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Westlund, P.-O. (2019). A proton T1-nuclear magnetic resonance dispersion study of water motion in snowflakes and hexagonal ice. Molecular Physics, 117(7-8), 960-967
Open this publication in new window or tab >>A proton T1-nuclear magnetic resonance dispersion study of water motion in snowflakes and hexagonal ice
2019 (English)In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 117, no 7-8, p. 960-967Article in journal (Refereed) Published
##### Abstract [en]

Snowflakes and ordinary hexagonal ice were studied measuring water proton spin–lattice relaxation rate R1(ωI)-nuclear magnetic resonance dispersion (NMRD) profiles at proton Larmor frequencies ranging from 1 to 30 MHz and at different temperatures ranging from −2◦C to −10◦C. The spin–spin relaxation rate 1/ 1/T2(ωI) was determined at a single Larmor frequency of 16.3 MHz. The high-field wing of the proton R1(ωI)-NMRD profile was characterised by two parameters: a correlation time τc which described the dipole–dipole spectral density, and the relaxation rate at low fields R max real (0) which was determined from T 2 . The correlation time τc depended on the dynamic model used. A rotation diffusion model yield approximatively 3μs at −3◦C to about 5μs at 10◦C, whereas for a more realistic six-site discrete exchange model, the correlation times decreased slightly to about 80% for the same temperature interval. Proton dipole–dipole interactions were divided into intramolecular and intermolecular contributions where the intermolecular contribution was about 0.4–0.8 × the intramolecular contribution. It was not possible to discriminate between the dynamic models or to detect ice/water interface effects by comparing the NMRD data from snowflakes with ordinary hexagonal ice data.

##### Place, publisher, year, edition, pages
Taylor & Francis, 2019
##### Keywords
Six-site exchange model, water dynamics in hexagonal ice, water proton spin–lattice relaxation dispersion
##### National Category
Theoretical Chemistry
##### Identifiers
urn:nbn:se:umu:diva-154547 (URN)10.1080/00268976.2018.1541197 (DOI)2-s2.0-85056004434 (Scopus ID)
Available from: 2018-12-19 Created: 2018-12-19 Last updated: 2019-05-28Bibliographically approved
Shamshir, A., Sparrman, T. & Westlund, P.-O. (2019). Analysis of the behaviour of confined molecules using 2H T1 nuclear magnetic relaxation dispersion. Molecular Physics
Open this publication in new window or tab >>Analysis of the behaviour of confined molecules using 2H T1 nuclear magnetic relaxation dispersion
2019 (English)In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028Article in journal (Refereed) Epub ahead of print
##### Abstract [en]

A four-site exchange model is developed in order to explain deuterium -nuclear magnetic relaxation dispersion (NMRD) profiles of acetonitrile in silica pore systems. The four-site exchange model comprises a bulk, surface and two types of burried or cavity sites. It is found that the residence time of acetonitrile- at a flat Si-surface is less than 100 ps. No bilayer-like ordering of acetonitrile is formed at the Si-surface because no quadrupole splitting was observed. The dispersion in the deuterium T1-NMRD profiles are due to relatively few so-called beta-sites with molecular residence time in the range 0.2-2 micro seconds. This deuterium T-NMR dispersion experiment suggest that the retention time of different analysts can be studied in terms of their residence time in beta sites.

##### Place, publisher, year, edition, pages
Taylor & Francis, 2019
##### Keywords
Spin-lattice relaxation time of acetonitrile-d3, NMRD, molecular origin of the retention time, 4-site exchange model
##### National Category
Physical Chemistry
##### Identifiers
urn:nbn:se:umu:diva-162676 (URN)10.1080/00268976.2019.1645367 (DOI)000479433000001 ()
Available from: 2019-09-02 Created: 2019-09-02 Last updated: 2020-03-30
Westlund, P.-O. & Wennerström, H. (2019). Disentanglement of a Singlet Spin State in a Coincidence Stern-Gerlach Device. Journal of Modern Physics, 10(10), 1247-1254
Open this publication in new window or tab >>Disentanglement of a Singlet Spin State in a Coincidence Stern-Gerlach Device
2019 (English)In: Journal of Modern Physics, ISSN 2153-1196, E-ISSN 2153-120X, Vol. 10, no 10, p. 1247-1254Article in journal (Refereed) Published
##### Abstract [en]

We analyze the spin coincidence experiment considered by Bell in the derivation of Bells theorem. We solve the equation of motion for the spin system with a spin Hamiltonian, Hz, where the magnetic field is only in the z-direction. For the specific case of the coincidence experiment where the two magnets have the same orientation the Hamiltonian Hz commutes with the total spin Iz, which thus emerges as a constant of the motion. Bells argument is then that an observation of spin up at one magnet A necessarily implies spin down at the other B. For an isolated spin system A-B with classical translational degrees of freedom and an initial spin singlet state there is no force on the spin particles A and B. The spins are fully entangled but none of the spin particles A or B are deflected by the Stern-Gerlach magnets. This result is not compatible with Bells assumption that spin 1/2 particles are deected in a Stern-Gerlach device. Assuming a more realistic Hamiltonian Hz + Hx including a gradient in x direction the total Iz is not conserved and fully entanglement is not expected in this case. The conclusion is that Bells theorem is not applicable to spin coincidence measurement originally discussed by Bell.

##### Keywords
Bells Theorem, Disentanglement, Stern-Gerlach Coincident Measurement, Singlet Spin State
##### National Category
Condensed Matter Physics
##### Identifiers
urn:nbn:se:umu:diva-164094 (URN)10.4236/jmp.2019.1010083 (DOI)
##### Funder
Swedish Research Council Available from: 2019-10-14 Created: 2019-10-14 Last updated: 2019-11-05Bibliographically approved
Skrobonja, A., Gojkovic, Z., Soerensen, A. L., Westlund, P.-O., Funk, C. & Björn, E. (2019). Uptake Kinetics of Methymerucy in a Freshwater Alga Exposed to Methylmercury Complexes with Environmentally Relevant Thiols. Environmental Science and Technology, 53(23), 13757-13766
Open this publication in new window or tab >>Uptake Kinetics of Methymerucy in a Freshwater Alga Exposed to Methylmercury Complexes with Environmentally Relevant Thiols
2019 (English)In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 53, no 23, p. 13757-13766Article in journal (Refereed) Published
##### Abstract [en]

Cellular uptake of dissolved methylmercury (MeHg) by phytoplankton is the most important point of entry for MeHg into aquatic food webs. However, the process is not fully understood. In this study we investigated the influence of chemical speciation on rate constants for MeHg accumulation by the freshwater green microalga Selenastrum capricornutum. We used six MeHg–thiol complexes with moderate but important structural differences commonly found in the environment. Rate constants for MeHg interactions with cells were determined for the MeHg–thiol treatments and a control assay containing the thermodynamically less stable MeHgOH complex. We found both elevated amounts of MeHg associated with whole cells and higher MeHg association rate constants in the control compared to the thiol treatments. Furthermore, the association rate constants were lower when algae were exposed to MeHg complexes with thiols of larger size and more “branched” chemical structure compared to complexes with simpler structure. The results further demonstrated that the thermodynamic stability and chemical structure of MeHg complexes in the medium is an important controlling factor for the rate of MeHg interactions with the cell surface, but not for the MeHg exchange rate across the membrane. Our results are in line with uptake mechanisms involving formation of MeHg complexes with cell surface ligands prior to internalization.

##### Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
##### National Category
Other Chemistry Topics
##### Identifiers
urn:nbn:se:umu:diva-166177 (URN)10.1021/acs.est.9b05164 (DOI)2-s2.0-85075442114 (Scopus ID)
Available from: 2019-12-16 Created: 2019-12-16 Last updated: 2019-12-20Bibliographically approved
Gösweiner, C., Lantto, P., Fischer, R., Sampl, C., Umut, E., Westlund, P.-O., . . . Scharfetter, H. (2018). Tuning Nuclear Quadrupole Resonance: A Novel Approach for the Design of Frequency-Selective MRI Contrast Agents. Physical Review X, 8(2), Article ID 021076.
Open this publication in new window or tab >>Tuning Nuclear Quadrupole Resonance: A Novel Approach for the Design of Frequency-Selective MRI Contrast Agents
2018 (English)In: Physical Review X, ISSN 2160-3308, E-ISSN 2160-3308, Vol. 8, no 2, article id 021076Article in journal (Refereed) Published
##### Abstract [en]

The interaction between water protons and suitable quadrupolar nuclei (QN) can lead to quadrupole relaxation enhancement (QRE) of proton spins, provided the resonance condition between both spin transitions is fulfilled. This effect could be utilized as a frequency selective mechanism in novel, responsive T-1 shortening contrast agents (CAs) for magnetic resonance imaging (MRI). In particular, the proposed contrast mechanism depends on the applied external flux density-a property that can be exploited by special field-cycling MRI scanners. For the design of efficient CA molecules, exhibiting narrow and pronounced peaks in the proton T-1 relaxation dispersion, the nuclear quadrupole resonance (NQR) properties, as well as the spin dynamics of the system QN-H-1, have to be well understood and characterized for the compounds in question. In particular, the energy-level structure of the QN is a central determinant for the static flux densities at which the contrast enhancement appears. The energy levels depend both on the QN and the electronic environment, i.e., the chemical bonding structure in the CA molecule. In this work, the NQR properties of a family of promising organometallic compounds containing Bi-209 as QN have been characterized. Important factors like temperature, chemical structure, and chemical environment have been considered by NQR spectroscopy and ab initio quantum chemistry calculations. The investigated Bi-aryl compounds turned out to fulfill several crucial requirements: NQR transition frequency range applicable to clinical 1.5- and 3 T MRI systems, low temperature dependency, low toxicity, and tunability in frequency by chemical modification.

##### Place, publisher, year, edition, pages
American Physical Society, 2018
##### National Category
Physical Sciences
##### Identifiers
urn:nbn:se:umu:diva-150772 (URN)10.1103/PhysRevX.8.021076 (DOI)000436196600001 ()
Available from: 2018-08-31 Created: 2018-08-31 Last updated: 2018-08-31Bibliographically approved
Wennerström, H. & Westlund, P.-O. (2017). A Quantum Description of the Stern–Gerlach Experiment. Entropy, 19(5), Article ID 186.
Open this publication in new window or tab >>A Quantum Description of the Stern–Gerlach Experiment
2017 (English)In: Entropy, ISSN 1099-4300, E-ISSN 1099-4300, Vol. 19, no 5, article id 186Article in journal (Refereed) Published
##### Abstract [en]

A detailed analysis of the classic Stern–Gerlach experiment is presented. An analytical simple solution is presented for the quantum description of the translational and spin dynamics of a silver atom in a magnetic field with a gradient along a single z-direction. This description is then used to obtain an approximate quantum description of the more realistic case with a magnetic field gradient also in a second y-direction. An explicit relation is derived for how an initial off center deviation in the y-direction affects the final result observed at the detector. This shows that the “mouth shape” pattern at the detector observed in the original Stern–Gerlach experiment is a generic consequence of the gradient in the y-direction. This is followed by a discussion of the spin dynamics during the entry of the silver atom into the magnet. An analytical relation is derived for a simplified case of a field only along the z-direction. A central question for the conceptual understanding of the Stern–Gerlach experiment has been how an initially unpolarized spin ends up in a polarized state at the detector. It is argued that this can be understood with the use of the adiabatic approximation. When the atoms first experience the magnetic field outside the magnet, there is in general a change in the spin state, which transforms from a degenerate eigenstate in the absence of a field into one of two possible non-degenerate states in the field. If the direction of the field changes during the passage through the device, there is a corresponding adiabatic change of the spin state. It is shown that an application of the adiabatic approximation in this way is consistent with the previously derived exact relations.

##### Place, publisher, year, edition, pages
Basel: MDPI, 2017
##### Keywords
Stern–Gerlach experiment, quantum description and interpretation, adiabatic approximation, spin dynamics, spin density matrix, relaxation
##### National Category
Chemical Sciences
##### Identifiers
urn:nbn:se:umu:diva-134055 (URN)10.3390/e19050186 (DOI)000404453700005 ()
Available from: 2017-04-26 Created: 2017-04-26 Last updated: 2018-06-09Bibliographically approved
Driver, G. W., Huang, Y., Laaksonen, A., Sparrman, T., Wang, Y. & Westlund, P.-O. (2017). Correlated/non-correlated ion dynamics of charge-neutral ion couples: the origin of ionicity in ionic liquids. Physical Chemistry, Chemical Physics - PCCP, 19(7), 4975-4988
Open this publication in new window or tab >>Correlated/non-correlated ion dynamics of charge-neutral ion couples: the origin of ionicity in ionic liquids
2017 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 7, p. 4975-4988Article in journal (Refereed) Published
##### 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.

##### Keywords
Spin-Lattice relaxation, NMR dispersion pro le, correlated cation-anion reorientation, Ionic Liquid, Ionicity, MD-simulation
##### National Category
Physical Chemistry
##### Identifiers
urn:nbn:se:umu:diva-128921 (URN)10.1039/C6CP05801A (DOI)000395671100007 ()28074972 (PubMedID)
Available from: 2016-12-19 Created: 2016-12-19 Last updated: 2018-06-09Bibliographically approved
Larsson, P. T., Karlsson, R.-M. P., Westlund, P.-O. & Wågberg, L. (2017). Internal Structure of Isolated Cellulose I Fibril Aggregates in the Water Swollen State. In: Agarwal, UP Atalla, RH Isogai, A (Ed.), Nanocelluloses: their preparation, properties, and applications. Paper presented at Anselme Payen Award Symposium in honor of Akira Isogai on Nanocelluloses, their Preparation, Properties and Applications / Spring ACS National Meeting, MAR 13-17, 2016, San Diego, CA (pp. 91-112). American Chemical Society (ACS)
Open this publication in new window or tab >>Internal Structure of Isolated Cellulose I Fibril Aggregates in the Water Swollen State
2017 (English)In: Nanocelluloses: their preparation, properties, and applications / [ed] Agarwal, UP Atalla, RH Isogai, A, American Chemical Society (ACS), 2017, p. 91-112Conference paper, Published paper (Refereed)
##### Abstract [en]

By combining H-2-NMRD and CP/MAS C-13-NMR measurements of water-based cellulose gels and of water swollen pulps it was possible to estimate the nature of the interior structure of cellulose fibril aggregates. A set of samples with high cellulose purity and low charge was used. The interpretation of data was based on a relaxation model describing the exchange dynamics for deuterium exchange between water molecules and cellulose hydroxyl groups. The theoretical model used made it possible to calculate cellulose surface-to-volume ratios (q-values) from both H-2-NMRD and CP/MAS C-13-NMR data. Good consistency between H-2-NMRD and CP/MAS C-13-NMR data was found. In all investigated samples the cellulose fibril aggregates showed a different degree of "openness" interpreted as the presence of interstitial water inside fibril aggregates. One result also showed that an increased degree of fibril aggregate openness results from the TEMPO-oxidation. Common to all samples was that in the water swollen state water molecules could access part of the fibril aggregate interior.

##### Place, publisher, year, edition, pages
American Chemical Society (ACS), 2017
##### Series
ACS Symposium Series, ISSN 0097-6156 ; 1251
##### National Category
Paper, Pulp and Fiber Technology Physical Chemistry
##### Identifiers
urn:nbn:se:umu:diva-143677 (URN)10.1021/bk-2017-1251.ch005 (DOI)000417770800005 ()978-0-8412-3218-1 (ISBN)978-0-8412-3217-4 (ISBN)
##### Conference
Anselme Payen Award Symposium in honor of Akira Isogai on Nanocelluloses, their Preparation, Properties and Applications / Spring ACS National Meeting, MAR 13-17, 2016, San Diego, CA
Available from: 2018-01-05 Created: 2018-01-05 Last updated: 2018-06-09Bibliographically approved
Westlund, P.-O. (2016). A Proton Water T1-NMRD Study of Ganglioside Micelles. Universal Journal of Chemistry, 4(2), 69-73
Open this publication in new window or tab >>A Proton Water T1-NMRD Study of Ganglioside Micelles
2016 (English)In: Universal Journal of Chemistry, ISSN 2332-3019, Vol. 4, no 2, p. 69-73Article in journal (Refereed) Published
##### Abstract [en]

Ganglioside GM1 (GM1) micelles have been studied by means of water proton T1 NMRD experiment. The ﬁeld dependent spin-lattice relaxation rates were measured for Larmor frequencies ranging from 0.1 to 40 MHz and for two micelle concentrations at three temperatures (T=10,15,20oC). The proton T1 NMRD-proﬁles are well described by assuming two proton pools are responsible for the dispersion curves. The proton pools are characterized by an effective correlation time and a proton fraction. The largest correlation time, τc,1 ≈ 130−160 ns, is determined by the low ﬁeld part of the NMRD proﬁle. The second correlation time, τc,2 ≈ 12 ns, is determined by the high ﬁeldpartoftheNMRDproﬁle. Theradiusoftheganglioside micelles has previously been determined as about 54 using ﬂuorescence experiments and with Stoke-Einstein relation the reorientation correlation time becomes τR= 120-165 ns depending on the temperature dependence of the water viscosity. It is thus plausible to identify one pool of waterprotons, characterized by the largest effective correlation time, as corresponding to waters residing in the headgroup withanorderparameterS6=0andτc,1 ≈ τR orcorresponding to labile protons with a τc,1as the mean life time. The proton NMRD proﬁle reveal a second Lorenzian which also can eitherbelabileandexchangingGangliosideprotonsorwater moleculesresidingintheheadgroupwithameanlifetimeas approximately 12 ns. The proton NMRD experiment cannot discriminate between these two cases.

##### Keywords
Proton T1.NMRD Profiels, Proton Spin-lattice Relaxation, Ganglioside Micelles
##### National Category
Chemical Sciences
##### Identifiers
urn:nbn:se:umu:diva-124908 (URN)10.13189/ujc.2016.040204 (DOI)
Available from: 2016-08-30 Created: 2016-08-30 Last updated: 2018-06-07Bibliographically approved
Huang, Y., Sparrman, T., Wang, Y.-l., Laaksonen, A. & Westlund, P.-O. (2015). Analysis of proton/fluoride spin-lattice NMR dispersion experiment of an ionic liquid, BMIM[PF6] by using molecular dynamics simulations and relaxation theory.
Open this publication in new window or tab >>Analysis of proton/fluoride spin-lattice NMR dispersion experiment of an ionic liquid, BMIM[PF6] by using molecular dynamics simulations and relaxation theory
##### Abstract [en]

Proton/Fluoride spin-lattice nuclear magnetic relaxation dispersion(NMRD) measurements of 1-Butyl-3-methylimidazolium-hexa fluorophosphate (BMIM[PF6])have been carried out using a 1T Stelar FFC2000 fast-field-cycling instrument at proton Larmor frequencies ranging from 10 kHz to 40 MHz and at different temperatures. The NMRD profiles are interpreted by means of a simple relaxation modelbased on the inter- and intra-molecular dipole dipole relaxation mechanims. Using an atomic and a coarse-grained (CG)Molecular Dynamics (MD) simulations at temperature 323 K the relevant dipole-dipole correlation functions are calculated. The result indicate that the NMRD profiles can be rationalized using a combination of intra and inter molecular dipole-dipole couplings. However, both are mainly modulated by molecular reorientation whereas translation diffusion plays a minor role. The molecular reorientation dynamics  of BMIM[PF6] ,BMIM+ ion are in the nano secondtime regime whereas the reorientation of  [PF6]- is much faster and loses its correlation in the ps regime. The relaxation mechanism for  [PF6]- is H-F inter-molecular dipole-dipole coupling which is modulated by the reorientation of  the H-containing molecule.

##### Keywords
proton, fluoride, spin-lattice, relaxation, ionic liquid, MD, BMIM[PF6]
##### National Category
Theoretical Chemistry
##### Research subject
Physical Chemistry
##### Identifiers
urn:nbn:se:umu:diva-110719 (URN)
##### Note

2015, in manuscript

Available from: 2015-10-26 Created: 2015-10-26 Last updated: 2018-06-07
##### Identifiers
ORCID iD: orcid.org/0000-0002-9277-4534

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