Peptide Bond Tautomerization Induced by Divalent Metal Ions: Characterization of the Iminol Configuration

摘要

A metal ion that attaches to a peptide backbone has the choice of binding to an amide carbonyl oxygen atom or to an amide nitrogen atom by replacement of the amide proton. Coordination to the nitrogen atom is normally accompanied by elimination of the proton, thereby resulting in deprotona-tion of the ligand. An alternative possibility, not involving deprotonation, is the unusual amide/iminol tautomerization. In the gas phase, outright elimination of the proton is energetically costly, so that metal complexation without deprotonation is frequently observed and could well be accompanied by tautomerization. The present results show that coordination of active metal ions to amide nitrogen atoms through iminol tautomerism (analogous to the well-known keto/enol tautomerism of ketones) can indeed be a favorable gas-phase binding pattern.