Biosensing approach for glutathione detection using glutathione reductase and sulfhydryl oxidase bienzymatic system

Chitosan membrane with glutathione reductase and sulfhydryl oxidase (SOX) was subsequently integrated onto the surface of spectrographic graphite rods for obtaining a glutathione biosensor. The working principle was based on the monitoring of O₂ consumption that correlates the concentration of glutathione during the enzymatic reaction. A linear relationship between sensor response and concentration was obtained between 0.5 and 2.0 mM for oxidized glutathione (GSSG), and 0.2–1.0 mM for reduced glutathione (GSH) in the presence of 2 μM nicotinamide adenine dinucleotide phosphate (NADPH) under the optimum working conditions. Also, reduced/oxidized glutathione were separated by HPLC and utility of bienzymatic system was investigated as an electrochemical detector for the analysis of these compounds. All data were given as a comparison of two systems: biosensor and diode array detector (DAD).     

Characterization of silk fibroin based films loaded with rutin–β-cyclodextrin inclusion complexes

In this study, cyclodextrin inclusion complexes with rutin were prepared via co-precipitation method. Stability constant and solubility energy of beta-cyclodextrin complex were calculated as 262 M^?1 and 1,737 kJ mol^?1, respectively. Aqueous solubility of rutin was increased with inclusion complex of beta-cyclodextrin. The effect of temperature on both aqueous solubility of free rutin, and its inclusion complex was also studied. Characterization of cyclodextrin complexes were conducted with UV–Vis spectrophotometry, Fourier transform infrared spectroscopy, X-ray diffractometry, differential scanning calorimetry, thermal gravimetric analysis, nuclear magnetic resonance spectroscopy and scanning electron microscopy techniques. Characterization results supported formation of inclusion complexes. Dissolution profiles of rutin, physical mixture and inclusion complex of rutin were observed at 37 °C. Dissolution results proved the effect of cyclodextrin addition on solubility rate of rutin. After loading rutin and its complexes into silk fibroin based films, release tests were performed at 37 °C in neutral pH conditions for 24 h. Most of the rutin were released from silk fibroin films within the first 5 h and the rest of it was released slowly (sustained release). Electron microscope analyses showed that films had homogenous and dense morphologies. These results revealed that silk fibroin is useful for preparing bioactive films loaded with natural compounds and for modifying their release behaviour at physiological conditions.     

Site-selective modification of proteins for the synthesis of structurally defined multivalent scaffolds

A combination of classical site-directed mutagenesis, genetic code engineering and bioorthogonal reactions delivered a chemically modified barstar protein with one or four carbohydrates installed at specific residues. These protein conjugates were employed in multivalent binding studies, which support the use of proteins as structurally defined scaffolds for the presentation of multivalent ligands.     

The Synthesis of Sodium Sulfide Pentahydrate,Na2S·5H2O,Through a Solid-Gas Reaction of Sulfidizing Gas Mixture with Sodium Carbonate,Na2CO3

In this study, the sulfidization of Na₂CO₃ was investigated by using a solid-gas reaction under a sulfidizing gas mixture, which consisted of COS, CS₂, and S₂ gases.

Sodium sulfide pentahydrate, Na₂S·5H₂O, was prepared from sodium carbonate, Na₂CO₃, via a sulfidizing gas mixture by a solid-gas reaction under the cooling of a nitrogen atmosphere. The observed phase was found to be the pentahydrated form of sodium sulfide. This crystalline form was determined by X-ray powder diffraction (XRD) technique. Since sodium sulfide is strongly hygroscopic, the pentahydrated crystalline form was observed in XRD measurements for all repeated experiments. The crystal unit cell parameters of the synthesized product were in excellent agreement with values given in the JCPDS card number 18-1249. The sodium sulfide pentahydrate has an orthorhombic crystal structure with the unit cell parameters of a = 6.475, b = 12.55, C = 8.655 Å, space group, Cmcm and Z = 4.     

Laterally‐Graded SiGe Crystals for High Resolution Synchrotron Optics

A novel type of optical element for synchrotron radiation applications in the X‐ray region: namely laterally‐graded aperiodic crystals on the basis of Si_1‐xGe_x mixed crystal is presented. The lattice parameter of such gradient crystals containing up to some at. % Ge changes nearly linearly along the plane of diffraction. Thus the variation of the Bragg angle of divergent incident light on the crystal can be compensated. This opens up the possibility to operate a crystal monochromator in nearly crystal limited resolution in the whole energy range above 2 keV at the full vertical synchrotron source divergence without a collimating pre‐mirror. Simultaneously the reflected spectral intensity can be increased considerably as compared with a conventional Si‐crystal monochromator.     

Nanoresolution interface studies in thin films by synchrotron x‐ray diffraction and by using x‐ray waveguide structure

In the last years we performed several measurements with synchrotron radiation of several facilities to reveal interesting interface phenomena on the nanoscale. We used both x‐ray diffraction [1] , [2] (XRD) and spectrometry techniques. In this paper, we briefly summarize the results obtained from diffraction measurements, which lead us to our recent grazing incidence x‐ray fluorescence analysis (GIXRF) and extended x‐ray absorption fine structure (EXAFS) experiments. We show how a combination of experimental methods of GIXRF analysis and EXAFS spectroscopy in fluorescence detection with x‐ray standing waves (XSW) technique was applied for the depth profiling of a‐Si/Co/a‐Si layers with nanometer resolution to monitor the growth of CoSi intermetallic phase. The investigated layers were placed into the waveguide structure formed by two Ta films to increase sensitivity and accuracy of the measurements. Copyright © 2009 John Wiley & Sons, Ltd.     

Advanced piezoelectric crystal Ca3TaGa3Si2O14: growth,crystal structure perfection,and acoustic properties

A five-component crystal of the lanthanum–gallium silicate family Ca₃TaGa₃Si₂O₁₄ (CTGS) was grown by the Czochralski method. The CTGS crystal, like the langasite crystal (La₃Ga₅SiO₁₄, LGS), possesses unique temperature properties and the fewer number of the Ga atoms in the unit cell makes the density much lower and, consequently, increases the velocity of acoustic wave propagation. The unit-cell parameters were determined by the powder diffraction technique. The defects in the CTGS crystal structure were studied by X-ray topography, which enables the visualization of growth banding characteristics of crystals grown by the Czochralski method. Surface acoustic wave (SAW) propagation in the CTGS crystal was investigated by the high-resolution X-ray diffraction method on the BESSY II synchrotron radiation source. The velocities of propagation and power flow angles of SAWs in the Y- and X-cuts of the CTGS crystal were determined from the X-ray diffraction spectra.     

Submicrometer hard X‐ray focusing using a single‐bounce ellipsoidal capillary combined with a Fresnel zone plate

A single‐bounce capillary with an ellipsoidal shape has been used for two‐step focusing in combination with a Fresnel zone plate (FZP). The FZP serves as a first microfocusing element and produces a demagnified micrometer image of the source, before the elliptical capillary makes a last final compression of the beam. With 15 keV X‐rays from the European Synchrotron Radiation Facility BM5 bending magnet, the two‐step demagnification system produced a focus of about 250 nm with a gain of more than 1000. The use of an ellipsoidal capillary as a micro‐mirror under off‐axis illumination using micro‐prefocusing optics might open up new opportunities in nanofocusing developments.     

Energetics of carbon nanotubes

We have investigated the energetics of carbon nanotubes. Calculations have been performed by using the empirical many-body potential energy function developed by Tersoff for carbon. Received: 30 March 1998 / Accepted: 28 July 1998