Oxygen fluorescence quencher

Even before the fluorescence-quencher hypothesis was proposed, however, it had been suggested that plastoquinone may be an important electron carrier in green-plant photosynthesis. Bishops reported in 1959 the significant finding that extraction of PQ from chloroplasts results in the loss ofthe ability to evolve oxygen but that upon reconstitution with plastoquinone, oxygen-evolution activity is restored. 

In spite of the use of oxygen as a fluorescence quencher for many decades, the fact that many hours may be required for equilibration, especially in biological systems, has recently been... 

The recombination of trapped electrons and holes produces the fluorescence. Adsorbed oxygen scavenges electrons producing O2" which also is adsorbed. OJ is a much better quencher than Oj. Its accumulation under illumination therefore leads to the decrease in fluorescence intensity. During the dark period disappears. During the illumination in the presence of oxygen, the colloid undergoes photoanodic dissolution (see Sect. 3.2). The ZnS particles become smaller in this way, and this finally leads to an increase in fluorescence yield as already described for CdS. 

In the silica nanomatrix, the low diffusion was also reported in both liquid and gas phases. In the gas-phase reaction, it was found that the luminescence signal of Ru(bpy)32+ doped in DDSNs remained stable when the air pressure increased from 1 to 8 psi, showing no quenching by oxygen in the air. When the air pressure was further increased to above 8 psi, a decrease in fluorescence emission intensity was observed. The results suggested a slow diffusion of quencher oxygen in the silica nanomatrix. 

In testing the possibility of proton transfer as a quenching mechanism of tyrosine in oligopeptide/polynucleotide complexes, Brun et a/.(102) compared the fluorescence emission spectra of the tyrosine and O-methyltyrosine tripeptides. They noted that, in the complex, the O-methyltyrosine tripeptide had a unique secondary emission near 410 nm. Whether this emission is related to that observed by Libertini and Small(94) is an important question. While one must consider the possibility that two tyrosine side chains could be converted to dityrosine, (96) which has a fluorescence at 400 nm, another intriguing possibility is ambient temperature tyrosine phosphorescence. This could happen if the tyrosine side chain is in a rigid, protective environment, very effectively shielded from collisions with quenchers, particularly oxygen. 

Small molecules that act as collisional quenchers may penetrate into the internal structure of proteins, diffuse, and cause quenching upon collision with the aromatic groups. Lakowicz and Weber(53) have shown that the interaction of oxygen molecules with buried tryptophan residues in proteins leads to quenching with unexpectedly high rate constants—from 2 x 109 to 7 x 109 M l s 1. Acrylamide is also capable of quenching the fluorescence of buried tryptophan residues, as was shown for aldolase and ribonuclease 7V(54) A more hydrophobic quencher, trichloroethanol, is a considerably more efficient quencher of internal chromophore groups in proteins.(55)... 

Kropp and Windsor also examined the effect of oxygen on the fluorescence properties of rare-earth solutions. They found that the lifetimes remained constant to 0.5 per cent for (a) normal air-equilibrated solutions, (b) solutions that had been flushed with helium, and (c) pure-oxygen-flushed solutions. This last effect is in variance with the well-established fact that dissolved oxygen is an efficient quencher of fluorescent aromatic compounds. 

Because of the spin exchange requirement, a close approach of the fluorescer and the quencher is required. Hence oxygen quenching is diffusion controlled. The increase in the rates of injersystem crossing has... 

Reaction in presence of oxygen The oxidation reaction proceeds from, the triplet state- of tli3 molecule as already postulated. Oxygen is kn to be a powerful quencher of fluorescence but for solutions in CO , except lot 9 ,/.l -diciiioro compouiio, me quenemug is practically coin... ... 

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