Studies in membrane processes. VIII. A deuterium and sodium nuclear magnetic resonance investigation into the hexadecylpyridinium/hexadecyltrimethylammonium liquid crystalline system

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Abstract
Novel lyotropic mesophases that spontaneously orient in magnetic fields have been prepared using hexadecylpyridinium chloride and hexadecyltrimethylammonium bromide as well as, in limited regions, mixtures of the two detergents. These mesophases of type II provide the opportunity to study the behaviour of oriented water (DOH) at the hydrophobic interface, sodium ions, and the effect on hydrocarbon chain motions of variations in composition of the constituent bilayers formed by the mixed detergent systems. The pyridinium head group is especially accessible to definitive studies using deuterium magnetic resonance spectra of specifically deuteriated ring and adjacent hydrocarbon chain segments. Such investigations reveal the lack of cylindrical symmetry of motion about the extended chain axis near the pyridinium head group.The deuterium resonance of the HOD species shows that both pyridinium and trimethylammonium head groups have a very small orienting effect on the adjacent water, which appears to be indifferent to the choice of these chemical identities. This is understandable in terms of the lack of hydrogen bonding to these moieties. Sodium ions also exhibit small quadrupole splittings in all systems studied here and thus probably play a passive role in the interface chemistry and structure.

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