We investigate the effect of the charge block length on the chain conformation and phase behavior of peptide polyampholytes (PAs) with equal numbers of cationic and anionic ionizable monomers. Peptide PAs were produced by using solid-phase peptide synthesis (SPPS), which enables precise control of the molecular weight, monomer sequence, and chain tacticity. Using circular dichroism (CD) and Fourier-transform infrared (FTIR) spectroscopy, we observe that the atactic peptide PAs show no evidence of secondary structure formation regardless of block length, whereas isotactic peptide PAs exhibit block length dependent secondary structures. Turbidity measurements show that the isotactic peptide PAs phase separate with increasing block length.
Amanda B. Marciel,
Rice University
In contrast, the atactic peptide PAs remain in solution over a wide-range of salt concentrations. Small-angle X-ray scattering (SAXS) measurements reveal that the chain conformation of peptide PAs is compressed compared to expectations for neutral systems. Interestingly, we find that the atactic peptide PAs form block length dependent multichain clusters in solution. These results are consistent with a recent theory predicting that PAs have a block length and concentration dependent threshold for phase separation.
Amanda B. Marciel is an Assistant Professor and William Marsh Rice Trustee Chair of Chemical and Biomolecular Engineering at Rice University. She earned a B.S. in Chemical Biology from the University of California at Berkeley in 2008 and Ph.D. in Biophysics from the University of Illinois at Urbana-Champaign with Professor Charles M. Schroeder in 2015. She worked at the Institute for Molecular Engineering (IME) at The University of Chicago as a Postdoctoral Fellow with Professor Matthew V. Tirrell. The Marciel group investigates how monomer chemistry and sequence influence the behavior of charged polymers in solution and at interfaces to design stimuli-responsive materials