Hydration networks

Fig. 7. Schematic representation of AMDH solution structures. The active structures have two parts a catalytically active core, conceivably similar to that in non-halophilic MDH, and protruding loops, required for stabilization in KCl, NaCl, and MgCl2 solvents. In potassium phosphate the protein dimer is stabilized by the hy-drophobicity of the core and the protruding loops are disordered. In KCl (or NaCl) the protein is stabilized by the interaction of the loops in a specific protein—water-salt hydration network. In MgCl2 a similar structure exists with the same amount of water molecules coordinated by fewer salt ions. In low salt concentration, the protein is unfolded and its hydration is like that of nonhalophilic proteins. From Zaccai el al. (1989), with permission.

Natural extracellular matrices in vivo consist of various protein fibrils and fibers, interwoven within a hydrated network of glycosaminoglycan chains and may require less than 1% solid materials to form mechanically robust... 

Guest species that reside within clathrate hydrates do not participate in strong interactions with the water framework and are most often hydrophobic in nature. Molecules that are good hydrogen bond donors or acceptors (such as carboxylic acids, amines or alcohols) will disrupt the interactions between the water molecules and therefore prevent the hydrate network from forming. The most suitable guests are relatively small, non-polar species, such as halides, noble gases and small hydrocarbons. 

Figure 29 (a) Molecular formula for poly(vinylpyrrolidone) (PVP). (b) Location of PVP relative to the water/methane interface (top) initially and (bottom) after 1 ns. PVP is represented by thick lines, water with thin lines, and methane as spheres N atoms are black, C dark grey, O light grey, and H white, (c) Snapshots of the hydrate network and PVP following insertion of PVP. Adapted from Refs. 121 and 127. (For a color version of this figure, please see plate 11 in color plate section.)... 

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