Hydrogen bonding patterns of 7,9-dimethylguanine and its transplatinum(II) complexes

Methylation at the N7 position is one of the most frequently naturally occurring modifications of guanosine. This alteration drastically changes the hydrogen bonding and acid–base properties of the guanine nucleobase. Here we show on the example of the model nucleobase 7,9-dimethylguanine that due to blockage of N7 of the purine ring, new hydrogen bonding patterns occur on the minor groove binding face of this nucleobase involving the ring nitrogen N3 and the exocyclic amino group N2H2. The free 7,9-dimethylguaninium ion and several transplatinum(II) complexes of the this ligand are presented and discussed. Methylation at N7 drastically changes the acid–base and hydrogen bonding properties of the nucleobase guanine. 7,9-Dimethylguanine, the model compound for this naturally occurring modified nucleobase, shows new and extensive hydrogen bonding patterns involving its minor groove binding face both in its free form as well as in several transplatinum(II) complexes.