Water molecules as a gluing factor in organic crystals and biological systems

Variability of two independent geometrical parameters ( interatomic distances R(O-H) and bond angles phi(HOH)) of water molecules in crystal structures of hydrated organic systems, is studied on the basis of precise neutron diffraction measurements of molecular geometry retrieved from the Cambridge Structural Database. The large values of variance for both these parameters suggest that the molecule of water is very elastic, and hence may readily be employed as a particular kind of glue between other molecules building up the condensed phase. We postulate that elasticity of water molecule and its amphoteric acid/base properties in the Bronsted and Lewis sense are the main reasons of its unique properties as a gluing factor in chemical and biological systems. The energetic gain due to the water molecules acting in this way, observed for simple inorganic hydrates in crystalline state, is as large as SO Kcal/mole per water molecule. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.