Nuclear magnetic resonance spectroscopy of carbohydrates

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Carbohydrate NMR Spectroscopy is the application of nuclear magnetic resonance (NMR) spectroscopy to structural and conformational analysis of carbohydrates. This tool allows the carbohydrate chemist to determine the structure of monosaccharides and oligosaccharides from synthetic and natural sources. It is also a useful tool for determining sugar conformations. Modern high field strength NMR instruments used for carbohydrate samples, typically 500 MHz or greater, are able to run a suite of 1D and 2D experiments to determine primary structure and conformation of carbohydrate compounds.

Main article: Nuclear magnetic resonance

Contents

Carbohydrate chemical shift [edit]

Main article: chemical shift

Common chemical shift ranges for nuclei within carbohydrate residues are:

  • Typical 1H NMR chemical shifts of carbohydrate ring protons are 3 – 6 ppm.
  • Typical 13C NMR chemical shifts of carbohydrate ring carbons are 60 – 110 ppm

In the case of simple monosaccharide molecules, all protons are typically separated at a high enough field strength (usually > 500 MHz).

Non-anomeric centers [edit]

Typically the non-anomeric protons are found from 3 - 4 ppm. As expected some spectral overlap is seen, but with today’s high field instruments individual resonances can usually be resolved for monosaccharides. Typically the non-anomeric carbons are found from 60 – 85 ppm. As expected the secondary carbons will be found further downfield from a primary carbon.

Oligosaccharide NMR [edit]

Oligosaccharide 1H NMR spectra tend to be a mess in the region of the spectra from 3 – 4 ppm. Quite often the individual signals are overlapped, and cannot be distinguished in the simple 1-D experiment. It is therefore advantageous to utilize 2D experiments. To aid structural elucidation of oligosaccharide NMR spectra a chemical shift database for carbohydrates has been devised and is available as an online interface called CASPER (computer assisted spectrum evaluation of regular polysaccharides).[1] Both C and H chemical shifts can be used to access structural information.

See also [edit]

References [edit]

  1. ^ http://www.casper.organ.su.se/casper/
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