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 le ngth of 9, 10, 11, 12, 13, 14, 16, or 18 carbon atoms, N,N'-bis(2-deoxy-D-g lucopyranosid-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 stud ied using energy-filtering transmission electron microscopy (EF-TEM). The b olaamphiphiles 1(n) (n = 10, 12, and 14) with an even-numbered carbon bridg e produced well-defined helically twisted fibers of 8-25 nm width with a hi gh axial ratio. The fiber morphology was found to display a pronounced even -odd dependence upon the number of carbons (n) in the connecting alkylene b ridge. 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) w ere approximately constant across the series and had no remarkable effect u pon the fiber morphology.