Quencher ionic

Furthermore, the quenching of internal residues in proteins by ionic quenchers, although not strong, is quite detectable.(56) A double-quenching method was developed to separate fluorescence quenching parameters characteristic of solvent-exposed and buried fluorophores.(57) The method uses two types of quenchers simultaneously, one type penetrating and the other not penetrating into the protein matrix. 

Because the mechanisms of 1-naphtol complexation with HA obtained by using these three techniques exhibit similar pathways, we present the results only from fluorescence spectroscopy. The ratio of fluorescence intensity in the absence (FJ and in the presence (F) of the quencher (HA) over time, as affected by pH and ionic strength, are illustrated in Fig. 16.20. The fluorescence intensity of a fluorophore in the absence of a quencher is directly proportional to its concentration in solution, and therefore time-dependent changes in E can be used to assess the stability of 1-naphtol under different pH and ionic strength. Quenching (FQ) of 1-naphtol fluorescence by humic acid increased with equilibration time from one to seven days. This time-dependent relationship was found to result from weak complexation of... 

Fig. 16.20 Fluorescence quenching (FQ) of 1-naphthol in the presence of HA as a function of pH and reaction time (1-naphthol = 8pmol LHA = 11 ppm C ionic strength of O.IM LiQ) F and F denote fluorescence intensities in the absence and in the presence of the quencher (HA), respectively. Reprinted with permission from Karthikeyan KG, Chorover J (2000) Effects of solution chemistry on the oxidative transformation of 1-naphtol and its complexation with humic acid. Environ Sci Technol 34 2939-2946. Copyright 2000 American Chemical Society...

For block copolymers with a polyacid or polybase block, the structure and properties of micellar solutions depend on the pH. For example, Morishima et al. (1982b) found that for a poly(9-vinylphenanthrene)-poly(methacrylic acid) (PVPT-PMA) diblock in water, the rate constant for the fluorescence quenching of phenanthrene groups by oxidative non-ionic quencher is pH dependent. These authors suggested that at low pH the polyacid units are not fully ionized and may participate in the formation of hydrophobic domains, cooperatively with PVPT. An alternative explanation is that the PM A chains are less solvated when... 

The ionic strength effect is not limited to ksv variation as described by eq. (22). The addition of large amounts of electrolytes may also modify the quencher solubility and thus its efficiency. This effect has been used by some authors, in systems very different from those examined in this work, in order to determine the association constant of the inhibitor salt (Mac, 1997 Mac and Tokarczyk, 1999) as the electrolyte concentration is increased, the quencher ion associates, so that the effective concentration of the inhibitor ion decreases, leading to a downward curvature of the Stern-Volmer plot. Such a curvature can be quantitatively related... 

The Stern-Volmer equation (see sect. 4) may be used to determine small amounts of a species which would behave as an inhibitor of a given luminescent probe. The detection limit depends, among other parameters, on and on the detection limits of the setup. The potentials of this method for analytical purposes are discussed, on a general aspect, in Borissevitch (1999), Rakicioglu et al. (1998) and the specific cases of Eu(III) or U(VI) are presented in Georges (1993), Lopez and Birch (1996), Kessler (1998). For example, a detection limit of 7 ngl-1 for Cu2+ is obtained (Lopez and Birch, 1996). Numerous factors may render the method difficult to apply besides the variations of ksv as a function of ionic strength, if more than one quencher is present in solution, it becomes difficult to determine their individual concentrations. This problem has been studied in the case of solutions that more or less mimic the nuclear fuel solutions in Katsumura et al. (1989). 

Enhanced electron transfer quenching has also been observed in copolymers containing both ionic and hydrophobic segments [153], probably as a consequence of static quenching from preferential binding of the redox participants in electrostatically favorable regions of the polymeric aggregate. The hydrophobic domains in such polymers act as traps for hydrophobic quenchers, while the hydrophilic interactions enhance dispersion and solubility [154],... 

Another study involved native cytochrome c (iron containing) and the quenchers [Fe(CN)6] , dioxygen and p-benzoquinone. The influences of ionic strength and pH on the quenching abilities of these molecules in solution were investigated [205b]. It was found that the assumption of uniform dispersion of small species... 

Rhodamine 6G in an ionically conducting polymer were formed as a result of the local decomposition of the quencher, methyl viologen. The latter was incorporated inside the film with the dye and quenched the fluorescence of the Rhodamine 6G. However, when a tungsten tip biased at -4 V versus the platinum substrate was scanned at 1 /xm- s the quencher was decomposed, probably due to its reaction with hydroxyl ions that were generated at the tip, and the fluorescence of the dye was recovered. The authors concluded that the factors governing the resolution of the patterns were the... 

Fig. 10. Covalent and ionic potential curves for some NO-quencher pairs. Equation (26) was used to calculate the ionic curves, using the electron affinities of Table III. The covalent curves are Leonard-Jones potential of NO and the respective quencher, displaced by the electronic excitation energy of the appropriate Rydberg state. See text for further details.

In the only reversible approach [144], quatemized acridinium was immobilized on a solid support such as cellulose. In slightly alkaline medium, hydrogen sulflde adds to the strongly fluorescent dye and renders it nonfluorescent. Interferences by ionic quenchers may be eliminated by covering the sensor with a 4-pm silicone-rubber membrane which is permeable to gases but not to ions. The detection limit is of the order of 0.1 mmol L. ... 

Micelles can be formed from ionic, cationic, or neutral surfactants. The ionic micelles are the most common ones, and quenchers behave differently according to their charge. The charge on the surfactant is of no relevance for neutral quenchers. When the quencher has the same charge as the micelle monomer, it will be repelled, and only limited data are available for this situation. When the charge of the quencher is opposite that of the surfactant, the quencher will bind to the micelle consequently, its behavior is more complex due to the attractive interaction with the surface potential. 

For ionic quenchers, it is expected that the overall quenching efficiency will decrease if the quencher has the same charge as the micelle. This was shown for the quenching of pyrene by iodide in SDS micelles where the value for the ratio was determined to be 1170 [100]. Quenchers with op-... 

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