Using 1 H-NMR spectroscopy, the assembly's composition was measured as a function of time. We used the fact that peptides in an assembly become NMR-silent. We can thus measure how much of the 10 mM initial peptide resides in the assemblies. Combined with the concentrations of the activated product as determined by HPLC, we could thus determine the ratio of precursor and product in the assemblies. Here we assume that all activated product is in the assemblies. Three minutes after the addition of EDC, we found that both the fibers and the vesicles were composed of a coassembly of precursor and product (Fig. ). However, 24 hours after starting the reaction cycle, we found no more NMR-silent peptide in the case of Fmoc-GGD, which points to complete disassembly. In contrast, for Fmoc-AVD, roughly 4.3 mM precursor remained kinetically trapped in assemblies (Fig. ). Only by annealing the kinetically trapped Fmoc-AVD at 95°C for 5 min, we could dissolve the precursor (Fig. ). Finally, we supported our finding that Fmoc-AVD is kinetically traps by a Nile Red assay. The Nile Red emission remained high for Fmoc-AVD, whereas no emission signal was visible for Fmoc-GGD after 24 hours (Fig. ).