RSC Advances p. 66339 - 66354 (2015)
Update date:2022-08-04
Topics:
Haldar, Saubhik
Karmakar, Koninika
A systematic investigation on gelation self-assembly has been performed on a hydrophobically modulated dipeptide based ambidextrous gelator, N-n-acyl-(l)Val-X(OBn), (X = 1,ω-amino acid). To elucidate the effect of hydrophobic tuning on gelator architecture towards its gelation self-assembly, three sets of gelators with a common formula: CmH2m+1C(=O)NH(l)Val(C=O)NH-(CH2)n-(C=O)OBn, were synthesized, Set-I includes gelators with n = 2, m = 9, 11, 13, 15, 17, for Set-II it is n = 2, 3, 5, m = 13 and Set-III comprises of two isomeric gelators (n = 2, m = 15; n = 10, m = 7). Gelation has been critically analyzed in various apolar (aromatic and aliphatic) and polar (protic and aprotic) solvents using FESEM, CD, IR, WAXRD and rheological studies. Obtained results reveal that π-π type interaction dictates the primary molecular alignment and positioning of amide functionality across the aliphatic chain which influences the peptidic orientation in parallel (when m > n) or antiparallel (when m < n) β-sheet type organization in their self-assembly. The thermal stability, gelation number (GN), Tgel and yield stress of gel systems increases with m, but for a given m, the trend goes apparently inverse with the increasing n. Circular dichroism (CD) studies suggest an intriguing evidence of non-planarity of amide plane during self-assembly, highlighting the involvement of conformational change taking place during molecular organization towards its gelation. Despite complex nature of solvent-gelator interaction, the effect of H-bonding component of solubility parameters was found to have a significant role on self-assembly. Overall, supramolecular forces acting at specific functionalities encrypted in gelator backbone must overcome the solvation energy with synergic assistance of solvophobic effect towards stabilization of gel-network with optimum gelator backbone conformation for achieving required enthalpic contribution for self-assembly.
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