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.

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.

Ultrafast fluorescence resonance energy transfer in a micelle.

Ultrafast fluorescence resonance energy transfer (FRET) from coumarin 153 (C153) to rhodamine 6G (R6G) is studied in a neutral PEO(20)-PPO(70)-PEO(20) triblock copolymer (P123) micelle and an anionic micelle (sodium dodecyl sulfate, SDS) using a femtosecond up-conversion setup. Time constants of FRET were determined from the rise time of the acceptor emission. It is shown that a micelle increases efficiency of FRET by holding the donor and the acceptor at a close distance (intramicellar FRET) and also by tuning the donor and acceptor energies.