Hydrogen-bonding formation and water dynamics in the nearest hydration shell of lipid membranes.

Aloi E., Bartucci R.

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The water properties of the hydration shell of model membranes within 1 nm from spin-labels located either on the polarhead or at the polar/apolar interface are investigated with D$_2$O-Electron-Spin-Echo-Envelope-Modulation (D$_2$O-ESEEM). The frequency-spectra consist of a component due to hydrogen-bonded D$_2$O-molecules to the spin-labels and a doublet due to nonbonded D$_2$O-molecules. Different fractions of singly or doubly hydrogen-bonded labels are quantified. The D$_2$O-ESEEM spectra resemble the solid-state D$_2$O-NMR lineshapes and narrow between 180-190 K, indicating the onset of isotropic water dynamics (rate around $10^{-5}$ s${}^{-1}$). The water molecular motion at cryogenic temperature interrelates with the dynamical transition observed in the bilayers.

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