Chi Bun Ching

High-performance asymmetric supercapacitor based on graphene hydrogel and nanostructured MnO2.

We have successfully fabricated an asymmetric supercapacitor with high energy and power densities using graphene hydrogel (GH) with 3D interconnected pores as the negative electrode and vertically aligned MnO(2) nanoplates on nickel foam (MnO(2)-NF) as the positive electrode in a neutral aqueous Na(2)SO(4) electrolyte. Because of the desirable porous structure, high specific capacitance and rate capability of GH and MnO(2)-NF, complementary potential window of the two electrodes, and the elimination of polymer binders and conducting additives, the asymmetric supercapacitor can be cycled reversibly in a wide potential window of 0-2.0 V and exhibits an energy density of 23.2 Wh kg(-1) with a power density of 1.0 kW kg(-1). Energy density of the asymmetric supercapacitor is significantly improved in comparison with those of symmetric supercapacitors based on GH (5.5 Wh kg(-1)) and MnO(2)-NF (6.7 Wh kg(-1)). Even at a high power density of 10.0 kW kg(-1), the asymmetric supercapacitor can deliver a high energy density of 14.9 Wh kg(-1). The asymmetric supercapacitor also presents stable cycling performance with 83.4% capacitance retention after 5000 cycles.

One-step electrochemical synthesis of PtNi nanoparticle-graphene nanocomposites for nonenzymatic amperometric glucose detection.

We report a facile one-step ultrasonication-assisted electrochemical method to synthesize nanocomposites of graphene and PtNi alloy nanoparticles (NPs) and their uses for highly selective nonenzymatic glucose detection. We have demonstrated that the obtained nanocomposites exhibit a collection of unique features including well-dispersed NPs with alloy features, high NP loading, and effective reduction of graphene oxide (GO). And the resulting nanoelectrocatalyst shows significantly improved electrochemical performance in nonenzymatic amperometric glucose detection, compared to a number of control electrode materials including the PtNi NP-chemically reduced GO nanocomposites fabricated in two steps (chemical reduction of GO followed by the electrodeposition of metal NPs). Under the physiological condition, the response current of the sensor is linear to glucose concentration up to 35 mM with a sensitivity of 20.42 μA cm(-2) mM(-1) at a substantially negative potential (i.e., -0.35 V). Operation under this potential eliminates the impact from the oxidation of common interfering species. This sensor with excellent sensitivity and selectivity also allows for reproducible detection of glucose in human urine samples.

Flexible All-Solid-State Asymmetric Supercapacitors Based on Free-Standing Carbon Nanotube/Graphene and Mn3O4 Nanoparticle/Graphene Paper Electrodes

We report the design of all-solid-state asymmetric supercapacitors based on free-standing carbon nanotube/graphene (CNTG) and Mn(3)O(4) nanoparticles/graphene (MG) paper electrodes with a polymer gel electrolyte of potassium polyacrylate/KCl. The composite paper electrodes with carbon nanotubes or Mn(3)O(4) nanoparticles uniformly intercalated between the graphene nanosheets exhibited excellent mechanical stability, greatly improved active surface areas, and enhanced ion transportation, in comparison with the pristine graphene paper. The combination of the two paper electrodes with the polymer gel electrolyte endowed our asymmetric supercapacitor of CNTG//MG an increased cell voltage of 1.8 V, a stable cycling performance (capacitance retention of 86.0% after 10,000 continuous charge/discharge cycles), more than 2-fold increase of energy density (32.7 Wh/kg) compared with the symmetric supercapacitors, and importantly a distinguished mechanical flexibility.

Cytotoxicity Evaluation of Oxidized Single-Walled Carbon Nanotubes and Graphene Oxide on Human Hepatoma HepG2 cells: An iTRAQ-Coupled 2D LC-MS/MS Proteome Analysis

Because of their attractive chemical and physical properties, graphitic nanomaterials and their derivatives have gained tremendous interest for applications in electronics, materials, and biomedical areas. However, few detailed studies have been performed to evaluate the potential cytotoxicity of these nanomaterials on living systems at the molecular level. In the present study, our group exploited the isobaric tagged relative and absolute quantification (iTRAQ)-coupled two-dimensional liquid chromatography-tandem mass spectrometry (2D LC-MS/MS) approach with the purpose of characterizing the cellular functions in response to these nanomaterials at the proteome level. Specifically, the human hepatoma HepG2 cells were selected as the in vitro model to study the potential cytotoxicity of oxidized single-walled carbon nanotubes (SWCNTs) and graphene oxide (GO) on the vital organ of liver. Overall, 30 differentially expressed proteins involved in metabolic pathway, redox regulation, cytoskeleton formation, and cell growth were identified. Based on the protein profile, we found oxidized SWCNTs induced oxidative stress and interfered with intracellular metabolic routes, protein synthesis, and cytoskeletal systems. Further functional assays confirmed that oxidized SWCNTs triggered elevated level of reactive oxygen species (ROS), perturbed the cell cycle, and resulted in a significant increase in the proportion of apoptotic cells. However, only moderate variation of protein levels for the cells treated with GO was observed and functional assays further confirmed that GO was less cytotoxic in comparison to oxidized SWCNTs. These finding suggested that GO was more biocompatible and could be a promising candidate for bio-related applications.

Improvement of biomass properties by pretreatment with ionic liquids for bioconversion process

Cassava pulp residue and rice straw were used as a precursor for pretreatment with ionic liquids to study the effects of pretreatment conditions on product yield and properties. Cassava pulp residue is a potential biomass in the bioconversion process due to it requiring mild pretreatment conditions while providing a high sugar conversion. The maximum sugar conversion and lignin extraction are attained from pretreatment of biomasses with particle size of <38 μm and ionic liquid of 1-Ethyl-3-methylimidazolium acetate at 120°C for 24h. The effectiveness of ionic liquid for biomass pretreatment process follows the sequence: 1-Ethyl-3-methylimidazolium acetate>1-Ethyl-3-methylimidazolium diethyl phosphate>1,3-Dimethylimidazolium methyl sulfate. The increase of pretreatment temperature from 25 to 120°C and decrease of biomass particle size renders higher sugar conversion, lignin extraction and lower crystallinity index. However, pretreatment at temperatures higher than 120°C shows a sharp decline of regenerated biomass yield, sugar conversion and lignin extraction and giving higher crystallinity index at pretreatment temperature of 180°C.

Experimental study of a simulated counter-current adsorption system—III. Sorbex operation

Abstract The separation of an aqueous mixture of fructose and glucose has been carried out in a simulated moving bed counter-current adsorption system, operated in a manner similar to the UOP “Sorbex” process. Concentration profiles measured under cyclic steady state conditions are close to the profiles predicted theoretically for the equivalent continuous counter-current system. The conditions on the flow rates which must be fulfilled in order to obtain an operable process are delineated and the effects of the process variables on product quality are examined. Under properly selected conditions product purities and recoveries of 85–95% are obtained. This is comparable with the values quoted for a commercial Sarex system.

Enantiomer separation of flavour and fragrance compounds by liquid chromatography using novel urea-covalent bonded methylated β-cyclodextrins on silica

A novel methylated beta-cyclodextrin chiral stationary phase (CSP-ME), which was chemically immobilised onto porous silica via multiple urea-linkages was synthesised. The CSP-ME chiral stationary phase depicted good enantiomer separation abilities for some well-known flavour as well as fragrance compounds using high-performance liquid chromatography under reverse phase conditions. The optimum resolution for alpha-ionone, 3-methyl-alpha-ionone, flavanone, 5-methoxyflavanone, 6-methoxyflavanone, 7-methoxyflavanone, hesperetin, naringenin and taxifolin was achieved using a mobile phase composition consisting of 1 wt.% triethylammonium acetate buffer (pH 4.68)-methanol. The effects of pH of triethylammonium acetate buffer and the methanol-acetonitrile content of the mobile phase composition on their retention time and resolution were examined to optimise the separation conditions.

Synthesis and chromatographic properties of a novel chiral stationary phase derived from heptakis(6-azido-6-deoxy-2,3-di-O-phenylcarbamoylated)-β-cyclodextrin immobilized onto amino-functionalized silica gel via multiple urea linkages

A novel chiral stationary phase (PPHCDN7) was prepared by immobilization of heptakis(6-azido-6-deoxy-2,3-di-O-phenylcarbamoylated)-beta-cyclodextrin (PPHCD) onto the surface of amino-functionalized silica gel via multiple urea linkages derived from an extended application of the Staudinger reaction. A wide range of structurally divergent racemic drugs and other compounds were successfully separated into their enantiomers under both normal and reversed-phase conditions. Beta-adrenergic blockers and racemic tertiary, secondary and primary amines were readily separated using a mixture of methanol and aqueous triethylammonium acetate buffer. The optimal pH value for the separation falls in the range of 4.65 to 6.30. With atropine and isoproterenol, good enantioseparations with separation factors of alpha>5 were easily attainable.

Production of bioactive human beta-defensin 5 and 6 in Escherichia coli by soluble fusion expression.

This work reports the first successful recombinant expression and purification of human beta-defensin 5 (HBD5) and human beta-defensin 6 (HBD6) in Escherichia coli. HBD5 and HBD6 are cationic antimicrobial peptides with three conserved cysteine disulfide bonds. Two codon-optimized sequences coding the HBD5 gene (sHBD5) and HBD6 gene (sHBD6), respectively, were synthesized, and each gene fused with thioredoxin A (TrxA) to construct the expression vectors. The plasmids were transformed into E. coli BL21 (DE3) strains and cultured in MBL medium, which gave high volumetric productivity of HBD5 and HBD6 fusion proteins of up to 1.49 g L(-1) and 1.57 g L(-1), respectively. Soluble HBD5 and HBD6 fusion proteins account for 95.2% and 97.6% of the total fusion proteins, respectively. After cell disruption, the soluble fusion proteins were recovered by affinity chromatography and cleaved by enterokinase. Pure HBD5 and HBD6 were recovered using cationic exchange chromatography. The overall recoveries of HBD5 and HBD6 were 38% and 35%, respectively. Importantly, both HBD5 and HBD6 products showed antimicrobial activity against E. coli but not Staphylococcus aureus. Antimicrobial activity against E. coli of both HBD5 and HBD6 were suppressed by NaCl.

Comparative protein profile of human hepatoma HepG2 cells treated with graphene and single-walled carbon nanotubes: An iTRAQ-coupled 2D LC–MS/MS proteome analysis

Graphitic nanomaterials are promising candidates for applications in electronics, energy, materials and biomedical areas. Nevertheless, few detailed studies related to the mechanistic understanding of these nanomaterials with the living systems have been performed to date. In the present study, our group applied the iTRAQ-coupled 2D LC-MS/MS approach to analyze the protein profile change of human hepatoma HepG2 cells treated with graphene and single-walled carbon nanotubes (SWCNTs), with the purpose of characterizing the interactions between living system and these nanomaterials at molecular level. Overall 37 differentially expressed proteins involved in metabolic pathway, redox regulation, cytoskeleton formation and cell growth were identified. Based on the protein profile, we found SWCNTs severely interfered the intracellular metabolic routes, protein synthesis and cytoskeletal systems. Moreover, our data suggested that SWCNTs might induce oxidative stress, thereby activating p53-mediated DNA damage checkpoint signals and leading to apoptosis. However, only moderate variation of protein levels for the cells treated with graphene was observed, which indicated graphene was less toxic and might be promising candidate for biomedical applications. We envision that this systematic characterization of cellular response at protein expression level will be of great importance to evaluate biocompatibility of nanomaterials.