Effects of Concentration and Freeze-Thaw on the First Hydration Shell Structure of Zn^(2+) Ions

To investigate the effects of salt concentration and freeze-thaw (FT) on the first hydration shell of Zn2+ ions in Zn(NO_3)_2 aqueous solutions, extended X-ray absorption fine structure (EXAFS) spectroscopy was used to examine Zn K-edge EXAFS spectra of Zn(NO_3)_2 aqueous solutions with various concentrations before and after FT treatment. The influences of salt concentration and freeze-thaw on the structural parameters of the first hydration shell of Zn2+ ions, including hydration number, Zn-O distance and thermal disorder, were analyzed. The results show that Zn2+ ions have 3.2―6.8 nearest oxygen neighbors with the Zn-O distance being 0.202―0.207 nm. In highly concen-trated solutions, Zn2+ ions are hydrated with four water molecules in a tetrahedral form. The dilution of Zn(NO_3)_2 aqueous solutions increases the number of water molecules in the first hydration shell of Zn2+ ions to six with their octahedral arrangement. Both the hydration number in the first hydration shell of Zn2+ ions and the degree of thermal disorder increase when the FT treatment is operated in Zn(NO_3)_2 aqueous solutions.

Study on the Hydration Shell of Single-helical of Konjac Glucomannan

The local maxima of water density in the space near the single-helical of Konjac glucomannan as well as the dominant conformation of the system was studied by molecular dyna-mics under the water environment. The results indicate that the hydration shell,potential energy,and its hydrogen bond network with water bridges of the left-handed single-helix conformation was favored compared to those of right-handed single-helix conformation. This work suggests that the left-handed single-helix conformation was the dominant conformation of KGM in the water environment.

IMPACT OF DYNAMICAL HYDRATION SHELL AROUND HA PROTEIN ON NONLINEAR CONCENTRATION DEPENDENT T-RAYS ABSORPTION

T rays is sensitive to covalently cross linked proteins and can be used to probe unique dynamic properties of water surrounding a protein.In this paper,we demonstrate the unique abeorption properties of the dynamic hydnation shells deternined by hemagglutinin(HA)protein in ter-ahertz frequency.We study the changes arising fom diferent concentrations in detail and show that nonlinear absorption coefficient is induced by the dynamic hydration water.The binary and ternary component model were used to interpret the nonlinearity absorption behaviors and predict the thickness of the hydration shells around the HA protein in aquous phase.

Fractional Stokes–Einstein relation in TIP5P water at high temperatures

Fractional Stokes–Einstein relation described by D ～（τ/T）~ξ is observed in supercooled water, where D is the diffusion constant, τ the structural relaxation time, T the temperature, and the exponent ξ =τ^（-1）. In this work, the Stokes–Einstein relation in TIP5 P water is examined at high temperatures within 400 K–800 K. Our results indicate that the fractional Stokes–Einstein relation is explicitly existent in TIP5P water at high temperatures, demonstrated by the two usually adopted variants of the Stokes–Einstein relation, D ～τ^（-1）τand D ～ T/τ, as well as by D ～ T/η, where η is the shear viscosity. Both D ～τ^（-1）τand D ～ T/τ are crossed at temperature Tx= 510 K. The D ～τ^（-1）τis in a fractional form as D ～ τ ξwith ξ =-2.09 for T ≤ Txand otherwise ξ =τ^（-1）.25. The D ～ T/τ is valid with ξ =τ^（-1）.01 for T ≤ Txbut in a fractional form for T Tx. The Stokes–Einstein relation D ～ T/η is satisfied below Tx = 620 K but in a fractional form above Tx. We propose that the breakdown of D ～ T/η may result from the system entering into the super critical region, the fractional forms of D ～τ^（-1）τand D ～ T/τ are due to the disruption of the hydration shell and the local tetrahedral structure as well as the increase of the shear viscosity.