Abstract
Bilayers of amphiphiles can organize into spherical vesicles, nanotubes, planar, undulating, and helical nanoribbons, and scroll-like cochleates. These bilayer-related architectures interconvert under suitable conditions. Here, a charged, chiral amphiphile (palmitoyllysine, C16-K1) is used to elucidate the pathway for planar nanoribbon to cochleate transition induced by salt (NaCl) concentration. In situ small- and wide-angle X-ray scattering (SAXS/WAXS), atomic force and cryogenic transmission electron microscopies (AFM and cryo-TEM) tracked these transformations over angstrom tomicrometer length scales. AFM reveals that the large length (L) to width (W) ratio nanoribbons (L/W > 10) convert to sheets (L/W → 1) before rolling into cochleates. A theoretical model based on electrostatic and surface energies shows that the nanoribbons convert to sheets via a first-order transition, at a critical Debye length, with 2 shallow minima of the order of thermal energy at L/W >> 1 and at L/W = 1. SAXS shows that interbilayer spacing (D) in the cochleates scales linearly with the Debye length, and ranges from 13 to 35 nm for NaCl concentrations from 100 to 5 mM. Theoretical arguments that include electrostatic and elastic energies explain the membrane rolling and the bilayer separation-Debye length relationship. These models suggest that the salt-induced ribbon to cochleate transition should be common to all charged bilayers possessing an intrinsic curvature, which in the present case originates from molecular chirality. Our studies show how electrostatic interactions can be tuned to attain and control cochleate structures, which have potential for encapsulating, and releasing macromolecules in a size-selective manner.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 22030-22036 |
| Number of pages | 7 |
| Journal | Proceedings of the National Academy of Sciences of the United States of America |
| Volume | 116 |
| Issue number | 44 |
| DOIs | |
| State | Published - Oct 29 2019 |
Funding
This research was primarily supported by the Department of Energy (DOE), Office of Basic Energy Sciences under Contract DE-FG02-08ER46539. 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) located at Sector 5 of the Advanced Photon Source (APS) and at APS Sector 12. The APS, an Office of Science User Facility operated for DOE by Argonne National Laboratory, is supported by DOE under Contract DE-AC02-06CH11357. GIXS was performed at the XRD Facility and TEM used the EPIC facility at Northwestern University. The authors thank M. Karver for peptide synthesis, Dr. Liam Palmer for discussions and for suggesting cryo-TEM, and Drs. S. Weigand (DND-CAT) and B. Lee (APS, sector 12) for the assistance with the X-ray scattering measurements. ACKNOWLEDGMENTS. This research was primarily supported by the Department of Energy (DOE), Office of Basic Energy Sciences under Contract DE-FG02-08ER46539. 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) located at Sector 5 of the Advanced Photon Source (APS) and at APS Sector 12. The APS, an Office of Science User Facility operated for DOE by Argonne National Laboratory, is supported by DOE under Contract DE-AC02-06CH11357. GIXS was performed at the XRD Facility and TEM used the EPIC facility at Northwestern University. The authors thank M. Karver for peptide synthesis, Dr. Liam Palmer for discussions and for suggesting cryo-TEM, and Drs. S. Weigand (DND-CAT) and B. Lee (APS, sector 12) for the assistance with the X-ray scattering measurements.
Keywords
- Bilayer assembly
- Cochleate
- Electrostatics
- Nanoribbon
ASJC Scopus subject areas
- General