1D and 2D NMR
- 1D NMR defines the types of anomeric configuration (a,b) present, provides information about non-carbohydrate substituents (e.g. acetyl or pyruvyl moieties) and quantify degree of substitution.
- 1D NMR provides information about the purity of the carbohydrate.
- For polysaccharides with a repeating sequence, both 13C-NMR and 1H-NMR give information regarding the number of monosaccharide residues contained in the repeating glycosyl.
- 13C-NMR can provide some information regarding glycosyl linkage and can detect the presence of unusual or rarely observed sugars. We can also acquire 31P-NMR spectra.
- If a sufficient amount of pure polysaccharide (>5 mmol) is available, 2-D NMR spectroscopy is probably the single most powerful technique for the elucidation of the precise carbohydrate structure.
- A routine set of experiments for structural determination of a polysaccharide would include COSY, TOCSY, HSQC, HMBC and NOESY or ROESY.
- Additional experiments include HSQC-TOCSY to correlate carbon resonances within a given monosaccharide residue, DOSY for the determination of molecular weight and of intermolecular bonding, band-selective homonuclear decoupled experiments for crowded spectra, and 1H-31P-HMQC and HMQC-TOCSY to establish the attachment sites of phosphomono-and diesters, as well as spin-diffusion experiments to determine the binding sites of small ligands to large receptors.