Anasuya Mishra

Comment on "The Interaction of 5-(Alkoxy)naphthalen-1-amine with Bovine Serum Albumin and Its Effect on the Conformation of Protein"

The effects of binding and conformational changes induced by the neutral amphiphilic ligand [5-(alkoxy)naphthalen-1-amine] with different alkyl chain lengths on bovine serum albumin (BSA) have been studied using UV-visible and fluorescence spectroscopic methods. The BSA fluorescence exhibits appreciable bathochromic shift along with a reduction in fluorescence intensity and fluorescence lifetime upon binding with ligands. Ligand quenches the fluorescence of BSA in a concentration-dependent manner and deviates positively from the linear Stern-Volmer equation. The calculated quenching rate constants and binding constants were shown to depend entirely on the alkyl chain length of the ligands. After binding of probes with protein, the distance between the donor and acceptor was calculated using Forster theory. Ligands bind near Trp-134 in the subdomain IA of the native BSA and they become accessible to Trp-212 when BSA gets unfolded. The spectral data well supports the idea that BSA changes its three-dimensional conformation incrementally during its unfolding.

Photoisomerization of trans-2-[4'-(dimethylamino)styryl]benzothiazole.

Photoreaction of trans‐2‐[4′‐(dimethylamino)styryl]benzothiazole (t‐DMASBT) under direct irradiation has been investigated in dioxane, chloroform, methanol and glycerol to understand the mechanism of photoisomerization. Contrary to an earlier report, isomerization takes place in all these solvents including glycerol. The results show that restriction on photoisomerization leads to the increase in fluorescence quantum yield in glycerol. The results are consistent with the theoretically simulated potential energy surface reported earlier using time‐dependent density functional theory (TDDFT) calculations. DFT calculations on cis isomers under isolated condition have suggested that cis‐B conformer is more stable than cis‐A conformer due to hydrogen‐bonding interaction. In the ground state, cis‐DMASBT is predominantly present as cis‐B. The fluorescence spectra of the irradiated t‐DMASBT suggested that photoisomerization follows not the adiabatic path as proposed by Saha et al., but the nonadiabatic path.

Interactions of a few azole derivatives with a transport protein: role of heteroatoms

The interaction of a few azole derivatives, 2‐(4′‐N,N‐dimethylaminophenyl)benzimidazole, 2‐(4′‐N,N‐dimethylaminophenyl)benzoxazole, 2‐(4′‐N,N‐dimethylaminophenyl)oxazolo[4,5‐b]pyridine with bovine serum albumin (BSA) were examined by absorption and fluorescence spectroscopy. The results were compared with the previously studied imidazopyridine derivative 2‐(4′‐N,N‐dimethylaminophenyl)imidazo[4,5‐b]pyridine. Displacement studies were carried out with site selective probes to locate the binding site of these ligands. The spectral shifts and the binding constant vary depending on the nature of the ligand. The fluorescence intensity of both oxazole derivatives 2‐(4′‐N,N‐dimethylaminophenyl)benzoxazole and 2‐(4′‐N,N‐dimethylaminophenyl) oxazolo[4,5‐b]pyridine increases substantially in the presence of BSA, whereas the intensity of 2‐(4′‐N,N‐dimethylaminophenyl)benzimidazole decreases. However, hypsochromic shift is observed in presence of BSA. The results obtained from the docking studies are also in good agreement with the experimental results. The location and orientation of binding depend upon the nature of the ligand. The studies revealed that apart from hydrophobic interaction, hydrogen bonding also plays a vital role in the molecular binding. Oxazoles have higher binding affinity than imidazoles and substitution of extra nitrogen further increases the binding affinity. Copyright