Synthesis, characterization and properties of chitosan modified with poly(ethylene glycol)-polydimethylsiloxane amphiphilic block copolymers

Synthesis of poly(ethylene glycol)-polydimethylsiloxane amphiphilic block copolymers is discussed herein. Siloxane prepolymer was first prepared via acid-catalyzed ring-opening polymerization of octamethylcyclotetrasiloxane (D₄) to form polydimethylsiloxane (PDMS) prepolymers. It was subsequently functionalized with hydroxy functional groups at both terminals. The hydroxy-terminated PDMS can readily react with acid-terminated poly(ethylene glycol) (PEG diacid) to give PEG-PDMS block copolymers without using any solvent. The PEG diacid was prepared from hydroxy-terminated PEG through the ring-opening reaction of succinic anhydride. Their chemical structures and molecular weights were characterized using ¹H NMR, FTIR and GPC, and thermal properties were determined by DSC. The PEG-PDMS copolymer was incorporated into chitosan in order that PDMS provided surface modification and PEG provided good water swelling properties to chitosan. Critical surface energy and swelling behavior of the modified chitosan as a function of the copolymer compositions and contents were investigated.     

Enhancement of sensitivity of glucose sensors from alizarin–boronic acid adducts in aqueous micelles

The sensitivity of glucose sensors fabricated from alizarin–boronic acid adducts was improved by an assistance of surfactants. Basically, Alizarin Red S (ARS) is not a fluorescence active compound. However, the fluorescence emission can be observed when forming an adduct with 2-formylphenyl boronic acid (2-FPBA). Using displacement strategy, the fluorescence intensity of the ARS/2-FPBA adduct decreased as a linear function of the glucose concentration. A simple and sensitive method was developed by incorporating the ARS/2-FPBA adduct in the hydrophobic core of micelles. Various parameters that could possibly affect the fluorescence quenching ability including solution pH, concentration of 2-FPBA, types of surfactants and concentrations of surfactants were investigated. The optimum condition for the determination of glucose by the proposed assay was 2 mM cetyltrimethylammonium bromide (CTAB) in 0.05 M phosphate buffer pH 7.0. The fluorescence intensity of the ARS/2-FPBA adduct in the presence of CTAB was remarkably 13 times higher than that in the buffer solution. Moreover, the linear working concentration range was found to be 1.2–80 mM, and the calibration sensitivity was 14 times higher than that from the system containing only buffer solution.     

Phase II enzyme induction and anti‐inflammatory effects of crude extracts and secondary fractions obtained from bran from five black glutinous rice cultivars

Methanolic extracts of bran from black glutinous rice cultivars were screened for potential health benefits using cellular bioassays for quinone reductase (QR) induction in murine hepatoma cells and inhibition of NO production in lipopolysaccharide (LPS)‐activated RAW 264.7 macrophages. Fractionation of the crude extract by semi‐preparative HPLC afforded respective fractions enriched in phenolic acids, anthocyanins and proanthocyanidins. The relative potency of QR induction was phenolic acids > proanthocyanidins > anthocyanins, and the activity of the crude extract was conserved among the aggregate of these fractions. In contrast, all three fractions were more potent than the crude extract in terms of anti‐inflammatory effect. This suggests synergism effects among anti‐inflammatory agents through partial purification. Inhibition of macrophage NO production by binary mixtures of gallic acid or caffeic acid with the anthocyanin‐rich fraction indicated potential synergism. These results warrant further efforts to identify the active agents and substantiate synergistic interactions through isobologram analysis.     

Kinetics and modeling of whole longan with combined infrared and hot air

The aim of this research was to evaluate the effects of operating variables on the drying behavior of whole longan undergoing a combined infrared and hot air drying process, to determine its kinetic parameters, and to develop drying kinetic models. The single-layer drying experiments were carried out at infrared powers of 300, 500 and 700 W, drying air temperatures of 40, 60 and 80 °C, and air velocities of 0.5, 1.0 and 1.5 m/s. The samples were dried until attaining a final moisture content of 0.2 kg water/kg dry solid. The results show that the drying had a short constant rate period followed by a falling rate period in all cases. The drying rate and product temperature were significantly influenced by infrared power, temperature and velocity of ambient air. In the constant rate period, the mass transfer coefficient varied from 3.646 × 10⁻³ to 1.914 × 10⁻² m/s. It increased with increasing infrared power, but decreased as air velocity and air temperature increased. In the falling rate period, theoretical and semi-empirical drying kinetic equations were used to describe the drying kinetics of the product. It was found that the overall effective diffusion coefficient and drying constant varied from 7.012 × 10⁻¹¹ to 6.681 × 10⁻¹⁰ m²/s and 0.026 to 0.234 h⁻¹, respectively. Both parameters increased with increasing infrared power and air temperature, but decreased with increasing air velocity. Combined regression equations developed to predict the drying kinetic parameters (h_D, D_eff and k) for all three models gave a fairly good fit.     

Surface and mechanical properties of microporous membranes of poly(ethylene glycol)-polydimethylsiloxane copolymer/chitosan

Poly(ethylene glycol)-polydimethylsiloxane (PEG-PDMS) block copolymers were prepared via a condensation reaction between PEG diacid and PDMS diol. PEG diacid was synthesized from the reaction between hydroxy-terminated PEG and succinic anhydride. PDMS diol was prepared from the ring-opening polymerization of octamethylcyclotetrasiloxane (D₄) followed by hydrosilylation with allyl alcohol. The copolymers were incorporated into chitosan in order that good water swellability and wettability of chitosan were retained due to hydrophilic PEG blocks, whereas PDMS block in the copolymers functioned as a toughening modifier. Percent crosslinking of 66-84 was observed once 5-10 wt% of the copolymers was incorporated. As compared to the unmodified sample, the copolymer-containing chitosan exhibited the decreases in both water contact angles and the rate of water vapor permeability. The studies on tensile properties indicated that incorporation of copolymers into chitosan improved the flexibility of the films.