Zhengbiao Gu

Improving the performance of starch-based wood adhesive by using sodium dodecyl sulfate

Sodium dodecyl sulfate (SDS) was used to improve the performance of starch-based wood adhesive. The effects of SDS on shear strength, viscosity and storage stability were investigated. It was shown that, although the addition of 1.5-2% (dry starch basis) SDS resulted in a slight decrease in shear strength, the mobility and storage stability of adhesive were significantly enhanced. Possible mechanisms regarding specific action of SDS were discussed. It was proved, using blue value or differential scanning calorimetry (DSC) analysis, that the amylose-SDS complexes were formed in the adhesive. The complex formation or simple adsorption of SDS with starch molecules might hinder the aggregation of latex particles, as shown by scanning electron microscopy images, and inhibit starch retrogradation, as observed by DSC analysis. As a result, in the presence of SDS, the adhesive had higher mobility and storage stability, indicating that SDS could be used to prepare starch-based wood adhesives with high performance.

Effects of urea on freeze-thaw stability of starch-based wood adhesive

Urea was used to improve the freeze-thaw (F/T) stability of a renewable starch-based wood adhesive (SWA). The improved stability was supported by the enhanced viscosity stability and bonding performance stability after repeated F/T cycling. The results of dynamic time sweep experiments, differential scanning calorimetry (DSC) and pulsed nuclear magnetic resonance (PNMR) showed that the improved stability can be due to the ability of urea to inhibit the retrogradation of starch molecules in the starch-based wood adhesive system. Urea can be used as an effective additive for improving storage properties of starch-based wood adhesive in low temperature environment. Approximately 15% (w/w) urea was the determined optimal dosage.

Mutations enhance β-cyclodextrin specificity of cyclodextrin glycosyltransferase from Bacillus circulans

The effects of amino acid residue at position 31 in the neighborhood of calcium binding site I (CaI) on product specificity of cyclodextrin glycosyltransferase (EC 2.4.1.19, CGTase) were investigated by replacing Ala31 in the CGTase from Bacillus circulans STB01 with arginine, proline, threonine, serine and glycine. The results showed that the mutations A31R, A31P, and A31T resulted in the increases in β-cyclodextrin-forming activity and β-cyclodextrin production, indicating that these mutations enhanced β-cyclodextrin specificity of the CGTase. Especially the mutant A31R displayed approximately 26% increase in β-cyclodextrin production with a concomitant 41% decrease in α-cyclodextrin production when compared to the wild-type CGTase. Thus, it was much more suitable for the industrial production of β-cyclodextrin than the wild-type enzyme. The enhanced β-cyclodextrin specificity of the mutants might be a result of stabilizing CaI, which also suggested that CaI might play an important role in cyclodextrin product specificity of CGTase.

Polyethylene glycols enhance the thermostability of β-cyclodextrin glycosyltransferase from Bacillus circulans.

We investigated the ability of six polyethylene glycols (PEGs), with molecular weights ranging from 400 to 20,000 Da, to enhance the thermostability of β-cyclodextrin glycosyltransferase (β-CGTase) from Bacillus circulans. We found that PEGs with different molecular weights could activate and stabilize this β-CGTase, but to different degrees. The most significant increase (about 20%) in β-cyclodextrin-forming activity was achieved by adding 10-15% PEG 400. PEGs with low molecular weights also significantly enhanced the thermostability of β-CGTase; 15% PEG 1000 prolonged its half-life at 60°C by 6.5-fold, compared to a control. Fluorescence spectroscopy and circular dichroism analysis indicated that PEGs helped protect the tertiary and secondary structure of β-CGTase, respectively. This study provides an effective approach for improving the thermostability of CGTases and related enzymes.

Effects of emulsifier on the bonding performance and freeze–thaw stability of starch-based wood adhesive

In this study, different emulsifiers were used to improve the bonding performance and freeze–thaw stability of renewable starch-based wood adhesive. The improved bonding performance and freeze–thaw stability were supported by the enhanced shear strength, grafted parameters, and viscosity stability after repeated freeze–thaw cycling. ζ-Potential determination, differential scanning calorimetry and pulsed nuclear magnetic resonance analysis indicated that the emulsifiers improve the grafting of vinyl acetate monomers into the starch bonds via free radical vinyl polymerization and hinder the aggregation of starch molecules. Among the emulsifiers tested, sodium dodecyl sulfate showed the highest improvement in the bonding performance and freeze–thaw stability of starch-based wood adhesives.

RETRACTED: Evaluation of amorphous debranched starch as extended-release matrices in tablets

This study aims to investigate the physicochemical and extended-release properties of amorphous debranched starch (ADBS) that is a linear short chain amylose derived from pullulanase enzymatic modification. The results show the completely amorphous ADBS was soluble in cold water, which developed into a disordered gel network at 25 °C. ADBS based tablets were able to extend drug release in different media. Drug release, which was accelerated by decreased pH and pancreatin, was barely affected by ionic strength. The kinetics of the drug release process that was dominated by Fickian diffusion was best fitted and interpreted by the Higuchi equation. The results indicate ADBS is an ideal hydrophilic excipient which extends the in vitro release of water-soluble drugs for 24 h.

Preparation and characterization of pullulanase debranched starches and their properties for drug controlled-release

Debranched starches (DBSs) with different degrees of debranching (low, L-DBS; moderate, M-DBS; high, H-DBS) were prepared and investigated. After pullulanase modification, the starch granules became more porous and many small particles containing short glucan chains were generated. DBSs adopt a single-helical V-type crystalline structure with low crystallinity. L-DBS samples contained fewer (20.70%) and longer (degree of polymerization, DP: 21.92) linear short glucan chains than their counterparts (M-DBS: 40.92%, 20.05 DP; H-DBS: 55.52%, 18.52 DP). Pullulanase enzymatic hydrolyzate for DBS samples with higher degrees of debranching inclined towards retrogradation at 20 °C. DBSs with higher degrees of debranching could form a hydrogel with higher G′ and G′′ values, indicating these samples formed a stronger gel network. L-DBS could hold more water and its digestibility was higher. The in vitro test showed that DBS is a good candidate to control drug release for over 12 h. Furthermore, the drug release profiles from both DBS-based and HPMC-based tablets showed an anomalous transport mechanism. The drug release from these four matrices was controlled by a combination of drug diffusion and matrix erosion. The drug release properties from DBS-based tablets were considerably influenced by the degree of debranching. The in vitro drug release profile of M-DBS was similar to that of HPMC (f2 = 60.75), while L-DBS and H-DBS differed from HPMC (f2 < 50). In summary, DBS is a good hydrogel candidate, and it can be used as an excipient in oral tablets to control drug release.

Mutations at calcium binding site III in cyclodextrin glycosyltransferase improve β-cyclodextrin specificity

Cyclodextrin glycosyltransferases (CGTases, EC 2.4.1.19) are industrially important enzymes that produce cyclodextrins from starch by intramolecular transglycosylation. In this study, the effects of amino acid residue at position 315 in calcium binding site III (CaIII) on product specificity of CGTase were investigated by replacing Ala315 in the CGTase from Bacillus circulans STB01 with arginine, aspartic acid, threonine, leucine and valine. The cgt gene, which encodes this enzyme, was expressed in B. subtilis WB600 alongside site-directed mutants A315R, A315D, A315T, A315L and A315V. The results showed that CaIII plays an important role in cyclodextrin product specificity. Replacement of Ala315 by charged amino acid residues enhanced β-cyclodextrin specificity, compared with the wild-type CGTase. Mutations A315R and A315D resulted in an approximately 10% increase in β-cyclodextrin activity. Furthermore, under conditions resembling the industrial production processes, the mutants A315R and A315D displayed obvious increases in the production of β-cyclodextrin, indicating they were much more suitable for the industrial production of β-cyclodextrin than the wild-type enzyme. The enhancement of β-cyclodextrin specificity for the mutants might be due to the stability of CaIII by charged amino acid substitutions.