Figure 2: FTIR of polyelectrolyte complexes.

FTIR spectra showing the amide I region for (a) individual polypeptides and the resulting liquid coacervates and solid precipitates, as well as (b) the polypeptides and block copolymers involved in the formation of related LCM and SCM. All samples were prepared in D₂O. Polypeptides were analysed at a concentration of 10 mM with respect to monomer, liquid coacervates and solid precipitates at a concentration of 6 mM with respect to monomer and 100 mM NaCl, while micellar complexes were prepared at a concentration of 0.186 mM polymer, with no salt. All materials show a peak at 1,644 cm⁻¹, characteristic of random coil polypeptide structure. However, the additional peaks associated with aggregated β-strands are present for the solid precipitates and SCMs. For solid precipitates formed from polypeptides with matching chirality (pLK+pLE, pDK+pDE), the main peak is located at 1,611 cm⁻¹ and is shifted to 1,613 cm⁻¹ for opposite chirality (pLK+pDE, pDK+pLE). For SCMs, this peak is located at 1,610 cm⁻¹. An additional low-intensity peak is also present near 1,680 cm⁻¹. The signal for the carbonyl stretching of the glutamic acid can also be observed at 1,564 cm⁻¹. Micelles were prepared using a polyethylene glycol-pLK block copolymer with an average N=50 and either pLE with N=50 for SCMs or N=100 for LCMs.