CHBE 565-International Paper Co Seminar-Prof. Amanda Marciel, Rice University (Host: Prof. Simon Rogers) "Influence of Block Length and Tacticity on Polyampholyte Conformation and Phase Behavior"

Bio: 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.

Abstract: In this work, 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 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. 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.