DFT/TDDFT theoretical investigation on the excited-state intermolecular hydrogen bonding interactions, photoinduced charge transfer, and vibrational spectroscopic properties of deprotonated deoxyadenosine monophosphate [dAMP-H]− anion in aqueous solution: Upon photoexcitation of hydrogen-bonded model complexes [dAMP-H]−–nH2O (n = 0, 1, 2, 3, 4)

Abstract

In this work, the excited-state intermolecular hydrogen bonding interactions, photoinduced charge transfer, and vibrational spectroscopic properties of deprotonated deoxyadenosine monophosphate [dAMP-H]− anion in aqueous solution were investigated by the DFT/TDDFT method. The intermolecular hydrogen-bonded model complexes [dAMP-H]−–nH2O (n=0, 1, 2, 3, 4) in both the ground state and electronic excited state were first discussed. Analysis of frontier molecular orbitals reveals an intramolecular charge transfer (ICT) state for [dAMP-H]−–nH2O (n=0, 1, 2) complexes in which charge transfer occurs from the phosphate group to the base. However, it becomes a locally excited (LE) state for [dAMP-H]−–nH2O (n=3, 4) complexes, which only locates on the adenine moiety. The excited energies of the first excited state of [dAMP-H]−–nH2O (n=0, 1, 2, 3) increase gradually during the introduction of water molecules, but decreases with the fourth water molecule at adenine site. The fourth water molecule has little influence on the structure but significant to the photoexcitation. Upon electronic excitation, stretching vibration frequencies of NH and OH of hydrogen bonds: N5H10⋯O9, O9H19⋯O10 and O10H21⋯O3 are red-shifted. The excited-state bond lengths of these hydrogen bonds are also shortened. Therefore, the total intermolecular hydrogen bonding interaction at the base moiety is significantly strengthened in the electronic excited state.