Concentration and pH-dependent aggregation behavior of an l-histidine based amphiphile in aqueous solution

Self-Assembly of Unconventional Low-Molecular-Mass Amphiphiles Containing a PEG Chain

The design and synthesis of biocompatible surfactants are important for a wide range of applications in cosmetics, personal care products, and nanomedicine. This feature article summarizes our studies over the past 8 years on the design, synthesis, surface activity, and self-assembly of a series of unconventional low-molecular-mass amphiphiles containing a poly(ethylene glycol) (PEG) tail or spacer and different ionic or zwitterionic headgroups, including carboxylate, sulfonate, and quaternary ammonium salts. Despite having a so-called polar PEG chain as a tail or spacer, these ionic amphiphiles are found to have a tendency to adsorb at the air/water interface and self-assemble in pH 7.0 buffers at 298 K in the same way that conventional hydrocarbon tail surfactants do. However, they are observed to be relatively less surface-active compared to hydrocarbon tail surfactants. Although these amphiphilic molecules have less surface activity, they do self-assemble in aqueous buffer at 298 K, producing a range of microstructures, including spherical micelles, disclike micelles, and vesicles. In fact, our group is the first to report the self-assembly of PEG-tailed ionic amphiphiles in water at room temperature. Some of these molecules are also found to gel various organic liquids on heat-cool treatment or by ultrasound irradiation. We think that the present article will arouse general interest among researchers working toward the development of new biocompatible amphiphiles and soft materials.

A new surfactant–copper(ii) complex based on 1,4-diazabicyclo[2.2.2]octane amphiphile. Crystal structure determination, self-assembly and functional activity

A new complex [Cu(L)Br₃] (where LBr is 1-cetyl-4-aza-1-azoniabicyclo[2.2.2]octane bromide) has been synthesized and characterized.

Composition and Concentration Gradient Induced Structural Transition from Micelles to Vesicles in the Mixed System of Ionic Liquid-Diclofenac Sodium

Catanionic surfactant-hydrotrope mixtures have proven to be a striking alternative to tune microstructures over a wide range of compositions and also to minimize precipitation that is normally observed in catanionic mixtures at an equimolar ratio. These mixtures are supposed to be of great relevance in biological systems when a hydrotrope is a "drug". Keeping this in view, here we report composition- and dilution-induced structural changes in a catanionic mixture comprising ionic liquids (ILs), such as 1-dodecyl-3-methylimidazolium bromide (C12mimBr)/1-tetradecyl-3-methylimidazolium bromide (C14mimBr), and a drug, diclofenac sodium (DFNa), in aqueous solution. The structural changes are probed by small-angle neutron scattering (SANS), dynamic light scattering (DLS), and zeta-potential measurements. SANS data and size distribution curves clearly depict the formation of low curvature structures on going from the cation-rich to anion-rich composition up to a 0.7 mole fraction of DFNa (XDFNa). The amphiphilic nature of DFNa is supposed to alter the surface charge density, which is provoked by its incorporation into resulting aggregates, as confirmed by modified zeta-potential values. The modification of the average packing parameter resulting from the IL and DFNa complexation equilibrium seems to play a vital role in bringing out structural transitions of mixed aggregates. We also focused our attention to study the effect of dilution in concentrations ranging from 100 to 25 mM. At XDFNa = 0.0 and 0.1, the size of prolate ellipsoids decreases on dilution, mimicking classic behavior, but an opposite trend is observed at other XDFNa values. Dilution-induced transformation to larger aggregates is thought to be driven by the release of DFNa molecules from the mixed micelles on account of the critical micelle concentration (cmc) (solubility) mismatch between the two components. The role of other interactions such as cation-π and π-π in stabilizing the mixed aggregates in addition to hydrophobic interactions is probed by (1)H NMR.