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Westlund, Per-Olof
Publications (10 of 44) Show all publications
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, 69-73 p.Article 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.

Keyword
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: 2016-12-01Bibliographically 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
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2015 (English)Manuscript (preprint) (Other academic)
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.

Keyword
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: 2015-11-11
Huang, Y., Siljebo, W. & Westlund, P.-O. (2015). Water proton and deuterium spin-lattice relaxation in Zeolite ZSM-5 by fast field-cycling NMR relaxometry. .
Open this publication in new window or tab >>Water proton and deuterium spin-lattice relaxation in Zeolite ZSM-5 by fast field-cycling NMR relaxometry
2015 (English)Manuscript (preprint) (Other academic)
Abstract [en]

The water dynamics in the confined space of the zeolite ZSM-5 has bee ninvestigated by means of the field dependence of 1H- and 2H- spin-lattice relaxation rates using a 1T Stelar FFC2000 fast field-cycling instrument. The NMRD analysis of  the experimental results indicates that the characteristic time dependence ( 50 ns to 1-2.4 μs) is due to water translational diffusion in narrow pores. The temperature dependence of the spin-lattice relaxation rates is weak.Zeolites with different counter ions( H+, NH4+ change the water hydration and the water translational diffusion in the pores drastically. The Zeolite-NH4+ slow down the water motion with a factor of 2.The NMRD profiles show somewhat stretched character and is described by two Lorenzian which indicates that the distribution of pore sizes is broaden.The water 1H and 2H spin lattice relaxation profiles give qualitatively information about water hydration in zeolites with different counter ions and is expected also to indicate structural changes of the zeolites. 

Keyword
proton, deuterium, spin lattice, relaxation, ZSM-5, zeolite
National Category
Theoretical Chemistry
Research subject
Physical Chemistry
Identifiers
urn:nbn:se:umu:diva-110716 (URN)
Note

2015, in manuscript

Available from: 2015-10-26 Created: 2015-10-26 Last updated: 2015-11-11
Han, G., Huang, Y., Koua, F. H., Shen, J.-R., Westlund, P.-O. & Messinger, J. (2014). Hydration of the oxygen-evolving complex of photosystem II probed in the dark-stable S1 state using proton NMR dispersion profiles. Physical Chemistry, Chemical Physics - PCCP (16), 11924-11935.
Open this publication in new window or tab >>Hydration of the oxygen-evolving complex of photosystem II probed in the dark-stable S1 state using proton NMR dispersion profiles
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2014 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, no 16, 11924-11935 p.Article in journal (Refereed) Published
Abstract [en]

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

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2014
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-87820 (URN)10.1039/c3cp55232b (DOI)24695863 (PubMedID)
Available from: 2014-04-10 Created: 2014-04-10 Last updated: 2017-12-05Bibliographically approved
Wennerström, H. & Westlund, P.-O. (2013). On Stern‐Gerlach coincidence measurements and their application to Bell's theorem. Physics essays, 26(2), 174-180.
Open this publication in new window or tab >>On Stern‐Gerlach coincidence measurements and their application to Bell's theorem
2013 (English)In: Physics essays, ISSN 0836-1398, Vol. 26, no 2, 174-180 p.Article in journal (Refereed) Published
Abstract [en]

We analyze a coincidence Stern-Gerlach measurement often discussed in connection with the derivation and illustration of Bell's theorem. The treatment is based on our recent analysis of the original Stern-Gerlach experiment (PCCP, 14, 1677‐1684 (2012)), where it is concluded that it is necessary to include a spin relaxation process to account for the experimental observations. We consider two limiting cases of a coincidence measurement using both an analytical and a numerical description. In on limit relaxation effects are neglected. In this case the correlation between the two spins present in the initial state is conserved during the passage through the magnets. However, at exit the z coordinate along the magnetic field gradient is randomly distributed between the two extreme values. In the other limit T2 relaxation is assumed to be fast relative to the time of flight through the magnet. In this case the z coordinate takes one of two possible values as observed in the original Stern‐Gerlach experiment. Due to the presence of a relaxation process involving transfer of angular momentum between particle and magnet the initially entangled spin state changes character leading to a loss of correlation between the two spins. In the original derivations of Bell's theorem based on a coincidence Stern‐Gerlach setup one assumes both a perfect correlation between the spins and only two possible values for the z‐coordinate on exit. According to the present calculations one can satisfy either of these conditions but not both simultaneously.

Place, publisher, year, edition, pages
Physics Essays Publication, 2013
Keyword
Stern‐Gerlach device, coincident measurement, entangled state, spin relaxation, Bell's theorem
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-64735 (URN)10.4006/0836-1398-26.2.174 (DOI)
Available from: 2013-02-06 Created: 2013-02-01 Last updated: 2017-12-06Bibliographically approved
Huang, Y., Nam, K. & Westlund, P.-O. (2013). The water R1(ω) NMRD profiles of a hydrated protein from molecular dynamics simulation. Physical Chemistry, Chemical Physics - PCCP, 15(33), 14089-14097.
Open this publication in new window or tab >>The water R1(ω) NMRD profiles of a hydrated protein from molecular dynamics simulation
2013 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 33, 14089-14097 p.Article in journal (Refereed) Published
Abstract [en]

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

Place, publisher, year, edition, pages
RSC Publishing, 2013
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-73724 (URN)10.1039/C3CP51147B (DOI)000322517800041 ()
Available from: 2013-06-27 Created: 2013-06-27 Last updated: 2017-12-06Bibliographically approved
Bergenstråhle-Wohlert, M., Berglund, L. A., Brady, J. W., Larsson, P. T., Westlund, P.-O. & Wohlert, J. (2012). Concentration enrichment of urea at cellulose surfaces: results from molecular dynamics simulations and NMR spectroscopy. Cellulose (London), 19(1), 1-12.
Open this publication in new window or tab >>Concentration enrichment of urea at cellulose surfaces: results from molecular dynamics simulations and NMR spectroscopy
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2012 (English)In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 19, no 1, 1-12 p.Article in journal (Refereed) Published
Abstract [en]

A combined solid-state NMR and Molecular Dynamics simulation study of cellulose in urea aqueous solution and in pure water was conducted. It was found that the local concentration of urea is significantly enhanced at the cellulose/solution interface. There, urea molecules interact directly with the cellulose through both hydrogen bonds and favorable dispersion interactions, which seem to be the driving force behind the aggregation. The CP/MAS 13C spectra was affected by the presence of urea at high concentrations, most notably the signal at 83.4 ppm, which has previously been assigned to C4 atoms in cellulose chains located at surfaces parallel to the (110) crystallographic plane of the cellulose Iβ crystal. Also dynamic properties of the cellulose surfaces, probed by spin-lattice relaxation time 13CT 1 measurements of C4 atoms, are affected by the addition of urea. Molecular Dynamics simulations reproduce the trends of the T 1measurements and lends new support to the assignment of signals from individual surfaces. That urea in solution is interacting directly with cellulose may have implications on our understanding of the mechanisms behind cellulose dissolution in alkali/urea aqueous solutions.

Place, publisher, year, edition, pages
Springer Science+Business Media B.V., 2012
Keyword
Cellulose, Urea, Solid state NMR, Molecular dynamics simulation
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-50768 (URN)10.1007/s10570-011-9616-x (DOI)
Note
Published online 15 November 2011Available from: 2011-12-21 Created: 2011-12-21 Last updated: 2017-12-08Bibliographically approved
Jonsson, S., Skyllberg, U., Nilsson, M. B., Westlund, P.-O., Shchukarev, A., Lundberg, E. & Björn, E. (2012). Mercury methylation rates for geochemically relevant HgII species in sediments. Environmental Science and Technology, 46(21), 11653-11659.
Open this publication in new window or tab >>Mercury methylation rates for geochemically relevant HgII species in sediments
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2012 (English)In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 46, no 21, 11653-11659 p.Article in journal (Refereed) Published
Abstract [en]

Monomethylmercury (MeHg) in fish from freshwater, estuarine and marine environments are a major global environmental issue. Mercury levels in biota are mainly controlled by the methylation of inorganic mercuric mercury (HgII) to MeHg in water, sediments and soils. There is, however, a knowledge gap concerning the mechanisms and rates of methylation of specific geochemical HgII species. Such information is crucial for a better understanding of variations in MeHg concentrations among ecosystems and, in particular, for predicting the outcome of currently proposed measures to mitigate mercury emissions and reduce MeHg concentrations in fish. To fill this knowledge gap we propose an experimental approach using HgII isotope tracers, with defined and geochemically important adsorbed and solid HgII forms in sediments, to study MeHg formation. We report HgII methylation rate constants, km, in estuarine sediments which span over two orders of magnitude depending on chemical form of added tracer: metacinnabar (β-201HgS(s)) < cinnabar (α-199HgS(s)) < HgII reacted with mackinawite (≡FeS-202HgII) < HgII bonded to natural organic matter (NOM-196HgII) < a typical aqueous tracer (198Hg(NO3)2(aq)). We conclude that a combination of thermodynamic and kinetic effects of HgII solid-phase dissolution and surface desorption control the HgII methylation rate in sediments and causes the large observed differences in km-values. The selection of relevant solid-phase and surface adsorbed HgII tracers will therefore be crucial to achieving biogeochemically accurate estimates of ambient HgII methylation rates.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2012
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-60708 (URN)10.1021/es3015327 (DOI)23017152 (PubMedID)
Available from: 2012-10-29 Created: 2012-10-23 Last updated: 2017-10-24Bibliographically approved
Lindgren, M. & Westlund, P.-O. (2012). The molecular mechanism of urea denaturation. In: James C. Taylor (Ed.), Advances in Chemistry Research: Volume 11. Nova Science Publishers, Inc..
Open this publication in new window or tab >>The molecular mechanism of urea denaturation
2012 (English)In: Advances in Chemistry Research: Volume 11 / [ed] James C. Taylor, Nova Science Publishers, Inc., 2012Chapter in book (Refereed)
Abstract [en]

Proteins are known to denature in high concentrations of compounds such as urea or guanidinium chloride. However, the mechanism by which urea and guanidinium chloride destabilizes proteins is not yet known, despite many decades of reasearch. Attempts have been made to understand protein denaturation on a thermodynamic level as well as on a molecular level. The long term goal in the field is to merge the results of these two types of studies into one mechanism that covers both the microscopic and the macroscopic level. In this text we firstly review thermodynamic studies as well as spectroscopic and computer simulation studies of chemical denaturation. The results of the different types of studies is then merged together in order to find a consistent view on chemical denaturation. In contrast to common belief in the field, a high degree of consensus is found between the different studies and a molecular mechanism of urea-induced protein denaturation can therefore be proposed.

Place, publisher, year, edition, pages
Nova Science Publishers, Inc., 2012
Series
Advances in Chemistry Research
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-54624 (URN)978-1-61324-815-7 (ISBN)
Available from: 2012-05-02 Created: 2012-05-02 Last updated: 2012-05-03Bibliographically approved
Wennerström, H. & Westlund, P.-O. (2012). The Stern-Gerlach experiment and the effects of spin relaxation. Physical Chemistry, Chemical Physics - PCCP, 14, 1677-1684.
Open this publication in new window or tab >>The Stern-Gerlach experiment and the effects of spin relaxation
2012 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 14, 1677-1684 p.Article in journal (Refereed) Published
Abstract [en]

The classical Stern-Gerlach experiment is analyzed with an emphasis on the spin dynamics. The central question asked is whether there occurs a relaxation of the spin angular momentum during the time the particle passes through the Stern-Gerlach magnet. We examine in particular the transverse relaxation, involving angular momentum exchange between the spin of the particles and the spins of the magnet. A method is presented describing relaxation effects at an individual particle level. This leads to a stochastic equation of motion for the spins. This is coupled to a classical equation of motion for the particle translation. The experimental situation is then modeled through simulations of individual trajectories using two sets of parameter choices and three different sets of initial conditions. The two main conclusions are: (A) if the coupling between the magnet and the spin is solely described by the Zeeman interaction with the average magnetic field the simulations show a clear disagreement with the experimental observation of Stern and Gerlach. (B) If one, on the other hand, also allows for a T(2) relaxation time shorter than the passage time one can obtain a practically quantitative agreement with the experimental observations. These conclusions are at variance with the standard textbook explanation of the Stern-Gerlach experiment.

Place, publisher, year, edition, pages
RSC Publishing, 2012
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-50825 (URN)10.1039/c2cp22173j (DOI)22193591 (PubMedID)
Note
First published on the web 21 Dec 2011 Available from: 2011-12-27 Created: 2011-12-27 Last updated: 2017-12-08Bibliographically approved
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