Method to determine critical current of poorly cooled short sample

Superconducting wire characterization can fail owing to many reasons. For example, unintentional sample heating may distort voltage–current-data, i.e. decrease the critical current and increase the n-value. This occurs rarely if a sample is immersed into liquid cryogen, but in conduction cooled measurements, constant sample temperature is difficult to achieve. Ohmic losses are generated at current contacts as well as inside the sample even at subcritical currents. Most of these losses can be extracted using a well designed sample holder, but in any case, significant amount of heat is generated rapidly when critical current is approached and overstepped, especially if n-value is low. Then, heat has no time to conduct away, and thus, the sample will warm up distorting the measurement. In this paper, we present a computational post-processing method to reduce the effect of heating on measured voltage–current characteristics. Simulations are performed for a Bi-2223/Ag tape, but the model can be applied to any other superconductor as well.     

Fractionation of polyphenols in hawthorn into polymeric procyanidins, phenolic acids and flavonoids prior to high-performance liquid chromatographic analysis

Polymeric procyanidins, phenolic carboxylic acids and flavonoids of hawthorn (Crataegus laevigata) were fractionated prior to HPLC analysis using column chromatography and solid-phase extraction (SPE). The flavonoid fraction also contained (-)-epicatechin. The three groups of phenolics, each with clearly different UV spectra, were examined by means of high-performance liquid chromatography-diode array detection (HPLC-DAD) analysis. The average repeatability of the method (RSD) was in the range of 8-13% for chlorogenic acid, (-)-epicatechin and hyperoside. The polymeric procyanidins of hawthorn flowers consisted mainly of (-)-epicatechin subunits, and their mean degree of polymerization (DP) was 22.2. The HPLC methods developed can be used for the qualitative and quantitative analysis of different phenolic compounds in hawthorn plant material and their extracts.     

Identification of bupropion urinary metabolites by liquid chromatography/mass spectrometry

Human urinary metabolism of the antidepressant bupropion was studied using liquid chromatography/time-of-flight mass spectrometry (LC/TOFMS) and liquid chromatography/tandem mass spectrometry (LC/MS/MS). A total of 20 metabolites were detected and identified. The phase I metabolism included formation of morpholinohydroxybupropion, threo- and erythrohydrobupropion, aromatic hydroxylation, butyl group hydroxylation with ketone hydrogenation and dihydroxylation. These metabolites were detected either as the free form or as glucuronide and/or sulphate conjugates. In addition also m-chlorohippuric acid was detected. Of the phase I metabolites, a dihydroxylation to the aromatic ring and to the methyl group in the middle of the substrate molecule was reported here for the first time, as well as eight of the glucuronide conjugates (to hydroxy, dihydroxy, hydroxy and hydrogenation metabolites) and three of the sulphate conjugates (to aromatic hydroxy and hydroxy and hydrogenation metabolites).     

In vitro interaction cocktail assay for nine major cytochrome P450 enzymes with 13 probe reactions and a single LC/MSMS run: analytical validation and testing with monoclonal anti-CYP antibodies

A sensitive and rugged LC/MSMS method was developed for a comprehensive in vitro metabolic interaction screening assay with N-in-1 approach reported earlier. A cocktail consisting of ten cytochrome P450 (CYP)-selective probe substrates with known kinetic, metabolic and interaction properties in vivo was incubated in a pool of human liver microsomes, and metabolites of melatonin (CYP1A2), coumarin (CYP2A6), bupropion (CYP2B6), amodiaquine (CYP2C8) tolbutamide (CYP2C9), omeprazole (CYP2C19 and CYP3A4), dextromethorphan (CYP2D6), chlorzoxazone (CYP2E1), midazolam (CYP3A4) and testosterone (CYP3A4) were simultaneously analysed with a single LC/MSMS run. Altogether, 13 metabolites and internal standard phenacetin were analysed in multiple reaction mode. Polarity switching mode was utilized to acquire negative ion mode electrospray data for hydroxychlorzoxazone and positive ionization data for the rest of the analytes. Fast gradient elution was applied, giving total injection cycle of 8 min. The method was modified for two different LC/MSMS systems, and was validated for linear range, detection limit, accuracy and precision for each metabolite. In addition, cocktail inhibition system was further tested using monoclonal anti-CYP antibodies as inhibitors for each probe reaction.     

Cross‐Linked Proteins with Gold Nanoclusters: A Dual‐Purpose pH‐Responsive Material for Controllable Cell Imaging and Antibiotic Delivery

This report describes the development of a facile method for the synthesis of cross‐linked proteins with gold nanoclusters (CP‐GNC). The synthesis reaction is completed within 15 min at 97 °C. The synthesized CP‐GNC are characterized by using UV–vis absorption, fluorescence, X‐ray photoelectron spectroscopy, and transmission electron microscopy. CP‐GNC are approximately 100 nm in diameter and 700 nm in length, whereas AuNCs within the nanorods are approximately 6 nm in size. These materials are highly fluorescent with quantum yield of 7.2% and can be absorbed onto and release from bacterial cells in a pH‐dependent and reversible manner. The recent data show that CP‐GNC can be a useful, new tool with potential applications in fluorescent cell imaging and antibiotic targeting.     

Protein phosphorylation in mitochondria – A study on fermentative and respiratory growth of Saccharomyces cerevisiae

Phosphorylation as a posttranslational protein modification is a common subject of proteomic studies, but phosphorylation in mitochondria is still poorly investigated. The study presented here applied 2‐DE to characterize phosphorylation in the yeast mitochondrial proteome and identified 59 spots corresponding to 34 phosphorylated mitochondrial or mitochondria‐associated proteins. Most of these proteins presented putative substrates of mitogen‐activated protein and target of rapamycin kinases, cAMP‐dependent protein kinase, cyclin‐dependent kinases and Snf1p suggesting them as key players in the phosphorylation of mitochondrial or mitochondria‐associated proteins. The dynamic behaviour of the phosphoproteome under a major metabolic change, the shift from fermentation to respiration (diauxic shift), was further studied. Eight proteins (Ald4p, Eft1p/2p, Eno1p, Eno2p, Om14p, Pda1p, Qcr2p, Sdh1p) had growth dependent changes in their phosphorylation, indicating a role of phosphorylation‐dependent regulation of translation, metabolic pathways (e.g. glucose fermentation, tricarboxylic acid cycle, pyruvate dehydrogenase and its bypass) and respiratory chain.     

The tungsten-188/rhenium-188 generator: Effective coordination of tungsten-188 production between the HFIR and BR2 reactors

The rapidly increasing therapeutic applications of ¹⁸⁸Re in nuclear medicine, oncology and interventional cardiology require routine production of large, multi-Curie levels of the ¹⁸⁸W parent. The capability and effective coordination of back-up production sites is important to insure that high level ¹⁸⁸W/¹⁸⁸Re generators are continually available. We have coordinated ¹⁸⁸W production at the High Flux Isotope Reactor (HFIR - Oak Ridge, US) with production at the BR2 Reactor (Mol, Belgium) characterized by peak thermal neutron fluxes of 2.51·0¹⁵ (HFIR) and 1·10¹⁵ (BR2) neutrons/cm²·sec, respectively. The long 69-day physical half-life permits receipt of ¹⁸⁸W from BR2 within 0.25 T _1/2's, even after the 12-day post irradiation cooling required for ¹⁸⁷W decay (T _1/2 = 24 hours). Since ¹⁸⁸W production by double neutron capture of enriched ¹⁸⁶W is a function of the square of the thermal neutron flux, HFIR production (4-5 Ci ¹⁸⁸W/g ¹⁸⁶W/cycle) is higher than at the BR2 (1.0-1.1 Ci/g ¹⁸⁶W/cycle). However, the specific activity (SA) of BR2-produced ¹⁸⁸W is still about 0.8-0.9 Ci/g after processing at ORNL following shipment from Belgium. This SA is sufficiently high to permit fabrication of 1 Ci generators suitable for clinical use, since simple post elution concentration of the saline bolus (30-50 ml) obtained from the generator can provide samples with high specific volume (1 ml volume). The time periods from reactor push in Mol and completion of processing, fabrication and shipment of generators from Oak Ridge have been 19-21 days. Six campaigns have been successfully completed since 1998, with processed levels of ¹⁸⁸W in Oak Ridge from 8-26 Curies/campaign. ¹⁸⁸W has been provided to MAP Medical technologies Oy (Tikkakoski, Finland) for fabrication and distribution of generators for use at IAEA-supported research projects in developing countries. We have thus established and demonstrated an effective collaboration between the Studiecentrum voor Kernenergie-Centre d'Etude de l'Energie Nucléaire (SCK·CEN) and ORNL for back-up production of ¹⁸⁸W. This collaboration continues to be especially helpful during periods when interruption of HFIR operation is necessary for maintenance and upgrades.     

Overpressured layer chromatography in comparison with thin-layer and high-performance liquid chromatography for the determination of coumarins with reference to the composition of the mobile phase

The retention behaviour of fifteen closely related coumarins in normal-phase overpressured layer chromatography (OPLC) was studied with the aim of comparing the retentions with those in normal-phase thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) when optimization of the mobile phase was carried out according to the PRISMA system. The mobile phase optimization was carried out on TLC plates in unsaturated chambers. The resulting mobile phases were transposed to off-line, non-equilibrated OPLC and further to HPLC. The retention in TLC was measured at 37 selectivity points and in OPLC and HPLC at 13 points. Capacity factors (k′) and separation factors () were calculated in order to study the retention behaviour in the different systems. Two- and three-dimensional evaluations of k′ against selectivity points showed similar retention behaviours for the coumarins in TLC, OPLC and HPLC. The values for TLC, OPLC and HPLC showed similar patterns in the three-dimensional evaluations. The retention behaviour at different solvent strengths was also examined. According to quadratic regression, k′ showed a dependence on the change in solvent strength. OPLC, which can be considered as a “planar column” technique, and TLC are closely related methods, whereas HPLC shows a different behaviour in the elution process with regard to solvent strength.     

B-Site Co-Alloying with Germanium Improves the Efficiency and Stability of All-Inorganic Tin-Based Perovskite Nanocrystal Solar Cells

Colloidal lead-free perovskite nanocrystals have recently received extensive attention because of their facile synthesis, the outstanding size-tunable optoelectronic properties, and less or no toxicity in their commercial applications. Tin (Sn) has so far led to the most efficient lead-free solar cells, yet showing highly unstable characteristics in ambient conditions. Here, we propose the synthesis of all-inorganic mixture Sn-Ge perovskite nanocrystals, demonstrating the role of Ge²⁺ in stabilizing Sn²⁺ cation while enhancing the optical and photophysical properties. The partial replacement of Sn atoms by Ge atoms in the nanostructures effectively fills the high density of Sn vacancies, reducing the surface traps and leading to a longer excitonic lifetime and increased photoluminescence quantum yield. The resultant Sn-Ge nanocrystals-based devices show the highest efficiency of 4.9 %, enhanced by nearly 60 % compared to that of pure Sn nanocrystals-based devices.