NMR Relaxation in Cholesterol and Cholesteric Liquid Crystals

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Abstract
The proton nuclear spin lattice relaxation has been measured in cholesterol and its esters (n‐propionate, n‐decanoate, myristate, and oleate) in the solid, mesophase, and liquid regions using conventional pulsed NMR techniques at a frequency of 30 MHz. All solid phases and the mesophases of all the esters except the oleate exhibited relaxation which could be fit within experimental error with a single exponential. Nonexponential relaxation, which was analyzed assuming two relaxation times, was observed in all liquid phases and throughout the mesophase of the oleate ester. Relaxation in the mesophases of all the esters had very little temperature dependence and this, plus its behavior at the phase transitions, indicated that the relaxation mechanism might be similar to that in nematic liquid crystals. It was not possible to determine the primary source of the nonexponential relaxation behavior but it did not require the presence of an ester group.

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