A 2H NMR Study of Macroscopically Aligned Bilayer Membranes Containing Interfacial Hydroxyl Residues

Abstract

The polar interface of membranes containing phosphatidylglycerol or cholesterol was studied by (2)H nuclear magnetic resonance (NMR) as a function of membrane hydration. The membranes were macroscopically aligned and hydrated with deuterium oxide. Water uptake and membrane annealing was achieved under NMR control, using a novel hydration technique. Well-resolved (2)H quadrupolar doublets were obtained from individual hydroxyl residues and from the interlamellar water. The response of the phosphatidylglycerol headgroup and of the cholesterol molecule to the spontaneous evaporation of interlamellar water could be thus monitored continuously. It is shown that the phosphatidylglycerol headgroup undergoes changes of conformation and average orientation with respect to the membrane surface and that the off-axis motion of the cholesterol molecule decreases. The deuteron exchange between hydroxyl residues and surface-associated D(2)O was determined by an inversion transfer technique. The exchange rates of the hydroxyl residues in the phosphatidylglycerol headgroup were different and depended strongly on the total hydration of the membrane. Significantly lower and almost hydration-independent rates were obtained for cholesterol. These results will be discussed with reference to earlier reports on the headgroup dynamics of phosphatidylglycerol and on the interaction of cholesterol with the membrane-water interface.

Thermodynamic and structural behaviour of equimolar POPC/CnE4 (n=8, 12, 16) mixtures by sorption gravimetry, 2H NMR spectroscopy and X-ray diffraction

“…The quadrupolar splitting Q was determined with the same Bruker MSL-300 spectrometer at the resonance frequency of 46.1 MHz at a temperature of 298.15 K. In the case of using 2 H 2 O with non-deuterated solutes, the question of hydrogen exchange has to be considered (Kurze et al, 2000). This especially applies to weakly bound hydrogen, such as in hydroxyl residues.…”

“…8 and 10. At all hydration degrees, there is a remaining quadrupolar splitting present, even if the curves are extrapolated to full hydration (between 500 and 800 Hz, see also Kurze et al, 2000). There is thus no isotropic signal present in the spectra representing the lamellar phase, and this indicates that all water molecules are more or less captured between the membranes.…”

“…Furthermore, the quadrupolar splitting is analysed as a function of the almost full hydration range. Hydration-dependent quadrupolar splitting was in the past usually analysed for pure phospholipids and data for mixtures are relatively rare (Kurze et al, 2000;Moraes and Bechinger, 2004).…”

Reduced coupling of water molecules near the surface of reverse micelles

“…Strongly altered hydrogen-bond dynamics in the lipid hydration shells have been observed in the experiments addressing water translational mobility, reorientation, and hydrogen-bond strength. [10][11][12][13][14][15] Interestingly, such studies indicate coupling between the dynamics of water and biological objects which may imply a strong interaction between the solute and the hydration shell. 16,17 It is well known that structure, dynamics and even macroscopic properties of water are determined by the strong intermolecular interactions between the hydrogen-bonded water molecules.…”

No Ice-Like Water at Aqueous Biological Interfaces

“…Membrane hydration drives the self-assembly of the bilayers, and studies of partially hydrated bilayers by X-ray scattering, neutron scattering and calorimetry indicated that the fluidity of the lipid phase-an essential parameter for membrane function-varies strongly with the degree of hydration [1]. Inversely, NMR experiments have shown that the lipid head groups have a strong influence on the local water structure [2][3][4].…”