The radiation degradation of a nanotube-polyimide nanocomposite

The radiation degradation of a nanotube-polyimide nanocomposite was studied. Radiation chemistry was observed that was not present in the unmodified polymer or in the imbedded single-walled carbon nanotubes (SWNTs) themselves. The tensile properties were found to be improved by the addition of SWNTs in the unirradiated materials, and no deterioration in these properties with irradiation was observed. The SWNTs were found to have a detrimental effect on the optical properties however. The transparency of the composite was degraded significantly faster by electron-beam radiation than the neat polymer was. This may make the SWNT/polyimide composites unsuitable for some space applications. Electron Spin Resonance (ESR) measurements determined that the SWNTs interfere with the radical chemistry in the irradiated materials. This could be due to energy dissipation by the SWNT network, preventing the formation of radical species, or alternatively, preferential reaction or termination of radicals by the nanotubes. FT-Raman spectroscopy was found to be a very useful tool for examining SWNTs embedded at low concentrations. It revealed no signs of SWNT degradation up to 10 MGy.     

Rapid capacitive detection of femtomolar levels of bisphenol A using an aptamer-modified disposable microelectrode array

A label-free and single-step method is reported for rapid and highly sensitive detection of bisphenol A (BPA) in aqueous samples. It utilizes an aptamer acting as a probe molecule immobilized on a commercially available array of interdigitated aluminum microelectrodes. BPA was quantified by measuring the interfacial capacitance change rate caused by the specific binding between bisphenol A and the immobilized aptamer. The AC signal also induces an AC electrokinetic effect to generate microfluidic motion for enhanced binding. The capacitive aptasensor achieves a limit of detection as low as 10 fM(2.8 fg ⋅ mL ^− 1) with a 20 s response time. The method is inexpensive, highly sensitive, rapid and therefore provides a promising technology for on-site detection of BPA in food and water samples.

A. AC electrokinetics effect plays a vital role in BPA detection by introducing microfluidic movement to accelerate the molecular transport to the electrode surface.

B. The ACEK capacitive aptasensor has a limit of detection as low as 10 fM (2.8 fg ⋅ mL ^− 1) with a 20-s response time.

     

Structural basis for oxygen sensing and signal transduction of the heme-based sensor protein Aer2 from Pseudomonas aeruginosa

The crystal structure of a truncated Aer2, a signal transducer protein from Pseudomonas aeruginosa, consisting of the heme-containing PAS and di-HAMP domains revealed that a distal tryptophan residue (Trp283) plays an important role in stabilizing the heme-bound O(2) and intra-molecular signal transduction upon O(2) binding.     

Detection of 22 antiepileptic drugs by ultra-performance liquid chromatography coupled with tandem mass spectrometry applicable to routine therapeutic drug monitoring

The purpose of this study was to develop an ultra‐performance liquid chromatography tandem mass spectrometry (UPLC‐MS/MS) method of 22 antiepileptics for routine therapeutic monitoring. The antiepileptics used in the analyses were carbamazepine, carbamazepine‐10,11‐epoxide, clobazam, N‐desmethylclobazam, clonazepam, diazepam, N‐desmethyldiazepam, ethosuximide, felbamate, gabapentin, lamotrigine, levetiracetam, N‐desmethylmesuximide, nitrazepam, phenobarbital, phenytoin, primidone, tiagabine, topiramate, valproic acid, vigabatrin and zonisamide. After protein precipitation of 50 μL plasma with methanol, the supernatant was diluted with water or was evaporated to dryness and reconstituted with mobile phase in the case of benzodiazepines. Separation was achieved on an Acquity UPLC BEH C₁₈ column with a gradient mobile phase of 10 mm ammonium acetate containing 0.1% formic acid and methanol at a flow rate of 0.4 mL/min. An Acquity TQD instrument in multiple reaction monitoring mode with ion mode switching was used for detection. All antiepileptics were detected and quantified within 10 min, with no endogenous interference. All the calibration curves showed good linearity in the therapeutic range (r² < 0.99). The precision and accuracy values for intra‐ and inter‐assays were within ±15% except for phenobarbital and tiagabine. A good correlation was observed between the concentration of clinical samples measured by the new method described here and the conventional methods. The values of carbamazepine and phenytoin by UPLC‐MS/MS were lower than those detected by the immunoassays, which might be caused by the cross‐reaction of antibodies with their metabolites. In conclusion, we developed a simple and selective UPLC‐MS/MS method suitable for routine therapeutic monitoring of antiepileptics. Copyright © 2012 John Wiley & Sons, Ltd.     

Electron localization or delocalization in incommensurate helical magnets

The electronic states in incommensurate helical magnets are studied theoretically from the viewpoint of the localization or delocalization. It is found that in the multiband system with a relativistic spin-orbit interaction, the electronic wave functions show both an extended and localized nature along the helical axis depending on the orbital, helical wave number, and the direction of the plane on which spins rotate. The possible realization of this localization is discussed.     

A Twist‐Assisted Biphenyl Photosensitizer Passable Through Glucose Channel

While the development of low‐molecular‐weight drugs is saturating, agents for photodynamic therapies (PDTs) may become alternative seeds in pharmaceutical industry. Among them, orally administrative, cancer‐selective, and side effect‐free photosensitizers (PSs) that can be activated by tissue‐penetrative near‐infrared (NIR) lights are strongly demanded. We discovered such a PS from scratch by focusing on a twist‐assisted spin‐orbit charge transfer intersystem crossing (ISC) mechanism in a biphenyl derivative, which was demonstrated by thorough photophysical studies. The unique ISC mechanism enables the PS to be small and slim so as to pass through glucose transporters and exert a PDT effect selectively on a cancer cell line. The smallness will allow for oral administration and fast clearance, which have been agenda of approved PSs with larger molecular weights. We also demonstrated that our PS was able to be activated with an NIR pulse laser through two‐photon excitation.     

Investigation of cadmium accumulation mechanism in hepatopancreas of Patinopecten yessoensis by synchrotron radiation X‐ray absorption fine structure and synchrotron radiation X‐ray fluorescence analyses

Chemical state of cadmium in a hepatopancreas of a scallop (Patinopecten yessoensis) was studied by means of synchrotron radiation‐based X‐ray analytical techniques. X‐ray absorption fine structure (XAFS) and X‐ray fluorescence (XRF) imaging were used to identify the chemical state and the distribution of cadmium in the hepatopancreas, respectively. The results of in vivo Cd K‐edge XAFS suggested that the neighboring atoms of the cadmium in the hepatopancreas are of sulfur. Therefore, we propose that cadmium was accumulated by a metalloprotein with sulfur. Micro XRF imaging of thin sections of the hepatopancreas showed that cadmium is distributed on the surface of intestinal epithelia and concentrated in the internal tissue of the hepatopancreas. These results indicated that scallops accumulate cadmium inside the hepatopancreas through the intestinal epithelium.     

Deviatoric stress and mean pressure in MgO compressed in a Kawai-type apparatus above 30 GPa: Evidence for reduction of deviatoric stress by annealing

By applying the numerical tensor analysis proposed by Yoneda and Kubo [Simultaneous determination of mean pressure and deviatoric stress based on numerical tensor analysis: a case study for polycrystalline X-ray diffraction of gold enclosed in a methanol-ethanol mixture. J. Phys.: Condens. Matter 18(2006)S979], we have determined deviatoric stress and mean pressure of polycrystalline MgO compressed in the Kawai-type apparatus. After the compression at room temperature, the mean pressure and the deviatoric stress in MgO were determined as 34.5 and 3.2 GPa, respectively. The mean pressure is significantly lower than the nominal pressure of 37.2 GPa determined by the conventional pressure determination method. By heating the sample to 1850 K with the constant press load, the deviatoric stress dramatically decreased to 0.1 GPa with a mean pressure of 34.2 GPa at room temperature after the heating. These results show both the importance of stress analysis to determine pressure more accurately and the effectiveness of annealing to reduce deviatoric stress in the sample.     

Mass spectrometric study on chemical transport of VO2

The analysis of gas in the chemical transport reaction of VO₂ using TeCl₄ as a transport agent was carried out with a quadrupole mass spectrometer. In the transport reaction from 600 to 500°C, it was found that the oxygen and vanadium of VO₂ were transported in the form of VOCl₃ and TeOCl₂ gases; the transport reaction was $\text{VO}{}_2\text{+}\text{3}\text{2}\text{TeCl}{}_4\text{= VOCl}{}_3\text{+ TeOCl}{}_2\text{+}\text{1}\text{2}\text{TeCl}{}_2$. The transport reaction from 900°C to 800°C was assumed to be $\text{VO}{}_2\text{+}\text{3}\text{2}\text{TeCl}{}_2\text{= VOCl}{}_3\text{+}\text{1}\text{2}\text{O}{}_2\text{+}\text{3}\text{4}\text{TeCl}{}_2$. In the transport at high temperature, the oxygen partial pressure estimated from the mass spectrum was considerably higher than that in equilibrium with VO₂ phase. In this paper a study of the chemical transport of the system VO₂-TeCl₄ is presented.     

Likelihood analysis of spatial inhomogeneity for marked point patterns

An objective method is developed for estimations of both spatial intensity of the point locations and spatial variation of a characteristic parameter of the distributions for the attached marks. Its utility is demonstrated by means of analyses of seismological and ecological data sets.