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.

Temperature- and Composition-Induced Multiarchitectural Transitions in the Catanionic System of a Conventional Surfactant and a Surface-Active Ionic Liquid.

The mixture of the cationic surfactant, cetyltrimethylammonium bromide (CTAB), and anionic surface-active ionic liquid, 1-butyl-3-methylimidazoliumdodecyl sulfate (bmimDS), has been studied as a function of the mole fraction of CTAB, X CTAB, with the total surfactant concentration fixed at 50 mM using turbidity measurements, rheology, dynamic light scattering, differential scanning calorimetry, small-angle neutron scattering, and small-angle X-ray scattering techniques. The catanionic mixture has been found to exhibit phase transitions from vesicles to micelles as a function of temperature, with some mole fractions of CTAB showing dual transitions. Solutions of X CTAB = 0.2 to 0.5 exhibited a single transition from vesicles to cylindrical micelles at 45 °C. With an increase in the mole fraction of CTAB from 0.55 to 0.65, dual structural transitions at 30 and 45 °C were observed. The microstructural transition at 30 °C is ascribed to the vesicle aggregation process with smaller vesicles fusing into bigger ones, whereas the transition at 45 °C was evaluated to be the vesicle-to-cylindrical micelle transition. However, at higher mole fractions of CTAB, X CTAB from 0.65 to 0.90, a single transition from vesicles to small cylindrical/spherical micelles was observed in the solutions, at a lower temperature of 30 °C. To the best of our knowledge, such a microstructural transitions as a function of temperature in a single mixture of cationic and anionic surfactants without any additive has not been reported so far.

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.

Co-solubilization of polycyclic aromatic hydrocarbon mixtures in aqueous micellar systems and its correlation with FRET for enhanced remediation processes.

Surfactant enhanced remediation (SER) is an effective approach for decontaminating the PAH polluted soils. Solubilization and Cosolubilization of Phenanthrene (Ph), Pyrene (Py) and Perylene (Pe) as single, binary and ternary mixtures have been studied employing cationic (CTAB), anionic (SDS), non-ionic surfactant (Brij 30) and block copolymer (P123) micelles. In the single solute solubilization studies, solubility of Pe follows the order Brij 30 > CTAB > SDS whereas Ph or Py followed the order of CTAB > Brij 30 > SDS. In the cosolubilization studies, an increase, decrease or no change in the mutual solubility of PAHs was observed. Synergism in solubilization was observed most in P123 in both binary and ternary PAH mixture where more PAHs could get solubilized in the dense micellar shell region, thereby enhancing the micellar core volume leading to enhanced solubilization of PAHs. The solubilizates as pairs (Ph-Pe and Py-Pe) were further tested for any possible energy transfer in presence of surfactant based restricted host environments using spectrofluorometry and spectrophotometry. Based on the solubilization and cosolubilization an efficient non-radiative energy transfer (FRET) was observed between Ph/Py (donor) and Pe (acceptor) in the non-ionic surfactant system as well as in CTAB-Brij 58 mixed system. The results of this work may improve the effective utilization of surfactants in their correct evaluation for the removal of PAHs from contaminated soils or aquifers treated with SER technology.

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.

Rheological response of methylcellulose toward alkanediyl-α,ω-bis(dimethylcetylammonium bromide) surfactants with varying spacer length.

The modulation of properties of methylcellulose (MC) by cationic gemini surfactants with varying spacer lengths was studied employing tensiometry, rheometry and turbidimetry. Surface tension measurements anticipate that the gemini surfactant with longer spacer chain length saturates MC at lower concentrations owing to its greater hydrophobicity compared to shorter spacer analogues. Rheometric and turbidimetric measurements suggest that at very low concentrations of gemini surfactants, ion-dipole type of interactions between MC and gemini surfactants promote the extension of polymer chains which is manifested by an initial increase in the low shear viscosity and gelation temperature of MC-gemini surfactant systems, and lowering of turbidity. Such interactions were found to be stronger in case of 16-4-16 than 16-5-16, and almost absent in case of 16-6-16 surfactant system. However at concentrations above CAC, hydrophobic forces operative between MC and gemini surfactants were found to be more for 16-6-16 than that of 16-5-16 and 16-4-16. The final levelling of MC viscosity in presence of all the three gemini surfactants and the variation of gelation temperature suggests the solubilization of network junctions in the surfactant micelles. Moreover, the presence of gemini surfactant strongly affects the interaction of MC with a model hydrophobic drug rifampicin.The results highlight the importance of gemini surfactants and their spacer length in controlling the structural dynamics of MC and its effective use in pharmaceutical and food industry.

Rheological behavior and Ibuprofen delivery applications of pH responsive composite alginate hydrogels.

Synthesis and structural characterization of hydrogels composed of sodium alginate, polyethylene oxide and acrylic acid with cyclodextrin as the hydrocolloid prepared at different pH values is presented. The hydrogels synthesized show significant variations in rheological properties, drug encapsulation capability and release kinetics. The hydrogels prepared at lower pH (pH 1) are more elastic, have high tensile strength and remain almost unaffected by varying temperature or frequency. Further, their Ibuprofen encapsulation capacity is low and releases it slowly. The hydrogel prepared at neutral pH (pH 7) is viscoelastic, thermo-reversible and also exhibits sol-gel transition on applying frequency and changing temperature. It shows highest Ibuprofen encapsulation capacity and also optimum drug release kinetics. The hydrogel prepared at higher pH (pH 12) is more viscous, has low tensile strength, is unstable to change in temperature and has fast drug release rate. The study highlights the pH responsiveness of three composite alginate hydrogels prepared under different conditions to be employed in drug delivery applications.

Hydrogels of sodium alginate in cationic surfactants: Surfactant dependent modulation of encapsulation/release toward Ibuprofen.

The interaction of cetyltrimethylammoium bromide (CTAB) and its gemini homologue (butanediyl-1,4-bis (dimethylcetylammonium bromide), 16-4-16 with biocompatible polymer sodium alginate (SA) has been investigated in aqueous medium. Addition of K2CO3 influences viscoelastic properties of surfactant impregnated SA via competition between electrostatic and hydrophobic interactions. Viscosity of these polymer-surfactant systems increases with increase in concentration of K2CO3, and a cryogel is formed at about 0.5M K2CO3 concentration. The thermal stability of gel (5% SA+0.5M K2CO3) decreases with increase in surfactant concentration, a minimum is observed with increase in 16-4-16 concentration. The impact of surfactant addition on the alginate structure vis-à-vis its drug loading capability and release thereof was studied using Ibuprofen (IBU) as the model drug. The hydrogel with 16-4-16 exhibits higher IBU encapsulation and faster release in comparison to the one containing CTAB. This higher encapsulation-cum-faster release capability has been related to micelle mediated solubilization and greater porosity of the hydrogel with gemini surfactant.

Cosolubilization of Coumarin30 and Warfarin in Cationic, Anionic, and Nonionic Micelles: A Micelle-Water Interfacial Charge Dependent FRET.

Solubilization of structurally varied coumarins, viz., Warfarin (WF; a 4-hydroxy coumarin) and Coumarin30 (C30, a 7-amino coumarin) individually and in mixed states (cosolubilization) within the aqueous surfactant self-assemblies of varying architectures has been explored, exploiting steady-state, time-resolved fluorimetric, and spectrophotometric techniques. Cosolubilization studies within micelles, which have rarely been done in the literature, were specifically undertaken with the aim of understanding the effect of micelles on their photophysical phenomena when simultaneously present within these nanocarriers and assess their prospective use as an efficient FRET pair. WF solubilizes within CTAB micelles, whereas little or no solubilization is observed in Brij30 and SDS micelles. On the other hand, C30 solubilizes deep into the palisade layer of CTAB micelles, between negatively charged head groups in SDS micelles and between OE groups in Brij30 micelles. C30 and WF maintain their solubilization sites during cosolubilization. In SDS and Brij30 micelles, an increase in WF causes fluorescence quenching of C30 molecules, while in CTAB, an increase in WF causes an increase in fluorescence of C30 by excited WF molecules indicating FRET between the two molecules.

An inhibitory effect of self-assembled soft systems on Fenton driven degradation of xanthene dye Rhodamine B.

Rhodamine B (RhB) is known to be a common organic pollutant despite having various technical applications. Treatment of effluents containing such compounds is important so as to minimize their effect on environment. Advanced Oxidation Processes (Fenton and Fenton like reactions) are such methods that can oxidize the contaminants powerfully and non-selectively. This work investigates the oxidation kinetics of dye RhB by hydroxyl radical (OH) generated via Fenton reaction in presence of surfactant assemblies of varying architectures using spectrophotometric, spectrofluorometic and tensiometric methods. The presence of surfactants viz. cationics, non-ionics and some binary mixtures in the pre-micellar and post micellar concentration ranges were found to inhibit the degradation of RhB to a varying degree. However, the reaction was totally inhibited in anionic surfactant. The experimental data was fitted to a pseudo first order kinetic model and the kinetic parameters obtained thereof were explained on the basis of the nature and type of interaction between the cationic form of RhB and the surfactants of varying architectures. The work has a critical significance in view of the fact that degradation studied in presence of surfactant assemblies is more representative than studied in aqueous solution because such conditions compare well with the conditions prevailing in the environment.

Pseudo-indicator behaviour of platinum electrode explored for the potentiometric estimation of non-redox systems.

A pseudo-indicator electrode based potentiometric method for estimation of non-redox metal ions is presented. In the proposed method, nature and concentration specific impact of analyte over the redox potential of ideally polarisable Pt/pregenerated-redox-couple interface forms the basis of quantification. Utility of the method in estimation of six non-redox metal ions viz. Zn(2+), Cu(2+), Ni(2+), Cd(2+), Pb(2+), Al(3+) in the concentration range of 10(-1)-10(-3) moldm(-3), individually and as binary mixtures is also presented. Three types of potentiometric behaviours, which we ascribe to the nature specific thermodynamic and kinetic aspects of metal-EDTA binding, were observed. While Cu(2+), Ni(2+), Pb(2+) and Al(3+) were found to bind EDTA efficiently, without exchanging Fe(3+); Zn(2+) and Cd(2+) were observed to replace Fe(3+) from EDTA. In contrast, Ca(2+) and Mg(2+) were found to show no binding affinity to EDTA in the pH range employed in the present work. The proposed method was also used to explore the reversibility and the Nernestian behaviour of ferricyanide/ferrocyanide redox couple through spectroelectrochemical titration of Zn(2+) with ferrocyanide. The presented method is presaged to be a reliable and low cost future replacement for costly and delicate ion selective electrodes (ISE) in the estimation of non-redox species like Zn(2+), Cu(2+), etc.

Solubilization of triphenylamine, triphenylphosphine, triphenylphosphineoxide and triphenylmethanol in single and binary surfactant systems.

Solubilization and co-solubilization of triphenyls (TPs) viz., triphenylphosphine (TPP), triphenylphosphineoxide (TPPO), triphenylamine (TPA) and triphenylmethanol (TPM) were studied in various single and binary surfactant systems at 25 °C using UV-visible spectroscopy and HPLC. The solubilization capacities of different micelles towards TPs were found to be a function of the nature and structure of solubilizates, locus of solubilization, size of micelles and the nature of interactions between the solubilizate and micelles. The effect of surfactant mixing on the solubilization of TPs was evaluated using the Regular Solution Approach (RSA). The solubility enhancement of TPs within mixed micelles relative to that observed in single surfactant systems was explained in light of the structural micellar changes associated with the mixing of ionic and non-ionic surfactants. Moreover, kinetics of oxidation of TPP by hydrogen peroxide investigated in these surfactant systems was found to be sensitive to the nature of micelle and the locus of solubilization of TPP within the micelles.

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.