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Supramolecular organogel based on di-Fmoc functionalized unnatural amino acid: An attempt to develop a correlation between molecular structure and ambidextrous gelation
Date Issued
05-06-2021
Author(s)
Arokianathan, Jaini Flora
Ramya, Koduvayur A.
Indian Institute of Technology, Madras
Leemarose, Ambrose
Shanmugam, Ganesh
Abstract
The supramolecular gels as soft material grasp more attention due to their increasing applications in diverse fields. Although numerous low molecular weight (LMW) gelators, which gelate either aqueous or organic solvents, have been developed in the past, the ambidextrous gelators (gelate both aqueous and organic solvents) are very limited. While many gelators have been discovered serendipitously, gelator's rational design is still a challenge, especially ambidextrous gelators. In these two contexts, herein, we demonstrate the organogelation of a hydrogelator Nα, Nβ-di-fluorenylmethoxycarbonyl(Fm) functionalized L-2,3-diaminopropionic acid [G1] and thereby introduced a new ambidextrous gelator with an unnatural amino acid. Further, comparing with previous ambidextrous gelators, a correlation between molecular structure and ambidextrous gelation has been proposed to design new aromatic ambidextrous gelators. G1 found to gelates various commonly used organic solvents with a diverse polarity ranging from polar (methanol and ethanol) to non-polar (benzene and toluene) solvents. Interestingly, among the non-polar solvents, gelator G1 showed selectivity in gelating aromatic solvents as it cannot gelate acyclic and cyclic non-polar solvents. Organogels have been thoroughly characterized using various biophysical techniques. All the organogels show an entangled nanofibrillar morphology with ordered self-assembly of gelators, which are stabilized by aromatic π–π interactions of fluorenyl moieties and hydrogen bonding interactions between ‒CO‒NH‒ groups. The mechanical property (viscoelastic and thixotropic) of G1 organogels are comparable with reported supramolecular gels in polar and non-polar solvents, except toluene. The current findings, together with previous reports of fluorene and pyrene-based ambidextrous gelators, suggest that the amidation of LMW diamine compounds containing a polar group by two larger aromatic moieties could provide a chemical structure (dumb-bell arrangement)/self-assembling property to yield “ambidextrous” gelator. While the organogelation of G1 has been identified and characterized extensively, the present contemporary study, together with the previous observation, attempted to establish a correlation between molecular structure and ambidextrous gelation, leading to the design new LMW ambidextrous gelator by following a “dumb-bell” design.
Volume
618