Studies on the voltammetric behavior of azo dyes and its determination in cosmetic products1

The voltammetric behaviors of azo dyes on glassy carbon electrode were investigated in an aqueous containing various supporting electrolyte. The possible reaction mechanisms were discussed by the relations of scan rate and peak potentials and currents. The electroreduction process is applied for the quantitative determination of Lithol Rubine B azo dyes cosmetic products. Comparison with results obtained from high performance liquid chromatography shows good agreement.     

Solvatochromism effects on the dipole moments and photo-physical behavior of some azo sulfonamide dyes

Absorption and emission spectra of three azo sulfonamide dyes with various molecular structures have been studied in different solvents. The solute photo-physical behavior depends strongly on the solvent-solute interactions and solvent microenvironment. In order to understand the effect of intermolecular interactions on spectral behaviors of these dyes in different solvents and to conceive nature and extent of solvent-solute interactions the spectral variations were analyzed by the linear solvation energy relationships concept. In addition, by means of solvatochromic method the dipole moments of these dyes, in ground and excited states, were investigated.     

Some triphenylmethane dyes as redox indicators in the titration of antimony(III) with cerium(IV) sulphate

Erioglaucine A, Eriogreen B, Patent Blue and Xylene Cyanol FF work satisfactorily for the titration of Sb(III) with Ce(IV) in 1-2N sulphuric acid medium with iodine as catalyst. In hydrochloric acid medium the colour of the oxidized dye is very evanescent but is very much improved in intensity and stability by the addition of manganese(II) sulphate; no catalyst is needed.     

Comparison of the characteristic behavior of two azo dyes on temperature dependent microstructure changes in micelles and vesicles

The new hydrophobic azo dye 4-(N-phenyl-N-decylamino)-4'-nitroazobenzene (AzoC10) has been synthesized. It is compared with 4-(N-phenylamino)-4'-nitroazobenzene (Azo) in terms of reactivity (k(iso) of the thermal cis-->trans isomerization, microsecond flash photolysis) and of the solvatochromic behavior (lambda(max) of the trans-isomer, UV/vis absorption), respectively, within membrane mimeting amphiphile microstructures in aqueous solutions of poly(ethylene oxide)(m)-poly(propylene oxide)(n)-poly(ethylene oxide)(m) micelles and of extruded vesicles. The temperature-induced micelle formation and phase transitions in bilayers of vesicles, respectively, caused characteristic discontinuous changes of k(iso) and lambda(max) with temperature. They differ between the two dyes due to their different solubilization sites and different impact on their microenvironment.     

Association of molecules of triphenylmethane dyes in poly(N-epoxypropyl carbazole) and its effect on the sensitizing properties of dyes

The association of triphenylmethane molecules in a poly(N-epoxypropyl carbazole) solid polymer matrix and its effect on the sensitizing properties of dyes were studied. Associates are formed from ion pairs involving triphenylmethane dyes, a process that can cause a decrease in the sensitizing ability of the dyes with respect to of poly(N-epoxypropyl carbazole). The rate of association depends strongly on the type of the counteranion of the cationic dye     

Screening and confirmation of triphenylmethane dyes and their leuco metabolites in trout muscle using HPLC-vis and ESP-LC-MS.

An extraction and clean-up protocol for the determination of Malachite Green and Crystal Violet and the corresponding leuco compounds in trout muscle has been developed. Final determination is by HPLC with visible (screening) or ESP-MS (confirmation) detection. In both cases lead(IV) oxide was used on-line to oxidise the leuco compounds back to the parent after chromatographic separation and prior to detection. The procedure was validated down to 2 micrograms kg-1. Intra- and inter-batch precision was measured at 3 levels for all compounds. Recoveries were in the range 66-116% with RSD of 1-17% for determination by HPLC with visible detection. For LC-MS determination, recoveries were in the range 61-94% with RSD of 4-15%. Limited surveillance data indicated that Malachite Green usage was more effectively monitored by including the leuco compound as well as the parent (9 positives for the leuco compound as opposed to 1 for Malachite Green out of 31 samples analysed).     

Effects of added metal ions on the interaction between polyvinylpyrrolidone and azo dyes carrying hydroxyl groups

The extent of binding of chrome violet, which is a monoazo dye and involves two hydroxyl groups in o and o′ positions to azo group, by polyvinylpyrrolidone is markedly enhanced in the presence of Co²⁺ ion. The amount of binding in the presence of 1 × 10^?4 mol/L of Co²⁺ ion increases by a factor of about 10 compared to that in the absence of the metal ion. Ni²⁺ and Zn²⁺ ions do not perceptively influence the binding affinity of the dye. Cu²⁺ ion, in contrast, suppresses the binding. To investigate further the action of added metal ions, a cobalt–complex dye was prepared and its binding property for the polymer was compared to that of chrome violet in the presence of metal ions. Some possible mechanisms for the enhancement of chrome violet binding by the addition of Co²⁺ ion are described.     

Ligand promoted reductive elimination from Zr(IV). The preparation of zirconacycles from alkylzirconium(IV) hydrides and alkynes

Alkynes induce reductive elimination of alkane from Cp₂Zr(H)(R); zirconacyclopentadienes are formed as well.     

The use of redox reactions in the analysis of dyes and dye intermediates: XVII. The influence of proton donors on direct current polarographic behavior of some water-insoluble azo pigments in acetonitrile

The influence of water and perchloric acid on the polarographic behavior of some water-insoluble azo pigments in acetonitrile has been investigated. The conditions were defined for the polarographic determination of the test substances in a mixed acetonitrile-water medium. The presence of strong acids prevents analytical use of these reactions.