As fluorescence quencher

Enzyme structure may be studied by fluorescence spectroscopy [238-244]. Excitation in the 280-310 nm absorption bands of proteins, usually results in fluorescence from tryptophan (Trp) residues in the 310-390 nm region. The fluorescence from the Trp residues is a convenient marker for protein denaturation and large decreases or red-shifts in fluorescence are observed when proteins are denatured. These changes are most often due to the exposure of the Trp residues that are buried in the protein and may be due to the changes in the proximities of specific residues that may act as fluorescence quenchers. Fluorescence emission characterization of the immobilized... 

For Lissamine attached to the smallest nanoparticles of 1 nm as fluorescence quenching of 99.8% is observed. This is made up from a 51-times decreased radiative rate and a 14-times increased nonradiative rate. Hence, for these small nanoparticles the effect of the reduced radiative rate prevails over the effect of an increased nonradiative rate due to energy transfer. The fact that the tiniest nanoparticles of just 1 nm radius quench the fluorescence by more than 99.8% makes them an interesting tool as fluorescence quenchers in biophysical applications, where it is essential that the nanoparticles do not mechanically disturb the sample. 

Figurel4 Molecular beacon utilizing a gold nanopaiticle as fluorescence quencher.

Emetine andcephaeline, the two major alkaloids of ipecacuanha, begin to fluoresce after treatment with iodine vapor [254], The molecular iodine, which acts as a quencher, must be removed by heating in the drying cupboard or on a hotplate... 

Factors such as dissociation, association, or solvation, which result in deviation from the Beer-Lambert law, can be expected to have a similar effect in fluorescence. Any material that causes the intensity of fluorescence to be less than the expected value given by equation (2) is known as a quencher, and the effect is termed quenching it is normally caused by the presence of foreign ions or molecules. Fluorescence is affected by the pH of the solution, by the nature of the solvent, the concentration of the reagent which is added in the determination of inorganic ions, and, in some cases, by temperature. The time taken to reach the maximum intensity of fluorescence varies considerably with the reaction. 

It is to be stressed that the action of quenchers is also accompanied by the effect of separation of conjugated blocks mentioned above. Thus, in the case of trinitrobenzene as a quencher, a concentration of trinitrobenzene of 1 x 10 3 mol/1 is quite sufficient for complete quenching of DPAcN fluorescence (7% double bonds, r0 =... 

T. Ando and H. Miyata, Pyruvate as a fluorescence quencher Anew specttoscopic assay for pyruvate reactions, Anal. Biochem. 129, 170-175 (1983). 

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)... 

Use of the pH-sensitive membrane-impermeable flurophore pyranine based on the ratiometric method, which determines directly level of dissociation of pyranine from the ratio between the charged (nnprotonated) pyranine and total pyranine in the intraliposome aqneons phase Addition of impermeable DPX, which acts as a quencher to pyranine fluorescence, into the liposome external medium ensures lack of contribution of extraliposome medium pyranine fluorescence (18,22). This method is considered invasive as the pyranine has to be added in the hydration medium prior to liposome preparation and cannot be used for pH determination of intraliposome aqueous phase... 

Here, is the rate constant for radiative decay (fluorescence), while k r is the combined rate constant for aU non-radiative decay processes, is virtually constant and is an inherent property of the material in question, and for this material is significantly greater than k r, given the high fluorescence efficiency. When a fluorescence quencher, such as TNT, is introduced, km increases because an additional efficient non-radiative pathway now exists. This, via Eq. (4), makes r smaller. 

Despite the high energy of the excitation, fluorescence emission may be quenched by a range of quenchers, such as iodide (I- and Cu ). The net effect of a quencher is that the observed fluorescence emission reduces as the quencher concentration increases (typically milli-molar concentrations are employed). This is due to an energy transfer between the excited fluorophore and the quencher. The quencher thus provides an alternative relaxation pathway for the excited molecule. Not surprisingly the effect of the... 

Fig. 49. Estimates for the rate coefficient of a second-order bimolecular reaction (such as fluorescence quenching) in solution. The quencher species, for instance, is present in large quantities, occupying a fraction c of the total volume. If this species has a spherical radius of R, the volume fraction is c = 4irI Jp/3, where p is the density of...

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