LIPID HEADGROUP HYDRATION STUDIED BY H-2-NMR - A LINK BETWEEN SPECTROSCOPY AND THERMODYNAMICS
The conformational and dynamic response of the phosphatidylcholine headgroup to hydration has been characterized by 2H-NMR measurements of selectively deuterated DOPC at positions α, β, and γ, and to complement the structural results from diffraction studies. Quadrupole splittings (ΔνQ) and spin-lat...
| Main Authors: | , |
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| Format: | Journal article |
| Language: | English |
| Published: |
1994
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| Summary: | The conformational and dynamic response of the phosphatidylcholine headgroup to hydration has been characterized by 2H-NMR measurements of selectively deuterated DOPC at positions α, β, and γ, and to complement the structural results from diffraction studies. Quadrupole splittings (ΔνQ) and spin-lattice relaxation rates (1/T1) were monitored over the range of water/lipid mole ratios from 4 to 100. Their hydration dependence reveals a concerted change in headgroup conformation together with an increase in mobility. Both spectroscopic parameters (ΔνQ and 1/T1) are found to be linearly correlated with the activity of the interbilayer water, and it is thus concluded that the 2H-NMR hydration curves are equivalent to lipid sorption isotherms. Using this thermodynamic correlation, the repulsive hydration force between apposing bilayers can be calculated from the 2H-NMR data and a decay constant is evaluated for DOPC of around 3.5 water molecules per lipid. The characterization of the headgroup properties by 2H-NMR is complemented by recent investigations on interbilayer 2H2O, which demonstrates that the lipid-water interface constitutes a single thermodynamic entity. © 1994. |
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