Studies on the Particle Morphology of Waterborne Cationic Polyurethane/Polyacrylate Microemulsions

Polyurethane containing tertiary nitrogen atoms was synthesized from polyol, diphenylmethane diisoccyanate (MDI) and N‐methyl diethanolamine. The polymer was converted into cationomers by quarternizing with methacrylic acid (MAA) and then dispersed in water. In this reaction, methyl methacrylate (MMA) was used to decrease viscosity; at the same time, it was the monomer in the later reaction. Finally the cationic polyurethane dispersions were further polymerized with an oil‐soluble initiator, azobisisobutyronitrile (AIBN), water‐soluble initiator, K₂S₂O₈ (KPS) and the mixture of AIBN and KPS. The different emulsion particles with shell‐core structure, “invert” shell‐core structure and “irregular” sandwich structure were obtained; the morphological structures were characterized by TEM observation, FT‐IR and particle size analysis.     

Preparation and Pervaporation Performances of PEA‐based Polyurethaneurea and Polyurethaneimide Membranes to Benzene/Cyclohexane Mixture

Pervaporation is promising in the separation of benzene/cyclohexane mixture for the petrochemical industry. Two kinds of pervaporation membrane materials, including PEA‐based polyurethaneurea (PUU) and polyurethaneimide (PUI), were successfully synthesized from the same soft segment of poly(ethylene adipate)diol (PEA) and different hard segments via a two‐step method. The hard segment of PUU was prepared from toluene diisocyanate (TDI) and 4,4′‐diaminodiphenyl methane (MDA), while that of PUI was from 4,4′‐methylene‐bis(phenylisocyanate) (MDI) and pyromellitic dianhydride (PMDA). The structures and properties of PUU and PUI were characterized by means of FT‐IR, DSC and TGA. During the pervaporation experiment, the PUI membranes had a flux of 12.13 kg µm m^?2 h^?1 and separation factor of 8.25, while the PUU membranes had a flux of 26.35 kg µm m^?2 h^?1 and separation factor of 6.29 for 50 wt% benzene in the benzene/cyclohexane mixture at 40°C. The effects of the structures of hard segments on pervaporation performances were discussed. The investigation of the relationship in molecular structure and PV performances will be helpful for the choice and design of membrane materials in the separation of benzene/cyclohexane mixture.     

Profiling primaquine metabolites in primary human hepatocytes using UHPLC‐QTOF‐MS with 13C stable isotope labeling

Therapeutic efficiency and hemolytic toxicity of primaquine (PQ), the only drug available for radical cure of relapsing vivax malaria are believed to be mediated by its metabolites. However, identification of these metabolites has remained a major challenge apparently due to low quantities and their reactive nature. Drug candidates labeled with stable isotopes afford convenient tools for tracking drug‐derived metabolites in complex matrices by liquid chromatography‐tandem mass spectrometry (LC‐MS‐MS) and filtering for masses with twin peaks attributable to the label. This study was undertaken to identify metabolites of PQ from an in vitro incubation of a 1:1 w/w mixture of ¹³C₆‐PQ/PQ with primary human hepatocytes. Acquity ultra‐performance LC (UHPLC) was integrated with QTOF‐MS to combine the efficiency of separation with high sensitivity, selectivity of detection and accurate mass determination. UHPLC retention time, twin mass peaks with difference of 6 (originating from ¹³C₆‐PQ/PQ), and MS‐MS fragmentation pattern were used for phenotyping. Besides carboxy‐PQ (cPQ), formed by oxidative deamination of PQ to an aldehyde and subsequent oxidation, several other metabolites were identified: including PQ alcohol, predictably generated by oxidative deamination of PQ to an aldehyde and subsequent reduction, its acetate and the alcohol's glucuronide conjugate. Trace amounts of quinone‐imine metabolites of PQ and cPQ were also detected which may be generated by hydroxylation of the PQ/cPQ quinoline ring at the 5‐position and subsequent oxidation. These findings shed additional light on the human hepatic metabolism of PQ, and the method can be applied for identification of reactive PQ metabolites generated in vivo in preclinical and clinical studies. Copyright © 2013 John Wiley & Sons, Ltd.     

A Yeast Chemical Genetic Screen Identifies Inhibitors of Human Telomerase

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Highlights? Growth arrest induced by human telomerase in yeast is chemically reversible ? Readout is sensitive to telomerase catalytic activity and telomere recruitment ? Three cell-permeable compounds also inhibit purified human telomerase ? Yeast can be successfully used to screen for human telomerase inhibitors     

Substrate Envelope-Designed Potent HIV-1 Protease Inhibitors to Avoid Drug Resistance

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Biochemical and Structural Studies of Conserved Maf Proteins Revealed Nucleotide Pyrophosphatases with a Preference for Modified Nucleotides

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TDAG51 deficiency promotes oxidative stress-induced apoptosis through the generation of reactive oxygen species in mouse embryonic fibroblasts

Apoptosis has an important role in maintaining tissue homeostasis in cellular stress responses such as inflammation, endoplasmic reticulum stress, and oxidative stress. T-cell death-associated gene 51 (TDAG51) is a member of the pleckstrin homology-like domain family and was first identified as a pro-apoptotic gene in T-cell receptor-mediated cell death. However, its pro-apoptotic function remains controversial. In this study, we investigated the role of TDAG51 in oxidative stress-induced apoptotic cell death in mouse embryonic fibroblasts (MEFs). TDAG51 expression was highly increased by oxidative stress responses. In response to oxidative stress, the production of intracellular reactive oxygen species was significantly enhanced in TDAG51-deficient MEFs, resulting in the activation of caspase-3. Thus, TDAG51 deficiency promotes apoptotic cell death in MEFs, and these results indicate that TDAG51 has a protective role in oxidative stress-induced cell death in MEFs.     

Evaluating a four-directional benzene-centered aliphatic polyamine curing agent for epoxy resins

A four-directional benzene-centered aliphatic polyamine, MXBDP, with high functionality and low volatility, is used to cure epoxy resin (DGEBA). Herein we originally report the isothermal cure kinetics and dynamic mechanical properties of DGEBA/MXBDP. Differential scanning calorimetry confirms that MXDBP is more reactive than commercial linear metaxylenediamine and branched Jeffamine T-403 and the isothermal curing reaction is autocatalytic. The Kamal model is found to be able to well describe the curing rate up to the onset of diffusion control, and the excellent match over the whole conversion range is achieved using the extended Kamal model. Interestingly, the isoconversional kinetic analysis indicates that the effective reaction activation energy (E _α ) changes substantially with conversion, and ultimately decreases to a very small value (<10 kJ mol^?1) because of the diffusion-controlled reaction kinetics. Then, dynamic mechanical analysis reveals that DGEBA/MXBDP exhibits the higher α- and β-relaxation temperatures and the much higher crosslink density than DGEBA/metaxylenediamine. Our experiment results support that MXBDP has the high reactivity and improved thermal resistance in combination with the advantages of the high functionality, low volatility and decreased CO₂ absorption. Therefore, MXBDP may be especially suitable for room temperature-cure epoxy coatings and adhesives.     

Highly sensitive lable-free electrochemical aptasensor for thrombin detection with cobalt hexacyanoferrate as the electrochemical probe

A highly sensitive label-free electrochemical aptasensor has been constructed for the electrochemical detection of thrombin (TB), where two layers of cobalt hexacyanoferrate (CoHCF) redox probes sandwiched with carbon nanotubes–Nafion were directly immobilized on the electrode surface by electrodeposition. Through the strong interaction between CN^? (CoHCF) and gold nanoparticles (GNPs), GNPs were assembled on the CoHCF-modified electrode for the immobilization of thiolated thrombin aptamers (TBA). In the presence of target TB, TBA on the electrode surface could catch TB to form TBA–TB complex, which made a barrier for the electron transfer, resulting in a greater decrease in CoHCF redox probe signals. Thus, the proposed aptasensor showed a high sensitivity and a much wider linearity to TB in the range of 1.0 pg/mL?～?1.0 μg/mL with a detection limit of 0.28 pg/mL.