2-chlorotrytil resin, O-Benzotriazole-N,N,N,N'-tetramethyl-uronium-hexafluoro-phosphate (HBTU), and Fmoc-protected amino acids were purchased from GL Biochem (Shanghai) Ltd. All solvents were purchased of analytical grade from Merck. All the other chemicals were from Sigma. High purity Milli-Qwater (MQ water) with a resistivity greater than 18 M Ω cm was obtained from an in-line Millipore RiOs/Origin system. 1H-NMR spectra were recorded at 400 MHz and 13C-NMR spectra were recorded at 101 MHz on a Varian Innova Instrument with chemical shift reported as ppm (in DMSO with tetramethylsilane as internal standard). ESI-MS spectra were recorded on an Agilent 6120 single quadrupole LC-MS system. Peptides were synthesized in solid phase using standard protocols and Fmoc protection (more details are provided in the ESI). Each peptide was dissolved by 10 min of ultrasonication and heating in sodium phosphate buffer (0.1 M pH 12.0) to a final concentration of 30 mM and then an equal volume of sodium phosphate buffer (0.1 M pH 5.8) was added to get a final pH of 7.2 ± 0.1 and a final concentration of 15 mM. All-atom MD simulations and analyses were performed with the AMBER22 and AmberTools23 software packages. The parameters for D/L N-terminal norleucine were taken from the literature, and the ff19SB AMBER force field was employed together with an OPC model for water. Simulations of single peptides in solution. First, we performed MD simulations of a single homo-(Nle-Leu-Phe-Phe) and hetero-(DNle-DLeu-Phe-Phe) chiral peptide in explicit water as follows. The initial structure of the homochiral peptide was generated using the sequence command from the xleap tool of AMBER22 and relaxing the structure. The heterochiral peptide was built from the homochiral structure using VMD1.9.3. Starting from these structures, three consecutive restrained structural optimizations (up to 25,000 steps) were performed in the presence of harmonic restraints (k=1 kcal/mol•Å) applied to: a) all non-hydrogenous atoms of the system; b) backbone atoms; c) Cα atoms. Reference structures at steps b) and c) were the final ones from the previous step. Next, up to 50,000 cycles of unrestrained optimization were performed. Each system was then heated to 298 K in 1 ns via constant-pressure-temperature (NTP) MD simulations (using the isotropic Berendsen barostat and the Langevin thermostat) followed by an equilibration phase of 10 ns. Starting from the equilibrated structure, a MD simulation in the NVT ensemble of 1 µs in length was performed using a time step of 2 fs. Next, heating to 363K in was simulated in 20 ns, followed by another equilibrium simulation of 1 µs in length at this temperature. Periodic boundary conditions were employed, and electrostatic interactions were estimated using the Particle Mesh Ewald scheme with a cutoff of 9.0 Å for the short-range evaluation in direct space and for Lennard-Jones interactions (with a continuum model correction for energy and pressure). Self-assembly. 5 independent MD simulations of the self-assembly of 512 heterochiral tetrapeptides in water solution were performed following published protocols. Briefly, the initial conformation of the assembling peptides was generated by placing their centers of mass on a 8x8x8 grid of 17.5 Å-spaced points. Initial orientations of peptides were randomized, and the systems were solvated with water molecules, for a total number of atoms around 235,000. Initial structures of the 5 independent simulations were taken from the optimized structure of the corresponding peptides (simulation 1) and from the most populated conformations extracted (simulations 2 to 5) from a cluster analysis performed on the 1 s-long MD simulation described in the previous paragraph. Hierarchical agglomerative clustering was performed, setting the number of clusters to 4 and using the average distance (average linkage keyword in cpptraj) and symmetric RMSD as metric (srmsd keyword). Each simulation was performed as described in the previous paragraph regarding the structural optimization and initial heating steps. Then, a MD simulation of 100 ns in length at 298 K (NVT ensemble) was performed, followed by: heating (in 20 ns) and equilibrium simulation (1 µs) at 363 K, cooling to 298 K in 100 ns, and finally another equilibrium simulation of 1 µs in length at this temperature.