Spontaneous formation of helically twisted fibers from 2-glucosamide bolaamphiphiles: Energy-filtering transmission electron microscopic observation and even-odd effect of connecting bridge

A series of nonionic sugar-based bolaamphiphiles having n-alkylene chain length of 9, 10, 11, 12, 13, 14, 16, or 18 carbon atoms, N,N'-bis(2-deoxy-D-glucopyranosid-2-yl)alkane-1,n-dicarboxamide, 1(n), have been synthesized in one step from commercially available glucosamine hydrochloride. Their self-assembling morphologies in 50% aqueous methanolic solutions have been studied using energy-filtering transmission electron microscopy (EF-TEM). The bolaamphiphiles 1(n) (n = 10, 12, and 14) with an even-numbered carbon bridge produced well-defined helically twisted fibers of 8-25 nm width with a high axial ratio. The fiber morphology was found to display a pronounced even-odd dependence upon the number of carbons (n) in the connecting alkylene bridge. A similar trend was also exhibited by the infrared band frequencies and by the wide-angle X-ray diffraction patterns. Anomeric ratios of 1(n) were approximately constant across the series and had no remarkable effect upon the fiber morphology.