Influence of One-Electron Oxidation and One-Electron Reduction on the Tautomeric Preferences for Purine

Quantum-chemical calculations {dft(b3lyp)/6-311+g**} were performedfor all possible nine tautomers of neutral purine (p) and its charged radicals, cation(p+•) and anion (p-•), which may be formed in the presence of oxidizing or reducingagents. comparison of the stabilities orders for the neutral and charged forms showsevidently that one-electron oxidation (p ? e ? p+•) has no important effect on thetautomeric preferences. the nh tautomer containing the moving proton at the n9 atompredominates for p+• (99.3%) as for p (99.8%). dramatical changes take place for p-•.one-electron reduction (p + e ? p-•) favors the c atoms for the moving proton,particularly at the 6- (72.8%), 8- (26.2%) and 2-position (0.1%), and also the n3 atom(0.9%). preference of the ch tautomers in the tautomeric mixture of p-• may partiallyexplain synthesis and degradation reactions of purine derivatives.