For no other class of molecule, have two-dimensional (2-D) methods been more useful than oligosaccharides and their conjugates, glycolipids, and glycopeptides. This is because of two factors. First, the natural allocation of protons within oligosaccharides yields all or most of their primary and secondary structure. Second, through 2-D nuclear magnetic resonance (NMR) the severe resolution problem peculiar to oligosaccharides has been overcome. The reason that oligosaccharide structures lend themselves to proton NMR analysis is that protons are spaced linearly around each oligosaccharide residue. The chapter discusses the criteria for selection of 2-D NMR experiments. At present, two general classes of 2-D NMR experiments exist—namely, J-resolved and correlated spectroscopy. The third dimension of resonance intensity is plotted as a contour. There is a detailed description of the procedure for primary structure determination and secondary structure studies. The scope of structural complexity amenable to 2-D analysis has been increased by improved experiments such as relay COSY or RECSY, pure absorption (multiple quantum filtered) COSY and pure absorption NOESY. Another trend is toward the simplification of spectra and shortening of experimental and computer processing time.
ASJC Scopus subject areas
- Molecular Biology