Kinetic analysis of oligo(C) formation from the 5'-monophosphorimidazolide of cytidine with Pb(II) ion catalyst at 10-75 degrees C.

The temperature dependence of the rate constants for the formation of oligocytidylate (oligo(C)) from the 5'-monophosphorimidazolide of cytidine (ImpC) in the presence of Pb(II) ion catalyst has been investigated at 10-75 degrees C. The rate constants for the formation of oligo(C) increased in the order of the formation of 2-mer < 3-mer < or = 4-mer; this trend resembles the trend in the cases of the template-directed and the clay-catalyzed formations of oligonucleotides. While the rate constants of the formation of oligo(C) increased with increasing temperature, the yield of oligo(C) decreased with increasing temperature. This is due to the fact that the relative magnitude of the rate constants of the formation of 2-mer, 3-mer, and 4-mer to that of the hydrolysis of ImpC decreased with increasing temperature. This is probably due to the fact that association between ImpC with the elongating oligo(C) decreases with increasing temperature. The apparent activation energy was 61.9 +/- 8.5 kJ mol(-1) for the formation of 2-mer, 49.3 +/- 2.9 kJ mol(-1) for 3-mer, 51.8 kJ mol(-1) for 4-mer, and 66.8 +/- 4.5 kJ mol(-1) for the hydrolysis of ImpC. The significance of the temperature dependence of the formation rate constants of the model prebiotic formation of RNA is discussed.