Conversely, peptide 4 was the only one with two negative minima at 199 and 217 nm. These features were reminiscent of those of similar self-assembling dipeptides that are represented by populations of conformers in solutions, and they confirmed that the presence of D-Phe resulted in negative spectra typical of sequences with D-amino acids, while the presence of L-Phe results in positive spectra in this region. Unfortunately, the formation of opaque gels impeded the acquisition of CD spectra in the assembled states, which were thus analyzed by attenuated total reflectance Fourier-transformed infrared spectroscopy (ATR-IR). In particular, the amide region of the spectra of the xerogels formed by 1 and 3 were strikingly similar (Fig. , left panels), in agreement with the Raman and XRPD data. The amide I signals occurred in the range of βstructures (1610-1622 cm -1 ) as well as in the range where β-turns are found for longer sequences (1676-1686 cm -1 ), as previously found for the gelling D-Phe-L-Ile, which also formed water channels whose cavity was defined by 6 peptide molecules. Peptides 2 and 4 displayed the typical signal at 1641 cm -1 too, which is associated with disordered structures.