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.

We compare the biophysical and structural aspects of the interaction of amphiphilic ionic liquids containing 1-alkyl-3-methylimidazolium cation ([C n MIM] + , n = 8, 12, or 16) with membranes composed of zwitterionic 1-palmitoyl-2-oleoyl-snglycero-3-phosphocholine (POPC) or anionic 1-palmitoyl-2-oleoyl-sn-glycero-3phospho-rac-glycerol (POPG). Liposome affinity and permeabilization were determined using ζ-potential and fluorescence studies, correlated with the cytoxicity of [C n MIM] + Br − toward HeLa cell lines. Membrane affinity is strongest in the case of [C 16 MIM] + Br − followed by [C 12 MIM] + Br − and [C 8 MIM] + Br − for both membranes, and trends remained the same in the case of membrane permeability and cytotoxicity. Solid-state NMR spectroscopy was used to localize [C n MIM] + inside the lipid bilayers and to study their impact on the head group and acyl chain structures and dynamics of the lipid molecules. The charged ring moiety of the [C n MIM] + is localized in the lipid−water interface of the membranes irrespective of the chain length and membrane surface charge. While [C 8 MIM] + binds the membrane most weakly, it induces the largest disorder in the lipid chain region. A lack of fast flip-flop motions of the amphiphiles in the case of long chain [C 16 MIM] + is suggested to render the membrane unstable, which increases its permeability. Between the lipid molecules, the POPC membrane incurs larger disorder in lipid chain packing upon insertion of [C n MIM] + molecules. The study provides structural details of the impact of increasing chain lengths in [C n MIM] + on the structural properties of lipid bilayers.

The interaction of amphiphilic ionic liquids containing an 1-alkyl-3-methylimidazolium cation ([CMIM]), which shows acute cytotoxicity toward marine and bacterial life, with zwitterionic 1-palmitoyl-2-oleoyl- sn-glycero-3-phospho-choline (POPC) and anionic 1-palmitoyl-2-oleoyl- sn-glycero-3-phospho- rac-glycerol (POPG) membranes was investigated. Biophysical parameters of this interaction were quantified by fluorescence spectroscopy, isothermal titration calorimeter, and solution-state NMR measurements. [CMIM] inserts into the membrane and induces vesicle leakage at relatively low concentration (<1 mM). Zwitterionic POPC membranes are more leakage-prone, but the binding of [CMIM] cations is stronger to anionic POPG membranes. A higher rate of exchange of membrane-bound [CMIM] is suspected to play a key role in membrane leakage. Furthermore, solid-state NMR spectroscopy was employed to determine the location of [CMIM] in lipid membranes and its impact on the structure and dynamics of the bilayer. The study provides a molecular understanding of the membrane permeabilizing effect of the [CMIM] mediated by its detergent-like structure.

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.

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.

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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.