Biennial Report 2005-2007 - Saha Institute of Nuclear Physics

Biophysical Sciences 2216.1.7.4 Interaction of 7-Hydroxyflavone with Human Serum Albumin: A SpectroscopicStudyWe performed 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. Thespectral data indicate that in the protein matrix, the neutral 7HF molecules are predominantlytransformed 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 (τ) values, significant decrease in non radiative decay rates (k nr ), aswell as pronounced changes in the fluorescence excitation and emission profiles of the fluorophore.Moreover, evidence for efficient Förster type resonance energy transfer (FRET, from tryptophan to7HFA) is found, from which we infer that the binding site of 7HF in HSA is proximal to the uniquetryptophan - 214 residue present in the inter-domain (between IIA and IIIA domains) loop regionof the protein. The binding constant and the Gibbs free energy change for 7HFA-HSA interactionhave been estimated from the emission data. Finally, the near-UV circular dichroism (CD) studiesshow that the electronic transitions of 7HF are strongly perturbed on binding to the chiral host(HSA), leading to the appearance of ICD bands.Anwesha Banerjee, Kaushik Basu, Pradeep K SenguptaBP6.1.7.5 Does phenazine form triplet excimer and dimer anion radical?Phenazine (PZ) undergoes photoinduced electron transfer with aromatic amines, N, N-dimethylaniline, N,N-diethylaniline, 4,4 ′ -bis(dimethylamino) diphenylmethane and triethylamineand DNA bases, adenine and thymine. During laser flash photolysis experiments with PZ we haveobserved a stable species with a long lifetime at 380 nm in addition to the usual triplet at 440nm. The former is suggested to be due to formation of triplet PZ excimer. The triplet excimeralso undergoes photoinduced electron transfer with the bases. The formation of transient radicalions is confirmed by external magnetic field effect studies. Measurement of B 1/2 , which estimateshyperfine interaction present in the system, also supports this assignment.Sharmistha Dutta Choudhury, Chitra Raha, Samita BasuCSD6.1.7.6 Magnetic field effect on photoinduced electron transfer between dibenzo[a,c]-phenazine and different amines in acetonitrile-water mixtureUnlike simple phenazine molecule, one of its derivatives, dibenzo[a,c]phenazine (DBPZ) forms acharge transfer complex in the triplet state ( 3 ECT) with different amines e.g. N,N-dimethylaniline,4,4 ′ -bis(dimethylamino)diphenylmethane and triethylamine (TEA). Formation of the 3 ECT andradical ion pairs (RIPs) due to electron transfer is identified by laser flash photolysis. A prominentmagnetic field effect (MFE) is observed in both the cases of 3 ECT and RIPs in homogeneousacetonitrile-water mixture. This rare observation of the 3 ECT and MFE in non-viscous mediumcould be explained by considering the extended planar structure of DBPZ and inter-radical hydrogenbonding, mediated by the intervening water molecules. The low B 1/2 value for DBPZ-TEA system