The Influence of the Substituent Position in Coumarin Derivatives on the Properties of Hydrogen Bonds

Coumarin derivatives (CoDe) have significant biological activity, and different substituent positions may influence their biological activity and efficacy. By studying the relationship between the position of substituents and the properties of hydrogen bonds, the specific mechanism and rule of hydrogen bonds in intermolecular interactions can be further revealed, which provides a theoretical basis for the synthesis of new coumarin derivatives with specific hydrogen bond properties and biological activities, and offers a research foundation for the development of new drug molecules. Therefore, the hydrogen bonding interactions between 3-hydroxycoumarin (3-HyCo), 4-hydroxycoumarin (4-HyCo), 7-hydroxycoumarin (7-HyCo) and 7-hydroxy-4-methylcoumarin (4-Me-7-HyCo) with ethanol and water were studied by density functional theory (DFT). Firstly, the molecular structure of coumarin (Co) monomer and the charge properties and electrostatic surface potential of its four derivatives were analyzed. The stable complex structures of four derivatives with ethanol and water were obtained by optimization, and the existence of hydrogen bonds was proved in these complex structures. Secondly, the hydrogen bond length, interaction energy, AIM topological parameters and hydrogen bond vibration spectra in ground state and excited state were analyzed. It was found that the hydrogen bond structure of 4-hydroxycoumarin complex was the most stable with the different hydroxyl positions, and the hydrogen bond structure after the introduction of methyl group was more stable. Finally, it is found that the frequency of the hydrogen bond vibration spectrum is red-shifted in the excited state, which makes the structure of the hydrogen bond more stable than that in the ground state.