Structural reactivity analyses of a neoflavonoid 4-methoxydalbergione using vibrational spectroscopy and quantum chemical calculations

Abstract In the present study, a combined theoretical and experimental approach is used to study the structure and properties of 4-methoxydalbergione (MD). The optimized geometry was calculated by B3LYP method using 6–311++G(d,p) basis set. Three conformers of MD (MD I, MD II and MD III) have been found by potential energy surface scan. The FT-Raman and FT-IR spectra were recorded in the solid phase, and interpreted in terms of potential energy distribution analysis. Good consistency is found between the calculated results and observed spectra. The detailed interpretation of electron delocalization from filled lone pair orbitals to unfilled antibonding molecular orbitals of most interacting molecular orbitals of the molecule has been done by natural bond orbital (NBO) analysis. HOMO-LUMO energy gap shows that chemical reactivity of MD II is higher than MD I and MD III. Molecular electrostatic potential (MEP) surface has also been predicted with the help of density functional theory. Global and local reactivity descriptors are used to study the chemical reactivity of the molecule. Chemical reactivity parameters show that MD II is softer and chemically more reactive than MD I and MD III. Topological parameters at bond critical points (BCP) have been evaluated by ‘Quantum theory of atoms in molecules’ (QTAIM). The docking studies revealed that the active sites C=O of MD showed best binding energies of −5.17, −5.43, −4.31,-4.77, −5.86 and −4.77for 5O3L, 1HTM, 3UV5, 5I1Q, 1MU7 and 1QZQ respectively, which are bacterial proteins of Escherichia coli .