The aggregation behavior of two cationic surfactants, i.e., cetyldimethylethanolammonium bromide (CDMEAB) and cetyltributylphosphonium bromide (CTBPB), within an aqueous deep eutectic solvent (DES) is studied. The synthesized DES is composed of 1:2 mole ratio of choline chloride and glycerol and is further characterized by Fourier transform infrared (FTIR) and 1 H NMR spectroscopy techniques. The critical micellar concentration (CMC), micellar size, and intermolecular interaction in surfactants within Gly-based DES solutions are investigated by various techniques including surface tension, conductivity, fluorescence, dynamic light scattering (DLS), FTIR, 1 H NMR, and two-dimensional (2D) nuclear Overhauser effect spectroscopy (NOESY). The various interfacial properties and thermodynamic parameters are determined in the presence of 5 wt % glyceline (Gly)-based DES in an aqueous solution. The CMC, aggregation number ( N agg ), and Stern–Volmer constant ( K sv ) have also been determined by a steady-state fluorescence method. DLS is used to obtain information regarding the size of the aggregates formed by the cationic surfactants in DES solutions. FTIR spectroscopy is used to study the surfactant–DES interactions that tune the micellar structure of the surfactants within the Gly-based DES solution. The functional groups involved in the interactions (H-bonding and electrostatic) are the head groups (HO–CH 2 –CH 2 –N + ion for CDMEAB and quaternary phosphonium (P + ) ion for CTBPB) of the surfactants with the −OH-containing Gly DES. The hydrophobic moieties are involved in the hydrophobic interactions. The 1 H NMR data show that differences in chemical shifts can provide significant information about the interactions taking place within the system. 1 H NMR and NOESY techniques are further employed to strengthen our claim on the feasible structural arrangements within the aqueous surfactant–DES self-assembled structures. It is observed that both the cationic surfactants, i.e., CDMEAB and CTBPB, form self-assembled nanostructures in the Gly-based DES solutions. The present results are expected to be useful for colloidal solutions of DES and their mixtures with water.

Silver nanoparticles (AgNPs) show immense application potential in many fields including biomedical sciences owing to their advanced antimicrobial property (antibacterial, antifungal and anti-inflammatory). Ionic liquids (ILs) known as designer solvents with a melting point below 100 °C are a new class of compounds with exclusive properties and great chemical variety. Since the past decade, ILs are vastly used in interdisciplinary research including the synthesis and stabilization of metal nanoparticles. In the present work, we have studied the interaction between IL 1-butyl-3-methylimidazolium octylsulfate [Bmim]­[OS] and AgNPs using a simple and sensitive UV–visible spectroscopic method via the response obtained from the surface plasmon resonance (SPR) band of AgNPs. The analysis of the SPR band at the 400–425 nm range and the Fourier transform infrared (FT-IR) spectral results show a transfer of N–H stretching frequency from 3367 to 3228 cm–1, which clearly suggests the formation of nanoparticles. FT-IR spectroscopy is systematically applied to explore information about the intermolecular interactions taking place within AgNPs-[Bmim]­[OS] micellar solutions. The critical micelle concentration (CMC) of [Bmim]­[OS] is determined using conductivity and UV–visible spectroscopy, and the size of micellar aggregates is obtained using dynamic light scattering (DLS) technique. Further, the above system is also utilized to consider the structural modify of human serum albumin (HSA) and bovine serum albumin (BSA). UV–vis, fluorescence, FT-IR, 1H nuclear magnetic resonance and DLS spectroscopic investigations reveal some interesting outcomes. It is observed that modification in the structures of both the globular proteins HSA and BSA takes place within the system, thus indicating significant IL–protein binding. Further, it is noticed that HSA shows more binding affinity toward [Bmim]­[OS] than compared to BSA.

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