Mixed Micellization of Cationic/Anionic Surfactants: Role of Matching Water Affinities between Oppositely Charged Headgroups and That between Oppositely Charged Constituent Counterions

Aggregation of Mixed (Cationic + Anionic) and (Cationic + Nonionic) Surfactant Systems within a (Lanthanide Salt:Urea) Deep Eutectic Solvent

Deep eutectic solvents (DESs) are emerging as versatile media to support and facilitate various molecular aggregation processes, including surfactant self-assembly. The effect of a type IV DES consisting of La(NO3)3·6H2O and urea in a 1:3.5 molar ratio named (La:U) as a solubilizing medium on the self-aggregation of (cationic + anionic) and (cationic + nonionic) surfactant mixtures with N-dodecyltrimethylammonium bromide (DTAB), sodium dodecyl sulfate (SDS), and Triton X-100 (TX-100) as cationic, anionic, and nonionic surfactants, respectively, is investigated. The surfactant mixtures are found to readily self-aggregate within the (La:U) DES across the complete composition range under ambient conditions. The critical aggregation concentrations (CACs) of both (DTAB + SDS) and (DTAB + TX-100) surfactant mixtures lie between the CACs of the respective surfactants in the mixture, indicating that, owing to its ionic nature, the (La:U) DES effectively screens the charges present on the surfactant headgroups. While for the (DTAB + SDS) mixture, this observation is in contrast to that in aqueous media, it is similar to that in water for the (DTAB + TX-100) mixture. Both investigated surfactant mixtures exhibit a mostly negative interaction parameter (β) within the DES, implying the presence of predominantly attractive interactions between DTAB and SDS/TX-100. The thermodynamic parameters estimated for both surfactant mixtures within the (La:U) DES indicate aggregation to be a spontaneous process. While it appears to be both enthalpically and entropically driven, it is predominantly entropically driven. Using fluorescence spectroscopic methods, the aggregation number (Nagg) of the self-assembly of mixed surfactant systems is estimated and the solute solvation microenvironment afforded by these aggregates within the (La:U) DES is also ascertained. The outcomes will help expand the application potential of such polar DESs by establishing them as alternate and effective media for mixed surfactant aggregation.

Synergistic Computational Modeling Approaches as Team Players in the Game of Solubility Predictions

Several approaches to predict and model drug solubility have been used in the drug discovery and development processes during the last decades. Each of these approaches have their own benefits and place, and are typically used as standalone approaches rather than in concert. The synergistic effects of these are often overlooked, partly due to the need of computational experts to perform the modeling and simulations as well as analyzing the data obtained. Here we provide our views on how these different approaches can be used to retrieve more information on drug solubility, ranging from multivariate data analysis over thermodynamic cycle modeling to molecular dynamics simulations. We are discussing aqueous solubility as well as solubility in more complex mixed solvents and media with colloidal structures present. We conclude that the field of computational pharmaceutics is in its early days but with a bright future ahead. However, education of computational formulators with broad knowledge of modeling and simulation approaches is imperative if computational pharmaceutics is to reach its full potential.