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 (<i>D</i>_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

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 <i>p</i>-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 ¹H 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

Explorations on Solute–Solvent Interactions of Tripotassium Citrate and Sodium Benzoate in Aqueous 1‑Ethyl-3-methylimidazolium Ethyl Sulfate Solutions: Physicochemical, Spectroscopic, and Computational Approaches

The present research work is concerned with the thermophysical properties of tripotassium citrate and sodium benzoate in aqueous (0.10, 0.15, and 0.20) mol·kg–1 1-ethyl-3-methylimidazolium ethyl sulfate solutions at temperatures ranging (293.15–313.15) K and 101.3 kPa pressure. The experimentally acquired density, sound speed, and viscosity data have been employed to determine numerous densimetric, acoustic, and viscometric parameters including the apparent molar volumes (Vϕ), partial molar volumes at infinite dilution (Vϕ0), limiting apparent molar expansibilities (Eϕ0), apparent molar isentropic compressibilities (Kϕ,s), transfer properties, hydration number (nH), viscosity B-coefficients, and thermodynamic parameters of viscous flow (Δμ10, Δμ20, ΔH20, and TΔS20). The above-mentioned parameters have been evaluated for the examination of interactions that are prevailing among tripotassium citrate/sodium benzoate and 1-ethyl-3-methylimidazolium ethyl sulfate in an aqueous medium. In addition, UV spectral analysis was used for the examination of interactions existing among the considered systems. Furthermore, the band gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital for the studied systems and the interaction characteristics have been calculated using density functional theory. The obtained results inferred the predominance of the hydrophilic–hydrophilic interactions in the systems under investigation

Self-Assembly of Azobenzene Bilayer Membranes in Binary Ionic Liquid–Water Nanostructured Media

Anionic azobenzene-containing amphiphile <b>1</b> (sodium 4-[4-(<i>N</i>-methyl-<i>N</i>-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 <b>1</b> 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 <b>1</b> 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

Micellization Behavior of Morpholinium-Based Amide-Functionalized Ionic Liquids in Aqueous Media

Morpholinium-based amide-functionalized ionic liquids (ILs) [C_<i>n</i>AMorph]­[Br], where <i>n</i> = 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 [C_<i>n</i>AMorph]­[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<i>_n</i>AMorph]­[Br] ILs. Conductivity measurements have been performed to obtain the cmc, degree of counterion binding (β), and standard free energy of micellization (Δ<i>G</i>_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 (<i>N</i>_agg) of the micelles. Both dynamic light scattering and atomic force microscopy have provided insights into the size and shape of the micelles. 2D ¹H–¹H 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

Gelatin-Based Highly Stretchable, Self-Healing, Conducting, Multiadhesive, and Antimicrobial Ionogels Embedded with Ag₂O Nanoparticles

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, [C₂mim]­[C₂OSO₃]. The highly polar nature of IL–H₂O mixture (50/50 v/v %) supported the high solubility of G, where the IGs are prepared by dissolving equal amount of G to IL–H₂O mixture (50/50 v/v %) in a stepwise manner at 45 °C while stirring. The combination of IGs with Ag₂O nanoparticles (NPs) prepared <i>in situ</i>, via photoreduction of AgNO₃ 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 shape-memory 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 Ag₂O 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 Ag₂O NPs

Photon upconverting bioplastics with high efficiency and in-air durability

There is an urgent demand for substituting synthetic plastics to bioplastics for sustainable renewable energy production. Here, we report a simple one-step approach to create bioplastics with efficient and durable photon upconversion (UC) by encapsulating non-volatile chromophore solutions into collagen-based protein films. By just drying an aqueous solution of gelatin, surfactant, and UC chromophores (sensitizer and annihilator), liquid surfactant microdroplets containing the UC chromophores are spontaneously confined within the gelatin films. Thanks to the high fluidity of microdroplets and the good oxygen barrier ability of the collagen-based fiber matrices, a high absolute TTA-UC efficiency of 15.6% and low threshold excitation intensity of 14.0 mW cm−2are obtained even in air. The TTA-UC efficiency was retained up to 8.2% after 2 years of storage under ambient conditions, hence displaying the significant durability desired for practical applications