Chiral separation of homocysteine by derivatization with 4-aminosulfonyl-7-fluoro-2,1,3-benzoxadiazole followed by capillary electrophoresis using gamma-cyclodextrin

Homocysteine was derivatized with 4-aminosulfonyl-7-fluoro-2,1,3-benzoxadiazole (ABD-F) to form an inclusion complex with cyclodextrin and to facilitate UV detection. ABD-homocysteine showed interaction with beta- and gamma-cyclodextrin in capillary electrophoresis at pH 2.25 as indicated by the decreased migration time. However, chiral separation of D,L-ABD-homocysteine was observed using gamma-CD only. Optimal separation was obtained at pH 2.25, 50 mM gamma-CD concentration, and 20 kV applied voltage. L-ABD-Homocysteine migrated faster than the D-isomer as demonstrated by a spiking experiment using dithiothreitol-reduced L-homocystine.     

Reduction of the IgE-binding ability and maintenance of immunogenicity of gamma-irradiated Dermatophagoides farinae

House dust mites, Dermatophagoides farinae (DF) and Dermatophagoides pteronyssinus, are major allergens in the most common indoor allergen and are important risk factor for asthma. The modified antigen has been studied to treat allergic disorder. This study was carried out to measure possibility of modified allergen using gamma irradiation to treat allergy such as asthma. DF solutions (2 mg/ml) as target allergen were irradiated with Co-60 at 50 and 100 kGy. Conformational alternation of irradiated DF was observed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Levels of anti-irradiated DF mouse IgGs (sub-isotypes) against intact DF were measured similar to that of anti-intact DF IgGs. The binding abilities of house dust mite-allergic patients’ IgE were reduced depending on radiation dose, and irradiation could inhibit the binding ability of patients’ IgE more than 40%. This study has shown that the binding ability of IgE was reduced by conformational alteration by irradiation and the irradiated DF had epitopes capable to induce immunogeniciy.     

Tuning chirality of single-wall carbon nanotubes by selective etching with carbon dioxide

CO2 molecule chemisorbs selectively on the zigzag tube edge without an activation barrier, whereas it physisorbs on the armchair edge of nanotubes. In addition, carbon nanotubes can be etched by an adsorbed oxygen atom of CO2 molecule. From our results, we suggest a selective etching mechanism for tuning the chirality of the mass-produced carbon nanotubes.     

A series of long-chain lamellar hydrated copper(II) alkylsulfonates with different chain molecular assemblies

Reaction of copper(II) salts with n-alkylsulfonate anions yields light blue lamellar Cu(C(n)H(2n + 1)SO3)2 x zH2O displaying distinct (mono/bi-layer) chain packing with increasing alkyl chain lengths. This may be attributed to the amphiphilic nature of the surfactants, i.e., the hydrophilic sulfonate head groups, mediating the coordination, and H-bonding interactions, and the hydrophobic alkyl chains.     

Surface modification of polyethylene terephthalate using PEO-polybutadiene-PEO triblock copolymers

The initial step of thrombus formation on blood-contacting biomaterials is known to be adsorption of blood proteins followed by platelet adhesion. It is generally accepted that surface modification of the biomaterials with poly(ethylene oxide) (PEO) substantially reduces protein adsorption and cell adhesion. Dacron® (polyethylene terephthalate) fabric, which is one of the biomaterials commonly used in blood-contacting devices, was grafted with PEO. A simple two-step procedure for covalent grafting of PEO onto the surface of Dacron® fabric was used. The surface was first treated with PEO-polybutadiene-PEO (PEO-PB-PEO) triblock copolymer, to introduce a layer of double bonds onto the surface. The Dacron® surface was then exposed to a solution of Pluronic® F108 (PF108), a commercially available PEO-poly(propylene oxide)-PEO (PEO-PPO-PEO) triblock copolymer. The surface with two adsorbed layers of PEO-PB-PEO and PF108 was γ-irradiated in the presence of PF108 in the bulk solution for a total radiation dose of 0.8 Mrad. The bulk concentrations of PEO-PB-PEO and PF108 were varied to maximize the efficiency of PEO grafting. Fibrinogen adsorption on PEO-grafted surfaces was reduced more than 90%, compared with that on control surfaces, irrespective of the bulk concentrations of polymers used for grafting. Platelet adhesion was also reduced substantially by PEO grafting. Only a few round platelets were able to adhere to the PEO-grafted surface, while the control surface was fully covered with aggregates of activated platelets. PEO grafting on polyethylene terephthalate using PEO-PB-PEO and PEO-PPO-PEO block copolymers is a simple approach that can be used for various other biomaterials.     

Determination of Glimepiride in Human Plasma by LC-MS-MS and Comparison of Sample Preparation Methods for Glimepiride

A sensitive and selective method for quantitation of glimepiride in human plasma was established using liquid chromatography-electrospray ionization tandem mass spectrometry. Three different methods for the sample preparation of glimepiride and an internal standard were investigated (liquid-liquid extraction, solid-phase extraction and protein precipitation). Glipizide was used as an internal standard. Compounds were separated on a C₁₈ column with 80% acetonitrile and 20% deionized water (adjusted to pH 3.5 with acetic acid), as mobile phase at a flow rate of 200 L min^–1. By use of multiple reaction monitoring mode in MS-MS with liquid-liquid extraction and solid-phase extraction, glimepiride and glipizide were detected without severe interference from the human plasma matrix. Glimepiride produced a protonated precursor ion ([M+H]⁺) at m/z 491 and a corresponding product ion at m/z 352, and the internal standard produced a protonated precursor ion ([M+H]⁺) at m/z 446 and a corresponding product ion at m/z 321. The limit of quantitation was 0.1 ng mL^–1, 0.5 ng mL^–1 and 1.0 ng mL^–1 when using liquid-liquid extraction, solid-phase extraction and protein precipitation, respectively. The validation, reproducibility, stability, and recovery of the different sample preparation methods were comparable and all the methods gave reliable results. The method has been successfully applied to pharmacokinetic study of glimepiride in human plasma.     

Amperometric Glucose Biosensor Based on Glucose Oxidase Encapsulated in Carbon Nanotube–Titania–Nafion Composite Film on Platinized Glassy Carbon Electrode

A highly sensitive and selective glucose biosensor has been developed based on immobilization of glucose oxidase within mesoporous carbon nanotube–titania–Nafion composite film coated on a platinized glassy carbon electrode. Synergistic electrocatalytic activity of carbon nanotubes and electrodeposited platinum nanoparticles on electrode surface resulted in an efficient reduction of hydrogen peroxide, allowing the sensitive and selective quantitation of glucose by the direct reduction of enzymatically‐liberated hydrogen peroxide at ?0.1 V versus Ag/AgCl (3 M NaCl) without a mediator. The present biosensor responded linearly to glucose in the wide concentration range from 5.0×10^?5 to 5.0×10^?3 M with a good sensitivity of 154 mA M^?1cm^?2. Due to the mesoporous nature of CNT–titania–Nafion composite film, the present biosensor exhibited very fast response time within 2 s. In addition, the present biosensor did not show any interference from large excess of ascorbic acid and uric acid.