Solubility Of Dyes Research Articles

Tuning the aqueous solubility, chemical reactivity and absorption wavelength of azo dye through systematic adjustment of molecular charge density: a DFT study

ABSTRACT Effects of substituent groups on aqueous solubility, chemical reactivity and absorption wavelength of Disperse red 73 (DR73) were theoretically investigated using density functional theory (DFT) method. This study is in view of introducing new monoazo disperse dyes with improved aqueous solubility, absorption behaviour, and degradation tendency. Aqueous solubility was calculated using Cramer et al. solubility equation and the parameters used were obtained using conductor-like screening model for realistic solvation (COSMO-RS). Chemical reactivity and catalytic affinity were evaluated using some molecular orbital dependent reactivity descriptors. Susceptibility of the molecules to radical attacks was predicted using Fukui functions. Absorption wavelength was calculated using the B3LYP functional with the 6-31G* basis set. The results showed that electron withdrawing −CN substituent promoted aqueous solubility of DR73 more than the −NO2 counterpart, while the solubility is mostly enhanced by −NH2 substituent compared to the other electron donating groups studied. Most of the derivatives yielded longer absorption wavelength in the visible region and are chemically less stable (i.e. more degradable) compared to the parent molecule. Among the photocatalysts considered, ZnO is predicted as the most efficient candidate for degradation of the dyes. Predicted properties showed remarkable sensitivity to substitution positions in the parent molecule.

Prediction of aqueous solubility by treatment of COSMO-RS data with empirical solubility equations: the roles of global orbital cut-off and COSMO solvent radius

Aqueous solubility values of (E)-2-(ethyl(4-((4-nitrophenyl)diazenyl)phenol)amino)ethanol [B1], (E)-2,2′-((4-((4-nitrophenyl)diazenyl)phenyl)azanediyl)diethanol [B2], (E)-2,2′-((3-methyl-4-((4-nitrophenyl)diazenyl)phenyl)azanediyl)diethanol [B3] and (E)-2-((4-((2,4-dinitrophenyl)diazenyl)phenyl)(ethyl)amino)ethanol [B4] were predicted by the treatment of relevant COSMO-RS data with Cramer et al. solubility equation (CSE) and general solubility equation (GSE). DMol3 computational code was employed for the study, where all calculations were carried out using VWN-BP level of theory with double numerical basis set containing polarization functions (DNP). Effects of global orbital cut-off and COSMO solvent radius (CSR) on the predicted results were examined. The results revealed that COSMO-RS data performed very well with both the CSE and GSE, but the latter exhibited a greater prediction strength on average. For nearly all the studied molecules, GSE calculated solubility (SGSE) was found to increase with orbital cut-off and reached an optimum value at a cut-off of 5.5 A. SGSE values obtained at this and higher cut-off values studied are comparable to experimental solubility values, especially for B1, B3 and B4, while better results were obtained for B2 at lower cut-off values. CSE calculated solubility (SCSE) showed no constant trend with cut-off variation, but at cut-off values ≥ 7.0 A the SCSE values compare well with the experimental values, especially in the cases of B2 and B3. For all the studied molecules, SGSE decreased with the increase in CSR and the most reliable CSR value for GSE was found to be 1.3 A. On the contrary, SCSE increased with CSR and for B1 and B4, this increase was followed by a drop in predicted values at CSR > 1.3 A. However, the best CSR value for CSE was found to be 0.5 A for almost all the molecules. Our findings have shown that aqueous solubility (in mol/L) of azo dyes can be accurately predicted using CSE or GSE with some COSMO-RS data and that global orbital cut and COSMO solvent radius are essential parameters for accurate prediction.

Multicomponent system of trichromatic disperse dye solubility in supercritical carbon dioxide

Using a mixture of dyes to produce a variety of shades is necessary for the industrialization of supercritical fluid dyeing. The solubility of the mixture in supercritical fluid is indispensable for combination dyeing but has been less well-studied. In this study, the solubility of trichromatic disperse dyes (C.I. Disperse Orange 30, C.I. Disperse Red 167 and C.I. Disperse Blue 79) and their blends in supercritical carbon dioxide were measured at temperatures of 333.15, 363.15, and 393.15 K and pressures of 12, 16, 20, and 24 MPa. Considering both the solubility enhancement value and the statistical significance, the solubility of a quaternary system was less than that of a binary system, particularly at higher pressure. To research the relationship between solubility and experimental conditions or properties of the solute, the experimental data were correlated with two semiempirical models (the Kumar–Johnston (K-J) and Sung–Shim (S-S) models) and a phase equilibrium thermodynamic model (a modified Redlich–Kwong equation of state (m-RK-EOS)). The results showed that the calculated solubility by the semiempirical and thermodynamic models had high consistency with the experimental values. In addition, the m-RK-EOS model had better accuracy than the K-J and S-S models for correlating solubility. Therefore, a calculated solubility can be used to offer basic information for the proper design of supercritical fluid dyeing in industry.

Cell culture medium and nano-confined water on nonlinear optical properties of Congo Red

Optical properties of Congo Red in the solvents and nano-confined water can be studied using techniques, including Z-scan, spectrophotometer and photon correlation spectroscopy The absorbance of Congo Red depends on environmental conditions that were considered as the rules of dielectric constant and solubility. The solubility of Congo Red in the solvent and of dye-water in nano-confined water determines the value of both nonlinear absorption and refractive index. The nonlinear optical properties of AOT/n-Decane/H2O are higher than AOT/Toluene/H2O. The photon correlation spectroscopy findings show higher dye aggregation in AOT/Toluene/H2O in comparison with AOT/n-Decane/H2O. According to the results, the nonlinear optical properties of Congo Red are enhanced by increasing the dye solubility in the nano-confined water, as well as the dye solubility changes in microemulsion by oil length scale and polarity. Incremental concentration of cell culture medium enhanced the nonlinear optical properties of Congo Red in nano-confined water.

Effect of Charge and Dielectric Constant on Linear and Nonlinear Optical Properties of Two Dyes

The enhancement of nonlinear optical properties of dye with surfactant can be applied in photodynamic therapy and medicine. The nonlinear optical properties of alizarin red S and rhodamine B mixed with cationic and anionic surfactant are studied by Z-scan technique. The nonlinear absorption coefficient values of cationic dye (rhodamine B) in aqueous solution are reduced with the increase of anionic surfactant concentration, while the nonlinear absorption coefficient values are enhanced by the interaction between anionic dye (alizarin red S) with anionic surfactant. The nonlinear refractive index (n2) of cationic and anionic dye is reduced with an increase of surfactant concentration. The nonlinear absorption coefficient values of a rhodamine B-doped droplet is reduced by the increase of cationic surfactant in the water droplet. In general, the nonlinear absorption coefficient values are reduced with an increase of dye solubility, and the value of n2 is reduced with an increase of dye solubility in solution. The fluorescence intensity is higher when dye and surfactant have the same charge. This effect can be due to the increase of solubility of cationic (anionic) dye with an increase of anionic (cationic) surfactant in the solution. The reduction of nonlinear absorption coefficient values with an increase of droplet size can be due to the change of rhodamine B solubility in microemulsion.

Mechanism of Accelerant on Disperse Dyeing for PET Fiber in the Silicone Solvent Dyeing System.

Disperse dyeing for polyethylene terephthalate (PET) fiber in different non-aqueous solvent dyeing systems have been extensively studied over the past decades. In the present work, disperse dyeing for PET was investigated in a silicone solvent dyeing system. The influence of accelerant on the fiber swelling, uptake of dye, K/S value of dyed fiber, and dye solubility in the silicone solvent were systematically investigated. Compared with no accelerant, the final uptake of the disperse dye (C. I. Disperse Blue 367) could increase to 81% with 20% accelerant in the silicone solvent dyeing system, and the K/S value of dyed fiber was also higher (3.3 for no accelerant vs. 13.2 for accelerant). The influence of accelerant on the performance of disperse dyeing was also studied. Firstly, the solubility of the disperse dye in the silicone solvent can be decreased by the accelerant. Moreover, the solubility of the disperse dye is inversely proportional to the K/S value and the uptake of the dye. In addition, although the silicone solvent can diffuse to the inner fiber and has a partial swelling in the PET fiber, the swelling of PET can be improved by the accelerant. Furthermore, the swelling of fiber can reach equilibrium when the amount of accelerant was 15% (the weight of fiber). Therefore, this eco-friendly dyeing technology has considerable potential for application to a broad array of chemical fibers.

Meso-Substituent-Directed Aggregation Behavior and Water Solubility: Direct Functionalization of Methine Chain in Thiazole Orange and Biological Applications in Aqueous Buffer.

A new strategy is presented to preclude aggregation and enhance water solubility of cyanine dyes. Namely, a heteroatom-containing substituent, for distorting molecular plane and increasing interaction with water molecules, is introduced to the methine chain of 2-thiazole orange (1, a monocyanine) via one-step, and 2-thiazole orange derivatives 2a-g are prepared accordingly. The X-ray crystal structures show that the molecular plane of 2a-g is drastically twisted, which reduces intermolecular π-π stacking. The derivatives 2a-g exhibit good to excellent water solubility and can be dissolved in aqueous phosphate-buffered saline (PBS) at concentrations suitable for biomedical applications. No aggregation in aqueous PBS, relatively high molar extinction coefficients, and low solvatochromism of 2a-g are reflected by the UV-vis spectra. Compound 2b shows fast response and high selectivity for biothiols (Cys, Hcy, and GSH) in aqueous PBS and is further employed to detect endogenous biothiols with decent biocompatibility as demonstrated by live cell fluorescence imaging.

Recent Advances on the Analysis of Polychrome Works of Art: SERS of Synthetic Colorants and Their Mixtures With Natural Dyes.

The development and application of proper sample pretreatments is often a key step toward the successful analysis of dyes used as artists' materials by surface-enhanced Raman spectroscopy (SERS). Complexation of the organic colorants with metal ions to dye fabrics and produce lake pigments, as well as undesired interactions with other matrix components such as substrate, binding media, fillers, and extenders, are just some of the issues that typically complicate dye identification in minute samples from invaluable artworks and museum objects. These concerns may be addressed by using, prior to SERS analysis, ad-hoc sample pretreatments that, in addition to increasing the technique's sensitivity, favorably affect its selectivity toward certain molecules or molecular classes. The present work describes a newly developed sample pretreatment based on the use of nitric acid that has proven crucial for the successful detection of aniline and xanthene dyes–the first synthetic organic colorants to be used in printing and painting, among other art forms–in microscopic samples from works of art such as a 19th-century silk fabric, paper cut-outs by Henri Matisse, Vincent Van Gogh's Irises, and Japanese woodblock prints. This treatment promotes the hydrolysis of the dye-metal bond in mordant dyes or lake pigments, resulting in a more efficient adsorption of the dye molecules on the SERS-active substrate and, hence, enabling the acquisition of high-quality spectra. In the case of synthetic colorants, this method shows advantages over hydrolysis with hydrofluoric acid–a procedure previously established for the analysis of red lakes prepared from natural dyes. The nitric acid treatment presented here may be integrated into a multi-step methodology that, by exploiting differences in solubility of various dyes and lake pigments, has enabled for the first time to successfully characterize intentional mixtures of natural and synthetic colorants of the xanthene and anthraquinone molecular classes, i.e., eosin Y and carmine, in a selection of Japanese prints of the Meiji era. The present study paves the way for the systematic identification of synthetic dyes in objects of artistic and archeological interest, even when they are present in mixtures with natural organic colorants.

Influence of Hard Water on Solubility and Colorimetric Properties of Reactive Dyes

The dyeing process in the textile industry is not only highly water intensive, but also the quality of water plays a substantial role in determining the final shade of the product. Hardness is one of the crucial factors of water quality influencing the final shade of dyed products. The influence of hard water on solubility of reactive dyes and colorimetric properties of reactive-dyed cotton were studied. It was concluded that the solubility of reactive dyes decreased with increased water hardness. Also, hard water significantly affected the colorimetric properties (L*, a*, b*, C*, h°, and DE values) of reactive-dyed cotton fabric. Lightness value increase was accompanied by the decrease in chroma values for all three primary colors studied in this work.

Effects of the side chain density of polycarboxylate dispersants on dye dispersion properties

Comb‐like polycarboxylates were synthesised by copolymerisation of methacrylic acid and nonylphenol polyethylene glycol methacrylate ester, and can be used as dye dispersants. In order to achieve good dispersive ability, three polycarboxylates were synthesised, each having a different side chain density. The side chain density of polymers was controlled by different ratios of monomers in the copolymerisation process. Acidic polymers were neutralised using sodium hydroxide. These polymers exhibit good dispersing performance, such that carboxylate groups are adsorbed onto the dye particle surface and the side chains enable the formation of a thick layer, thus providing the steric hindrance effect. Improvement of dye dissolution in the presence of polycarboxylates was studied. Polymers with a lower side chain density demonstrated a higher dye dissolution in water, which could be as a result of more effective adsorption of dispersant on the dye surface (CI Disperse Blue 79). The dyeing performance of the prepared dye dispersions on polyester was investigated. Spectrophotometric analysis of dyed fabrics using synthesised polycarboxylates demonstrates that there should be an optimum side chain density of polymer in order to control both dye solubility and dispersive ability. The result of turbidimetry and particle size analysis have proven this phenomenon. A comb‐like polycarboxylate with optimum side chain density was a better dye dispersant compared with a commercial sodium naphthalene sulphonate compound, as a result of its better heat stability.

Experimental measurements and thermodynamic modeling of Coumarin-7 solid solubility in supercritical carbon dioxide: Production of nanoparticles via RESS method

For the first time, solubility of coumarin-7 dye (C7) in supercritical carbon dioxide (SC-CO2) was measured in temperature and pressure ranges of (308–338) K and (90–330) bar, respectively, for binary (C7-CO2) and ternary systems (C7-CO2-methanol). Mole fractions were determined to range from 0.415 × 10−5 to 1.009 × 10−5 and 0.1089 × 10−4 to 1.2007 × 10−4 for binary and ternary systems, respectively. The solubility data was correlated using two thermodynamic models, namely quadrupolar cubic plus association theory (qCPA) and perturbed-chain polar statistical associating fluid theory (PCP-SAFT). Continuing with the research, the rapid expansion of supercritical solution (RESS) process was used to produce coumarine-7 nanoparticles. Effects of temperature, pressure, nozzle diameter, and spraying distance on the particle size were investigated. For this purpose, unprocessed and processed particles were characterized by FTIR, XRD, DSC, SEM, and DLS. A significant decline (21.37 ≤ x50 ≤ 224.13 nm) was observed in the final particle size, as compared to the original one (40.35 μm).

Quantifying Surface Properties of Silica Particles by Combining Hansen Parameters and Reichardt's Dye Indicator Data

AbstractTo obtain quantitative understanding of the effects of a chemisorbed organic modification on the surface of particles, the use of Reichardt's dye (RD) and Hansen solubility parameter (HSP) is discussed, whereby the S should be understood in terms of “similarity” rather than solubility as dispersibility is in focus. Silica nanoparticles modified to different extents with a medium chain silane including completely hydrophilic and hydrophobic particles are chosen. During spray‐drying such particles form fully redispersible micro‐raspberry superstructures. After qualitative estimations of the particles' polarity based on measuring both immersion time and ability of modified particles to stabilize oil–water emulsions, surface properties are quantified by HSP and RD. With increasing hydrophobicity, i.e., increasing amount of silane at the surface, all three contributions to HSP change. At the same time, RD analysis reveals that the normalized solvent polarity parameter decreases progressively. HSP and RD analysis are in good agreement, giving strong confidence on each method applied individually. This work demonstrates that after noticeable attempts for combined solubility parameters in case of molecules, carbon allotropes, and gelators, such studies can be extended toward functional (nano)particles and that a full picture of particle surface properties is possible via the combination of different, quantitative techniques.

PREPARATION AND EVALUATION OF MICROEMULSION CONTAINING ANTIHYPERTENSIVE DRUG

Objective: The aim of the present study was to design novel drug delivery system containing ramipril microemulsion. Ramipril is an antihypertensive drug having very low aqueous solubility and bioavailability. Ramipril microemulsion could be used as a possible alternative to the traditional oral formulation to improve dissolution rate and hence its bioavailability with avoidance of the first-pass metabolism.Methods: The microemulsion existence region was determined by constructing pseudoternary phase diagram and prepared by using four components orange oil, tween 80 as a surfactant, propylene glycol as co-surfactant and distilled water as the aqueous phase. The water titration method was employed for its determination. All formulated microemulsion were subjected for visual inspection, centrifugation and stability test. The all stable formulations were selected for further study.The optimized microemulsion formulation B-9 was subjected for various evaluation parameters such as, visual inspection, stability studies, pH, viscosity measurements, electrical conductivity, content uniformity and dye solubility test.Results: Results revealed that construction of phase diagram and use of phase titration method was a suitable technique for the preparation of microemulsion as most of the formulations were transparent. It was found that the best microemulsion result was found for ratio 2:1. The results of stress tests conclude that the optimized formulation was both physically and chemically stable for 8 mo. Also, The Fourier transform infrared (FTIR) radiation measurement and Differential scanning calorimetry (DSC) of optimized formulation indicate the compatibility of ramipril with orange oil, surfactant-tween 80 and cosurfactant-propylene glycol. From electrical conductivity 0.283 σ and staining test the prepared optimized formulation B-9 was found to be o/w type of microemulsion. The optimized B-9 formulation showed good viscosity 13.52±0.01cps and pH 3.21±0.02 with highest drug content uniformity was found to be 84.98±0.02 %.Conclusion: In the present study a satisfactory attempt was made to formulate a novel o/w microemulsion of ramipril which improves the gastrointestinal absorption by raising its water solubility and hence oral bioavailability is also enhanced.

Solubility and data correlation of a reactive disperse dye in a quaternary system of supercritical carbon dioxide with mixed cosolvents

Abstract Mixed cosolvents involving acetone and water were applied in hydrophobically supercritical carbon dioxide medium for modifying the solubility behavior of a new reactive disperse orange SCF-AOL2 dye. Then the equilibrium solubility of the dye solute in the quaternary system of supercritical carbon dioxide with the mixed cosolvents was measured at temperature from 333.2 K to 393.2 K and pressure from 8.0 MPa to 22.0 MPa with an equilibrium time of 60 min in a home-built batch circulation system. The experimental results show that a significant improvement of the dye solubility and its behavior was achieved in the presence of the mixed cosolvents in supercritical carbon dioxide, especially with the tested system pressure in different solubility isotherm curves. Moreover, the achieved experimental data were further correlated, validated and predicted successfully by employing several typically semi-empirical models for the quaternary system with mixed cosolvents. It is most important that a new and specially derived model based on the conventional and modified Mendez-Santiago–Teja ones was also proposed and successfully applied to the quaternary system with a significant improvement and highest accuracy than the employed other ones. Furthermore, better correlations were also achieved from the conventional Chrastil and the Del Valle-Aguilera models than other ones for the employed system.

Chromonic self-assemblies in a series of dialkyl-thiacarbocyanine dyes and generalization of a facile route for the synthesis of fluorescent nanostructured silica fibers

Abstract In the search for new chromonic liquid crystals, we have explored the self-assembly behavior in water of a series of high-purity dialkylthiacarbocyanine dyes with different alkyl chain lengths and acetate as counterion. The dimer model was used to fit the UV–vis spectra and estimate the dissociation energy between molecules, which increases with the alkyl chain length suggesting that not only aromatic π–π interactions but also entropic/steric effects contribute to the aggregation process. NMR spectra suggest the existence of aromatic stacking interactions within the aggregates. At high concentrations, the dyes form nematic and hexagonal chromonic liquid crystals (CLC) in water within a limited range of alkyl chain lengths (ethyl to butyl); for longer lengths (pentyl) no liquid crystals were observed because of insufficient dye solubility. From small angle X-ray scattering patterns, it can be inferred that dye aggregates have cylindrical morphology with a multimolecular cross-section. The dye aggregates template the formation of silica nanofibers synthetized via sol–gel method in alkaline media. After removing excess dye, the silica/dye nanofibers showed high fluorescence emission with superb photochemical stability. The present report demonstrates a generalized route for the wet synthesis of nanostructured silica nanofibers with tunable optical properties.

Photophysical properties of novel functionalized fluorescent dyes based on diketopyrrolopyrrole and application in inkjet printing ink

The novel fluorescent dyes based on diketopyrrolopyrrole materials were developed as a basic component for use in inkjet ink formulations. N-substituted DPP derivatives of ethyl formate and ethyl acetate (symmetric and asymmetric) were synthesized and characterized. Then, quantum chemical calculations were performed to investigate the observed changes in the photophysical properties of synthesized materials. Photophysical investigations of fluorescence dyes in various solvents and the effect of solvatochromism and the solubility of dyes in inkjet inks and solid state emission of dyes were used to select symmetric and asymmetric derivatives for application in inkjet formulation. In addition, the inkjet ink based on the symmetric N-substituted DPP derivatives of N,N-diethylformate and ethyl acetate was formulated. Inkjet inks were printed on polymeric substrate and their fluorescence were studied. The solubility of the asymmetric N-ethyl acetate dye in ink formulation was lower than symmetric derivatives due to stronger inter-particle interactions. From photophysical features of printed substrate, the final formulation based on symmetric ethyl acetate dye was performed for further investigation. The effect of concentration on the intensity of emission and also on the color properties (Lab) of formulation was studied. The optimum dye concentration of symmetric N,N-diethylacetate dye with highest fluorescent intensity was 0.3wt% in ink formulation. Finally, the symmetric ethyl acetate dyes formulation for security inkjet ink was performed.

Colour modulation of blue anthocyanin-derivatives. Lignosulfonates as a tool to improve the water solubility of natural blue dyes

The impact of a lignosulfonate (calcium) (L) on the chromatic features of two anthocyanin-derived bluish dyes (portisin, P and pyranoanthocyanin dimer, PD) was evaluated in aqueous solutions using UV–Visible spectroscopy. It was demonstrated that the interaction between each dye and this macromolecule at pH 1 occurs by two mechanisms, association and copigmentation that are dependent on L concentration. For instance, at low concentrations of L (up to 0.27 μM) it is observed the association of dyes promoted by their complexation with lignin (different molecules of dye are bound to the same binding sites of L). At higher concentrations of L (25 μM), the aggregation of dyes decreases and each molecule is bound to a different site of L resulting in the formation of a charge-transfer complex (copigmentation). Moreover, the titration of both dyes (P and PD) in the presence of L (19 μM) showed a strong stabilization of their pyranoflavylium cation forms revealed by the considerably higher pKa1 (6.6 ± 0.1 and 6.2 ± 0.1 for P and PD, respectively) in the presence of this macromolecule when compared to the values obtained in the absence (pKa1 = 4.61 ± 0.03 and 4.93 ± 0.04).In addition, the water solubility of the dyes in the absence and presence of L was also evaluated by turbidimetry and the results showed that the water soluble lignosulfonate improved the solubility of the dyes over time.

A Comparative Study on Micellar and Solubilizing Behavior of Three EO-PO Based Star Block Copolymers Varying in Hydrophobicity and Their Application for the In Vitro Release of Anticancer Drugs.

The temperature and pH dependent self-assembly of three star shaped ethylene oxide-propylene oxide (EO-PO) block copolymers (Tetronics® 304, 904 and 908) with widely different hydrophobicity was examined in aqueous solutions. Physico-chemical methods viz. viscosity, cloud point, solubilization along with thermal, scattering and spectral techniques shows strongly temperature and salt dependent solution behavior. T304 possessing low molecular weight did not form micelles; moderately hydrophilic T904 remained as micelles at ambient temperature and showed micellar growth while very hydrophilic T908 formed micelles at elevated temperatures. The surface activity/micellization/solubilization power was favored in the presence of salt. The copolymers turn more hydrophilic in acidic pH due to protonation of central ethylene diamine moiety that hinders micelle formation. The solubilization of a model insoluble azo dye 1-(o-Tolylazo)-2-naphthol (Orange OT) and hydrophobic drugs (quercetin and curcumin) for copolymer solutions in aqueous and salt solutions are also reported. Among the three copolymers, T904 showed maximum solubility of dye and drugs, hence the in vitro release of drugs from T904 micelles was estimated and the effect on cytotoxicity of loading the drugs in T904 micelles was compared with the cytotoxicity of free drugs on the CHO-K1 cells. The results from the present work provide a better insight in selection of Tetronics® for their application in different therapeutic applications.

DMol3/COSMO-RS prediction of aqueous solubility and reactivity of selected Azo dyes: Effect of global orbital cut-off and COSMO segment variation

Aqueous solubility and reactivity of four azo dyes were investigated by DMol3/COSMO-RS calculation to examine the effects of global orbital cut-off and COSMO segment variation on the accuracies of theoretical solubility and reactivity. The studied dyes are (E)-2,2′-((4-((2-chloro-4-nitrophenyl)diazenyl)-3-methylphenyl)azanediyl)diethanol [D1], (E)-2,2′-((4-((2,4-dinitrophenyl)diazenyl)-3-methylphenyl)azanediyl)diethanol [D2], (E)-2,2′-((4-((2,6-dichloro-4-nitrophenyl)diazenyl)-3-methylphenyl)azanediyl)diethanol [D3] and (E)-2,2′-((4-((2-chloro-4,6-dinitrophenyl)diazenyl)-3-methylphenyl)azanediyl)diethanol [D4]. The VWN-BP level of theory in conjunction with the double numerical basis set containing polarization function (DNP) was employed for the calculations. The aqueous solubility was calculated from the COSMO-RS data using the Cramer et al. solubility equation (CSE) and the general solubility equation (GSE) by Yalkowsky. The results showed that GSE calculated solubility (SGSE) increases with orbital cut-off and reached optimum value at 5.5Å orbital cut-off. SGSE values obtained at 5.5Å orbital cut-off for D1 and D3 are comparable to experimental values, while the best results were obtained for D2 and D4 at 4.5Å cut-off. The CSE calculated solubility (SCSE) showed no definite trend with cut-off variation but the best CSE cut-off for the dyes seemed to exhibit an inverse linear relationship with the molecular weights of the dyes. The reactivity of the dyes was enhanced in water and the minimum cut-off value for the reactivity study was 4.5Å. Both the calculated solubility and reactivity indices generally showed low sensitivity to change in COSMO segment. We conclude that the DMol3/COSMO-RS model is appropriate for predicting the aqueous solubility and reactivity of azo dyes and that the CSE and the GSE are reliable for solubility determination using COSMO-RS data, but their dependence on orbital cut-off differ.

The role of auxiliaries in the immersion dyeing of textile fibres: Part 9 practical aspects of the role of inorganic electrolytes in dyeing cellulosic fibres with pure reactive dyes

The colour strength, as well as the extents of both exhaustion and fixation, achieved for three pure reactive dyes on cotton were promoted by the addition of 50 gl-1 NaCl at each of seven liquor ratios employed (1:50, 1:20, 1:10, 1:6, 1:3, 1:2 and 1:1.5). The depth of shade of dyeings obtained in the absence of added electrolyte using a1:1.5 liquor ratio were of similar magnitude to those secured using 1:10–1:20 liquor ratios in the presence of 50 gl-1 NaCl. The promotional effect on dye uptake imparted by both added electrolyte and reduced liquor ratio was interpreted in terms of their effects on the substantivity of the reactive dyes towards the cotton substrate. The two, seemingly different actions of adding electrolyte such as NaCl or Na2SO4 to the reactive dye dyebath and reducing the liquor ratio used for immersion dyeing have the same result, namely that of encouraging dye aggregation in the dyebath, which reduces the solubility of the direct dye in the dyebath, which, in turn, shifts the inherent preference of the dye to favour the aqueous phase towards the fibre phase. It is thus possible to dye cotton using pure reactive dyes in the complete (ie 100%) absence of added inorganic electrolyte. The ensuing dyeings were of realistic depths of shade and displayed excellent levels of wash fastness.