Abstract
We investigate the effect of charge block length on polyampholyte chain conformation and phase behavior using small-angle X-ray scattering (SAXS) and implicit-solvent molecular simulations. To this end, we use solid phase peptide synthesis to precision-tailor a series of polyampholytes consisting of l-glutamic acid (E) and l-lysine (K) monomers arranged in alternating blocks from 2 to 16 monomers. We observe that the polyampholytes tend to phase separate as block size increases. With addition of NaCl, phase separated polyampholytes exhibit a salting-in effect dependent on charge block length. Fourier-transform infrared (FTIR) spectroscopy reveals the presence of intramolecular hydrogen bonds that are disrupted upon the addition of NaCl, implicating both electrostatic interactions and hydrogen bonding in the phase behavior. SAXS spectra at no-added salt conditions show minimal dependence of charge block length on the radius of gyration (Rg) for soluble polyampholytes, but local chain stiffening is found to be dependent on charge block length. With increasing NaCl, consistent with electrostatic screening, all polyampholytes expand and behave as neutral or swollen chains in good solvent conditions. Molecular simulations are qualitatively consistent with experiments. Implications for understanding intracellular condensates and material design are noted.
| Original language | English |
|---|---|
| Pages (from-to) | 195-200 |
| Number of pages | 6 |
| Journal | ACS Macro Letters |
| Volume | 12 |
| Issue number | 2 |
| DOIs | |
| State | Published - Feb 21 2023 |
Funding
We thank the Shared Equipment Authority at Rice University for access to MALDI-ToF spectrometer, microplate reader, NMR spectrometer, and FTIR microscope. We further thank Wong and Landes groups for access to Zetasizer and CD spectrophotometer, respectively. This research was supported by the Welch Foundation (C-2003-20190330 and C-1241). SAXS experiments were carried out at beamline 12-ID-B, Advanced Photon Source (APS), Argonne National Laboratory (ANL). This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science user facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Research at Oak Ridge National Laboratory is supported under Contract DE-AC05-00OR22725 from the U.S. Department of Energy to UT-Battelle, LLC. This research used resources of National Energy Research Scientific Computing Center, which is supported by the Office of Science of the U.S. Department of Energy under Contract #DE-AC02-05CH11231.