Molecular design controls kinetic trapping. We used the tripeptides Fmoc-GGD and Fmoc-AVD (Fig. ), where G is the amino acid glycine, A is the amino acid alanine, and V is the amino acid valine, and D stands for aspartic acid. These peptides are dissolved at 10 mM in an aqueous buffer of MES at pH 6.0. A Nile Red assay found no evidence of assembly, confirming that these peptides were well-dissolved in their precursor state (Fig. , D, Fig. ). The addition of 100 mM EDC to these precursor solutions initiated the reaction cycle. It led to the formation of a turbid solution and a turbid hydrogel for Fmoc-GGD and Fmoc-AVD, respectively. Notably, the turbidity by Fmoc-GGD was transient and faded as the reaction cycle had consumed all fuel. In contrast, the hydrogel of Fmoc-AVD was not transient and remained intact far after all fuel was consumed (Fig. ). Confocal microscopy was used to study the morphology of the assembly and found, in line with previous work, that Fmoc-GGD formed transient vesicles, whereas Fmoc-AVD assembled into fibers (Fig. ). We studied the evolution of the reaction cycle by applying fuel, and at predetermined time points, we used a benzylamine quench to stop the reaction cycle and measure its contents by HPLC (Fig. ). The anhydride product was temporarily present, and, as the system was running out of fuel, the product disappeared.