Structural insights, protein-ligand interactions and spectroscopic characterization of isoformononetin
Isoformononetin, a methoxylated isoflavone present in medicinal plants, has non-estrogenic bone forming effect via differential mitogen-activated protein kinase (MAPK) signaling. Spectroscopic (FT-Raman, FT-IR, UV-vis and NMR spectra) and quantum chemical calculations using density functional theory (DFT) and 6-311++G(d,p) as a large basis set have been employed to study the structural and electronic properties of isoformononetin. A detailed conformational analysis is performed to determine the stability among conformers and the various possibilities of intramolecular hydrogen bonding formation. Molecular docking studies with different protein kinases were performed on isoformononetin and previously studied isoflavonoid, formononetin in order to understand their inhibitory nature and the effect of functional groups on osteogenic or osteoporosis associated proteins. It is found that the oxygen atoms of methoxy, hydroxyl groups attached to phenyl rings R1, R3 and carbonyl group attached to pyran ring R2, play a major role in binding with the protein kinases that is responsible for the osteoporosis; however, no hydrophobic interactions are observed between rings of ligand and protein. The electronic properties such as HOMO and LUMO energies were determined by time-dependent TD-DFT which predict that conformer II is a little bit more stable and chemically low reactive than conformer I of isoformononetin. To estimate the structure-activity relationship, the molecular electrostatic potential (MEP) surface map, and reactivity descriptors are calculated from the optimized geometry of the molecule. From these results, it is also found that isoformononetin is kinetically more stable, less toxic, weak electrophile and chemically less reactive than formononetin. The atoms in molecules and natural bond orbital analysis are applied for the detailed analysis of intra and intermolecular hydrogen bonding interactions.