Correlating steric hydration forces with water dynamics through surface force and diffusion NMR measurements in a lipid–DMSO–H₂O system

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 112; no. 34; pp. 10708 - 10713
• Main Authors: Schrader, Alex M., Donaldson, Stephen H., Song, Jinsuk, Cheng, Chi-Yuan, Lee, Dong Woog, Han, Songi, Israelachvili, Jacob N.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 25-08-2015; National Acad Sciences
• Subjects: 1,2-Dipalmitoylphosphatidylcholine - chemistry; Biological Sciences; Diffusion; Dimethyl Sulfoxide - chemistry; Gels; Hydrodynamics; Lipid Bilayers - chemistry; Membrane Lipids - chemistry; Models, Chemical; Molecular Dynamics Simulation; Nuclear Magnetic Resonance, Biomolecular - methods; Organophosphorus Compounds - chemistry; Osmolar Concentration; Quaternary Ammonium Compounds - chemistry; Solubility; Solvents - chemistry; Surface Properties; Surface Tension; Water - chemistry; dimethyl sulfoxide; lipid solvation; hydration shell; membrane interactions; hydrodynamic radius
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1512325112

Dimethyl sulfoxide (DMSO) is a common solvent and biological additive possessing well-known utility in cellular cryoprotection and lipid membrane permeabilization, but the governing mechanisms at membrane interfaces remain poorly understood. Many studies have focused on DMSO–lipid interactions and the subsequent effects on membrane-phase behavior, but explanations often rely on qualitative notions of DMSO-induced dehydration of lipid head groups. In this work, surface forces measurements between gel-phase dipalmitoylphosphatidylcholine membranes in DMSO–water mixtures quantify the hydration- and solvation-length scales with angstrom resolution as a function of DMSO concentration from 0 mol% to 20 mol%. DMSO causes a drastic decrease in the range of the steric hydration repulsion, leading to an increase in adhesion at a much-reduced intermembrane distance. Pulsed field gradient NMR of the phosphatidylcholine (PC) head group analogs, dimethyl phosphate and tetramethylammonium ions, shows that the ion hydrodynamic radius decreases with increasing DMSO concentration up to 10 mol% DMSO. The complementary measurements indicate that, at concentrations below 10 mol%, the primary effect of DMSO is to decrease the solvated volume of the PC head group and that, from 10 mol% to 20 mol%, DMSO acts to gradually collapse head groups down onto the surface and suppress their thermal motion. This work shows a connection between surface forces, head group conformation and dynamics, and surface water diffusion, with important implications for soft matter and colloidal systems.