Water-insoluble Dyes Research Articles

The aggregation of sodium dehydrocholate in water

We used a battery of different methods to study the association in aqueous sodium dehydrocholate (NaDHC) solutions. This salt associates by a stepwise mechanism. Below (9.6 ± 4.2) × 10−4 mol dm−3 there is a molecular solution with some strongly insoluble dehydrocholic acid produced by hydrolysis. Between (9.6 ± 4.2) × 10−4 and (5.2 ± 2.2) × 10−3 mol dm−3, an aggregate similar to acid soap (NaDHC.HDHC) appears and its amount and the aggregate's size increase with concentration. At =(2.20 ± 0.85) × 10−2 mol dm−3 the aggregates formed have properties usually associated with true micelles, such as solubilisation of water-insoluble dyes. These aggregates increase in size with concentration and change their shape at 8 × 10−2 mol dm−3, giving nonsymmetrical aggregates. The changes in the solution physicochemical properties at these concentrations may be misinterpreted and this explains the different values of the critical micelle concentration reported in the literature for substances with similar structure, such as bile salts.

Thermodynamics of the Solubilization of Water-Insoluble Dyes by Complexes of Cationic Surfactants with Poly(vinyl sulfate) of Different Charge Densities

The solubilization of two water-insoluble dyes, o-(2-amino-1-naphthylazo)toluene (OY) and 1-pyrene-calbaldehyde (PyA), by complexes of anionic polyelectrolyte and alkyltrimethylammonium bromide (C 12 -TAB, C 14 TAB, C 16 TAB) was examined using sodium poly(vinyl sulfate) (PVS) with different charge densities at 298.2 K. The change in the Gibbs function was estimated for this solubilization equilibrium. These complexes showed a larger solubilizing capacity for OY than for PyA. Their capacity for OY was larger than that of the corresponding surfactant micelles. The charge density of PVS influenced the solubilizing capacity in C 12 TAB and C 14 TAB solutions but had little effect in C 16 TAB solutions. PVS with a 40% charge density had the lowest solubilizing capacity. Bound short-chain surfactants are expected to have a smaller lateral interaction with neighboring surfactants bound to PVS with a lower charge density, thus forming a less hydrophobic complex with a lower solubilization capacity. The observed weak solubilization by PVS with a low charge density was ascribed to this less hydrophobic complex.

Solubilization of Water-Insoluble Dyes by Polyion/Surfactant Complexes

Abstract Solubilization data for the water-insoluble dyes o-(2-amino-1-naphthylazo)toluene (OY) and 1-pyrenecarbaldehyde (PyA) in mixed solutions of anionic polyelectrolyte and a cationic surfactant are reported. The polymers used were sodium dextran sulfate (DxS) and the sodium salt of poly(styrenesulfonic acid) (PSS). The surfactants used were dodecyltrimethylammonium bromide (DTAB) and tetradecyltrimethylammonium bromide (TTAB). DxS exhibited a highly cooperative binding of the surfactant ions, while binding to PSS occured at lower surfactant concentrations, but was less cooperative. DxS/surfactant complexes had a larger solubilization capacity per bound surfactant ion for both OY and PyA than did PSS/surfactant complexes. The standard Gibbs energy changes for solubilization in DxS/DTAB were determined to be 4.0 kJ mol−1 for OY and 5.4 kJ mol−1 for PyA; the values in PSS/DTAB were 6.5 kJ mol−1 for OY and 9.3 kJ mol−1 for PyA. The solubilization capacities and standard Gibbs energy changes of polyion/surfactant complexes strongly relate to the binding mode of the surfactant. The differences in the solubilization capacities and standard Gibbs energy changes between polyion/surfactant complexes and DTAB or TTAB micelles, and between OY and PyA, are discussed in relation to the aggregate size and solubilizate location.

ChemInform Abstract: The Synthesis of Some Water Insoluble Dyes for the Measurement of pH in Water Immiscible Solvents

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The synthesis of some water insoluble dyes for the measurement of pH in water immiscible solvents

A series of water insoluble dyes for the measurement of pH in an inaccessible water phase in water immiscible solvents have been designed and synthesised based upon the fluorescein system. The solubilities of the anionic forms of the dyes depend strongly upon the nature of the ester substituent and the degree of substitution of the aromatic rings. For dye molecules with long chain alkyl esters and with bromine substituents in the rings, the sodium or potassium salts are soluble in organic solvents such as diethyl ketone or ethyl acetate and the anions do not partition measurably into aqueous solution. Other less highly substituted dyes can be solubilised as their anions by the addition of quaternary ammonium salts or crown ethers. Titration curves for the dyes show that they are able to respond reproducibly to the pH of a water phase in contact with the organic phase although the detailed physical chemistry of the ion exchange is complex. Certain of the dyes are suitable for monitoring the pH in reaction systems using enzymes as catalysts in water immiscible solvents.

Solubilities of water-insoluble dyes in internal water of swollen Sephadex gels.

It was found that internal water of swollen Sephadex gels could dissolve appreciable amounts of water-insoluble dyes, azobenzene (AB) and dimethylaminoazobenzene (DMAB). The solubilities of AB and DMAB increased exponentially with the concentration of dextran chain in swollen Sephadex gels, i.e., plots of solubility (CG) vs. dextran-chain concentration (Cf) were well described by a family of quartic regression curves (CG=kcf4+C0,k and C0 being constants). The thermodynamic parameters pertaining to the transfer of the dyes from external water to internal water indicate that in water extensively hydrated by gel matrices, "iceberg" formation is markedly hindered and hence the hydrophobic free energy is correspondingly reduced, thereby increasing the solubilities of hydrophobic dyes. Since the solubilities of the dyes are proportional to the fourth power of the dextran-chain concentration in swollen Sephadex gels, it can be assumed that the dyes are accommodated in cooperatively hydrated water contained in unit cells made up of four dextran chains.

Thermodynamics of micellar solubilization of various water-insoluble dyes

A linear relation between the free energy of micellar solubilization,ΔG 0 , and surfactant alkyl chain length is shown. This relation is found to be valid for various water-insoluble dyes in different homologous series of surfactants. It is further shown that the change inΔG 0 per added CH2 group is constant in these various systems, within the experimental accuracy.

A New Technique Using Insoluble Dyestuffs for the Study of Water Movements in Soil

The authors describe the application of a range of water insoluble dyestuffs for use in soil water studies. These water insoluble dyes are easy to prepare, are not washed out of the soil, and can be extracted with simple inexpensive apparatus.

Colloidal Studies on Surface Active Agents. XXIV.

In order to obtain information on the mode of solubilization of water-insoluble dyes into the micelles of nonionic surfactants, polyoxyethylene alkyiphenylethers, the solubilization ratios of dyes to the micelle and their flow dichroism have been investigated. Dyes used are Orange OT and 1, 4-diaminoanthraquinone. Experimental results showed that in every case one molecule of dye is solubilized per micelle at saturation. Above 100g/l of the surfactant concentration flow dichroism was clearly observed and constant differential dichroism was obtained. These facts suggest that above this concentration the shape of the surfactant micelles deviates markedly from sphere and the solubilized dyes orientate in the non-spherical micelles.

Gleichgewichtsuntersuchungen an basischen Triphenylmethan-Farbstoffen in Methanol / Investigations of Equilibria on Basic Triphenylmethane-dyes in Methanol

The pKs* of the equilibrium between the monoacid dyecation and the methylester of twelve organometalically synthesised triphenylmethane dyes were measured spectrophotometrically in methanolic buffer solutions. The pKs of the water-soluble dyes were used to derive an equation, which allows calculation of the pKs (aqueous) of the water-insoluble dyes. The experimental equilibrium constants, which can be interpreted by HMO calculations, satisfy the Hammett ρ-σ-equation.

Successive and Simultaneous Solubilizations of Two Different Water-insoluble Dyes by Detergents

Successive and Simultaneous Solubilizations of Two Different Water-insoluble Dyes by Detergents

Solubilization of orange OT and dimethylaminoazobenzene

Summary Solubilization data have been obtained for aqueous solutions of Na‐laurate, K‐ laute, dodecylamine‐HCL, Tween 20, Span 20, N‐dodecyl‐alanine‐HCl, Na‐oleate, Tergitol 4, and Ultrawet K, using the water insoluble dyes, Orange OT, and dimethylaminoazobenzene as the solubilized substances. Results indicate that the dye solubility method is fairly reproducible. Filtration of samples was found to be an important part of the technique. A slight excess of fatty acid or of alkali in Na‐ and K‐laurate solutions was found to have no appreciable effect on solubilization. In agreement with Kolthoff's but not with Mc‐Bain's findings, the Na‐ and K‐laurates were found to yield the same solubilization of either DMAB or Orange OT, indicating that the solubilizing species in solution depends upon the nature of the long chain ion. Agreement on solubilization for dodecylamine‐HCl with previous workers is poor. The present work indicates no solubilization below the critical micelle concentration. The apparent solubilization reported by Kolthoff was attributed to suspended dye. The use of solubilization data in the determination of critical micelle concentration is examined, and values are compared with previous works.

Bactericidal Activity of Phenols in Aqueous Solutions of Soap

INVESTIGATIONS begun in 1940 concerning the bactericidal action of phenols solubilized by aqueous soap solutions were interrupted during the War but resumed in 1946. Results with a water-insoluble phenol (5-chloro-2 hydroxy-diphenyl methane) using potassium laurate as the soap will be published shortly and have shown (a) that the solubilization of the phenol in the soap solution commences at the critical concentration for initial formation of micelles, and that the solubility curve is of the same form as that quoted for solubilization of water-insoluble dyes by soap solutions1,2 ; (b) that the bactericidal activity of the phenol soap solutions is a function of the concentration of the phenol in the micelles.