Amino Acid- and Dipeptide Amphiphile-Based Supramolecular Eutectogels: Soft Materials for Drug Entrapment–Release and Wastewater Treatment

Abstract

Supramolecular gels prepared in solvents of extreme polarities have received widespread importance across scientific disciplines. In this regard, soft materials based on deep eutectic solvents (DESs) have been receiving notable attention owing to their low toxicity, low volatility, and ability to solubilize hydrophobic drugs and natural products. A DES is a mixture of two or more compounds having a melting point lower than that of the individual components. Reports on supramolecular eutectogels derived from small molecules are very few and serendipitous. Therefore, designing a low-molecular-weight eutectogelator (LMWEG) remains challenging and demands comprehensive structure–property correlation. To this end, we have developed amino acid- and dipeptide amphiphile-based LMWEGs that immobilized choline chloride/phenylacetic acid-based DES with a minimum gelation concentration (MGC) of 0.5–10.0%, w/v. Variation of amino acids, protecting groups at the N-terminal, and hydrophobic chain length of the gelator delineated the crucial influence of the hydropathy index of amino acids and thereby the hydrophilic–lipophilic balance in eutectogelation. Replacement of the aromatic moiety in the gelator and/or in the DES with an aliphatic one ascertained the optimal necessity of aromaticity for efficient eutectogelation. Eutectogels were thermoreversible and showed considerable thermal stability (Tgel ∼ 50–70 °C). Spectroscopic and microscopic studies confirmed the fiber-like morphology of the eutectogels and the participation of hydrogen bonding in eutectogelation. Newly derived eutectogels exhibited considerably good mechanical strength (γc ∼ 7.5–16.5%) and interesting injectable as well as thixotropic properties. The ability to adsorb cationic and anionic dyes by the eutectogels ensured their potential in wastewater treatment. Importantly, these supramolecular eutectogels can be used in drug delivery owing to their ability to entrap the hydrophobic drug curcumin and subsequently its pH-dependent sustained release.