Abstract
Sodium chloride (NaCl) is a very common molecule in biotic and abiotic aqueous environments. In both cases, variation of ionic strength is inevitable. In addition to the osmotic variation posed by such perturbations, the question of whether the interactions of monovalent ions Na+ and Cl-, especially with the neutral head groups of phospholipid membranes are impactful enough to change the membrane rigidity, is still not entirely understood. We investigated the dynamics of 1,2-di-(octadecenoyl)-sn-glycero-3-phosphocholine (DOPC) vesicles with zwitterionic neutral head groups in the fluid phase with increasing external salt concentration. At higher salt concentrations, we observe an increase in bending rigidity from neutron spin echo (NSE) spectroscopy and an increase in bilayer thickness from small-Angle X-ray scattering (SAXS). We compared different models to distinguish membrane undulations, lipid tail motions, and the translational diffusion of the vesicles. All of the models indicate an increase in bending rigidity by a factor of 1.3-3.6. We demonstrate that even down to t > 10 ns and for Q > 0.07 Å-1, the observed NSE relaxation spectra are influenced by translational diffusion of the vesicles. For t < 5 ns, the lipid tail motion dominates the intermediate dynamic structure factor. As the salt concentration increases, this contribution diminishes. We introduced a time-dependent analysis for the bending rigidity that highlights only a limited Zilman-Granek time window in which the rigidity is physically meaningful.
| Original language | English |
|---|---|
| Pages (from-to) | 9356-9367 |
| Number of pages | 12 |
| Journal | Langmuir |
| Volume | 36 |
| Issue number | 32 |
| DOIs | |
| State | Published - Aug 18 2020 |
Funding
The neutron scattering work is supported by the U.S. Department of Energy (DOE) under EPSCoR grant no. DE-SC0012432 with additional support from the Louisiana Board of Regents. Access to the neutron spin echo spectrometer and small-angle scattering instruments was provided by the Center for High Resolution Neutron Scattering, a partnership between the National Institute of Standards and Technology and the National Science Foundation under agreement no. DMR-1508249. Research conducted at the Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory (ORNL) was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. DOE. We thank Lin Yang and Shirish Chodankar from 16-ID, LIX beamline at the National Synchrotron Light Source (NSLS) II. The LiX beamline is part of the Life Science Biomedical Technology Research resource, primarily supported by the National Institute of Health, National Institute of General Medical Sciences under grant P41 GM111244, and by the Department of Energy Office of Biological and Environmental Research under grant KP1605010, with additional support from NIH grant S10 OD012331. As an NSLS II facility resource at the Brookhaven National Laboratory, work performed at Life Science and Biomedical Technology Research is supported in part by the U.S. Department of Energy, Office of Basic Energy Sciences Program under contract DE-SC0012704. CG-3 Bio-SANS instrument and HFIR are sponsored by the Office of Biological and Environmental Research, and the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy, respectively. We would like to thank Rafael Cueto (LSU) for his support in DLS experiments, Ralf Biehl (Forschungszentrum Jülich GmbH, Germany) for his support in performing viscosity measurements, and Jibao He (Tulane University) for his support in cryo-TEM. We would like to acknowledge Antonio Faraone (NIST) for his support to the NSE experiments and Cedric Gagnon (NIST) for his support at the VSANS beamline.
| Funders | Funder number |
|---|---|
| Department of Energy Office of Biological and Environmental Research | KP1605010 |
| Life Science Biomedical Technology Research | |
| Office of Basic Energy Sciences Program | DE-SC0012704 |
| Scientific User Facilities Division | |
| National Science Foundation | DMR-1508249 |
| National Science Foundation | |
| National Institutes of Health | |
| U.S. Department of Energy | |
| NIH Office of the Director | S10OD012331 |
| NIH Office of the Director | |
| National Institute of General Medical Sciences | P41 GM111244 |
| National Institute of General Medical Sciences | |
| National Institute of Standards and Technology | |
| Office of Experimental Program to Stimulate Competitive Research | DE-SC0012432 |
| Office of Experimental Program to Stimulate Competitive Research | |
| Basic Energy Sciences | |
| Biological and Environmental Research | |
| Oak Ridge National Laboratory | |
| Louisiana Board of Regents |