Comparative X‐ray and Fourier‐transform‐infrared investigations of conformational properties of bacterial and synthetic lipid A of Escherichia coli and Salmonella minnesota as well as partial structures and analogues thereof

Abstract

By using the X‐ray and infrared spectroscopic characteristics of various synthetic analogues and partial structures of lipid A in the dried state, a comparison of these compounds with their natural counterparts was undertaken. As judged by their X‐ray diffraction and infrared spectroscopic features, the compounds tested could be divided into two main groups. The first group covered those samples synthesized in accordance with a previously assumed structure, while those synthesized in accordance with present knowledge on the lipid‐A primary structure formed the second group. Members of the first group were characterized by a liquid‐like, α‐type arrangement of their fatty acyl chains in a non‐lamellar supramolecular structure, while all members of the second group formed bilayered phases with a much more ordered, β,‐type conformation of their fatty acyl chains. Synthetic Escherichia coli‐type lipid A (compound 506), proved to be essentially identical to its natural counterpart with respect to those conformational properties accessible by our methods. The synthetic hepta‐acyl species of Salmonella minnesota lipid A (compound 516) revealed an unexpected conformational behaviour, whereby a fattyacyl‐chain packing could be detected which was different from the hexagonal arrangement found for all other compounds of the second group. Copyright © 1989, Wiley Blackwell. All rights reserved