Anna Maciejowska, Agnieszka Godziek, Ewa Talik, Mieczysław Sajewicz, Teresa Kowalska, Irving R Epstein

We report observations of pulsating peptide formation and depeptidization in 70% aqueous acetonitrile solutions of l-Pro-l-Phe and l-Cys, resulting in the oscillatory appearance and disappearance of solid masses of microfibers and microspheres, respectively. We monitor the concentration changes of the monomeric amino acids by high-performance liquid chromatography. The concentration of all amino acid solutions used is 1.0 mg mL(-1), due to solubility limitations in 70% aqueous acetonitrile. The nonlinear concentration changes of l-Pro, l-Phe and l-Cys, and the amounts of the main peptidization products observed within our monitoring periods (for l-Pro-l-Phe, 250 h, and for l-Cys, 70 h) are typically from several to 20% of the original monomer concentrations. We follow the formation and decay of the insoluble peptides by turbidimetry. We also investigate the materials formed using scanning electron microscopy and mass spectrometry. We carry out numerical simulations on a simple model that reflects the main features of spontaneous pulsation of peptide fiber or sphere formation in this abiotic liquid system.