SINP Triennial Report - Saha Institute of Nuclear Physics

Biophysical Sciences Including Chemistry 13
tau = 1 (where tau(0) and tau are the unquenched and quenched tryptophan fluorescence lifetimes,
respectively) Absorption spectrophotometric assays reveal that robinetin inhibits EYPC membrane lipid
peroxidation and HbA glycosylation with high efficiency.
Chaudhuri, Sudip; Pahari, Biswapathik; Sengupta, Bidisha † ; Sengupta, Pradeep K
Ground- and excited-state proton transfer and antioxidant activity of 3-hydroxyflavone in egg
yolk phosphatidylicholine liposomes: absorption and fluorescence spectroscopic studies
Excited-state intramolecular proton transfer (ESIPT) and dual luminescence behaviour of 3hydroxyflavone
(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(max)(abs) similar to 410 nm appears in addition to the principal absorption at
lambda(max)(abs) = 345nm. Selective excitation of the 410 nm band produces the characteristic emission
(lambda(max)(em) similar to 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(max)(em) = 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.
Chaudhuri, Sudip; Basu, Kaushik † ; Sengupta, Bidisa † ; Banerjee, Anwesha † ; Sengupta, Pradeep K
Ground and excited state proton transfer and antioxidant activity of 7-hydroxyflavone in model
membranes: Absorption and fluorescence spectroscopic studies
Steady state and time resolved fluorescence spectroscopy have been used to probe microenvironments
of the therapeutically active intrinsically fluorescent flavonoid, 7-hydroxyflavone (7-HF), in model
membranes consisting of multilamellar phosphatidylcholine liposomes. Additionally, the antioxidant
effects of 7-HF against lipid peroxidation have been evaluated using spectrophotometric assay. Large
Stokes shifted emissions with distinct spectroscopic signatures, are observed from the excited state
proton transfer (ESPT) tautomer (which is generated by a solvent mediated mechanism) and the ground
state anion of 7-HF. The neutral (7-HFN) and anionic (7-HFA) species’ appear to be located in the
non-polar acyl chain and the polar head group regions of the lipid vesicles respectively. The partition
coefficients of 7-HFN and 7-HFA in these vesicles have also been estimated using their intrinsic
fluorescence. Anisotropy (r) versus temperature (T) measurements reveal the utility of the tautomer
fluorescence anisotropy as a sensitive parameter for exploring structural changes in the membranes.
Fluorescence decay kinetics studies indicate heterogeneity in the microenvironments of both 7-HFN
and 7-HFA. Furthermore, we demonstrate that lipid peroxidation of the model membranes is partially
arrested upon 7-HF binding, suggesting its potential usefulness as an inhibitor of peroxidative damage
of cell membranes.
Chaudhuri, Sudip; Pahari, Biswapathik; Sengupta, Pradeep K