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. 2013 Mar 20;135(11):4175-8.
doi: 10.1021/ja3112912. Epub 2013 Mar 11.

Nonlinear scaling of surface water diffusion with bulk water viscosity of crowded solutions

John M Franck  1 , John A Scott, Songi Han
Affiliations

Nonlinear scaling of surface water diffusion with bulk water viscosity of crowded solutions

John M Franck et al. J Am Chem Soc. .

Abstract

The translational hydration dynamics within 0.5-1.5 nm of the surface of a DPPC liposome, a model biomacromolecular surface, is analyzed by the recently developed Overhauser dynamic nuclear polarization (ODNP) technique. We find that dramatic changes to the bulk solvent cause only weak changes in the surface hydration dynamics. Specifically, both a >10-fold increase in bulk viscosity and the restriction of diffusion by confinement on a multiple nm length-scale change the local translational diffusion coefficient of the surface water surrounding the lipid bilayer by <2.5-fold. By contrast, previous ODNP studies have shown that changes to the biomacromolecular surface induced by folding, binding, or aggregation can cause local hydration dynamics to vary by factors of up to 30. We suggest that the surface topology and chemistry at the ≤1.5 nm scale, rather than the characteristics of the solvent, nearly exclusively determine the macromolecule's surface hydration dynamics.

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Figures

Figure 1
Figure 1
A schematic of the three LUV samples employed in this study. Plain DPPC (left), DPPC + Ficoll 70 (center), DPPC + sucrose (right) are all dissolved in PBS buffer (to enforce a constant pH). Ficoll 70 has a radius of 5.5 nm (and at these concentrations, the different Ficoll molecules likely interact with each other). Sucrose exhibits an effective hydrodynamic radius of between 0.44 nm and 0.52 nm, depending on the method of determination
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