein are important in urea-induced denaturation.

  • 29.
    Lindström, Fredrick
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Bokvist, Marcus
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Sparrman, Tobias
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Gröbner, Gerhard
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Association of amyloid-β peptide with membrane surfaces monitored by solid state NMR2002Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 4, nr 22, s. 5524-5530Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Amyloid-β peptide (Aβ), a key substance in Alzheimers disease (AD), is characterized by its abnormal folding into neurotoxic aggregates. Since Aβ comprises an extracellular and transmembrane domain, some of its neurotoxic actions might be exerted via interactions with neuronal membranes. Wideline and magic angle spinning 14N and 31P NMR have been used in combination with differential scanning calorimetry and circular dichroism spectroscopy to investigate the association between Aβ1–40 peptide and membranes with different electrostatic surface potentials. Calorimetric measurements showed that all membrane systems were in the liquid crystalline state at 308 K. Binding of Aβ1–40 at a 30 1 lipid/peptide ratio to membranes composed of neutral dimyristoyl-phosphatidylcholine (DMPC) and negatively charged dimyristoylphosphatidylglycerol (DMPG) at a 4 : 1 molar ratio is mainly driven electrostatically, reflected in characteristic changes of the isotropic 31P chemical shift values for both lipids. In addition, the average orientation of the choline headgroup of DMPC, with its electric P–N+(CH3)3 dipole, changed directly in response to the reduced negative membrane surface potential. The deviation in tilt angle of the PN vector relative to the membrane surface is manifested in the observed 14N NMR quadrupole splitting and can therefore be described semiquantitatively. Adding Aβ1–40 to membranes with nominal neutral surface charge, but composed of a ternary mixture of DMPC with DMPG and the cationic amphiphile didodecyldimethyl–ammonium bromide (DDAB) at a 3 : 1 : 1 molar ratio revealed surprisingly electrostatic interactions visible in the NMR spectra. Since Aβ1–40 does not bind to neutral DMPC bilayers a model is proposed, in which on a molecular level the charged residues of Aβ1–40 peptide can interact independently with lipid headgroups of various charges in these microscopically heterogeneous systems.

  • 30.
    Lindström, Fredrick
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Thurnhofer, Saskia
    Vetter, Walter
    Gröbner, Gerhard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Impact on lipid membrane organization by free branched-chain fatty acids2006Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 8, nr 41, s. 4792-4797Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Here, we exploit the non-invasive techniques of solid-state NMR (nuclear magnetic resonance) and differential scanning calorimetry (DSC) to study the effect of free iso and ante-iso branched chain fatty acids (BCFAs) on the physicochemical properties of lipid membranes. Free fatty acids are present in biological membranes at low abundance, but can influence the cellular function by modulating the membrane organization. Solid state NMR spectra of dimyristoylphosphatidylcholine (DMPC) lipid membranes containing either free 12-methyltetradecanoic acid (a15:0) or free 13-methyltetradecanoic acid (i15:0), show significant differences in their impact on the lipid bilayer. Chain order profiles obtained by deuterium NMR on fully deuterated DMPC-d67 bilayers revealed an ordering effect induced by both fatty acids on the hydrophobic membrane core. This behavior was also visible in the corresponding DSC thermograms where the main phase transition of DMPC bilayers—indicative of the hydrophobic membrane region—was shifted to higher temperatures, with the iso isomer triggering more pronounced changes as compared to the ante-iso isomer. This is probably due to a higher packing density in the core of the lipid bilayer, which causes reduced diffusion across membranes. By utilizing the naturally occurring spin reporters nitrogen-14 and phosphorus-31 present in the hydrophilic DMPC headgroup region, even fatty acid induced changes at the membrane interface could be detected, an observation reflecting changes in the lipid headgroup dynamics.

  • 31.
    Liu, Xianghui
    et al.
    State Key Lab of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, China.
    Chang, Qi
    State Key Lab of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, China.
    Yan, Max
    State Key Lab of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, China.
    Wang, Xin
    State Key Lab of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, China.
    Zhang, Haiwen
    State Key Lab of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, China.
    Zhou, Han
    State Key Lab of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, China.
    Fan, Tongxiang
    State Key Lab of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, China.
    Scalable spectrally selective mid-infrared meta-absorbers for advanced radiative thermal engineering2020Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 22, nr 25, s. 13965-13974Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Metamaterials with spectrally selective absorptance operating in the mid-infrared range have attracted much interest in numerous applications. However, it remains a challenge to economically fabricate scalable meta-absorbers with tailorable absorptance bands. This work demonstrates a conceptually simple and low-cost yet effective design strategy to achieve spectrally selective absorption with tailorable band positions at MIR by colloidal lithography. The strategy ingeniously uses residual diameter fluctuations of circular resonators etched through monodisperse colloidal particles for achieving superposition of multiple magnetic resonances and thereby a more than doubled absorption band, which is neglected in previous works. The proposed meta-absorber features densely packed thick aluminum resonators with a rather narrow diameter distribution and enhanced capacitive coupling among them. Moreover, the tailorability of the absorption band can be achieved by a parameterized variation in the fabrication process. As a proof of concept, infrared stealth and radiative cooling are demonstrated based on our meta-absorbers. The design and fabrication strategy create versatile metamaterials for advanced radiative thermal engineering.

  • 32. Lubart, Quentin
    et al.
    Hannestad, Jonas K.
    Pace, Hudson
    Umeå universitet, Medicinska fakulteten, Institutionen för integrativ medicinsk biologi (IMB).
    Fjällborg, Daniel
    Westerlund, Fredrik
    Esbjörner, Elin K.
    Bally, Marta
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk mikrobiologi. Umeå universitet, Medicinska fakulteten, Wallenberg centrum för molekylär medicin vid Umeå universitet (WCMM).
    Lipid vesicle composition influences the incorporation and fluorescence properties of the lipophilic sulphonated carbocyanine dye SP-DiO2020Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 22, nr 16, s. 8781-8790Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Lipophilic carbocyanine dyes are widely used as fluorescent cell membrane probes in studies ranging from biophysics to cell biology. While they are extremely useful for qualitative observation of lipid structures, a major problem impairing quantitative studies is that the chemical environment of the lipid bilayer affects both the dye's insertion efficiency and photophysical properties. We present a systematic investigation of the sulphonated carbocyanine dye 3,3 '-dioctadecyl-5,5 '-di(4-sulfophenyl) (SP-DiO) and demonstrate how its insertion efficiency into pre-formed lipid bilayers and its photophysical properties therein determine its apparent fluorescence intensity in different lipid environments. For this purpose, we use large unilamellar vesicles (LUVs) made of lipids with distinct chain unsaturation, acyl chain length, head group charge, and with variation in membrane cholesterol content as models. Using a combination of absorbance, fluorescence emission, and fluorescence lifetime measurements we reveal that SP-DiO incorporates more efficiently into liquid disordered phases compared to gel phases. Moreover, incorporation into the latter phase is most efficient when the mismatch between the length of the lipid and dye hydrocarbon chains is small. Furthermore, SP-DiO incorporation is less efficient in LUVs composed of negatively charged lipids. Lastly, when cholesterol was included in the LUV membranes, we observed significant spectral shifts, consistent with dye aggregation. Taken together, our study highlights the complex interplay between membrane composition and labeling efficiency with lipophilic dyes and advocates for careful assessment of fluorescence data when attempting a quantitative analysis of fluorescence data with such molecules.

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  • 33.
    Luong, N. Tan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Oderstad, Hanna
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Boily, Jean-Francois
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Temperature-resolved nanoscale hydration of a layered manganese oxide2023Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 25, nr 26, s. 17352-17359Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Water films captured in the interlayer region of birnessite (MnO2) nanosheets can play important roles in biogeochemical cycling, catalysis, energy storage, and even atmospheric water harvesting. Understanding the temperature-dependent loadings and properties of these interlayer films is crucial to comprehend birnessite reactivity when exposed to moist air and temperature gradients. Using vibrational spectroscopy we show that birnessite intercalates one water (1W) monolayer at up to ∼40 °C, but that loadings decrease by half at up to 85 °C. Our results also show that the vibrational properties of intercalated water are unaffected by temperature, implying that the hydrogen bonding network of water remains intact. Using molecular simulations, we found that the lowered water storage capacity at high temperatures cannot be explained by variations in hydrogen bond numbers or in the solvation environments of interlayer K+ ions initially present in the interlayer region. It can instead be explained by the compounded effects of larger evolved heat, as inferred from immersion energies, and by the larger temperature-driven mobility of water over that of K+ ions, which are electrostatically bound to birnessite basal oxygens. By shedding new light on the temperature-driven intercalation of water in a nanolayered mineral, this study can guide future efforts to understand the (geo)chemical reactivity of related materials in natural and technological settings.

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  • 34.
    Messinger, Johannes
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Lubitz, Wolfgang
    Shen, Jian-Ren
    Photosynthesis: from natural to artificial2014Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, nr 24, s. 11810-11811Artikkel i tidsskrift (Annet vitenskapelig)
  • 35.
    Mitev, Pavlin D.
    et al.
    Department of Chemistry - Ångström Laboratory, Uppsala University, Box 538, S-751 21 Uppsala, Sweden .
    Eriksson, Anders
    Department of Chemistry - Ångström Laboratory, Uppsala University, Box 538, S-751 21 Uppsala, Sweden .
    Boily, Jean-Francois
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Hermansson, Kersti
    Department of Chemistry - Ångström Laboratory, Uppsala University, Box 538, S-751 21 Uppsala, Sweden .
    Vibrational models for a crystal with 36 water molecules in the unit cell: IR spectra from experiment and calculation2015Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, nr 16, s. 10520-10531Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present experimental and calculated IR spectra of the water molecules in crystalline aluminium nitrate nonahydrate and a method to generate a realistic and well resolved isotope-isolated spectrum from periodic DFT calculations. Our sample crystal contains 18 structurally different OH groups and is a perfect benchmark compound to validate vibrational models and the structure-property relationship of bound water molecules. FTIR spectra (ATR technique) were recorded for the Al(NO3)(3)center dot 9H(2)O crystal at 138 and 298 K, and due to a multitude of OH contributions and couplings, they are naturally poorly resolved and yield a broad OH band in the range 3500 to 2700 cm(-1) at both temperatures. Isotope-isolated IR spectra have the clear advantage over non-deuterated spectra that they are better resolved and easier to interpret - here we have extended the experimental study by simulating the isotope-isolated IR spectrum, using PBE-D2 and auxiliary B3LYP calculations and an anharmonic OH vibrational model. We find excellent agreement between the shapes and frequency ranges of the experimental and calculated OH spectral bands. We make use of four different vibrational models: (i) a harmonic lattice-dynamical model for the isotope-isolated crystal with 1 H among 71 D, (ii) a harmonic lattice-dynamical model for the normal undeuterated crystal involving all the vibrational couplings, (iii) a harmonic 1-dimensional uncoupled OH vibrational model, and (iv) the anharmonic variant of the previous model, which yields the final spectrum. We also use the individual frequencies, resolved by the calculations, to quantify new or extended relationships involving OH frequencies versus local electric fields and H-bond distances. We explore the correlation between OH frequency and molecular dipole moment for bound water molecules.

  • 36.
    Nordenström, Andreas
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Iakunkov, Artem
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Baburin, Igor
    echnische Universitat Dresden, Physical Chemistry, Dresden, Sachsen, Germany.
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Acetylation of graphite oxide2020Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 22, nr 37, s. 21059-21067Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Unlike many methods of chemical modification of Graphite Oxide (GO) reported during 1930-1960 and re-studied in much detail over the last decade, acetylation somehow escaped attention and remained almost completely unexplored. Acetylated Graphite Oxide (AcGO) was prepared using a reaction with acetic anhydride. Successful acetylation is evidenced by an increase in the average interlayer distance fromd(001) = 7.8 angstrom in the precursor GO to 10 angstrom in AcGO. The amount of oxygen in AcGO significantly decreased compared to the precursor GO (C/O = 2.2), reflecting partial reduction of GO in the process of acetylation and resulting in a scarcely functionalized material with C/O = 6.2. A theoretical model of the complete acetylation of GO results in a non-porous close packed molecular structure with an interlayer distance of similar to 10 angstrom, in good agreement with experiment. Remarkably, AcGO shows significant swelling despite the oxidation degree being comparable to that of reduced GO, which does not swell in polar solvents. Moreover, AcGO shows swelling in acetonitrile similar to that of the precursor GO but not in water, thus providing an example of selectivity in the sorption of common polar solvents. The low oxidation degree combined with selective swelling properties makes AcGO a promising material for membrane applications.

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  • 37.
    Norlin, Nils
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Håkansson, Per
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Westlund, Per-Olof
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Johansson, Lennart B-Å
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Extended Förster theory for determining intraprotein distances: Part III. Partial donor–donor energy migration among reorienting fluorophores2008Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 10, s. 6962-70Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An extended Förster theory (EFT) is derived and outlined for electronic energy migration between two fluorescent molecules which are chemically identical, but photophysically non-identical. These molecules exhibit identical absorption and fluorescence spectra, while their fluorescence lifetimes differ. The latter means that the excitation probability becomes irreversible. Unlike the case of equal lifetimes, which is often referred to as, donor–donor energy migration (DDEM), the observed fluorescence relaxation is then no longer invariant to the energy migration process. To distinguish, the present case is therefore referred to as partial donor–donor energy migration (PDDEM). The EFT of PPDEM is described by a stochastic master equation (SME), which has been derived from the stochastic Liouville equation (SLE) of motion. The SME accounts for the reorienting as well as the translational motions of the interacting chromophores. Synthetic fluorescence lifetime and depolarisation data that mimics time-correlated single photon counting experiments have been generated and re-analysed. The rates of reorientation, as well as the orientational configurations of the interacting D-groups were examined. Moreover the EFT of PPDEM overcomes the classical 2-problem and the frequently applied approximation of 2 = 2/3 in the data analyses. An outline for the analyses of fluorescence lifetime and depolarisation data is also given, which might prove applicable to structural studies of D-labelled macromolecules, e.g. proteins. The EFT presented here brings the analyses of PDDEM data to the same level of molecular detail as that used in ESR- and NMR-spectroscopy.

  • 38.
    Ohlin, C. André
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Computational exploration of heterometal substitution into the decaniobate framework, [Nb10O28]6-2021Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 23, nr 17, s. 10402-10408Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The factors governing the substitution of group 4B-12B metals into the decaniobate framework are explored using density functional theory in order to ascertain whether (1) recently isolated [MNb9O28]x- clusters are kinetic or thermodynamic products, (2) density functional theory is a sufficient level of theory to accurately predict substitution patterns in polyoxometalates where ion pairing and other effects may operate, and (3) it can be used to guide future synthetic efforts. Computations using restricted, unrestricted and open-shell density functional theory at PBE0/def2-tzvp were found to correctly predict substitution patterns in known clusters, and were subsequently used to calculate the relative energies of a large series of [MNb9O28]x- clusters, to reveal trends and suggest potential synthetic approaches. OPBE/def2-tzvp correctly predicted favoured spin states of known substituted decametalates.

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  • 39.
    Ohlin, C. André
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Energetics of paramagnetic oxide clusters: the Fe(iii) oxyhydroxy Keggin ion2020Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 22, nr 7, s. 4043-4050Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The energetics of the different spin states of the five Baker-Figgis isomers of the iron(iii) Keggin ion, [Fe(O-4)(Fe(OH)(2)(OH2))(12)](7+), have been investigated using density functional theory in order to demonstrate how the energy landscape of medium-to-large discrete paramagnetic transition metal oxide clusters with large numbers of antiferromagnetically coupled centres can be resolved. Antiferromagnetic coupling causes the energies to span a surprisingly large range of 30 kcal mol(-1), as determined by calculating the energies of all 664 unique spin configurations based on determination of the antiferromagnetic coupling constants by density functional theory. A program which simplifies the resolution of the energetics of this type of system is also provided.

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  • 40.
    Opanasyuk, Oleg
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Johansson, Lennart B-Å
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Extended Förster theory: a quantitative approach to the determination of inter-chromophore distances in biomacromolecules2010Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, nr 28, s. 7758-7767Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This review highlights recent theoretical and experimental advances in the study of biomacromolecular structure by using electronic transfer. The considered electronic transport in the extended Förster theory occurs within donor–acceptor pairs, donor–donor pairs, as well as within regular arrangements of many donors which may undergo reorienting and translational dynamics. The classical and the extended FoЁ rster theory are compared. Applications concern the determination of structural properties of proteins and non-covalent protein polymers. Studies of energy migration by means of two-photon excited fluorescence spectroscopy, as well as the relevant extension of the Förster theory are presented.

  • 41.
    Opanasyuk, Oleg
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Johansson, Lennart B-Å
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    On the analyses of fluorescence depolarisation data in the presence of electronic energy migration: Part I. Theory and general description2012Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 14, s. 1907-1916Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new and general procedure is described for a detailed analysis of time-resolved fluorescence depolarisation data in the presence of electronic energy migration. An isotropic ensemble of bifluorophoric molecules (D1-R-D2) has been studied to demonstrate its utility. Intramolecular donor-donor energy migration occurs between the two donor groups (D), which are covalently connected to a rigid linker group (R). These groups undergo restricted reorientational motions with respect to the R group. The analysis of depolarisation data basically involves the search for best-fit parameters which describe the local reorienting motions, the intermolecular D1-D2 distance, as well as the mutual orientations of the donors. For this, the analysis is partly performed in the Fourier domain and the best-fit parameters are determined by using an approach based on a Genetic Algorithm. The energy migration process has been described by using Monte Carlo simulations and an extended Förster theory (EFT). It is found that the EFT provides the least time-consuming computational method. Since one-photon and two-photon excited fluorescence experiments can be applied for energy migration studies, a general and unified theoretical formulation is given.

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  • 42.
    Opanasyuk, Oleg
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Mikaelsson, Therese
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Ryderfors, Linus
    Department of Photochemistry and Molecular Science, Uppsala University, P. O. Box 523, S-751 20 Uppsala, Sweden.
    Mukhtar, Emad
    Department of Photochemistry and Molecular Science, Uppsala University, P. O. Box 523, S-751 20 Uppsala, Sweden.
    Johansson, Lennart B-Å
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    On the analyses of fluorescence depolarisation data in the presence of electronic energy migration.: II. Applying & Evaluating Two-Photon Excited Fluorescence2012Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 14, s. 1917-1922Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electronic energy migration within a bifluorophoric molecule has been studied by time-resolved two-photon excited (TPE) fluorescence depolarisation experiments. Data were analysed by using a recently developed quantitative approach [Opanasyuk, O. & Johansson, L. B.-Å., On the Analyses of Fluorescence Depolarisation Data in the Presence of Electronic Energy Migration. I. Theory & General Description. Phys. Chem. Chem. Phys., Submitted.]. The energy migration occurs between the 9-anthrylmethyl groups of the bifluorophoric molecule, bis-(9-anthrylmethylphosphonate) bisteroid. These groups undergo local reorientations, while overall tumbling of the bisteroid is strongly hampered in the used viscous solvent, 1,2-propanediol. To solely obtain information about local reorientations of the 9-anthrylmethyl group, also the mono-(9-anthrylmethylphosphonate) bisteroid was studied, which enabled modelling of the ordering potential shape. The analysis of data is partly performed in the Fourier domain and the best-fit parameters are determined by using an approach based on a Genetic Algorithm. The energy migration process was described by an extended Förster theory (EFT). A reasonable value of the distance between the 9-anthrylmethyl groups is found, as well as for the mutual orientation of the ordering potentials. Furthermore, values of the two-photon tensor components were obtained.

  • 43.
    Opanasyuk, Oleg
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Ryderfors, Linus
    Department of Photochemistry and Molecular Science, Uppsala University, P. O. Box 523, S-751 20 Uppsala, Sweden.
    Mukhtar, Emad
    Department of Photochemistry and Molecular Science, Uppsala University, P. O. Box 523, S-751 20 Uppsala, Sweden.
    Johansson, Lennart B-Å
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Two-photon excited fluorescence depolarisation and electronic energy migration within donor–donor pairs2009Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, nr 11, s. 7152-7160Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A unified theoretical description is presented for one- and two-photon excited fluorescence depolarisation and electronic energy migration within pairs of chromophores. Two weakly coupled donor groups are linked via a rigid macromolecule with the ability to undergo restricted reorienting motions. Describing these reorienting motions as well as their influence on the coupling is rather complex, but can be accounted for by using the extended Förster theory. Here explicit expressions have been derived for chromophores belonging to the point groups D2h,D2 andC2v when residing in uniaxial potentials (i.e. C∞v symmetry). From the given basic equations, it is possible however, to derive the relevant equations for molecules of arbitrary symmetry in any uniaxial orienting potential. The expected time-resolved fluorescence anisotropy for different two-photon absorption tensors are compared for reorienting fluorophores in liquids, as well as in anisotropic systems. Simulated fluorescence depolarisation data are also displayed that mimic energy migration within pairs of two-photon excited donor molecules, which simultaneously undergo reorienting motions within effectively isotropic and uniaxially anisotropic environments. The obtained results demonstrate that the time-resolved fluorescence anisotropy strongly depends on the properties of the two-photon absorption tensor, as well as on using a linear or a circular polarisation of the excitation field.

  • 44. Pantazis, Dimitrios A
    et al.
    Orio, Maylis
    Petrenko, Taras
    Zein, Samir
    Lubitz, Wolfgang
    Messinger, Johannes
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Neese, Frank
    Structure of the oxygen-evolving complex of photosystem II: information on the S(2) state through quantum chemical calculation of its magnetic properties.2009Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 11, nr 31, s. 6788-6798Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Twelve structural models for the S(2) state of the oxygen-evolving complex (OEC) of photosystem II are evaluated in terms of their magnetic properties. The set includes ten models based on the 'fused twist' core topology derived by polarized EXAFS spectra and two related models proposed in recent mechanistic investigations. Optimized geometries and spin population analyses suggest that Mn(iii), which is most often identified with the manganese ion at site D, is always associated with a penta-coordinate environment, unless a chloride is directly ligated to the metal. Exchange coupling constants were determined by broken-symmetry density functional theory calculations and the complete spectrum of magnetic sublevels was obtained by direct diagonalization of the Heisenberg Hamiltonian. Seven models display a doublet ground state and are considered spectroscopic models for the ground state corresponding to the multiline signal (MLS) of the S(2) state of the OEC, whereas the remaining five models display a sextet ground state and could be related to the g = 4.1 signal of the S(2) state. It is found that the sign of the exchange coupling constant between the Mn centres at positions A and B of the cluster is directly related to the ground state multiplicity, implying that interconversion between the doublet and sextet can be induced by only small structural perturbations. The recently proposed quantum chemical method for the calculation of (55)Mn hyperfine coupling constants is subsequently applied to the S(2) MLS state models and the quantities that enter into the individual steps of the procedure (site-spin expectation values, intrinsic site isotropic hyperfine parameters and projected (55)Mn isotropic hyperfine constants) are analyzed and discussed in detail with respect to the structural and electronic features of each model. The current approach performs promisingly. It reacts sensitively to structural distortions and hence may be able to distinguish between different structural proposals. Thus it emerges as a useful contributor to the ongoing efforts that aim at establishing correlations between the body of spectroscopic data available for the various S(i) states of the OEC and their actual geometric features.

  • 45. Perera, Ishanie Rangeeka
    et al.
    Gupta, Akhil
    Xiang, Wanchun
    Daeneke, Torben
    Bach, Udo
    Evans, Richard A.
    Ohlin, C. Andre
    Spiccia, Leone
    Introducing manganese complexes as redox mediators for dye-sensitized solar cells2014Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, nr 24, s. 12021-12028Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The abundance and low toxicity of manganese have led us to explore the application of manganese complexes as redox mediators for dye sensitized solar cells (DSCs), a promising solar energy conversion technology which mimics some of the key processes in photosynthesis during its operation. In this paper, we report the development of a DSC electrolyte based on the tris(acetylacetonato) manganese(III)/(IV), [Mn(acac)(3)](0/1+), redox couple. PEDOT-coated FTO glass was used as a counter electrode instead of the conventionally used platinum. The influence of a number of device parameters on the DSC performance was studied, including the concentration of the reduced and oxidized mediator species, the concentration of specific additives (4-tert-butylpyridine, lithium tetrafluoroborate, and chenodeoxycholic acid) and the thickness of the TiO2 working electrode. These studies were carried out with a new donor-pi-acceptor sensitizer K4. Maximum energy conversion efficiencies of 3.8% at simulated one Sun irradiation (AM 1.5 G; 1000 W m(-2)) with an open circuit voltage (V-OC) of 765 mV, a short-circuit current (J(SC)) of 7.8 mA cm(-2) and a fill factor (FF) of 0.72 were obtained. Application of the commercially available MK2 and N719 sensitizers resulted in an energy conversion efficiency of 4.4% with a V-OC of 733 mV and a J(SC) of 8.6 mA cm(-2) for MK2 and a V-OC of 771 mV and a J(SC) of 7.9 mA cm(-2) for N719. Both dyes exhibit higher incident photon to current conversion efficiencies (IPCEs) than K4.

  • 46.
    Revoju, Srikanth
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Biswas, Subhayan
    Eliasson, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Sharma, Ganesh D.
    Asymmetric triphenylamine–phenothiazine based small molecules with varying terminal acceptors for solution processed bulk-heterojunction organic solar cells2018Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, nr 9, s. 6390-6400Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Three compounds consisting of the electron-donating triphenylamine–phenothiazine conjugate backbone and each of the electron-withdrawing groups 3-ethylrhodanine, malononitrile and 1,3-indandione have been synthesized and used as donors in blends with [6,6]-phenyl-C70-butyric acid methyl ester (PC71BM) for organic solar cell devices. After improvements of the active layer structure by a selected donor-to-acceptor weight ratio and a two-step solvent and thermal annealing, the organic solar cells showed power conversion efficiency (PCE) values in the range of 4.79–7.25%. The highest PCE was obtained for the bulk heterojunction device with the indandione compound, which can be attributed to its better absorption profile, higher crystallinity, more balanced electron and hole transport, higher charge collection efficiency and reduced recombination, in comparison with the photovoltaic cells from the other two compounds. DFT-calculated characteristics, absorption spectra and cyclic voltammetry of the compounds, along with X-ray diffraction patterns of the blend films, are used to validate the photovoltaic results.

  • 47.
    Sachl, Radek
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Boldyrev, Ivan
    Shemyakin & Ovchinnikov Institute, Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia.
    Johansson, Lennart B-Å
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Localisation of BODIPY-labelled phosphatidylcholines in lipid bilayers2010Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, s. 6027-6034Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A series of sn-2 acyl-labelled phosphatidyl-cholines (PC), bearing 4,4-difluoro-1-3-5-7-tetra-methyl-4-bora-3a,4a-diaza-s-indacene-8-yl (Me4-BODIPY) at the end of the Cn-acyl chains were solubilised in unilamellar vesicles and studied with respect to the order and location of the Me4-BODIPY (denoted: B) group. The obtained results are based on time-resolved electronic energy transfer from donors (2-(9-anthroyloxy)-stearic acid) localised in the lipid–water interface to acceptors BnPC (n = 3, 5, 7, 9, 11, 13, 15), as well as the energy migration among the Me4-BODIPY groups of BnPC:s. The donor–acceptor and the donor–donor experiments strongly suggest that the Me4-BODIPY group in BnPC tends to loop back close to the lipid–water interface. The Me4-BODIPY groups, residing in the two bilayer leaflets, are located at approximately the same depth, and transversally separated by ca. 27 Å for all n-values. Close to the interface, the optimal transversal distribution widens somewhat with increasing length of the sn-2 acyl chain. The obtained order parameter profile of the BnPC:s is also compatible with such a location.

  • 48.
    Sachl, Radek
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Mikhalyov, Ilya
    Shemyakin & Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia.
    Gretskaya, Natalia
    Shemyakin & Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia.
    Olżyńska, Agnieszka
    J. Heyrovsky´ Institute of Physical Chemistry, v.v.i., Academy of Sciences of the Czech Republic, Dolejsˇkova 3, 182 23 Prague 8, Czech Republic.
    Hof, Martin
    J. Heyrovsky´ Institute of Physical Chemistry, v.v.i., Academy of Sciences of the Czech Republic, Dolejsˇkova 3, 182 23 Prague 8, Czech Republic.
    Johansson, Lennart B-Å
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Distribution of BODIPY-labelled phosphatidylethanolamines in lipid bilayers exhibiting different curvatures2011Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, s. 11694-11701Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we have investigated the behaviour of newly synthesised mono-palmitoyl- and dipalmitoyl-phosphatidylethanolamine probes (abbreviated as mPE and dPE, respectively) labelled in the polar headgroup region by either the FL-BODIPY or the 564/570-BODIPY fluorophore and solubilised in lipid systems that exhibit different curvatures. Because of the bulky BODIPY-groups, the monoacyl-form derivatives have a conic-like shape, whereas that for the diacyl derivatives is rather cylindrical. A careful analysis of time-resolved resonance energy transfer experiments by means of analytical models as well as Monte Carlo simulations shows that the mPE derivatives have a comparable affinity to highly curved bilayer regions (torroidal pores formed by magainin-2 in lipid bilayers, or the rims of discoid bicelles) and to planar bilayer regions (i.e. the flat region of lipid bilayers and bicelles). Furthermore, the monoacyl-probes are as compared to the diacyl-probes effectively closer to each other in a lipid bilayer, while none of these probes seems to be randomly distributed. Self-aggregation is most efficiently induced by the larger aromatic 564/570-BODIPY chromophore, but it is suppressed when using the diacyl instead of the monoacyl-form, and/or by attaching BODIPY-groups to the acyl-chain.

  • 49.
    Sachl, Radek
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Mikhalyov, Ilya
    Shemyakin & Ovchinnikov Institute, Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia.
    Hof, Martin
    J. Heyrovsky´ Institute of Physical Chemistry of the Academy of Sciences of the Czech Republic, Dolejsˇkova 3 182 23 Prague 8,Czech Republic.
    Johansson, Lennart B-Å
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    A comparative study on ganglioside micelles using electronic energy transfer, fluorescence correlation spectroscopy and light scattering techniques2009Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 11, nr 21, s. 4335-4343Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ganglioside (GM1) micelles have been studied by means of three different techniques: fluorescence correlation spectroscopy (FCS), electronic energy transfer, as monitored by time-resolved fluorescence spectroscopy, as well as static and dynamic light scattering. The aggregation numbers obtained, 168 ± 4, remain constant over a wide range of GM1 concentrations (0.764-156 M), are very consistent when using different donor-acceptor energy transfer pairs and have served as reference values in tests of the FCS method. It is recommended to calibrate the focal volume by using known dye concentrations. For this the rhodamine dye, 5-TAMRA, turns out to be most suitable. It is also shown that FCS provides correct values of the aggregation numbers, provided that the focal volume is calibrated by using updated values of the diffusion constant of Rhodamine 6G. These results also support recent methodological advances in FCS.

  • 50.
    Sadiek, Ibrahim
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Leibniz Institute for Plasma Science and Technology, Greifswald, Germany.
    Hjältén, Adrian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Roberts, Frances C.
    School of Chemistry, University of Leeds, United Kingdom.
    Lehman, Julia H.
    School of Chemistry, University of Birmingham, United Kingdom.
    Foltynowicz, Aleksandra
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Optical frequency comb-based measurements and the revisited assignment of high-resolution spectra of CH2Br2 in the 2960 to 3120 cm−1 region2023Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 25, artikkel-id 8743Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Brominated organic compounds are toxic ocean-derived trace gases that affect the oxidation capacity of the atmosphere and contribute to its bromine burden. Quantitative spectroscopic detection of these gases is limited by the lack of accurate absorption cross-section data as well as rigorous spectroscopic models. This work presents measurements of high-resolution spectra of dibromomethane, CH2Br2, from 2960 cm−1 to 3120 cm−1 by two optical frequency comb-based methods, Fourier transform spectroscopy and a spatially dispersive method based on a virtually imaged phased array. The integrated absorption cross-sections measured using the two spectrometers are in excellent agreement with each other within 4%. A revisited rovibrational assignment of the measured spectra is introduced, in which the progressions of features are attributed to hot bands rather than different isotopologues as was previously done. Overall, twelve vibrational transitions, four for each of the three isotopologues CH281Br2, CH279Br81Br, and CH279Br2, are assigned. These four vibrational transitions are attributed to the fundamental ν6 band and the nearby nν4 + ν6 − nν4 hot bands (with n = 1–3) due to the population of the low-lying ν4 mode of the Br–C–Br bending vibration at room temperature. The new simulations show very good agreement in intensities with the experiment as predicted by the Boltzmann distribution factor. The spectra of the fundamental and the hot bands show progressions of strong QKa(J) rovibrational sub-clusters. The band heads of these sub-clusters are assigned and fitted to the measured spectra, providing accurate band origins and the rotational constants for the twelve states with an average error of 0.0084 cm−1. A detailed fit of the ν6 band of the CH279Br81Br isotopologue is commenced after assigning 1808 partially resolved rovibrational lines, with the band origin, rotational, and centrifugal constants as fit parameters, resulting in an average error of 0.0011 cm−1.

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