MODELING OF THE PREBIOTIC SYNTHESIS OF OLIGOPEPTIDES - SILICATE CATALYSTS HELP TO OVERCOME THE CRITICAL STAGE

On the basis of experimental studies of the initial stages of glycine oligomerization in aqueous suspension of zeolite and kaolinite catalys ts, a model is suggested for the prebiotic synthesis of oligopeptides from a-amino acids. The formation of linear dipeptides by hydrolysis o f one amide bond in the cyclic piperazinedione intermediate (formed fr om glycine spontaneously) is found to be the critical stage of the rea ction. This stage is base catalyzed and its rate increases when pH of the medium goes up. The linear glycyl-glycine yield rises under effect of hydroxyl anions generated from different sources including insolub le silicates and soluble sodium bicarbonate. During prebiotic evolutio n silicates capable of cation-exchange can serve as local sources of t he hydroxyl anions which dramatically accelerate formation of linear d ipeptides from cyclic ones. Oligopeptides of higher molecular weight a re then easily formed from the linear dipeptides at neutral pH, even i n the absence of catalysts or sources of energy (e.g. such as light). The described catalytic synthesis could occur in the proximity of subm arine hydrothermal vents.