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21.
Abstract In this study, we followed in situ changes in the infrared spectrum at different conditions of pressure and temperature. Cooperative changes were observed when temperature or pressure was increased. Plotting the midpoints of cooperative transitions in a pressure-temperature plane results in an outline similar to the stability curve of proteins. We can assume that it is the first time that the pressure-temperature dependent gelation diagram is determined in situ for starch. 相似文献
22.
High hydrostatic pressure can induce partially unfolded protein conformations that are highly aggregation prone under conditions that normally favour the native state. We investigated the pressure stability of insulin at pH 2 with Fourier transform infrared spectroscopy. We do not observe any cooperative change up to 13 kbar. All spectral changes in the amide I area are fully reversible and are assumed to arise from the elastic effect of pressure, which causes no conformational changes. Moreover, insulin has no higher temperature-induced aggregation tendency when pressure pre-treated. 相似文献
23.
Elementary growth processes such as kink initiation, adding a molecule to a kink, and adding a molecule between two neighboring kinks and between two grains are theoretically studied in pentacene films by adding one molecule at a time to a predefined aggregate. For each molecule, the potential energy surface is calculated using the MM3 molecular mechanics force field, which allowed one to identify useful parameters like the energy barrier for diffusion and the energy to create kinks, as well as defect configurations. Depending on the properties of the potential energy surface and the resulting growth-condition-dependent probabilities of initiating defect configurations in the film, three types of pentacene defects are identified: a thermally activated defect, an intrinsic defect, and a kinetic defect. Upon film growth, most defects relax into the ideal crystal configuration. Bulk defects that resist relaxation have densities lower than 10(16) defects/cm3 at typical growth conditions. Grain boundary defects, on the other hand, are very stable. Moreover, interstitial molecules at grain boundaries are identified as a source of compressive stress. 相似文献
24.
Protein folding or unfolding can lead to the population of intermediates or partially unfolded conformations that have a high aggregation tendency. Some of these states associate in vivo to form fibrillar structures. These fibrils are the hallmark of molecular diseases such as Alzheimer's disease. It has been suggested that in vitro fibril formation is a generic property of all proteins. Insulin has been chosen as a model protein to study the process of fibrillation with Fourier-transform infrared spectroscopy. It is found that the formation of fibrils is preceded by amorphous aggregation. We also investigated the effect of hydrostatic pressure on insulin fibrils. The observed spectral changes are interpreted in terms of fibril dissociation into protofilaments. Preliminary results indicate that pressure is an interesting tool to characterize the interactions that maintain the fibril structure. 相似文献
25.
Li X Kadashchuk A Fishchuk II Smaal WT Gelinck G Broer DJ Genoe J Heremans P Bässler H 《Physical review letters》2012,108(6):066601
While it is known that the charge-carrier mobility in organic semiconductors is only weakly dependent on the electric field at low fields, the experimental mobility in organic field-effect transistors using silylethynyl-substituted pentacene is found to be surprisingly field dependent at low source-drain fields. Corroborated by scanning Kelvin probe measurements, we explain this observation by the severe difference between local conductivities within grains and at grain boundaries. Redistribution of accumulated charges creates very strong local lateral fields in the latter regions. We further confirm this picture by verifying that the charge mobility in channels having no grain boundaries, made from the same organic semiconductor, is not significantly field dependent. We show that our model allows us to quantitatively model the source-drain field dependence of the mobility in polycrystalline organic transistors. 相似文献
26.
Bulk Bi2Te3 is known to be a topological insulator. We investigate surface states of Bi2Te3(111) thin films of one to six quintuple layers using density-functional theory including spin-orbit coupling. We construct a method to identify topologically protected surface states of thin film topological insulators. Applying this method to Bi2Te3 thin films, we find that the topological nature of the surface states remains robust with the film thickness and that the films of three or more quintuple layers have topologically nontrivial surface states, which agrees with experiments. 相似文献
27.
28.
Claude Moussebois Joseph F. Heremans Robert Merenyi Walthre Rennerts 《Helvetica chimica acta》1977,60(1):237-242
Synthesis of two phenolic amino acids containing the 1,2,4-oxadiazole ring The synthesis of α-amino-β [3-(p-hydroxyphenyl)-1,2,4, oxadiazol-5-yl]propionic acid (9) and its β-amino isomer (10) (see scheme 3) is reported. By condensation of p-benzyloxy-benzamide oxime and N-benzyloxycarbonyl asparagine the derivatives 4 and 5 (see scheme 1) are obtained leading after deprotection to 9 and 10 . The synthesis of N-carboxyanhydride of 4 (6) and its corresponding amino acid (7) and amide (8) is also described. 相似文献
29.
The kinetics of carbohydrate binding to dimeric concanavalin A have been studied by the fluorescence temperature-jump method at 24°C in the range of 1–600 atm. From the pressure dependence of the reaction rate parameters, a positive activation volume for association and a small negative activation volume for dissociation have been obtained
24°C 1–600 . , .相似文献
30.