3.2. Structural Characterization of P1A3 and P2C7
To confirm the cyclic structure of the peptides, a SAXS study was performed. P1A3 and P2C7 peptides are expected to form circular rings with ten amino acids and an approximate molecular weight (MW) of 1.5 kDa. The theoretical sizes of such rings, which are assumed to have a typical distance of 3.6 Å between amino acids, would be 12–14 Å in diameter or to have an approximately 6–7 Å radius. The theoretical intensity of this circular ring ranged from 0.05 Å−1 ≤ q ≤ 1.0 Å−1. Within this range, information about the ring structure can be determined. The SAXS data and obtained p(r) curve for P2C7 are shown in Figure 2a,b. Interestingly, the shape of the p(r) curve is similar to the curves obtained for hollow objects [27], which was expected for circular rings. Further results are shown in Tables S1 and S2 (Supplementary Materials) for both peptides. The Dmax value obtained for the data at 38 cm was similar to the theoretical size of the circular ring (~14Å), which provides an important indication about the formation of peptide rings in the system. The estimated molecular weight of the scattering particle was 1.54 ± 0.16 kDa, which is consistent with the expected value for a 10-amino acid ring (Figure 2c). In summary, the SAXS results confirmed the cyclic structures of both peptides.