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1.
Oleinikova A Smolin N Brovchenko I Geiger A Winter R 《The journal of physical chemistry. B》2005,109(5):1988-1998
The formation of spanning hydrogen-bonded water networks on protein surfaces by a percolation transition is closely connected with the onset of their biological activity. To analyze the structure of the hydration water at this important threshold, we performed the first computer simulation study of the percolation transition of water in a model protein powder and on the surface of a single protein molecule. The formation of an infinite water network in the protein powder occurs as a 2D percolation transition at a critical hydration level, which is close to the values observed experimentally. The formation of a spanning 2D water network on a single rigid protein molecule can be described by adapting the cluster analysis of conventional percolation studies to the characterization of the connectivity of the hydration water on the surface of finite objects. Strong fluctuations of the surface water network are observed close to the percolation threshold. Our simulations also furnish a microscopic picture for understanding the specific values of the experimentally observed hydration levels, where different steps of increasing mobility in the hydrated powder are observed. 相似文献
2.
I. V. Shcherbakova V. G. Brovchenko E. V. Kuznetsov 《Chemistry of Natural Compounds》1985,21(6):774-777
The reaction of 6,7-dimethoxy-1-methyl-2-benzopyrylium salt with ammonia forms the corresponding isoquinoline, and its reaction with methylamine and benzylamine forms mixtures of the corresponding isoquinolinium salts and naphthylamines. The reduction of 2-benzyl-1-methyl-6,7-dimethoxyisoquinolinium perchlorate with sodium tetrahydroborate has given the corresponding tetrahydroisoquinoline, the hydrogenolysis of which has led to salsolidine. The products have been characterized by elementary analyses and IR and PMR spectroscopy. 相似文献
3.
We report on an observation of the phase transition between two liquid phases of supercooled confined water in simulations. The temperature of the liquid-liquid transition of water at zero pressure slightly decreases due to confinement in the hydrophobic pore. The hydrophilic confinement affects this temperature in the opposite direction and shifts the critical point of the liquid-liquid transition to a higher pressure. As a result, in a strongly hydrophilic pore the liquid-liquid phase transition becomes continuous at zero pressure, indicating the shift of its critical point from negative to a positive pressure. These findings indicate that experimental studies of water confined in the pores of various hydrophobicity/hydrophilicity may clarify the location of the liquid-liquid critical point of bulk water. 相似文献
4.
Brovchenko I. Geiger A. Oleinikova A. 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,44(3):345-358
The phase behavior of fluids near weakly attractive substrates is studied by computer simulations of the coexistence curve of a Lennard-Jones (LJ) fluid confined in a slitlike pore. The temperature dependence of the density profiles of the LJ fluid was used to study the surface critical behavior. A universal critical behavior of the local order parameter, defined as the difference between the local densities of the coexisting liquid and vapor phases at some distance
from the pore walls,
, is observed in a wide temperature range and found to be consistent with the surface critical behavior of the Ising model. Near the surface the dependence of the order parameter on the reduced temperature
obeys a scaling law ~1 with a critical exponent 1 of about 0.8, corresponding to the
surface transition. A crossover from bulk-like to surface-like critical behavior occurs, when the distance to the surface is about twice the correlation length at the given temperature. Relations between the
and
transitions in Ising systems and the surface critical behavior of fluids are discussed. 相似文献
5.
Yu. A. Zhdanov V. G. Brovchenko M. A. Klyuev E. V. Kuznetsov 《Chemistry of Heterocyclic Compounds》1989,25(4):375-380
3-Carboxy-2-benzopyrylium salts form 3-carboxyisoquinolinium salts, their decarboxylated analogs, or products of contraction of the heterocycle, namely, cyclic ketols, depending on the nature of the amine and solvent. Upon treatment with acids, these ketols are demethylated through the intermediate formation of -acylcarbenium ions and are converted to quinonemethides.For communication 33, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 454–459, April, 1989. 相似文献
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Pártay LB Jedlovszky P Brovchenko I Oleinikova A 《Physical chemistry chemical physics : PCCP》2007,9(11):1341-1346
Formation of the macroscopically-infinite hydrogen-bonded water network in various aqueous systems occurs via 3D percolation transition when the probability of finding a spanning water cluster exceeds 95%. As a result, in a wide interval of water content below the percolation threshold, rarefied quasi-2D water networks span over the mesoscopic length scale. Formation and topology of spanning water networks, which affect various properties of aqueous systems, can be described within the framework of the percolation theory. 相似文献
9.
Consolute phenomena in the aqueous solutions of the polymers are considered In view of the temperature induced structural changes of the hydrogen bonds between water and functional groups of polymer. The lower and upper critical consolute points are attributed to the appearance of the “critical” concentration of the complexes with one hydrogen bond between single water molecule and functional group of polymer. Namely such kind of the hydrogen bonds are responsible for the formation of the strongly associated water clusters, that may be followed by phase separation. Experimentally observed dependences of the critical consolute temperatures for the aqueous solutions of polyethylene glycol on the molecular weight of polymer and adding of salts are well reproduced in the framework of the proposed model. 相似文献
10.
Clustering of water molecules in the hydration shells of spherical structureless solutes was studied in dependence on thermodynamic state, solute radius R(sp) and strength U(0) of water-solute interaction. Two qualitatively different clustering states of hydration water have been found: an "ordered" state with a hydrogen-bonded (H-bonded) network, which includes most of the hydration water, and a "disordered" state with small H-bonded clusters of hydration water. The transition from the ordered to disordered state occurs upon increasing temperature and decreasing pressure. This percolation transition is rounded due to the finite solute size and occurs in some temperature (pressure) interval. A finite-size scaling was applied to determine the transition temperature T(∞) in the limit R(sp)→∞. Strengthening of the water-solute interaction strongly enhances the stability of the ordered state: the transition temperature increases by about 35 °C, when U(0) decreases by 1 kcal mol(-1). At T > T(∞) and fixed U(0), the stability of the H-bonded water network increases upon decreasing solute size. 相似文献