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.

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.

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Amide-functionalized surface active ionic liquids (SAILs), 1-methyl-1-dodecyl piperidinium chloride, [C12APip][Cl]; 1-methyl-1-dodecyl pyrrolidinium chloride, [C12APyrr][Cl]; 1-methyl-3-dodecyl imidazolium chloride, [C12Amim][Cl], and 1-methyl-1-dodecyl morpholinium chloride, [C12AMorph][Cl], have been synthesized, characterized and investigated for thermal stability, and micellization behavior in aqueous medium. The introduction of an amide moiety in the alkyl chain decreased the thermal stability of the functionalized SAILs compared to non-functionalized SAILs bearing a simple alkyl chain. A variety of state of the art techniques, viz. tensiometry, conductometry, steady-state fluorescence, isothermal titration calorimetry (ITC), dynamic light scattering (DLS) and atomic force microscopy (AFM), have been employed to investigate the micellization behavior. Amide-functionalized SAILs have shown much lower critical micelle concentration, cmc, and better surface active properties as compared to homologous non-functionalized SAILs. Steady-state fluorescence has provided information about cmc, aggregation number (Nagg) and polarity of the cybotactic region of the micelles, whereas ITC has provided insights into the thermodynamics of micellization. Furthermore, the size and shape of the micelles have been investigated using DLS and AFM techniques.

The polyionic nature of gelatin (G), derived from partial hydrolysis of collagen, is utilized to prepare ionogels (IGs) in conjunction with aqueous mixtures of a polar ionic liquid (IL), 1-ethyl-3-methylimidazolium ethylsulfate, [C 2 mim][C 2 OSO 3 ]. The highly polar nature of IL−H 2 O mixture (50/50 v/v %) supported the high solubility of G, where the IGs are prepared by dissolving equal amount of G to IL−H 2 O mixture (50/50 v/v %) in a stepwise manner at 45 °C while stirring. The combination of IGs with Ag 2 O nanoparticles (NPs) prepared in situ, via photoreduction of AgNO 3 led to induction of antimicrobial activity in IGs, while enhancing the mechanical properties. The prepared IGs show fast self-healing (<1 min) and multiadhesive nature along with reversible stretching efficiency and high conductivity. The conductivity (2 mS cm −1 ) of prepared IG is highest among all biopolymer-based IGs reported, until date. The multiadhesive and highly conducting nature, transparency, inherent shapememory effect, and mechanical stability of the prepared the IGs are expected to be utilized in various electrical and bioelectronic applications. Moreover, these properties can be controlled by tuning the morphology of Ag 2 O NPs and water content in IGs. The method used for preparation of IGs provides a new way for easy, green, and economical preparation of antimicrobial IGs at a reduced temperature, where no harmful reducing agent or UV light is used for in situ preparation of Ag 2 O NPs.

The complexation behaviour of an imidazolium based ionic liquid surfactant (ILS) 3-methyl-1-dodecylimidazolium chloride, [Cmim][Cl], and its amide and ester functionalized counterparts 3-(2-(dodecylamino)-2-oxoethyl)-1-methyl-1H-imidazol-3-ium chloride, [CAmim][Cl], and 3-methyl-1-dodecyloxycarbonylmethylimidazolium chloride, [CEmim][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 [Cmim][Cl] with an amide ([CAmim][Cl]) or ester ([CEmim][Cl]) moiety owing to their additional hydrogen bonding (H-bonding) ability along with rigidity ([CAmim][Cl]) or flexibility ([CEmim][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.

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