Hydrogen bonding in alkali metal cation-bound i-motif-like dimers of 1-methyl cytosine: an IRMPD spectroscopic and computational study.

The structures of alkali metal cation bound 1-methylcytosine (1-mCyt) dimers were explored using vibrational spectroscopy in the form of infrared multiple photon dissociation (IRMPD) spectroscopy and by computational methods. For the smaller alkali metal cations, Li+ and Na+, only non-hydrogen bonded symmetric anti-parallel structures were observed in agreement with the lowest energy computed structures. For K+, Rb+, and Cs+ the vibrational spectra in the N-H stretch region showed strong evidence for hydrogen bonding in agreement with the lowest energy structures which contained hydrogen bonding interactions between the amine group of one cytosine and the carbonyl oxygen of the other cytosine. The lowest energy structures for these complexes were compared to previously studied cytosine complexes [(Cyt)2M]+ where M = Li, Na, and K. The calculations are in agreement that only the non-hydrogen bonded structures would be observed for these cytosine complexes.