Solid-state deuterium NMR spectroscopy is a powerful method for addressing how material properties emerge from atomistic level interactions in the case of surfactants and lipid membranes. We show how solid-state 2H NMR gives atomistically resolved structure and dynamics of flexible phospholipids within the liquid-crystalline state. For lamellar mesophases, the average structure is manifested by the segmental order parameters (SCD) of the molecules. Bilayer deformation in response to external perturbations allows one to unravel how the bulk material properties emerge from atomistic-level interactions. Moreover, the extent to which lipid bilayers are deformed by osmotic pressure is integral to how lipid-protein interactions affect membrane functions. Measurements of the order parameters versus osmotic pressure yield the elastic area compressibility modulus and the corresponding bilayer thickness at an atomistic level. Notably, this approach reveals that membrane elasticity involves bilayer deformations over a range of length scales, from the nanostructure dimensions down to the size of the flexible lipid segments. In addition, NMR relaxation rates provide complementary information about molecular dynamics. Particular attention is paid to the magnetic field dependence of the NMR relaxation rates in terms of various simplified power laws. We show how analytical NMR relaxation models can guide the continued development of atomistic and coarse-grained force fields. Our interpretation suggests that lipid diffusion and collective order fluctuations are implicitly governed by the viscoelastic nature of the liquid-crystalline ensemble. Collective bilayer excitations are emergent over mesoscopic length scales that fall between the molecular and nanoscale dimensions, and are important for lipid organization and lipid-protein interactions. Future conceptual advances and theoretical reductions will foster understanding of biomembrane structural dynamics through a synergy of NMR measurements and molecular simulations.

Deuterium NMR spectroscopy in colloid and surface chemistry

2019 Spring National Meeting

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