Lipid membranes are highly dynamic to accommodate the motions of biological molecules and bilayer deformations needed in cell functions. Yet compared to our understanding of the structural integrity of complex biomembranes, much less is known about the membrane dynamics. Neutron scattering techniques are uniquely suited to provide important insights into structure and dynamics of lipid membranes as they access materials properties in atomic to molecular length and time scales. Some of us have developed a probe-free means to estimate the membrane viscosity through measurements of the collective thermal fluctuations of lipid bilayers using neutron spin echo (NSE) spectroscopy. The membrane viscosity is one of two key parameters that characterizes the membrane transport properties, the other is the molecular diffusion constant of molecules within the membrane. According to a theory proposed by Saffman and Delbrück for two-dimensional molecular diffusion in a membrane, the molecular diffusion constant is non-linear in both the size of the molecule and the membrane viscosity. Studies of protein, particles, and lipid domains of different sizes in membranes have confirmed the non-linear dependence of the diffusion constant on the molecular size. However, no direct comparison between the molecular diffusion constant and membrane viscosity has been reported. Here, we combine neutron backscattering measurements of the lipid diffusion constant (D) and NSE measurements of the membrane viscosity (ηm) and show that D is linearly proportional to ηm-1. Together these results show that the predicted nonlinearity for D on ηm is not significant for common saturated lipid bilayers in water.

Direct comparison between molecular lateral diffusion constant and lipid membrane viscosity using quasi-elastic neutron scattering techniques

2019 Spring National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.