Photo‐cidnp in Guanine Nucleic Acid Derivatives. A Mechanistic Study

A mechanistic study of the photo‐CIDNP effect of guanosine derivatives is presented. The pH dependence of the CIDNP effect of 5′‐GMP shows a sign reversal at pH 3.3. Using methylated guanosine derivatives evidence has been obtained that the protonation state of the N7 atom influences the radical pair generation. The mechanism involves a guanine radical dication (protonated radical cation) at low pH and a radical cation at high pH. The CIDNP behaviour of 5′‐GMP is compared with that of 5′‐AMP, that was previously studied.