Water structure Hydrogen bond

Many salts crystallized from aqueous solutions are not water-free but take the form of well-defined hydrates. Other solid phases contain water associated in changing amounts. A classic case is water coordinated onto oxoanions, for example, 

Polywater (also called anomalous water), which was first described in the 1960s in the Soviet Union and controversially discussed in the 1970s, does not exist, however, and was probably a mixture of colloidal silicic acid. 

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Hydrophobic effect — Effect that nonpolar compounds possess a low solubility in water. The reason for the low solubility is that nonpolar compounds when they dissolve in water destroy the water structure (hydrogen bonds) because of cavity formation, what is accompanied by a loss of entropy, and the water molecules are forced to order around the solute molecule ( iceberg structure), which is a further loss of entropy. These entropy losses are not compensated for by formation of strong bonds between the solute and water, as it happens in case of polar molecules or esp. in case of ions. 

Fig. 18 2D hydrogen bonded network structure of [(DMF)(CTV)]2(H20)4(o-carborane)] 35 with water tetramers hydrogen bonding to CTV molecules [82]... 

Study of hydrated kaolinites shows that water molecules adsorbed on a phyllosilicate surface occupy two different structural sites. One type of water, "hole" water, is keyed into the ditrigonal holes of the silicate layer, while the other type of water, "associated" water, is situated between and is hydrogen bonded to the hole water molecules. In contrast, hole water is hydrogen bonded to the silicate layer and is less mobile than associated water. At low temperatures, all water molecules form an ordered structure reminiscent of ice as the temperature increases, the associated water disorders progressively, culminating in a rapid change in heat capacity near 270 K. To the extent that the kao-linite surfaces resemble other silicate surfaces, hydrated kaolinites are useful models for water adsorbed on silicate minerals. 

The precise chemical interactions between an adhesin and its receptor are also important. For example, direct- and water-mediated hydrogen bonds are the most important interactions within the carbohydrate-recognition domain in carbohydrate-binding adhesins on the host cell surface (Weis and Drickamer, 1996). Nonpolar van der Waals interactions and hydrophobic "stacking of the receptor oligosaccharide rings with aromatic amino acid side chains of the bacterial adhesin protein also contribute to oligosaccharide-protein interactions. X-ray structural... 

Figure 14. A stereoview of a typical "snapshot" from a molecular dynamics simulation of a-D-glucopyranose in aqueous solution, showing selected water molecules close to the 01 and 02 hydroxyl groups. The hydrophobic hydration requirements of the aliphatic hydrogen atoms on Cl and C2 impose additional structuring restrictions of the orientations of the water molecules hydrogen bonding to the 02 hydroxyl group. (Reproduced from Ref. 32. Copyright 1989 American Chemical Society.)...

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