The crystal packing of N-( n-octyl)- d-gulonamide containing tail-to-tail sheets compared to its gluconamide diastereomer showing head-to-tail arrangement

Abstract

N-Octylamides of diastereomeric gluconic and gulonic acids form molecular aggregates of extremely different curvature, namely helical micellar rods with a diameter of 4 nm and planar bilayers. In the crystal structure of the gulonamide compound, symmetric “tail-to-tail” bilayer sheets are observed, whereas the gluconamide derivative (whose crystal structure was determined previously) forms an unusual “head-to-tail” arrangement. These differences are unexpected because both diastereomers contain one pair each of syn- and anti-oriented hydroxyl groups in 1,3-positions of the extended aldonic acid chains. The experimental results are explained by the occurrence of hydrogen-bond patterns between hydroxyl groups, either within one crystal sheet or hydrophobic bilayer (gluconamide) or between the end groups of neighboring sheets (gulonamide).