NOPR Collection:

Fluorescence quenching and flash photolysis studies of photo-induced electron transfer across Zn-tetraphenyl porphyrin-encapsulated liposomes: Evidences for reductive quenching by EDTA

1995-02-01T00:00:00Z

Title: Fluorescence quenching and flash photolysis studies of photo-induced electron transfer across Zn-tetraphenyl porphyrin-encapsulated liposomes: Evidences for reductive quenching by EDTA Authors: Karmakar, Anjan; Chaudhuri, Rupali; Bera, Subhash C; Rohatgi-Mukherjee, K K Abstract: The photosensitizer, zinc-tetraphenyl porphyrin (ZnTPP), encapsulated liposomes incorporating reductive quencher (EDTA) (O.5M) in the inner pool have been used to initiate photo-induced electron transfer across liposome membrane using (i) BQ, (ii) MV²⁺ and (ill) 1,5-AQDS^2- as oxidative quenchers in the outer pool. Two types of lipids have been used: egg-phosphatidyl choline, EPC (T_c.~ 15°C) and dipalmitoyl-phosphatidyl choline, DPPC (T_c.~ 38°C). The EPC liposome matrix has been further modulated by cholesterol and the localisation of the photosensitizer studied by fluorescence quenching technique. From modified Stern-Volmer equation it is observed that about 60% of ZnTPP is not available for quenching by AQDS^2- added to the outer pool. Availability is 100% for cholesterol modified liposomes, K_sv =2.7 X 10³M ^-¹. For DPPC, the liposomes contained two different concentrations of EDTA in the inner pool, Lip A 0.5M and Lip B 0.25M. On addition of AQDS^2- as the quencher in the outer pool, K_sv is found to be a function of [EDTA] in the inner pool suggesting definite rate determining role of the reductive quencher EDTA in transmembrane electron transfer process. These observations are confirmed by flash photolysis studies on the DPPC liposomes, Lip A and Lip B, of composition as above and the Lip C obtained by adding AQDS^2- to the outer pool of Lip B. Biexponential decay for Lip A and Lip B and single exponential decay for Lip C is observed. From both singlet and triplet quenching studies it has been inferred that the first step is the reductive quenching of photoexcited ZnTPP by EDTA in the inner pool, followed by electron transfer to AQDS^2- in the outer pool, promoting ET from inside to outside. Page(s): 83-93

Solvent dependent absorption and fluorescence of a ketocyanine dye in neat and binary mixed solvents

1995-02-01T00:00:00Z

Title: Solvent dependent absorption and fluorescence of a ketocyanine dye in neat and binary mixed solvents Authors: Banerjee, Debashis; Laha, Ashis Kumar; Bagchi, Sanjib Abstract: The environmental effect on the ground and excited state properties of a ketocyanine dye has been studied by monitoring its absorption and fluorescence characteristics in various pure and binary mixed solvents. The spectroscopic transition leading to the longest wavelength absorption or fluorescence has been found to involve considerable intramolecular charge transfer as evidenced by semiempirical MO calculations at the AM1 level. Ground state complexation is indicated in protic solvents, aromatic hydrocarbons and cyclic ethers. The fluorescence maximum, E (F), shows a correlation with E_T (30) scale of solvent polarity. A multiple linear correlation of E(F) with Kamlet-Taft parameter representing solvent dipolarity (p*) and hydrogen bonding ability (α and β) suggests that apart from dipolar interactions specific solute-solvent interactions are important in determining fluorescence maxima. Study of E (F) in mixed binary solvents points to a preferential solvation of the solute in the S₁ state. Page(s): 94-101

Some new aspects of luminescence in perylene doped pyrene

1995-02-01T00:00:00Z

Title: Some new aspects of luminescence in perylene doped pyrene Authors: Patil, S R Abstract: Pyrene is a crystalline aromatic hydrocarbon and is found photoluminescent. Pure and doped pyrenes exhibit interesting luminescent properties. Electroluminescence in perylene doped pyrene has been studied. The observed emission is explained by considering formation of mixed excimer in the excited state due to interaction between excited pcrylene molecule and pyrene molecules. The effect of voltage of applied electric field on electroluminescence help to study optical characteristics. At lower concentration of perylene in pyrene the voltage dependence is exponential. However, at higher concentrations the voltage dependence becomes linear. The effect of temperature on emission has been studied. The study of temperature dependence supports the proposed mechanism of formation of mixed excimer. Page(s): 102-105

Apparent molal volumes of alcohols in aqueous solutions at different temperatures

1995-02-01T00:00:00Z

Title: Apparent molal volumes of alcohols in aqueous solutions at different temperatures Authors: Kaulgud, M V; Dhondge, S S; Moharil, A G Abstract: Apparent molal volumes. (φ_v) of methyl. ethyl. n-propyl, isopropyl. n-butyl. isobutyl, sec-butyl and lert-butyl alcohols in aqueous solutions are reported at 2°, 4°, 6°, 8°, and 10°C for the first time. The trends of φ_v against molality (m) curves have been interpreted in terms of effect of dissolved solute (alcohol) on structure of water. It has been concluded that lower alcohols even at lower temperatures get dissolved in the natural cavities available in the water structure whereas higher alcohols have difficulty in finding suitable cavities in water structure and hence tend to indicate phase separation. The results have also been interpreted in terms of predominance of solute-solute interactions at lower temperatures. Page(s): 106-110