Dicyclohexylurea derivatives of amino acids as dye absorbent organogels and anion sensors

• Published in: Organic & biomolecular chemistry Vol. 17; no. 11; pp. 3026 - 3039
• Main Authors: Roy, Karabi, Ghosh, Suvankar, Chetia, Monikha, Satpati, Priyadarshi, Chatterjee, Sunanda
• Format: Journal Article
• Language: English
• Published: CAMBRIDGE Royal Soc Chemistry 13.03.2019; Royal Society of Chemistry
• Subjects: Acetic acid; Amino acids; Anions; Binding; Chemistry; Chemistry, Organic; Derivatives; Dyes; Fluorescence; Fluorides; Gelation; Gels; Hydrogen bonds; Hydrophobicity; Low molecular weights; Molecular weight; NMR; Nuclear magnetic resonance; Organic solvents; Physical Sciences; Science & Technology; Self-assembly; Sensors; Titration; Urea; Ureas; γ-Aminobutyric acid; ROOM-TEMPERATURE; SOFT MATERIALS; GELATORS; HYDROGELS; REMOVAL; GELS; EFFICIENT; LIQUIDS
• ISSN: 1477-0520; 1477-0539
• DOI: 10.1039/c9ob00014c

Dicyclohexyl urea (DCU) derivatives of amino acids Fmoc-Phe-DCU (M1), Fmoc-Phg-DCU (M2) and Fmoc-Gaba-DCU (M3) have been shown to form phase selective, thermoreversible and mechanically robust gels in a large range of organic solvents. This is the first report of low molecular weight gelators (LMWG) from DCU derivatives of amino acids. The self-assembly mechanism of the organogels has been probed using concentration dependent H-1 NMR, DMSO titration H-1 NMR, fluorescence, FTIR, PXRD and FESEM techniques. Self-assembly leading to gelation process is mainly driven by hydrophobicity and p-p stacking interactions in between Fmoc groups. Interestingly, the gels can absorb several kinds of organic dyes efficiently and can be reused for dye absorption for multiple cycles. Additionally, M1-M3 act as sensors for anions like fluoride, acetate and hydroxide, for which they have specific fluorescence response. Gel formation by M1-M3 is completely arrested in the presence of fluoride. The possible binding mode of fluoride has been delineated using DFT studies. Calculations suggest, involvement of urea NH in a six membered intramolecular hydrogen bond, rendering it unavailable for fluoride binding. Backbone -NH of the amino acids of M1-M3 is responsible for fluoride binding. The reported small, economically viable, synthetically facile molecules not only enrich the repertoire of LMWG molecules, but can have multifaceted applications.