We explain the pKa difference between assemblies of Fmoc-AVD and Fmoc-GGD by valine's high propensity to form flat ß-sheets compared to glycine. The formation of these flat β-sheets implies that the C-terminal aspartic acids are packed in a relatively high density known to shift pKas. We measured the assembly's ability to bind Thioflavin (ThT), which measures the flatness of βsheets. We measured a high ThT signal when we fueled Fmoc-AVD with EDC, while we found no significant emission of THT when we fueled Fmoc-GGD with EDC (Fig. ). Fourier-Transform Infrared Spectroscopy (FT-IR) revealed that both peptides had two predominant peaks around 1690 cm -1 and 1630 cm -1 , which we assign to the Fmoc-OCNH band and the amide I band (Fig. ). The amide I band (carbonyl stretch vibration) is particularly sensitive to hydrogen bonding in the peptide assembly. For Fmoc-AVD, this peak was located at 1632 cm -1 and relatively sharp, which is indicative of elements of β-sheet (1625 cm -1 -1640 cm -1 ). The same peak for Fmoc-GGD broadened drastically and shifted towards the region of 1650 cm -1 , which points towards elements of a random coil (1640 cm -1 -1650 cm -1 ). The FT-IR data further corroborate that Fmoc-GGD is mainly engaged in random coil hydrogen bonds, whereas flat β-sheets are present in Fmoc-AVD assemblies. These flat β-sheets pack the carboxylates closely such that their pKas shift. To test which of the amides in the peptide contributed to the organization of the C-termini and thus the shift in pKa and kinetic trapping, we synthesized Fmoc-AVD(NMe) (Fig. ). This compound is similar to Fmoc-AVD but lacks the last NH-bond due to methylation, which shifted the pKa from 5.8 to 4.2 (Fig. , Fig. ). In other words, the pKashift upon self-assembly had disappeared entirely. Furthermore, transient aggregates emerge upon fueling 10 mM Fmoc-AVD(NMe) with 100 mM EDC (Fig. ). 1 H-NMR and HPLC studies on the reaction cycle of Fmoc-AVD(NMe) showed a complete lack of coassembly of the precursor and thus also no kinetic trapping (Fig. ). In other words, methylation of this crucial amide means that the precursor does not coassemble, and we can recover the dynamic character of the chemically fueled self-assembly.