Stem-Volmer quenching constants

The constant K is known as the Stem-Volmer quenching constant /cQ is the rate constant for the quenching reaction, and t0 the lifetime in the absence of quencher. Fluorescence quenching of tryptophan in proteins by acrylamide or 02 has been used to determine whether tryptophan side chains are accessible to solvent or are "buried" in the protein.141 142 The long-lived phosphorescence of tryptophan can be studied in a similar... 

In this equation, F0 and F are the fluorescence intensities in the absence and presence of the quencher, t0 and x are the lifetimes of the fluorophore in the absence and presence of the quencher, kq is the biomolecular quenching constant, and [Q] is the concentration of the quencher (in this case, molecular oxygen). The Stem-Volmer quenching constant is Kn, and is calculated as the product of kq and r0. The Smoluchowski equation describes the biomolecular quenching constant, kq, and is given by... 

As Table I Indicates, Stem-Volmer quenching constants obtained in SDS by measuring either excited state lifetimes or luminescence Intensities were within experimental error, moreover the observed quenching constants are strongly dependent on surfactant concentration. The decay of the... 

Quenching studies performed with acrylamide that can penetrate the protein interior and quench buried tryptophans show that only 16% of the tryptophans in a-toxin were quenched. The value found for Ksv is 0.58 a value much lower than that obtained to the Stem-Volmer quenching constant for a fully exposed tryptophan as in the case of A-acetyl-L-tryptophanamide in water (A sv = 17.5 M ) (Eftink and Ghiron, 1976), indicating the buried nature of most of the tryptophans in a-toxin. 

The oxygen-sensing properties of PtOEP immobilized in a poly-Sty -co-PFS film is characterized by the Stem-Volmer quenching constant, obtained from Eq. (10-3), where /q and I are the luminescence intensities in the absence and presence of oxygen, respectively. Ksw was obtained from a linear plot of (/q//) - 1 versus [O2]. 

The Eq. (7) is known as the Stem-Volmer equation [33] and /sTsv = qTo as the Stem-Volmer quenching constant. Plotting the tq/t ratio as a function of [Q] thus... 

Equation (33) is the well-known Stem-Volmer equation and SV - ( q is the Stem-Volmer quenching constant. In practice, the ratio of lifetime without to that with quencher is plotted against [B] (figure 12) and k is obtained by dividing the slope by 1. ... 

TABLE I. Stem-Volmer Quenching Constants ( K y, mmol dm for the effect of halide ions on the Eu complexes, 5a and 7a. 

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