RESUMEN
On the basis of experimental studies of the initial stages of glycine oligomerization in aqueous suspension of zeolite and kaolinite catalysts, a model is suggested for the prebiotic synthesis of oligopeptides from alpha-amino acids. The formation of linear dipeptides by hydrolysis of one amide bond in the cyclic piperazinedione intermediate (formed from glycine spontaneously) is found to be the critical stage of the reaction. 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 insoluble silicates and soluble sodium bicarbonate. During prebiotic evolution silicates capable of cation-exchange can serve as local sources of the hydroxyl anions which dramatically accelerate formation of linear dipeptides from cyclic ones. Oligopeptides of higher molecular weight are then easily formed from the linear dipeptides at neutral pH, even in the absence of catalysts or sources of energy (e.g. such as light). The described catalytic synthesis could occur in the proximity of submarine hydrothermal vents.
Asunto(s)
Evolución Molecular , Glicina/química , Glicilglicina/química , Oligopéptidos/síntesis química , Piperazinas/síntesis química , Silicatos/química , Silicatos de Aluminio/química , Catálisis , Arcilla , Evolución Química , Concentración de Iones de Hidrógeno , Origen de la Vida , Zeolitas/síntesis química , Zeolitas/químicaRESUMEN
Two-dimensional (2D) J-resolved 13C NMR spectroscopy has been used to analyze the products of ethylene conversion inside the channels of zeolite H-ZSM-5 at 373 K. The observed 13C signals of aliphatic hydrocarbon fragments have been attributed to various CHn (n = 1-3) groups. Multiplicities and positions of these signals suggest that a mixture of branched and linear ethylene oligomers is formed inside zeolite H-ZSM-5.
