Scanning Electron Microscopic Evidence of Spontaneous Heteropeptide Formation in Abiotic Solutions of Selected α‐Amino Acid Pairs

Abstract

AbstractSpontaneous nonlinear peptidization of the monomeric and enantiomerically pure α‐amino acids in abiotic aqueous and nonaqueous solutions is still regarded by some as a somewhat puzzling phenomenon, and therefore it needs additional experimental authentication. In our earlier studies, we employed several analytical techniques to prove its occurrence. In this study, we present the scanning electron microscopic (SEM) evidence of spontaneous heteropeptide formation in the binary L‐Cys−L‐Phe, L‐Cys−L‐Phg, and L‐Cys−L‐Pro mixtures dissolved in 70 % aqueous methanol. With each α‐amino acid pair, one amino acid (L‐Cys) is equipped with three functionalities (−SH, −NH2, and −COOH), enabling formation of the spherical homopeptide microstructures, while its counterpart (L‐Phe, L‐Phg, or L‐Pro, respectively) is equipped with the two functionalities only (−NH2 or =NH, and −COOH). The SEM micrographs of the peptidization products originating from the three investigated α‐amino acid pairs show three different, yet spherical, structures, which seem suggestive of the heteropeptide formation involving both L‐Cys and its counterpart α‐amino acid. Additional confirmation of heteropeptide formation is furnished by high performance liquid chromatography (HPLC), the biuret test, and mass spectrometry (MS).