Refining hydrogelator design: soft materials with improved gelation ability, biocompatibility and matrix for in situ synthesis of specific shaped GNP

Abstract

Despite the continuous surge in the development of new supramolecular gels, the prediction of a gelator's structure still remains elusive. It is also imperative to consolidate the existing inventory of gelators and devise ways to make the gels functional. In the present work, L-phenylalanine based poor (C-16) or non-gelating (C-12 tail) amphiphiles were converted to excellent gelators with the simple incorporation of N-terminal protected amino acid/dipeptide at the end of the alkyl tail. More than 6-fold enhancement in gelation efficiency was observed for amino acid/dipeptides incorporated at the tail of amphiphile in comparison to the corresponding unmodified alkyl tail. Interestingly, amphiphile with the tertiary butyloxycarbonyl (Boc) protected amino acid at the tail had better gelation ability than the amphiphile with the aromatic Fmoc (N-fluorenyl-9-methoxycarbonyl) protecting group. Spectroscopic investigations (XRD and FTIR) revealed that the modification at the tail compels the amphiphiles to take a different course of self-assembly than that adopted by their predecessors (alkyl tailed gelator, C-16). For example, in the case of the amphiphile having a dipeptide at the tail, formation of β-sheet structure through anti-parallel arrangement between the molecules results in notable improvement in its gelation ability. Most importantly, these tail modified amphiphiles were capable of in situ synthesis of gold nanoparticles (GNPs) of specific shape without the help of any external reducing agents in the newly developed soft materials. The biocompatibility of hydrogels is also crucial for their prolific biomedicinal functions. MTT assay showed dramatic improvement in the biocompatibility of the tail modified hydrogelators towards mammalian cells in comparison to the amphiphiles having no amino acid at the tail.