Stern Volmer analysis

Stern-Volmer analysis for the quenching of the Norrish type 2 reaction of hexan-2-one by penta-1,3-diene results in a nonlinear plot... 

In fact, quenching effects can be evaluated and linearized through classic Stem-Volmer plots. Rate constants responsible for dechlorination, decay of triplets, and quenching can be estimated according to a proposed mechanism. A Stern-Volmer analysis of photochemical kinetics postulates that a reaction mechanism involves a competition between unimolecular decay of pollutant in the excited state, D, and a bimolecular quenching reaction involving D and the quencher, Q (Turro N.J.. 1978). The kinetics are modeled with the steady-state approximation, where the excited intermediate is assumed to exist at a steady-state concentration ... 

Salem5 has reported detailed calculations analysing several photochemical reactions with special reference to the way by which the excited state of the molecule decays back to the ground state. Another publication has dealt with the classification of photochemical reactions and is in part an elaboration of an earlier paper.7 Further attention has been directed at the Stern-Volmer analysis of photochemical reactions dealing with non-linearity when two excited states are reactive and one or both are quenched.8 9 A generalized treatment of the equation has resulted.10... 

Samson G, Morissette JC, Popovic R. Determination of four apparent mercury interaction sites in photos) tem II by using a new modification of the Stern-Volmer analysis. Biochem Biophys Res... 

We can observe emission from both PS excimer and PPO. The Xj = 12 ns due to pure PS in solution decreases with PPO increase and the relative intensity of the short-lived PPO component increases in the presence of PS. The decrease in the lifetime of PS subjected to Stern-Volmer analysis gave the slope 5.2 x 10 1 mol h Semi-quantitative analysis, assuming the mutual diffusion coefficient of 2 x 10 m s gave the distance of interaction in the order of magnitude 10 nm. Quenching efficiencies of this magnitude would be possible only... 

MODIFICATION OF THE STERN-VOLMER ANALYSIS FOR THE STUDY OF THE MERCURY QUENCHING EFFECT IN DUNALIELLA TERTIOLECTA... 

Similarly, selective 635 nm excitation of Pt° Tetraphenyltetrabenzoporphyrin in the presence of perylene generated the fluorescence of the latter, centered at 451 nm. A Stern-Volmer analysis of dynamic quenching of the phosphorescence of the complex showed the involvement of triplet-triplet energy... 

This result and the fact that a Stern-Volmer quenching plot for (75) and (77) had somewhat different slopes (no statistical analysis given) led the author to propose that the (75) and (76) were n -> n triplet products and (77), (78), and (79) were triplet products. 

W. R. Laws and P. B. Contino, Fluorescence quenching studies Analysis of non-linear Stern-Volmer data, Methods Ernymol. 210 (in press). 

Baird and Escott [49] suggested that the departures from the Stern— Volmer law could be explained if there was competition between the excited fluorophors and quenchers. However, because the concentration of excited fluorophors is 103—106 times less than the quencher concentration, to an excellent approximation the excited fluorophor molecules are statistically independent. Baird et al. [50] have also developed a more detailed analysis of fluorescence quenching based upon the Wilemski and Fixman [51] approach (see Chap. 9). They wrote many-body equations... 

Depending on the number of these cycles the final oxygen concentration is determined by the residual pressure of the pump. Quantitative analysis of traces of oxygen in liquids can be done by the measurements of long-lived luminescence lifetimes (e.g. pyrene fluorescence) and applying the Stern-Volmer equation. 

It is probably appropriate to note at this point that Stern-Volmer type of analysis of luminescence data obtained using modern gated spectrometers (such as the Perkin-Elmer LS5) follows different mathematical expressions than those used for data obtained under continuous irradiation conditions. This is true even for homogeneous systems where the excited state decays with simple monoexponential behaviour. 

Although this relationship looks similar to Eq. (3.257) for irreversible transfer, the Stern-Volmer constant of the latter (ko = k,) is different from Kf, which accounts for the reversibility of ionization during the geminate stage. The difference between Kg = R (0) and its irreversible analog K from (3.372) is worthy of special investigation based on the analysis of pair distribution functions obeying Eqs. (3.359). 

Figure 10.6 shows fluorescence emission spectra of lens culinaris agglutinin (LCA) (a) (Lmax = 330 nm), of inaccessible Trp residues (b) (A.max = 324 nm) obtained by extrapolating to [I-] = oo, and of quenched Trp residues (c) obtained by subtracting spectrum (b) from spectrum (a). The emission maximum of accessible Trp residues is located at 345 nm, a characteristic of emission from Trp residues near the protein surface. Thus, both classes of Trp residues contribute to the fluorescence spectrum of LCA (Albani 1996). The presence of five Trp residues makes the analysis by the modified Stern-Volmer equation very approximate nevertheless, a selective quenching method allows the percentage of accessible fluorophores to the quencher to be determined. 

The photocatalytic isomerization reactions were markedly inhibited by the addition of O2, and the photooxidation of trans-l-C W , occurred instead of isomerization. Analysis of the slope of the Stern-Volmer plots as a function of pressure of added O2 (and trans-2-CnRs) showed the reactivity... 

Analysis of this scteme ows that for steady-state excitation, the Stern-Volmer relationship (62) and quantum yield ratio of excimer to monomer fluorescence (63) are obtained. 

Different problems are encountered when quenching studies are carried out on fluid solutions at room temperature (2,18). Analysis of the quenching effect is usually made using the Stern-Volmer equation ... 

Pyrene excimer formation still continues to be of interest and importance as a model compound for various types of study. Recent re-examinations of the kinetics have been referred to in the previous section. A non a priori analysis of experimentally determined fluorescence decay surfaces has been applied to the examination of intermolecular pyrene excimer formation O. The Kramers equation has been successfully applied to the formation of intermolecular excimer states of 1,3-di(l-pyrenyl) propane . Measured fluorescence lifetimes fit the predictions of the Kramer equation very well. The concentration dependence of transient effects in monomer-excimer kinetics of pyrene and methyl 4-(l-pyrenebutyrate) in toluene and cyclohexane have also been studied . Pyrene excimer formation in polypeptides carrying 2-pyrenyl groups in a-helices has been observed by means of circular polarized fluorescence" . Another probe study of pyrene excimer has been employed in the investigation of multicomponent recombination of germinate pairs and the effect on the form of Stern-Volmer plots ". 

As long as r > 3R0, the fluorescence decay is close to exponential, the lifetime of the donor fluorescence decreases linearly with increasing concentration of A and fluorescence quenching obeys Stern Volmer kinetics (Section 3.9.8, Equation 3.36). However, the bimolecular rate constants ket of energy transfer derived from the observed quenching of donor fluorescence often exceed the rate constants of diffusion kd calculated by Equation 2.26, because resonance energy transfer does not require close contact between D and A. Finally, when r < 3R0, at high concentrations and low solvent viscosity, the kinetics of donor fluorescence become complicated, but an analysis is possible,109,110 if required. 

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