Sodium chloride enhanced oligomerization of L-arginine.

NaCl significantly enhanced the longer oligoarginine formation in the oligomerization of L-arginine activated by N,N'-carbonyldiimidazole (CDI) in homogeneous aqueous solution. The optimal concentration of NaCl for the highest yield of longer oligoarginine formation is around 1M. It is suggested that the weak interactions of Cl(-) with the positive-charged guanidinium group of the oligoarginines formed in the oligomerization of L-arginine are responsible for the enhancement by NaCl.

Catalysis and selectivity in prebiotic synthesis: initiation of the formation of oligo(U)s on montmorillonite clay by adenosine-5'-methylphosphate.

Adenosine-5'-methylphosphate (MepA) initiates the oligomerization of the 5'-phosphorimidazolide of uridine (ImpU) in the presence of montmorillonite clay. Longer oligomers form because the 5'-phosphate is blocked with a methyl group that prevents the formation of cyclic- and pyrophosphate-containing compounds. The MepA initiates 69-84% of the 5-9 charge oligomers, respectively. The montmorillonite catalyst also provides selectivity in the oligomerization reactions so that the main reaction pathway is MepA --> MepA3'pU --> MepA3'pU2'pU --> MepA3'pU2'pU3'pU. MepA did not enhance the oligomerization of ImpA. The relative rates of the reactions were determined from an investigation of the products in competitive reactions. Selectivity was observed in the reaction of ImpU with equimolar amounts of MepA3'pU and MepA2'pU where the relative reaction rates are 10.3:1, respectively. In the reaction of ImpA with MepA3'pA and MepA2'pA the ImpA reacts 5.2 times faster with MepA3'pA. In the competitive reaction of ImpU and ImpA with MepA3'pA and MepA3'pU the elongation proceeds on MepA3'pA 5.6 times more rapidly than with MepA3'pU. There is no correlation between the extent of binding to the montmorillonite and reaction rates in the formation of longer oligomers. The formation of more than two sequential 2',5'-linkages in the oligomer chain proceeds more slowly than the addition to a single 2',5'-link or a 3',5'-link and either chain termination or elongation by a 3',5'-linage occurs. The central role that catalysis may have had in the prebiotic formation of biopolymers is discussed.

Sodium chloride enhanced oligomerization of L-glutamic acid in aqueous solution.

The presence of NaCl was found to significantly enhance the formation of longer peptides in N,N'-carbonyldiimidazole induced oligomerization of L-glutamic acid in homogeneous aqueous solution. The enhancement was detected in the presence of as low as 0.01-M NaCl and the highest yield of longer oligomers was achieved in the presence of 1-M NaCl. The possible prebiotic relevance is discussed.