Thermal versus photochemical tautomerization of cytosine and guanine: a BLYP computational study along the IRC curves

We performed a theoretical study, at the BLYP/aug-cc-pVDZ level, of mechanisms H-transfer between biologically relevant tautomers cytosine and guanine. The analysis ground- excited state energy barriers conversions showed that in some cases they are lower as compared to ground reactions. inclusion one water molecule catalyst oxo-amino form guanine drastically changes mechanism reactions well state. For example, reaction path reduces barrier from 165 60 kJ.mol-1 for guanine, this reduction is 92 24 kJ.mol-1. results obtained support high photostability nucleic acid bases which guarantee normal biological function acids.