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  • 1. Abrahamsson, Christoffer
    et al.
    Nordstierna, Lars
    Nordin, Matias
    Dvinskikh, Sergey V.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. St. Petersburg State University, Russian Federation.
    Nyden, Magnus
    Magnetic orientation of nontronite clay in aqueous dispersions and its effect on water diffusion2015In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 437, p. 205-210Article in journal (Refereed)
    Abstract [en]

    The diffusion rate of water in dilute clay dispersions depends on particle concentration, size, shape, aggregation and water-particle interactions. As nontronite clay particles magnetically align parallel to the magnetic field, directional self-diffusion anisotropy can be created within such dispersion. Here we study water diffusion in exfoliated nontronite clay dispersions by diffusion NMR and time-dependant 1H-NMR-imaging profiles. The dispersion clay concentration was varied between 0.3 and 0.7 vol%. After magnetic alignment of the clay particles in these dispersions a maximum difference of 20% was measured between the parallel and perpendicular self-diffusion coefficients in the dispersion with 0.7 vol% clay. A method was developed to measure water diffusion within the dispersion in the absence of a magnetic field (random clay orientation) as this is not possible with standard diffusion NMR. However, no significant difference in self-diffusion coefficient between random and aligned dispersions could be observed.

  • 2. Castro, Vasco
    et al.
    Dvinskikh, Sergey V.
    Widmalm, Gran
    Sandstrom, Dick
    Maliniak, Arnold
    NMR studies of membranes composed of glycolipids and phospholipids2007In: Biochimica et Biophysica Acta - Biomembranes, ISSN 0005-2736, E-ISSN 1879-2642, Vol. 1768, no 10, p. 2432-2437Article in journal (Refereed)
    Abstract [en]

    Lipid membranes composed of monogalactosyldiacylglycerol (MGDG) and dimyristoylphosphatidylcholine (DMPC) were studied by means of NMR spectroscopy. The macroscopic phase behaviour was investigated by P-31 NMR under stationary conditions, whereas microscopic properties such as segmental ordering were probed by two-dimensional H-1-C-13 separated local field experiments under magic-angle spinning conditions. Our results clearly show that ordering/disordering effects occur for the headgroups as well as for the acyl chains when the sample composition is varied. In particular, the H-1-C-13 dipolar couplings within the galactose headgroup of MGDG exhibited significant concentration dependence.

  • 3. Castro, Vasco
    et al.
    Stevensson, Baltzar
    Dvinskikh, Sergey V.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Hogberg, Carl-Johan
    Lyubartsev, Alexander P.
    Zimmermann, Herbert
    Sandstrom, Dick
    Maliniak, Arnold
    NMR investigations of interactions between anesthetics and lipid bilayers2008In: Biochimica et Biophysica Acta - Biomembranes, ISSN 0005-2736, E-ISSN 1879-2642, Vol. 1778, no 11, p. 2604-2611Article in journal (Refereed)
    Abstract [en]

    Interactions between anesthetics (lidocaine and short chain alcohols) and lipid membranes formed by dimyristoylphosphatidylcholine (DMPC) were studied using NMR spectroscopy. The orientational order of lidocaine was investigated using deuterium NMR on a selectively labelled compound whereas segmental ordering in the lipids was probed by two-dimensional H-1-C-13 separated local field experiments under magic-angle spinning conditions. In addition, trajectories generated in molecular dynamics (MD) computer simulations were used for interpretation of the experimental results. Separate simulations were carried out with charged and uncharged lidocame molecules. Reasonable agreement between experimental dipolar interactions and the calculated counterparts was observed. Our results clearly show that charged lidocaine affects significantly the lipid headgroup. In particular the ordering of the lipids is increased accompanied by drastic changes in the orientation of the P-N vector in the choline group.

  • 4.
    Cifelli, M.
    et al.
    Univ Pisa, Dipartimento Chim & Chim Ind, I-56124 Pisa, Italy..
    Domenici, V.
    Univ Pisa, Dipartimento Chim & Chim Ind, I-56124 Pisa, Italy..
    Chizhik, V. I.
    St Petersburg State Univ, Dept Phys, St Petersburg 199034, Russia..
    Dvinskikh, Sergey
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry. St Petersburg State Univ, Lab Biomol NMR, St Petersburg 199034, Russia.
    N-15-C-13 Dipole Couplings in Smectic Mesophase of a Thermotropic Ionic Liquid2018In: Applied Magnetic Resonance, ISSN 0937-9347, E-ISSN 1613-7507, Vol. 49, no 6, p. 553-562Article in journal (Refereed)
    Abstract [en]

    Unique combination of ionic conductivity and anisotropic physical properties in ionic liquid crystals leads to new dynamic properties exploited in modern technological applications. Structural and dynamics information at atomic level for molecules and ions in mesophases can be obtained by nuclear magnetic resonance (NMR) spectroscopy through the measurements of dipole-dipole spin couplings. While C-13-H-1 and N-15-H-1 dipolar NMR spectra can be routinely acquired in samples with natural isotopic abundance, recording N-15-C-13 dipolar NMR spectra is challenging because of the unfavourable combination of two rare isotopes. In the present study, an approach to measure N-15-C-13 dipole-dipole NMR spectra in static liquid crystalline samples with natural abundance is introduced. We demonstrate that well-resolved spectra can be recorded within 10 h of experimental time using a conventional NMR probe and a moderately strong magnetic field. The technique is applied to a thermotropic smectic mesophase formed by an ionic liquid with imidazolium-based organic cation.

  • 5. Cifelli, M.
    et al.
    Domenici, V.
    Dvinskikh, Sergey
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Luckhurst, G. R.
    Timimi, B. A.
    The twist-bend nematic phase: translational self-diffusion and biaxiality studied by H-1 nuclear magnetic resonance diffusometry2017In: Liquid crystals (Print), ISSN 0267-8292, E-ISSN 1366-5855, Vol. 44, no 1, p. 204-218Article in journal (Refereed)
    Abstract [en]

    Recently, there has been a surge of interest in mesogens exhibiting the twist-bend nematic (N-TB) phase that is shown to be chiral even though formed by effectively achiral molecules. Although it now seems to be clear that the N-TB phase in the bulk is formed by degenerate domains having opposite handedness, the presence of a supramolecular heliconical structure proposed in the Dozov model has been contradicted by the Hoffmann et al. model in which the heliconical arrangement is replaced by a polar nematic phase. The evidence in support of this is that the quadrupolar splitting tensor measured in various experiments is uniaxial and not biaxial as expected for the twist-bend nematic structure. In this debate, among other evidence, the molecular translational diffusion, and its magnitude with respect to that in the nematic phase above the N-TB phase, has also been invoked to eliminate or to confirm one model or the other. We attempt to resolve this issue by reporting the first measurements of the translational self-diffusion coefficients in the nematic and twist-bend nematic phases formed 1 '',7 ''-bis-4-(4'-cyanobiphenyl-4'-yl) heptane (CB7CB). Such measurements certainly appear to resolve the differences between the two models in favour of that for the classic twist-bend nematic phase. [GRAPHICS] .

  • 6. Cifelli, M.
    et al.
    Domenici, V.
    Gorecka, E.
    Wojcik, M.
    Dvinskikh, Sergey
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. St. Petersburg State University, Russian Federation.
    NMR investigation of a thermotropic liquid crystal showing isotropic-isotropic'-(columnar)-cubic phase transitions2017In: Molecular Crystals and Liquid Crystals, ISSN 1542-1406, E-ISSN 1563-5287, Vol. 649, no 1, p. 20-30Article in journal (Refereed)
    Abstract [en]

    In this work, we report a first detailed study of the mesophasic behaviour of the calamitic liquid crystal, a (4,4′-bis(4″-carboxybelzyloxy)biphenyl derivate, labelled 9/2 RS/RS, showing an isotropic-isotropic-(columnar)-cubic phase behaviour on cooling. 1H NMR diffusometry allowed to distinguish between the two isotropic phases in terms of diffusion characterized by different Arrhenius activation energy, while 13C NMR static measurements and 2H NMR investigations were of help in understanding the orientational ordering properties of the metastable columnar phase and confirmed the isotropic state of the sample in the cubic phase.

  • 7. Cifelli, M.
    et al.
    Domenici, V.
    Kharkov, Boris B.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Dvinskikh, Sergey V.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. St. Petersburg State University, Russian Federation.
    Study of Translational Diffusion Anisotropy of Ionic Smectogens by NMR Diffusometry2015In: Molecular Crystals and Liquid Crystals, ISSN 1542-1406, E-ISSN 1563-5287, Vol. 614, no 1, p. 30-38Article in journal (Refereed)
    Abstract [en]

    Thermotropic ionic liquid crystals are considered very promising for a wide range of applications, such as anisotropic conductors as well as electrolytes in dye-synthesized solar cells. Their potential comes from the unique combination of ionic conductivity and high polarizability. In this paper we present a study of the diffusional properties of the ionic smectic A phase formed by the cationic smectogen, N-docecyl-N'-methyl-imidazolium (C12mim), with two different counter ions. Experimental translational diffusion data measured by NMR diffusometry are collected both for cations and anions and discussed in terms of their different anisotropy.

  • 8. Cifelli, Mario
    et al.
    Domenici, Valentina
    Dvinskikh, Sergey V.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Glogarova, Milada
    Veracini, Carlo Alberto
    Translational self-diffusion in the synclinic to anticlinic phases of a ferroelectric liquid crystal2010In: SOFT MATTER, ISSN 1744-683X, Vol. 6, no 23, p. 5999-6003Article in journal (Refereed)
    Abstract [en]

    In this work, the first direct measurement of inter and intra-layer molecular self-diffusion in the smectic phases of a chiral smectogen (S)-2-methylbutyl-[4'-(4 ''-heptyloxyphenyl)-benzoyl-4-oxy-(S)-2-((S)-2')benzoyl)-propionyl)]-pro pionate (ZLL7/*) by means of pulsed field gradient NMR is reported. Self-diffusion coefficients as low as 10(-13) m(2) s(-1) have been measured by combining magic echo spin decoupling with a stimulated echo sequence. The transitions among synclinic-anticlinic smectic phases are associated with a change in the self-diffusion coefficients.

  • 9. Cifelli, Mario
    et al.
    Domenici, Valentina
    Dvinskikh, Sergey V.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Veracini, Carlo Alberto
    Zimmermann, Herbert
    Translational self-diffusion in the smectic phases of ferroelectric liquid crystals: an overview2012In: Phase Transitions, ISSN 0141-1594, E-ISSN 1029-0338, Vol. 85, no 10, p. 861-871Article in journal (Refereed)
    Abstract [en]

    In this work, we present our recent results obtained in the field of translational self-diffusion studies by means of H-1 NMR diffusometry in smectic phases formed by calamitic chiral liquid crystals. In particular, the diffusional behavior of chiral smectic phases with different clinicity, such as the ferroelectric and antiferroelectric phases, will be discussed on the basis of the results obtained on three different chiral smectogens. This research demonstrates that, despite previous assertions, out-of-plane translational diffusion in smectic phases is poorly affected by the clinicity of the phases, showing no discontinuity at the transition from synclinic to anticlinic structures, typical of the smectic C* phases. We can conclude that diffusion basically reflects the layered smectic structure where in-plane diffusion is much faster and less hindered than the out-of-plane one.

  • 10.
    Dahlberg, Carina
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Dvinskikh, Sergey V.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Furó, István
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Polymer mobilization and drug release during tablet swelling: A 1H NMR and NMR microimaging study2007In: Journal of Controlled Release, ISSN 0168-3659, E-ISSN 1873-4995, Vol. 122, p. 199-205Article in journal (Refereed)
    Abstract [en]

    The objective of this study was to investigate the swelling characteristics of a hydroxypropyl methylcellulose (HPMC) matrix incorporating the hydrophilic drug antipyrine. We have used this matrix to introduce a novel analytical method, which allows us to obtain within one experimental setup information about the molecular processes of the polymer carrier and its impact on drug release. Nuclear magnetic resonance (NMR) imaging revealed in situ the swelling behavior of tablets when exposed to water. By using deuterated water, the spatial distribution and molecular dynamics of HPMC and their kinetics during swelling could be observed selectively. In parallel, NMR spectroscopy provided the concentration of the drug released into the aqueous phase. We find that both swelling and release are diffusion controlled. The ability of monitoring those two processes using the same experimental setup enables mapping their interconnection, which points on the importance and potential of this analytical technique for further application in other drug delivery forms.

  • 11.
    Dahlberg, Carina
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Dvinskikh, Sergey V.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Schuleit, Michael
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Polymer Swelling, Drug Mobilization and Drug Recrystallization in Hydrating Solid Dispersion Tablets Studied by Multinuclear NMR Microimaging and Spectroscopy2011In: Molecular Pharmaceutics, ISSN 1543-8384, E-ISSN 1543-8392, Vol. 8, no 4, p. 1247-1256Article in journal (Refereed)
    Abstract [en]

    Despite the advantages offered by solid dispersions, the marketed products based on this technology are few. The most frequent concern is the stability of the amorphous drug. The state of the drug in solid dispersions is, in general, poorly characterized as the number of characterization techniques available to monitor nanometer-sized drug particles embedded in a matrix are limited. Here we present a combination of localized NMR spectroscopic and NMR imaging techniques which allow in situ monitoring of the state of the drug during tablet disintegration and dissolution. (19)F NMR relaxation is shown to be sensitive to both the crystalline/amorphous state and the size of the model nanoparticles made of the drug substance flutamide. The time course of drug mobilization and recrystallization is detected with spatial resolution within swelling solid dispersion tablets. Comparing results from spatially resolved (19)F, (2)H and (1)H NMR experiments, recrystallization is related to its enabling factors such as local hydration level and local mobility of the polymer matrix. The initially amorphous drug may recrystallize either by nanoparticle coalescence or by ripening of crystalline grains.

  • 12.
    Dahlberg, Carina
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Dvinskikh, Sergey V.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Schuleit, Michael
    Furó, István
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Recrystallization of drug nanoparticles in solid dispersion tablets by multinuclear NMR spectroscopy and NMR microimagingManuscript (preprint) (Other academic)
  • 13.
    Dvinskikh, Sergey
    KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Chapter 13: Characterization of Liquid-crystalline Materials by Separated Local Field Methods2018In: New Developments in NMR, Royal Society of Chemistry, 2018, no 15, p. 391-423Chapter in book (Refereed)
    Abstract [en]

    A unique feature of liquid crystals is a high degree of molecular mobility combined with orientational and positional order. Solid-state NMR contributes to fundamental understanding of diverse molecular organizations and complex dynamic processes in these exciting materials. The focus of this chapter is on the development and application of advanced solid-state NMR methodologies for liquid crystal studies, with emphasis on techniques for measuring anisotropic spin couplings. The discussion centers on applications of separated dipolar local field NMR spectroscopy, which is used in an increasing number of directions in studies of novel liquid-crystalline materials for emerging technological applications.

  • 14.
    Dvinskikh, Sergey
    Institute of Physics, St. Petersburg State University.
    Separated Local Field Nmr Spectroscopy In Columnar Liquid Crystals2007In: Thermotropic liquid crystals: recent advances / [ed] Ayyalusamy Ramamoorthy, Springer, 2007, p. 117-140Chapter in book (Refereed)
  • 15.
    Dvinskikh, Sergey
    et al.
    St Petersburg State University.
    Chizhik, Vladimir
    St Petersburg State University.
    Spin exchange under off-resonance cross-polarization with refocused chemical shift interaction2006In: Vestnik SPbGU, ISSN 1024-8579, Vol. 4, no 4, p. 18-23Article in journal (Refereed)
  • 16.
    Dvinskikh, Sergey
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Furó, István
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Sandberg, Dick
    Linnæus University, School of Engineering.
    Söderström, Ove
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology.
    Moisture content profiles and uptake kinetics in wood cladding materials evaluated by a portable nuclear magnetic resonance spectrometer2011In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 6, no 3, p. 119-127Article in journal (Refereed)
    Abstract [en]

    This study evaluated the capability of nuclear magnetic resonance (NMR) technology based on small portable magnets for in situ studies of the local moisture content in wood. Low-field and low-resolution [1H]NMR with a unilateral permanent magnet was used to monitor and map the moisture content of wood cladding materials of various types in a spatially resolved manner. The results show that portable NMR equipment based on small open-access permanent magnets can be successfully used for non-invasive monitoring of the moisture content in various extended wood specimens. The moisture content was measured with a depth resolution of 0.2 mm and a maximum penetration depth of 3 mm. This makes the technique suitable for in situ local moisture content measurements beneath a coating layer in the cladding, for example, and it is also possible to relate the moisture level to specific properties of the wood material.

  • 17.
    Dvinskikh, Sergey
    et al.
    Institute of Physics, St. Petersburg State University.
    Sandström, Dick
    Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University.
    Zimmermann, Herbert
    Department of Biomedical Optics, Max-Planck-Institut für Medizinische Forschung, Jahnstrasse 29, D-69120 Heidelberg, Germany.
    Maliniak, Arnold
    Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University,.
    13C Nmr Studies Of Columnar Liquid Crystals2007In: New Research on Magnetic Resonance / [ed] Bernard C. Castleman, New York: Nova Science Publishers, Inc., 2007, p. 137-186Chapter in book (Refereed)
  • 18.
    Dvinskikh, Sergey V.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Pulsed-Field-Gradient NMR Study of Anisotropic Molecular Translational Diffusion in nOCB Liquid Crystals2013In: Applied Magnetic Resonance, ISSN 0937-9347, E-ISSN 1613-7507, Vol. 44, no 1-2, p. 169-180Article in journal (Refereed)
    Abstract [en]

    Pulsed-field-gradient nuclear magnetic resonance (NMR) combined with magic echo decoupling is applied to study anisotropic diffusion in samples with strong static dipolar spin interactions. The approach, due to its moderate demands on the NMR hardware, can be implemented on standard commercial equipment for routine diffusion studies of liquid crystals. Using a microimaging probe, measurement of diffusion in arbitrary spatial direction is possible. Hence, the principal components of the diffusion tensor are directly obtained. Anisotropic diffusion is investigated in the thermotropic mesophases of a homologous series of nOCB liquid crystals and an analogous compound with hydroxyl groups. The geometric average diffusion coefficient changes continuously at the isotropic-nematic phase transition. Experimental data are described in terms of the molecular translation models in the nematic phase and for the second-order nematic-smectic A phase transition. The diffusion anisotropy is higher for the sample with terminal hydroxyl groups suggesting significant molecular association via hydrogen bonding.

  • 19. Dvinskikh, Sergey V.
    et al.
    Castro, V.
    Sandstrom, D.
    Efficient solid-state NMR methods for measuring heteronuclear dipolar couplings in unoriented lipid membrane systems2005In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 7, no 4, p. 607-613Article in journal (Refereed)
    Abstract [en]

    Recently (Dvinskikh et al., J. Magn. Reson., 2003, 164, 165 and Dvinskikh et al., J. Magn. Reson., 2004, 168, 194), some of us introduced two efficient solid-state NMR techniques for the determination of heteronuclear dipolar couplings under magic-angle spinning (MAS). These two-dimensional (2D) recoupling methods have been applied previously to simple amino acids, and to columnar systems with high positional and orientational order. In this work, we show that the 2D MAS sequences produce unparalleled H-1-C-13 dipolar resolution in unoriented lipid membranes. The recoupling experiments were applied to hydrated dimyristoylphosphatidylcholine (DMPC) in the liquid-crystalline L-alpha phase, and the results agreed well with previous NMR investigations using specifically deuterated phospholipids.

  • 20. Dvinskikh, Sergey V.
    et al.
    Castro, V.
    Sandstrom, D.
    Heating caused by radiofrequency irradiation and sample rotation in C-13 magic angle spinning NMR studies of lipid membranes2004In: Magnetic Resonance in Chemistry, ISSN 0749-1581, E-ISSN 1097-458X, Vol. 42, no 10, p. 875-881Article in journal (Refereed)
    Abstract [en]

    Application of rapid sample rotation and radiofrequency irradiation in magic angle spinning (MAS) NMR of lipid bilayers can significantly increase the sample temperature. In this work, we studied the extent of heating during the acquisition of H-1-decoupled C-13 MAS spectra of hydrated dimyristoylphosphatidyl-choline (DMPC) in the L. phase. First, we describe a simple procedure for determining the increase in temperature by observing the shift of the H-1 water signal. The method is then used to identify and assess the various factors that contribute to the sample heating. The important factors discussed in this paper include: (i) the spinning speed, (ii) the variable-temperature gas pressure, (iii) the rotor geometry, (iv) the power, duration and frequency of the radiofrequency irradiation and (v) the hydration level. A comparison of different heteronuclear decoupling schemes in terms of their ability to produce highly resolved C-13 spectra of DMPC is also reported.

  • 21. Dvinskikh, Sergey V.
    et al.
    Castro, V.
    Sandstrom, D.
    Probing segmental order in lipid bilayers at variable hydration levels by amplitude- and phase-modulated cross-polarization NMR2005In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 7, no 18, p. 3255-3257Article in journal (Refereed)
    Abstract [en]

    The conformational response of dimyristoylphosphatidylcholine bilayers in the liquid crystalline phase to hydration is investigated by a novel magic-angle spinning cross-polarization NMR technique.

  • 22. Dvinskikh, Sergey V.
    et al.
    Chizhik, V. I.
    Cross-polarization with radio-frequency field phase and amplitude modulation under magic-angle spinning conditions2006In: Journal of Experimental and Theoretical Physics, ISSN 1063-7761, E-ISSN 1090-6509, Vol. 102, no 1, p. 91-101Article in journal (Refereed)
    Abstract [en]

    Nucleus cross-polarization technique in a rotating frame of reference is analyzed as applied to NMR experiments with sample magic-angle spinning. The concept of simultaneous phase and amplitude modulation is suggested. According to this suggestion, the form of the Hamiltonian of recoupled dipolar interaction remains unchanged if phase inversion is accompanied by inversion of the difference of radio-frequency (RF) field amplitudes. A theoretical treatment is given in terms of the average Hamiltonian theory. The concept is demonstrated experimentally and by numerical analysis for several particular cases. Periodic phase inversion in cross-polarization experiments was shown to have the practically important advantage of suppressing chemical shift interactions and the effect of inaccurate tuning of RF field parameters.

  • 23. Dvinskikh, Sergey V.
    et al.
    Durr, U.
    Yamamoto, K.
    Ramamoorthy, A.
    A high-resolution solid-state NMR approach for the structural studies of bicelles2006In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 128, no 19, p. 6326-6327Article in journal (Refereed)
  • 24. Dvinskikh, Sergey V.
    et al.
    Durr, Ulrich H. N.
    Yamamoto, Kazutoshi
    Ramamoorthy, Ayyalusamy
    High-resolution 2D NMR spectroscopy of bicelles to measure the membrane interaction of ligands2007In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 129, no 4, p. 794-802Article in journal (Refereed)
    Abstract [en]

    Magnetically aligned bicelles are increasingly being used as model membranes in solution- and solid-state NMR studies of the structure, dynamics, topology, and interaction of membrane-associated peptides and proteins. These studies commonly utilize the PISEMA pulse sequence to measure dipolar coupling and chemical shift, the two key parameters used in subsequent structural analysis. In the present study, we demonstrate that the PISEMA and other rotating-frame pulse sequences are not suitable for the measurement of long-range heteronuclear dipolar couplings, and that they provide inaccurate values when multiple protons are coupled to a C-13 nucleus. Furthermore, we demonstrate that a laboratory-frame separated-local-field experiment is capable of overcoming these difficulties in magnetically aligned bicelles. An extension of this approach to accurately measure C-13-P-31 and H-1-P-31 couplings from phospholipids, which are useful to understand the interaction of molecules with the membrane, is also described. In these 2D experiments, natural abundance C-13 was observed from bicelles containing DMPC and DHPC lipid molecules. As a first application, these solid-state NMR approaches were utilized to probe the membrane interaction of an antidepressant molecule, desipramine, and its location in the membrane.

  • 25.
    Dvinskikh, Sergey V.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Anisotropic self-diffusion in nematic, smectic-A, and reentrant nematic phases2012In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 86, no 3, p. 031704-Article in journal (Refereed)
    Abstract [en]

    The nature of the reentrant nematic phase has been actively investigated both experimentally and theoretically during the past few decades. Most studies concluded that, as concerning molecular dynamics, a reentrant nematic phase is essentially analogous to a conventional nematic one. Recent computer simulations [Mazza et al., Phys. Rev. Lett. 105, 227802 (2010)], however, predicted molecular translational self-diffusion along the phase director that was dominated by a collective transport mode and was, relative to that observed in a conventional nematic phase, enhanced by an order of magnitude. In the present work, the principal components of the diffusion tensor in a reentrant nematic phase are determined experimentally and compared to those in conventional nematic and smectic-A phases. We find that the temperature dependence of the translational diffusion in the two nematic phases, within experimental error, follows a uniform trend and can be adequately described in terms of available diffusion models in nematics. Hence, we find no evidence for enhanced diffusion but confirm instead the similarity of conventional and reentrant nematic phases with respect to molecular translational dynamics.

  • 26.
    Dvinskikh, Sergey V.
    et al.
    KTH, Superseded Departments, Chemistry.
    Furo, Istvan
    KTH, Superseded Departments, Chemistry.
    Anisotropic self-diffusion in the nematic phase of a thermotropic liquid crystal by H-1-spin-echo nuclear magnetic resonance2001In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 115, no 4, p. 1946-1950Article in journal (Refereed)
    Abstract [en]

    The orientation-dependent molecular diffusion in the nematic liquid crystal 4-pentyl-4'-cyanobiphenyl is measured to high accuracy. The applied nuclear magnetic resonance method combines multiple-pulse homonuclear dipolar decoupling with pulsed-field-gradient stimulated echo and slice selection. The obtained temperature dependencies of the principal diffusion coefficients are not described by a simple Arrhenius relationship but reflect the decrease of the molecular orientational order close to the nematic-to-isotropic phase transition. The geometric average of the principal diffusion coefficients is continuous with the diffusion coefficient in the isotropic phase. The results are best described in terms of the affine transformation model of diffusion in hard-ellipsoid nematics.

  • 27.
    Dvinskikh, Sergey V.
    et al.
    KTH, Superseded Departments, Chemistry.
    Furo, Istvan
    KTH, Superseded Departments, Chemistry.
    Combining PGSE NMR with homonuclear dipolar decoupling2000In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 144, no 1, p. 142-149Article in journal (Refereed)
    Abstract [en]

    A new robust approach for combining multiple-pulse homonuclear decoupling and ROSE NMR is introduced for accurately measuring molecular diffusion coefficients in systems with nonvanishing static homonuclear dipolar couplings. Homonuclear decoupling suppresses dipolar dephasing during the gradient pulses but its efficiency and scaling factor for the effective gradient vary across the sample because of the large variation of the frequency offset caused by the gradient. The resulting artifacts are reduced by introducing a slice selection scheme. The method is demonstrated by F-19 PGSE NMR experiments in a lyotropic liquid crystal.

  • 28.
    Dvinskikh, Sergey V.
    et al.
    KTH, Superseded Departments, Chemistry.
    Furo, Istvan
    KTH, Superseded Departments, Chemistry.
    Cross-relaxation effects in stimulated-echo-type PGSE NMR experiments by bipolar and monopolar gradient pulses2000In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 146, no 2, p. 283-289Article in journal (Refereed)
    Abstract [en]

    Exchange of longitudinal spin polarization by dipolar cross relaxation between nonequivalent spins results in a modulation of the stimulated echo signal on increasing the encoding/decoding delays and in a multiexponential decap on increasing the diffusion time. These artifacts are suppressed by 180 degrees pulses inserted in the middle of the gradient encoding/decoding periods. The efficiency of the gradient encoding is preserved if bipolar gradient pulses are used instead of monopolar pulses. The behavior of the different pulse sequences is demonstrated by F-19 PGSE NMR experiments in a lyotropic liquid crystal in both isotropic micellar and oriented nematic phases.

  • 29.
    Dvinskikh, Sergey V.
    et al.
    KTH, Superseded Departments, Chemistry.
    Furo, Istvan
    KTH, Superseded Departments, Chemistry.
    Domain structure in an unoriented lamellar lyotropic liquid crystal phase studied by H-2 NMR2001In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 17, no 21, p. 6455-6460Article in journal (Refereed)
    Abstract [en]

    The spatial variation of the phase director in an unoriented lamellar lyotropic liquid crystal is investigated by H-2 two-dimensional and one-dimensional exchange and PGSE NMR. Exchange NMR probes the single-particle orientational correlation function of D2O molecules that diffuse among regions with different director orientations. The obtained correlation time and the water diffusion coefficient, measured by H-2 PGSE NMR, provide the persistence length of director orientation that is defined as domain size. The nature of spatial variation is revealed by the decay of the H-2 stimulated echo signal recorded with different evolution times. The persistence length of the director is found to be strongly dependent on the rate of cooling the sample from its isotropic phase.

  • 30.
    Dvinskikh, Sergey V.
    et al.
    KTH, Superseded Departments, Chemistry.
    Furo, Istvan
    KTH, Superseded Departments, Chemistry.
    Measurement of the principal values of the anisotropic diffusion tensor in an unoriented sample by exploiting the chemical shift anisotropy: F-19 PGSE NMR with homonuclear decoupling2001In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 148, no 1, p. 73-77Article in journal (Refereed)
    Abstract [en]

    NMR methods (S. V. Dvinskikh et al. J. Magn. Reson. 142, 102-110 (2000) and S. V. Dvinskikh and I. Furo, J. Magn. Reson. 144, 142-149 (2000)) that combine PGSE with dipolar decoupling are extended to polycrystalline solids and unoriented liquid crystals. Decoupling suppresses dipolar dephasing not only during the gradient pulses but also under signal acquisition so that the detected spectral shape is dominated by the chemical shift tensor of the selected nucleus. The decay of the spectral intensity at different positions in the powder spectrum provides the diffusion coefficient in sample regions with their crystal axes oriented differently with respect to the direction of the field gradient. Hence, one can obtain the principal values of the diffusion tensor. The method is demonstrated by F-19 PGSE NMR with homonuclear decoupling in a lyotropic lamellar liquid crystal.

  • 31. Dvinskikh, Sergey V.
    et al.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Nuclear magnetic resonance studies of translational diffusion in thermotropic liquid crystals2006In: Uspehi himii, ISSN 0042-1308, E-ISSN 1817-5651, Vol. 75, no 6, p. 557-568Article, review/survey (Refereed)
  • 32.
    Dvinskikh, Sergey V.
    et al.
    KTH, Superseded Departments, Chemistry.
    Furo, Istvan
    KTH, Superseded Departments, Chemistry.
    Order parameter profile of perfluorinated chains in a lamellar phase2000In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, no 6, p. 2962-2967Article in journal (Refereed)
    Abstract [en]

    Cesium perfluorooctanoate molecules are investigated by NMR spectroscopy in the lamellar phase of their aqueous solution. The particular NMR method, C-13-detected, F-19-decoupled separated-local-field (SLF) spectroscopy, provides the dipolar splitting of each C-13 spin to its F-19 neighbors. These dipolar splittings are interpreted in terms of the molecular C-F bond order parameters of each difluoromethylene and trifluoromethyl group. The obtained variation of this order parameter along the fluoroalkyl chain strengthens the conclusion from an earlier, model-dependent study (Fur6, I.; Sitnikov, R. Langmuir 1999, 15, 2669): perfluorinated surfactant chains are significantly more rigid than their hydrogenated counterparts.

  • 33. Dvinskikh, Sergey V.
    et al.
    Furo, Istvan
    KTH, Superseded Departments, Chemistry.
    Sandstrom, D.
    Maliniak, A.
    Zimmermann, H.
    Deuterium stimulated-echo-type PGSE NMR experiments for measuring diffusion: Application to a liquid crystal2001In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 153, no 1, p. 83-91Article in journal (Refereed)
    Abstract [en]

    The accessibility of molecular self-diffusion coefficients in anisotropic materials, such as liquid crystals or solids, by stimulated-echo-type H-2 PGSE NMR is examined. The amplitude and phase modulation of the signal in the stimulated-echo-type sequence by the static quadrupole coupling during the encoding/decoding delays is suppressed by adjusting the pulse flip angles and the phase cycle. For nuclei that experience both nonnegligible quadrupole and dipole couplings, the application of magic echoes during the evolution periods of stimulated echo is demonstrated as a helpful technique in the case of slow diffusion. These findings are demonstrated by experimental results in the thermotropic liquid crystal of partially deuterated 8CB. The obtained diffusion coefficients are also compared to data obtained by a H-1 homonuclear-decoupling-type PGSE NMR method in the same material.

  • 34. Dvinskikh, Sergey V.
    et al.
    Furo, Istvan
    KTH, Superseded Departments, Chemistry.
    Zimmermann, H.
    Maliniak, A.
    Anisotropic self-diffusion in thermotropic liquid crystals studied by H-1 and H-2 pulse-field-gradient spin-echo NMR2002In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 65, no 6Article in journal (Refereed)
    Abstract [en]

    The molecular self-diffusion coefficients in nematic and smectic-A thermotropic liquid crystals are measured using stimulated-echo-type H-2 and H-1 pulse-field-gradient spin-echo nuclear magnetic resonance (PGSE NMR) combined with multiple-pulse dipolar decoupling and slice selection. The temperature dependence of the principal components of the diffusion tensor in the nematic phase follows a simple Arrhenius relationship except in the region of nematic-isotropic phase transition where it reflects, merely, the decrease of the molecular orientational order. The average of the principal diffusion coefficients in the isotropic-nematic phase transition region is close to the diffusion coefficient in the isotropic phase. At the nematic-smectic-A phase transition the diffusion coefficients change continuously. The results in nematic phase are best described in terms of the affine transformation model for diffusion in nematics formed by hard ellipsoids. In the smectic-A phase the data are interpreted using a modified model for diffusion in presence of a periodic potential along the director.

  • 35. Dvinskikh, Sergey V.
    et al.
    Furo, Istvan
    KTH, Superseded Departments, Chemistry.
    Zimmermann, H.
    Maliniak, A.
    Molecular self-diffusion in a columnar liquid crystalline phase determined by deuterium NMR2002In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 65, no 5Article in journal (Refereed)
    Abstract [en]

    We report translational-diffusion coefficients in a columnar phase of a discotic liquid crystal formed by a triphenylpne-based compound. The experiments were performed using H-2 stimulated-echo-type pulsed-field-gradient spin-echo NMR applied to a chain-deuterated sample. The diffusion coefficients were found in the range of 1 x 10(-14)-4 x 10(-14) m(2)/s, three orders of magnitude lower than in the isotopic phase of the same compound. This, together with the high activation energy obtained in, columnar phase, indicates that the diffusion is dominated by solidlike jump processes.

  • 36.
    Dvinskikh, Sergey V.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Furó, István
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Magnetic resonance imaging and nuclear magnetic resonance investigations of bentonite systems2009Report (Refereed)
  • 37.
    Dvinskikh, Sergey V.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Henriksson, Marielle
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Furó, István
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    A multinuclear magnetic resonance imaging (MRI) study of wood with adsorbed water: Estimating bound water concentration and local wood density2011In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 65, no 1, p. 103-107Article in journal (Refereed)
    Abstract [en]

    The interaction between moisture and the macromolecular wood tissue is of critical importance to wood properties. In this context, magnetic resonance imaging (MRI) is very promising as this method could deliver molecular information on the submillimeter scale (i.e., along concentration gradients) about both free and adsorbed water and the cell wall polymers. In the present study, it is demonstrated for the first time that wood containing adsorbed heavy water ((H2O)-H-2) can be studied by MRI based on separated images due to water (H-2 MRI) and cell wall polymers (H-1 MRI). Data confirm that in specimens equilibrated at controlled humidity there is a direct correlation between bound water content and relative density of the polymers in wood tissue; there is a strong variation across annual rings.

  • 38.
    Dvinskikh, Sergey V.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre. KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Henriksson, Marielle
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Mendicino, Antonio Lorenzo
    Fortino, Stefania
    Toratti, Tomi
    NMR imaging study and multi-Fickian numerical simulation of moisture transfer in Norway spruce samples2011In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 33, no 11, p. 3079-3086Article in journal (Refereed)
    Abstract [en]

    Wood has potential as a renewable material for a large variety of applications that often call for improved properties such as dimensional stability, moisture insensitivity, and durability. Moisture migration in wood is a particularly important factor in determining the cost-effective service life of wooden construction. Within the present research, proton NMR imaging was applied for recording the moisture spatial distribution of various samples of Norway Spruce. Moisture distribution along the radial, tangential and longitudinal directions in wood was monitored at different times upon three consecutive changes of relative humidity: (1) from 65% to 94%; (2) from 94% to 33%; (3) from 33% to 65%. Uncoated samples and specimens treated with different types of surface coatings were studied. The experiments were numerically simulated by using the multi-Fickian model. The model describes the moisture transport process in wood which is characterized by three phenomena: (a) bound water diffusion, (b) water vapor diffusion and (c) coupling between the two phases through sorption. The model is implemented into the Abaqus FEM code. The numerical results are found to be in agreement with the experimental data.

  • 39. Dvinskikh, Sergey V.
    et al.
    Luz, Z.
    Zimmermann, H.
    Maliniak, A.
    Sandstrom, D.
    Molecular characterization of hexaoctyloxy-rufigallol in the solid and columnar phases: A local field NMR study2003In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 107, no 9, p. 1969-1976Article in journal (Refereed)
    Abstract [en]

    Separated local field NMR spectroscopy was used to obtain H-1-C-13 dipolar interactions in the solid and columnar phases of the discotic compound 1,2,3,5,6,7-hexaoctyloxy-rufigallol (RufH8O). The couplings were measured and assigned by a variety of advanced NMR techniques performed under both static and magic-angle spinning conditions. The analysis of the dipolar couplings shows that the three nonequivalent aliphatic chains in RufH8O exhibit vastly different structural and dynamical characteristics. It was also found that one of the alpha methylene signals exhibits two H-1-C-13 dipolar splittings at low temperatures in the columnar phase. Similar pairs of doublets have previously been observed in a H-2 NMR study of RufH8O-H-2(alpha) and were there interpreted in terms of dynamic packing fluctuations along the columns. We will present an alternative explanation and show that these two doublets most likely originate from nonequivalent protons (or deuterons) in the alpha methylene group and not from density modulations.

  • 40. Dvinskikh, Sergey V.
    et al.
    Sandstrom, D.
    Frequency offset refocused PISEMA-type sequences2005In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 175, no 1, p. 163-169Article in journal (Refereed)
    Abstract [en]

    The popular PISEMA experiment is highly sensitive to the H-1 chemical shift dispersion and the choice of the H-1 carrier frequency. This is due to the off-resonance H-1 irradiation in the FSLG-CP sequence employed during the dipolar evolution period. In the modified approach described in this work, the interfering frequency offset terms are suppressed. In the new pulse schemes, conventional FSLG-CP is intercalated with 180 degrees pulses applied Simultaneously to both frequency channels, and with phases set orthogonal to those of the spin-lock fields. The technique is demonstrated on a nematic liquid-crystalline sample. Extensions to amplitude-modulated FSLG-CP recoupling under MAS are also presented.

  • 41. Dvinskikh, Sergey V.
    et al.
    Sandstrom, D.
    Luz, Z.
    Zimmermann, H.
    Maliniak, A.
    Molecular structure and order of hexaoctyloxy-rufigallol in the solid and columnar phases: Analysis of H-2-C-13 dipolar and C-13 chemical-shift interactions2003In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 119, no 1, p. 413-422Article in journal (Refereed)
    Abstract [en]

    We report a C-13 NMR investigation of 1,2,3,5,6,7-hexaoctyloxy-rufigallol in the solid and columnar phases using various H-2- and C-13-labeled isotopomers. The measurements were performed under both static and magic-angle spinning conditions. The conformations of the aliphatic side chains were derived from an analysis of H-2-C-13 dipolar and C-13 chemical-shift interactions. The nonequivalent chains exhibit significantly different structural behavior in both solid and columnar phase. It emerged that one of the side chains adopts an in-plane structure, while the other two chains prefer antiparallel out-of-plane conformations. Quantum-chemical calculations of the C-13 chemical-shift tensors were also carried out. These calculations support the experimental findings.

  • 42. Dvinskikh, Sergey V.
    et al.
    Sandstrom, D.
    Zimmermann, H.
    Maliniak, A.
    C-13-detected H-1-H-2 separated local field NMR spectroscopy2003In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 382, no 04-mar, p. 410-417Article in journal (Refereed)
    Abstract [en]

    We present a new NMR method for measuring H-1-H-2 dipolar couplings in macroscopically oriented media. To overcome the lack of dipolar resolution in 1D H-1 and H-2 spectra of deuterated molecules, we use a 2D heteronuclear correlation experiment where H-1 chemical shifts and H-1-H-2 dipolar interactions in the first dimension are. correlated with C-13 chemical shifts and H-2-C-13 dipolar interactions in the second dimension. The technique is demonstrated on a columnar liquid-crystalline phase.

  • 43. Dvinskikh, Sergey V.
    et al.
    Sandstrom, Dick
    Zimmermann, Herbert
    Maliniak, Arnold
    Carbon-13 NMR spectroscopy applied to columnar liquid crystals2006In: Progress in nuclear magnetic resonance spectroscopy, ISSN 0079-6565, E-ISSN 1873-3301, Vol. 48, no 03-feb, p. 85-107Article, review/survey (Refereed)
  • 44.
    Dvinskikh, Sergey V.
    et al.
    KTH, Superseded Departments, Chemistry.
    Sitnikov, R.
    Furo, Istvan
    KTH, Superseded Departments, Chemistry.
    C-13 PGSE NMR experiment with heteronuclear dipolar decoupling to measure diffusion in liquid crystals and solids2000In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 142, no 1, p. 102-110Article in journal (Refereed)
    Abstract [en]

    A new PGSE NMR experiment, designed to measure molecular diffusion coefficients in systems with nonvanishing static dipolar coupling, is described. The fast static dipolar dephasing of the single-quantum C-13 coherences is removed by multiple-pulse heteronuclear decoupling. The resulting slow dephasing of the C-13 coherences allows for inserting appropriate gradient pulses into the pulse sequence. The presence of the large magnetic field gradient reduces the efficiency of the decoupling sequences which is compensated for by introducing a scheme of sequential slice selection across the sample. The method is demonstrated by F-19-decoupled C-13 PGSE NMR experiments in a lyotropic nematic and lamellar liquid crystal,

  • 45.
    Dvinskikh, Sergey V.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Szutkowski, Kosma
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    MRI profiles over very wide concentration ranges: Application to swelling of a bentonite clay2009In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 198, no 2, p. 146-150Article in journal (Refereed)
    Abstract [en]

    In MRI investigation of soils, clays, and rocks, mainly mobile water is detected, similarly to that in biological and medical samples. However, the spin relaxation properties of water in these materials and/or low water concentration may make it difficult to use standard MRI approaches. Despite these limitations, one can combine MRI techniques developed for solid and liquid states and use independent information on relaxation properties of water, interacting with the material of interest, to obtain true images of both water and material content. We present procedures for obtaining such true density maps and demonstrate their use for studying the swelling of bentonite clay by water. A constant time imaging protocol provides 1D mapping of the clay distribution in regions with clay concentration above 10 vol%. T-1 relaxation time imaging is employed to monitor the clay content down to 10(-3) vol%. Data provided by those two approaches are in good agreement in the overlapping range of concentrations. Covering five orders of magnitude of clay concentration, swelling of sodium-exchanged bentonite clays from pre-compacted pellets into a gel phase is followed in detail.

  • 46. Dvinskikh, Sergey V.
    et al.
    Thaning, Johan
    Stevensson, Baltzar
    Jansson, Kjell
    Kumar, Sandeep
    Zimmermann, Herbert
    Maliniak, Arnold
    Mesomorphism in columnar phases studied by solid-state nuclear magnetic resonance2006In: Physical Review E, ISSN 1539-3755, Vol. 74, no 2Article in journal (Refereed)
    Abstract [en]

    In this paper, we present C-13 and H-1 NMR investigations of 2, 3, 6, 7, 10, 11-hexahexyl-thiotriphenylene (HHTT). The measurements were carried out under both static and magic-angle spinning conditions. The phase diagram of HHTT is K <-> H <-> D-hd <-> I, where H is a helical phase and D-hd is a columnar liquid crystal. The motivation was to characterize the molecular order and dynamics and to investigate differences at the molecular level between the two mesophases: H and D-hd. It is shown that D-hd is a conventional columnar liquid crystal, where the molecular core undergoes fast rotation about the symmetry axis. The orientational order in this mesophase is lower and the temperature dependence of the order parameter is steeper than in other triphenylene-based compounds. On the other hand, in the helical phase the core, similarly to the solid phase, is essentially rigid. The difference between the solid and helical phases is mainly manifested in an increased mobility of the aliphatic chains observed in the latter phase. In addition, the sample exhibits thermal history effects, which are observed in the different behavior upon cooling and heating.

  • 47. Dvinskikh, Sergey V.
    et al.
    Yamamoto, K.
    Ramamoorthy, A.
    Separated local field NMR spectroscopy by windowless isotropic mixing2006In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 419, no 03-jan, p. 168-173Article in journal (Refereed)
    Abstract [en]

    A new separated local field NMR experiment, designed for accurate measurements of heteronuclear dipolar couplings, is described. The pulse sequence is based on a homonuclear decoupling windowless heteronuclear isotropic mixing approach to achieve the coherent polarization exchange between the z-components of the magnetizations in heteronuclear spin system. This technique suppresses chemical shifts and frequency offset variations irrespective of the dipolar coupling value. The experiment is demonstrated on a columnar liquid. crystal.

  • 48. Dvinskikh, Sergey V.
    et al.
    Yamamoto, Kazutoshi
    Durr, Ulrich H. N.
    Ramamoorthy, Ayyalusamy
    Sensitivity and resolution enhancement in solid-state NMR spectroscopy of bicelles2007In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 184, no 2, p. 228-235Article in journal (Refereed)
    Abstract [en]

    Magnetically aligned bicelles are becoming attractive model membranes to investigate the structure, dynamics, geometry, and interaction of membrane-associated peptides and proteins using solution- and solid-state NMR experiments. Recent studies have shown that bicelles are more suitable than mechanically aligned bilayers for multidimensional solid-state NMR experiments. In this work, we describe experimental aspects of the natural abundance C-13 and N-14 NMR spectroscopy of DMPC/DHPC bicelles. In particular, approaches to enhance the sensitivity and resolution and to quantify radio-frequency heating effects are presented. Sensitivity of C-13 detection using single pulse excitation, conventional cross-polarization (CP), ramp-CP, and NOE techniques are compared. Our results suggest that the proton decoupling efficiency of the FLOPSY pulse sequence is better than that of continuous wave decoupling, TPPM, SPINAL, and WALTZ sequences. A simple method of monitoring the water proton chemical shift is demonstrated for the measurement of sample temperature and calibration of the radio-frequency-induced heating in the sample. The possibility of using N-14 experiments on bicelles is also discussed.

  • 49. Dvinskikh, Sergey V.
    et al.
    Yamamoto, Kazutoshi
    Ramamoorthy, Ayyalusamy
    Heteronuclear isotropic mixing separated local field NMR spectroscopy2006In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 125, no 3Article in journal (Refereed)
    Abstract [en]

    This paper presents a theoretical, numerical, and experimental study of a new class of separated local field (SLF) techniques. These techniques are based on the heteronuclear isotropic mixing leading to spin exchange via the local field (HIMSELF). It is shown that highly efficient and robust SLF experiments can be designed based on double channel windowless homonuclear decoupling sequences. Compared to rotating frame techniques based on Hartmann-Hahn cross polarization, the new approach is less susceptible to the frequency offset and chemical shift interaction and can be applied in the structural studies of macromolecules that are uniformly labeled with isotopes such as C-13 and N-15. Furthermore, isotropic mixing sequences allow for transfer of any magnetization component of one nucleus to the corresponding component of its dipolar coupled partner. The performance of HIMSELF is studied by analysis of the average Hamiltonian and numerical simulation and is experimentally demonstrated on a single crystalline sample of a dipeptide and a liquid crystalline sample exhibiting motionally averaged dipolar couplings.

  • 50.
    Dvinskikh, Sergey V.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Yamamoto, Kazutoshi
    Scanu, David
    Deschenaux, Robert
    Ramamoorthy, Ayyalusamy
    High-resolution characterization of liquid-crystalline 60 fullerenes using solid-state nuclear magnetic resonance spectroscopy2008In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 112, no 39, p. 12347-12353Article in journal (Refereed)
    Abstract [en]

    Liquid-crystalline materials containing fullerenes are valuable in the development of supramolecular switches and in solar cell technology. In this study, we characterize the liquid-crystalline and dynamic properties of fullerene-containing thermotropic compounds using solid-state natural abundance C-13 NMR experiments under stationary and magic angle spinning sample conditions. Chemical shifts spectra were measured in isotropic, liquid-crystalline nematic and smectic A and crystalline phases using one-dimensional 13C experiments, while two-dimensional separated local-field experiments were used to measure the H-1-C-13 dipolar couplings in mesophases. Chemical shift and dipolar coupling parameters were used to characterize the structure and dynamics of the liquid-crystalline dyads. NMR data of fullerene-containing thermotropic liquid crystals are compared to that of basic mesogenic unit and mesomorphic promoter compounds. Our NMR results suggest that the fullerene-ferrocene dyads form highly dynamic liquid-crystalline phases in which molecules rotate fast around the symmetry axis on the characteristic NMR time scale of similar to 10(-1) s.

12 1 - 50 of 96
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