Tejwant Singh Kang

Micellization behavior of morpholinium-based amide-functionalized ionic liquids in aqueous media.

Morpholinium-based amide-functionalized ionic liquids (ILs) [C(n)AMorph][Br], where n = 8, 12, and 16, have been synthesized and characterized for their micellization behavior in aqueous medium using a variety of state of the art techniques. The adsorption and micellization behavior of [CnAMorph][Br] ILs at the air-solution interface and in the bulk, respectively, has been found to be much better compared to that observed for nonfunctionalized homologous ILs and conventional cationic surfactants, as shown by the comparatively higher adsorption efficiency, lower surface tension at the critical micelle concentraiton (γ(cmc)), and much lower critical micelle concentration (cmc) for [C(n)AMorph][Br] ILs. Conductivity measurements have been performed to obtain the cmc, degree of counterion binding (β), and standard free energy of micellization (ΔG(m)°). Isothermal titration calorimetry has provided information specifically about the thermodynamics of micellization, whereas steady-state fluorescence has been used to obtain the cmc, micropolarity of the cybotactic region, and aggregation number (N(agg)) of the micelles. Both dynamic light scattering and atomic force microscopy have provided insights into the size and shape of the micelles. 2D (1)H-(1)H nuclear Overhauser effect spectroscopy experiments have provided insights into the structure of the micelle, where [C16AMorph][Br] has shown distinct micellization behavior as compared to [C8AMorph][Br] and [C12AMorph][Br] in corroboration with observations made from other techniques.

Micellization Behavior of Surface Active Ionic Liquids Having Aromatic Counterions in Aqueous Media.

Amphiphilic ionic liquids (ILs) based on 3-hexadecyl-1-methyl imidazolium cation, [C16mim](+), having aromatic anions, 4-hydroxybenzenesulfonate, [HBS], benzenesulfonate, [BS], and p-toluenesulfonate, [PTS], as counterions have been synthesized and investigated for their micellization behavior in aqueous medium. The surface activity of investigated ILs has been established by surface tension measurements, whereas bulk behavior has been investigated by conductivity and steady-state fluorescence measurements. The investigated ILs exhibited 2-3 fold lower critical micelle concentration (cmc) as compared to analogous ILs or conventional surfactants with nonaromatic counterions. The polarity of the cybotactic region of pyrene decreases along with decrease in extent of water penetration toward palisade layer of micelle with increase in hydrophobicity of counterion. Relatively more hydrophobic anions, i.e., [BS](-) and [PTS](-), have been found to form excimer in palisade layer of micelle, whereas [HBS](-) remains in close vicinity of imidazolium head groups of micelle as established from inherent fluorescence of aromatic anions. Isothermal titration calorimetry measurements have provided insights into thermodynamics of micelles. The strength of binding and relative position of aromatic anions in micelle has been found to affect the characteristic properties of micelle as deduced from (1)H NMR measurements. The micelles with different sizes and shapes such as spherical, partially elongated, or long rod-like micelles have been observed for different ILs depending of nature of aromatic anions as established from dynamic light scattering and transmission electron microscopy measurements.

Ionic Liquid Surfactant Mediated Structural Transitions and Self-Assembly of Bovine Serum Albumin in Aqueous Media: Effect of Functionalization of Ionic Liquid Surfactants

The self-assembly of globular protein bovine serum albumin (BSA) has been investigated in aqueous solutions of ionic liquid surfactants (ILSs), 1-dodecyl-3-methyl imidazolium chloride, [C12mim][Cl], and its amide, [C12Amim][Cl], and ester, [C12Emim][Cl], functionalized counterparts. Dynamic light scattering (DLS) has provided insights into the alterations in hydrodynamic radii (D(h)) of BSA as a function of concentration of ILSs establishing the presence of different types of BSA-ILS complexes in different concentration regimes of ILSs. Isothermal titration calorimetry (ITC) has been exploited to quantify the ILSs interacting with BSA in dilute concentration regime of ILSs. The zeta-potential measurements shed light on changes in the charged state of BSA. The morphology of various self-assembled structures of BSA in different concentration regimes of ILSs have been explored using confocal laser scanning microscopy (CLSM) and scanning electron microscopy. The structural variations in ILSs have been found to produce remarkable effect on the nature and morphology of self-assembled structures of BSA. The presence of nonfunctionalized [C12mim][Cl] IL at all investigated concentrations has led to the formation of unordered large self-assembled structures of BSA. On the other hand, in specific concentration regimes, ordered self-assembled structures such as long rods and right-handedly twisted helical amyloid fibers have been observed in the presence of functionalized [C12Amim][Cl] and [C12Emim][Cl] ILSs, respectively. The nature of the formed helical fibers as amyloid ones has been confirmed using FTIR spectroscopy. Steady-state fluorescence and circular dichroism (CD) spectroscopy have provided insights into folding and unfolding of BSA as fashioned by interactions with ILSs in different concentration regimes supporting the observations made from other studies.

Aggregation behavior of non-cytotoxic ester functionalized morpholinium based ionic liquids in aqueous media

Ester functionalized surface active ionic liquids (SAILs), [CnEMorph][Br], where n=8, 12 and 16, comprising of long hydrophobic chain appended with ester functionality connected to N-methylmorpholine group have been synthesized and investigated for their aggregation behavior and cytotoxicity. A variety of state of art techniques viz. tensiometry, conductometry, isothermal titration calorimetry (ITC), spectrofluorometry, dynamic light scattering (DLS) and atomic force microscopy (AFM) have been employed to get insight into the various aspects of aggregation behavior. The investigated SAILs have been found to possess lower critical aggregation concentration (cac) and greater adsorption efficacy at air-solution interface as compared to earlier reported non-functionalized SAILs or conventional ionic surfactants. Further, the thermal stability of these morpholinium cationics has been evaluated by thermal gravimetric analysis (TGA). These SAILs have been found to be non-cytotoxic in the concentration range generally required for different biological applications as judged by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay on the C6 glioma cell line. The dependence of characteristic properties of aggregation on alkyl chain length has been established.

Nicotine-based surface active ionic liquids: Synthesis, self-assembly and cytotoxicity studies

New ester-functionalized surface active ionic liquids (SAILs) based on nicotine, [CnENic][Br] (n=8, 10 and 12), with bromide counterions have been synthesized, characterized and investigated for their self-assembly behavior in aqueous medium. Conductivity measurements in aqueous solutions of the investigated SAILs have provided information about their critical micelle concentration (cmc), and degree of counterion binding (β), where cmc was found to be 2-3-fold lower than homologous SAILs or conventional cationic surfactants. The inherent fluorescence of SAILs in the absence of any external fluorescent probe have shed light on cmc as well as interactions prevailing between the monomers in micelle at molecular level. The thermodynamic parameters related to micellization have been deduced from isothermal titration calorimetry (ITC) and conductivity measurements. 1H NMR, spin-lattice (T1) relaxation time and 2D 1H-IH ROESY measurements have been exploited to get detailed account of internal structure of micelle. The size and shape of the micelles have been explored using dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements. The synthesized SAILs have been found to be non-cytotoxic towards C6-Glioma cell line, which adds to the possible utility of these SAILs for diverse biological applications.

Greener synthetic route for superparamagnetic and luminescent α-Fe2O3 nanoparticles in binary mixtures of ionic liquid and ethylene glycol

α-Fe2O3 nanoparticles have been synthesized by a facile route employing inherently green binary mixtures of ionic liquid (IL), 1-ethyl-3-methyl imidazolium ethylsulphate, [C2mim][C2OSO3] and ethylene glycol, EG. A room temperature grinding of Fe(NO)3·9H2O in the given binary mixture in the presence of NaOH led to the formation of amorphous particles, which on calcination, yielded α-Fe2O3 nanoparticles (NPs). The obtained NPs have been characterized by various state of the art techniques such as X-ray diffraction, Raman spectroscopy, UV-Vis and photoluminescence spectroscopy. The surface and morphological features of NPs have been investigated using scanning and transmission electron microscopy. The prepared NPs have shown weak ferromagnetic character with an essence of superparamagnetism as probed by vibrating sample magnetometry (VSM) and Mossbauer spectroscopy. The composition of the binary mixture of solvent has been found to affect the size, morphology and characteristic properties of the prepared α-Fe2O3 NPs.

Complexation of triblock reverse copolymer 10R5 with surface active ionic liquids in aqueous medium: a physico-chemical study

A comprehensive study on the interactions of surface active ionic liquids (SAILs) 1-alkyl-3-methyl imidazolium chlorides, [Cnmim][Cl], where n = 8, 10, and 12, with a triblock reverse copolymer, 10R5, [(PPO)8–(PEO)22–(PPO)8] has been performed using various physico-chemical techniques viz. surface tension, conductivity, isothermal titration calorimetry (ITC), turbidity, fluorescence spectroscopy, and dynamic light scattering (DLS). The interactions between triblock reverse copolymer with SAILs have been emphasized in terms of three concentration regions due to different modes of interactions between them whereas the previous studies reported that interactions between cationic surfactants and triblock copolymers are moderately weak. Different transitions corresponding to different stages of interactions of 10R5 with SAILs are observed from different techniques. Various thermodynamic parameters are calculated using conductivity and ITC measurements, whereas fluorescence studies have provided useful information about the polarity of the cybotactic region of the probe in the complexes formed by 10R5 and SAILs. The size of polymer–SAIL complexes has been investigated using dynamic light scattering and ITC measurements. The results obtained from different techniques have been correlated with each other to get a concise picture regarding the type of interactions prevailing between polymer and SAILs.

Self-assembly of azobenzene bilayer membranes in binary ionic liquid-water nanostructured media

Anionic azobenzene-containing amphiphile 1 (sodium 4-[4-(N-methyl-N-dodecylamino)phenylazo]benzenesulfonate) forms ordered bilayer membranes in binary ionic liquid (1-ethyl-3-methylimidazolium ethyl sulfate, [C2mim][C2OSO3])-water mixtures. The binary [C2mim][C2OSO3]-water mixture is macroscopically homogeneous at any mixing ratio; however, it possesses fluctuating nanodomains of [C2mim][C2OSO3] molecules as observed by dynamic light scattering (DLS). These nanodomains show reversible heat-induced mixing behavior with water. Although the amphiphile 1 is substantially insoluble in pure water, it is dispersible in the [C2mim][C2OSO3]-water mixtures. The concentration of [C2mim][C2OSO3] and temperature exert significant influences on the self-assembling characteristics of 1 in the binary media, as shown by DLS, transmission electron microscopy (TEM), UV-vis spectroscopy, and zeta-potential measurements. Bilayer membranes with rod- or dotlike nanostructures were formed at a lower content of [C2mim][C2OSO3] (2-30 v/v %), in which azobenzene chromophores adopt parallel molecular orientation regardless of temperature. In contrast, when the content of [C2mim][C2OSO3] is increased above 60 v/v %, azobenzene bilayers showed thermally reversible gel-to-liquid crystalline phase transition. The self-assembly of azobenzene amphiphiles is tunable depending on the volume fraction of [C2mim][C2OSO3] and temperature, which are associated with the solvation by nanoclusters in the binary [C2mim][C2OSO3]-water media. These observations clearly indicate that mixtures of water-soluble ionic liquids and water provide unique and valiant environments for ordered molecular self-assembly.

Thermally stable microemulsions comprising imidazolium based surface active ionic liquids, non-polar ionic liquid and ethylene glycol as polar phase

Ionic liquid (IL), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, [C2mim] [Tf2N], as a non-polar phase in conjunction with polar ethylene glycol (EG) forms microemulsions stabilized by surface active ionic liquids (SAILs), N-methyl-N-alkylimidazolium chlorides, [Cnmim] [Cl], where n = 8, 12 and 16 in conjunction with decanol as co-surfactant. The phase behaviour of the ternary systems has been investigated and three regions of microemulsions - polar-in-ionic liquid, bicontinuous and ionic liquid-in-polar, have been identified using electrical conductivity measurements. The effect of alkyl chain length on the phase behavior has been discussed in detail. The one-phase microemulsion region is found to decrease with the increase in the alkyl chain length of the SAILs. The microstructural characteristics have been investigated by using FTIR and NMR spectroscopy. The micropolarity of reverse micelles present in the microemulsions has been investigated using UV-Vis spectroscopy employing methyl orange as a polarity probe. The dynamics of solvent relaxation in microemulsions have been investigated by steady-state and time-resolved fluorescence spectroscopy using coumarin 153 (C-153) as fluorescence probe at different compositions of microemulsions. The dynamic light scattering measurements (DLS) reveals the expansion of reverse micelles formed by [Cnmim][Cl] in non polar [C2mim] [Tf2N] upon the addition of polar component. Interestingly, the microemulsions have been found to be thermally stable in a wide temperature range as revealed from temperature dependence UV-Vis, fluorescence and DLS measurements.

Effect of alkyl chain functionalization of ionic liquid surfactants on the complexation and self-assembling behavior of polyampholyte gelatin in aqueous medium

The complexation behaviour of an imidazolium based ionic liquid surfactant (ILS) 3-methyl-1-dodecylimidazolium chloride, [C12mim][Cl], and its amide and ester functionalized counterparts 3-(2-(dodecylamino)-2-oxoethyl)-1-methyl-1H-imidazol-3-ium chloride, [C12Amim][Cl], and 3-methyl-1-dodecyloxycarbonylmethylimidazolium chloride, [C12Emim][Cl], with a model protein gelatin (G) in aqueous solution has been investigated. Complexation of G with ILSs at the air-solution interface has been monitored by tensiometry, whereas complexation and ILS mediated self-assembly of G-ILS complexes in the bulk have been followed by dynamic light scattering (DLS), zeta-potential measurements, conductivity, and fluorescence techniques. The morphology of different self-assembled architectures has been monitored by scanning electron microscopy (SEM). Different transitions observed from various techniques in different concentration regimes of ILSs have been assigned to the varying extent of complexation and ILS mediated self-assembly of G-ILS complexes. The functionalization of the alkyl chain of the ILS [C12mim][Cl] with an amide ([C12Amim][Cl]) or ester ([C12Emim][Cl]) moiety owing to their additional hydrogen bonding (H-bonding) ability along with rigidity ([C12Amim][Cl]) or flexibility ([C12Emim][Cl]) near the imidazolium head group has been found to exert great influence on their complexation with G. This influence is fashioned as self-assembled structures of G-ILS complexes into discrete large hexagonal sheet-like or near spherical architectures, depending on the concentration and type of functionality of the alkyl chain of ILSs. The thermodynamic forces behind the complexation and self-assembly processes have been monitored by isothermal titration calorimetry (ITC) measurements and are discussed in detail. As both the nature of the ILS and protein (charge and structure) could affect their interactional behavior, the present results are expected to be very useful in deeply understanding the structure-property relationship between the nature of the ILS and proteins, which would be of great importance in the field of functional soft-materials.