Halogen-free COOH functionalized surface-active ionic liquids: surface activity, aggregation behavior, and antimicrobial activity

Investigating the Influence of Aromatic Counterions on the Micellar Structure and Aggregation Behavior of Morpholinium-Based Surface-Active Ionic Liquids in an Aqueous Solution

Two morpholinium-based surface-active ionic liquids (SAILs) with aromatic counterions were synthesized, namely, n-dodecyl-n-methylmorpholinium salicylate [C12mmor][Sal] and n-dodecyl-n-methylmorpholinium 3-hydroxy-2-naphthoate [C12mmor][3-h-2-n], and explored their aggregation behavior in aqueous solutions systematically. Electrical conductivity, small-angle neutron scattering (SANS), surface tension (ST), and UV-vis spectroscopy measurements were employed to determine various thermodynamic, micellar, and interfacial parameters, like the degree of counterion binding (β), critical micelle concentration (CMC), minimum area per molecule (Amin), surface excess concentration (Γmax), standard Gibbs free energy of adsorption (ΔGad0), aggregation number (Nagg), standard Gibbs free energy of micellization (ΔGm0), standard enthalpy of micelle formation (ΔHm0), and the standard entropy of micellization (ΔSm0) in an aqueous solution. Incorporating the aromatic counterions favors significantly excellent micellization properties over conventional halogenated SAILs such as [C12mmor][Br]. SANS analysis revealed that upon changing the counterion from salicylate to 3-hydroxy-2-naphthoate, the structure changed from prolate ellipsoidal micelles to large unilamellar vesicles. Also, increasing the concentration in the case of [C12mmor][Sal] resulted in a lower aggregation number.

Synthesis, Self-Aggregation, Surface Characteristics, Electrochemical Property, Micelle Size, and Antimicrobial Activity of a Halogen-Free Picoline-Based Surface-Active Ionic Liquid

We present a new approach toward the design of a halogen-free picoline-based surface-active ionic liquid (SAIL) (1-octyl-4-methyl pyridinium dodecyl sulfate) [C₈γPic]DS consisting of long dodecyl sulfate (DS) as an anion. The surface properties, micellization behavior, and antimicrobial activity in an aqueous solution were investigated using tensiometry, conductometry, and ultraviolet (UV) spectroscopy. Incorporating the DS group in SAIL leads to lower critical micellar concentration (CMC) and enhanced adsorption at the air/water interface of the functionalized ionic liquid compared to the C₈-alkyl chain-substituted pyridine ionic liquids. The antimicrobial activity was evaluated against a representative Gram-negative and Gram-positive bacteria panel. Antibacterial activities increased with the alkyl chain length, C₈ being the homologous most effective antimicrobial agent. The micelle size of [C₈γPic]DS was determined by the dynamic light-scattering (DLS) study. Cyclic voltammetry (CV) measurements have been employed to evaluate the interaction between the SAIL micelle and working electrode, diffusion coefficient, and micelle size of the SAIL solution. The diffusion coefficient explored the correlation of surface properties and the antimicrobial activity of [C₈γPic]DS. This halogen-free SAIL is the future of wetting agents and emulsion studies in agriculture due to its small micelle size and surface characteristics.