Studies of metal-sugar complexes in the solid state by the 13C-n.m.r. c.p.-m.a.s. method

✍ Scribed by Laurence D. Hall; T.K. Lim

• Publisher: Elsevier Science
• Year: 1986
• Tongue: English
• Weight: 795 KB
• Volume: 148
• Category: Article
• ISSN: 0008-6215
• DOI: 10.1016/0008-6215(86)80032-5

✦ Synopsis

Several metal-sugar conjugates have been prepared. Chelate coordination complexes of copper(I1) and zinc(H) were prepared from salicylaldimine ligands derived from combinations of methyl 3,4,6-tri-0-acetyl-2-amino-2-deoxy-@glucopyranoside or 1,3,4,~tetra-O-acetyl-2-amino-2-deoxy-&D-gluoopyranose and salicylaldehyde. Similar Schiff's bases were prepared from chitosan and complexed to copper( Cross-polarisation-magic angle spinning 13C-n.m.r. spectroscopy showed that paramagnetic ions have profound effects on the resolution obtainable and, at high concentration, result in broad, featureless spectra. In contrast, diamagnetic ions have little effect on the isotropic chemical shifts of the sugar chelates.

INTRODUCI'ION

The ability of sugars and their derivatives to sequester metals is of interest to the possible development of novel classes of metal-based affinity chromatography materialsl, of chiral homogeneous catalyst9, of metal-chelators for clinical use3, and of models for biologically important chelates4. Other ongoing interests include n.m.r. investigations of metal ion-binding to sugars. In this study, we examine, in the solid state, metal complexes which are diamagnetic and others which are paramagnetic.

Initially, specific, monomeric metal-sugar compounds were synthesised. Schiff's base ligands were obtained by combining amino sugars with aromatic aldehydes, followed by complexation with suitable metal ions. Subsequently, studies were made of the chelating polymers chitin and alginate, which can be obtained in enormous quantities from natural sources. Then, following from other recent attempts to improve the metal-chelating capability by chemical derivatisation of the native polyme&, chitosan Schiff's bases were studied. This work also provided an opportunity to evaluate further the diagnostic potential of solid-state 13Gn.m.r. methods6-8 for examining carbohydrate structures.