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Issue 17, 2011
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Dynamics and state of lipid bilayer-internal water unraveled with solution state 1H dynamic nuclear polarization

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Abstract

The dynamics and state of lipid bilayer-internal hydration water of unilamellar lipid vesicles dispersed in solutions is characterized. This study was enabled by a recently developed technique based on Overhauser dynamic nuclear polarization (DNP)-driven amplification of 1H nuclear magnetic resonance (NMR) signal of hydration water. This technique can, in the full presence of bulk water, selectively quantify the translational dynamics of hydration water within ∼10 Å around spin labels that are specifically introduced to the local volume of interest within the lipid bilayer. With this approach, the local apparent diffusion coefficients of internal water at different depths of the lipid bilayer were determined. The modulation of these values as a response to external stimuli, such as the addition of sodium chloride or ethanol and the lipid phase transitions, that alter the fluctuations of bilayer interfaces together with the activation energy values of water diffusivity shows that water is not individually and homogeneously solvating lipid's hydrocarbon tails in the lipid bilayer. We provide experimental evidence that instead, water and the lipid membrane comprise a heterogeneous system whose constituents include transient hydrophobic water pores or water structures traversing the lipid bilayer. We show how these transient pore structures, as key vehicles for passive water transport can better reconcile our experimental data with existing literature data on lipid bilayer hydration and dynamics.

Graphical abstract: Dynamics and state of lipid bilayer-internal water unraveled with solution state 1H dynamic nuclear polarization

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Publication details

The article was received on 12 Nov 2010, accepted on 26 Jan 2011 and first published on 21 Mar 2011


Article type: Perspective
DOI: 10.1039/C0CP02512G
Citation: Phys. Chem. Chem. Phys., 2011,13, 7732-7746
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    Dynamics and state of lipid bilayer-internal water unraveled with solution state 1H dynamic nuclear polarization

    R. Kausik and S. Han, Phys. Chem. Chem. Phys., 2011, 13, 7732
    DOI: 10.1039/C0CP02512G

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