Turbidity patterns of spontaneous peptidization in an aqueous abiotic system and possible secondary peptide structures

Abstract

The non-linear dynamics of spontaneous peptidization running in 10 monocomponent and binary abiotic liquid systems of L- and D-Ala and L- and D-Phe is investigated with use of turbidimetry with continuous registration, high-performance liquid chromatography with light scattering detection (HPLC-ELSD), mass spectrometry (MS), and spectroscopy of far UV circular dichroism (CD). The turbidity patterns represent a sum of the light scattering effects caused by insoluble peptides of unknown yields, structures, and molecular weights. The auxiliary analytical techniques confirm the non-linear nature of peptidization (HPLC-ELSD) and spontaneous formation of the homo- and heteropeptides (MS). CD spectroscopy seems to confirm the presence of the secondary α-helix structures. The similarity of turbidity patterns is revealed with the monocomponent (L or D) and binary (L-L or D-D) systems of equichiral α-amino acids, and dissimilarity of patterns is observed with the binary systems of inequichiral α-amino acids (L-D). The tentative conclusion is drawn that the peptides assembled of equichiral α-amino acid units are able to assume the secondary (right- or left-handed α-helix) structures, which in a certain way could foster the similarity of turbidity patterns, and the peptides built of inequichiral α-amino acid units cannot ensure an efficient enough stringing of monomer molecules into equichiral heptades to form complete segments of an α-helix. This randomness of the α-amino acids arrangement in the inequichiral peptide molecules most probably manifests itself as a lack of similarity among the respective turbidity patterns.