Simultaneous analysis of single-photon timing data with a reference method: Application to a poisson distribution of decay rates

Identifiability of Models for Fluorescence Quenching in Aqueous Micellar Systems

The first deterministic identifiability analysis is presented for four commonly used kinetic models of fluorescence quenching of an excited probe in aqueous micelles: A) model with immobile quenchers, B) model with mobile quenchers, C) an extension of model B in which exchange of quenchers both via the aqueous phase and during micelle collisions is taken into account, and D) model with probe migration. It is shown that these specific models for fluorescence decay of an excited probe solubilized in a micelle and quenched by molecules or ions that are Poisson-distributed over the micelles, resulting in the generalized four-parameter equation f(t)=A(1) exp{-A(2)t-A(3)[1-A(4)t]}, are uniquely identifiable in terms of four descriptive A parameters. Moreover, each model also can be uniquely identified in terms of the underlying rate constants and micellar concentration or mean micellar aggregation number. This means that these parameters can be extracted in a unique way from time-resolved fluorescence quenching experiments on a probe in micelles. For each model the recommended analysis approach is given.

The role of polymer flexibility on the interaction with surfactant micelles: poly(vinyl alcohol) and sodium dodecyl sulphate aqueous micelle interactions studied by dynamic fluorescence quenching

The interactions between poly(vinyl alcohol) and the surfactant sodium dodecyl sulphate in aqueous solutions have been investigated by means of static and dynamic fluorescence measurements. By static fluorescence measurements the onset of interaction, the critical aggregation concentration, is determined to be 6.5 mM at 20 °C and 7.0 mM at 40 °C. By dynamic fluorescence measurements without added quencher the influence on the lifetime of the fluorescent probe, pyrene, by the presence of the polymer is investigated. From measurements with an added quencher, dimethylbenzophenone, the surfactant aggregation numbers of the micellar aggregates formed upon interaction between the surfactant and the polymer and the quenching rate constant are obtained. At the two polymer concentrations, i.e., 0.2% and 2.0%, the surfactant aggregation numbers at low surfactant concentration are very small, but increase rapidly with increasing surfactant concentration. Comparisons are made with results from a system where poly(ethylene oxide) instead of poly(vinyl alcohol) is the polymer. Key words: dynamic fluorescence quenching, polymer–surfactant interactions, aggregation numbers.

Simultaneous analysis of single-photon timing data for the one-step determination of activation energies, frequency factors and quenching rate constants. Application to tryptophan photophysics

A general global analysis of single-photon timing data is presented in which each fluorescence decay curve can be described by a different decay law. The model parameters can be held in common within one curve and/or between related curves. Any or all parameters can be kept fixed, or they may be variable to seek optimum values. This general analysis allows the determination of activation energies, frequency factors and quenching rate constants in one step. The construction of the global mapping table which relates parameters in one experiment to those in another is explained in detail. The use and performance of this general simultaneous analysis are examined using tryptophan fluorescence decays at pH 6.0 obtained at various emission wavelengths as a function of temperature and added solute quencher. The results show that tryptophan at pH 6.0 decays as a biexponential with decay times which are independent of the analysis wavelength. The decay component with the short lifetime has a deactivation rate constant of 1.4 x 10(9) s-1 independent of temperature. The decay component with the long lifetime has an activation energy of 28 kJ/mol and a frequency factor of 3 x 10(13) s-1; its temperature-independent decay rate constant equals 1 x 10(8) s-1. Recursion formulas for a computer program to estimate activation energies, frequency factors, and decay rate constants are provided.