Hydrogels formed from Fmoc amino acids

Abstract

A number of Fmoc amino acids can be effective low molecular weight hydrogelators. The type of gel formed depends on the amino acid used and, in the case of FmocF, the final pH of the system. The single crystal structure of two of the gelators (FmocF and FmocY) have been determined and the data compared to the fibre X-ray diffraction data. FmocF, which forms metastable gels, crystallises easily and the data for the fibre phase and crystal phase are relatively similar. For FmocF, the fibre axis in b is consistent with the hydrogen bonding repeat distances and the diffraction pattern calculated from the single crystal structure is a good match with the experimental fibre X-ray diffraction data. On the other hand, there are significant differences between the crystalline phase determined and the fibre phase for FmocY. The packing of FmocY within the crystal structure is created by interactions between the planar Fmoc groups, whilst it is clear that hydrogen bonding drives the self-assembly into fibrillar structures within the gels. This shows that understanding the packing in gel phase by analogy to isolated crystal structures has the potential to lead to erroneous conclusions. CrystEngCommThis journal is

Weak bond-based injectable and stimuli responsive hydrogels for biomedical applications

“…This makes Fmoc-F-OH, Fmoc-Y-OH and Fmoc-W-OH self-assemble into hydrogels at a lower critical concentration than Fmoc-G-OH and Fmoc-I-OH without an aromatic group on the side chains (Table 1). 144 This phenomenon was also observed in the pentapeptide derivatives. The aromatic rings on N-termini of VYGGG and YGFGG together with the aromatic ring on Y and F side chains enabled the two pentapeptide derivatives to more easily assemble into a hydrogel compared to other pentapeptide derivatives (Table 1).…”

“…140–142 Recently, an aromatic moiety containing short peptides and N-terminal Fmoc-amino acids have been reported for robust self-assembly into supramolecular architectures for biomedical applications. 136–138, 143, 144 Table 1 summarizes the categories of these gelators and their gelation conditions.…”

“…In addition to the π-π stacking interaction on N-terminal Fmoc groups, the final fibrous gel formation is also dependent on other intermolecular interactions such as the hydrogen bond, ionic interaction and additional π-π stacking between the side chains on the amino acids. 137, 138, 143, 144 For example, F, Y and W molecules bear an aromatic ring on their side chains. This makes Fmoc-F-OH, Fmoc-Y-OH and Fmoc-W-OH self-assemble into hydrogels at a lower critical concentration than Fmoc-G-OH and Fmoc-I-OH without an aromatic group on the side chains (Table 1).…”

“…136–138, 143, 144 This is because they all have free carboxylic acid groups on the C-termini and some species, such as VTEEI derivatives, have carboxylic acid on the E side chain as well. The hydrophilicity and hydrophobicity of these molecules are balanced by the degree of deprotonation of the carboxylic acid group, their hydrophobic side groups and the aromatic moieties on N-termini.…”

Low-Molecular-Weight Gels: The State of the Art

“…Indeed, although it has been widely assumed that there is a link, there are a number of examples that now specifically show that packing is different in the gel phase and crystals grown even from the same solvent. [24][25][26] As a specific example, we showed that fiber X-ray diffraction data from the gel phase did not match the crystal structure of a crystal grown directly from the gel phase. 24 In many cases, the crystals formed in one solvent are compared with a gel formed in another.…”