Kinetics of fluorescence quenching of n(9-anthroyloxy) stearic acids by tertiary amines in non-ionic micelles of Triton X-100
Abstract
Fluorescence quenching phenomena were studied in non-ionic micelles of Triton X-100 using n(9-anthroyloxy) stearic acid probes nAS (n= 2, 6, 9, 12) and dimethylaniline (DMA) and triethylamine (TEA) as quenchers. The steady-state and transient data obtained adjusted well to a kinetic formalism deduced on the basis of a spherical micelle geometry with a reflecting boundary surface. Deviations from linearity in the experimental data were attributed to transient effects which enable the calculation of reactional distance–effective diffusion coefficient pairs (Re–Deff) of the order of (6–12)× 10–8 cm (Re) and (2–10)× 10–7 cm2 s–1(Deff) in these systems. In microregions of high viscosity the transient effects are clearly observed, supporting the existence of geometric confinement that increases the effective concentration of the donor (amine) thereby imposing a time dependence on these transient effects. The distances Re increase with the decrease of [(ΔG≠/kBT)+ In Deff] as expected for a charge-transfer diffusion-controlled interaction. Diffusion coefficients decrease as the fluorescence probe penetrates deeper into the micelle, pointing out to a lesser fluidity in the inner core. Estimated micro-viscosities depending whether the nAS probe is considered ‘fixed’ or ‘mobile’ inside the micelle, range from (13–43) cP or (22–71) cP.