Antioxidants fluorescence quenching

Mooradian (1993) has studied the antioxidant properties of 14 steroids in a non-membranous system in which the fluorescence of the protein phycoerythrin was measured in the presence of a lipid peroxyl radical generator (ABAP). Oxidation of the protein produces a fluorescent species. Quenching of fluorescence by a test compound indicates antioxidant activity. Oestrone, testosterone, progesterone, androstenedione, dehydroepian-drosterone, cortisol, tetrahydrocortisone, deoxycorti-... 

Additive and impurity rejection at the growing crystal front leads to uneven distribution in a crystalline polymer. This redistribution process has been studied by UV and fluorescence microscopy and by an electron microscope with energy dispersive x-ray analysis. In polymer samples which are quenched after rapid crystallization, the additive distribution is kinetically determined and may be modeled in a computer as a three-dimensional zone-refining process. In annealed polymer samples, low molecular weight additives are uniformly concentrated in the amorphous phase. The additive distribution reflects that of crystalline material within the polymer. Antioxidant and uv stabilzer redistribution probably does not have a major effect on polymer stability, but the redistribution of partially oxidized, impure polymer may be important... 

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... 

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. 

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