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  • 1.
    Aghbolagh, Mahdi Shahmohammadi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Meynaq, Mohammad Yaser Khani
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shimizu, Kenichi
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Aspects on mediated glucose oxidation at a supported cubic phase2017In: Bioelectrochemistry, ISSN 1567-5394, E-ISSN 1878-562X, Vol. 118, p. 8-13Article in journal (Refereed)
    Abstract [en]

    A supported liquid crystalline cubic phase housing glucose oxidase on an electrode surface has been suggested as bio-anode in a biofuel. The purpose of this investigation is to clarify some aspect on the mediated enzymatic oxidation of glucose in such a bio-anode where the mediator ferrocene-carboxylic acid and glucose were dissolved in the solution. The enzyme glucose oxidase was housed in the water channels of the mono-olein cubic phase. The system was investigated with cyclic voltammetry at different scan rates and the temperature was varied between 15 degrees C and 30 degrees C. The diffusion coefficient of the mediator and also the film resistance was estimated showing a large decrease in the mass-transport properties as the temperature was decreased. The current from mediated oxidation of glucose at the electrode surface increased with decreasing film thickness. The transport of the mediator in the cubic phase was the rate-limiting step in the overall reaction, where the oxidation of glucose took place at the outer surface of the cubic phase.

  • 2.
    Aisenbrey, Christopher
    et al.
    Institut de Chimie Universit0 Louis Pasteur Strasbourg—CNRS, UMR 7177 4, Rue Blaise Pascal, 67000 Strasbourg (France); Max-Planck-Institut f>r Biochemie Am Klopferspitz 18A, 82152 Martinsried (Germany).
    Cusan, Monica
    Lambotte, Stephan
    Jasperse, Pieter
    Georgescu, Julia
    Harzer, Ulrike
    Bechinger, Burkhard
    Specific Isotope Labeling of Colicin E1 and B Channel Domains For Membrane Topological Analysis by Oriented Solid-State NMR Spectroscopy2008In: ChemBioChem (Print), ISSN 1439-4227, E-ISSN 1439-7633, Vol. 9, no 6, p. 944-951Article in journal (Refereed)
    Abstract [en]

    An approach is presented to selectively label the methionines of the colicin E1 and B channel domains, each about 200 residues in size, and use them for oriented solid-state NMR investigations. By combining site-directed mutagenesis, bacterial overexpression in a methionine auxotroph E. coli strain and biochemical purification, quantitative amounts of the proteins for NMR structural investigations were obtained. The proteins were selectively labeled with 15N at only one, or at a few, selected sites. Multidimensional heteronuclear correlation high-resolution NMR spectroscopy and mass spectrometry were used to monitor the quality of isotopic labeling. Thereafter the proteins were reconstituted into oriented phospholipid bilayers and investigated by proton-decoupled 15N solid-state NMR spectroscopy. The colicin E1 thermolytic fragment that carries a single 15N methionine within its hydrophobic helix 9 region exhibited 15N resonances that are characteristic of helices that are oriented predominantly parallel to the membrane surface at low temperature, and a variety of alignments and conformations at room temperature. This suggests that the protein can adopt both umbrella and pen-knife conformations.

  • 3.
    Ajaikumar, Samikannu
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ahlkvist, Johan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Larsson, William
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Kordas, K
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Laboratory of Industrial Chemistry and Reaction Engineering, Process Chemistry Centre, Åbo Akademi University, Piispankatu 8, FIN-20500, Turku/Åbo, Finland.
    Oxidation of α-pinene over gold containing bimetallic nanoparticles supported on reducible TiO2 by DPU method2011In: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 392, no 1-2, p. 11-18Article in journal (Refereed)
    Abstract [en]

    A series of bimetallic catalysts Au–M (where M = Cu, Co and Ru) were supported on a reducible TiO2 oxide via deposition-precipitation (DP) method with a slow decomposition of urea as the precipitating agent. The characteristic structural features of the prepared materials were characterized by various physico-chemical techniques such as X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). XPS results indicated the formation of alloyed bimetallic particles on the TiO2 support. TEM results confirmed the fine dispersion of metal nanoparticles on the support with an average particle size in the range of 3–5 nm. An industrially important process, oxy-functionalization of α-pinene was carried out over the prepared bimetallic heterogeneous catalysts under liquid phase conditions. Reaction parameters such as the reaction time, temperature, and the effect of solvent were studied for optimal conversion of α-pinene into verbenone. The major products obtained were verbenone, verbenol, α-pinene oxide and alkyl-pinene peroxide. The activity of the catalysts followed the order; AuCu/TiO2 > AuCo/TiO2 > Cu/TiO2 > Au/TiO2 > AuRu/TiO2. Upon comparison of the various catalysts, AuCu/TiO2 was found to be an active and selective catalyst towards the formation of verbenone. The temperature, nature of the catalysts and the choice of solvents greatly influenced the reaction rate.

  • 4. Alonso-Mori, R.
    et al.
    Asa, K.
    Bergmann, U.
    Brewster, A. S.
    Chatterjee, R.
    Cooper, J. K.
    Frei, H. M.
    Fuller, F. D.
    Goggins, E.
    Gul, S.
    Fukuzawa, H.
    Iablonskyi, D.
    Ibrahim, M.
    Katayama, T.
    Kroll, T.
    Kumagai, Y.
    McClure, B. A.
    Messinger, Johannes
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Motomura, K.
    Nagaya, K.
    Nishiyama, T.
    Saracini, C.
    Sato, Y.
    Sauter, N. K.
    Sokaras, D.
    Takanashi, T.
    Togashi, T.
    Ueda, K.
    Weare, W. W.
    Weng, T-C
    Yabashi, M.
    Yachandra, V. K.
    Young, I. D.
    Zouni, A.
    Kern, J. F.
    Yano, J.
    Towards characterization of photo-excited electron transfer and catalysis in natural and artificial systems using XFELs2016In: Faraday discussions (Online), ISSN 1359-6640, E-ISSN 1364-5498, Vol. 194, p. 621-638Article in journal (Refereed)
    Abstract [en]

    The ultra-bright femtosecond X-ray pulses provided by X-ray Free Electron Lasers (XFELs) open capabilities for studying the structure and dynamics of a wide variety of biological and inorganic systems beyond what is possible at synchrotron sources. Although the structure and chemistry at the catalytic sites have been studied intensively in both biological and inorganic systems, a full understanding of the atomic-scale chemistry requires new approaches beyond the steady state X-ray crystallography and X-ray spectroscopy at cryogenic temperatures. Following the dynamic changes in the geometric and electronic structure at ambient conditions, while overcoming X-ray damage to the redox active catalytic center, is key for deriving reaction mechanisms. Such studies become possible by using the intense and ultra-short femtosecond X-ray pulses from an XFEL, where sample is probed before it is damaged. We have developed methodology for simultaneously collecting X-ray diffraction data and X-ray emission spectra, using an energy dispersive spectrometer, at ambient conditions, and used this approach to study the room temperature structure and intermediate states of the photosynthetic water oxidizing metallo-protein, photosystem II. Moreover, we have also used this setup to simultaneously collect the X-ray emission spectra from multiple metals to follow the ultrafast dynamics of light-induced charge transfer between multiple metal sites. A Mn-Ti containing system was studied at an XFEL to demonstrate the efficacy and potential of this method.

  • 5.
    Andersson, Ove
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johari, Gyan P.
    Department of Materials Science and Engineering, McMaster University, Hamilton, Ontario, Canada.
    Thermal conductivity of Glycerol’s liquid, glass, and crystal states, glass-liquid-glass transition, and crystallization at high pressures2016In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 144, article id 064504Article in journal (Refereed)
  • 6.
    Andersson, Ove
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yasuhiro, Nakazawa
    Research Center for Structural Thermodynamics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
    Thermal Properties and Transition Behavior of Host –Guest Compounds under High Pressure2014In: Current inorganic chemistry, ISSN 1877-9441, Vol. 4, no 1, p. 2-18Article in journal (Other academic)
    Abstract [en]

    The thermal properties and transition behavior of the host-guest inclusion compounds: urea, thiourea, Dianin’s compound, clathrate hydrates and hydroquinone have been reviewed. In particular, we summarize their thermal conductivities, heat capacities and transitions at high pressures. Two of the systems: urea inclusion compounds and clathrate hydrates, show unusual glass-like thermal conductivity k, i.e. their k is low and only weakly dependent on temperature  despite their crystalline structure. Moreover, results for k of Dianin’s compound with guests such as ethanol and CCl4 indicate a change from glass-like k  at atmospheric pressure to crystalline-like k at elevated pressure, whereas k of hydroquinone and thiourea inclusion compounds appears not to have been studied. Despite the technological and fundamental importance of the unusual glass-like k, e.g. the use of inclusion compounds as structural model systems for finding improved thermoelectrical materials, the origin of the glass-like k is not established. More specifically, the commonly employed rattling model, in which rattling guest motions cause resonance scattering of the acoustic host phonons, has recently been challenged, and we discuss alternative models. Heat capacity studies of these compounds reveal numerous transitions, which are associated with guest and host disorder-order transitions upon cooling and pressurization. A transition in hydroquinone may be of second order, or have only a small first-order component, which can explain discrepancies in the observed transition behavior. On pressurization at low temperatures, clathrate hydrates collapse to an amorphous state, which appears to be a glassy state of a water solution with perfectly spaced solute molecules.

  • 7. Andrew, Rhiann E.
    et al.
    Ferdani, Dominic W.
    Ohlin, C. Andre
    Chaplin, Adrian B.
    Coordination Induced Atropisomerism in an NHC-Based Rhodium Macrocycle2015In: Organometallics, ISSN 0276-7333, E-ISSN 1520-6041, Vol. 34, no 5, p. 913-917Article in journal (Refereed)
    Abstract [en]

    Reversible interaction with carbon monoxide results in the onset of dynamic atropisomerism at 298 K in an otherwise static NHC-based rhodium pincer complex, [Rh(C boolean AND N boolean AND C-(CH2)(12))(CO)][BArF4] (1, ArF = 3,5-C6H3(CF3)(2)). The mechanism of this process has been comprehensively interrogated by a combination of variable-temperature NMR spectroscopy, IR spectroscopy, and computational modeling. In addition, a structural analogue of a high-energy symmetrical intermediate species-invoked in the process but not directly observed spectroscopically-has been prepared and characterized in solution and the solid-state.

  • 8.
    Annamalai, Alagappan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sandström, Robin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Boulanger, Nicolas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Muehlbacher, Inge
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Double donor Sb5+doped hematite (Fe3+) photoanodes for surface-enhanced PEC water splitting2018In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 256Article in journal (Other academic)
  • 9. Arafa, Wael A. A.
    et al.
    Kärkäs, Markus D.
    Lee, Bao-Lin
    Åkermark, Torbjörn
    Liao, Rong-Zhen
    Berends, Hans-Martin
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Messinger, Johannes
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Siegbahn, Per E. M.
    Åkermark, Björn
    Dinuclear manganese complexes for water oxidation: evaluation of electronic effects and catalytic activity2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 24, p. 11950-11964Article in journal (Refereed)
    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.

  • 10. Bandyopadhyay, Sulalit
    et al.
    Singh, Gurvinder
    Sandvig, Ioanna
    Sandvig, Axel
    MI Lab and Department of Circulation and Medical Imaging, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
    Mathieu, Roland
    Kumar, P. Anil
    Glomm, Wilhelm Robert
    Synthesis and in vitro cellular interactions of superparamagnetic iron nanoparticles with a crystalline gold shell2014In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 316, p. 171-178Article in journal (Refereed)
    Abstract [en]

    Fe@Au core-shell nanoparticles (NPs) exhibit multiple functionalities enabling their effective use in applications such as medical imaging and drug delivery. In this work, a novel synthetic method was developed and optimized for the synthesis of highly stable, monodisperse Fe@Au NPs of average diameter similar to 24 nm exhibiting magneto-plasmonic characteristics. Fe@Au NPs were characterized by a wide range of experimental techniques, including scanning (transmission) electron microscopy (S(T)EM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), dynamic light scattering (DLS) and UV-vis spectroscopy. The formed particles comprise an amorphous iron core with a crystalline Au shell of tunable thickness, and retain the superparamagnetic properties at room temperature after formation of a crystalline Au shell. After surface modification, PEGylated Fe@Au NPs were used for in vitro studies on olfactory ensheathing cells (OECs) and human neural stem cells (hNSCs). No adverse effects of the Fe@Au particles were observed post-labeling, both cell types retaining normal morphology, viability, proliferation, and motility. It can be concluded that no appreciable toxic effects on both cell types, coupled with multifunctionality and chemical stability make them ideal candidates for therapeutic as well as diagnostic applications.

  • 11.
    Barzegar, Hamid Reza
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Jia, Xueen
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Palladium nanocrystals supported on photo-transformed C-60 nanorods: effect of crystal morphology and electron mobility on the electrocatalytic activity towards ethanol oxidation2014In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 73, p. 34-40Article in journal (Refereed)
    Abstract [en]

    We report on the synthesis and decoration of high-aspect-ratio crystalline C-60 nanorods (NRs) by functionalized palladium nanoparticles with an average size of 4.78 +/- 0.66 nm. In their pristine form, C-60 NRs suffer from partial damage in the solution-based decoration process resulting in poor crystallinity. However, by modifying the NR surface via in situ photochemical transformation in the liquid state, we are able to prepare highly stable NRs that retain their crystalline structure during the decoration process. Our method thus opens up for the synthesis of highly crystalline nanocomposite hybrids comprising Pd nanoparticles and C-60 NRs. Bys measuring the electron mobility of different C-60 NRs, we relate both the effect of electron mobility and crystallinity to the final electrocatalytic performance of the synthesized hybrid structures. We show that the photo-transformed C-60 NRs exhibit highly advantageous properties for ethanol oxidation based on both a better crystallinity and a higher bulk conductivity. These findings give important information in the search for efficient catalyst support.

  • 12.
    Barzegar, Hamid Reza
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Solution-Based Phototransformation of C-60 Nanorods: Towards Improved Electronic Devices2013In: Particle & particle systems characterization, ISSN 0934-0866, E-ISSN 1521-4117, Vol. 30, no 8, p. 715-720Article in journal (Refereed)
    Abstract [en]

    A modified liquid-liquid interface precipitation synthesis of C-60 nanorods, effects and opportunities following an in situ photochemical transformation in the liquid state, and an electronic characterization using a field-effect transistor (FET) geometry are reported. The nanorods feature a high aspect ratio of approximate to 10(3) and a notably small average diameter of 172 nm. Interestingly, it is found that a decreased nanorod diameter appears to correlate with distinctly improved electronic properties, and an average electron mobility of 0.30 cm(2) V-1 s(-1), as measured in a FET geometry, is reported for as-grown nanorods, with the peak value being an impressive 1.0 cm(2) V-1 s(-1). A photoexposure using green laser light ( = 532 nm) is demonstrated to result in the formation of a polymer-C-60 shell encapsulating a monomer-C-60 bulk; such photo-transformed nanorods exhibit an electron mobility of 4.7 x 10(-3) cm(2) V-1 s(-1). It is notable that the utilized FET geometry only probes the polymer-C-60 nanorod surface shell, and that the monomer-C-60 bulk is anticipated to exhibit a higher mobility. Importantly, photoexposed nanorods can be conveniently processed as a stabile dispersion in common hydrophobic solvents, and this finding is attributed to the insoluble character of the polymer-C-60 shell.

  • 13.
    Bengtsson, Åsa
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Phase Transformations, Ion-Exchange, Adsorption, and Dissolution Processes in Aquatic Fluorapatite Systems2009In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 4, p. 2355-2362Article in journal (Refereed)
    Abstract [en]

    A synthetic fluorapatite was prepared that undergoes a phase transformation generated during a dialysis step. A surface layer with the composition Ca9(HPO4)2(PO4)4F2 is formed, which is suggested to form as one calcium atom is replaced by two protons. A surface complexation model, based upon XPS measurements, potentiometric titration data, batch experiments, and zeta-potential measurements was presented. The CaOH and OPO3H2 sites were assumed to have similar protolytic properties as in a corresponding nonstoichiometric HAP (Ca8.4(HPO4)1.6(PO4)4.4(OH)0.4) system. Besides a determination of the solubility product of Ca9(HPO4)2(PO4)4F2, two additional surface complexation reactions were introduced; one that accounts for a F/OH ion exchange reaction, resulting in the release of quite high fluoride concentrations (∼1 mM) that turned out to be dependent on the surface area of the particles. Furthermore, to explain the lowering of pHiep from around 8 in nonstoichiometric HAP suspensions to about 5.7 in FAP suspensions, a reaction that lowers the surface charge due to the readsorption of fluoride ions to the positively charged Ca sites was introduced: ≡CaOH2+ + F− ⇋ ≡CaF + H2O. The resulting model also agrees with predictions based upon XPS and ATR-FTIR observations claiming the formation of CaF2(s) in the most acidic pH range.

  • 14.
    Biasi, Pierdomenico
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Industrial Chemistry and Reaction Engineering, Process Chemistry Center (PCC), Department of Chemical Engineering, Åbo Akademi University,Turku/Åbo, Finland.
    Sterchele, Stefano
    Bizzotto, Francesco
    Manzoli, Maela
    Lindholm, Sten
    Ek, Paul
    Bobacka, Johan
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Industrial Chemistry and Reaction Engineering, Process Chemistry Center (PCC), Department of Chemical Engineering, Åbo Akademi University,Turku/Åbo, Finland.
    Salmi, Tapio
    Application of the Catalyst Wet Pretreatment Method (CWPM) for catalytic direct synthesis of H2O22015In: Catalysis Today, ISSN 0920-5861, E-ISSN 1873-4308, Vol. 246, no Special Issue, p. 207-215Article in journal (Refereed)
    Abstract [en]

    This work concerns a new technique to post-modify the catalytic material intended for use in H2O2 direct synthesis. The catalyst chosen was a commercially available 1 wt.% Pd/C. The catalyst was modified with the so-called Catalyst Wet Pretreatment Method (CWPM) that is used to post-modify prepared catalysts with aqueous solutions of NaBr, in different concentrations. The performance of pristine and the pretreated materials were then compared in the H2O2 direct synthesis and characterized before and after the catalytic tests in order to understand the role of the different concentrations of bromide in the CWPM procedure. The surface features of the different catalysts were analyzed with CO chemisorption (metal dispersion and mean particle size), Transmission Electron Microscopy (TEM, for Pd morphology and Pd particle size distributions), Inductive Coupled Plasma (ICP, for Pd content) and Ion Chromatography (IC, for bromide content). Various features of the materials prepared with the CWPM were correlated with the catalytic performance. It was found that the bromide has an active role in the reconstruction of metal phase and it does not only act as a poison for the most active catalytic sites as often reported in literature. By using this new protocol, the production H2O2 was almost doubled compared to the non-modified material when no direct promoters were added to the reaction environment.

  • 15.
    Bokvist, Marcus
    Umeå University, Faculty of Science and Technology, Chemistry.
    Membrane mediated aggregation of amyloid-β protein: a potential key event in Alzheimer's disease2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The pathogenesis of Alzheimer’s disease (AD), the most common senile dementia, is a complex process. A crucial event in AD is the aggregation of amyloid-β protein (Aβ), a cleavage product from the Amyloid Precursor Protein (APP). Aβ40, a common component in amyloid plaques found in patients, aggregates in vitro at concentrations, much higher than the one found in vivo. But in the presence of charged lipid membranes, aggregations occurs at much lower concentration in vitro compared to the membrane-free case. This can be understood due to the ability of Aβ to get electrostatically attracted to target membranes with a pronounced surface potential. This electrostatically driven process accumulates peptide at the membrane surface at concentrations high enough for aggregation while the bulk concentration still remains below threshold. Here, we elucidated the molecular nature of this Aβ-membrane process and its consequences for Aβ misfolding by Circular Dichroism Spectroscopy, Differential Scanning Calorimetry and Nuclear Magnetic Resonance Spectroscopy. First, we revealed by NMR that Aβ40 peptide does indeed interact electrostatically with membranes of negative and positive surface potential. Surprisingly, it even binds to nominal neutral membranes if these contain lipids of opposite charge. Combined NMR and CD studies also revealed that the peptide might be shielded from aggregation when incorporated into the membrane. Moreover, CD studies of Aβ40 added to charged membranes showed that both positively and negatively membranes induce aggregation albeit at different kinetics and finally that macromolecular crowding can both speed up and slow down aggregation of Aβ.

  • 16.
    Bui, Thai Q.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Khokarale, Santosh G.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shukla, Shashi Kant
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Industrial Chemistry & Reaction Engineering, Department of Chemical Engineering, Johan Gadolin Process Chemistry Centre, Åbo Akademi University, Biskopsgatan 8, FI-20500 Åbo-Turku, Finland.
    Switchable Aqueous Pentaethylenehexamine System for CO2 Capture: an Alternative Technology with Industrial Potential2018In: ACS Sustainable Chemistry & Engineering, ISSN 2168-0485, Vol. 6, no 8, p. 10395-10407Article in journal (Refereed)
    Abstract [en]

    Herein we report the application of polyamine pentaethylenehexamine (PEHA, 3,6,9,12-tetraazatetradecane-1,14-diamine) in CO2 absorption with both neat PEHA and aqueous solutions thereof. The absorption of molecular CO2 in pure PEHA and in PEHA-water systems resulted in the formation of two chemical species, namely, PEHA carbamate and bicarbonate. It was observed that, upon formation of these species, both the CO2 absorption capacity and CO2 absorption rate were controlled by the amount of water in the system. During the CO2 absorption, the neat PEHA and 92 wt % PEHA were capable of forming carbamate species only while other aqueous analogues with higher dilution allowed for the formation of both carbamate and bicarbonate species upon exceeding 8 wt % water in the mixture. The CO2 uptake steadily increased with an increase in the water concentration in the solvent mixture and reached the maximum value of 0.25 g of CO2/(g of solvent) in the case of 56 wt % PEHA in water. However, in the case of more dilute systems (i.e., <56 wt % PEHA in water), the trend reversed and the CO2 loading decreased linearly to 0.05 g of CO2/(g of solvent) for 11 wt % PEHA in water. Meanwhile, it usually took shorter time to achieve the full CO2 absorption capacity (equilibrium) with increasing water content in all cases. The C-13 NMR analysis was used to quantify the relative amount of PEHA carbamate and bicarbonate, respectively, in reaction mixtures. The Kamle-Taft parameters (alpha, beta, and pi*) of aqueous solutions for different concentrations of PEHA were also studied taking advantage of various solvatochromic dyes and correlated with the CO2 absorption capacity. The thermally induced switchable nature of CO2-saturated neat and aqueous PEHA solutions for transformation of ionic PEHA carbamate and bicarbonate moieties to molecular PEHA is also represented. A comparison between aqueous PEHA and aqueous monoethanolamine (industrial solvent) for CO2 capture is reported. Hence, most importantly, a switchable PEHA system is demonstrated for reversible CO2 absorption processes.

  • 17. Cano, A.
    et al.
    Lartundo-Rojas, L.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Reguera, E.
    Contribution to the coordination chemistry of transition metal nitroprussides: a cryo-XPS study2019In: New Journal of Chemistry, ISSN 1144-0546, E-ISSN 1369-9261, Vol. 43, no 12, p. 4835-4848Article in journal (Refereed)
    Abstract [en]

    The series of coordination polymers under investigation was formed by the assembly of a pentacyanonitrosylferrate(ii) anionic block, [Fe(CN)(5)NO](2-), through monovalent and divalent transition metal ions, e.g. Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+ and Ag+. For divalent ions, the resulting materials have a 3D porous framework with attractive features for applications in gas storage and separation, as electroactive solids, light-driven molecular magnets, and so on; in this study, we report the results obtained for a series of coordination polymers using the cryogenic X-ray photoelectron spectroscopy (cryo-XPS) data; comprehensive details regarding their coordination chemistries were obtained from the acquired spectra in addition to their comparison with the structural and spectroscopic information obtained from other techniques. The results discussed herein are original and contribute towards the understanding of the electronic structures and related properties for this family of coordination polymers. This series of solids was found to be highly susceptible to strong damage induced by X-ray beams throughout the conventional XPS experiment; therefore, the analysis was conducted under cryogenic conditions.

  • 18. Chatterjee, Ruchira
    et al.
    Lassalle, Louise
    Gul, Sheraz
    Fuller, Franklin D.
    Young, Iris D.
    Ibrahim, Mohamed
    de Lichtenberg, Casper
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Department of Chemistry – Ångström, Molecular Biomimetics, Uppsala University, Uppsala 75237, Sweden.
    Cheah, Mun Hon
    Zouni, Athina
    Messinger, Johannes
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Department of Chemistry – Ångström, Molecular Biomimetics, Uppsala University, Uppsala 75237, Sweden.
    Yachandra, Vittal K.
    Kern, Jan
    Yano, Junko
    Structural isomers of the S-2 state in photosystem II: do they exist at room temperature and are they important for function?2019In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 166, no 1, p. 60-72Article in journal (Refereed)
    Abstract [en]

    In nature, an oxo‐bridged Mn4CaO5 cluster embedded in photosystem II (PSII), a membrane‐bound multi‐subunit pigment protein complex, catalyzes the water oxidation reaction that is driven by light‐induced charge separations in the reaction center of PSII. The Mn4CaO5 cluster accumulates four oxidizing equivalents to enable the four‐electron four‐proton catalysis of two water molecules to one dioxygen molecule and cycles through five intermediate S‐states, S0 – S4 in the Kok cycle. One important question related to the catalytic mechanism of the oxygen‐evolving complex (OEC) that remains is, whether structural isomers are present in some of the intermediate S‐states and if such equilibria are essential for the mechanism of the O‐O bond formation. Here we compare results from electron paramagnetic resonance (EPR) and X‐ray absorption spectroscopy (XAS) obtained at cryogenic temperatures for the S2state of PSII with structural data collected of the S1, S2 and S3 states by serial crystallography at neutral pH (∼6.5) using an X‐ray free electron laser at room temperature. While the cryogenic data show the presence of at least two structural forms of the S2 state, the room temperature crystallography data can be well‐described by just one S2 structure. We discuss the deviating results and outline experimental strategies for clarifying this mechanistically important question.

  • 19. Chen, Xi
    et al.
    Venkatachalapathy, Muthukumaran
    Dehmelt, Leif
    Wu, Yao-Wen
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Multidirectional Activity Control of Cellular Processes by a Versatile Chemo-optogenetic Approach2018In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 57, no 37, p. 11993-11997Article in journal (Refereed)
    Abstract [en]

    The spatiotemporal dynamics of proteins or organelles plays a vital role in controlling diverse cellular processes. However, acute control of activity at distinct locations within a cell is challenging. A versatile multidirectional activity control (MAC) approach is presented, which employs a photoactivatable system that may be dimerized upon chemical inducement. The system comprises second-generation SLF*-TMP (S*T) and photocaged NvocTMP-Cl dimerizers; where, SLF*-TMP features a synthetic ligand of the FKBP(F36V) binding protein, Nvoc is a caging group, and TMP is the antibiotic trimethoprim. Two MAC strategies are demonstrated to spatiotemporally control cellular signaling and intracellular cargo transport. The novel platform enables tunable, reversible, and rapid control of activity at multiple compartments in living cells.

  • 20. Chumakova, Natalia A.
    et al.
    Rebrikova, Anastasya T.
    Talyzin, Aleksandr V.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Paramonov, Nikita A.
    Vorobiev, Andrey Kh
    Korobov, Mikhail, V
    Properties of Graphite Oxide Powders and Membranes as Revealed by Electron Paramagnetic Resonance Spectroscopy2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 39, p. 22750-22759Article in journal (Refereed)
    Abstract [en]

    The spin probe technique was used to study graphite oxide (GO) powders swelled in polar liquids (CH3CN, CH3OH, and H2O) and liquid-free GO membranes (GOM). The nitroxide radicals TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) and TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl) readily penetrated into the interplane space of GO from the solution. Electron paramagnetic resonance (EPR) spectra of these radical probes were sensitive to molecular mobility and orientation ordering within the internal space of GO. The radicals embedded in swelled GO were in two states with different rotational mobilities. The small fraction of radicals located in the interplane space of GO and detected in the broad range of temperatures was in the state of fast rotation, similar to the same radicals dissolved in bulk liquids, thus providing experimental evidence of formation of a liquid-like media within the interplane space of GO. Such mobile media may be responsible for the unusual permeation properties of GOM, which is reported in the literature. Second, less-mobile fraction of radicals was found to be immobilized at the internal surface of GO and was sensitive to phase transformations in the swelled GO structures. The transformations were detected as anomalies at temperature dependences of rotational mobility of radicals. The detected dependence of EPR spectra of probe radicals on orientation of GOM, relative to the direction of magnetic field in the EPR spectrometer, was used for quantitative characterization of orientation alignment of GO planes within the membranes. Such an approach may serve as an elegant method to estimate the relative quality of membranes and other GO-layered structures.

  • 21. Cui, Wen
    et al.
    Yao, Mingguang
    Yao, Zhen
    Ma, Fengxian
    Li, Quanjun
    Liu, Ran
    Liu, Bo
    Zou, Bo
    Cui, Tian
    Liu, Bingbing
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Reversible pressure-induced polymerization of Fe(C5H5)(2) doped C-702013In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 62, p. 447-454Article in journal (Refereed)
    Abstract [en]

    High pressure Raman, IR and X-ray diffraction (XRD) studies have been carried out on C-70(Fe(C5H5)(2))(2) (hereafter, "C-70(Fc)(2)") sheets. Theoretical calculation is further used to analyze the Electron Localization Function (ELF) and charge transfer in the crystal and thus to understand the transformation of C-70(Fc)(2) under pressure. Our results show that even at room temperature dimeric phase and one dimensional (1D) polymer phase of C-70 molecules can be formed at about 3 and 8 GPa, respectively. The polymerization is found to be reversible Upon decompression and the reversibility is related to the pressure-tuned charge transfer, as well as the overridden steric repulsion of counter ions. According to the layered structure of the intercalated ferrocene molecules formed in the crystal, we suggest that ferrocene acts as not only a spacer to restrict the polymerization of C-70 molecules within a layer, but also as charge reservoir to tune the polymerization process. This supplies a possible way for us to design the polymerization of fullerenes at suitable conditions.

  • 22. da Hora, G. C. A.
    et al.
    Archilha, N. L.
    Lopes, J. L. S.
    Mueller, D. M.
    Coutinho, K.
    Itri, R.
    Soares, T. A.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Departamento de Quı´mica Fundamental, Universidade Federal de Pernambuco, 50740-560 Cidade Universita´ria, Recife, Brazil.
    Membrane negative curvature induced by a hybrid peptide from pediocin PA-1 and plantaricin 149 as revealed by atomistic molecular dynamics simulations2016In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 12, no 43, p. 8884-8898Article in journal (Refereed)
    Abstract [en]

    Antimicrobial peptides (AMPs) are cationic peptides that kill bacteria with a broad spectrum of action, low toxicity to mammalian cells and exceptionally low rates of bacterial resistance. These features have led to considerable efforts in developing AMPs as an alternative antibacterial therapy. In vitro studies have shown that AMPs interfere with membrane bilayer integrity via several possible mechanisms, which are not entirely understood. We have performed the synthesis, membrane lysis measurements, and biophysical characterization of a novel hybrid peptide. These measurements show that PA-Pln149 does not form nanopores, but instead promotes membrane rupture. It causes fast rupture of the bacterial model membrane (POPG-rich) at concentrations 100-fold lower than that required for the disruption of mammalian model membranes (POPC-rich). Atomistic molecular dynamics (MD) simulations were performed for single and multiple copies of PA-Pln149 in the presence of mixed and pure POPC/POPG bilayers to investigate the concentration-dependent membrane disruption by the hybrid peptide. These simulations reproduced the experimental trend and provided a potential mechanism of action for PA-Pln149. It shows that the PA-Pln149 does not form nanopores, but instead promotes membrane destabilization through peptide aggregation and induction of membrane negative curvature with the collapse of the lamellar arrangement. The sequence of events depicted for PA-Pln149 may offer insights into the mechanism of action of AMPs previously shown to induce negative deformation of membrane curvature and often associated with peptide translocation via non-bilayer intermediate structures.

  • 23. Davidovich, P. B.
    et al.
    Fischer, A. I.
    Korchagin, D. V.
    Panchuk, V. V.
    Shchukarev, Andrey V.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Garabadzhiu, A. V.
    Belyaev, A. N.
    Synthesis, structure, biochemical, and docking studies of a new dinitrosyl iron complex [Fe-2(mu-SC4H3SCH2)(2)(NO)(4)]2015In: Journal of Molecular Structure, ISSN 0022-2860, E-ISSN 1872-8014, Vol. 1092, p. 137-142Article in journal (Refereed)
    Abstract [en]

    A new dinitrosyl iron complex of binuclear structure [Fe-2(mu-S-2-methylthiophene)(2)(NO)(4)] was first synthesized and structurally characterized by XRD and theoretical methods. Using caspase-3 as an example it was shown that [Fe-2(mu-S-2-methylthiophene)(2)(NO)(4)] and its analog [Fe-2(mu-S-2-methylfurane)(2)(NO)(4)] can inhibit the action of active site cysteine proteins; the difference in inhibitory activity was explained by molecular docking studies. Biochemical and in silico studies give grounds that the biological activity of dinitrosyl iron complexes is a mu-SR bridging ligand structure function. Thus the rational design strategy of [Fe-2(mu-SR)(2)(NO)(4)] complexes can be applied to make NO prodrugs with high affinity to therapeutically significant targets involved in cancer and inflammation.

  • 24.
    Demir, Ayhan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    NMR-the basic principles and its use in studies of water/ethanol/mixture2012Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
  • 25. Domashevskaya, EP
    et al.
    Ryabtsev, SV
    Turishchev, S Yu
    Kashkarov, VM
    Yurakov, Yu A
    Chuvenkova, OA
    Shchukarev, Andrey V
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    XPS and XANES studies of SnOx nanolayers2008In: Journal of Structural Chemistry, ISSN 0022-4766, E-ISSN 1573-8779, Vol. 49, no Suppl 1, p. 80-91Article in journal (Refereed)
    Abstract [en]

    This paper presents the results of our XPS (X-ray photoelectron spectroscopy) and XANES (X-ray absorption near edge structure) Studies of tin oxide nanolayers obtained by magnetron spraying of the metal and its further oxidation in air at different temperatures. It was shown that at 240 degrees C (annealing temperature), tin monoxide was dominant in the surface layer of the samples. When the temperature was increased to 450 degrees C, the phase composition corresponded to tin dioxide. Increased sorption ability was found for the samples oxidized at 450 degrees C. The band structure model of SnOx nanolayers obtained by superposition of the XANES and XPS data revealed cross transitions with energy similar to 3.7 eV in the presence of the SnO and SnO, phases. Surface doping of nanolayers with palladium gave the Pd, PdO, and PdO2 components, among which PdO was most intense. Alternate treatments with O-2 and H-2 gases led to the disappearance of palladium dioxide and the reduction of PdO to the Pd metal. After the volume doping of nanoplayers with palladium, the surface layer contained PdO and PdO2; the latter was represented by two types of particles with different sizes.

  • 26. Drager, Luciano F.
    et al.
    Yao, Qiaoling
    Hernandez, Karen L.
    Shin, Mi-Kyung
    Bevans-Fonti, Shannon
    Gay, Jason
    Sussan, Thomas E.
    Jun, Jonathan C.
    Myers, Allen C.
    Olivecrona, Gunilla
    Umeå University, Faculty of Medicine, Department of Medical Biosciences, Physiological chemistry.
    Schwartz, Alan R.
    Halberg, Nils
    Scherer, Philipp E.
    Semenza, Gregg L.
    Powell, David R.
    Polotsky, Vsevolod Y.
    Chronic Intermittent Hypoxia Induces Atherosclerosis via Activation of Adipose Angiopoietin-like 42013In: American Journal of Respiratory and Critical Care Medicine, ISSN 1073-449X, E-ISSN 1535-4970, Vol. 188, no 2, p. 240-248Article in journal (Refereed)
    Abstract [en]

    Rationale: Obstructive sleep apnea is a risk factor for dyslipidemia and atherosclerosis, which have been attributed to chronic intermittent hypoxia (CIH). Intermittent hypoxia inhibits a key enzyme of lipoprotein clearance, lipoprotein lipase, and up-regulates a lipoprotein lipase inhibitor, angiopoietin-like 4 (Angptl4), in adipose tissue. The effects and mechanisms of Angptl4 up-regulation in sleep apnea are unknown. Objectives: To examine whether CIH induces dyslipidemia and atherosclerosis by increasing adipose Angptl4 via hypoxia-inducible factor-1 (HIF-1). Methods: ApoE(-/-) mice were exposed to intermittent hypoxia or air for 4 weeks while being treated with Angptl4-neutralizing antibody or vehicle. Measurements and Main Results: In vehicle-treated mice, hypoxia increased adipose Angptl4 levels, inhibited adipose lipoprotein lipase, increased fasting levels of plasma triglycerides and very low density lipoprotein cholesterol, and increased the size of atherosclerotic plaques. The effects of CIH were abolished by the antibody. Hypoxia-induced increases in plasma fasting triglycerides and adipose Angptl4 were not observed in mice with germline heterozygosity for a HIF-1 alpha knockout allele. Transgenic overexpression of HIF-1 alpha in adipose tissue led to dyslipidemia and increased levels of adipose Angptl4. In cultured adipocytes, constitutive expression of HIF-1 alpha increased Angptl4 levels, which was abolished by siRNA. Finally, in obese patients undergoing bariatric surgery, the severity of nocturnal hypoxemia predicted Angptl4 levels in subcutaneous adipose tissue. Conclusions: HIF-1-mediated increase in adipose Angptl4 and the ensuing lipoprotein lipase in activation may contribute to atherosclerosis in patients with sleep apnea.

  • 27.
    Driver, Gordon W.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Huang, Yang
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Laaksonen, Aatto
    Sparrman, Tobias
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Wang, Yonglei
    Westlund, Per-Olof
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Correlated/non-correlated ion dynamics of charge-neutral ion couples: the origin of ionicity in ionic liquids2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 7, p. 4975-4988Article in journal (Refereed)
    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.

  • 28. Du, Mingrun
    et al.
    Zhou, Miao
    Yao, Mingguang
    Ge, Peng
    Chen, Shuanglong
    Yang, Xigui
    Liu, Ran
    Liu, Bo
    Cui, Tian
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics. State Key Laboratory of Superhard Materials, Jilin University, Changchun, PR China.
    Liu, Bingbing
    High pressure infrared spectroscopy study on C60*CS2 solvates2017In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 669, p. 49-53Article in journal (Refereed)
    Abstract [en]

    High pressure IR study has been carried out on C-60*CS2 solvates up to 34.8 GPa. It is found that the intercalated CS2 molecules significantly affect the transformations of C-60 molecules under pressure. As a probe, the intercalated CS2 molecules can well detect the orientational ordering transition and deformation of C-60 molecules under pressure. The chemical stability of CS2 molecules under pressure is also dramatically enhanced due to the spacial shielding effet from C-60 molecules around in the solvated crystal. These results provide new insight into the effect of interactions between intercalants and fullerenes on the transformations in fullerene solvates under pressure.

  • 29. Dyson, P J
    et al.
    Laurenczy, G
    Ohlin, C A
    Vallance, J
    Welton, T
    Determination of hydrogen concentration in ionic liquids and the effect (or lack of) on rates of hydrogenation2003In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, no 19, p. 2418-2419Article in journal (Refereed)
    Abstract [en]

    The solubility of hydrogen and the corresponding Henry coefficients for 11 ionic liquids have been determined in situ at 100 atm H(2) pressure and are much lower than expected; attempts to correlate the solubility of hydrogen in the ionic liquids with the rate of reaction for the hydrogenation of benzene to cyclohexane in these solvents have been made.

  • 30.
    Dzwilewski, Andrzej
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Matyba, Piotr
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Facile fabrication of efficient organic CMOS circuits2010In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 114, no 1, p. 135-140Article in journal (Refereed)
    Abstract [en]

    Organic electronic circuits based on a combination of n- and p-type transistors (so-called CMOS circuits) are attractive, since they promise the realization of a manifold of versatile and low-cost electronic devices. Here, we report a novel photoinduced transformation method, which allows for a particularly straightforward fabrication of highly functional organic CMOS circuits. A solution-deposited single-layer film, comprising a mixture of the n-type semiconductor [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and the p-type semiconductor poly-3-hexylthiophene (P3HT) in a 3:1 mass ratio, was utilized as the common active material in an array of transistors. Selected film areas were exposed to laser light, with the result that the irradiated PCBM monomers were photochemically transformed into a low-solubility and high-mobility dimeric state. Thereafter, the entire film was developed via immersion into a developer solution, which selectively removed the nonexposed, and monomeric, PCBM component. The end result was that the transistors in the exposed film areas are n-type, as dimeric PCBM is the majority component in the active material, while the transistors in the nonexposed film areas are p-type, as P3HT is the sole remaining material. We demonstrate the merit of the method by utilizing the resulting combination of n-type and p-type transistors for the realization of CMOS inverters with a high gain of ∼35.

  • 31. Emilsson, Gustav
    et al.
    Röder, Evelyn
    Malekian, Bita
    Xiong, Kunli
    Manzi, John
    Tsai, Feng-Ching
    Cho, Nam-Joon
    Bally, Marta
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology. Umeå University, Faculty of Medicine, Wallenberg Centre for Molecular Medicine at Umeå University (WCMM).
    Dahlin, Andreas
    Nanoplasmonic Sensor Detects Preferential Binding of IRSp53 to Negative Membrane Curvature2019In: Frontiers in Chemistry, E-ISSN 2296-2646, Vol. 7, article id 1Article in journal (Refereed)
    Abstract [en]

    Biosensors based on plasmonic nanostructures are widely used in various applications and benefit from numerous operational advantages. One type of application where nanostructured sensors provide unique value in comparison with, for instance, conventional surface plasmon resonance, is investigations of the influence of nanoscale geometry on biomolecular binding events. In this study, we show that plasmonic "nanowells" conformally coated with a continuous lipid bilayer can be used to detect the preferential binding of the insulin receptor tyrosine kinase substrate protein (IRSp53) I-BAR domain to regions of negative surface curvature, i.e., the interior of the nanowells. Two different sensor architectures with and without an additional niobium oxide layer are compared for this purpose. In both cases, curvature preferential binding of IRSp53 (at around 0.025 nm(-1) and higher) can be detected qualitatively. The high refractive index niobium oxide influences the near field distribution and makes the signature for bilayer formation less clear, but the contrast for accumulation at regions of negative curvature is slightly higher. This work shows the first example of analyzing preferential binding of an average-sized and biologically important protein to negative membrane curvature in a label-free manner and in real-time, illustrating a unique application for nanoplasmonic sensors.

  • 32. Genoni, Andrea
    et al.
    Chirdon, Danielle N.
    Boniolo, Manuel
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Univ Padua, Padua, Italy ; UoS Padova, Padua, Italy.
    Sartorel, Andrea
    Bernhard, Stefan
    Bonchio, Marcella
    Tuning Iridium Photocatalysts and Light Irradiation for Enhanced CO2 Reduction2017In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 7, no 1, p. 154-160Article in journal (Refereed)
    Abstract [en]

    Efficient photocatalytic conversion of carbon dioxide into valuable reduction products is a priority goal for artificial photosynthesis. Iridium(III) photocatalysts with a combined 2-phenylpyridine (ppy) and 2,2':6',2 ''-terpyridine (tpy) ligand set have been shown to selectively reduce CO, to CO. Here, terpyridine modifications have been investigated that yield a turnover number (TON) of up to 265, a quantum yield of 0.10, and a photocatalyst lifespan of over 10 days. The key to success is the combined effect of adding aromatic substituents to the tpy ligand 4'-position and optimizing lighting conditions. Insights into the photocatalyst fate are provided by kinetics analysis and spectroelectrochemistry, which point out the critical role of the reductively quenched catalyst and its evolution to a spent "green" state via a dark deactivation pathway. The stereoelectronic effect of adding a 9-anthryl substituent together with the use of low-energy blue light proves instrumental in the management of excited and reduced species, dictating the overall performance of the molecular photocatalyst.

  • 33.
    Ghorbani, Ramin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    ICL-based TDLAS sensor for real-time breath gas analysis of carbon monoxide isotopes2017In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 25, no 11, p. 12743-12752Article in journal (Refereed)
    Abstract [en]

    We present a compact sensor for carbon monoxide (CO) in air and exhaled breath based on a room temperature interband cascade laser (ICL) operating at 4.69 µm, a low-volume circular multipass cell and wavelength modulation absorption spectroscopy. A fringe-limited (1σ) sensitivity of 6.5 × 10−8 cm−1Hz-1/2 and a detection limit of 9 ± 5 ppbv at 0.07 s acquisition time are achieved, which constitutes a 25-fold improvement compared to direct absorption spectroscopy. Integration over 10 s increases the precision to 0.6 ppbv. The setup also allows measuring the stable isotope 13CO in breath. We demonstrate quantification of indoor air CO and real-time detection of CO expirograms from healthy non-smokers and a healthy smoker before and after smoking. Isotope ratio analysis indicates depletion of 13CO in breath compared to natural abundance.

  • 34. Gorkina, Alexandra L
    et al.
    Tsapenko, Alexey P
    Gilshteyn, Evgenia P
    Koltsova, Tatiana S
    Larionova, Tatiana V
    Talyzin, Alexandr
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Anisimov, Anton S
    Anoshkin, Ilya V
    Kauppinen, Esko I
    Tolochko, Oleg V
    Nasibulin, Albert G
    Transparent and conductive hybrid graphene/carbon nanotube films2016In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 100, p. 501-507Article in journal (Refereed)
    Abstract [en]

    Carbon nanomaterials (carbon nanotubes (CNTs) and graphene) are promising materials for optoelectronic applications, including flexible transparent and conductive films (TCFs) due to their extraordinary electrical, optical and mechanical properties. However, the performance of CNT- or graphene-only TCFs still needs to be improved. One way to enhance the optoelectrical properties of TCFs is to hybridize CNTs and graphene. This approach leads to creation of a novel material that exhibits better properties than its individual constituents. In this work, the novel hybrid CNT-graphene nanomaterial was fabricated by graphene oxide deposition on top of CNT films. The graphene oxide was then reduced by thermal annealing at ambient atmosphere or in H2 atmosphere. At the final step the CNT-graphene hybrids were chemically doped using gold(III) chloride. As a result, we show that the hybrids demonstrate excellent optoelectrical performance with the sheet resistance as low as 73 Ω/□ at 90% transmittance.

  • 35.
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Behind the Synergistic Effect Observed on Phosphorus Nitrogen Codoped Graphene during the Oxygen Reduction Reaction2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 49, p. 27849-27857Article in journal (Refereed)
    Abstract [en]

    Ab initio calculations are performed to investigate how the simultaneous introduction of phosphorus and nitrogen into graphene modifies the availability and spatial distribution of catalytic active sites for an oxygen reduction reaction (ORR). A phosphoryl group (R-3-P=0) is selected as a representative for the phosphorus doping, and the ORR is studied under alkaline conditions where a 4e(-) mechanism is used to determine the limiting step and overpotential (eta(ORR)) along the entire graphene surface. A scanning procedure is used to construct eta(ORR) maps for pristine-, N-, P-, and diverse PN codoped graphenes. The results indicate that a single N (P) atom activates up to 17 (3) C atoms, while the simultaneous introduction of P and N activates up to 55 C atoms equivalent to 57% of the surface. Additionally, PN codoped graphenes reveals that the relative location of both dopants has significant effects on the ORR performance, where a P N separation distance of at least 4 angstrom minimizes the localization of electronic states on the neighboring C atoms and improves the quantity and distribution of active sites. The results shows the importance of designing synthesis procedures to control the dopant concentration and spatial distribution to maximize the number of active sites. Furthermore, the eta(ORR) maps reveal features that could be obtained by scanning tunneling microscopy allowing us to experimentally identify and possibly quantify the catalytic active sites on carbon-based materials.

  • 36.
    Gracia-Espino, Eduardo
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Barzegar, Hamid Reza
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sharifi, Tiva
    Yan, Aiming
    Zettl, Alex
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Fabrication of One-Dimensional Zigzag [6,6]-Phenyl-C-61-Butyric Acid Methyl Ester Nanoribbons from Two-Dimensional Nanosheets2015In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 9, no 10, p. 10516-10522Article in journal (Refereed)
    Abstract [en]

    One-dimensional (10) zigzag [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) nanoribbons are produced by folding two-dimensional ultrathin PCBM nanosheets in a simple solvent process. The unique 1D PCBM nanostructures exhibit uniform width of 3.8 +/- 0.3 nm, equivalent to four PCBM molecules, and lengths of 20-400 nm. These nanoribbons show well-defined crystalline structure, comprising PCBM molecules in a hexagonal arrangement without trapped solvent molecules. First-principle calculations and detailed experimental characterization provide an insight into the structure and formation mechanism of the 1D PCBM nanoribbons. Given their dimensions and physical properties, we foresee that these nanostructures should be ideal as acceptor material in organic solar cells.

  • 37.
    Gracia-Espino, Eduardo
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Science and Technology, Department of Chemistry. Advanced Materials Department, IPICYT, México.
    López-Urías, Florentino
    Terrones, Humberto
    Terrones, Mauricio
    Self-assembly synthesis of decorated nitrogen-doped carbon nanotubes with ZnO nanoparticles: anchoring mechanism and the effects of sulfur2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 1, p. 741-747Article in journal (Refereed)
    Abstract [en]

    Hybrid systems consisting of ZnO nanoparticles (ZnO-NPs) anchored on the surface of nitrogen-doped multiwalled carbon nanotubes (CNX-MWNTs) have been synthesized. The anchoring process consists of a self-assembly method involving the mixing of CNX-MWNTs in a solution with N,N-dimethylformamide, zinc acetylacetonate, and thiophene. Thiophene is used as a capping agent for controlling the size and distribution of ZnO-NPs, as well as an anchoring element between the NPs and the nanotube walls. Scanning and transmission electron microscopy characterization revealed that the ZnO-NPs are homogeneously deposited on the surface of CNX-MWNTs. X-ray powder diffraction analysis demonstrated that the ZnO-NPs exhibit a Wurtzite-type crystal structure with an average particle diameter of 5 nm. We also show that the ZnO-NPs do not exhibit a preferential growth direction with respect to the nanotube surface, and their formation is simply controlled by the concentration of the passivating agent. Density functional theory (DFT) calculations confirm that sulfur (from thiophene) is an effective passivating agent for ZnO by preferentially binding low-coordinated Zn atoms. However, the ZnO-NPs could be chemically bonded to the nanotubes through oxygen atoms close to the nitrogenated sites of the tubes. Our results also demonstrate that isolated and sulfur passivated ZnO-NPs become magnetic and exhibit half-metallicity (electronic states with only one spin component are present at the Fermi level). Sulfur-passivated ZnO retains these properties even after forming ZnO/CNX-MWNT hybrid materials.

  • 38. Harley, Steven J.
    et al.
    Ohlin, C. Andre
    Casey, William H.
    Geochemical kinetics via the Swift-Connick equations and solution NMR2011In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 75, no 13, p. 3711-3725Article in journal (Refereed)
    Abstract [en]

    Signal analysis in Nuclear Magnetic Resonance spectroscopy is among the most powerful methods to quantify reaction rates in aqueous solutions. To this end, the Swift-Connick approximations to the Bloch-McConnell equations have been used extensively to estimate rate parameters for elementary reactions. The method is primarily used for O-17 NMR in aqueous solutions, but the list of geochemically relevant nuclei that can be used is long, and includes Si-29, Al-27, F-19, C-13 and many others of particular interest to geochemists. Here we review the derivation of both the Swift-Connick and Bloch-McConnell equations and emphasize assumptions and quirks. For example, the equations were derived for CW-NMR, but are used with modern pulse FT-NMR and can be applied to systems that have exchange rates that are shorter than the lifetime of a typical pulse. The method requires a dilute solution where the minor reacting species contributes a negligible amount of total magnetization. We evaluate the sensitivity of results to this dilute-solution requirement and also highlight the need for chemically well-defined systems if reliable data are to be obtained. The limitations in using longitudinal relaxation to estimate reaction rate parameters are discussed. Finally, we provide examples of the application of the method, including ligand exchanges from aqua ions and hydrolysis complexes, that emphasize its flexibility. Once the basic requirements of the Swift-Connick method are met, it allows geochemists to establish rates of elementary reactions. Reactions at this scale lend themselves well to methods of computational simulation and could provide key tests of accuracy. (C) 2011 Elsevier Ltd. All rights reserved.

  • 39. Harley, Steven J.
    et al.
    Ohlin, C. Andre
    Johnson, Rene L.
    Panasci, Adele F.
    Casey, William H.
    The Pressure Dependence of Oxygen Isotope Exchange Rates Between Solution and Apical Oxygen Atoms on the [UO2(OH)(4)](2-) Ion2011In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 50, no 19, p. 4467-4469Article in journal (Refereed)
  • 40. He, Hanbing
    et al.
    Ji, Xiaoyan
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Öhman, Marcus
    Mechanism of Quartz Bed Particle Layer Formation in Fluidized Bed Combustion of Wood-Derived Fuels2016In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 30, no 3, p. 2227-2232Article in journal (Refereed)
    Abstract [en]

    Agglomeration is among one of the major problems in the operation of fluidized bed boilers. The formation of bed particle layers is thought to play an important role on the occurrence of agglomeration in wood-fired fluidized (quartz) beds. In spite of frequent experimental reports on the quartz bed particle layer characteristics, the underlying bed layer formation process has not yet been presented. By combining our previously experimental results on layer characteristics for samples with durations from 4 h to 23 days, with phase diagrams, thermochemical equilibrium calculations, and a diffusion model, a mechanism of quartz bed particle layer formation was proposed. For younger bed particles (<around 1 day), the layer growth process is accelerated due to a high diffusion of calcium in a K-rich silicate melt. However, with continuous addition of calcium into the layer, the amount of melt decreases and crystalline Ca-silicates starts to form. Ca2SiO4 is the dominating crystalline phase in the inner layer, while the formation of CaSiO3 and possibly Ca3SiO5 are favored for younger and older bed particles, respectively. The decreasing amount of melt and formation of crystalline phases result in low diffusion rates of calcium in the inner layer and the layer growth process becomes diffusion controlled after around 1 day.

  • 41.
    Hedenström, Mattias
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johnels, Dan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Characterization of Hydrogenated Fullerenes by NMR Spectroscopy2010In: Fulleranes: The Hydrogenated Fullerenes / [ed] Franco Cataldo, Susana Iglesias-Groth, Dordrecht: Springer Netherlands, 2010, Vol. 2, p. 171-202Chapter in book (Other academic)
    Abstract [en]

    NMR spectroscopy is so far the only analytical technique that has been used to get a detailed structural characterization of hydrogenated fullerenes. A substantial amount of information derived from different NMR experiments can thus be found in the literature for a number of fullerenes hydrogenated to various degrees. These studies have benefitted from the fact that chemical shifts of H-1 and C-13 and in some cases also He-3 can be used to obtain structural information of these compounds. Such results, together with discussions about different NMR experiments and general considerations regarding sample preparations, are summarized in this chapter. The unique information, both structural and physicochemical, that can be derived from different NMR experiments ensures that this technique will continue to be of central importance in characterization of hydrogenated fullerenes.

  • 42. Holmboe, Michael
    et al.
    Bourg, Ian C.
    Molecular Dynamics Simulations of Water and Sodium Diffusion in Smectite Interlayer Nanopores as a Function of Pore Size and Temperature2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 2, p. 1001-1013Article in journal (Refereed)
    Abstract [en]

    The diffusion coefficients (D) of water and solutes in nanoporousNa-smectite clay barriers have been widely studied because of their importancein high-level radioactive waste (HLRW) management and in the isolation of contaminated sites. However, few measurements have been carried out at the high temperatures that are expected to occur in HLRW repositories. We address this knowledge gap by using molecular dynamics (MD) simulations to predict the temperature dependence of diffusion in clay interlayer nanopores, expressed as a pore scale activation energy of diffusion (Ea). Our sensitivity analysis shows that accurate prediction of pore scale Dand Eavalues requires careful consideration of the influence of pore size, simulation cell size, and clay structure flexibility on MD simulation results. We find that predicted Dvalues in clay interlayer nanopores are insensitive to the size of the simulation cell (contrary to the behavior observed in simulation of bulk liquid water) but sensitive to the vibrational motions of clay atoms (particularly in the smallest pores investigated here, the one-, two-, and three-layer hydrates). Our predicted DandEavalues are consistent with experimental data. They reveal,for both water and Na+, that Eaincreases by∼6 kJ mol−1with increasing confinement, when going from bulk liquid water to theone-layer hydrate of Na-montmorillonite.

  • 43.
    Hu, Guangzhi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Laboratory of Environmental Science and Technology, The Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi 830011, China.
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sandström, Robin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sharifi, Tiva
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Cheng, Shaodong
    Shen, Hangjia
    Wang, Chuanyi
    Guo, Shaojun
    Yang, Guang
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Atomistic understanding of the origin of high oxygen reduction electrocatalytic activity of cuboctahedral Pt3Co-Pt core-shell nanoparticles2016In: Catalysis Science & Technology, ISSN 2044-4753, E-ISSN 2044-4761, Vol. 6, no 5, p. 1393-1401Article in journal (Refereed)
    Abstract [en]

    PtM-based core-shell nanoparticles are a new class of active and stable nanocatalysts for promoting oxygen reduction reaction (ORR); however, the understanding of their high electrocatalytic performance for ORR at the atomistic level is still a great challenge. Herein, we report the synthesis of highly ordered and homogeneous truncated cuboctahedral Pt3Co-Pt core-shell nanoparticles (cs-Pt3Co). By combining atomic resolution electron microscopy, X-ray photoelectron spectroscopy, extensive first-principles calculations, and many other characterization techniques, we conclude that the cs-Pt3Co nanoparticles are composed of a complete or nearly complete Pt monolayer skin, followed by a secondary shell containing 5-6 layers with similar to 78 at% of Pt, in a Pt3Co configuration, and finally a Co-rich core with 64 at% of Pt. Only this particular structure is consistent with the very high electrocatalytic activity of cs-Pt3Co nanoparticles for ORR, which is about 6 times higher than commercial 30%-Pt/Vulcan and 5 times more active than non-faceted (spherical) alloy Pt3Co nanoparticles. Our study gives an important insight into the atomistic design and understanding of advanced bimetallic nanoparticles for ORR catalysis and other important industrial catalytic applications.

  • 44.
    Humpolickova, Jana
    et al.
    J. Heyrovský Institute of Physical Chemistry, Prague, Czech Republic.
    Stefl, Martin
    J. Heyrovský Institute of Physical Chemistry, Prague, Czech Republic.
    Sachl, Radek
    J. Heyrovský Institute of Physical Chemistry, Prague, Czech Republic.
    Cebecauer, Marek
    J. Heyrovský Institute of Physical Chemistry, Prague, Czech Republic.
    Machan, Radek
    J. Heyrovský Institute of Physical Chemistry, Prague, Czech Republic.
    Johansson, Lennart B-Å
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Hof, Martin
    J. Heyrovský Institute of Physical Chemistry, Prague, Czech Republic.
    Dynamics and size of crosslinking-induced lipid nanodomains in model membranes2012In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 102, no 3, p. 294a-Article in journal (Refereed)
    Abstract [en]

    Changes of membrane organization upon crosslinking of its components trigger cellsignaling response to various exogenous factors. Crosslinking of raft gangliosides GM1with cholera toxin (CTxB) was demonstrated to cause microscopic phase separation inmodel membranes and the CTxB-GM1 complexes forming a minimal lipid raft unit aresubject of ongoing cell membrane research. Yet, those subdiffraction sized rafts havenever been described in terms of size and dynamics. By means of two-color z-scanfluorescence correlation spectroscopy, we show that the nano-sized domains are formedin model membranes at lower sphingomyelin content than needed for the large scalephase separation and that the CTxB-GM1 complexes are confined in the domains poorlystabilized with sphingomyelin. Fluorescence resonance energy transfer together withMonte Carlo modeling of the donor decay response reveal the domain radius ofapproximately 8 nm, which increases at higher sphingomyelin content. We observed twotypes of differently behaving domains, which suggests a dual role of the crosslinker: first,local transient condensation of the GM1 molecules compensating lack of sphingomyelinand second, coalescence of existing nanodomains ending in large scale phase separation.

  • 45.
    Håkansson, Pär
    Umeå University, Faculty of Science and Technology, Chemistry.
    Simulation of Relaxation Processes in Fluorescence, EPR and NMR Spectroscopy2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Relaxation models are developed using numerical solutions of the Stochastic Liouville Equation of motion. Simplified descriptions such as the stochastic master equation is described in the context of fluorescence depolarisation experiments. Redfield theory is used in order to describe NMR relaxation in bicontinuous phases. The stochastic fluctuations in the relaxation models are accounted for using Brownian Dynamics simulation technique. A novel approach to quantitatively analyse fluorescence depolarisation experiments and to determine intramolecular distances is presented. A new Brownian Dynamics simulation technique is developed in order to characterize translational diffusion along the water lipid interface of bicontinuous cubic phases.

  • 46.
    Håkansson, Pär
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Isaksson, Mikael
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Westlund, Per-Olof
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Johansson, Lennart B-Å
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Extended Förster theory for determining intraprotein distances: 1. The K2-dynamics and fluorophore reorientation2004In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 108, no 44, p. 17243-17250Article in journal (Refereed)
    Abstract [en]

    A detailed analysis of the previously developed (J. Chem. Phys. 1996, 105, 10896) extended Förster theory (EFT) is presented for analyzing electronic energy migration within pairs of donors (D). Synthetic data that mimics experimental time-correlated single photon counting data were generated and re-analyzed. To cover a wide dynamic range and various orientational restrictions, the rates of reorientation, as well as the orientational configurations of the interacting D-groups were varied. In general DD distances are recovered within an error limit of 5%, while the errors in orientational configurations are usually larger. The Maier−Saupe and cone potentials were used to generate an immense variety of orientational trajectories. The results obtained exhibit no significant dependence on the choice of potential function used for generating EFT data. Present work demonstrates how to overcome the classical “κ2-problem” and the frequently applied approximation of κ2 = 2/3 in the data analyses. This study also outlines the procedure for analyzing fluorescence depolarization data obtained for proteins, which are specifically labeled with D-groups. The EFT presented here brings the analyses of DDEM data to the same level of molecular detail as in ESR- and NMR-spectroscopy.

  • 47.
    Iakunkov, Artem
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Klechikov, Alexey
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sun, Jinhua
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Steenhaut, Timothy
    Hermans, Sophie
    Filinchuk, Yaroslav
    Talyzin, Alexandr
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gravimetric tank method to evaluate material-enhanced hydrogen storage by physisorbing materials2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 44, p. 27983-27991Article in journal (Refereed)
    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.

  • 48. Irfan, Muhammad
    et al.
    Iqbal, Javed
    Eliasson, Bertil
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ayub, Khurshid
    Rana, Usman Ali
    Khan, Salah Ud-Din
    Benchmark study of UV/Visible spectra of coumarin derivatives by computational approach2017In: Journal of Molecular Structure, ISSN 0022-2860, E-ISSN 1872-8014, Vol. 1130, p. 603-616Article in journal (Refereed)
    Abstract [en]

    A benchmark study of UV/Visible spectra of Simple coumarins and Furanocoumarins derivatives was conducted by employing the Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TD-DFT) approaches. In this study the geometries of ground and excited states, excitation energy and absorption spectra were estimated by using the DFT functional CAM-B3LYP, WB97XD, HSEH1PBE, MPW1PW91 and TD-B3LYP with 6-31 + G (d,p) basis set. CAM-B3LYP functional was found to have close agreement with the experimental values of Furranocoumarin class of coumarins while MPW1PW91 gave close results for simple coumarins. This study provided an insight about the electronic characteristics of the selected compounds and provided an effective tool for developing and designing the better UV absorber compounds.

  • 49.
    Isaksson, Mikael
    Umeå University, Faculty of Science and Technology, Chemistry.
    On the quantitative analysis of electronic energy transfer/migration in proteins studied by fluorescence spectroscopy2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Two recently developed theories of electronic energy transfer/migration were for the first time applied to real protein systems for extracting molecular distances. The partial donor-donor energy migration (PDDEM) is an extension to the previously developed donor-donor energy migration (DDEM, F Bergström et al PNAS 96, 1999, 12477) which allows using chemically identical but photophysically different fluorophores in energy migration experiments. A method based on fluorescence quenching was investigated and applied to create an asymmetric energy migration between fluorophores which were covalently and specifically attached to plasminogen activator inhibitor type 2 (PAI-2). It was also shown experimentally that distance information can be obtained if the fluorescence relaxation for photophysically identical donors, exhibits multi-exponential relaxation.

    An extended Förster theory (EFT) that was previously derived (L. B.-Å. Johansson et al J. Chem. Phys., 1996, 105) ha been developed for analysis of donor-acceptor energy transfer systems as well as DDEM systems. Recently the EFT was also applied to determine intra molecular distances in the protein plasminogen activator inhibitor type 1 (PAI-1) which was labelled with a sulfhydryl specific derivative of BODIPY. The EFT explicitly accounts for the time-dependent reorientations which in a complex manner influence the rate of electronic energy transfer/migration. This difficulty is related to the “k2-problem”, which has been solved. It is also shown experimentally that the time-correlated single-photon counting (TCSPC) data is sensitive to the mutual configuration between the interacting fluorophores. To increase the accuracy in the extracted parameters it is furthermore suggested to collect the fluorescence data under various physico-chemical conditions. It was also shown that the Förster theory is only valid in the initial part of the fluorescence decay.

  • 50. Jenske, Ramona
    et al.
    Lindström, Fredrick
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Camurus AB, Solvegatan 41, Ideon Science Park Gamma 1, SE-223 70 Lund, Sweden.
    Gröbner, Gerhard
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Vetter, Walter
    Impact of free hydroxylated and methyl-branched fatty acids on the organization of lipid membranes2008In: Chemistry and Physics of Lipids, ISSN 0009-3084, E-ISSN 1873-2941, Vol. 154, no 1, p. 26-32Article in journal (Refereed)
    Abstract [en]

    Differential scanning calorimetry (DSC) has been applied to study the effect of free hydroxylated and methyl-branched fatty acids on the physico-chemical properties of lipid membranes. First, the impact of free hydroxy fatty acids (HFAs) on dimyristoylphosphatidylcholine (DMPC) model membranes was monitored only as a function of chain length and position of the attached hydroxyl group. Second, racemic vs. enantiopure anteiso fatty acids (AFAs) and HFAs were investigated to address the question of which role does a fatty acid's chirality play on its membrane pertubing effect.

    The DSC thermograms revealed that the main gel to liquid–crystalline phase transition of the DMPC bilayers which results in a disordering effect of the lipid hydrocarbon chains was affected in different ways depending on the nature of the incorporated fatty acid. Long-chain 2- and 3-HFAs stabilized the gel phase by reducing the phase transition temperature (Tm), whereas short-chain HFAs and long-chain HFAs with the hydroxy group remote from the head group stabilized the more disordered liquid–crystalline state. Additionally, we observed that enantiopure (S)-14-methylhexadecanoic acid ((S)-a17:0) and (R)-2-hydroxy octadecanoic acid and the corresponding racemates had contrary effects upon incorporation into DMPC bilayers. In both cases, the pure enantiomers alleviated the liquid–crystalline state of the biological model membrane.

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