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od 2020-09-20 |
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1. |
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Molecular dynamics in supercooled di-isobutyl phthalate close to the glass transition The dynamics of the alpha -relaxation in a glass-forming low-molecular-weight system, diisobutyl phthalate (DIBP), has been studied by means of dielectric, nuclear magnetic and mechanical spectroscopies. By using these techniques we have covered a wide timescale ranging from 10(-11) to 10(2) s. Vogel-Fulcher con elation time behaviour and the Davidson-Cole distribution function make possible a simultaneous fitting of T-1, the nuclear Overhauser enhancement (NOE) factor and dielectric data over the temperature range (Tg - 4 K) < T < (Tg + 155 K). These results together with the viscosity data have been analysed in terms of the Debye diffusion.
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Journal of Physics - Condensed Matter, 12(46), 9551-9562, (2000) |
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Preliminary crystallographic studies of Y25F mutant of periplasmic Escherichia Coli L-asparaginase Periplasmic Escherichia coli L-asparaginase II with Y25F mutation in the active-site cavity has been obtained by recombinant techniques. The protein was crystallized in a new hexagonal form (P6(5)22). Single crystals of this polymorph, suitable for X-ray diffraction, were obtained by vapor diffusion using 2-methyl-2,4-pentanediol as precipitant (pH 4.8). The crystals are characterized by a = 81.0, c = 341.1 Angstrom and diffract to 2.45 Angstrom resolution. The asymmetric unit contains two protein molecules arranged into an AB dimer. The physiologically relevant ABA'B' homotetramer is generated by the action of the crystallographic a-fold axis along [1, -1, 0]. Kinetic studies show that the loss of the phenolic hydroxyl group at position 25 brought about by the replacement of Y with F strongly impairs k(cat) without significantly affecting K-m.
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Acta Biochimica Polonica, 47(3), 807-814, (2000) |
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3. |
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Molecular Physics Reports, 29, 130-134, (2000) |
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4. |
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New aproach to assessment of aging processes at the cellular level by NMR spectroscopy The paper presents results of the proton relaxation time T1 measurements by 1H NMR for oral epithelium samples taken from 320 subjects, men and women, in different age, from 19 to 95 year old. The times of nuclear magnetic relaxation T1 were found to be correlated with the age of the subjects.
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Molecular Physics Reports, 29, 228-231, (2000) |
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5. |
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A study of interdygitated-noninterdygitated phase transition on n-octadecylammonium chloride C18H37NH3Cl by 13C CPMAS NMR An interrelation between the interdigitated-noniterdigitated phase transition and molecular dynamics of the alkylammonium chains in C18H37NH3Cl is studied by means of 13C CPMAS experiment . The results of the measurements of 13C spectra as a function of temperature show that the observed phase transition is related with a motional freedom of the methylene groups.
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Molecular Physics Reports, 29, 47-50, (2000) |
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6. |
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Crystallization and preliminary crystallographic studies of a new crystal form of Escherichia Coli L-asparaginase II (Ser58Ala mutant) Periplasmic Escherichia coli L-asparaginase II with an Ser58Ala mutation in the active-site cavity has been crystallized in a new orthorhombic form (space group P2(1)2(1)2). Crystals of this polymorph suitable for X-ray diffraction have been obtained by vapour diffusion using two sets of conditions: (i) 1% agarose gel using MPD as precipitant (pH 4.8) and (ii) liquid droplets using PEG-MME 550 (pH 9.0). The crystals grown in agarose gel are characterized by unit-cell parameters a = 226.9, b = 128.4, c = 61.9 Angstrom and diffract to 2.3 Angstrom resolution. The asymmetric unit contains six protein molecules arranged into one pseudo-222-symmetric homotetramer and an active-site competent dimer from which another homotetramer is generated by crystallographic symmetry.
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Acta Crystallographica Section D-Biological Crystallography, 56(4), 509-511, (2000) |
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7. |
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Molecular dynamics in poly[(R)-3-hydroxybutyric acid] biopolymer as studied by NMR Nuclear magnetic resonance line shapes and spin-lattice relaxation rimes T-1 of H-1 and H-2 nuclei of poly[(R)-3-hydroxybutyric acid] have been measured in the temperature range 100-413 K. The results provide information on the local dynamics of the compound. Activation parameters of the revealed motion are determined.
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Applied Magnetic Resonance, 18(1), 37-45, (2000) |
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8. |
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NMR microimaging studies of the union between stock and scion In this study we demonstrate the applicability of nuclear magnetic resonance (NMR) microimaging in examining the efficiency of grafting coniferous plants. Grafting is a method of propagating plants. It is used mainly in gardening. In some cases it is the only possible way to propagate certain varieties (e.g., apple varieties). The biology of grafting is nor well investigated yet. Therefore we have decided to rake advantage of the magnetic resonance imaging techniques in order to estimate which of the commonly used grafting methods gives the best quality unions. Results of our experiment indicate that the quality of union depends very much on the grafting method. NMR images give more information about the graft than microscopic images. We hope that our technique can select the best way to prepare plants for grafting and indicate average time of union process.
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Applied Magnetic Resonance, 18(1), 147-153, (2000) |
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9. |
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Molecular dynamics in comb-like ionene as studied by NMR Proton and fluorine second moment and spin-lattice relaxation times T-1 and T-1p have been employed to study molecular dynamics in the comb-like 1-6,6-16-Me-BF4 ionene in the temperature range from 110 up to 300 K. The existence of motions of methyl groups, trans-gauche isomerization, and/or rotation of the main- and side-chain methylene groups, as well as isotropic reorientation of tetrafluoroborate ions were established. The observed relaxation behaviors are explained by motional models which assume Davidson-Cole asymmetrical distribution of correlation rimes. The best-fit motional parameters are given.
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Applied Magnetic Resonance, 18(1), 63-70, (2000) |
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10. |
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Molecular dynamics of n-dodecylammonium chloride studied by nuclear magnetic resonance The relation between molecular dynamics and phase properties of the bilayered compound C12H25NH3Cl is studied by differential scanning calorimetry, proton second moment, and spin-lattice relaxation Limes. In the low-temperature Phase I of the compound methyl and ammonium groups execute a classical threefold reorientation, while the alkylammonium chains are rigid on the nuclear magnetic resonance time scale. In the intermediate-temperature phase delta a trans-gauche isomerization of the alkyl chains is observed. In the high-temperature phase alpha the reorientation of the whole chains about their long axes, which are parallel to the normal to the ionic layer is evidenced. In the meta-stable epsilon phase the dynamics involves classical rotation of methyl and ammonium groups and CH2 groups motion of the trans-gauche isomerization type.
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Applied Magnetic Resonance, 19(3-4), 413-420, (2000) |
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11. |
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Molecular dynamics in solid pregnenolone studied by 1H spin-lattice relaxation Spin-lattice relaxation times T-1 in solid pregnenolone have been studied over a wide range of temperatures, from 77 up to 417 K. The dynamic processes arising from C-3 motion of the three methyl substituents are separated, and their activation parameters are determined.
(C) 2000 Elsevier Science B.V. All rights reserved. |
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Solid State Nuclear Magnetic Resonance, 15(4), 227-230, (2000) |
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12. |
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2H and 13C CPMAS NMR study of chain dynamics in n-dodecylammonium chloride The H-2 NMR spectra of the selectively deuterated polycrystalline n-dodecylammonium chloride as well as C-13 CPMAS spectra of this compound are studied over a wide range of temperature. The results reveal a variety of phase transitions occurring in this model bilayer system and make it possible to relate them to the local molecular dynamics of the alkyl chains.
(C) 2000 Elsevier Science B.V. All rights reserved. |
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Journal of Molecular Structure, 555, 107-117, (2000) |
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13. |
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Molecular dynamics in solid riboflavin as studied by 1H NMR Spin-lattice relaxation times T-1 and T-1d as well as NMR second moment were employed to study the molecular dynamics of riboflavin (vitamin B-2) in the temperature range 55-350 K. The broad and flat T-1 minimum observed at low temperatures is attributed to the motion of two nonequivalent methyl groups. The motion of the methyl groups is interpreted in terms of Haupt's theory, which takes into account the tunneling assisted relaxation. An additional mechanism of relaxation in the high temperature region is provided by the motion of a proton in one of the hydroxyl groups. The Davidson-Cole distribution of correlation times for this motion is assumed.
(C) 2000 Academic Press. |
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Solid State Nuclear Magnetic Resonance, 18(1-4), 89-96, (2000) |
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14. |
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Visualisation of fluid migration into porous poly(vinylalkohol) using MRI techniques Information on migration of liquids into porous media and on mobility of the absorbed fluids is of great relevance for the theory and for many branches of the materials science. In this paper we use magnetic resonance microimaging to visualise migration of water and chloroform into porous poly(vinylalkohol) (PVA). The images taken using gradient echo fast imaging (GEFI) and constant time imaging (CTI) methods show differences, which are assumed to reflect the restriction of mobility of water molecules due to formation of hydrogen bonds with hydrophilic PVA.
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Molecular Physics Reports, 28, 106-108, (2000) |
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15. |
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Nuclear magnetic relaxation and molecular dynamics in polycrystalline estrogens: estrone and estriol Spin-lattice relaxation times T1 and T1ρ in polycrystalline estrone and estriol are measured as a function of temperature. It is found that T1 relaxation in both compounds is dominated by C-3 reorientation of the single C18 methyl group. The behaviour of T1ρ at high temperatures reveal the existence of another motion, which may involve conformational changes of the rings system.
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Molecular Physics Reports, 29, 110-113, (2000) |
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16. |
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Quarry-Laboratory-Monument, 1, 287-292, (2000) |
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17. |
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Dynamics in tert-butyl chloride confined to MCM-41 The molecular dynamic of tert-butyl chloride confined to pores of 24.4 Angstrom of MCM-41 is investigated by deuterium NMR spectroscopy. The temperatures of the all phase transitions are depressed by about 10 K in porous MCM-41 relative to the bulk transitions. The rotation of the (CD3)(3) about C-CI (C) axis is less restricted than CD3 rotation about C-C bond (C-3) axis. Variable temperature lineshape analysis yield the activation energy for C3 rotation of E-a = 5.2 kcal/mol in good agreement with E-a = 4.5 kcal/mol obtained from the temperature dependence of spin-lattice relaxation times.
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Molecular Physics Report, 29, 50-54, (2000) |
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18. |
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Molecular dynamics simulations of ionic copolymers Molecular Dynamics (MD) studies of ionic diblock copolymers are reported. The symmetrical
diblocks are shown to exhibit a microphase separation transition (MST) similar to that of neutral diblocks.
The MST was investigated by measuring thermodynamic, structural and dynamic properties: density, simulation
box dimensions, structure factor, anisotropy in structure factor and directional diffusion constants. The
slow cooling of the system from a high-temperature disordered phase to low-temperature ordered microphase
separated phase was achieved in both temperature controlled ('NVT') MD, and temperature and pressure
controlled ('NPT') MD.
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Computational Methods in Science and Technology, 6, 15-24, (2000) |
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Zaktualizowano: podstrony 2021-06-21 / bazę danych: 2024-04-23 by Webmaster: Zbigniew Fojud