Hyperbranched Polysaccharide Research Articles

Shrinking factors of hyperbranched polysaccharide from fungus

The branched structure properties of hyperbranched polysaccharides (TM3a and TM3b), extracted from sclerotia of Pleurotus tuber-regium, were studied by using laser light scattering and viscometry. The configurational shrinking factor ( g) and viscometric shrinking factor ( g′) of TM3a and TM3b were discussed, where curdlan and pullulan were taken as the linear references for derivation of g and g′. The dependences of g factor, g′ factor, and Flory factor ( Φ branched) on weight average molecular weight ( M w) were established to be g = 1.07 × 10 2 M w - 0.48 ± 0.09 , g′ = 3.63 × 10 1 M w - 0.43 ± 0.01 , and Φ branched = 7.08 × 10 20 M w 0.39 ± 0.1 for TM3a in 0.25 M LiCl/DMSO at 25 °C, when curdlan acted as the linear reference. A power law relationship g′ = 2.71 × 10 −1 g −0.61±0.1 for TM3a was found, and the exponent was approximately same to 0.60 established by Kurata et al. for polystyrene star molecules. The dependence of g factor on M w for TM3b was found to be g = 1.99 × 10 2 M w - 0.53 ± 0.02 , when pullulan was used as the linear reference. On the basis of Zimm–Stockmayer equation for tetrafunctional units, molecular weight of branching unit ( M 0) deduced from nonlinear curve fitting of g versus M w was 8739 ± 564 g/mol and 3961 ± 1245 g/mol for TM3a and TM3b, respectively. The effect of different linear reference curves and polydispersity was discussed. This work gave valuable information on branched structure characterization and insights into the biosynthetic pathways of the hyperbranched polysaccharide from fungus.

Microwave-assisted solubilization and solution properties of hyperbranched polysaccharide

A water-insoluble hyperbranched β- d-glucan (TM3a), extracted from sclerotia of Pleurotus tuber-regium, was treated by microwave exposure to improve its solubility in water. This method led to complete dissolution of the TM3a polysaccharide in 0.02 wt % aqueous NaN 3. Various treatment periods were tested, and optimal conditions corresponded to 35 s at 765 W. The solution properties of TM3a in water were studied systematically by using size-exclusion chromatography combined with laser light scattering, viscometry, and dynamic light scattering at 25 °C. The dependences of intrinsic viscosity ([ η]), radius of gyration ( 〈 S 2 〉 z 1 / 2 ), and hydrodynamic radius ( R h) on weight average molecular weight ( M w) for TM3a in 0.02 wt % aqueous NaN 3 at 25 °C were found to be [ η ] = 3.02 × 10 - 2 M w 0.44 ± 0.1 ( cm 3 g - 1 ) , 〈 S 2 〉 z 1 / 2 = 8.32 × 10 - 2 M w 0.38 ± 0.2 ( nm ) , and R h = 4.37 × 10 - 2 M w 0.46 ± 0.08 ( nm ) in the M w range from 8.20 × 10 5 to 4.88 × 10 6. The fractal dimension, ratio of ρ = 〈 S 2 〉 z 1 / 2 R h , and the < r 2> o/ M w value of TM3a were calculated and discussed. The results indicated that TM3a existed in a sphere-like conformation in 0.02 wt % aqueous NaN 3. Furthermore, by using transmission electron microscopy, we observed directly the spherical molecules of TM3a. This work gave valuable information on improvement of solubility and chain conformation characterization of the water-insoluble polysaccharide in water.

Chain Conformation of Water-Insoluble Hyperbranched Polysaccharide from Fungus

Water-insoluble polysaccharide (TM3a), extracted from sclerotia of Pleurotus tuber-regium, was identified as a hyperbranched beta-d-glucan from the results of one- and two-dimensional NMR and GC-MS analysis. The degree of branching of TM3a is 65.5%. TM3a was fractionated by using a non-solvent addition method into 14 fractions, and its solution properties in 0.25 M LiCl/dimethylsulfoxide (DMSO) solution were studied systematically by using static laser light scattering, dynamic light scattering, and viscometry at 25 degrees C. The dependences among the values of intrinsic viscosity ([eta]), radius of gyration (<S2>z 1/2), and hydradynamic radius (Rh) on weight-average molecular weight (Mw) were found as the following: [eta] = 0.46Mw0.30+/-0.01, <S2>z 1/2 = 4.79 x 10-2Mw0.43+/-0.04, and Rh = 5.01 x 10-2Mw0.41+/-0.02 in the Mw range from 1.94 x 105 to 2.06 x 107 for TM3a in a 0.25 M LiCl/DMSO solution at 25 degrees C. The current theory of polymer solution was applied to explain the relationship among the fractal dimension, ratio of geometric to hydrodynamic radius (rho = <S2>z 1/2/Rh), and MwA2/[eta] of TM3a. The results indicated that TM3a existed as a compact chain conformation with a sphere-like structure in LiCl/DMSO solution. Furthermore, by using transmission electron microscopy, we observed directly the spherical molecules with an average diameter of 23.0 +/- 1.8 nm.

Determination of molecular size and shape of hyperbranched polysaccharide in solution

The chemical structure of a water-soluble polysaccharide, coded as TM3b, extracted from sclerotia of Pleurotus tuber-rigium was analyzed to be a hyperbranched beta-D-glucan with beta-(1-->6), beta-(1-->4), and beta-(1-->3)-linked residues, with degree of branching (DB) of 57.6%. The results from size-exclusion chromatography combined with laser light scattering (SEC-LLS) revealed that the hyperbranched polysaccharide easily aggregated in 0.15 M aqueous NaCl, whereas it dispersed as individual chains in DMSO. The weight-average molecular weight (M(w)), radius of gyration, intrinsic viscosity, and chain density of TM3b in DMSO and in 0.15 M aqueous NaCl were measured with SEC-LLS, LLS, and viscometry. The results indicated that single chains and aggregates with aggregation number of 12 coexisted in the aqueous solution, whereas individual molecules of TM3b occurred in DMSO. In view of the molecular parameters, the aggregates in aqueous solution exhibited more compact chain structure than the individual molecules in DMSO. Furthermore, transmission electron microscopy and atomic force microscopy showed that all of the aggregates and individual molecules exhibited spherical particles in the solutions. This work provided the valuable information of chain conformation and molecular morphology of the hyperbranched polysaccharide in different solvents.

Synthesis, Branched Structure, and Solution Property of Hyperbranched d-Glucan and d-Galactan

The ring-opening multibranching polymerizations of 1,6-anhydro-β-d-glucopyranose (1) and 1,6-anhydro-β-d-galactopyranose (2) have been studied in order to synthesize hyperbranched polysaccharides. The solution polymerization in propylene carbonate and the bulk polymerization of 1 and 2 using a thermally induced cationic initiator proceeded through a ring-opening reaction and a proton transfer reaction to afford highly water-soluble polysaccharides, i.e., poly-1 and poly-2, respectively. For the polymers from 1 and 2 with the same polymerization conditions, the Mw,SLS and yield of poly-1 were higher than those of poly-2. Here, poly-1 and poly-2 were characterized as hyperbranched polysaccharides consisting of α- and β-linked d-hexopyranosyl and d-hexofuranosyl repeating units, hyperbranched d-glucan and d-galactan, respectively. In addition, poly-1 and poly-2 had ca. 30−40 mol % nonreducing d-hexopyranosyl and d-hexofuranosyl terminal units, and the degree of branching was ca. 0.38 for poly-1 and 0.44−0.60 for poly-2. The respective viscosities of poly-1 and poly-2 in aqueous NaNO3(0.2 mol·L-1) solution were very low with the intrinsic viscosity values of 0.023−0.042 dL·g-1. The steady shear flow of poly-1 in aqueous solution exhibited a Newtonian behavior with steady shear viscosities independent of the shear rate, even at high concentrations. The results indicated that the characteristics of the viscosities were attributed to the spherical structure of the hyperbranched polysaccharide in aqueous solution.

Synthesis of Hyperbranched Polysaccharide by Thermally Induced Cationic Polymerization of 1,6‐Anhydrohexopyranose

AbstractThe thermally induced cationic polymerizations of 1,6‐anhydro‐β‐D‐glucopyranose (1a), 1,6‐anhydro‐β‐D‐mannopyranose (1b) and 1,6‐anhydro‐β‐D‐galactopyranose (1c) as a latent cyclic AB4‐type monomer were carried out using (S‐2‐butenyl)tetramethylenesulfonium hexafluoroantimonate (2) as an initiator. The solution polymerization in propylene carbonate proceeded without gelation to produce the water‐soluble hyperbranched polysaccharides (3a‐c) with controlled molecular weights and narrow polydispersities. The degree of branching (DB), estimated by the methylation analysis of 3a‐c, was in the range of 0.38 – 0.49. The thermally induced cationic polymerization of 1a‐c using 2 is a facile method leading to a hyperbranched polysaccharide with a high DB value.

Synthesis of Hyperbranched Polysaccharide by Thermally Induced Cationic Polymerization of 1,6-Anhydro-β-d-mannopyranose

The thermally induced cationic polymerization of 1,6-anhydro-β-d-mannopyranose (1) as a latent cyclic AB4-type monomer was carried out using 2-butenyltetramethylenesulfonium hexafluoroantimonate (2) as the initiator. The solution polymerization in propylene carbonate proceeded without gelation to produce the water-soluble hyperbranched polysaccharides (3) with controlled molecular weights and narrow polydispersities. The weight-average molecular weight (Mw,SLS) values of 3 measured by static laser light scattering (SLS) varied in the range 6.5 × 103 to 6.4 × 105, which were significantly higher than the weight-average molecular weight (Mw,SEC) values by size exclusion chromatography (SEC). The viscosity of the solution of 3 was very low, and the intrinsic viscosities were from 0.032 to 0.047 dL·g-1. Polymer 3 was composed of α- and β-linked hyperbranched polysaccharides consisting of 19 kinds of d-mannopyranosyl and d-mannofuranosyl repeating units, which had numerous nonreducing d-mannopyranosyl terminal units. The degree of branching (DB), estimated by the methylation analysis of 3, was in the range of 0.38−0.44. The thermally induced cationic polymerization of 1 using 2 is a facile method leading to the hyperbranched polysaccharide with a high DB value.