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Abstract:
Deuterium NMR and X-ray diffractometry studies of the lyomesophases of the disodium/cromoglycate-water system are reported. The deuterium NMR studies were made on three specifically labelled compounds, viz. disodium cromoglycate-6,8,6′,8′-d4, disodium cromoglycate-3,3′-d2 and disodium cromoglycate-10-d1. The deuterium spectra of these species consist of doublets caused by the corresponding average quadrupolar interaction in the N and M phases; however, in phase III only the methine deuteron of disodium cromoglycate-10-d1 could be seen. The splittings of the chromone moiety deuterons, 3,6 and 8, are essentially identical over the whole temperature and concentration range of the N and M phases, ranging between 50 and 65 kHz. The methine deuteron splitting in the M phase is similar to that of the chromone deuterons, but is considerably higher (115 to 117 kHz) in phase III.
The X-ray diffraction studies were made on a 20 wt% solution as a function of temperature between −15°C and 60°C. Two diffraction bands were observed corresponding to approximately 37 Å and 3.4 Å d-values at room temperature. Distinct changes in the diffraction pattern have been observed in the phase transition regions, Isotropic → N → M → III → solid. The results are consistent with a model in which the N and M phases consist of highly ordered cylindrical micelles of stacked disodium cromoglycate molecules whose chromone planes lie perpendicular to the cylinder axes. The 37 Å and 3.4 Å spacings are identified with respectively the intermicellar and intramicellar stacking distances, and from the NMR results the effective orientational order parameter of the micelles is calculated to be between 0.75 and 1.0 depending on the concentration.
