A molecular orbital and chemical study of aminoacetonitrile: a possible prebiotic peptide precursor.

Abstract In this report we present a detailed molecular orbital description of aminoacetonitrile using the iterative extended Huckel theory (IEHT) and, guided by these calculations, discuss some of its chemistry in the context of chemical evolution. The experimental work to be discussed indicates that under aqueous conditions similar to those thought to have prevailed on the primitive earth, aminoacetonitrile will not form polypeptide precursors by self-condensation, unless the nitrile carbon is “activated” in some fashion. Even under such conditions dipeptide yields are very low in aqueous media suggesting that such a pathway for prebiotic peptide formation was unlikely and extremely inefficient at best. The results of the theoretical analysis indicate that inability to self-condense resides primarily in the low electrophilicity of the nitrile carbon rather than in the reduced nucleophilicity of the amine nitrogen. However, hydrolysis and other competing reactions for which we indicate mechanisms consistent with its calculated properties, can convert aminoacetonitrile into amino and imino acids which could further have enriched the prebiotic soup and may have been involved ultimately in peptide formation through dehydration-condensation reactions.