Solid-state deuterium NMR measurements were used to characterize the flipping motion of the water molecule in barium chlorate monohydrate, Ba(ClO3)2·2H2O. In particular, temperature-dependent quadrupole echo line shapes, their τ dependence and spectral intensities, and the anisotropy of the spin−lattice relaxation observed in inversion recovery experiments permit measurement of the 2-fold flipping rates. These were studied as a function of temperature and yield an activation energy E a = 30 kJ/mol and pre-exponential factor A 0 = 1.5 × 1014, which are typical for molecular motion constrained by hydrogen bonds of moderate strength. A discussion of experimental considerations is also presented.

The molecular mobility of a polymer model membrane is studied by 2H NMR. The lipid analogue consists of a quaternary ammonium ion, to which a methacryloylic moiety is attached via a spacer to the hydrophilic head group. A methylene group of the spacer, the methyl‐head group and methylene groups in the 1‐, 2‐, and 7‐position of the lipid chains are selectively deuterated. Temperature dependent 2H NMR spectra are reported for both, the monomer and the polymer membrane below and above the main phase transition. The data are quantitatively analyzed in terms of a simple motional model, in which the complex molecular dynamics is approximated by a six‐site jump model describing rotations about the long axis of the molecule and conformational changes. The increasing mobility with increasing temperature is only in part due to an increase of the jump rate between different sites. It also reflects the increase in the number of conformations accessible. As a quantitative measure of the mobility at a given site, a mean jump frequency is extracted from the data. For the monomer Ω˜ and its temperature dependence in the liquid crystalline phase is almost independent of the site being studied. In the polymer, however, major differences are observed, Ω˜ for the head group and the 7‐position of the lipid chain differing by two orders of magnitude. The mobility of the spacer is even lower. This 2H NMR study thus shows that although the polymerization largely hinders the head group mobility, the chain flexibility most important for membrane applications is retained.

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Pulsed ' H NMR was used to study the molecular mobility of a polymer model membrane.The polymerizable lipid analogue consists of a quaternary ammonium ion with two C,, alkyl chains and a methacryloyl moiety attached to the hydrophilic head group via an alkyl spacer.The bilayer spacing as obtained from small angle X-ray scattering was found to be 3 nm in the lamellar gel phase of the monomer and 3 3 nm in the polymer indicating an interdigitated structure. The molecular mobility in both the monomer and the polymer below and above the phase transition + & was investigated by the NMR lineshapes and the transverse relaxation time at five positions of the monomeric unit: a methylene group of the spacer, the head group and three methylene groups of the alkyl chains (I-, 2-, and 7-position). In contrast to the monomer a pronounced motional gradient was observed in the polymer, where the spacer is almost completely immobilized, whereas the mobility in the middle of the hydrophobic chains is largely retained. A quantitative analysis of the NMR lineshapes shows a gradual increase of molecular mobility in the polymer above the phase transition due to an increase in both the jump rate and the number of conformational transitions.

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