AMPHIPHILIC PROPERTIES OF SYNTHETIC GLYCOLIPIDS BASED ON AMIDE LINKAGES .4. C-13 NMR SPECTROSCOPIC STUDIES ON THE GELATION OF N-OCTYL-D-GLUCONAMIDE IN AQUEOUS-SOLUTION

C-13 NMR measurements were taken on cooling of aqueous solutions of N-octyl-D-gluconamide to follow the process of gelation. On cooling from 90-degrees-C gelation sharply occurs at 60-62-degrees-C. In the pre-stage of gelation at 64-degrees-C an aggregated species, probably a dimeric form of octylgluconamide, is detected. Additional signals for sugar carbons C-1, C-4 and C-6 indicate hydrogen bonding. As a side reaction conversion of the octylgluconamide to the ammonium salt takes place. Assignments of the new signals were made with the ammonium salt formed from D-gluconamide and the corresponding octylammonium salt of gluconic acid. When the solution of octygluconamide is kept at 64-degrees-C for a longer period, octylgluconamide, free and aggregated, and its ammonium salt coexist. At 64-degrees-C relaxation times t1 of the sugar carbons corresponding to the octylgluconamide species are much shorter than those of the salt, indicating a decrease of the mobility of the sugar carbons of the former in the pre-stage of gelation.