Structural Studies of Pullulan by Nuclear Magnetic Resonance Spectroscopy

Nuclear Magnetic Resonance (NMR) spectroscopy was used to probe the primary structure of the glucan pullulan. Carbon-13, proton and phosphorus-31 NMR spectra in aqueous solution of the intact poly-saccharide obtained from three different sources indicate that significant structural differences can occur among these samples. In particular, two samples consist solely of α(1 → 6) linked maltotriose units, in accord with the generally accepted structure. However a third sample has fewer α(1 → 6) linkages and appears to consist of higher α(1 → 6) linked maltooligosaccharides in addition to maltotriose. Unlike the other samples, this sample was also phosphorylated. Enzymatic digestion of pullulan followed by NMR spectroscopy using pullulanase confirmed these results, as did HPLC analysis of the resulting digest, which showed the presence of maltooligosaccharides consisting of ten and more glucose units. However, HPLC analysis of acid hydrolysed pullulan indicated that no sugars other than glucose were present in any of the samples examined.