NMR spectra of oligosaccharides at ultra-high field (900 MHz) have better resolution than expected due to favourable molecular tumbling

Nuclear magnetic resonance (NMR) remains the most promising technique for acquiring atomic-resolution information in complex carbohydrates. Significant obstacles to the acquisition of such data are the poor chemical-shift dispersion and artifacts resultant from their degenerate chemical structures. The recent development of ultra-high-field NMR (at 900 MHz and beyond) gives new potential to overcome these problems, as we demonstrate on a hexasaccharide of the highly repetitive glycosaminoglycan hyaluronan. At 900 MHz, the expected increase in spectral dispersion due to higher resonance frequencies and reduction in strong coupling-associated distortions are observed. In addition, the fortuitous molecular tumbling rate of oligosaccharides results in longer T2-values that further significantly enhances resolution, an effect not available to proteins. Combined, the resolution enhancement can be as much as twofold relative to 600 MHz, allowing all 1H-resonances in the hexasaccharide to be unambiguously assigned using standard natural-abundance experiments. The use of ultra-high-field spectrometers is clearly advantageous and promises a new and exciting era in carbohydrate structural biology.