Hydrated biomolecules

The study of hydrated biomolecules has only just begun and very few papers have been published on that topic [103-107]. Hydration enthalpies and entropies for the peptides LHRH and bradykinin [108] and for the protein BPTI [106,107] have been measured and the amount of water addition to folded vs unfolded states of cytochrome c has been studied [103-105]. At this point it is too early to draw general conclusions but it is already apparent that only a few water molecules can have significant structural consequences [107,108]. 

Water has C2v symmetry. In the gas phase, the measured O-H bonds are 0.957 A, and the H-O-H angle is 104.5° (12). Liquid water and ice have stmctures controlled by the formation of hydrogen bonds. These bonds make it possible for hydrogen ions to exchange among water molecules on the millisecond to picosecond time scale (13), depending on pH. The extensive and dynamic hydrogen bond networks account for many unusual properties of water and hydrated biomolecules (12). 

Interactions of electrons with bare and hydrated biomolecules From nucleic acid bases to DNA segments 12CRV5603. 

Gu J, Leszczynski J, Schaefer 111 HF (2012) Interactions of electrons with bare and hydrated biomolecules Horn nueleic acid bases to DNA segments. Chem Rev 112 5603-5640... 

Effect of hydration on the properties of biosystems was extensively studied both experimentally and by computer simulations. We have already considered how biological activity and conformational dynamics of hydrated biomolecules (Section 6) as well as conductivity of biosystems (Section 7.1) develop upon hydration. Now we analyze some other physical properties of hydrated biosystems (first, their dynamical properties) in relation to the percolation transition of water. Typical biomolecular surface is characterized by heterogeneity (presence of strongly hydrophilic and strongly hydrophobic groups), roughness, and finite size (closed surface of a single biomolecule). These features determine several steps in the process of hydration of biomolecules. 

The time dependence of is essentially nonlinear at aU hydration levels studied. Translational motion of water molecules in such complex system as low-hydrated biomolecules is determined by the following factors restriction of the motions in the direction normal to the protein surface restriction of the motion due to the finite size of a biomolecule spatial disorder due to fractal-like structure of diffusion pathway temporal disorder due to the presence of the strongly attractive sites on the surface. Relative importance of these factors depends on the time and length scales considered, on the properties of a biomolecule and on the hydration level. In pores, MSD of molecules normally to the pore wall (axis) nonlinearly increases at short times and achieves saturation at longer times. As a result, the time dependence of the total MSD is... 

J. Gn, J. Leszczynski, and H. RSchaefer, HI, Chem. Rev., 112, 5603-5640 (2012). Interaction of Electrons with Bare and Hydrated Biomolecules From Nucleic Acid Bases to DNA Segments. 

Gascoyne, P.R.C., Pethig, R. Experimental and theoretical aspects of hydration isotherms for biomolecules. J. Chem. Soc. Faradey Trans. 1 (1977) 171-180... 

Since hydration of biomolecules is of particular importance in molecular biology, uracil - water (U-W) complexes have been studied by many groups [98 JCS(F) 1277, 98JST307, 99JPC(A)1611, 00PCCP1281]. In the cyclic U-W complex the most stable hydrogen bond is formed at the site characterized by the lowest proton... 

Because biomolecules normally exist in liquid water, this article will be largely concerned with their ordered structures in aqueous media and therefore with hydration effects. In order to understand better the influence of solute-solvent interactions on molecular order, also solvation in organic liquids will be considered to some extent. 

One of the most thoroughly investigated examples of polymeric biomolecules in regard to the stabilization of ordered structures by hydration are the DNAs. Only shortly after establishing the double-helix model by Watson and Crick 1953 it became clear, that the hydration shell of DNA plays an important role in stabilizing the native conformation. The data obtained by the authors working in this field up until 1977 are reviewed by Hopfinger155>. 

Protein recovery via disruption has also been achieved by adsorbing water from the w/o-ME solution, which causes protein to precipitate out of solution. Methods of water removal include adsorption using silica gel [73,151], molecular sieves [152], or salt crystals [58,163], or formation of clanthrate hydrates [154]. In most of the cases reported, the released protein appeared as a solid phase that, importantly, was virtually surfactant-free. In contrast to the dilution technique, it appears that dehydration more successfully released biomolecules that are hydrophilic rather than hydrophobic. 

This bimodal dynamics of hydration water is intriguing. A model based on dynamic equilibrium between quasi-bound and free water molecules on the surface of biomolecules (or self-assembly) predicts that the orientational relaxation at a macromolecular surface should indeed be biexponential, with a fast time component (few ps) nearly equal to that of the free water while the long time component is equal to the inverse of the rate of bound to free transition [4], In order to gain an in depth understanding of hydration dynamics, we have carried out detailed atomistic molecular dynamics (MD) simulation studies of water dynamics at the surface of an anionic micelle of cesium perfluorooctanoate (CsPFO), a cationic micelle of cetyl trimethy-lainmonium bromide (CTAB), and also at the surface of a small protein (enterotoxin) using classical, non-polarizable force fields. In particular we have studied the hydrogen bond lifetime dynamics, rotational and dielectric relaxation, translational diffusion and vibrational dynamics of the surface water molecules. In this article we discuss the water dynamics at the surface of CsPFO and of enterotoxin. 

The problems being addressed in recent work carried out in various laboratories include the fundamental nature of the solute-water intermolecular forces, the aqueous hydration of biological molecules, the effect of solvent on biomolecular conformational equilibria, the effect of biomolecule - water interactions on the dynamics of the waters of hydration, and the effect of desolvation on biomolecular association 17]. The advent of present generation computers have allowed the study of the structure and statistical thermodynamics of the solute in these systems at new levels of rigor. Two methods of computer simulation have been used to achieve this fundamental level of inquiry, the Monte Carlo and the molecular dynamics methods. 

Recently, the investigations of nitrobenzisoxazoles mainly 6-nitrobenzisoxazole-3-carboxilate ions have received considerable interest due to their participation in reverse micellar systems [679-682], Reverse micelles are of considerable interest as reaction media because they are powerful models for biological compartmental-ization, enzymatic catalysis, and separation of biomolecules. Solutions of ionic surfactants in apolar media may contain reverse micelles, but they may also contain ion pairs or small clusters with water of hydration [679], Molecular design of nonlinear optical organic materials based on 6-nitrobenzoxazole chromophores has been developed [451],... 

Berndt M, Kwiatkowski JS (1986) Hydration of biomolecules. In N4ray-Szab6 G (ed) Theoretical chemistry of biological systems. Studies in physical and theoretical chemistry, vol. 41. Elsevier, Amsterdam, pp 349-422... 

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