Huashi Guan

Sequence analysis of alginate-derived oligosaccharides by negative-ion electrospray tandem mass spectrometry.

Negative-ion electrospray tandem mass spectrometry (ES-MS/MS) with collision-induced dissociation (CID) is attempted for sequence determination of alginate oligosaccharides, derived from polyanionic alginic acid, polymannuronate, and polyguluronate by partial depolymerization using either alginate lyase or mild acid hydrolysis. Sixteen homo- and hetero-oligomeric fragments were obtained after fractionation by gel-filtration and strong anion exchange high performance liquid chromatography. The product-ion spectra of these alginate oligosaccharides were dominated by intense B-, C-, Y-, and Z-type ions together with 0,2A- and 2,5A-ions of lower intensities. Internal mannuronate residues (M) produce weak but specific decarboxylated Zint-ions (Zint − 44 Da; int: denotes internal), which can be used for distinction of M and a guluronate residue (G) at an internal position. A reducing terminal M or G, although neither gives rise to a specific ion, can be identified by differences in the intensity ratio of fragment ions of the reducing terminal residue [2,5Ared]/[0,4Ared] (red: denotes reducing terminal).

Preparation and characterization of guluronic acid oligosaccharides degraded by a rapid microwave irradiation method

Guluronic acid oligosaccharides (GOS) with degree of polymerization (DP) ranging from 1 to 10 were prepared by a rapid microwave degradation method. Polyguluronic acid, fractionated from alginate hydrolysate, was dissolved in dilute ammonia water at a concentration of 20 mg/mL (pH 5) and then hydrolyzed under microwave irradiation (1600 W) at 130°C for 15 min to produce GOS mixture. The GOS mixture was separated by a Bio-Gel P6 column and ten fractions were obtained. Each GOS fraction was further characterized by electrospray ionization mass spectrometry, (1)H NMR, (13)C NMR, and 2D NMR spectroscopy techniques. The data showed that the GOS fractions were saturated oligoguluronates with general molecular formula C(6n)H(8n+2)O(6n+1) (n=1-10). This microwave degradation method was not only convenient, less time consuming, and environment-friendly, but also produced GOS with high yield (71%) and eliminating a desalting procedure compared to conventional acid hydrolysis method.