Nitroxides fluorescence quenching

Rachel, K., Asuncionpunzalan, E. and London, E. (1995) Anchoring of tryptophan and tyrosine analogs at the hydrocarbon polar boundary in model membrane-vesicles - paralax analysis of fluorescence quenching induced by nitroxide-labelled phospholipids. Biochemistry 34,15475-15479. 

Figure 26 also depicts the distances calculated from fluorescence quenching experiments by enzyme-bound Co2+ on the s-adenosine moiety of s-ATP adenylylated glutamine synthetase (e-AMP-GS). Additional data were gathered by an EPR method that measured the decrease in EPR amplitude of the nitroxide spin-labeled adenylylated enzyme (TEMPO-AMP-GS) owing to enzyme-bound Mn2+ (122). Distances between Mn2+ and the N—O of the spin label are also shown in Fig. 26. 

Lozinsky E., Shames A., and Likhtenshtein G.I. (2001) Dual fluorophore-nitroxide molecules Models for study of intramolecular fluorescence quenching and novel redox probes. In Recent Research Development in Photochemistry and Photobiology., V. 2, Transworld Research Network. Trivandrum, pp. 41-55. 

Hideg fi, Kilai T, Hideg K et al. Photoinhibidon of photosynthesis in vivo results in singlet ojcj en production detection via nitroxide-induced fluorescence quenching in broad bean leaves. Biochemistry 1998 37 11405-11411. 

In such hybrid compounds, the nitroxide moiety quenches the fluorescence of the fluorophore (stilbene moiety). The reduction of nitroxide segment by an antioxidant (ascorbic acid) caused a rise in fluorescence of the fluorophore. The rate constant of the stilbene fragment photoisomerization in such systems depended on the viscosity of the medium. The synthesized dual stilbene-nitroxide probe was covalently immobilized onto the surface of a quartz plate as an eventual sensor. The immobilization procedure included a cyanogen bromide surface activation followed by smoothing with a protein tether. The rate of fluorescence change was monitored in aqueous glycerol solution of different viscosities and content of ascorbic acid. The dependence of kapp on the reciprocal absolute viscosity 1 /T] of the bulk mixture glycerin-water and the dependence of the initial intensity of fluorescence (/o) on solution viscosity were also studied. 

Lipid peroxidation caused a decrease in phospholipid molecule mobility both in the region of polar heads and in the region of acyl chains till the depth of at least 1.7 nm from water-lipid interface (Panasenko et al. 1991). Under relative high levels of oxidation (>6 pmol malondialdehyde/g LDL phospholipid) the polarity of lipid phase increased. The decrease in efficiency of tryptophan fluorescence quenching by nitroxide fragments incorporated into hydrophobic regions at the depth of 2 nm from water-lipid interface indicated that lipid-protein interaction was disturbed as a result of oxidation of LDL lipids. 

Nitroxides have the property of quenching fluorescence. Thus radical trapping with nitroxides containing fluorophores (e.g. 114) can be monitored by observing the appearance of fluorescence.511015 The method is highly sensitive and has been applied to quantitatively determine radical yields in PLP experiments (Section... 

The physical basis of the second type of approach rests upon the effect of the local electrostatic potential upon dynamic interactions at encounters with charged quenching molecules resulting in fluorescence (phosphorescence) (Vogel et al., 1986 Anni et al., 1994) or between a stable radical, e.g. nitroxide, and another charged paramagnetic species (Likhtenshtein et al., 1972 Likhtenshtein, 1976, 1988,1993). In such cases, the relaxation parameters, i.e. the life-time of the fluorescence (phosphorescence) chromophore or spin-spin and spin-lattice relaxation rates of paramagnetic species are dependent upon the frequency of encounters, and, therefore, on local electrostatic fields... 

From a study of fluorescence and triplet quenching of a series of aromatic hydrocarbons by tetramethylpiperidine nitroxide (TEMPO) in methylcyclohexane it has been concluded that both quenching processes (10) and (11) are the result of... 

As shown in Fig. 1.16a, upon addition of CATl the fluorescence of P6 is efficiently quenched. The ( )-6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid (trolox) is added and allowed to equilibrate for 35 min, which reverses the quenching due to the scavenging of nitroxide radicals via hydrogen transfer from trolox to CATl. The fluorescence recovery depends on the concentration of trolox (Fig. 1.16b). The trolox can be detected in the range of 10 100 pM. The same probe can also be used to detect the capabilities of a variety of antioxidants. Sensing for ascorbic acid can be accomplished with high sensitivity and selectivity because of its excellent antioxidant capabilities. The ascorbic acid concentration can be determined in the 50 nM to 200 pM range (Fig. 1.17a). Control experiments were also done with a nonspecific quencher. A , A -dimethyl-d, 4 -bipyridinium (MV +) for ascorbic acid. As shown in Fig. 1.17b, upon addition of MV +, the fluorescence of P6 is... 

Perylene bisimide-linked nitroxide (PBILN) is used as a fluorescent reagent, which permits the selective determination of AA. The fluorescence of the perylene bisimide moiety in PBITN is quenched by the nitroxide moiety, which is linked to the perylene bisimide. When a stream of AA is merged with a stream of PBITN, the AA reacts with the nitroxide moiety of PBITN to form hydroxylamine, and the fluorescence properties of the perylene bisimide moiety are recovered 0.28 10 1.0 Fruit juices, soft drinks 2011 151... 

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