Electrostatic Control of Shape Selection and Nanoscale Structure in Chiral Molecular Assemblies

Joseph M. McCourt, Sumit Kewalramani, Changrui Gao, Eric W. Roth, Steven J. Weigand, Monica Olvera De La Cruz*, Michael J. Bedzyk*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

12 Scopus citations

Abstract

How molecular chirality manifests at the nano- to macroscale has been a scientific puzzle since Louis Pasteur discovered biochirality. Chiral molecules assemble into meso-shapes such as twisted and helical ribbons, helicoidal scrolls (cochleates), or möbius strips (closed twisted ribbons). Here we analyze self-assembly for a series of amphiphiles, Cn-K, consisting of an ionizable amino acid [lysine (K)] coupled to alkyl tails with n = 12, 14, or 16 carbons. This simple system allows us to probe the effects of electrostatic and van der Waals interactions in chiral assemblies. Small/wide-angle X-ray scattering (SAXS/WAXS) reveals that at low pH, where the headgroups are ionized (+1), C16-K forms high aspect ratio, planar crystalline bilayers. Molecular dynamics (MD) simulations reveal that tilted tails of the bilayer leaflets are interdigitated. SAXS shows that, with increasing salt concentration, C16-K molecules assemble into cochleates, whereas at elevated pH (reduced degree of ionization), helices are observed for all Cn-K assemblies. The shape selection between helices and scrolls is explained by a membrane energetics model. The nano- to meso-scale structure of the chiral assemblies can be continuously controlled by solution ionic conditions. Overall, our study represents a step toward an electrostatics-based approach for shape selection and nanoscale structure control in chiral assemblies.

Original languageEnglish (US)
Pages (from-to)1169-1181
Number of pages13
JournalACS Central Science
Volume8
Issue number8
DOIs
StatePublished - Aug 24 2022

Funding

This research was primarily supported by the Department of Energy (DOE), Office of Basic Energy Sciences under Contract DE-FG02-08ER46539. M.O.d.l.C. is thankful to the Sherman Fairchild Foundation for computational support. Peptide synthesis was performed in the Peptide Synthesis Core Facility of the Simpson Querrey Institute at Northwestern University. The SAXS/WAXS experiments were performed at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) beamline 5ID-D located at Sector 5 of the Advanced Photon Source (APS) and at the APS beamline 12 ID-C. DND-CAT is supported by Northwestern University, The Dow Chemical Company, and DuPont de Nemours, Inc. The APS, an Office of Science User Facility operated for DOE by Argonne National Laboratory, is supported by DOE under Contract DE-AC02-06CH11357. CD measurements were performed at the Keck Biophysics facility at Northwestern University and Cryo-TEM made use of the BioCryo facility of Northwestern University’s NUANCE Center, which has received support from the SHyNE Resource (NSF ECCS-2025633), the IIN, and Northwestern’s MRSEC program (NSF DMR-1720139). The authors thank M. Karver for peptide synthesis and Dr. S. Seifert (APS, sector 12) for the assistance with the X-ray scattering measurements. This research was primarily supported by the Department of Energy (DOE), Office of Basic Energy Sciences under Contract DE-FG02-08ER46539. M.O.d.l.C. is thankful to the Sherman Fairchild Foundation for computational support. Peptide synthesis was performed in the Peptide Synthesis Core Facility of the Simpson Querrey Institute at Northwestern University. The SAXS/WAXS experiments were performed at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) beamline 5ID-D located at Sector 5 of the Advanced Photon Source (APS) and at the APS beamline 12 ID-C. DND-CAT is supported by Northwestern University, The Dow Chemical Company, and DuPont de Nemours, Inc. The APS, an Office of Science User Facility operated for DOE by Argonne National Laboratory, is supported by DOE under Contract DE-AC02-06CH11357. CD measurements were performed at the Keck Biophysics facility at Northwestern University and Cryo-TEM made use of the BioCryo facility of Northwestern University's NUANCE Center, which has received support from the SHyNE Resource (NSF ECCS-2025633), the IIN, and Northwestern's MRSEC program (NSF DMR-1720139). The authors thank M. Karver for peptide synthesis and Dr. S. Seifert (APS, sector 12) for the assistance with the X-ray scattering measurements

ASJC Scopus subject areas

  • General Chemistry
  • General Chemical Engineering

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