Efficiency\nEnhancement in Peptide Hydrogelators: The\nCrucial Role of Side Chain Hydrogen Bonding Over Aromatic π–π\nInteractions

Short peptide assemblies that form supramolecular hydrogels\nare\nstabilized by both intermolecular noncovalent interactions among amino\nacid side chains and hydrogen bonding between peptide backbone amides.\nPrevious research has emphasized the inclusion of aromatic amino acids\nin short peptide sequences, positing that aromatic π–π\ninteractions contribute significantly to inducing efficient hydrogelation\ni.e., at low minimum gelation concentrations (MGCs). However, herein,\nwe demonstrate that additional hydrogen bonding interactions from\namino acid side chains play a more pivotal role in the efficiency\nof peptide hydrogelation compared to aromatic π–π\ninteractions. We investigated two sets of Fluorenylmethoxycarbonyl\n(Fmoc)-functionalized α-synuclein and human islet amyloid peptide\nfragments [Fmoc-NVGGAVVT (Syn-N) and Fmoc-NFGAIL (IAP-N)], substituting\nasparagine (N) with phenylalanine (Syn-F/IAP-F), alanine (Syn-A/IAP-A),\nand glutamine (Syn-Q/IAP-Q). This allowed us to explore the effects\nof aromatic (π-system), aliphatic (hydrophobic), and hydrogen\nbonding effects with varying chain lengths on hydrogel formation.\nOur results reveal that Syn-N and Syn-Q exhibit MGC of 0.03 and 0.05\nwt %, respectively, classifying them as super hydrogelators (MGC <\n0.1 wt %). These values are 4.0–6.6-fold lower than Syn-F and\nSyn-A, with Syn-N demonstrating greater efficiency than Syn-Q. Similarly,\nIAP-N exhibited a substantial decrease in MGC by 8.75, 3.75, and 2.5\nfolds compared to IAP-A, IAP-F, and IAP-Q, respectively. Experimental\nevidence and molecular dynamic simulation suggest that −CO-NH<sub>2</sub> of asparagine side chains effectively engaged in hydrogen\nbonding, thereby immobilizing water molecules at low gelator concentrations.\nAlthough glutamine shares similar −CO-NH<sub>2</sub> functionality,\nits hydrogelation efficiency is less pronounced compared to asparagine,\nlikely due to its longer alkyl chain, which may hinder the formation\nof a hydrogen bonding network in the self-assembled structure compared\nto asparagine-containing peptides. These findings offer valuable insights\nfor designing efficient peptide hydrogelators or lowering MGCs by\nsubstituting amino acids with asparagine/glutamine in peptide sequences.\nAdditionally, modifying peptide properties through asparagine/glutamine\nsubstitution could optimize hydrogel properties for specific applications.