Density functional theory study on hydrogen bonding interaction of luteolin-(H2O)n

Density functional B3LYP method with 6-31++G∗∗ basis set is applied to optimize the geometries of the luteolin, water and luteolin-(H2O)n complexes. The vibrational frequencies are also studied at the same level to analyze these complexes. We obtained four steady luteolin-H2O, nine steady luteolin-(H2O)2 and ten steady luteolin-(H2O)3, respectively. Theories of atoms in molecules (AIM) and natural bond orbital (NBO) are used to investigate the hydrogen bonds involved in all the systems. The interaction energies of all the complexes corrected by basis set superposition error, are within −13.7 to −82.5 kJ/mol. The strong hydrogen bonding mainly contribute to the interaction energies, Natural bond orbital analysis is performed to reveal the origin of the interaction. All calculations also indicate that there are strong hydrogen bonding interactions in luteolin-(H2O)n complexes. The OH stretching modes of complexes are red-shifted relative to those of the monomer.