Binding of Methyl Viologen and its Radical to p-Sulfonatocalix[4]arene

Abstract

Binding of N,N′-dimethyl-4,4′-bipyridinium (methyl viologen, MV2+) and its radical (MV+•) to novel p-sulfonatocalix[n]arene (CX[4]-S,) host has been investigated using the density functional theory (DFT). The hydrogen bonded interactions between α-, β- and -CH3 protons of methyl viologen with SO3 − groups of CX[4]-S render stability to their complexes. In the lowest energy structures, one of the methyl groups of MV2+ was partially penetrated within the cavity of CX[4]-S host owing to C-H···O interactions with upper rim of host while the remaining methyl group excluded from the cavity. The radical MV+• revealed qualitatively similar binding patterns to CX[4]-S host as that of MV2+. Moreover, interaction energy of methyl viologen dication was predicted to be larger than that of the corresponding radical cation.