Formation of spanning water networks on protein surfaces via 2D percolation transition

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.     

Synthesis and transformations of 2-(2-furyl)-and 2-[β;-(2-furyl)vinyl]naphth[1,2-d]imidazoles

The corresponding 2-(2-furyl)naphth[1,2-d]imidazoles were obtained by heating Schiff bases, prepared from 1,2-naphthalenediamine and furfural and 5-bromo- and 5-nitrofurfurals, in nitrobenzene. 2-[-(2-Furyl)vinyl]naphth[1,2-d]imidazoles were synthesized by condensation of 2-methylnaphth[1,2-d]imidazole with furfural and 5-bromo- and 5-nitrofurfural. The methylation, nitration, and acetylation of the compounds obtained were studied, and the replacement of the bromine atom in the furan ring by a nitro group was also investigated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1555–1557, November, 1972.     

Effect of confinement on the liquid-liquid phase transition of supercooled water

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.     

Surface critical behavior of fluids: Lennard-Jones fluid near a weakly attractive substrate

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.     

Crystal and molecular structure of 3β-acetoxy-22S,25-epoxyholosta-7,9(11)-dien-17α-ol

A complete x-ray structural investigation has been made of 3-acetoxy-22S,25-epoxyholosta-7,9(11)-dien-17-ol. Important conformational differences between this compound and its 17-deoxy derivative have been found which show the mobility of the conformation of rings B and C of the holostane series and the tetrahydrofuran ring of the side chain of the molecule. It has been shown that the conformation of the side chain of the molecule is stabilized by an 017-H...022 intramolecular hydrogen bond, without excluding the possibility of the participation of the hydroxy group in the formation of intermolecular hydrogen bonds (bifurcated).Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Branch, Russian Academy of Sciences, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, Nos. 3,4, pp. 341–344, May–August, 1992.