Sodium-23 NMR in the Lyomesophases of Disodiumcromoglycate

Abstract

²³Na NMR spectra are reported for the various lyomesophases of disodiumcromoglycate (DSCG). The spectra were studied as function of DSCG concentration, temperature, and added NaCl as well as some other electrolytes. In the isotropic liquid phase there is a steep increase in the ²³Na MNR linewidth upon cooling, in a range of 10 to 15 ° C above the clearing point. This is interpreted in terms of the formation of DSCG micelles before the onset of the mesomorphic phases. Within all mesophases distinct splittings due to quadrupolar interaction were observed. These splittings were found to decrease upon addition of NaCl and appear to change sign above a certain salt concentration. As function of DSCG concentration, the splitting first increases and then decreases. The results are qualitatively interpreted in terms of two distinct solvation sites in which the sodium ions experience quadrupole interaction of opposite signs. Possible assignment for the two sites are discussed.