DEUTERIUM NMR-STUDY OF A PROBE MOLECULE DISSOLVED IN A CARBOHYDRATE LIQUID-CRYSTAL

A deuterium NMR investigation of C6D6 dissolved in the discotic mesoge n octa-O-decanoyl-beta-cellobiose (Gel-II-10) is reported. The liquid- crystalline phase was found to be uniaxial in agreement with a previou s X-ray study. The influence of magnetic held strength and thermal tre atment on the mesophase alignment was investigated. From H-2 NMR lines hape simulations, the form of the director distribution function was e stimated. In contrast to most discotics, the columns of Gel-II-10 orie nt parallel to the external field indicating that the anisotropic diam agnetic susceptibility of this mesophase is positive. An increase of t he quadrupolar splitting of C6D6 was observed when the sample was heat ed. This behaviour is interpreted in terms of a fast dynamic equilibri um between different solvation sites in the carbohydrate liquid crysta l. The H-2 NMR spectra recorded in the solid phase also indicated an e xchange process between several sites.