The CH‥O H-Bond as a Determining Factor in Molecular Structure

Abstract

The factors that affect the strength of CH‥O hydrogen bonds (HBs) are enumerated, along with the source of their stability, and the structural and spectroscopic features that signal their presence. Their influence upon a number of chemical and biological processes is discussed. Within the context of proteins, the CαH group of protein residues can engage in CH‥O HBs, as can the CH groups of a number of amino acid side chains including aromatic residues. CH‥O HBs have the potential to make a major contribution to protein folding, particularly in an aqueous environment. These unconventional HBs may play as important a role in the formation of protein β-sheet structures as do NH‥O HBs. The strength of CH‥O HBs is magnified several-fold by the presence of positive charge on the proton donor. The implications of these principles are discussed for a number of specific biological and chemical problems, which include the catalytic mechanisms of methyltransferases and serine proteases, and the structural properties of fluoroamides.