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od 2020-09-20 |
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1. |
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Synchrotron radiation small angle scattering studies of thermal stability of xylanase XYNII from Trichoderma Longibrachiatum Xylanase XYNII from Trichoderma longibrachiatum is a small protein of the molecular weight 21 kDa, belonging to the family I I of glycosyl hydrolases, which catalyses hydrolysis of xylan. This article reports thermal stability study of xylanase XYN II conformation in the temperature range 15-65 degrees C by the small angle synchrotron radiation scattering. The study has been performed at different pH conditions: at pH 4.0 (below the physiological optimum of the enzyme activity) at pH 5.8 close to the optimum for enzymatic activity and at pH 8.0. The radius of gyration and the pair distance distribution function p(r) have been analyzed to characterize the changes of the enzyme conformation on heating. In the environment of the pH close to that of the optimum for the enzymatic activity, xylanase shows the greatest thermal stability and undergoes denaturation only above 55 degrees C. In the acidic and basic environments, the enzyme stability is much lower and denaturation begins at 45 degrees C. On the basis of the SAXS data, the shape of the Xylanase molecule in solution in different temperatures has been reconstructed using ab initio method and program DAMMIN. The shape of the xylanase molecule at room temperature is similar to the right hand, which is typically observed for xylanase crystal structure. In higher temperatures (close to the enzyme activity optimum), the conformation of the right hand is loosened and half opened.
(C) 2006 Wiley Periodicals, Inc. |
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Biopolymers, 83(6), 668-674, (2006) |
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2. |
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A comparative study of water distribution, free radical production and activation of antioxidative metabolism in germinating pea seeds The aim of this study was to investigate whether there is a relationship between hydration of the embryo axes and cotyledons and the resumption of the oxidative metabolism in both organs of germinating seeds of pea (Pisum sativum L. cv. Piast). Nuclear magnetic resonance (H-1-NMR) spectroscopy and imaging were used to study temporal and spatial water uptake and distribution in pea seeds. The observations revealed that water penetrates into the seed through the hilum, micropyle and embryo axes, and cotyledons hydrate to different extents. Thus, inhomogeneous water distribution may influence the resumption of oxidative metabolism. Electron paramagnetic resonance (EPR) measurements showed that seed germination was accompanied by the generation of free radicals with g(1) and g(2) values of 2.0032 and 2.0052, respectively. The values of spectroscopic splitting coefficients suggest that they are quinone radicals. The highest content of free radicals was observed in embryo axes immediately after emergence of the radicle. Glutathione content decreased during the entire germination period in both embryo axes and cotyledons. A different profile was observed for ascorbate, with significant increases in embryo axes, coinciding with radicle protrusion. Etectrophoretic analysis showed that superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11), dehydroascorbate reductase (DHAR, EC 1.8.5.1)and glutathione reductase (GR, EC 1.6.4.2) were present in dry seeds and were activated later during germination, especially in embryo axes. The presence of all antioxidative enzymes as well as low molecular antioxidants in dry seeds allowed the antioxidative machinery to be active as soon as the enzymes were reactivated by seed imbibition. The observed changes in free radical levels, antioxidant contents and enzymatic activities in embryo axes and cotyledons appear to be more closely related to metabotic and developmental processes associated with preparation for germination, and do not correspond directly to the hydration of the tissues.
(C) 2006 Elsevier GmbH. All rights reserved. |
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Journal of Plant Physiology, 163(12), 1207-1220, (2006) |
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3. |
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Polyurethane anionomers synthesised with aromatic, aliphatic or cycloaliphatic diisocyanates, polyoxyethylene glycol and 2,2-bis-(hydroxymethyl)propionic acid Small angle X-ray scattering and differential scanning calorimetry methods were employed to characterise the internal order of structural phases present in polyurethane coatings obtained as a result of water evaporation from anionomer dispersions. Those anionomers were produced in the reaction of aromatic, cycloaliphatic and aliphatic diisocyanates with polyoxyethylene glycol, 2,2-bis-(hydroxymethyl)propionic acid and 1,6-hexamethylenediamine. The decisive effects were found from ionic and polar structures within the rigid urethane and urea segments on the ordered arrangement degree of the supermolecular structures in the obtained anionomers. That becomes apparent in differential scanning calorimetry thermograms and contributes to improved thermal stability of the produced polyurethane coatings.
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Colloid and Polymer Science, 285(2), 169-175, (2006) |
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4. |
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Solution scattering studies of conformation stability of xylanase XYNII from Trichoderma Longibrachiatum Xylanase (endo-1,4-beta-xylanase; EC 3.2.1.8) is an enzyme that catalyzes the hydrolysis reaction of xylan. The structure of the xylanase H (XYNII) molecule from Trichoderma longibrachoatum (formerly Trichoderma reesei) in a solution and at different pH values has been studied by small- and wide-angle scattering of synchrotron radiation (SAXS-WAXS). Analysis of the radius of gyration that characterizes xylanase has confirmed the stability of the above enzyme structure (the radius of gyration varied from 1.65 to 1.74 nm). On the basis of the SAXS data, the low-resolution structure of the xylanase molecule in solution has been reconstructed by using ab initio methods and programs DALAI_GA and DAMMIN. The full SAXS-WAXS data set (0.15 > s > 9.5 nm(-1)) fed to the program GASBOR permitted us to construct a chain-like spatial distribution of a dummy residues model of the xylanase molecule. The shape of the model molecules is similar to that of xylanase molecule in the crystal and shows the characteristic asymmetry that makes the molecule to resemble a right hand.
(C) 2006 Wiley Periodicals, Inc. |
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Biopolymers, 83(1), 95-102, (2006) |
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5. |
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Studies on the structure of polyethylene-modified bentonite nanocomposites LDPE modified with vinyltriethoxysilane and lactic acid and a natural bentonite organophilized with hexadecyltrimethylammonium bromide were used to extrude biodegradable nanocomposites contg. 4% bentonite and 30% lactic acid. Elongation-at-break and stretching strength were improved by 29% and 12% as compared with the starting composites. Microstructure examn. showed the polymer matrix to be more compact with the nanofiller added. The m.p. and the m. enthalpy of the nanocomposite were 114.7 degrees C (higher by 2 degrees C) and -134.2 J/g (higher by similar to 10 degrees/6), resp.
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Przemysł Chemiczny, 85(8-9), 840-843, (2006) |
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(Pobrane: aktualizowanie) |
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6. |
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Struktura modułów alkiloamino-fulerenowych z polimerami Zastosowanie pochodnych fulerenowych do modyfikacji struktury molekularnej i powierzchniowej polimerów ma istotne znaczenie przy wytwarzaniu nanokompozytów do zastosowań w elektronice, przemyśle elektrooptycznym, tekstylnym i opakowaniowym. Pochodne te charakteryzują się znaczną reaktywnością elektrofilową w stosunku do nieorganicznych i organicznych cząstek paramagnetycznych. W szczególności mogą stanowić układy molekularne rekombinujące wolne rodniki w materiałach polimerowych. Celem niniejszej pracy było otrzymanie adduktów fulerenu C60 z tlenkiem tetracyjanoetenu (TCNEO) oraz z n-decyloaminą (NH2C10H21), które jako makroinicjatory, wprowadzone w różnych proporcjach do polimerów alkilo-fenylenowych stanowią nanokompozyty o potencjalnym znaczeniu praktycznym.
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Mat. VIII Środowiskowa Konf. Nauk. Chemików "Chemia w zrównoważonym rozwoju", 165-168, (2006) |
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7. |
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Preparation and physicochemical analysis of layered silicates modified with silane coupling agents Natural Na bentonite contg. 65% montmorillonite and synthetic Na montmorillonite were mixed 2 hrs. in aq. 50% EtOH with 2 wt. parts of 3-chloropropyl (I) or 3-methacryloxypropyl trimethoxysilane (II). The av. particle size of modified montmorillonite was 10-15 lm vs. the 10 in the original. The II-modifted bentonite had particles up to 60 lm. The interlayer distance in Na montmorillonite was changed by I only slightly, 1.244 vs. 1.265 nm, and likewise in bentonite, regardless of the coupler type. Up to 1000 degrees C, wt. loss was 1%. In I- or II-moditled montmorillonite, the loss was 2.8 and 4.7% and the DTG peaks at 390-460 and 345-465 degrees C, resp., were attributed to the decompg. silanes. Only the silane surface was affected and penetration of silane mols. into the interlayer space was insignificant.
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Przemysł Chemiczny, 85(8-9), 844-846, (2006) |
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(Pobrane: aktualizowanie) |
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8. |
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Phase behaviour of dipalmitoylphosphatidylcholine/surfactant/water systems studied by infrared spectroscopy Phospholipids are the most important components of membranes taking part in stabilization of the functional structure of biological cells. The main aim of the present study is to determine the influence of selected antimicrobial surfactants on the phospholipids structure. The water solutions of dipalmitoylphosphatidylcholine (DPPC) in the presence of two quaternary ammonium surfactants: dodecyidimethyl(hexyloxymethyl)ammonium chloride (HMDDAC) and (decyloloxymethyl)dodecydimethylammonium chloride (DMDDAC) were studied using FTIR spectroscopy. The thermal behaviour of these systems was analyzed using spectral parameters of CH2 and C=O vibrations bands. We have observed a lowering of temperature corresponding to the main phase transition of the surfactant/DPPC systems due to disordering of the phospholipids structure by the surfactants and phospholipids interaction.
(C) 2006 Published by Elsevier B.V. |
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Journal of Molecular Structure, 794(1-3), 168-172, (2006) |
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9. |
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Molecular dynamics of poly(L-lactide) biopolymer studied by wide-line solid-state 1H and 2H NMR spectroscopy The molecular dynamics of poly(L-lactide) (PLLA) biopolytner was characterized through analyses of H-1 and H-2 NMR line-shapes and spin-lattice relaxation times at different temperatures. At low temperatures (e.g. 90K), the methyl group rotation is dominant leading to a significant reduction in the proton second moment. Fast methyl group reorientation occurs at ca. 130 K. In additional to the fast methyl group rotation, hydroxyl groups start to reorient as the temperature increases further, eventually leading to the breakdown of the segments of the biopolymer chains above its glass transition temperature Tg of 323K. The analyses of the H-2 NMR line-shapes indicate that both the methyl and hydroxyl reorientations can be described by the so-called cone model, in which the former has three equilibrium positions with theta(C-D) = 70.5 degrees and phi = 120 degrees while the latter one exhibits two equilibrium positions with theta(C-D) = 78 degrees and phi = 180 degrees.
(C) 2005 Elsevier Inc. All rights reserved. |
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Solid State Nuclear Magnetic Resonance, 29(4), 258-266, (2006) |
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10. |
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Effect of polymer-to-silica ratio on the formation of large threedimensional cage-like mesostructures This work shows the influence of polymer-to-silica ratio on the formation of cage-like ordered mesoporous silica, FDU1, having a three-dimensional face-centered cubic symmetry. The FDU1 samples studied were synthesized from tetraethyl orthosilicate (TEOS) under acidic conditions in the presence of poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide) (EO39BO47EO39) triblock copolymer. The molar ratio of triblock copolymer to TEOS in the reaction mixture was varied from 0.0037 to 0.0148. Small angle X-ray scattering, argon adsorption-desorption and high resolution thermogravimetry studies indicate that an optimal EO39BO47EO39/TEOS ratio, which led to a high-quality FDU1 material with uniform cage openings, narrow pore size distribution and high specific surface area, was about 0.0074. The FDU1 silicas obtained for lower and higher ratios than the aforementioned value possessed non-uniform cage entrances, broader pore size distributions, lower BET specific surface areas and smaller mesopore diameters.
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New Journal of Chemistry, 30, 1071-1076, (2006) |
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11. |
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The effect of ionizing radiation on chloramphenicol No significant changes relative to the unirradiated sample were observed as a result of irradiation with the dose of 25 kGy - a standard dose for radiation sterilization, besides free radicals generation. Higher doses were found to produce a change in colour, increase in absorbance (UV), changes in the XRD spectra and appearance of products of radiolysis. The presence of the radiolysis products was confirmed by the TLC method, indirectly by DSC showing a decrease in the melting point from 0.2 to 4.5 degrees C and enthalpy from 3.8 to 23.3 J g(-1), respectively. A linear relationship was obtained between the irradiation dose (25-400 kGy) and the melting point of chloramphenicol, characterised by the correlation coefficient r=0.9968.
The EPR signal intensity increased with increasing dose of irradiation and the lifetime of the free radicals was longer than 6 months. No changes were detected in SEM and IR spectra.
As follows from our results, the DSC method is most suitable for a fast monitoring of the drugs subjected to sterilization by irradiation as it permits detection of changes occurring even on irradiation with low doses and their quantitative description.
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Journal of Thermal Analysis and Calorimetry, 84(3), 741-746, (2006) |
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12. |
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An apparent critical point in binary mixtures: Experimental and simulation study We report the experimental and simulation studies for the system of nitrobenzene-cyclododecane, showing an apparent critical point, which lies in their metastable, experimentally inaccessible state, below their melting point, affecting physical and chemical properties of this system in the stable liquid phase. The nonlinear dielectric effect (NDE) was measured in the mixture of nitrobenzene with cyclododecane. The mixture has been found to show an apparent critical point which lies below the melting point, manifested as anomalous NDE behavior in the vicinity of the critical concentrations in the stable liquid phase. The melting temperature of this system was estimated using the differential scanning calorimetry method. For such a system, we also performed Monte Carlo (MC) simulations that aimed to analyze the kinds of phase transitions observed and the conditions of their occurrence in Lennard-Jones mixture. The enthalpy, configurational energy, and radial distribution function have been estimated by the MC simulation method in the N-P-T system. Immiscibility conditions according to the approach by Schoen and Hoheisel [Mol. Phys. 57, 65 (1986)] are also discussed.
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Journal of Chemical Physics, 124(14), 144516, (2006) |
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13. |
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Ferroelectric ordering in imidazolium perchlorate Imidazolium perchlorate has been synthesized and studied over a wide range of temperatures by differential scanning calorimetry, x-ray diffraction, proton magnetic resonance, optical observation, and dielectric spectroscopy. Polymorphic solid-solid phase transitions have been disclosed at 487, 373, and 247 K. The crystal structure at 298 K has been determined as trigonal, space group R (3) over barm, Z=1 with alpha=5.484(1) angstrom and alpha=95.18(2)degrees. The imidazolium cations are strongly disordered, while the perchlorate ions are well ordered. At 385 K the crystal structure remains trigonal, space group R (3) over barm, alpha=5.554(1) angstrom and alpha=95.30(2)degrees. Both ionic sublattices are orientationally disordered. Temperature evolution of the molecular dynamics of the imidazolium cation has been characterized. In spite of a high cationic disorder, dielectric measurements have revealed the polar properties of the crystal. It appears to be a new ferroelectric compound with the Curie point at 373 K. The spontaneous polarization originates predominantly from the behavior of slightly distorted perchlorate anion.
(C) 2006 American Institute of Physics. |
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Journal of Chemical Physics, 124(14), 144502, (2006) |
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14. |
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Structure of N-6-furfurylaminopurine (kinetin) dihydrogenphosphateStructure of N-6-furfurylaminopurine (kinetin) dihydrogenphosphate The crystal structure of kinetin dihydrogenphosphate has been determined at 115 and 293 K. Kinetin dihydrogenphosphate undergoes a polymorphic phase transition at 291.1 K. In both phases the crystal belongs to the triclinic system with the symmetry described by the space group P (1) over bar . In the low-temperature phase, the unit cell is doubled along the a axis. There is a dynamic equilibrium between different tautomeric forms of the adenine residue, determined by the distribution of H atoms within the network of hydrogen bonds.
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Acta Crystallographica Section B - Structural Science Crystal Engineering and Materials, 62(1), 102-108, (2006) |
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Zaktualizowano: podstrony 2021-06-21 / bazę danych: 2024-04-23 by Webmaster: Zbigniew Fojud