Observing the Water Molecule

Although no hexane molecules were found in the protein s interior for the CTWAT and CTMONO systems, hydrophobic contacts were observed between hexane molecules near the protein surface and hydrophobic side chains in all three systems. Hexane molecules on the protein surface tend to reside in the surface "clefts" formed by the hydrophobic side chains extended into the hexane solvent. At the same time, the hydrophilic residues tended to fold back onto the surface of the protein in order to minimize surface contacts. In our CTMONO simulation, we further observed the water molecules clustered around charged hydrophilic residues, while leaving the hydrophobic residues exposed to the soIvent.(Fig. 1) It has been reported that preferential solvation of the hydrophobic regions of the protein surface by the non-polar solvent is due to the thermodynamically unfavorable formation of a complete monolayer of water in a non-polar solvent. Klibanov and co-workers have also shown that hexane does not strip the water layer - nor does it immobilize the water molecules at the protein/solvent interface. Instead, rearrangements of the water molecules on the protein surface is the more favored process. Our simulations clearly support these experimental observations. 

Marechal, Y. (2004) Observing the water molecule in macromolecules using infrared spectrometry stmcture of the hydrogen bond network and hydration mechanism. Journal of Molecular Structure, 700, 217-223. 

Recently, this observation has been confirmed experimentally through neutron scattering studies, making use of isotopic substitution . These studies have revealed that the water molecules in the... 

As is suggested frequently , this term might well result from the restriction of the hydrogen bonding possibilities experienced by the water molecules in the first hydration shell. For each individual water molecule this is probably a relatively small effect, but due to the small size of the water molecules, a large number of them are entangled in the first hydration shell, so that the overall effect is appreciable. This theory is in perfect agreement with the observation that the entropy of hydration of a nonpolar molecule depends linearly on the number of water molecules in the first hydration shell ". ... 

Aluminum hydroxide and aluminum chloride do not ionize appreciably in solution but behave in some respects as covalent compounds. The aluminum ion has a coordination number of six and in solution binds six molecules of water existing as [Al(H20)g]. On addition of a base, substitution of the hydroxyl ion for the water molecule proceeds until the normal hydroxide results and precipitation is observed. Dehydration is essentially complete at pH 7. 

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