FLUORESCENCE QUENCHING OF CHLOROPHYLL-A IN NONIONIC MICELLES - EFFECTOF MICELLAR AND QUENCHER CONCENTRATIONS ON THE STATIC AND DYNAMIC QUENCHING PARAMETERS

Fluorescence quenching of chlorophyll-a by two electron acceptors, tet razolium blue, TB2+, (system I) and anthraquinone-2-sulfonate, AQS-, ( system II), in a non-ionic Triton X-100 micellar medium, pH = 7.00, wa s studied using steady-state and time-resolved fluorescence quenching data, with nanosecond and picosecond resolution. A combined analysis o f the steady-state and time-resolved data (ns regime) showed that the excited state interaction via electron transfer is essentially static, with a small diffusion contribution, higher in system II than in syst em I, in agreement with the lower diffusion coefficient of TB2+ as com pared with that of AQS-. Transient effects play an important role at s hort times (up to a few ns) in the more concentrated quencher solution s of both systems. An electron tunnelling model (including a diffusion term for long observation times) was fitted to the time-resolved data obtained with ps resolution, and enabled the evaluation of effective concentrations and effective reactional distances when transient effec ts are operating. In order to obtain information on the micro-heteroge neity of the systems, a spectral-fractal model was also fitted to the time-resolved data, which enabled the evaluation of the spectral dimen sions of the systems. The parameters obtained are discussed in terms o f the physical meaning of the kinetic formalisms used.