Aijaz Ahmad Dar

Effect of Surfactant Mixing on Partitioning of Model Hydrophobic Drug, Naproxen, between Aqueous and Micellar Phases

Mixed surfactants may improve the performance of surfactant-enhanced solubilization of drugs and thus can serve as the tool for increased bioavalaibility, controlled drug release, and targeted delivery. Solubilization of Naproxen by micellar solutions at 25 degrees C using single and mixed surfactant systems was measured and compared. Solubilization capacity determined with spectrophotometry and tensiometry has been quantified in terms of molar solubilization ratio, micelle-water partition coefficient, and locus of solubilization. Cationic surfactants exhibited higher solubilization capacity than nonionics and anionics, the efficiency increasing with chain length. Mixing effect of surfactants on mixed micelle formation and solubilization efficiency has been discussed in light of regular solution approximation (RSA). Equimolar cationic-nonionic surfactant combinations showed better solubilization capacity than pure cationics or nonionics, which, in general, increased with increase in hydrophobic chain length. Equimolar cationic-nonionic-nonionic ternary surfactant systems exhibited intermediate solubilization efficiency between their single and binary counterparts. Use of RSA has been extended, with fair success, to predict the partition coefficient of ternary surfactant systems using data from binary mixtures. The theoretical micelle-water partition coefficients calculated from the geometric mean equation compared well with experimental values. Locus of solubilization of NAP in different micellar solutions was probed by UV-visible spectroscopy.

Micellization and interfacial behavior of binary and ternary mixtures of model cationic and nonionic surfactants in aqueous NaCl medium

Mixed micelle formation and interfacial properties of aqueous binary and ternary combinations of hexadecyltrimethylammonium bromide (C(16)Br), hexadecylbenzyldimethylammonium chloride (C(16)BzCl) and polyoxyethylene (20) cetyl ether (Brij58) at 25 degrees C in 30 mM aqueous NaCl have been studied in detail employing tensiometric and fluorimetric techniques. The micellar and adsorption characteristics like composition, activity coefficients, mutual interaction parameters and free energy of micellization have been estimated using the theoretical approaches of Clint, Rosen, Rubingh, Blankschtein et al., Rubingh-Holland and Maeda. A comprehensive account of the comparative performance of these models on the selected cationic-cationic-nonionic surfactant mixtures at constant ionic strength has been presented. The Blankschtein model predicted lower synergism than from Rubinghs method because it neglects the contribution due to steric interaction between surfactant head groups of different sizes and charges. Free energy of micellization calculated using Maedas approach, which employs interaction parameter and micellar mole fraction from Rubinghs model as inputs, shows good correlation with that calculated from commonly used phase separation model. The present study also reveals that the modified Rubingh-Holland method along with the Rosens model can be applied to analyze the interfacial characteristics of ternary surfactant mixtures with a fair degree of success thereby widening the domain of applicability of this model.

Solubilization capabilities of mixtures of cationic Gemini surfactant with conventional cationic, nonionic and anionic surfactants towards polycyclic aromatic hydrocarbons.

Solubilization capabilities of equimolar mixed micellar solutions of Gemini surfactant, C(16)H(33)N(+)(CH(3))(2)(CH(2))(5)N(+)(CH(3))(2) C(16)H(33) 2Br(-) (G) with cetylpyridinium chloride (CPC), sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and Brij56 towards polycyclic aromatic hydrocarbons (PAHs), viz pyrene and anthracene are studied spectophotometrically at 25 degrees C and then compared. The results showed that irrespective of the surfactant type, the solubility of PAHs increases linearly with increasing surfactant concentration, as a consequence of association between the PAH and micelles. Solubilization capacity has been quantified in terms of molar solubilization ratio (MSR), micelle-water partition coefficient (K(m)), ratio of binding constant (K(1)) between the micelle and PAH to the aggregation number (N) of surfactant solution and free energy of solubilization (DeltaG(s)(0)) of PAHs. Equimolar binary surfactant mixtures showed higher solubilization capacity than their respective individual surfactants except G-CPC wherein the values were intermediate between the two. The mixed micellization parameters viz interaction parameter, beta, micellar mole fraction within the mixed micelle, X(i), and activity coefficients, f(i,) were evaluated using Rubingh approach. The values of X(i) were then employed to evaluate solubilization efficiency of mixed micelles using Regular solution approach (RSA). In addition experimental micelle-water partition coefficients of hydrocarbons have been compared with those predicted theoretically by geometric mean equation for mixed Gemini-conventional surfactant systems. Such mixed systems promise to improve the performance of surfactant enhanced remediation of soils and sediments by decreasing the applied surfactant level and thus remediation cost.

Interaction of a cationic gemini surfactant with conventional surfactants in the mixed micelle and monolayer formation in aqueous medium

Mixed micellization and surface properties of binary mixtures of cationic gemini surfactant butanediyl-alpha,omega-bis(dimethylcetylammonium bromide) (G4, 16-4-16) with conventional surfactants cetylpyridinium chloride (CPC), sodium bis(2-ethylhexyl)sulfosuccinate (AOT), and polyoxyethylene 10 cetyl ether (Brij56) have been studied using conductometric and tensiometric methods. To explain and compare the results theoretical models of Rubingh, Rosen, Clint, and Maeda have been used to obtain the interaction parameter, minimum area per molecule, surface excess, mixed micelle composition, free energies of micellization and adsorption, and activity coefficients. The activity coefficients and experimental critical micelle concentration (cmc) values are less than unity indicating synergism in micelles as well as at interface. Also, expansion of the minimum area per molecule was observed in the binary systems supported by low values of packing parameter.

Analysis of mixed micellar and interfacial behavior of cationic gemini hexanediyl-1,6-bis(dimethylcetylammonium bromide) with conventional ionic and nonionic surfactants in aqueous medium.

The interaction between cationic gemini hexanediyl-1,6-bis(dimethylcetylammonium bromide) (16-6-16, abbreviated as G6) with conventional cationic cetylpyridinium chloride (CPC), anionic sodium bis(2-ethyl hexyl)sulfosuccinate (AOT) and nonionic polyoxyethylene 10 cetyl ether (Brij56) in aqueous medium has been investigated at 25 degrees C. Different physicochemical properties such as critical micelle concentration (cmc), surface excess concentration (Gamma(max)), minimum area per molecule (A(min)), and interaction parameters (beta(m), beta(sigma)) as well as other thermodynamic and micellar properties have been determined. The interfacial and bulk behaviors were explored using theoretical models of Clint, Rubingh, Rosen, Motomura, and Maeda for justification and comparison of results of different binary combinations with the geminis of alkanediyl-alpha,omega-bis(dimethylcetylammonium bromide) series. Synergism was observed in all the binary combinations in the micelle and at interface with lowering of packing parameter due to slight expansion of A(min). The results of the present study could be of interest for selection of surfactant mixtures for surfactant-enhanced remediation (SER) of soils and aquifers contaminated by hydrophobic organic compounds (HOCs).

Interaction of Bovine Serum Albumin with Cationic Single Chain+Nonionic and Cationic Gemini+Nonionic Binary Surfactant Mixtures

The interaction of bovine serum albumin (BSA) with cetyltrimethylammonium bromide (CTAB), C(16)C(4)C(16)Br(2), Brij58, and their binary mixtures has been studied using tensiometry, spectrofluorometry, and circular dichroism at physiological pH and 25 degrees C. The tensiometric profiles of CTAB and C(16)C(4)C(16)Br(2) in the presence of BSA exhibit a single break at a lower surfactant concentration termed as C(1) (concentration corresponding to saturation of the interface) compared to their critical micelle concentration (CMC) in the buffered solution. However, for Brij58, CTAB+Brij58, and C(16)C(4)C(16)Br(2)+Brij58, two breaks were observed, first at the critical aggregation concentration (CAC), corresponding to onset of interaction with BSA and the second at C(1) corresponding to saturation of the interface. The interaction of CTAB+Brij58 and C(16)C(4)C(16)Br(2)+Brij58 mixtures with the BSA solution is discussed in terms of competition between surfactant-surfactant and surfactant-BSA interactions. CTAB+Brij58 and C(16)C(4)C(16)Br(2)+Brij58 mixtures show nonideality with respect to mixed micelle formation, which is reflected in their interaction with the BSA. The interaction of CTAB+Brij58 with BSA decreases with increase in the mole fraction of CTAB in the mixture, whereas in C(16)C(4)C(16)Br(2)+Brij58 the reverse is the case. The results of the present study may prove fruitful in optimizing the properties of surfactant-protein mixtures relevant for many formulations.

Effect of spacer length of alkanediyl-α,ω-bis(dimethylcetylammonium bromide) gemini homologues on the interfacial and physicochemical properties of BSA

The interactions of bovine serum albumin (BSA) with cationic gemini surfactants alkanediyl-alpha,omega-bis(dimethylcetylammonium bromide) (designated as C(16)C(s)C(16)Br(2), s=4, 5, and 6) and single chain surfactant cetyltrimethylammonium bromide (CTAB) have been investigated with tensiometry, Rayleighs scattering, fluorescence spectroscopy, and circular dichroism at physiological pH and 25 degrees C. The results of the multi-technique approach showed that the gemini surfactants interact more efficiently with the proteins than their conventional single chain counterparts and their efficiency increases with decrease in the length of the spacer. The saturation in interfacial tension occurred at a lower concentration in presence of BSA compared to CMC of the surfactants in absence of BSA and the concentration of gemini surfactants corresponding to interfacial saturation decreases with decrease in the spacer length. Fluorescence and circular dichroism spectroscopy results revealed increase in unfolding of BSA with decrease in spacer length of gemini surfactants.

Competitive solubilization of naphthalene and pyrene in various micellar systems

Cosolubilization of polycyclic aromatic hydrocarbons (PAHs) (naphthalene and pyrene) has been studied in surfactant systems of varying nature of their head-group viz. nonionic: Brij30 and Brij56, cationic: DDEAB and CTAB and anionic: SDS. Solubilization capacity of micelles was quantified in terms of molar solubilization ratio, the micelle-water partition coefficient, the first stepwise association constant and average number of solubilizate molecules per micelle determined by employing spectrophotometric and tensiometric techniques. Solubilization capacity of all the surfactant systems was generally higher for naphthalene than pyrene and followed the order: nonionics>cationics>anionic surfactant. Solubility of naphthalene decreased during cosolubilization in all surfactant systems studied while the solubility of pyrene decreased only in Brij30 and Brij56 surfactant systems due to competitive solubilization of PAHs for the same solubilization site. The solubility of pyrene, however, enhanced in presence of naphthalene in CTAB, DDEAB and SDS surfactant systems owing to increase in core volume of the micelles by the palisade layer solubilization of naphthalene. The results of this study can provide valuable information on the selection of particular surfactant systems for selective separation of naphthalene and pyrene from their mixture relevant to surfactant enhanced remediation (SER) technology at the contaminated sites.

Role of added counterions in the micellar growth of bisquaternary ammonium halide surfactant (14-s-14): 1H NMR and viscometric studies.

The change in the morphology of a series of dicationic gemini surfactants C(14)H(29)(CH(3))(2)N(+)-(CH(2))(s)-N(+)(CH(3))(2)C(14)H(29), 2Br(-) (14-s-14; s=4-6) on their interaction with inorganic (KBr, KNO(3), KSCN) and organic salts (NaBenz, NaSal) have been thoroughly investigated by means of (1)H NMR spectral analysis and the results are well supported by viscosity measurements. The presence of salt counterions results in structural transition (spherical to nonspherical) of gemini micelles in aqueous solution. With an increase in salt concentration all the three gemini surfactants showed changes in their aggregate morphology. This change is dependent on the nature and size of the added counterion. The effect of inorganic counterions on the micellar growth is observed to follow the Hofmeister series (Br(-) < NO(3)(-) < SCN(-)). The roles of organic counterions are discussed on the basis of probable solubilization sites of the substrate molecule in the gemini micelles, showing more growth in case of Sal(-) than Benz(-). The results are confirmed in terms of the obtained values of chemical shift (δ), line width at half height (lw), and relative viscosity (η(r)). Also, the growth of micelles was most pronounced for the gemini surfactant with the shortest spacer (s=4). This was attributed to the unique molecular structure of gemini surfactant micelles having flexible polymethylene spacer chain linking the twin polar headgroups.

Effects of surfactant micelles on solubilization and DPPH radical scavenging activity of Rutin

The interaction of the antioxidant Rutin with the radical DPPH (2,2-diphenyl-1-picrylhydrazyl) in presence of cationic (CTAB, TTAB, DTAB), non-ionic (Brij78, Brij58, Brij35), anionic (SDS) and mixed surfactant systems (CTAB-Brij58, DTAB-Brij35, SDS-Brij35) has been followed by spectrophotometric and tensiometric methods to evaluate the DPPH radical scavenging activity (RSA) of Rutin in these model self-assembled structures. The results show that the solubilization capacity of various single surfactant systems for both DPPH as well as Rutin followed the order cationics > non-ionics > anionic. The radical scavenging activity of Rutin in the solubilized form was higher within ionic micelles than in non-ionic micelles. However, the antioxidant exhibited enhanced activity for the radical in mixed cationic-non-ionic micelles compared with any of the single component micelles. In contrast, anionic-non-ionic mixed micelles modulated the activity of Rutin in-between that seen for pure anionic and non-ionic micelles only.