Reduction of methylene blue and related dyes by gamma-irradiated alkali halides

A spectrophotometric study is reported of the reduction of some dyes having the methylene blue structure used in bacteriological staining. The reduction is effected by the species liberated during the dissolution of -irradiated sodium chloride, in the same way as by direct low -dose. The G values for the two modes of the reduction are compared and the effects of radical scavengers on the reactions are studied. Results are found to be similar to the chemically and biologically induced reductions. The dyes studied include besides Methylene Blue, Janus Green B and Nile Blue sulfate.     

Picosecond rotational diffusion by differential single-photon fluorescence spectroscopy

The rotational diffusion contants of rhodamine-6G, coumarin-1 and N-acetyltryptophanamide in various solvents have been determined by an experimental method where the vertically and horizontally polarized fluorescence spectra are measured simultaneously by the same detector. The results indicate that the Debye—Stokes—Einstein model does not hold for coumarin-1 and N-acetyltryptophanamide in ethylene glycol.     

Comparison of dye (oxazine and thiazine) materials as a photosensitizer for use in photogalvanic cells based on molecular interaction with sodium dodecyl sulphate by spectral study

The photochemistry of dye is playing a significant role for understanding the mechanism of electron transfer reactions in photoelectrochemical devices such as photogalvanic cells, DSSC, semiconductor photo-catalysis, photoconductors, etc. Oxazines (Brilliant Cresyl Blue and Nile Blue O) and thiazines (Azur A, Azur B, Azur C, Methylene Blue and Toluidine Blue O) dyes have been used widely as a photosensitizer with and without surfactants in the photogalvanic cells for solar power conversion and storage. Since, the stability and solubility of photosensitizers (dyes) are increased in the presence of surfactant and these properties lead to enhance the electrical output of the photogalvanic cells. Therefore, here we have studied the extent of interaction of different dyes with sodium dodecyl sulphate (SDS), find out the order of stability of dye–SDS on the basis of magnitudes of shifting in λ_max of dye monomer and try to correlate order of dye–SDS interaction with already reported electrical output data of photogalvanic cells. Brilliant Cresyl Blue, Nile Blue O, Azur A and TB O have shown red shifting while Azur B, Azur C and MB have shown blue shifting in their λ_max value with SDS, which indicates formation of dye–surfactant complex. But, the extent of formation of complex for different dyes with SDS was different due to change in their alkyl groups. Dyes with red shifting have greater stability in excited state as well as higher electrical output data of the cell than dye with blue shifting. On the basis of both red and blue shifting, order of stability of dyes–SDS complex was found as: Brilliant Cresyl Blue?>?Toluidine Blue O?>?Azur A?>?Nile Blue?>?Azur B?>?Methylene Blue?>?Azur C. The order of electrical output values of these dyes in photogalvanic cells have also been supported by literature data in the presence of SDS. Hence, the dye–surfactant complex which would have greater stability in excited state might be more useful for improvement of conversion efficiency and storage capacity of photogalvanic cells in the future.     

Development of water-soluble far-red fluorogenic dyes for enzyme sensing

A series of Nile Blue analogs, 5-amino-9-dialkylamino benzo[a]phenoxazine dyes, 7-9, were prepared by condensation of N-alkyl or N-sulfo-propyl 4-arylazo-substituted 3-hydroxyaniline with 4-arylazo-substituted 1-naphthlamines or 8-amino-2-naphthalenesulfonic acid in the presence of perchloric acid. These fluorochromes have excitation and emission maxima near 640 and 680 nm, respectively. The fluorescence intensity in aqueous solution increases as additional sulfonate groups are added to the benzo[a]phenoxazine core. Compound 7, which has two sulfonate groups, is ten-times brighter than Nile Blue. Fluorogenic substrates containing this hydrophilic far-red dye were synthesized and applied to detect enzymatic activities of two model proteases, trypsin and leucine aminopeptidase. Given their excellent fluorogenic property, these novel far-red dyes should be useful for enzyme sensing in biological assays.     

On the reaction kinetics of electrogenerated superoxide ion with aryl benzoates

The reactions between electrogenerated superoxide ion O₂^? and two benzoate esters in N, N-dimethylformamide containing tetrabutylammonium perchlorate have been investigated. By using cyclic voltammetric techniques an e.c.e. type mechanism was found to be operative; this was confirmed by controlled potential electrolysis experiments. Secondorder rate constants for nucleophilic displacement by O₂^? on p-chlorophenyl benzoate and phenyl benzoate were estimated to be 25.0±5 and 3.0±0.3 M^?1 s^?1 respectively by fitting potential step reduction data to i_k/i_d vs. log kt working curves.     

A novel method for the synthesis of coumarin laser dyes derived from 3-(1H-benzoimidazol-2-yl) coumarin-2-one under microwave irradiation

We want to achieve the synthesis of 3-(1H-benzoimidazol-2-yl)-7-(diethylamino) coumarin-2-one (1), 3-(1H-benzoimidazol-2-yl)-7-(dimethylamino) coumarin-2-one (2), 3-(1H-benzoimidazol-2-yl) coumarin-2-one (3) that are important dyes in industries (Soko owska et al., 2001). Methods for the synthesis of some of these compounds have been the title in some pervious patents, but enough information about separation and purification of them was not clearly indicated. We carried out several methods for the synthesis of the mentioned compound and purification with different yields. Now, we can synthesise these dyes under microwave irradiation in solid phase and solvent free methods with 80% yield, which is a high and remarkable percentage.     

A stereoselective synthesis of symmetrical and unsymmetrical bibenzo[e][1,3]oxazine-2,2′-dione derivatives induced by low-valent titanium reagent

A series of symmetrical and unsymmetrical bibenzo[e][1,3]oxazine-2,2′-dione derivatives were synthesized by the reaction of various o-hydroxy Schiff bases and triphosgene induced by low-valent titanium reagent (TiCl₄/Sm). A variety of substrates can participate in the process with good yields. The present method provides a useful preparation of 3,3′,4,4′-tetrahydro-4,4′-bibenzo[e][1,3]oxazine-2,2′-dione derivatives, which cannot be prepared otherwise. The mechanistic course of the reaction suggests the involvement of reduction, coupling, and cyclization by one-pot.     

Titania nanowires as substrates for sensing and photocatalysis of common textile industry effluents

Sensing and photocatalysis of textile industry effluents such as dyes using mesoporous anatase titania nanowires are discussed here. Spectroscopic investigations show that the titania nanowires preferentially sense cationic (e.g. Methylene Blue, Rhodamine B) over anionic (e.g. Orange G, Remazol Brilliant Blue R) dyes. The adsorbed dye concentration on titania nanowires increased with increase in nanowire dimensions and dye solution pH. Electrochemical sensing directly corroborated spectroscopic findings. Electrochemical detection sensitivity for Methylene Blue increased by more than two times in magnitude with tripling of nanowire average length. Photodegradation of Methylene Blue using titania nanowires is also more efficient than the commercial P25-TiO₂ nanopowders. Keeping illumination protocol and observation times constant, the Methylene Blue concentration in solution decreased by only 50% in case of P25-TiO₂ nanoparticles compared to a 100% decrease for titania nanowires. Photodegradation was also found to be function of exposure times and dye solution pH. Excellent sensing ability and photocatalytic activity of the titania nanowires is attributed to increased effective reaction area of the controlled nanostructured morphology.     

Spectrophotometric and thermodynamic study on the dimerization equilibrium of ionic dyes in water by chemometrics method

The monomer-dimer equilibrium and thermodynamic of several ionic dyes (Neutral Red, Nile Blue A, Safranine T and Thionine) has been investigated by means of spectrophotometric and chemometrics methods. The dimerization constants of these ionic dyes have been determined by studying the dependence of their absorption spectra on the temperature in the range 20-75 degrees C at concentrations of Neutral Red (1.73 x 10(-5) M), Nile Blue A (3.94 x 10(-5) M), Safranine (6.59 x 10(-5) M) and Thionine (6.60 x 10(-5) M). The monomer-dimer equilibrium of these dyes has been determined by chemometrics refinement of the absorption spectra obtained by thermometric titrations performed. The processing of the data carried out for quantitative analysis of undefined mixtures, based on simultaneous resolution of the overlapping bands in the whole set of absorption spectra. The enthalpy and entropy of the dimerization reactions were determined from the dependence of the equilibrium constants to the temperature (van't Hoff equation).     

Spectroscopic and Spectroelectrochemical Studies of Interaction of Nile Blue with DNA

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Electrogenerated chemiluminescence. XXIV. Electrochemistry and electrogenerated chemiluminescence of 9,10-dichloro-9,10-dihydro-9,10-diphenylanthracene

A study of the electrochemistry and electrogenerated chemiluminescence (e.c.l.) of 9,10-dichloro-9,10-dihydro-9,10-diphenylanthracene (DPACl₂) in acetonitrile solutions using rotating ring—disk electrode and stationary electrode techniques is described. The measured e.c.l. efficiency was about 0.1 to 0.8%, smaller than that observed for the corresponding DPA radical ion annihilation e.c.l. The emission is independent of applied external magnetic field, supporting the mechanism involving direct formation of emitting singlet. The e.c.l. emission and the electroreduction of DPACl₂ depend on the chloride concentration in the solution; the results suggest that this dependence is an electrode surface effect.     

Degradation of textile dyes mediated by plant peroxidases

The peroxidase enzyme from the plants Ipomea palmata (1.003 IU/g of leaf) and Saccharum spontaneum (3.6 IU/g of leaf) can be used as an alternative to the commercial source of horseradish and soybean peroxidase enzyme for the decolorization of textile dyes, mainly azo dyes. Eight textiles dyes currently used by the industry and seven other dyes were selected for decolorization studies at 25–200 mg/L levels using these plant enzymes. The enzymes were purified prior to use by ammonium sulfate precipitation, and ion exchange and gel permeation chromatographic techniques. Peroxidase of S. spontaneum leaf (specific activity of 0.23 IU/mg) could completely degrade Supranol Green and Procion Green HE-4BD (100%) dyes within 1 h, whereas Direct Blue, Procion Brilliant Blue H-7G and Chrysoidine were degraded >70% in 1 h. Peroxidase of Ipomea (I. palmata leaf; specific activity of 0.827 U/mg) degraded 50 mg/L of the dyes Methyl Orange (26%), Crystal Violet (36%), and Supranol Green (68%) in 2–4 h and Brilliant Green 54%), Direct Blue (15%), and Chrysoidine (44%) at the 25 mg/L level in 1 to 2 h of treatment. The Saccharum peroxidase was immobilized on a hydrophobic matrix. Four textile dyes, Procion Navy Blue HER, Procion Brilliant Blue H-7G, Procion Green HE-4BD, and Supranol Green, at an initial concentration of 50 mg/L were completely degraded within 8 h by the enzyme immobilized on the modified polyethylene matrix. The immobilized enzyme was used in a batch reactor for the degradation of Procion Green HE-4BD and the reusability was studied for 15 cycles, and the halflife was found to be 60 h.     

Coulometric determination of serum iron

The iron in 500 μl of serum is determined by a coulometric titration developed for ferroin. The titration step is preceded by chloroform extraction from a protein-free filtrate of serum iron as ferroin perchlorate. Evaporation of chloroform in the presence of an acetate buffer of pH 4.6 causes the ferroin perchlorate to back-extract into the aqueous layer. The ferroin is introduced into a titration cell and titrated with electrogenerated cerium(IV), a modified amperometric end-point detection system being used.     

Polymerized Nile Blue derivatives for plasticizer-free fluorescent ion optode microsphere sensors

Lipophilic H⁺-selective fluorophores such as Nile Blue derivatives are widely used in ISE-based pH sensors and bulk optodes, and are commonly dissolved in a plasticized matrix such as PVC. Unfortunately, leaching of the active sensing ingredients and plasticizer from the matrix dictates the lifetime of the sensors and hampers their applications in vivo, especially with miniaturized particle based sensors. We find that classical copolymerization of Nile Blue derivatives containing an acrylic side group gives rise to multiple reaction products with different spectral and H⁺-binding properties, making this approach unsuitable for the development of reliable sensor materials. This limitation was overcome by grafting Nile Blue to a self-plasticized poly(n-butyl acrylate) matrix via an urea or amide linkage between the Nile Blue base structure and the polymer. Optode leaching experiments into methanol confirmed the successful covalent attachment of the two chromoionophores to the polymer matrix. Both polymerized Nile Blue derivatives have satisfactory pH response and appropriate optical properties that are suitable for use in ion-selective electrodes and optodes. Plasticizer-free Na⁺-selective microsphere sensors using the polymerized chromoionophores were fabricated under mild conditions with an in-house sonic microparticle generator for the measurement of sodium activities at physiological pH. The measuring range for sodium was found as 10⁻¹-10⁻⁴ M and 1-10⁻³ M, for Nile Blue derivatives linked via urea and amide functionalities, respectively, at physiological pH. The observed ion-exchange constants of the plasticizer-free microsphere were log K_exch = −5.6 and log K_exch = −6.5 for the same two systems, respectively. Compared with earlier Na⁺-selective bulk optodes, the fabricated optical sensing microbeads reported here have agreeable selectivity patterns, reasonably fast response times, and more appropriate measuring ranges for determination of Na⁺ activity at physiological pH in undiluted blood samples.     

A perfluorinated micellar reaction system in lithium perchlorate/acetonitrile; enhanced efficiency in anodic electron-transfer and intermolecular cycloaddition

A micellar electrolytic reaction system composed of lithium perfluorooctanesulfonate (LiFOS), highly concentrated lithium perchlorate in acetonitrile, effectively dispersed slightly soluble compounds to promote anodic electron transfers, and it further accelerated the formation of desired cycloadducts between electrogenerated quinones and dienes.     

Environmental photochemistry: Electron transfer from excited humic acid to TiO2 colloids and semiconductor mediated reduction of oxazine dyes by humic acid

The ability of naturally occurring Suwanee River Humic acid to sensitize a large bandgap semiconductor such as colloidal TiO₂ has been investigated by fluorescence emission. The charge injected from the humic acid sensitizer into the semiconductor was used to reduce a series of oxazine dyes viz:, N,N,N’,N’-tetraethyloxonine and Nile Blue A. The mechanism of such a sensitized reduction process was elucidated by laser flash photolysis methods. The quantum yield for such a reduction calculated from these transient absorption techniques was 0.005.     

Synthesis,structure, electronic and vibrational spectra of 9-(Diethylamino)-benzo(a)phenoxazin-7-ium-5-N-methacrylamide

The electronic and vibrational spectra of 9-(Diethylamino)-benzo(a)phenoxazin-7-ium-5-N-methacrylamide (Nile Blue-5-N-methacrylamide) are measured, and the results are compared with the theoretical values obtained by quantum chemical calculations. The geometry, electronic transitions, charge distribution, and the IR normal modes of this new dye and of its precursor Nile Blue have been computed by using Density Functional Theory (DFT) method with the functional B3LYP and the 6-31G(d) Gaussian basis set. The molecular properties of the two dyes, predicted and observed, are very similar in the electronic ground state. In the excited state, however, the longer lifetime and larger fluorescence quantum yield of the Nile Blue-5-methacrylamide is ascribed to an inhibition of the twisted intramolecular charge transfer (TICT) process, when the NH2 is substituted by the methacrylamide in the 5-position of the aromatic extended ring of the dye. The change in charge density of the N atom in 5-position, as well as the difference in dipole moment and ionization potential of the two dyes molecules, explain the attenuation of TICT process. The vibration spectra of both dyes are simulated properly by using the DFT method.     

UV-Vis spectroscopic and chemometric study on the aggregation of ionic dyes in water

The monomer-dimer equilibrium in several ionic dyes (Methylene Blue, Acridine Orange, Nile Blue A, Neutral Red, Rhodamine 6G and Safranine O) has been investigated by means of UV-Vis spectroscopy. The data have been processed by a recently developed method for quantitative analysis of undefined mixtures, based on simultaneous resolution of the overlapping bands in the whole set of absorption spectra. In the cases of Acridine Orange a second chemometric approach has been used as a reference. It is based on a decomposition of the recorded spectra into a product of target and projection matrices using non iterative partial least squares (NIPALS). The matrices are then rotated to give the correct concentrations, spectral profiles of the components and the equilibrium constant. The dimeric constants determined by the two methods were in excellent agreement, evidencing the accuracy of the analysis. From the calculated dimeric constant and monomer and dimer spectra, the structures of the dimeric forms of the studied dyes are estimated.     

Non-covalent interactions of coumarin dyes with cucurbit[7]uril macrocycle: modulation of ICT to TICT state conversion

Non-covalent interaction of coumarin laser dyes, namely coumarin-1 (C1), coumarin-481 (C481) and coumarin-6H (C6H), with a versatile macrocyclic host molecule cucurbit[7]uril (CB7), has been investigated in aqueous solution using photophysical methods. Steady-state and time-resolved fluorescence studies illustrate significant enhancements/modifications in the fluorescence yields, lifetimes and spectral features of C1, C481 and C6H on interaction with CB7, and are assigned to 1 : 1 complex formation between the dyes and the CB7 host. The complex formation is mainly driven by charge-dipole interaction, as evident from the binding constant values (K ~ 10(4)-10(5) M(-1)). The large changes in the excited state behaviour of C1 and C481 as compared to C6H in the presence of CB7 indicate that CB7 binds C1 and C481 through the encapsulation of the 7-N,N'-diethylamino group of the dyes and the structural rigidity imposed by this interaction dramatically alters the excited state properties of the dyes by preventing the conversion of their emissive intramolecular charge transfer (ICT) state to the non-radiative twisted intramolecular charge transfer (TICT) state. The present results direct towards the probable supramolecular approach using water soluble macrocyclic CB7, in the development of aqueous dye laser systems in the blue-green region.     

Photocatalytic reduction of azo dyes Naphthol Blue Black and Disperse Blue 79

Photocatalytic reduction of two textile azo dyes, Naphthol Blue Black (NBB) and Disperse Blue 79 (DB79) has been carried out in colloidal WO₃ and TiO₂ suspensions. Under bandgap excitation of the semiconductor colloids these dyes undergo irreversible reduction as they react with the trapped electrons. The quantum efficiency for the photocatalytic reduction of these dyes were 5.4% and 4.8% for NBB and DB79 respectively. The kinetics and mechanism of the interfacial charge transfer in these colloidal suspension has been elucidated with transient absorption spectroscopy. The reaction between the dye and trapped electrons is diffusion limited and occurs with rate constants of 1.1×10⁸ M⁻¹s⁻¹ and 4.0×10⁷ M⁻¹s⁻¹ for NBB and DB79 respectively.