Cyanine bleaching

Nonmedical uses envisaged include as growth promoters, indicators for copying processes, analytical complexing agents, cyanine dyes and dye-bleaching catalysts. 

Analysis. Be can be quantitatively determined by colorimetry down to 40 ppb using eriochrome cyanine R or acetylacetone. The sensitivity may be improved by electrothermal absorption spectroscopy (ETAS) to 1 ppb and to 0.1 ppb by inductively-coupled plasma emission spectroscopy (ICPES) or inductively-coupled plasma mass spectroscopy (ICPMS). A simple spot test for qualitative detection of Be is one with quinalizarin in alcoholic NaOH which can detect 3 ppm. The color is produced by both Be and Mg. If the color persists after the addition of Br2 water. Be is present. If the color is bleached. Mg is indicated. 

Sulfonated Fe and Mn phthalocyanines are catalysts for the oxidative degradation of chlorinated phenols such as 2,4,6-trichlorophenol, a contaminant from paper mills that use chlorine for bleaching. Fe-tetrasulfophthalo-cyanine supported on poly(vinyl-4-methylpyridinium) converts 2,4,6-trichlorophenol with the K+ salt of Caro s acid, KHSO5, or H2O2 as the oxidant (112) ... 

Much larger RISC values were found for the cyanine dyes 56-58 [38]. A similar two-color technique was used to measure these yields with the exception that meyo-tetraphenylporphyrin was used in place of Aberchrome 540 as the two-laser actinometer. As Table 4 shows, there is an inverse relationship between the triplet depletion (bleaching) quantum yield, 4>B1, and the 5 —> T ISC yield, 1SC. Thus a large value for 4>B1 was accompanied by a small 4>ISC. This reflects the cyclic flow of energy following excitation of Tx to Tn. Once RISC has occurred, decay of the S, state partitions between ISC and fluorescence. If 4>ISC is small, relatively few Sj states will be cycled back to T and 4>B1 will be large. This effect masks the actual efficiency of RISC. Thus the ratio < B1/(1 — isc) s giyen as 311 indicator of RISC efficiency. 

Several fluorescent labeling dyes are commercially available (Alexa series, Oregon green, Rhodamine and Cyanine dyes, etc.). They are all characterized by the presence of double bonds on every other carbon atom of a cyclic structure, containing the electron that once on excitation emitted fluorescent light. The cyanine dyes are the most widely used at the moment. They are bright, easily added to the nucleotides, stable to photo-bleaching and with a Stokes shift value of about 20 nm. The cyanine dyes used in microarray analysis are Cy3 (absorption at 550 nm and emission at 570 nm) and Cy5 (absorption at 649 nm and emission at 670 nm) that are already available as phosphoramidite derivatives. 

More recently, Schuster [25] has demonstrated that cyanine dyes, i.e., cyanine borates or cyanine dye-borate mixtures, provide visible light activated initiation of free radical polymerization [26]. The photoexcited cyanine dye oxidizes alkyltriphenylborates by PET to produce the bleached reduced cyanine along with an alkyl radical. The alkyl radical can then initiate free radical polymerization [27], This visible light activated PET bond cleavage is of considerable importance in photoimaging and photocuring [28]. 

Other interesting photosensitive materials are alkylborates of cyanine dyes [5, 6]. An electron transfer from the alkylborate anion to the photoexcited cyanine dye causes the decomposition of the alkylborate to produce colorless alkyl-substituted cyanine dye derivatives (Scheme 3). The color of the cyanine dyes is bleached by photoirradiation. By mixing three kinds of alkylborates of cyanine dyes, yellow, magenta, and cyan, with vinyl monomers it is possible to construct a full color printing system. 

Figure 2. a) Transient absorption spectra recorded after excitation of di- -butyltetramethylindo-carbocyanine benzyltriphenylborate in benzene solution with a 18 ps laser pulse. Negative absorbance related to the bleaching of the dye absorption. The band at Amax = 430 nm is attributed to the presence of the cyanine dye radical b) transient absorption spectra recorded after excitation of naphthyltriphenyl borate in benzene solution with a 18 ps laser pulse. The new feature is attributed to the presence of the (2-naphthyl)methyl radical c) the difference spectrum obtained by subtracting spectrum A from spectrum B the maximum at 385 nm is characteristic for the 2-methylnaphthyl radical. Data are taken from [25],... 

This surfactant possesses a CMC value of 3 x 1(T4 M. The micellar aggregates formed are relatively large, the molecular weight being 6.3 x 106 as determined by quasielastic light scattering technique. A variety of sensitizers, when solubilized in aqueous micellar solutions of II were shown to be oxidatively bleached under simultaneous formation of Ag°. Consider, for example, the cyanine dye ... 

Its fluorescence emission is totally quenched (0jpmicellar solutions of II. Instead, under visible light illumination one observes a rapid bleaching of the cyanine and formation of a new stable absorption band with a maximum at X = Ul5 nm. The spectrum can be attributed to silver atoms stabilized by the macrocyclic ligand. It appears that through insertion in the crown ether cavity Ag is prevented from aggregation and hence preserved in the monoatomic state. 

This method is based on the bleaching action of fluoride ion content of the sample. The color of fhe red Zr-solochrome cyanine R (Aldrich Cat. No. 23,406-0, Sigma Prod. No. E2502) [52] complex fades as ZrOp2 is formed in the medium. As a matter of fact, no simple stoichiometric relationship exists between the fluoride and the zirconium complex with the dye. Therefore, in order to obfain reliable results, the reaction conditions need to be controlled very carefully. The absorbance of fhe reaction media is measured at 540 nm. The fluoride concenfrafion is evaluated using an absorbance-fluoride concentration calibration curve prepared with standard solutions. The method can be used for samples containing 0-2.5 pg fluoride. 

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