LONG-LIVED MICELLAR N-ALKYLALDONAMIDE FIBER GELS - SOLID-STATE NMR AND ELECTRON-MICROSCOPIC STUDIES

Aqueous geis containing 1% of N-octylgluconamide usually crystallize within a few hours. They remain stable for more than 2 months if 0.1-0.4% of sodium dodecylsulfate (SDS) is added. It was shown by2H NMR spectroscopy and electron microscopy that the gels contained fibers of bimolecular thickness (4 nm) and several micrometers lengths in equilibrium with micelles. Relatively high concentrations of micelles extended the gel's lifetime, presumably because the micelles dissolved the head-to-tail sheets of crystallization nuclei too rapidly to allow crystal growth. At temperatures below the gelation point the micelles are as unfit solvents for magnesium octaethylporphyrin as the fibers themselves and show immobile oligomethylene chains in1Ή NMR solution spectra. Comparisons with the diastereomeric gulon- and mannonamide molecular bilayer sheets indicate that the gluconamide rods with the highest curvature contain the least mobile core. Water-insoluble N-octadecyl-mannonamide precipitates from micellar solutions either in the form of a statistical mixture of P- and M-helices or as pure M-helices depending on added detergent and time. The results determine two rules for syntheses of organized systems based on micellar fibers: guest molecules must be tailored in order to fit into the amide hydrogen-bonded fibers and micelles, and the fibers must be chiral and kept in a medium that dissolves crystallization nuclei. © 1990, American Chemical Society. All rights reserved.