No abstract

Excited state intramolecular proton transfer (ESIPT) reaction along the O-H[Symbol: see text][Symbol: see text][Symbol: see text][Symbol: see text]O hydrogen bond of o-hydroxy benzaldehyde (OHBA), methyl salicylate (MS) and salicylic acid (SA) was investigated by ab-initio quantum chemical calculation and theory of atoms and molecules (QTAIM) for the first time. Variation in several geometric as well as QTAIM parameters along the reaction coordinate was monitored in the fully relaxed excited state potential energy curve (PEC) obtained from intrinsic reaction coordinate (IRC) analysis. Although, the excited state barrier height for the forward reaction (∆E (0) (#) ) reduces substantially in all the systems, MS and SA do not show any obvious asymmetry for proton transfer. For MS and SA, the crossover of the bond index as well as the lengths of the participating bonds at the saddle point is assigned due to this symmetry in accordance with bond energy - bond order (BEBO) model, which does not hold true in OHBA both in the ground and excited states. Bond ellipticity, covalent and metallic character were examined for different structures along the reaction path within the QTAIM framework. The QTAIM analysis was found to be able to uniquely distinguish between the ground and excited states of the OHBA molecule as well as both determining the effects on the bonding character of adding different substituent groups and differentiating between the ESIPT reactions in the SA and MS molecules.

No abstract

The binding behavior of antibacterial drug sulfadiazine (SDZ) with water soluble globular proteins like bovine as well as human serum albumin (BSA and HSA, respectively) and lysozyme (LYS) was monitored by fluorescence titration and molecular docking calculations. The experimental data reveal that the quenching of the intrinsic protein fluorescence in presence of SDZ is due to the strong interaction in the drug binding site of the respective proteins. The Stern-Volmer plot shows positive deviation at higher quencher concentration for all the proteins and was explained in terms of a sphere of action model. The calculated fluorophore-quencher distances vary within 4 ~ 11 Å in different cases. Fluorescence experiments at different temperature indicate thermodynamically favorable binding of SDZ with the proteins with apparently strong association constant (~10(4)-10(5) M(-1)) and negative free energy of interaction within the range of -26.0 ~ -36.8 kJ mol(-1). The experimental findings are in good agreement with the respective parameters obtained from best energy ranked molecular docking calculation results of SDZ with all the three proteins.

No abstract