Fluorescence quenching Stern-Volmer plots

Figure 10 illustrates Stern-Volmer plots for the fluorescence quenching of APh-x by MV2+ and SPV in aqueous solution [74]. With MV2+, the quenching is so effective that it occurs at very low quencher concentrations (in the range of 10 6 M), whereas with SPV, it proceeds to about the same extent at two-orders of magnitude higher quencher concentration (in the range of 10 4 M). 

Figure 11 shows Stern-Volmer plots for fluorescence quenching of the amphiphilic cationic copolymer QPh-x [74]. The quenching of QPh-x with MV2+ is expected to be much less effective than that of APh-x. The quenching data for the QPh-x system are presented in Table 3. For comparison, the data for a related... 

Fig. 1. a) UV-Vis absorption and fluorescence emission spectra of riboflavin (RF, 20 pM) and Gum Arabic aqueous solutions at pH 7 (phosphate buffer 100 mM). b) Transient absorption spectra of RF (35 pM) in N2-saturated MeOH-Water (1 1) solution. The insets show the transient decay at 720 nm for the RF species and the Stern-Volmer plot for the quenching of 3RF by GA, eqn 11. 

Figure 4. Stern-Volmer plots and quenching constants derived from the fluorescence quenching of DMA (T), 1,2,3,4-tetra-hydro-BA ( ), 5,6-dihydro-BA (A), 8,9,10,11-tetrahydro-BA ( ) and anthracene ( ) by DNA in 15% methanol at 23° C. Emission and excitation wavelengths and details concerning the experimental conditions are given in refs. 12 and 14. The open symbols, o and V, show I /I for 1,2,3,4-tetrahydro-BA and DMA respectively in denatured DNA([P04"] 4.4 x 10 4 M).

Figure 6.1 A Stern-Volmer plot of fluorescence quenching...

Figure 5.3. Simulated Stern-Volmer plots of the ratio of the initial fluorescence intensity F0 to the intensity Fin the presence of quencher of concentration [Q] showing (a)static quenching, (b) dynamic quenching (linear), and (c) binding and/or inaccessible quenchers.

To verify the quenching interaction between the Re-complex and the di-methyl-/7-toluidine, a Stem-Volmer plot of the results of a concentration dependent study of Re-complex fluorescence intensity as a function of amine concentration in fluid MMA was prepared (Figure 3). The samples contained 1.6 X IQ- mol Re-complex, and up to a maximum of 2.6 X 10 mol of amine, in —2.5 g of MMA. Re-complex CT band peak heights at 612 nm were measured from uncorrected fluorescence spectra taken in single scans following excitation at 350 nm. The Stern-Volmer plot is linear over the range of amine concentrations studied. A linear Stem-Volmer plot. 

Figure 3.41 Example of the Stern- Volmer plot of dynamic quenching. The fluorescence of anthracene is quenched by bromobenzene (heavy atom effect)...

Figure 2. (Top) Stern-Volmer plots for the quenching of the fluorescence of colloi fcl CdS in AOT-entrapped water pools in isooctane by RMV + (0), MV2+ 4Q), and PhSH (0) (Bottom) Absorption and emission spectra of colloidal CdS in AOT entrapped water pools in isooctane. The shoulder observed at 400 nm is due to a spectrometer artifact.

Figure 38 Stern-Volmer plot for self-quenching of the fluorescence lifetime of the intercalated component (0.008% BAZrP) as a function of Ru(bpy)2+ concentration. koha is the inverse of the luminescence lifetime. (From Ref. 76. Copyright 1995 The American Chemical Society.)...

Figure 42 Stern-Volmer plots for fluorescence quenching of PBAC by Co(phen)3+ in the presence of 0.008% BAZrP. Using 200 nsec as the singlet lifetime of PBAC, the rate constant for quenching is calculated to be 3 X 1012 M-1sec. This is much too fast for a dynamic process and may involve long-range electron transfer. (From Ref. 17. Copyright 1995 Overseas Publishers Association.)...

The Ksv value shows the importance of fluorophore accessibility to the quencher, while the value of A q gives an idea of the importance of the diffusion of the quencher within the medium. Figure 10.1 shows a Stern-Volmer plot of fluorescence intensity quenching with iodide of flavin free in solution and of flavin bound to flavocytochrome ba- The Ksv values found are 39 and 14.6 M-1 for free and bound flavins, respectively, i.e., values of kq equal to 8.3 x 109 and 3.33 x 109 M-1 s-1, respectively. Accessibility of flavin to KI is more important when it is free in solution, and the presence of protein matrix prevents frequent collisions between iodide and FMN thereby decreasing the fluorophore accessibility to the quencher. Also, as revealed by the Aq values, diffusion of iodide in solution is much more important than in flavocytochrome b2. The protein matrix inhibits iodide diffusion, thereby decreasing the A q value. 

Figure 10.2 shows a Stern-Volmer plot for the fluorescence intensity quenching by oxygen of zinc protoporphyrin IX embedded in the heme pocket of apomyoglobin (Mbdes Fe). The slope of the plot yields Ksv and A q values of 15.96 M-1 s-1 and 7.6 x 109 M-1 s-1,... 

Figure 10.1 Stern-Volmer plots of fluorescence intensity quenching with iodide of FMN free in solution (plot b) and of FMN bound to flavocytochrome b2 (plot a). Reproduced from Albani, J.R., Sillen, A., Engel borghs, Y. and Gervais, M. (1999). Photochemistry and Photobiology, 69, 22-26, with the permission of the American Society for Photobiology.

A Stern-Volmer plot can be obtained also from fluorescence lifetime quenching. In fact, the fluorescence lifetime in the absence of a quencher is... 

When a protein possesses two or several Trp residues, when quenchers such as iodide, cesium, or acrylamide are used, and if all Trp residues are not accessible to the quencher, the Stern-Volmer equation yields a downward curvature. In this case, we have selective quenching (Figure 10.5b). From the linear part of the plot, we can calculate the value of the Stern-Volmer constant corresponding to the interaction between the quencher and accessible Trp residues. Upon complete denaturation and loss of the tertiary structure of a protein, all Trp residues will be accessible to the quencher. In this case, the Stern-Volmer plot will show an upward curvature. In summary, inhibition of the protein fluorescence with two or several Trp residues can yield three different representations for the Stern-Volmer equations, depending on the accessibility of the fluorophore to the quencher. 

Figure 10.9 Stern-Volmer plots of the fluorescence intensity quenching of by oxygen. The Arg...

Figure 15.9 Stern-Volmer plot of fluorescence-intensity quenching of free Trp in solution with TNS.

Figure 4. Stern Volmer plots and ion quenching plots of scavenging precursors of fluorescence in the radiolysis and two photon laser photolysis of aromatic liquids.

The Stern-Volmer plot of fluorescence quantum yields for the quenching of lO-methylacridinium chloride by the nucleotide guanosine-5 -monophosphate shown in Figure 5.36 provides an excellent example in which both static and dynamic quenching occur. Since lifetime measurements were available, the contribution of static quenching could be separated off the Stern-Volmer plot of the purely dynamic quenching was obtained using... 

In cases b, c, and d, the singlet lifetime tS can be calculated from the slope of the Stern-Volmer plot if kg is known. However, the singlet lifetime, calculated from absorption spectra and the quantum yield of fluorescence was in the subnanosecond range and, furthermore, the reaction could be sensitized. It was also highly Improbable that triplet quenching should not occur since the triplet energy of the used quencher was lower than that of the chroraophore (E.j. of the chromophore 66 + 1 kcal). 

Finally, a phenomenon called concentration quenching or static quenching can lead to upward curvature of Stern Volmer plots even at moderate quencher concentrations (c q > 0.01 M). Molecules that are located next to a quencher at the time of excitation will be quenched immediately. Therefore, the fluorescence decay curve will be nonexponential initially, exhibiting a very fast initial component. Moreover, the initial depletion of these molecules will result in an inhomogeneous distribution of the remaining excited molecules around the quenchers. As a result, the diffusion coefficient kA is no longer a constant, but becomes a function of time, kd(t), until the statistical distribution of excited molecules is re-established. The impact of these effects has been analysed in detail.231 Intrinsic rates of electron transfer in donor acceptor contact pairs can be extracted from the resulting curvature in Stern Volmer plots.232... 

Although dynamic Stern-Volmer plots for pyrene fluorescence quenching by CA, were curved, activation energies could be derived from the limiting slopes which yield k5r (Eqn. 11b). Activation parameters obtained from the Stern-Volmer treatments agree well with those which assume k3+k2 for pyrene in M is the same as in liquid paraffin(33) and which take k3 from the limiting slopes of Fig. 2a. In both, the activation energy for... 

Whereas the observed decay profile no longer is characterized by a single decay rate, the steady-state fluorescence intensity becomes dependent on both 7obs and fc>bs. The typical Stern-Volmer plot is no longer represented by equation 7a, but rather by equation 7b, where fcobs is defined by equation 6b, fc q is the bimolecular quenching rate constant, fco is the probe s mean excited-state unimolecular decay rate constant, fcobs is the mean observed decay rate constant, 70 is the distribution parameter of the Gaussian for the unimolecular decay, and 7obs is the distribution parameter for the observed unimolecular decay rate. 

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