Sahar Uzair

Conductometric and fluorometric studies of sodium dodecyl sulphate in aqueous solution and in the presence of amino acids

The critical micelle concentration (CMC) of sodium dodecyl sulphate (SDS) in pure water and in the presence of amino acids (0.01, 0.02 and 0.03 mol kg−1), L-valine (Val) and L-leucine (Leu) was determined from conductometric and fluorometric methods using pyrene as luminescence probe. Depression in the CMC at low concentration of amino acids is attributed to the increased hydrophobic–hydrophobic interaction between the non-polar groups of the surfactant, while, at high concentration, amino acids bind strongly with the anion, DS−, head groups of SDS, thereby, delaying the micelle formation, resulting in increased CMC. A pronounced decrease in the CMC, while a marked increase in λ0+, with decrease in the solvated radius (rather than crystal radius) of the counterions is observed. Negative values of ΔG0m and ΔH0m indicate that micellisation of SDS in the presence of amino acids is thermodynamically spontaneous and exothermic. Highest negative value of ΔH0m in 0.01 m Val, with lowest CMC value, shows that 0.01 m aqueous Val is the most suitable medium favouring the micellisation of SDS. Decrease in I1/I3 from Val to Leu confirms the relative hydrophobicity of two amino acids. The observed values of the packing parameter, P, of SDS in water and in aqueous amino acids suggest that micelles formed are spherical in nature.

Hexadecyltrimethylammonium bromide micellization in glycine, diglycine, and triglycine aqueous solutions as a function of surfactant concentration and temperatures

Micellization behavior of hexadecyltrimethylammonium bromide (HTAB) was investigated conductometrically in aqueous solutions containing 0.02 mol kg−1glycine (Gly), diglycine (Gly-Gly), and triglycine (Gly-Gly-Gly) as a function of surfactant concentration at different temperatures. The critical micelle concentration (CMC) of HTAB exhibits a decreasing trend as the number of carbon atoms increases from Gly to Gly-Gly-Gly, favoring the micelle formation. The values of CMC and the degree of counterion dissociation of the micelles were utilized to evaluate the standard free energy for transferring the surfactant hydrophobic chain out of the solvent to the interior of the micelle, ΔGHP○, free energy associated with the surface contributions, ΔGS○, standard free energy, ΔGm○, enthalpy, ΔHm○, and entropy, ΔSm○ of micellization were also calculated. The results show that the micellization of HTAB in aqueous solutions as well as in aqueous Gly/Gly-Gly/Gly-Gly-Gly solutions is primarily governed by the entropy gain due to the transfer of the hydrophobic groups of the surfactant from the solvent to the interior part of the micelle. The CMC obtained by fluorometric method is in close agreement with those obtained conductometrically. Furthermore, decrease in the I1/I3 ratio of pyrene fluorescence intensity suggests the solubilization of the additives by the surfactant micelles and that this solubilization increases as the hydrophobicity increases from Gly to Gly-Gly-Gly.

Unusual solvatochromic absorbance probe behaviour within mixtures of poly(ethylene glycol)-400 + ionic liquid, [bmim][Tf2N]

The potentially green solvents made up of ionic liquids (ILs) and poly(ethylene glycols) may have wide range of the applications in many chemical and biochemical fields. In the present work, solvatochromic absorbance probe behaviour is used to assess the physicochemical properties of the mixtures composed of PEG-400+IL, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [bmim][Tf2N]. Lowest energy intramolecular charge-transfer absorbance maxima of a betaine dye, i.e., E(T)(N), indicates the dipolarity/polarizability and/or hydrogen-bond donating (HBD) acidity of the [bmim][Tf2N]+PEG-400 mixtures to be even higher than that of neat [bmim][Tf2N], the solution component with higher dipolarity/polarizability and/or HBD acidity. Dipolarity/polarizability (π(∗)) obtained separately from the electronic absorbance response of probe N,N-diethyl-4-nitroaniline, and the HBD acidity (α) of PEG-400+[bmim][Tf2N] mixtures are also observed to be anomalously high. A comparative study of the PEG+IL mixtures has also been done with PEG-400+molecular organic solvents (protic polar [methanol], aprotic polar [N,N-dimethylformamide], and non polar, [benzene]) mixtures, but these mixtures do not show this type of unusual behaviour. A four-parameter simplified combined nearly ideal binary solvent/Redlich-Kister (CNIBS/R-K) equation is shown to satisfactorily predict the solvatochromic parameters within PEG-400+different solvent mixtures.

Effect of the nature of counterion on the micellar properties of cationic surfactants: a conductometric study

ABSTRACT Interaction of cationic surfactants, tetradecyltrimethylammium bromide (TTAB) and tetradecyltrimethylammonium chloride (TTAC) with anionic dye, tartrazine in aqueous solution has been investigated employing conductometric technique. The free energy of transfer of hydrophobic chain, , surface contribution, and their transfer values, and , free energy, , enthalpy, , and entropy, of micellisation have been calculated. A marked decrease in the critical micelle concentration for TTAB compared to TTAC indicates dramatic role of the smaller counterion Br− over the bigger counterion Cl−. Formation of dye–surfactant ion-pairs which behave as nonionic surfactant has been proposed. Higher negative and positive values for TTAB than TTAC are attributed to difference in the size and nature of the counterions Br− and Cl−. Negative and values clearly suggest that micellisation of TTAB and TTAC is thermodynamically spontaneous and exothermic in nature. As ), it suggests that the process of micellisation is entropy dominated for the two surfactants.

Physico-Chemical Studies of Glycine, L-Alanine, L-Phenylalanine and Glycylglycine in Aqueous Triton X-100 at Different Temperatures

Abstract The densities, ρ and viscosities, η of glycine (Gly), L-alanine (Ala), L-phenylalanine (Phe) and glycylglycine (Gly-Gly) in aqueous Triton X-100 (TX-100) solutions have been measured as a function of amino acid/peptide concentration at 298.15, 303.15, 308.15 and 313.15 K. The experimental data have been utilized to evaluate various thermodynamic parameters, viz., apparent molar volumes, V2, partial molar volumes at infinite dilution, V02, partial molar isobaric expansibilities, ϕ02, partial molar volumes of transfer, ΔtrV02 and A and B-coefficients of viscosity, respectively. The hydration numbers have also been calculated. The results have been discussed in terms of interactions taking place in the present systems. The structure-making/-breaking ability of the solute (amino acid/peptide) in the presence of surfactant, Triton X-100 has also been considered.

A Thermodynamic Study of Lipid–Surfactant Interactions in Non-aqueous Media

Interactions between the cationic surfactant cetyltrimethyl ammonium bromide, dimethylsulphoxide and lauric acid, have been studied in detail using volumetric and viscometric techniques. The critical micelle concentration (cmc) values have been determined using two different methods. The experimental data have been correlated against temperature and concentration using standard relations. From the density of the surfactant, the change of the apparent molar volumes at infinite dilution,

Study of interaction between cationic surfactants and cresol red dye by electrical conductivity and spectroscopy methods

V_{\phi }^{\text{o}}

Solvatochromic Absorbance Probe Behavior within Mixtures of the Ionic Liquid 1-Butyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide + Molecular Organic Solvents

Vϕo, apparent molar volumes at the cmc,