Determination of individual proton affinities of ofloxacin from its UV-Vis absorption, fluorescence and charge-transfer spectra: effect of inclusion in beta-cyclodextrin on the proton affinities.

Individual proton affinities of the four dissociable functional groups of (+/-)-9-fluoro-2,3-dihydro-3-methyl-10-(4-methyl-1-piperazinyl)-7-oxo-7H-pyrido[1,2,3-de]-1,4-benzoxazine-6-carboxylic acid (commonly called "ofloxacin" and to be denoted henceforth as OflH), have been determined from the pH-dependent variation of the UV-vis absorption and fluorescence spectra of the compound itself and of its charge transfer complexes (CT) with p-bromanil and p-chloranil (in aqueous medium containing 0.1% ethanol, v/v). To utilize the CT spectra for determination of the proton affinity of the anilinic N, the CT absorption band of the ofloxacin-p-bromanil complex has been studied by changing the pH of the medium.

Fluorimetric study of water-ethanol interaction and its effect on the micellisation of sodium dodecyl sulphate in the presence of bovine serum albumin.

The model for self-association of ethanol in water which was established earlier by compressibility and infrared absorption measurements, has been further supported in the present work by monitoring fluorimetrically the variation of the solvatochromic Kamlet-Taft pi* parameter of ethanol-water mixtures over the entire mole fraction range. This model has been used to interpret the variation of the critical micellisation concentration (cmc) of sodium dodecyl sulphate in the presence of bovine serum albumin (BSA) in aqueous ethanol mixtures (as obtained from the tryptophan fluorescence intensity of BSA) in low ethanol mole fraction range.

Inclusion of riboflavin in beta-cyclodextrin: a fluorimetric and absorption spectrometric study.

Formation of inclusion complexes between riboflavin and beta-cyclodextrin (beta-CD) with both 1:1 and 1:2 stoichiometry has been established by fluorimetric titration. However, in absorption spectrometric experiment, spectral change of riboflavin in the visible range could be observed only by taking beta-CD at a much higher concentration (about 100 times) than riboflavin and under such condition only 1:2 complexes could be detected. Its formation constant (K) was determined by a multiple linear regression analysis of the absorption data.

Determination of individual proton affinities of reserpine from its UV-vis and charge-transfer spectra.

Proton affinities of the two N atoms of reserpine (methyl-11,17alpha-dimethoxy-18beta-[(3,4,5-trimethoxybenzoyl)oxy]-3beta,20alpha-yohimban-16beta-carboxylate) have been determined in two ways from the pH-dependent variation of the UV-vis absorption spectra (i) of reserpine itself and (ii) of the charge-transfer (CT) spectra of its complexes with o-chloranil, p-chloranil, and DDQ in aqueous medium (containing 0.1% ethanol v/v). For the second method, the CT absorption bands of the complexes were determined, their formation constants were estimated by a modified Benesi-Hildebrand equation, and variation of CT absorption spectra with a change in pH was noted.

Use of fluorescence probes for studying Kamlet-Taft solvatochromic parameters of micellar system formed by binary mixture of sodium dodecyl sulfate and Triton-X 100.

Fluorescence probes have been used to estimate Kamlet-Taft solvatochromic parameters alpha and pi* representing hydrogen-bond donation ability and dipolarity/polarizability, respectively, of sodium dodecyl sulfate (SDS)-Triton X 100 (TX100) mixed aggregates with varying compositions. The hydrogen-bond donation ability of the mixed aggregate has been found to increase with SDS composition, whereas the dipolarity/polarizability parameter decreases. The relative contribution of electrostatic and steric effect toward the total free energy of micellization have been calculated for the mixture.