Showing papers by "Pradeep K. Sengupta published in 2008"
TL;DR: Evidence for efficient Förster type resonance energy transfer (FRET, from tryptophan to 7HFA) is presented, and the near-UV circular dichroism studies show that the electronic transitions of 7HF are strongly perturbed on binding to the chiral host (HSA), leading to the appearance of ICD bands.
Abstract: Numerous recent investigations have revealed that various synthetic as well as therapeutically active natural flavonoids possess novel luminescence properties that can serve as highly sensitive monitors for exploring their interactions with relevant physiological targets. Here we report a detailed study on the interactions of the model flavone, 7-hydroxyflavone (7HF) with the plasma protein human serum albumin (HSA), employing electronic absorption, fluorescence (steady state and time resolved) and induced circular dichroism (ICD) spectroscopy. The spectral data indicate that in the protein matrix, the neutral 7HF molecules are predominantly transformed to a conjugate anion (7HFA) by a proton abstraction in the ground state. The protein (HSA) environment induces dramatic enhancements in the fluorescence emission intensity, anisotropy (r) and lifetime (tau) values, as well as pronounced changes in the fluorescence excitation and emission profiles of the fluorophore. Moreover, evidence for efficient Forster type resonance energy transfer (FRET, from tryptophan to 7HFA) is presented, from which we infer that the binding site of 7HF in HSA is proximal (estimated distance, R=23.6A) to the unique tryptophan - 214 residue present in the inter-domain (between IIA and IIIA domains) loop region of the protein. The binding constant (K=9.44x10(4)M(-1)) and the Gibbs free energy change (DeltaG=-28.33kJ/mol) for 7HFA-HSA interaction have been estimated from the emission data. Finally, the near-UV circular dichroism (CD) studies show that the electronic transitions of 7HF are strongly perturbed on binding to the chiral host (HSA), leading to the appearance of ICD bands. Implications of these results are discussed.
57 citations
TL;DR: It is demonstrated that lipid peroxidation of EYPC liposomes is significantly inhibited upon 3- HF binding, suggesting that 3-HF can be potentially useful as an inhibitor of peroxidative damage of cell membranes.
Abstract: Excited-state intramolecular proton transfer (ESIPT) and dual luminescence behaviour of 3-hydroxyflavone (3-HF) have been utilized to monitor its binding to liposomal membranes prepared from egg yolk phosphatydilcholine (EYPC). Additionally, absorption spectrophotometric assay has been performed to evaluate the antioxidant activity of 3-HF against lipid peroxidation in this membrane system. When 3-HF molecules are partitioned into EYPC liposomes, a weak long-wavelength absorption band with lambda(abs)(max) approximately 410 nm appears in addition to the principal absorption at approximately lambda(abs)(max) = 345 nm. Selective excitation of the 410 nm band produces the characteristic emission (lambda(em)(max) approximately 460 nm) of the ground-state anionic species, whereas excitation at the higher energy absorption band leads to dual emission with predominatly ESIPT tautomer fluorescence (lambda(em)(max) = 528 nm). Both ESIPT tautomer and the anionic species exhibit fairly high fluorescence anisotropy (r) values (r = 0.122 and 0.180, respectively). Biexponential fluorescence decay kinetics are observed for the ESIPT tautomer as well as the ground-state anionic forms, indicating heterogeneity in the microenvironments of the corresponding emitting species. Furthermore, we demonstrate that lipid peroxidation of EYPC liposomes is significantly inhibited upon 3-HF binding, suggesting that 3-HF can be potentially useful as an inhibitor of peroxidative damage of cell membranes.
42 citations