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A model for the interrelationship between asymmetric interbase hydrogen bonding and base–base stacking in hemiprotonated polyribocytidylic acid: Crystal structure of 1‐methylcytosine hemihydroiodide hemihydrate

An x‐ray structural study of the 1‐methylcytosine H+ complex reveals asymmetrically hydrogen‐bonded dimers which are further stacked such that the molecular overlaps are between charged and neutral bases. This study supports the assignment of the asymmetry in the interbase hydrogen bonding in the cytidine–cytidine H+ hydrogen‐bonded complex. Furthermore, it is suggested that hemiprotonated, helical polyribocytidylic acid has as its translational repeat unit a set of highly stacked pairs of asymmetrically hydrogenbonded bases. The asymmetry in the interbase hydrogen bonding is stimulated, at least in part, by base‐stacking considerations.