Qingbin Guo

Physicochemical characterization of a high molecular weight bioactive β-d-glucan from the fruiting bodies of Ganoderma lucidum

A purified polysaccharide coded as GLP20 was obtained by precipitating a hot-water extract from Ganoderma lucidum fruiting bodies with 20% (V/V) ethanol. Its total carbohydrate content was 95.9%. Structural analysis showed that GLP20 was a β-(1→3)-linked d-glucan with a (1→6)-β-d-glucopyranosyl side-branching unit on every third residue. Cell culture study revealed that GLP20 can significantly increase NO production of RAW264.7 macrophages. The analysis of light scattering and high performance size exclusion chromatography (HPSEC) showed that the molecular weight and polydispersity of GLP20 was 3.75 × 10(6)Da and 1.36, respectively. GLP20 had a rigid chain conformation in aqueous solution. A conformation transition occurred in the alkaline solution with NaOH concentration larger than 0.15M. The transition from ordered structure to single chain happened when GLP20 was heated above 135°C in water solution and was irreversible as demonstrated by differential scanning calorimetry (DSC). GLP20 existed as random coils in DMSO.

Structural characterization of a low-molecular-weight heteropolysaccharide (glucomannan) isolated from Artemisia sphaerocephala Krasch.

Using 60% (w/v) ammonium sulfate precipitation, a heteropolysaccharide (designated 60S), with relatively low molecular weight (38.7kDa), was isolated from the seeds of Artemisiasphaerocephala Krasch. The structural properties of 60S were elucidated by partial acid hydrolysis, methylation analysis, 1D and 2D NMR spectroscopy, and MALDI-TOF-MS. The results of the partial acid hydrolysis and methylation analysis indicated that the main chain of 60S consisted of (1→4)-linked d-Manp and (1→4)-linked d-Glcp in a molar ratio of 1:1.3. Over half of the glucosyl residues in the main chain were branched at the O-6 position. The terminal sugar residues were mainly composed of T-Araf, T-Arap, T-Galp, T-GlcpA, and T-Glcp. Besides, 3-Araf and 2-Galp were also observed in comparable amounts. Based on all the aforementioned results and the data obtained by 1D and 2D NMR spectroscopy as well as MALDI-TOF-MS, a structure of 60S is proposed as follows: R could be one or some of -(3-α-Araf)(n)-(A), T-α-Galp(B), T-α-Glcp(C), T-Araf(H) or T-Arap.

Effect of calcium on solution and conformational characteristics of polysaccharide from seeds of Plantago asiatica L.

Polysaccharide from seeds of Plantago asiatica L. is rich in calcium, which is important for keeping viscous and weak gelling properties of the polysaccharide. However, few studies reported effect of calcium on solution and conformational characteristics of the polysaccharide. In this study, polysaccharide was prepared from seeds of P. asiatica L. and named as PLCP. PLCP was treated with EDTA to remove calcium ion to get PLCP-E. PLCP and PLCP-E were characterized by Ubbelohde capillary viscometer, light scattering and HPSEC with refractive index, light scattering and viscometric detectors. The results showed that PLCP had much higher intrinsic viscosity, hydrodynamic radius (Rh), radius of gyration (Rg) and molecular weight than that of PLCP-E when measured in the same solvent. PLCP and PLCP-E were in random coil conformation in aqueous solutions according to light scattering and HPSEC measurements. HPSEC data showed PLCP-E had lower intrinsic viscosity than that of PLCP with the same molecular weight. Persistence length of Lp was 2.5nm for PLCP and 2.3nm for PLCP-E, respectively. In conclusion, PLCP exhibited higher intrinsic viscosity and molecular weight, and stiffer conformation than that of PLCP-E, which could explain the reason of higher viscosity of PLCP.

Structural investigation of a glycoprotein from gum ghatti

The glycoprotein structure of gum ghatti was investigated. The covalent bonding between polysaccharides and proteins was firstly confirmed by high performance size exclusion chromatography (HPSEC) using refractive index (RI) and UV detectors. Partial acid hydrolysis and enzymatic degradation were also utilized. Several structural fragments such as AraHex2-HexA-HexNAc, Hex4HexNAc2, AraHex4HexNAc, Hex10HexNAc and Hex4HexNAc-Asn were identified from MALDI-TOF spectrum; using 1D and 2D NMR spectra, the linkage site of amino acids and polysaccharides was determined as N-linked (Hex)n-GlcNAc-Asn. Combined with the polysaccharide structure obtained before, a glycoprotein structure model was proposed. It was composed of 1,6-linked galactose backbone, which were attached by numerous of sugar side chains and peptide chains.

Xyloglucans from flaxseed kernel cell wall: Structural and conformational characterisation

The structure of ethanol precipitated fraction from 1M KOH extracted flaxseed kernel polysaccharides (KPI-EPF) was studied for better understanding the molecular structures of flaxseed kernel cell wall polysaccharides. Based on methylation/GC-MS, NMR spectroscopy, and MALDI-TOF-MS analysis, the dominate sugar residues of KPI-EPF fraction comprised of (1,4,6)-linked-β-d-glucopyranose (24.1mol%), terminal α-d-xylopyranose (16.2mol%), (1,2)-α-d-linked-xylopyranose (10.7mol%), (1,4)-β-d-linked-glucopyranose (10.7mol%), and terminal β-d-galactopyranose (8.5mol%). KPI-EPF was proposed as xyloglucans: The substitution rate of the backbone is 69.3%; R1 could be T-α-d-Xylp-(1→, or none; R2 could be T-α-d-Xylp-(1→, T-β-d-Galp-(1→2)-α-d-Xylp-(1→, or T-α-l-Araf-(1→2)-α-d-Xylp-(1→; R3 could be T-α-d-Xylp-(1→, T-β-d-Galp-(1→2)-α-d-Xylp-(1→, T-α-l-Fucp-(1→2)-β-d-Galp-(1→2)-α-d-Xylp-(1→, or none. The Mw of KPI-EPF was calculated to be 1506kDa by static light scattering (SLS). The structure-sensitive parameter (ρ) of KPI-EPF was calculated as 1.44, which confirmed the highly branched structure of extracted xyloglucans. This new findings on flaxseed kernel xyloglucans will be helpful for understanding its fermentation properties and potential applications.

A molecular modeling approach to understand the structure and conformation relationship of (GlcpA)Xylan

The structure and conformation relationships of a heteropolysaccharide (GlcpA)Xylan in terms of various molecular weights, Xylp/GlcpA ratio and the distribution of GlcpA along xylan chain were investigated using computer modeling. The adiabatic contour maps of xylobiose, XylpXylp(GlcpA) and (GlcpA)XylpXylp(GlcpA) indicated that the insertion of the side group (GlcpA) influenced the accessible conformational space of xylobiose molecule. RIS-Metropolis Monte Carlo method indicated that insertion of GlcpA side chain induced a lowering effect of the calculated chain extension at low GlcpA:Xylp ratio (GlcpA:Xylp = 1:3). The chain, however, became extended when the ratio of GlcpA:Xylp above 2/3. It was also shown that the spatial extension of the polymer chains was dependent on the distribution of side chain: the random distribution demonstrated the most flexible structure compared to block and alternative distribution. The present studies provide a unique insight into the dependence of both side chain ratio and distribution on the stiffness and flexibility of various (GlcpA)Xylan molecules.

Synthesis of TiC–TiB–TiB2 composite powders by solid reaction of powders

In the present work, TiC–TiB–TiB2 diffusion-layer-coated B4C composite powders were synthesised via a powder immersion method using Ti and B4C powders as reactants. The phase compositions and microstructure of the treated powders were characterised by employing X-ray diffraction and scanning electron microscopy. No significant reaction between B4C and Ti could be detected at 800°C. After treatment at 900°C, the products generated were composed of TiC and TiB. After treatment at 1000°C, the products generated were primarily composed of TiC and TiB, with a small amount of TiB2. The composition and proportions of the produced phases varied with process temperatures and the composition of the initial powders used. Powder mixtures with a Ti/B4C molar ratio of 3.5:1 and treated at 1000°C for 14 h were more suitable for synthesis of TiC–TiB–TiB2-coated B4C composite powders.

Oligosaccharides: Structure, Function and Application

Oligosaccharides are carbohydrates of low degree of polymerization (DP) and low molecular weight composed of monosaccharides. Specific types of oligosaccharides, named non-digestible oligosaccharides, resist hydrolysis and absorption in the upper gastrointestinal tract, but can be fermented in the large bowel by gut bacteria. The structural factors of non-digestible oligosaccharides can affect the selective utilization and metabolites produced by gut bacteria. Therefore, some non-digestible oligosaccharides have prebiotic activity, which may promote human health by increasing populations of beneficial microbes and/or their metabolic activity. For this reason, industrial applications for non-digestible oligosaccharides have rapidly increased. The natural sources of non-digestible oligosaccharides cannot meet the high need for industrial applications, but they also can be obtained by either polysaccharide hydrolysis or enzymatic/chemical synthesis from disaccharide substrates. Both natural sources and commercial production of non-digestible oligosaccharides usually contain mixtures with different structures. The gut bacteria can cooperate with each other when they utilize non-digestible oligosaccharides, as they have different oligosaccharide digestive abilities, preferences and metabolic processes.

Polysaccharides From Dendrobium Officinal, Cordyceps Sinensis and Ganoderma: Structures and Bioactivities

In the past decades, polysaccharides isolated from natural sources (herbs) have attracted much attention due to their various types of bioactivities. A variety of polysaccharides extracted from botanical plants and fungi have been reported for their bioactivities, with claimed health benefits including immune regulation, anti-tumour and antioxidant activity. The paper focuses on polysaccharides isolated from three sources: Dendrobium officinal, Cordyceps sinensis and Ganoderma. The structural information, bioactive properties as well as their structural & function relationships are discussed.