Ab initio and density-functional theory electronic structure calculations have been performed for the 1:1 complexes of tetrahydrofuran with water, hydrogen fluoride, and ammonia. Upon hydrogen bonding with H2O and HF, the structure of tetrahydrofuran (THF) remains relatively unchanged with the exception of THF sites involved in hydrogen-bonding interaction. But the similar findings are not true, upon hydrogen bonded with NH3, where the C2 symmetry of THF changed. The hydrogen-bonding strength for the 1:1 complexes of THF with water, HF, and NH3 is found to be in the order HF>H2O>NH3, which is well characterized by the order in bond angles O2H15F14, O2H16O14, and O2H15N14 closer to linearity, respectively, and the redshifted of stretching frequencies of vFH, vOH, and vNH, respectively. This work is an attempt to provide important predictions and to aid in future experimental and theoretical studies towards the understanding of such hydrogen-bonded van der Waals systems.

The bacterial DNA gyrase is an attractive target to identify the novel antibacterial agents. The flavonoid derivatives possess various biological activities such as antimicrobial, anti-inflammatory and anticancer activities. The aim of present study is to identify the potential molecule from flavonoid derivatives against Staphylococcus aureus using atomistic simulation namely Molecular Docking, Quantum Chemical and Molecular Dynamics. The molecules Cpd58, Cpd65 and Cpd70 are identified as potential molecules through molecular docking approaches by exploring through the N – H…O hydrogen bonding interactions with Asn31 and Glu35 of Gyrase B. To confirm the intramolecular charge transfer in the flavonoid derivatives, Frontier Molecular Orbital (FMO) calculation was performed at M06/6-31g(d) level in gas phase. The lowest HOMO-LUMO gap was calculated for Cpd58, Cpd65 and Cpd70 among the selected compounds used in this study. Molecular dynamics simulation were carried out for Cpd58 and Cpd70 for a time period of 50 ns and found to be stable throughout the analysis. Therefore, the identified compounds are found to be a potent inhibitor for GyrB of S. aureus that can be validated by experimental studies. Communicated by Ramaswamy H. Sarma