Anthraquinone sensitizer

In the anthraquinone-sensitized photopolymerization of acrylate monomers, the percent conversion depends markedly on the nature of the solvent as well as on the type of monomer. Ethyl and n-butyl methacrylate, for example. 

Sensitizers such as benzophenone, anthrone and xanthene were also observed to catalyze these reactions [327]. Anthraquinone sensitized photoreactions of N-allylamines with a,jff-unsaturated esters also yield lactams as the main product. Minor amounts of tandem radical addition products were also formed [328]. 

Stannett and coworkers (17, 18) have shown that anthraquinone-sensitized photopolymerizations on celluloses and nylon involve the triplet state of the dye and semiquinone intermediates in photoinitiation. In addition, anthraquinones (17, 18) were also known to photosensitize degradation of polymers. 

Bortolus and Galiazzo18 have studied the photochemical trans-cis-isomerization of the styrylnaphthalenes (12) and (13), by both direct and anthraquinone-sensitized irradiation. The influence of oxygen upon the irradiation has shown... 

In addition to the color and the tinctorial strength, which ate very important factors for the molecular design of anthraquinone dyes, affinity for fibers, various kinds of fastness (light, wet, sublimation, nitrogen oxides (NO ) gas, washing, etc), and apphcation properties (sensitivity for dyeing temperature, pH, etc) must be considered thoroughly as well. 

The dyes used in the ink sheet must satisfy various requirements (/) optimum color characteristics of the three primary colors (hue, color density, shape of absorption spectmm) (2) sensitivity, ie, sublimabiHty from ink sheet to acceptor sheet (3) fastness for light and migration and (4) compatibiHty with the resin in the ink sheet. With respect to these characteristics, a large number of anthraquinone dyes have been proposed particularly for magenta and cyan colors. Typical examples are given in Table 8 and Table 9. 

Electrospray has been successful for numerous azo dyes that are not ionic salts. Several anthraquinone dyes have been analysed by LC-ESI-MS [552]. Electrospray achieves the best sensitivity for compounds that are precharged in solution (e.g. ionic species or compounds that can be (de)protonated by pH adjustment). Consequently, LC-ESI-MS has focused on ionic dyes such as sulfonated azo dyes which have eluded analysis by particle-beam or thermospray LC-MS [594,617,618]. Techniques like LC-PB-MS and GC-MS, based on gas-phase ionisation, are not suitable for nonvolatile components such as sulfonated azo dyes. LC-TSP-MS on... 

Anthraquinones are nearly perfect sensitizers for the one-electron oxidation of DNA. They absorb light in the near-UV spectral region (350 nm) where DNA is essentially transparent. This permits excitation of the quinone without the simultaneous absorption of light by DNA, which would confuse chemical and mechanistic analyses. Absorption of a photon by an anthraquinone molecule initially generates a singlet excited state however, intersystem crossing is rapid and a triplet state of the anthraquinone is normally formed within a few picoseconds of excitation, see Fig. 1 [11]. Application of the Weller equation indicates that both the singlet and the triplet excited states of anthraquinones are capable of the exothermic one-electron oxidation of any of the four DNA bases to form the anthraquinone radical anion (AQ ) and a base radical cation (B+ ). 

Fig. 2 Structures of the anthraquinone-linked sensitizers. AQ is covalently attached to the 5 -end of one strand. UAQ can be placed at any position, and the attached anthraquinone intercalates in duplex DNA at the 3 -side of its linked nucleotide...

The anthraquinone group of the UAQ sensitizer is intercalated on the 3 -side of its linkage site [15]. Use of UAQ permits assessment of the directionality of long-range radical cation migration. Both AQ and UAQ enable the selective and efficient introduction of a radical cation in duplex DNA, whose lifetime is controlled by its relatively slow bimolecular reaction primarily with H20. 

Irradiation of alcohols (ethanol, isopropanol, etc.) with maleic acid in the presence of benzophenone or anthraquinone as sensitizer leads to 1 1 addition products<78) ... 

Statistical evaluation of HPLC UV MS[19] and CE UV MS[20] methods proves that MS detection of anthraquinone dyes is more sensitive than UV, especially in the case of chromatographic analysis of laccaic acids (almost 20 times) and purpurin (almost 40 times). However, detection limits of HPLC ESI MS determination of alizarin and purpurin (0.03 gg ml ) are about 20 times lower than those of CE ESI MS (0.52 0.58 gg ml x). 

Rate constants and the products formed in the hydrolysis of Cl Reactive Red 194 (7.76) at 50 °C and pH values in the 10-12 region were determined by high-pressure liquid chromatography. In addition to the normal hydrolysis of the two reactive systems, the imino link between the triazine and benzene nuclei was also hydrolysed [67]. The heterobifunctional copper formazan dye Cl Reactive Blue 221 and two blue anthraquinone monofunctional reactive dyes of the bromamine acid type, namely the aminochlorotriazine Blue 5 and the sulphatoethylsulphone Blue 19, were compared in terms of their sensitivity to... 

A number of papers have reported studies on pyrimidine radical cations. 1-Methylthymine radical cations generated via a triplet-sensitized electron transfer to anthraquinone-2,6-disulfonic acid were detected by Fourier transform electron paramagnetic resonance (FTEPR). The parent 1-methylthymine radical cation, and its transformation to the N(3)-deprotonated radical cation, were observed. Radical cations formed by addition of HO and POs" at C(6) were also detected depending on the pH. Similarly, pyrimidine radical cations deprotonated at N(l) and C(5)-OH were detected from the reaction of 804 with various methylated pyrimidines." These radicals are derived from the initial SO4 adducts of the pyrimidines. Radical cations of methylated uracils and thymines, generated by electron transfer to parent ions of... 

ILs have been used to separate and determine the purity of anthraqui-nones. Rapid and sensitive determination of anthraquinones in Chinese herb using l-butyl-3-methylimidazolium-based IL with p-cyclodextrin (p-CD) as a modifier in CZE was provided by Qi et al. [49]. Successful separation and identification of four anthraquinones of Paedicalyx attopevensis Pierre ex Pitard extracts has been achieved. In the running electrolyte the anthraquinones may associate with the imidazolium ions or with the p-CDs. They may be entirely or partly embedded in the cavity of the p-CDs, so the association with the free imidazolium ions in the bulk solution was weak and those analytes, that were not embedded in the cavity of the p-CDs had rather stronger association with the imidazolium ions in the system. The mechanism of separation is illustrated in Figure 6.6. 

Qi, S., Cui, S., Chen, X., and Hu, Z., Rapid and sensitive determination of anthraquinones in Chinese herb using l-butyl-3-methylimidazolium-based ionic liquid with P-cyclodextrin as modifier in capillary zone electrophoresis, /. Chromatogr. A, 1059,191-198, 2004. 

More extensive studies using somewhat higher wavelengths have been reported by Geacintov et al. (111, 112). These authors used phototendering dyestuffs notably the sodium salt of anthracene 2,7 disulfonic acid as the sensitizer in aqueous solution. For grafting to cellulose acetate and ethyl cellulose 2-methyl anthraquinone which is soluble in organic solvents was used. The mechanism proposed was the removal of a... 

Functional dyes - p YES, SENSITIZING] (Vol 8) -from anthraqumones [DYES, ANTHRAQUINONE] (Vol 8)... 

Acylation of 1-amino- or 1,5-diaminoanthraquinones yields yellow vat dyes and affords red to ruby colored dyes when 1,4-diaminoanthraquinones are used. Use of 4,8-diamino-l,5-dihydroxy-anthraquinones gives violet to blue dyes. The relatively low lightfastness of the yellow acylaminoanthraquinones may be improved greatly by using azodiphenyl-4,4 -dicarboxv 1 ic acid. Acylaminoanthraquinones are relatively sensitive to atmospheric conditions. 

The mechanisms involved in dimer cleavage have been examined in simple model systems [90,261-263], including bifunctional ones in which a sensitizer (e.g. indole) is linked to the pyrimidine dimer [264, 265]. For example, the cw-head-to-head dimer of dimethylthymine (88) was cleaved efficiently upon irradiation of anthraquinone-2-sulfonate CIDNP effects observed during this reaction failed to reveal any evidence for the existence of the dimer radical cation [90]. Time-resolved... 

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