Experimental and Theoretical Study on the Hydrogen Bonding between Ascorbic Acid and Cytosine

The intermolecular interactions of DNA/RNA with drugs exhibit important applications in human health and drug design. We investigated the interaction between ascorbic acid (AA), a commonly used drug in clinic, and cytosine, an important base of nucleic acids in DNA/RNA, using cyclic voltammetry (CV), 1H NMR, density functional theory (DFT), quantum theory of atoms in molecules (QTAIM), natural bond orbital (NBO) and independent gradient model based on Hirshfeld partition (IGMH). The CV and 1H NMR results revealed that the hydroxyl groups on the enediol of AA interacted with cytosine, making the electro-oxidation of AA difficult to occur and the downfield shift of H atoms (CH) on cytosine ring. Quantum chemistry calculations further proved the existence of O–H⋅⋅⋅N, O–H⋅⋅⋅O, C‒H⋅⋅⋅N, C–H⋅⋅⋅O, and N–H⋅⋅⋅O hydrogen bonding in the mixed system. It was found that the H atoms (H9 and H11) on enediol of AA, the N atom (N31) and carbonyl oxygen atom (O32) on the cytosine ring were the main action sites, for which H11 and N31 are more prone to be interacted with than H9 and O32.