Hardy Sze On Chan

Purification, characterization and selective inhibition of human prostaglandin G/H synthase 1 and 2 expressed in the baculovirus system.

Human prostaglandin G/H synthase 1 and 2 were expressed in the baculovirus expression system and purified to high levels. Both enzymes were glycosylated. PGHS-1 appeared to be homogeneous by SDS-PAGE analysis but two closely migrating bands were detected in PGHS-2 preparation which were evidently due to heterogeneity in glycosylation. The amino-acid sequence of the N-termini of both isoforms indicated that the signal sequences were efficiently cleaved by the insect cells. The recombinant human PGHS-1 and PGHS-2 possessed both cyclooxygenase and peroxidase activities. Both had high affinities for arachidonate as substrate and underwent self-inactivation during catalysis. The recombinant isoforms were not pharmacologically identical, since some NSAIDs were selective inhibitors of either PGHS-1 or PGHS-2. This is the first report of high levels of expression and purification of human PGHS isoforms. The recombinant enzymes are invaluable in developing potent PGHS-2 selective inhibitors that may be efficacious anti-inflammatory drugs with no or low levels of toxicity.

Synthesis, characterization and applications of thiophene-based functional polymers

This review on some recent developments in thiopene-based functional polymers concentrates on (i) the synthetic trends for low bandgap and regioregular materials which occupy a central place in the recent advances in polythiopene, (ii) the interesting physics and chemistry of special properties such as chromism and luminescence, (iii) the effect of C60 on the polymer and (iv) the formation and property of polythiopene LB films. Much progress has been made in the past few years in ameriolating the serious problems of solubility and processability of thiopene-based functional polymers. The same degree of effort should now be spent on the equally serious drawback concerning stability. Many potential applications can only be realised if the stability is able to cope with hostile device environments.

Nanostructured MnO2/graphene composites for supercapacitor electrodes: the effect of morphology, crystallinity and composition

Nanostructured MnO2 with different morphologies, i.e. amorphous, lamellar and needle-like, is incorporated with tetrabutylammonium hydroxide stabilized graphene (GTR) with different mass ratios. A systematical approach has been used to investigate the morphology, structure and electrochemical performances of these materials for supercapacitor electrodes. It is found that the morphology, crystallinity and composition all play important roles in the capacitor performance. Needle-like MnO2 (N-Mn)/GTR composites with high surface area and good crystallinity show better performance compared with the other two systems. A new morphology emerges in N-Mn/GTR13; meanwhile high specific capacitances of 280 F g−1 for the N-Mn/GTR13 composite and 631 F g−1 for MnO2 are achieved. The inclusion of graphene significantly improves the cycling stability.

Surfactant-intercalated, chemically reduced graphene oxide for high performance supercapacitor electrodes

A series of surfactant-stabilized graphene materials were prepared by intercalation of graphene oxide (GO) with different surfactants, tetrabutylammonium hydroxide (TBAOH), cetyltrimethylammonium bromide (CTAB) and sodium dodecylbenzene sulfonate (SDBS), followed by reduction using hydrazine. The materials were fully characterized, and the surfactants were found to be successfully intercalated in both GO and the reduced graphene oxide. As well as stabilizing the morphology of single layer or few-layer structure of graphene sheets during reduction, the presence of surfactants in graphene materials can also enhance the wettability of the graphene surface and thus improve its performance as a supercapacitor electrode. When the graphene materials were used as an electrode for a supercapacitor, the highest specific capacitance of 194 F g−1 was obtained from the TBAOH stabilized graphene at a specific current density of 1 A g−1 in 2 M H2SO4 electrolyte.

Surfactant-stabilized graphene/polyaniline nanofiber composites for high performance supercapacitor electrode

Polyaniline nanofibers were prepared by in situ polymerization of aniline in the presence of surfactants such as tetrabutylammonium hydroxide and sodium dodecyl benzenesulfonate stabilized graphene under acidic condition. A homogeneous dispersion of individual graphene sheets within the polymer matrix was achieved due to the good dispersibility of surfactant-stabilized graphene in aqueous phase. The morphology and electrochemical properties of both components were well preserved due to the mild reaction conditions. The composite materials were used for supercapacitor electrode and a high specific capacitance of 526 F g−1 was obtained at a current density of 0.2 A g−1 with good cycling stability.

High-performance polymer semiconducting heterostructure devices by nitrene-mediated photocrosslinking of alkyl side chains

Heterostructures are central to the efficient manipulation of charge carriers, excitons and photons for high-performance semiconductor devices. Although these can be formed by stepwise evaporation of molecular semiconductors, they are a considerable challenge for polymers owing to re-dissolution of the underlying layers. Here we demonstrate a simple and versatile photocrosslinking methodology based on sterically hindered bis(fluorophenyl azide)s. The photocrosslinking efficiency is high and dominated by alkyl side-chain insertion reactions, which do not degrade semiconductor properties. We demonstrate two new back-infiltrated and contiguous interpenetrating donor-acceptor heterostructures for photovoltaic applications that inherently overcome internal recombination losses by ensuring path continuity to give high carrier-collection efficiency. This provides the appropriate morphology for high-efficiency polymer-based photovoltaics. We also demonstrate photopatternable polymer-based field-effect transistors and light-emitting diodes, and highly efficient separate-confinement-heterostructure light-emitting diodes. These results open the way to the general development of high-performance polymer semiconductor heterostructures that have not previously been thought possible.

Investigation of the sites of dark spots in organic light-emitting devices

Poor environmental stability has been a major concern for organic light-emitting devices. Exposure to ambient conditions leads to the formation of nonemissive areas (dark spots) that result in a decrease in device luminescence. Although a number of mechanisms for the formation of dark spots have been proposed, the causes underlying their initiation, and their nucleation sites are still far from being clear. In this study, optical microscopy is used to investigate the sites of dark spots of devices in which the original cathodes are peeled off and replaced by newer cathodes. Results confirm that the growth of dark spots occurs primarily due to cathode delamination. The growth of dark spots is also associated with changes in the organic layers, especially at the organic/cathode interface. Results also suggest that the nucleation of dark spots takes place at the organic/cathode interface and originates during the deposition of the cathode. On the other hand, both the anode and the hole transport layer do not appear to play a role in the formation of dark spots.

NiFe2O4 nanoparticles formed in situ in silica matrix by mechanical activation

Nanocrystalline nickel ferrite (NiFe2O4) particles were successfully synthesized in situ in an amorphous silica matrix by mechanical activation at room temperature. Phase development in the amorphous precursors, derived via a modified sol–gel synthesis route, with increasing mechanical activation time was studied in detail by employing transmission electron microscopy, x-ray diffraction, and Raman spectroscopy. NiFe2O4 nanoparticles of 8.05 nm in mean particle size with a standard deviation of 1.24 nm, which were well dispersed in the silica matrix, were realized by 30 h of mechanical activation. The phase formation of nanocrystalline NiFe2O4 particles involves the nucleation of Fe3O4 in amorphous silica at the initial stage of mechanical activation, followed by the growth of nickel ferrite by incorporation of Ni2+ caions into Fe3O4. Their magnetic anisotropy, surface spin disorder, and cation distribution are investigated by considering both the strain imposed by silica matrix and the buffer effect durin...

Overexpression, purification and characterization of human recombinant 15-lipoxygenase

Human 15-lipoxygenase was expressed to high levels (approx. 20% of cellular protein) in a baculovirus/insect cell expression system. Catalytically active enzyme was readily purified (90-95% pure) from cytosolic fractions by anion-exchange chromatography on a Mono Q column with approx. 95% recovery of enzymatic activity. Routinely, a yield of 25-50 mg of pure enzyme per L of culture and a specific activity of 7.1-21 mumol 13-hydroxyoctadecadienoic acid (13-HODE)/mg.min (turnover rate of 8.4-25 s-1) were obtained. Both the specific activity and the enzymes iron content was significantly increased by the addition of ferrous ions to either the purified enzyme or to the insect cell culture medium during production. An isoelectric point of 5.85 was determined and the N-terminal amino acid sequence was found to be identical to that predicted from the cDNA. The purified recombinant enzyme exhibits a dual positional specificity with arachidonic acid (formation of 15S- and 12S-hydroxyeicosatetraenoic acid (12S-HETE) in a ratio of 12:1). Double oxygenation products 14R,15S- and various 8,15-DiHETE isomers were also identified. With linoleic acid as substrate, a pH-optimum of 7.0 and a KM of 3 microM were determined. The enzyme undergoes suicidal inactivation during fatty acid oxygenation, is sensitive to standard lipoxygenase inhibitors, and oxygenates phospholipids, cholesterol esters, biomembranes and human low-density lipoprotein. Contrary to prior studies on the rabbit enzyme, no glycosylation was detected.

Protein stability in the amorphous carbohydrate matrix: relevance to anhydrobiosis.

The formation of intracellular glass is proposed to be relevant to protein stabilization and survival of anhydrobiotic organisms in the dry state. The stability of proteins in the amorphous carbohydrate matrix and its relevance to seed survival have been investigated in the present study. Glucose-6-phosphate dehydrogenase (G6PDH) was preserved in the amorphous glucose/sucrose (1:10, w/w) matrix by freeze-drying. The stability of freeze-dried G6PDH was examined at temperatures above and below the glass transition temperature (Tg). The rate of G6PDH inactivation in the amorphous carbohydrate matrix deviated significantly from the Arrhenius kinetics, and conformed to the Williams-Landel-Ferry (WLF) relationship. The temperature dependence of G6PDH inactivation in two sets of samples with different Tg values was compared. Identical temperature dependence of G6PDH inactivation was observed after temperature normalization by (T-Tg). Seed survival of Vigna radiata Wilczek (mung bean) showed a similar WLF kinetics at storage temperatures T > or = Tg. In situ protein stability in mung bean embryonic axes was studied using differential scanning calorimetry (DSC). Thermal stability of seed proteins exhibited a strong dependence on the Tg of intracellular glass. These results indicate an important role of the glassy state in protein stabilization. Our data suggest an association between protein stability in intracellular glass and seed survival during storage.