A theoretical study on 2′-deoxyguanosine and its mono-hydration: Intermolecular hydrogen bonding weakening induces the fluorescence strengthening

The time-dependent density functional theory (TDDFT) method has been applied to investigate the excited states of 2′-deoxyguanosine (2′-dG) and its monohydrated complex (2′-dG-W1). The intramolecular hydrogen bonding N3⋯H2–O2 of the keto conformer is weakened in the S1 state, while that of the enol conformers is strengthened. The two intermolecular hydrogen bondings of 2′-dG-W1 are weakened in the S1 state, while N3⋯H2–O2 gets more strengthened. Moreover, the fluorescence of 2′-dG-W1 is shifted to higher frequencies compared with that of monomer 2′-deoxyguanosine. Therefore, it is concluded that the weakening of intermolecular hydrogen bonding in the S1 state induces fluorescence strengthening of 2′-deoxyguanosine.