Kashif Naeem

Differential absorbance measurements of amphiphilic hemicyanine dyes, solubilization study in anionic surfactant

Abstract The solubilization of trans -amphiphilic hemicyanine dyes by the micelles of an ionic surfactant was studied by differential spectroscopic method. The critical micelle concentration (CMC) of sodium dodecylbenzenesulfonate (SDBS) with and without hemicyanine dyes was determined by conductivity measurements. The partition coefficient between the bulk water and micelles of SDBS, K x , was calculated using both differential spectroscopic and conductance data at 25.0°C. The standard free energy change of solubilization, Δ G ° p , of these amphiphilic hemicyanine dyes was determined from the partition coefficient values. The linear dependence of the free energy change on the length of dialkyl hydrocarbon chains of the dyes on solubilization predicted the contribution of a methylene group to the free energy change, i.e. −1.091 kJ mol −1 . The increase in K x values with the hydrophobicity of the dyes indicated that the solubilization was controlled mainly by the hydrophobic interaction between the dyes and the micelles. The interaction coefficient ( θ ) and relative solubility ( S t / S o ) of dyes within the SDBS micelles has also been evaluated and discussed.

SYNTHESIS OF CATIONIC HEMICYANINE DYES AND THEIR INTERACTIONS WITH IONIC SURFACTANTS

Abstract Cationic hemicyanine dyes, 1-methyl-4[4-(di-n-alkylamino)styryl] pyridinium betaines containing dialkyl chains in the range C1 to C4 were synthesized and characterized. The interactions of dyes with cationic surfactant, cetyltrimethylammonium bromide (CTAB) and an anionic surfactant, sodium dodecyl sulfate (SDS) were studied by measuring their visible absorption spectra as a function of surfactant concentration below and above their critical micelle concentrations. Owing to lower hydrophobicity of the dyes, the electrostatic interactions between the dyes and the surfactants seemed to play an important role in the penetration of the dyes into the surfactant micelles.

A spectroscopic study of hemicyanine dyes in anionic micellar solutions

The interaction of amphiphilic hemicyanine dyes i.e. (dialkylamino)stilbazolium butyl sulphonate (R = −CH3 to −C5H11) with sodium dodecyl sulphate (SDS), an anionic surfactant, in the process of solubilization was studied by absorption spectra as a function of surfactant concentrations above and below critical micelle concentration. Absorption spectra showed a red shift for dyes with small dialkyl chains and a blue shift for dyes with long dialkyl chains. Electronic transition energies (ΔET) and the approximate number of dye molecules incorporated per micelle were estimated at particular surfactant concentrations. Hydrophobic-hydrophilic force balance plays an important role in the process of solubilization of dyes in aqueous micellar solution.

Partition Coefficient of Amphiphilic Hemicyanine Dyes between the Aqueous and the Micellar Phase of Sodium Dodecyl Sulfate by Differential Absorbance Spectroscopy

Abstract Solubilization in terms of hydrophobic interactions of amphiphilic hemicyanine dyes by micelles of the anionic surfactant sodium dodecyl sulfate was studied. The critical micelle concentration was determined by a specific conductivity method. The water–micelle partition coefficient ( K x ) of these dyes was determined using a differential absorbance technique. The standard free energy change of solubilization (Δ G ° p ) and free energy change per methylene group of the dyes, Δ G °(CH 2 ) at 25°C was also calculated. K x , Δ G ° p , and Δ G °(CH 2 ) were also calculated using both conductivity and differential absorbance data. Lengthening of the dialkyl chains of the hemicyanine dyes led to greater hydrophobic interaction and consequently enhanced solubility within micelles of sodium dodecyl sulfate.

SOLUBILIZATION OF SHORT CHAIN PHENYLALKANOIC ACIDS BY A CATIONIC SURFACTANT, CETYLTRIMETHYLAMMONIUM BROMIDE

Abstract The solubilization of short chain phenylalkanoic acids by the aqueous micellar solution of cetyltrimethylammonium bromide (CTAB) has been studied as a function of surfactant concentration. The micelle-water partition coefficient, Kx, and the standard free energy change of solubilization, ΔG°p, of these additives in the CTAB micelles was determined by using both differential spectroscopic and conductance data at 25.0°C. The critical micelle concentration (CMC) of CTAB in the presence of small amount of these additives was determined by conductivity method. The relative solubility and approximate number of additive molecules per micelle was also estimated at a particular concentration of the surfactant.

Spectroscopic analysis of naphtholazobenzimidazole in organised solution

Micelle–water partition coefficient (Kx ) of naphtholazobenzimidazole dye (NAB) in aqueous solutions of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulphate (SDS) has been determined spectrophotometerically. Changes in absorption patterns of dye caused by surfactants and solvents were quantified in terms of dye–surfactant ratio (n D/n S) and solvent water partition coefficients (P), respectively. Multiple residence sites have been suggested for dye molecules within micelles, based on shifts in azo-hydrazone tautomeric equilibrium. Micelle–water partition coefficients were used to evaluate the influence of dye on critical micelle concentration of CTAB and SDS. At same micelle concentration, M, the relative solubility of NAB was greater in cationic surfactant CTAB than in anionic surfactant SDS.