Transient Effect in Fluorescence Quenching by Electron Transfer. 4. Long-Range Electron Transfer in a Nonpolar Solvent

Abstract

The transient effect in fluorescence quenching observed in a viscous nonpolar solvent, liquid paraffin, was measured and analyzed in order to study the mechanism of electron transfer fluorescence quenching in such solvents. The method of analysis is similar to that adopted in previous papers (J. Phys. Chem. 1995, 99, 5354; 1996, 100, 4064) to study electron transfer in polar solvents. The difference from the previous method is that a function of the form A exp[− b(r − r 0)] was used as the electron transfer rate constant k(r) instead of the Marcus equation and that the dependence of the steady-state fluorescence intensity on the quencher concentration was also analyzed in addition to the fluorescence decay at high quencher concentrations (≥50 mM). The parameters A and b and the diffusion coefficient D were determined from these analyses. The distribution of quenching distance was calculated using these parameter values. The distribution shows that the quenching occurs at distances longer than the contact distances of the fluorescer and quencher molecules. It was concluded that, even in nonpolar liquid paraffin, quenching occurs by long-range electron transfer rather than by exciplex formation as long as the ΔG of electron transfer is negative and far from 0 eV. The relation between electron transfer and exciplex formation in nonpolar solvents was discussed.

On the Coherent Description of Diffusion‐Influenced Fluorescence Quenching Experiments II: Early Events

“…Equation (9) has the solution shown in Equation (10), in which the rate constant for the ionization (quenching) reaction is defined as in Equation (11).…”

On the Coherent Description of Diffusion‐Influenced Fluorescence Quenching Experiments

“…A typical simulation consisted of 10 5 Monte Carlo (MC) cycles to equilibrate the system followed by another 10 5 MC cycles to obtain averages. Each MC cycle consisted of N p attempted displacements of randomly chosen particles.…”

“…Bimolecular reactions between the excited fluorophore and a quencher have been studied mainly either by steady-state or time-resolved fluorescence spectroscopies. [1][2][3][4][5] Increasingly, a big number of applications (chemical sensing, biomolecular recognition) base their analysis on the conclusions previously obtained with chemical model systems. [6] These methods have been extensively used to obtain relevant parameters of elementary reactions such as electron, energy or proton transfer.…”

“…One of the most intriguing facts, very often observed, is the non-linearity of the Stern-Volmer (SV) plots. A SV plot is constructed from the fluorescence intensity, I, recorded at different quencher concentrations (IA C H T U N G T R E N N U N G (c=0)/I(c) vs c), with a slope equal to the SV constant (K SV ), which is defined as the product of the quenching rate constant, k, and the lifetime of the fluorophore, t. [1][2][3][4][5] If this quenching rate constant does not depend on the concentration the plot is a straight line. Several reasons can be invoked if a positive deviation is observed at high quencher concentrations: i) ground state complex formation (we refer to this as pseudo-static quenching); ii) excited state quenching without diffusion (static quenching); or iii) diffusion assisted quenching with a nonstationary stage (dynamic quenching).…”

Kinetics and mechanism of oxidation of GSH by cis-(diaqua)-bis-(ethylenediamine) Cobalt(III) ion

“…Studies on the chemistry of electron transfer reaction of cobalt(III) complexes have received a sustained high level of attention from the scientific community for decades due to their relevance in various redox processes in biological system and act as promising agent for antitumor (Osinsky et al 2003, Osinsky et al 2004), anthelmintic (Behm et al 1993), antiparasitic (Behm et al 1995, Karaman et al 1995, antibiotics (Ghirlanda et al 1998), and antimicrobial activities (Srinivasan et al 2005). Numerous studies have been performed, addressing the dependence of electron transfer on different environments including metalloproteins (Bernauer et al 1999), vitamin B 12 (Wolak et al 2003) , liquids (Burel et al 1999, Saik et al 2004, micelles (Weidemaier et al 1997, Travernier et al 1998, vesicles (Gerasimov et al 1988), and DNA (Srinivasan et al 2005). We report here redox reactions of GSH with Co (III) complex as oxidant and GSH as reductant.…”