and Fmoc-Phe-Phe-Arg-NH2,15 and ferrocenyl-Phe-Phe-His. The introduction of D-amino acids can confer further advantages, such as increased resistance against enzymatic degradation. For this reason, we designed L-His-D-Phe-D-Phe that is catalytic only in its assembled state.17 Subsequent studies demonstrated that C-terminal amidation enables a five-fold improvement in catalytic activity under analogous conditions.18 Conversely, other modifications, such as N-acetylation or peptide elongation to include Ser to serve as nucleophile, resulted in detrimental effects in catalytic performance and/or gelation ability, thus demonstrating that the design of such minimalistic supramolecular catalysts is not trivial. In light of these results, we selected the best-performing catalytic gelator identified from our previous research endeavours, i.e. L-His-D-Phe-D-Phe-NH2 (Hff), and studied its equimolar co-assembly with its enantiomer, D-His-L-Phe-L-Phe-NH2 (hFF) (Fig. ), as a different strategy to further improve catalytic activity. We took inspiration from studies led by Schneider that reported racemic peptide assemblies with synergistic assembling behaviour leading to more rigid hydrogels, relative to each enantiomer alone.20 Subsequently, the same group demonstrated the molecular basis for such an effect, revealing that the two enantiomers were alternating in the co-assembled rippled β-sheet,21 which is a structure that was predicted by Pauling and Corey in 1953. The racemic co-assembly is held together by hydrogen bonds within the sheet, thus, creating nested hydrophobic interactions between enantiomers in the dry fibrils' interior that do not occur in the case of enantiopure assemblies. We reasoned that the maximization of such hydrophobic regions could enhance hydrophobic substrate binding for catalysis. The two enantiomers were synthesised, purified by HPLC, freeze-dried, and their identity and purity were confirmed by 1H-and 13C-NMR, and ESI-MS spectra (ESI, S1-S4). Their circular dichroism (CD) spectra (Fig. ) were mirror-imaged, while their equimolar mixture was featureless, as expected. The CD signatures were reminiscent of those of other heterochiral tripeptides forming amphipathic β-sheets upon assembly, and characterised by two main peaks at 200 and 220 nm.23 Upon assembly conditions at higher concentrations, the CD spectra could be acquired only above 215 nm due to scattering, and maintained the same features (ESI, Section S5). Fourier-transformed infrared spectra (FT-IR, Fig. ) revealed the typical signals of β-sheets in the amide I and II regions, at 1632 and 1542 cm-1, respectively. Microscopy analyses were also performed. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) images revealed anisotropic structures. No significant difference was found in the fibers' width across samples (Fig. , bottom), corresponding to a median of 105 ± 18 nm for hFF, 104 ± 17 nm for Hff, and 107 ± 18 nm for the racemic mixture (n = 100 counts).