Raman spectral studies of nucleic acids. 18. Kinetics of hydrogen-deuterium exchange in guanosine 5'-monophosphate and guanosine 3':5'-monophosphate determined by laser-Raman spectroscopy

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Abstract
Pseudo-1st-order rate constants (k.psi.) governing the deuterium exchange of 8-CH groups in (5''-rGMP) and c(cyclic)GMP were determined as a function of temperature in the range 30-80.degree. C by laser-Raman spectroscopy. For each guanine nucleotide the logarithm of the rate constant exhibits a strictly linear dependence on reciprocal temperature: i.e., k.psi. = Ae-Ea/RT with A (frequency factor) = 8.84 .times. 1014 h-1 and Ea (Arrhenius activation energy) = 24.6 kcal/mol for 5''-rGMP and A = 3.33 .times. 1013 h-1 and Ea = 22.2 kcal/mol for cGMP. Exchange of the 8-CH groups in guanine nucleotides is generally 2-3 times more rapid than in adenine nucleotides. As in the case of adenine nucleotides, cyclic and 5'' nucleotides of guanine exchange at markedly different rates at lower temperatures, with exchange in the cyclic nucleotide being the more facile. Each of the guanine nucleotides was prepared in 4 different isotopic modifications for Raman spectral analysis. The Raman frequency shifts resulting from the various isotopic substitutions were tabulated and assignments were given for most of the observed vibrational frequencies.