Tushar J. Trivedi

Aggregation behavior of amino acid ionic liquid surfactants in aqueous media.

Self-aggregation of amino acid ionic liquid surfactants (AAILSs) in aqueous solution has been investigated through surface tension, conductivity, steady-state fluorescence, dynamic light scattering (DLS), and transmission electron microscopy (TEM). The critical aggregation concentration (cac) of AAILSs obtained from different techniques showed fairly good agreement. Surface tension measurements have been used to derive surface adsorption properties such as adsorption efficiency (pC(20), effectiveness of surface tension reduction (Π(cac)), and minimum surface area per molecule (A(min)) at the air-water interface. Temperature-dependent conductivity measurements have been used to obtain the degree of counterion binding (β), and the thermodynamic parameters such as standard free energy (ΔG(agg)(0)), enthalpy (ΔH(agg)(0)), and entropy (ΔS(agg)(0)) of aggregation. The aggregation number (N(agg)) for various AAILSs has been derived by using the fluorescence quenching technique. Size of the aggregates has been obtained from DLS and TEM measurements. The aggregation properties of AAILSs have been analyzed as a function of structure of amino acids and compared with those of analogous ionic liquids (ILs) and conventional ionic surfactants. Surface activity of the AAILSs has been found superior to that of analogous ILs and conventional ionic surfactants of the same alkyl chain length.

Aqueous-biamphiphilic ionic liquid systems: self-assembly and synthesis of gold nanocrystals/microplates.

Biamphiphilic ionic liquids (BAILs) based on 1,3-dialkylimidazolium cation and alkyl sulfate anions ([C(n)H(2n+1)mim][C(m)H(2m+1)OSO(3)]; n = 4, 6, or 8; m = 8, 12) have been synthesized and characterized for their self-assembling behavior in the aqueous medium. Effects of alteration of alkyl chain length in cation and anion on surfactant properties of BAILs have been examined from surface tension measurements. The effectiveness of surface tension reduction for BAILs has been found to be exceptionally higher as compared to single chain surface active ILs/conventional surfactants. The thermodynamics of the aggregation process has been studied using isothermal titration calorimetry (ITC) and temperature dependent conductivity experiments. Dynamic light scattering (DLS), nuclear magnetic resonance (NMR), and transmission electron microscopy (TEM) studies showed that BAILs formed distinct aggregated structures depending upon the amphiphilic character present in the cation and anion. BAILs ([C(n)H(2n+1)mim][C(m)H(2m+1)OSO(3)]) form micelles when n = 4, 6; m = 8, intermicellar aggregates when n = 4, 6; m = 12, and vesicles when n = 8; m = 8, 12. Gold nanoparticles and microplates have been synthesized in micellar and vesicle solutions of BAILs using a simple photoreduction method. The studies show the potential of BAILs for constructing micelles and supramolecular assemblies, such as bilayer vesicles, which are effective in preparation of nanomaterials of controlled size and morphology.

Dissolution, regeneration and ion-gel formation of agarose in room-temperature ionic liquids

The suitability of several ionic liquids, containing imidazolium or pyridinium cations with different alkyl chains and anions ranging from small hydrogen-bond acceptors to those of a large and non-coordinating nature, has been tested for solubilization of a widely used biopolymer, agarose. The solubility of agarose was found to depend on both the nature of anion and amphiphilicity of the cation. Dissolved agarose was regenerated using methanol, and ionic liquids were recovered and recycled for different experiments. Regenerated agarose largely maintained the features of native agarose in terms of molecular weight, polydispersity, thermal stability and crystallinity but varied slightly in conformation preferences. Subsequently, agarose-based highly conducting soft ion-gels having small thermal hysteresis were prepared and characterized. Such ion-gels have possible applications as electrochemical devices.

Biamphiphilic Ionic Liquid Induced Folding Alterations in the Structure of Bovine Serum Albumin in Aqueous Medium

3-Methyl-1-octylimidazolium dodecylsulfate, [C8mim][C12OSO3], a vesicle forming biamphiphilic ionic liquid (BAIL) (J. Phys. Chem. B 2012, 116, 14363-14374), has been found to induce significant folding alterations in the structure of bovine serum albumin (BSA) in the aqueous medium at pH 7.0. Such alterations have been investigated in detail using various physicochemical and spectroscopic techniques. Different concentration regimes (monomeric, shared aggregation, and post-vesicular) of [C8mim][C12OSO3]-BSA interactions have been defined through adsorption and binding isotherms using tensiometry and isothermal titration calorimetry (ITC). Fluorimetry, circular dichroism (CD), and dynamic light scattering (DLS) measurements have shown that [C8mim][C12OSO3] induces a small unfolding of BSA in the monomeric regime at low concentration (designated as C(f)), which is followed by a refolding up to critical aggregation concentration (CAC) (designated as C1). Above C1, i.e., in the shared aggregation concentration regime, again a small unfolding of BSA was observed up to critical vesicular concentration (CVC) (designated as C2). In the vesicular and post-vesicular regimes, the BSA remained stable against folding alterations. The kinetic stability of BSA in the vesicular concentration regimes was studied for a month using turbidimetry. It has been found that [C8mim][C12OSO3] stabilizes BSA against the aggregation which is the major cause of protein destabilization. The present study gives insights for the design of surface active ILs for protein stabilization as a potential replacement for the mixed micelles of conventional surfactants used in detergent industries for enzyme stabilization and as an artificial chaperone.

Task‐Specific, Biodegradable Amino Acid Ionic Liquid Surfactants

Besides several conventional uses, such as in cleaning products, food, beverages, dairy processing, water treatment, healthcare, fuel and lubricant additives, and emulsifiers or stabilizers in paints or cosmetics, there is an increasing interest in the synthesis of new surfactants for high-end applications such as gene transfection agents, the denaturation/encapsulation of proteins or drugs, or templates for shapeor size-selective and highly ordered nanomaterials. Because of their modular nature and unique physicochemical properties, ionic liquids (ILs) have found widespread application and are used in many areas of chemistry. The inherent amphiphilic character of some ILs has yielded surface-active properties that are different (and better) than those of conventional surfactants, and thus they have emerged as a superior class of surfactants. Also, conventional ionic surfactants suffer from phase separation, owing to solubility limitations, and the fact that the creation of hierarchical micellar systems is usually thermodynamically unfavorable. This restricts their use in many applications, for example, as templates for a desired nanomaterial architectures. In contrast, owing to their strong and directional polarizability and excellent water solubility ILs have been shown to self-assemble into highly structured forms, useful for the preparation of a variety of nanomaterials (e.g. , metals, metal oxides, zeolites). Although IL surfactants used so far are “green” in terms of their negligible vapor pressure, they generally contain synthetic quaternary nitrogen cations (such as alkylammonium, dialkylimidazolium, or pyridinium) with halogen atoms as anions (such as Cl or F). They can release HCl or HF by hydrolysis under certain conditions, which may pose a hazard when they are released into the environment through wastewater effluents. Therefore, toxicity and biodegradation are vital issues when dealing with ILs. In this context, the green credentials of ILs have been tremendously improved by the development of biobased ILs. Herein, we choose natural amino acids and sodium lauryl sulphate (SLS) as precursors for amino acid ionic liquid surfactant (AAILS) architectures. Amino acid-based surfactants, featuring amino acids modified with long aliphatic chains to generate linear, dimeric, or glycerolipid-like structures, have been reported extensively, however, ionic liquid surfactants based on amino acids having a superior surface activity and solvent miscibility are reported here for the first time. From the natural amino acids, l-glycine, l-alanine, l-valine, l-glutamic acid, and l-proline were chosen allow simple variations in the side chain through branching, the addition of another COOH group, or cyclization. Because the incorporation of an ester group into an amino acid has been shown decrease the melting point and significantly increase biodegradability, esterification of the amino acids was carried out by using either isopropyl or isobutyl alcohol. For esterification, thionyl chloride was slowly added to isopropyl or isobutyl alcohol at 0 8C. Amino acids were slowly added to the reaction mixtures, which were then refluxed for 4 h. The reaction mixtures were concentrated in a rotary evaporator, and crude amino acid ester hydrochlorides were titurated with hexane at 0 8C. Pure crystals of amino acid ester hydrochlorides (AAECls) were obtained by recrystallization with methanol/hexane. Equimolar amounts of the AAECls and SLS were then dissolved in hot water. After the completion of reaction, water was removed under vacuum and AAILSs were extracted by the addition of dichloromethane. All of the AAILSs except the one obtained from glutamic butyl ester hydrochloride (white crystalline solid at room temperature) were clear but slightly viscous liquids at room temperature. The reaction sequence is shown in Scheme 1. Detailed preparation, washing, and drying procedures can be found in the Supporting Information. The structures of the AAILSs were confirmed by

Facile preparation of agarose–chitosan hybrid materials and nanocomposite ionogels using an ionic liquid via dissolution, regeneration and sol–gel transition

We report simultaneous dissolution of agarose (AG) and chitosan (CH) in varying proportions in an ionic liquid (IL), 1-butyl-3-methylimidazolium chloride [C4mim][Cl]. Composite materials were constructed from AG–CH–IL solutions using the antisolvent methanol, and IL was recovered from the solutions. Composite materials could be uniformly decorated with silver oxide (Ag2O) nanoparticles (Ag NPs) to form nanocomposites in a single step by in situ synthesis of Ag NPs in AG–CH–IL sols, wherein the biopolymer moiety acted as both reducing and stabilizing agent. Cooling of Ag NPs–AG–CH–IL sols to room temperature resulted in high conductivity and high mechanical strength nanocomposite ionogels. The structure, stability and physiochemical properties of composite materials and nanocomposites were characterized by several analytical techniques, such as Fourier transform infrared (FTIR), CD spectroscopy, differential scanning colorimetric (DSC), thermogravimetric analysis (TGA), gel permeation chromatography (GPC), and scanning electron micrography (SEM). The result shows that composite materials have good thermal and conformational stability, compatibility and strong hydrogen bonding interactions between AG–CH complexes. Decoration of Ag NPs in composites and ionogels was confirmed by UV-Vis spectroscopy, SEM, TEM, EDAX and XRD. The mechanical and conducting properties of composite ionogels have been characterized by rheology and current–voltage measurements. Since Ag NPs show good antimicrobial activity, Ag NPs –AG–CH composite materials have the potential to be used in biotechnology and biomedical applications whereas nanocomposite ionogels will be suitable as precursors for applications such as quasi-solid dye sensitized solar cells, actuators, sensors or electrochromic displays.

Functionalized Agarose Self-Healing Ionogels Suitable for Supercapacitors

Agarose has been functionalized (acetylated/carbanilated) in an ionic liquid (IL) medium of 1-butyl-3-methylimidazolium acetate at ambient conditions. The acetylated agarose showed a highly hydrophobic nature, whereas the carbanilated agarose could be dissolved in water as well as in the IL medium. Thermoreversible ionogels were obtained by cooling the IL sols of carbanilated agarose at room temperature. The ionogel prepared from a protic-aprotic mixed-IL system (1-butyl-3-methylimidazolium chloride and N-(2-hydroxyethyl)ammonium formate) demonstrated a superior self-healing property, as confirmed from rheological measurements. The superior self-healing property of such an ionogel has been attributed to the unique inter-intra hydrogen-bonding network of functional groups inserted in the agarose. The ionogel was tested as a flexible solid electrolyte for an activated-carbon-based supercapacitor cell. The measured specific capacitance was found to be comparable with that of a liquid electrolyte system at room temperature and was maintained for up to 1000 charge-discharge cycles. Such novel functionalized-biopolymer self-healing ionogels with flexibility and good conductivity are desirable for energy-storage devices and electronic skins with superior lifespans and robustness.

Agarose processing in protic and mixed protic–aprotic ionic liquids: dissolution, regeneration and high conductivity, high strength ionogels

We have shown that low viscosity alkyl or hydroxyalkyl ammonium formate (ILs) can dissolve agarose, and higher dissolution can be achieved in the mixed, alkyl or hydroxyalkyl ammonium + imidazolium or pyridinium ILs. The polarity parameters α, β, π*, ET(30) and ETN of these IL systems were measured to explain their dissolution ability for agarose. Dissolved agarose was either regenerated using methanol as a precipitating solvent or ionogels were formed by cooling the agarose–IL solutions to ambient temperature. Exceptionally high strength ionogels were obtained from the agarose solutions in N-(2-hydroxyethyl)ammonium formate or its mixture with 1-butyl-3-methylimidazolium chloride. Regenerated material and ionogels are characterized for their possible degradation/conformational changes and gel properties (thermal hysteresis, strength, viscoelasticity and conductivity) respectively. A high strength, high conducting ionogel was demonstrated to be able to build an electrochromic window. Such ionogels can also be utilized for other soft matter electronic devices and biomedical applications.

Self-assembly of new surface active ionic liquids based on Aerosol-OT in aqueous media

New anionic ionic liquid surfactants have been synthesized by replacing the sodium cation of Aerosol-OT (sodium dioctylsulfosuccinate, [Na]AOT) with various biocompatible moieties, such as 1-butyl-3-methyl imidazolium ([C4mim]), proliniumisopropylester ([ProC3]), cholinium ([Cho]), and guanidinium ([Gua]). The Aerosol-OT derived ionic liquids (AOT-ILs) were found fairly soluble in water and formed vesicles above a critical vesicle concentration (CVC) which depended upon the nature of cation, and followed the order: [ProC3]<[C4mim]<[Gua]<[Cho]<Na(+). The self-assembly process was characterized using surface tension (ST), isothermal titration calorimetry (ITC), conductivity, dynamic light scattering (DLS), nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM). Unlike other AOT-ILs, a structural transformation has been observed for [C4mim]AOT above CVC, because of certain amphiphilic character in the cation [C4mim]. Thermodynamic parameters calculated from ITC and conductivity techniques revealed that the vesicle formation process is entropy driven for [C4mim]AOT, whereas the process is both enthalpy and entropy driven for other AOT-ILs. In order to check the versatility of synthesized AOT-ILs we have tested their dissolution behavior in a different class of ionic liquids. All the AOT-ILs were found fairly soluble in the hydrophilic IL, ethanolammonium formate (EOAF), whereas only [C4mim]AOT and [ProC3]AOT were found soluble in hydrophobic IL, [C4mim]Tf2N. Such combinations can have potential for construction of stable colloidal formulations or microemulsions in ionic liquid media.

A reciprocal binary mixture of protic/aprotic ionic liquids as a deep eutectic solvent: physicochemical behaviour and application towards agarose processing

Apart from structural tuning, the desired properties of ionic liquids (IL) can be achieved through judicious mixing of two or more ionic liquids. Herein we have investigated the alterations in the physicochemical properties of protic/aprotic ILs, (2-hydroxyethylammonium formate/1-butyl-3-methylimidazolium chloride) upon reciprocal binary mixing. Melting point analysis of the mixtures at various mole fractions showed their deep eutectic solvent nature. The variation in physical properties like density, speed of sound, and viscosity have been measured and utilized to derive the volume of mixing, isentropic compressibility, and activation energy of the viscous flow. Unlike the binary mixtures of ILs having common cations or anions, the investigated reciprocal binary mixture showed significant non-ideality, normally desired to take advantage of improved solvent properties. The polarity and ion–ion interactions have been studied through solvatochromic parameters (normalized Reichardts parameter, dipolarity/polarizability, and hydrogen bond donor and acceptor coefficients) derived using solvatochromic probes. The prepared binary mixtures have been utilized for the dissolution of a gelling biopolymer agarose and formation of ionogels. Dissolution of agarose has been correlated with the solvatochromic parameters and the viscoelastic behaviour of ionogels is discussed in light of rheological measurements. The work gives fundamentally useful insights into tuning the properties of ILs for a specific application purpose.