YAG:Ce and YAP:Ce – Suitable Fast Detectors for Transmission Mössbauer Spectroscopy

Yttrium aluminum garnet and perovskite activated by cerium are fast mechanically and chemically resistant scintillation materials. Their mechanical properties enable easy and precise machining. Both scintillation materials have a decay time shorter than 100 ns and, therefore, are suitable to use for high counting rates. The luminescence maximum of YAP:Ce and YAG:Ce are 360 and 550 nm, respectively. Their luminescence bands correspond with the sensitivity spectral range of the most widely used photomultipliers. Moreover, the semiconductor light detectors can be used with YAG:Ce scintillation crystals. Theoretical and experimental comparative analysis of characteristics for both YAP:Ce and YAG:Ce detectors and good experience over relatively long periods of using these detectors allow us to draw a conclusion regarding their unconditional advantages over other commonly used detectors for transmission Mössbauer spectroscopy. The considerable improvement in data production enhances the capabilities of Mössbauer spectroscopy as a research and analytical tool.     

Determination of pesticides fenoxycarb and permethrin by sequential injection chromatography using miniaturized monolithic column

Sequential injection chromatography system equipped with miniaturized 10 mm monolithic column was used for fast simultaneous determination of two pesticides—fenoxycarb (FC) and permethrin (PM). The system was composed of a commercial sequential injection analysis (SIA) system (FIAlab^® 3000, 6-port selection valve and 5.0 mL syringe pump), commercially available column Chromolith™ RP-18e (10 mm × 4.6 mm i.d.) (Merck^®, Germany) and CCD UV-vis detector (USB 2000, Ocean-optics) with 1.0 cm Z-flow cell, absorbance was monitored at 225 nm. The mobile phase used for analysis was acetonitrile/water (60:40, v/v), flow rates were 0.6 mL min⁻¹ for elution of fenoxycarb and 1.2 mL min⁻¹ for elution of permethrin. For each analysis 4.8 mL of mobile phase was used. The chromatographic resolution between both compounds was >8 and analysis time was <6.5 min under the optimal conditions. Limits of detection were determined at 2.0 μg mL⁻¹ for fenoxycarb and 1.0 μg mL⁻¹ for permethrin. Samples were prepared by diluting with mobile phase and injected volume was 10 μL for each analysis. Developed method was applied to analysis of both pesticides in veterinary pharmaceutical foams and sprays ARPALIT^® Neo (Aveflor, Czech Republic). SIC method was compared with validated method (HPLC, reverse phase 100 mm monolithic column, gradient elution).     

A luminescent sensor for tyrosine phosphorylation

We have developed a luminogenic probe for tyrosine phosphorylation based on a short peptide sequence containing an iminodiacetate moiety near the site of phosphorylation. In response to kinase activity, the probe provides a strong luminescence enhancement, resulting from the increased ability of the probe to bind and sensitize Tb3+ and Eu3+ ions upon phosphorylation.     

Reaction of graphite fluoride with NaOH-KOH eutectic

Graphite fluoride has been generally considered chemically inert against strong alkalis under ambient conditions. In the present study we demonstrate that treatment of graphite fluoride with eutectic NaOH-KOH mixture at 250 °C induces dramatic structural and textural changes in the solid as evidenced by XRD, FT-IR, Raman, UV-vis absorption and fluorescence and microscopy techniques (TEM, AFM). The reaction proceeds in the molten state leading to water-soluble, graphitized carbon particles which unlike graphite fluoride, adopt a variety of morphologies, like platy, tetragonal, triangular, discoid and spherical. The resulting carbon particles are dispersible in water and fluoresce under UV excitation.     

Reactions of P4S10 and pyPS2Cl with N,N′-diphenylurea and N,N′-diphenylthiourea

The reaction of P₄S₁₀ (1) with N,N′-diphenylurea (PhNH)₂CO (2) results in new heterocyclic compounds: the pyridinium salt of 1,3-diphenyl-2-sulfido-2-thioxo-1,3-diaza-2λ⁵-phosphetidine (3) (with a P–N–C–N cycle) and the pyridinium salt of 1,4-diphenyl-2,5-disulfido-2,5-dithioxo-1,4-dithiadiaza-2λ⁵,5λ⁵-diphosphinane (4), containing the (P–S–N)₂ cycle and the cyclic thiophosphates [pyH]₂[P₂S₈] (5), [pyH]₂[P₂S₇] (6) and [pyH]₃[P₃S₉] (7). A similar reaction, but carried out with N,N′-diphenylthiourea (PhNH)₂CS (8), leads to the formation of 4 and 6. pyPS₂Cl (9), used as an alternative starting material, also yields compounds 3, 4, 5, and further [pyH][PS₂Cl₂] (10) and S₈ after reaction with 2. Compound 3 reacts with Pd(CH₃COO)₂, with the formation of the complex [Pd(Ph₂N₂COPS₂)₂] (11). The crystal structures of 3 and 7 were determined by single-crystal X-ray diffraction.     

Harnessing functional plasticity of enzymes: a fluorogenic probe for imaging 17beta-HSD10 dehydrogenase, an enzyme involved in Alzheimer's and Parkinson's diseases

In this paper, we describe the development of a fluorogenic substrate for 17beta-hydroxysteroid-dehydrogenase type 10 (17beta-HSD10), which is a multifunctional metabolic enzyme fulfilling several metabolic roles (beta-oxidation of fatty acids, catabolism of isoleucine, and metabolism of steroids). In recent years, it has emerged as an important stress and pathological marker in neurons and glial cells (expression down-regulation in Parkinson's disease, up-regulation and association with beta-amyloid peptide in Alzheimer's disease). Through the iterative molecular design and chemical synthesis described herein, compound 1 was developed, which possesses all required properties for a selective optical reporter substrate: alcohol-ketone optical switching, the ability to function as a good enzyme substrate (expressed in kinetic parameters), cell permeability, and cell retention. Probe 1 provides a blue-to-green/yellow bright switch and enables non-invasive, real-time imaging of 17beta-HSD10 in live human cells. The selectivity of reporter 1 was established by the quantitative correlation of metabolic activity to protein expression in human kidney cell line HEK-293T.     

Wiring of glucose oxidase with graphene nanoribbons: an electrochemical third generation glucose biosensor

A reagentless third generation electrochemical glucose biosensor was fabricated based on wiring the template enzyme glucose oxidase (GOx) with graphene nanoribbons (GN) in order to create direct electron transfer between the co-factor (flavin adenine dinucleotide, FAD) and the electrode. The strategy involved: (i) isolation of the apo-enzyme by separating it from its co-enzyme; (ii) preparation of graphene nanoribbons (GN) by oxidative unzipping of multi-walled carbon nanotubes; (iii) adsorptive immobilization of GNs on the surface of a screen printed carbon electrode (SPCE); (iv) covalent attachment of FAD to the nanoribbons; (v) recombination of the apo-enzyme with the covalently bound FAD to the holoenzyme; and (vi) stabilization of the bio-layer with a thin membrane of Nafion. The biosensor (referred to as GN/FAD/apo-GOx/Nafion/SPCE) is operated at a potential of +0.475 V vs Ag/AgCl/{3 M KCl} in flow-injection mode with an oxygen-free phosphate buffer (pH 7.5) acting as a carrier. The signals are linearly proportional to the concentration of glucose in the range from 50 to 2000 mg?L^?1 with a detection limit of 20 mg?L^?1. The repeatability (10 measurements, at 1000 mg?L^?1 glucose) is ±1.4% and the reproducibility (5 sensors, 1000 mg?L^?1 glucose) is ±1.8%. The biosensor was applied to the determination of glucose in human serum.

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Graphical abstract Wiring of the apo-enzyme of glucose oxidase (apo-GOx) with graphene nanoribbons (GN) bound to FAD at a screen-printed carbon electrode (SPCE). Cyclic voltammetric and amperometric responses to various glucose concentrations.

     

Exponential attractors for a class of reaction-diffusion problems with time delays

We consider a reaction-diffusion system subject to homogeneous Neumann boundary conditions on a given bounded domain. The reaction term depends on the population densities as well as on their past histories in a very general way. This class of systems is widely used in population dynamics modelling. Due to its generality, the longtime behavior of the solutions can display a certain complexity. Here we prove a qualitative result which can be considered as a common denominator of a large family of specific models. More precisely, we demonstrate the existence of an exponential attractor, provided that a bounded invariant region exists and the past history decays exponentially fast. This result will be achieved by means of a suitable adaptation of the l-trajectory method coming back to the seminal paper of Málek and Nečas. The first author was partially supported by the Italian PRIN 2006 research project Problemi a frontiera libera, transizioni di fase e modelli di isteresi. The second author was supported by the research project MŠM 0021620839 and by the project LC06052 (Jindřich Nečas Center for Mathematical Modeling).     

Critical evaluation of a new method for quantitative determination of minerals in solid samples

The new method for the Chemical Quantitative Mineral Analysis (CQMA) is presented and critically evaluated. The percentages of minerals are calculated of the elemental bulk chemical analysis using identified minerals and their crystallochemical formulas. For this calculation an optimization procedure is used. CQMA enables also the feedback calculation of the bulk chemical analysis from CQMA calculated mineral contents. Subsequent comparison of the feedback calculated bulk chemical analysis and actual bulk chemical analysis of the same sample is used for critical evaluation of the input data. If necessary the input data are completed and/or reanalyzed and used for repeated calculation to achieve better match between the feedback calculated and actual chemical analyses, which consequently leads to more accurate mineral analysis. Moreover the feedback bulk chemical analysis can be also separately calculated from any mineral analyses determined e.g. by XRD, FTIR and/or optical method. Six German rock reference samples representing a very wide range of minerals and chemical composition of materials were selected and their mineral analyses carried out by CQMA and Rietveld X‐ray diffraction methods. The results were compared with reference mineral analyses and critically evaluated.     

An Ethanol Biosensor Based on Simple Immobilization of Alcohol Dehydrogenase on Fe3O4@Au Nanoparticles

An ethanol biosensor based on alcohol dehydrogenase (ADH) attached to Au seeds decorated on magnetic nanoparticles (Fe₃O₄@Au NPs) is presented. ADH was immobilized on Fe₃O₄@Au NPs, which were subsequently fixed by a magnet on a carbon paste electrode modified with 5 % (m : m) MnO₂. Optimum conditions for the amperometric determination of ethanol with the biosensor were as follows: working potential +0.1 V (vs. Ag/AgCl); supporting electrolyte: 0.1 M phosphate buffer solution at pH 6.8 containing 0.25 mM of the coenzyme (NAD⁺); working electrode: carbon paste with magnetically attached Fe₃O₄@Au NPs (0.012 mg ? cm^?2 electrode area) with immobilized alcohol dehydrogenase (120 units per cm² of electrode area). Linearity between signal and concentration was found for the range from 0.1 to 2.0 M ethanol (r²=0.995) with a detection limit of 0.07 M, a sensitivity of 0.02 µA ? mM^?1 ? cm^?2, a reproducibility of 4.0 % RSD, and a repeatability of 2.7 % RSD. The results for the determination of ethanol in alcoholic beverages showed good agreement with gas chromatography (GC) with recovery of 96.0 – 108.8 %.