A CPMAS C-13 NMR-STUDY OF MOLECULAR-CONFORMATIONS AND DISORDER OF N-OCTYLHEXONAMIDES IN MICROCRYSTALS AND SUPRAMOLECULAR ASSEMBLIES

Solid molecular mono- and bilayers in bulk aqueous media are usually made of amphiphiles with a chiral head group, a secondary amide group, and long alkyl chains. Their uniform helical pitches or rod and tubule diameters suggest uniform molecular conformations within the curved supramolecular assemblies. These conformations are characterized by chemical shift patterns in CPMAS C-13-NMR solid state spectra. The assignment of such spectra obtained for microcrystals and lyophilized fibrous assemblies of five N-octylhexonamides is based on comparisons with (i) known single crystal structures, (ii) unequivocally assigned C-13-NMR solution spectra, and (iii) application of established gauche effects. The crystal structure data may be taken from single crystal structures of corresponding amphiphiles, which are notoriously difficult to obtain, or from nonamphiphilic analogues. The procedure also detects crystal disorders. It is generally applicable to assemblies of molecules with at least four interconnected carbon atoms in a uniform conformation.