Intramolecular hydrogen bonding in silanediols

The analysis of equilibrium geometries and energies of silanediols with NH2 and carbonyl groups in their side chains shows that the intramolecular hydrogen bonding exist in all studied systems. In the (CH2NH2)(CH3)Si(OH)(2) system, these bonds are weak and do not play the decisive role in the relative stabilities of isomers, while in molecules, containing a carbonyl group in the gamma position to silicon, the hydrogen bond between the carbonyl oxygen and the hydroxyl group protons makes the isomers containing these hydrogen bonds, far more stable than other isomers. The energies of these C=O...H-O intramolecular bonds are comparable to intermolecular H-bonds. This fact prevents association of silanediol molecules containing carbonyl groups into infinite chains, i.e. the process which is usual for silanediols with alkyl groups. This difference may explain the activity of silanediols containing carbonyl groups as protease inhibitors in contrast to silanediols containing only alkyl groups. (C) 2004 Elsevier B.V. All rights reserved.