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1H NMR characterization of chitin tetrasaccharide in binary H2O:DMSO solution: Evidence for anomeric end-effect propagation

Li, Kecheng, Green, Andrew R., Dinges, Meredith M., Larive, Cynthia K.
International journal of biological macromolecules 2019 v.129 pp. 744-749
bioactive compounds, chitin, chitosan, elicitors, immune response, microstructure, nodulation, nuclear magnetic resonance spectroscopy, oligosaccharides, solvents
Chitin oligosaccharides, composed of homogeneous β(1 → 4)-linked N-acetyl-D-glucosamine (GlcNAc) sequences, is a well-known elicitor of plant immune defense, and also occur as structural elements of chitosan and nodulation (Nod) factor. Detailed microstructure characterization is required for understanding the function mode of these bioactive molecules. Herein, experimental conditions for detection and elucidation of the 1H NMR resonances of amide groups in chitin oligosaccharides are presented. The binary mixture of 70% H2O: 30% DMSO‑d6 was found to be the optimal solvent for amide proton measurements in homogeneous GlcNAc sequences, facilitating differentiation of the local chemical microenvironments of all four amide groups of the chitin tetrasaccharide. Experimental evidence that anomeric end-effect triggers amide proton resonance differentiation at the adjacent residue has potential to provide important insights into the solution structure of chitin and other amino sugars containing GlcNAc sequences.