Environment-Responsive Alkanol-Based Supramolecular Solvents: Characterization and Potential as Restricted Access Property and Mixed-Mode Extractants

Abstract

Self-assembly, the process by which supramolecular solvents (SUPRAS) with an ordered structure are produced, provides unique opportunities to obtain tailored solvents with advanced functional features. In this work, environment-responsive (C7–C14) alkanol-based SUPRAS were synthesized and their potential for analytical extractions was assessed. The global composition of the solvent, the size of the coacervate droplets that form it, and the aqueous cavities of the inverted hexagonal arrangement of the alkanols can be tailored by controlling the environment [specifically, the tetrahydrofuran (THF):water ratio in the bulk solution] for alkanol self-assembly. Interestingly, supramolecular solvents are highly adaptive and the previous features can all be reversed by modifying the environment. The spontaneous self-assembly of these solvents followed predictable routes, and their composition and volume can be accurately predicted from equations derived in this work. The solvents were structurally elucidated by light and cryo-scanning electron microscopy. Extractive applications exploiting the molecular size-based restricted access properties of SUPRAS were developed and their ability to engage in mixed-mode mechanisms for solute solubilization was established. Thus, solutes of increasing molecular weight were extracted from food and environmental samples with recoveries dependent on vacuole size in the SUPRAS, while macromolecules such as proteins, carbohydrates, and humic acids were excluded. The ability of SUPRAS to establish hydrogen-bonding and dispersion interactions was exploited to extract carcinogenic chlorophenols (CCPs) from environmental waters, and a simple and fast method was developed with quantitation limits (e.g., 0.21–0.23 μg/L) low enough to comply with legislation (e.g., maximum permitted levels for pentachlorophenol are in the range 0.4–1 μg/L).