The molecular organization of xylan diacetate and acetylated d-xylose oligosaccharides at the air-aqueous interface

Abstract

In a condensed monolayer, xylan diacetate (XDA) molecules are oriented in an extended chain conformation in which the chain axes are parallel to the substrate and the xylose rings are approximately perpendicular to it. This closely resembles the conformation of cellulose triacetate (CTA) molecules in condensed monolayers. However, the β,1–4 linkage in the xylan backbone is more flexible than the same linkage in CTA, which allows the residues to tilt independently out of the surface during compression, permitting closer packing. While cellobiose octaacetate proved to be a good model for the monolayer behavior of CTA (15), xylobiose hexaacetate was not adequate as a model for XDA. It is not until the chain length is increased to 4 that the xylose rings assume a vertical orientation as proposed for the polymer. This supports the greater ease of rotation about the two bonds linking the residues to the glycosidic oxygen in XDA than in CTA.