Abstrakt

Several conformations of the solvated glycine-based polypeptides were investigated using molecular dynamics simulations. Some properties of water in the neighbouring space around these molecules were investigated. It was found, that water forms a well-defined layer - the first solvation shell - around the peptide molecule, and thickness of this layer is independent of the peptide structure, and it equals to approximately 0.28 nm. Within this layer water molecules show marked orientations relative to a peptide surface. Using the two-particle contribution to entropy as a measure of structural ordering of water we found, that the first solvation shell contributes 95% or more to the total water ordering around the peptide molecule. Investigating the dynamic properties of water - diffusion coefficients and lifetime of the hydrogen bond - clear differences between solvation layer and the bulk water were observed. It was found, that the translational diffusion coefficient, DT, decreases by 30% or more compare to bulk water; also the lifetime of the water-water hydrogen bond clearly increases. The rotational diffusion coefficient, however, decreases only slightly, no more than 10% approximately. These differences correspond to the slightly higher energy of the hydrogen bond, and to its slightly distorted geometry. Analysing the translational dynamics of water in the vicinity of the peptide molecule it was deduced, that the structure of the first solvation shell becomes more rigid than the structure of the bulk water. Investigation of a "pure hydrophobic" form of the polypeptide shows, that the structure and the properties of water within the solvation shell are predominantly determined by the hydrophobic effect. The specific interactions between water molecules and various charge groups of the peptide molecule modifies this effect only slightly.

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