Temperature dependencies of amide 1 H‐ and 15 N‐chemical shifts in hyaluronan oligosaccharides

Temperature coefficients (Δδ/ΔT) of amide chemical shifts of N ‐acetylglucosamine residues have been measured in a range of oligosaccharides of the important vertebrate polysaccharide hyaluronan. Odd‐ and even‐numbered oligosaccharides with glucuronic acid, Δ‐4,5‐unsaturated glucuronic acid and N ‐acetylglucosamine at the termini were investigated. All amide proton temperature coefficients were only slightly less negative (−6.9 to − 9.1 ppb/ °C) than those of amide protons in free exchange with water (≈− 11 ppb/ °C), indicating an absence of persistent intramolecular hydrogen bonds. With the exception of amide groups in reducing‐terminal N ‐acetylglucosamine rings, all amide proton environments have the same temperature coefficient (−6.9 ppb/ °C), irrespective of differences in amide group chemical shifts and 3 J HH coupling constants, i.e. they do not sense subtle differences in orientation of the amide group. Amide nitrogen temperature coefficients report the same phenomena but with greater sensitivity. These data provide a set of reference values for temperature coefficients measured in other carbohydrates with acetamido sugars. Copyright © 2007 John Wiley & Sons, Ltd.