Effect of in situ mixed micellization of ester-functionalized gemini surfactant at different pHs on solubilization and cosolubilization of various polycyclic aromatic hydrocarbons of varying hydrophobicities.

A pH controlled cleavability unfolds the 3-in-1 surfactant feature of an ester-bonded gemini surfactant, 2, 2'-[(oxybis (ethane-1,2-diyl))bis (oxy)]bis (N-hexadecyl-N,Ndimethyl-2-oxoethanaminium) dichloride (C16-C4O2-C16), by reinforcing in-situ mixed micellization between cleaved components at non-neutral pH (pH 3,12). The triplicity is assigned to two mixed-micelle variants at pH 3 and pH 12 besides the unhydrolyzed C16-C4O2-C16 at pH 7. The pH-controlled aggregation of such trichotomic surfactant dramatically enhances the micellar solubilization/cosolubilization of PAHs viz. naphthalene (Np), phenanthrene (Ph), pyrene (Py), perylene (Pe). The cosolubilization of binary/ternary PAH mixtures in such remarkable micellar assemblies at pH 3, 7 and 12 yields intriguing synergistic or antagonistic solubility outcomes correlated to PAH-PAH and PAH-micelle interactions. This study provides valuable insights into the potential applications of the ester-bonded gemini surfactant for the cosolubilization of undesirable hydrophobic compounds at natural sites having variable pH.

Structural changes in trypsin induced by the bile salts: An effect of amphiphile hydrophobicity.

The present study reports the multi-technique results of the interaction of a series of bile salts, sodium cholate (NaC), sodium taurocholate (NaTC), sodium deoxycholate (NaDC), and sodium taurodeoxycholate (NaTDC) with trypsin under the experimental conditions of 25 °C and pH 7.0. The interactions between trypsin and the bile salts were characterized by the surface tension measurements and various spectroscopic techniques like UV-Visible absorption, steady-state fluorescence, and circular dichroism. The results of surface tension measurements reveal a strong interaction of trypsin (50 µM) with the increasing concentration of bile salts, being higher with the bile salt of greater hydrophobicity. The critical aggregation concentration of bile salts in the presence of trypsin (C1) showed that the bile salts interact strongly with the trypsin in the order of NaTDC > NaDC > NaTC > NaC. UV-visible, steady-state fluorescence, and circular dichroism spectroscopic results confirmed significant unfolding of trypsin due to its interaction with the bile salts, the extent of which followed the same sequence as observed in the surface tension results. It could be concluded that the hydrophobic bile salts that show lower C1 values and have less delocalized charge, are more effective in unfolding the trypsin. The study would help understand the hydrophobicity-driven unfolding of proteins aided by biological surfactants like bile salts and help devise efficient proteolytic enzyme-based detergent formulations and understand the role of such amphiphiles as antimicrobial agents.

Energy transduction through FRET in self-assembled soft nanostructures based on surfactants/polymers: current scenario and prospects.

The self-assembled systems of surfactants/polymers, which are capable of supporting energy funneling between fluorophores, have recently gained significant attraction. Surfactant and polymeric micelles form nanoscale structures spanning a radius of 2-10 nm are generally suitable for the transduction of energy among fluorophores. These systems have shown great potential in Förster resonance energy transfer (FRET) due to their unique characteristics of being aqueous based, tendency to remain self-assembled, spontaneous formation, tunable nature, and responsiveness to different external stimuli. This review presents current developments in the field of energy transfer, particularly the multi-step FRET processes in the self-assembled nanostructures of surfactants/polymers. The part one of this review presents a background and brief overview of soft systems and discusses certain aspects of the self-assemblies of surfactants/polymers and their co-solubilization property to bring fluorophores to close proximity to transduce energy. The second part of this review deals with single-step and multi-step FRET in the self-assemblies of surfactants/polymers and links FRET systems with advanced smart technologies including multicolor formation, data encryption, and artificial antenna systems. This review also discusses the diverse examples in the literature to present the emerging applications of FRET. Finally, the prospects regarding further improvement of FRET in self-assembled soft systems are outlined.

Exploiting self-assembled soft systems based on surfactants, biopolymers and their mixtures for inhibition of Citral degradation under harsh acidic Conditions.

The chemical instability of Citral in acidic conditions is viewed as hurdle to commercialize it in food/beverage industries. We attempted to stabilize citral in various single and mixed surfactant systems at pH 1.0 and temperature 25 °C. The study highlights the importance of amount and density of positive charge of cationic surfactants and oxyethylene content of nonionic surfactants at the interface of self-assembly in inhibiting citral degradation. The hybrid of Chitosan and P123 showed a significant increase in the half-life of citral compared to that in its individual components. The results of the study suggest that it is possible to stabilize citral in strong acidic environs having a pH as low as 1.0 using mixed surfactant or polymer-amphiphile systems with significant positive charge/number of oxyethylene in their single components. Such polymer-surfactant systems formulations if biocompatible/food grade may act as promising media to enhance shelf life of citral.

Transforming micelles into mixed micelles: a promising approach to tune the catalytic performance of imidazolium-based surface active ionic liquids toward degradation of rhodamine B.

Herein, we demonstrate that the catalytic performance of imidazolium-based surface-active ionic liquid (SAIL) micelles can be significantly enhanced through the addition of an appropriate type and amount of intelligently conceived amphiphile to form mixed micelles. Specifically, we show that the catalytic performance of 1-dodecyl-3-methyl imidazolium chloride (DDMIMCl) micelles toward the reductive degradation of rhodamine B (RhB), a carcinogenic dye extensively used in multiple industrial applications, can be appreciably boosted through addition of Brij56, a nonionic surfactant. Detailed kinetic investigations on the catalytic performance of pre- and post-micellar concentrations of DDMIMCl and its mixed micelles with Brij56 over various mole fractions, toward the reductive degradation of RhB, are presented. The data analyzed in light of Berezin's kinetic model suggest that the addition of Brij56 to DDMIMCl micelles significantly enhances their catalytic performance. The catalytic activity exhibited by the DDMIMCl-Brij56 (XBrij56 = 0.2) mixed micellar system is better than that reported for many state-of-the-art nanoparticle/homogenous catalysts. The results explained in light of Berezin's kinetic model are well supported by physico-chemical studies like conductometry, fluorimetry and dynamic light scattering. The presented results anticipate stimulation of extensive research activity for exploiting the mixed micellization approach as a novel avenue for modulating the catalytic performance of SAILs.

Broad Spectrum Tunable Photoluminescent Material Based on Cascade Fluorescence Resonance Energy Transfer between Three Fluorophores Encapsulated within the Self-Assembled Surfactant Systems.

A broad spectrum tunable photoluminescent material with dual encryption based on a two-step fluorescence resonance energy transfer (FRET) between pyrene (Py), coumarin 480 (Cou480), and rhodamine 6G (R6G) in micelles of SDS and bmimDS is presented. The phenomenon is achievable due to the encapsulation of the fluorophores within these micelles. The transfer of energy as FRET between the pair Py and Cou480 showed ON at 336 nm and OFF at 402 nm in contrast to the FRET observed between the pair Cou480 and R6G that showed ON at 402 nm and OFF at 336 nm. However, the transfer of energy as FRET occurs from Py to R6G in the presence of Cou480 when excited at 336 nm, thereby making it a chain of three fluorophores with Cou480 acting as a relay fluorophore receiving energy from Py and transferring it to R6G. The different FRET scenarios between the three fluorophores in micelles provide a window for the generation of a matrix of colors, which occupies a significant 2D area in the chromaticity diagram, having potential applications in security printing. The different fluorophoric ratios generate different colors based on their individual photonic emissions and the FRET processes taking place between them. Writing tests were carried out using varied ratios of the fluorophores in the micellar systems producing different colored outputs under the UV light with insignificant visibility under the white light. We envision that this as-discovered three fluorophoric FRET system could form the basis for the future development of multi-FRET light-harvesting devices and anti-counterfeiting security inks based on much simpler non-covalent interaction aided encapsulation of the fluorophores within the self-assembled soft systems.

Aggregation and Rheological Behavior of the Lavender Oil-Pluronic P123 Microemulsions in Water-Ethanol Mixed Solvents.

The effect of lavender oil on aggregation characteristics of P123 in aqueous-ethanolic solutions is investigated systematically by DLS, SANS, and rheology. The solubilization capacity of the P123 based formulations toward Lavender oil increased by increasing P123 concentration. The study unveiled the importance of the short chain alcohol-ethanol, as solubilization enhancer. The apparent hydrodynamic radius (Rh) increased significantly with an increase in lavender oil concentration up to maximum oil solubilization capacity of the copolymer at a particular ethanol concentration. DLS measurements on 5, 10, and 15 wt% P123 in the presence of 25% ethanol revealed the presence of large-sized micellar clusters in addition to the oil swollen micelles. The core size (RC), radius of hard sphere (RHS), and aggregation number (N) obtained from SANS profiles showed considerable enhancement with the addition of lavender oil confirming penetration of oil inside the copolymer. Rheological studies showed that viscosity also increased significantly with the addition of lavender oil near the maximum loading limit of the P123 concentration. Quite interestingly, the sol-gel transition temperature displayed a strong dependence on both P123 as well as oil concentration and decreased almost linearly by increasing oil concentration. This study demonstrates the use of a biocompatible and temperature sensitive self-assembled P123 based formulation for lavender oil solubilization that can be beneficial in the cosmetic industry wherein controlled release of fragrances and so forth is demanded.

Exploiting Co-solubilization of Warfarin, Curcumin, and Rhodamine†B for Modulation of Energy Transfer: A Micelle FRET On/Off Switch.

Two new FRET pairs, warfarin (WF)-curcumin (CUR) and curcumin-rhodamine B (RhB), are explored by using surfactant-based self-assembled soft systems as scaffolds. The study is extended to design a two-step concurrent FRET system based on these three fluorophores, which is an important mechanism to devise artificial light-harvesting/antenna systems. Surfactant systems of varying nature (cationic, anionic, nonionic, and zwitterionic) are exploited to modulate the energy transfer in different FRET systems. Interestingly, micelle/water interfacial-charge-responsive FRET is observed owing to selective solubilization of the fluorophores during co-solubilization. The step-one FRET (WF→CUR) is switched on in cationic and zwitterionic media but switched off in anionic/nonionic media, whereas the step-two FRET from CUR to RhB is switched on in anionic/nonionic and zwitterionic media. However, both the FRET steps (WF→CUR→RhB) are observed to be active only in zwitterionic medium. Co-solubilized, appropriately mixed fluorophores having multistep FRET possibilities can be switched on/off selectively as and when required and energy efficiency can be tuned to an optimal level by varying the nature and geometry of the micellar scaffold. Thus, the two FRET pairs selectively acknowledge all types of media for their anticipated applications in biological systems, as structural tools, and for the development of artificial light-harvesting/antenna systems and lasers.

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.

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.