Cerimetric determination of triphenylmethane dyes

Summary The cerimetric determination of the carbinol bases of crystal violet, magenta, and ethyl violet is described. Best results are obtained by applying reverse titration.

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Zusammenfassung Die Carbinolbasen von Kristallviolett, Fuchsin und Äthylviolett werden cerimetrisch bestimmt. Die besten Ergebnisse erhält man bei umgekehrter Titration.

     

A convenient preparation of xanthene dyes

A facile synthetic route utilizing readily available reagents affords a series of regioisomerically pure xanthene dye derivatives. Advantages include relatively mild conditions and good to excellent yields. Nonpolar, highly crystalline intermediates are isolable by standard chromatographic techniques. The intermediates are in the requisite xanthene oxidation state, thus avoiding the need for relatively inefficient oxidation chemistry and/or harsh conditions. During the course of this work, a new boron-mediated 1,2-aryl migration reaction was discovered.     

Photostabilization of xanthene,triarylmethane, and azine dyes in polymeric matrix

Lightfast of red xanthene and blue azine and triphenylmethane dyes in mixtures with azo dyes of 1-phenyl-3-methyl-5-pyrazolone in the polymer films from cellulose acetobutirate were studied.     

Inverse voltammetry of antimony with triphenylmethane dyes

A method is suggested for the determination of traces of antimony by inverse voltammetry of the solid phases formed with triphenylmethane dyes (Crystal Violet, Methyl Violet and Malachite Green) as the precipitants. The authors have studied the effect of concentration, adsorption and oxidation of the triphenylmethane dyes, potential and time of pre-electrolysis, and concentration of antimony(III) and some other elements on the polarogram shape and stripping current. A method for determining antimony traces in chromic salts is described as an example.     

The optical properties of molecules and chromogenic aggregates of xanthene dyes

The UV absorption spectra of rhodamine B and G molecules isolated from industrial dye samples were obtained. Two procedures were used. In one of them, rhodamine B molecules were displaced with water into a heptane layer from a solution of the dye in an alcohol-heptane mixture. The second procedure involved heating of the dye introduced into cellulose triacetate films. Individual rhodamine molecules (namely, dye cation-chlorine anion ion pairs) prepared by both methods did not absorb visible light. The spectra of individual rhodamine molecules coincided with the spectra of so-called pseudoleucobases of xanthene dyes reported in the literature. The conclusion was drawn that the chromaticity property in the series of xanthene dyes appeared because of the formation of supramolecular dimeric and larger aggregates, as was earlier established for triphenylmethane dyes (TPMDs) and copper phthalocyanine (CuPc). At the same time, individual xanthene dye molecules, like TPMD and CuPc molecules, are not chromogens.     

Synthesis and properties of polymeric azine and thiazine dyes

Some polymeric azine or thiazine dyes were prepared by radical polymerization of dye monomers or by polymer reactions between dyes and suitable prepolymers, and their photoredox reactivities were studied. The thionine polymers containing labile ? OH groups exhibited photochromism and thermochromism, which were extremely sensitive to the moisture content of the polymer film. The reversibility of the photochromism and thermochromism increased with the water content in the film. The water-soluble polymeric dyes were photobleached under the influence of suitable reducing agents. The degree of photobleaching was smaller than for the monomeric systems except for the dye polymers containing ? OH groups, probably because of the large steric hindrance of the polymers.     

Photophysics of xanthene dyes in surfactant solution

The spectral (both absorption and fluorescence) and photoelectrochemical studies of some anionic xanthene dyes namely erythrosine B, rose bengal and eosin have been carried out in micellar solution of cationic cetyl trimethyl ammonium bromide (CTAB), anionic sodium dodecyl sulphate (SDS) and neutral triton X-100 (TX-100). The results show that all these dyes form 1:1 electron-donor-acceptor (EDA) or charge-transfer (CT) complexes with TX-100, which acts as an electron donor. There is no interaction of these dyes with SDS, whereas the interaction with CTAB is mainly electrostatic in nature. In presence of TX-100, these dyes show enhancement of fluorescence intensity with a red shift and develop photovoltage in a photoelectrochemical cell. A good correlation has been found among the photovoltage generation in the systems consisting of these dyes and TX-100, spectral shift due to complex formation and thermodynamic properties of these complexes.     

Adsorption of xanthene dyes by lysozyme crystals

Adsorption characteristics of cross-linked lysozyme crystals of different morphologies (tetragonal, orthorhombic, triclinic and monoclinic) were examined using four anionic dyes (fluorescein, eosin, erythrosin, and rose bengal), one zwitterionic dye (rhodamine B), and one cationic dye (rhodamine 6G). The adsorption isotherms were of the Langmuir type for all examined systems with the exception of rhodamine B adsorption by monoclinic crystals. The weakest adsorption was observed for the cationic dye, rhodamine B, whereas dianionic dyes, eosin, rose bengal, and erythrosin were strongly adsorbed on the protein surface. The adsorption capacities of the crystals for the dyes were found to depend on both charge and hydrophobicity of the dye, reflecting the heterogeneous character of the lysozyme pore surface. The adsorption affinity of the crystals for the dyes was a function of the dyes' hydrophobicity. Furthermore, the crystal morphology was identified as an additional factor determining capacity and affinity for dye adsorption. Differences between crystals prepared in the presence of the same precipitant were lower than between morphologies prepared with different precipitants.     

Aptamers switch on fluorescence of triphenylmethane dyes

MG and SRB aptamers, which are short RNA sequences originally selected only for binding to malachite green or sulforhodamine B, can greatly enhance the fluorescence of normally nonfluorescent triphenylmethane dyes. MG aptamer enhances the quantum yields of malachite green (MG) and a novel rigidized derivative, indolinyl malachite green (IMG) by >2000-fold. SRB aptamer brightens patent blue V and VF by >90-fold. These enhancements are specific because MG aptamer has no effect on patent blue dyes and SRB aptamer has little or no effect on MG and IMG. Such sequence-specific fluorescence labeling of short RNA motifs is a first step toward genetically encodable fusion tags for imaging selected RNAs in vitro and in cells.     

The structure of dimers and the nature of azulene chromaticity

The structure of supramolecular azulene dimers responsible for the blue coloration of its crystals and solutions has been discussed on the basis of result of optical spectroscopy and literature data. It is established that two types of these dimers (I and II) absorb the light in the red region of the visible (VIS) spectrum and differ by the mutual orientation of the molecules. Dimers I have a VIS band with a vibronic structure; the azulene molecules in dimers I match their own seven-membered rings in type (stacking structure), and five-membered rings of the molecules are separated so that the molecular C _2v axes form an obtuse angle. The spectra of dimers II do not have a vibronic structure in the VIS band. The dipole moments of the molecules in these dimers are oriented antiparallel (five-membered rings are located over (or under) seven-membered rings, forming a structure with a center of inversion). It is concluded that due to their structure, dimers I should have a certain dipole moment, while dimers II have no dipole moment.     

One-pot synthesis of new symmetric and asymmetric xanthene dyes

Symmetric and asymmetric xanthene dyes have been prepared by a convenient one-step procedure from aldehyde and diol or m-aminophenol precursors using concentrated phosphoric acid as a solvent. This protocol provides access to water-soluble dyes with large Stoke’s shifts and far-red fluorescence emission. These compounds are envisioned as components of fluorescence-based sensors for a variety of imaging applications.     

Adsorption of xanthene food additive dyes to cellulose granules

It was found that three kinds of the synthetic food additive dyes, red nr. 3 (erythrosine), nr. 104 (phloxine), and nr. 105 (rose bengal) were adsorbed to the surface of charred cellulose granules and the maximum amounts of adsorption of these dyes were 3.75, 3.42, and 4.74 mg/g cellulose, respectively. Scanning electron microscopy-electron probe micro analysis (SEM-EPMA) showed a coating of the dyes on the surface of charred cellulose granules. Electron spectroscopy for chemical analysis (ESCA) suggested the presence of NH₃ ⁺ in the surface of charred cellulose granules. Since all three dye compounds have both anionic carboxylate and hydrophobic groups and were released from the surface of charred cellulose granules by 0.1 N NaOH solution, it was surmised that these three food additive dyes were bound to the surface of cellulose granules by both ionic and physical interactions.     

Spectral and photophysical studies of thiazine dyes in triton X-100

The absorption spectra of several thiazine dyes such as thionine, azure A, azure B, azure C and methylene blue in aqueous solution of Triton X-100 show that dyes as electron acceptors form 11 charge-transfer (CT) or electron-donor-acceptor (EDA) complexes with Triton X-100, which acts as an electron donor. From the thermodynamic and spectrophotometric properties of these complexes, the abilities of dyes to accept an electron are in the order: azure C > thionine > azure A > azure B > methylene blue. The photogalvanic effect in the aqueous solution dye-surfactant has been studied. Generation of photovoltage supports a CT or EDA interaction between thiazine dyes and Triton X-100. There is a good correlation among the photophysical (photovoltage), spectral and thermodynamic properties of these complexes.