Naphthalene fluorescence quenching

Proteases are enzymes that break peptide bonds in proteins. As such they lend themselves to a variety of homogeneous assay techniques. Most employ labeling both ends of the substrate with a different tag, and looking for the appearance (disappearance) of the signal generated in the intact substrate (product). As an example, for a fluorescence quench assay, the N-terminal of a peptide is labeled with DNP and the C-terminal with MCA. As such, the peptide is fluorescently silent since the fluorescence from DNP is quenched by absorption by the MCA. Another very popular donor/acceptor pair is EDANS 5-[(2-aminoethyl)amino] naphthalene-1-sulfonic acid and DABCYL 4-(4-dimethylaminophenylazo)benzoic acid) (a sulfonyl derivative (DABSYL) [27], Upon peptide cleavage, the two products diffuse, and due to a lack of proximity, the fluorescence increases. 

A recent study of Murov and co-workers<106) indicates that the activation energies for isomerization are not the controlling factors. Thus the fluorescence of naphthalene is quenched (5 x 108M-1sec-1) by cis-trans-1,3-cyclooctadiene with isomerization to form cis-cis-1,3-cyclooctadiene. However, the compound bicyclo[4,2.0]oct-7-ene is not formed despite the low activation energy for this process ... 

Similarly, 2,3-dimethyl-l,3-butadiene quenches naphthalene fluorescence (1.7 x 107 M-1 sec-1) but does not rearrange ... 

A singlet naphthalene or a singlet exciplex is thought to be the reactive species in this reaction since the quantum yield of cycloaddition parallels the quenching of naphthalene fluorescence by acrylonitrile. 

Photo-oxidation of protoporphyrin IX and its dimethyl ester Norrish type II reaction of amphiphilic ketoacid Quenching of naphthalene fluorescence by Ni2 +... 

Samples (3 mL) of substrate containing cultures were taken at 24, 48 and 120 h after substrate addition and extracted with equal volumes of ethyl acetate. The organic phases were separated by centrifugation for 3 min in a desktop centrifuge and used for TLC analysis. 30 0 pL of sample extracts were spotted onto TLC plates that were developed with ethyl acetate hexane (v/v). Visualization of TLC plates was done by fluorescence quenching under 254 nm UV light. 7 f values were naphthalene, 0.90 ... 

The confusion generated in the initial report185 on photoracemization of sulfoxides has recently been removed with the postulate that naphthalene singlet forms an excited complex with sulfoxides.186 Thus, despite the fact that the singlet state of 36 lies at 113 kcal, some 23 kcal above that of naphthalene, 36 quenches the fluorescence of this hydrocarbon with kes = 3.2 x 107Af -1 sec-1. From the dependence of the quantum yield of racemization on sulfoxide concentration (Eq. 34), a value of kes = 2.3 x 107Af-1 sec-1 was deduced. Since these values are the same within experimental error, it follows that the singlet state of naphthalene is responsible for photoracemization. 

Steel and coworkers194 have also noted that 2,3-diazabicyclo[2.2.1]-heptene-2 (39) quenches the fluorescence of naphthalene. A more extensive study of this compound was carried out by Engel195 who reported that there was a sharp drop in the efficiency of sensitized decomposition and in the rate of sensitizer fluorescence quenching as the sensitizer singlet energy fell below that of 39. This points out a key difference between azo compounds and the cases discussed previously namely, there is a spectroscopic azo singlet state lying below that of the sensitizer. 

Similarly, the luminescence of complexes 38,39,40,41, and 42 can be modulated by changing the redox states of the respective metal ions. Complexes 38 and 39 show emission in the Ni(II) state, whereas the emission is quenched in the Ni(III) state generated after oxidation.46 The fluorescence due to the naphthalene unit in complex 40 is observed in the Ni(II) state after reduction to the corresponding Ni(I) state the naphthalene fluorescence is distinctly reduced.47 Water-soluble complexes 41 and 42 also works as redox-responsive fluorescence switches in a similar way 48... 

Assuming that the true encounter distance is about 1.20 nm (the exact value is not very important), feact > 4 x 109 dm3 mol-1 s-1. The quenching of 1,2-benzanthracene and naphthalene fluorescence by carbon tetrabromide can also be followed by illuminating a solution with light of constant intensity and measuring the fluorescence intensity, /, for a number-of solutions containing different quencher concentrations. These steady-state experiments of Nemzek and Ware [7] are discussed in Sect. 5.5. 

While no spectroscopic evidence of a ground-state complex between anthracene and carbon tetrachloride, naphthalene or 1,2-benzanthracene and carbon tetrabromide has been found, Nemzek and Ware [7] were unable to explain their steady-state fluorescence quenching measurements with the parameters deduced from the determination of the time-dependent rate coefficients unless a ground-state complex was present. This cannot be regarded as a satisfactory and consistent analysis because the time-dependent rate coefficient would be modified by the presence of the initial distribution of quencher and fluorophor in the ground state. 

Morra, M. J., Corapcioglu, M. O., von Wandruszka, R. M. A., Marshall, D. B. Topper, K. (1990). Fluorescence quenching and polarization studies of naphthalene and 1-naphthol interaction with humic acid. Soil Science Society of America Journal, 54, 1283—9. 

Wilkinson has recently described a novel approach.113 It has long been known that solvents containing heavy atoms markedly quench the fluorescence of aromatic hydrocarbons, and it has been shown that this effect arises from an enhancement of the rate of intersystem crossing. Thus the ratio of phosphorescence to fluorescence for naphthalene irradiated at 77°K can be increased more than a hundredfold upon addition of some isopropyl iodide to the solvent.114 The same effect has been noted upon changing from hydrocarbon glasses to frozen krypton and xenon matrices.115 Wilkinson found that the decrease in fluorescence intensity from irradiated solutions of anthracene and some of its derivatives upon addition of bromobenzene is attended by an increase in T-T absorption intensity.116 The fluorescence quenching follows the Stern-Volmer law ... 

Dienes quench naphthalene fluorescence although they have no excited state of lower energy than the Sx state of naphthalene. Apparently, quenching is due to an exciplex that either undergoes radiationless transition to ground-... 

Using the temperature effect, it was proven that non-emitting exciplex intermediates were also involved in the cycloaddition. For example, in the reaction of naphthalene with diphenylacetylene, with increasing temperature both the quantum yields of photoaddition and the quenching of the naphthalene fluorescence by acetylene decrease by the same magnitude [65],... 

When considering the rates of chemical processes in polymers which require diffusion of reagents and products, it is necessary to estimate the internal viscosity q. to substitute in expressions such as Equations 6 and 7. We ave made estimates for q in solid polyethylene from luminescence quenching of naphthalene fluorescence in ethylene -OO copolymers [24]. (Table VII)... 

The electron-transfer-induced chemistry of bicyclobutane systems offer a rich variety of reactions. Irradiation of naphthalene in the presence of 46 resulted in rapid fluorescence quenching without rearrangement. In contrast, irradiation with either 1-cyanonaphthalene or 9,10-dicyanoanthracene in solutions containing derivatives of 46 resulted in product formation. The product distribution obtained under electron-transfer conditions is compatible with radical cations of structure type 46 +, which is firmly established by ESR and CIDNP results. Nucleophilic capture of the 1,2,2-trimethyl derivative, 50", led to cleavage of the transannular bond. The initial eapture is followed by net addition, producing 51, or dehydrogenation, yielding 52 [179]. 

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