Solid-state Reactions and Phase Relations in the Ti-Si-O System at 1373 K

Reactions between Ti and SiO₂ were studied at 1373 K (1100°C) under vacuum conditions using planar diffusion couples. A method to correct for the presence of surface oxide was developed which led to improved oxygen measurements with the electron probe microanalyzer. An isothermal section through the Ti-Si-O phase diagram at 1373 K was determined using measured diffusion paths and phase compositions in equilibrated alloys. The experimentally determined isothermal section was compared to isothermal sections calculated using thermodynamic data. In addition the sequence of reaction layers formed in the diffusion couples is discussed in terms of thermodynamic activity diagrams.     

Cloning and sequencing of the URA3 gene of Kluyveromyces marxianus CBS 6556

The URA3 gene, coding for orotidine-5′-phosphate decarboxylase, from Kluyveromyces marxianus CBS 6556, was isolated from a genomic DNA library. The K. marxianus URA3 gene encodes a protein of 267 amino acids with a calculated molecular weight of 29·3 kDa. Comparison of the K. marxianus protein with the corresponding enzymes of Saccharomyces cerevisiae and Kluyveromyces lactis showed amino acid sequence identifies of 81% and 88%, respectively. Using contour-clamped homogeneous electric field gel electrophoresis, the genomic copy was found to be located on chromosome VI. We have used the cloned gene for the construction of a K. marxianus leu2 mutant. This mutant contains no heterologous sequences, which is essential to make it acceptable for application in the food industry.     

The effect of processing conditions on glucosinolates in cruciferous vegetables

Summary Glucosinolates are found naturally in cruciferous plants, such asbrassica vegetables, which are important in the human diet. Glucosinolates are readily converted into a range of physiologically active compounds by hydrolysis under the influence of an endogenous thioglucosidase, which becomes active when plant cells are disrupted. Cruciferous vegetables are eaten raw, they are also consumed in the processed form. The influence of processing conditions on glucosinolate degradation and on the type and levels of the reaction products formed is reviewed.

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Der Einfluß von Prozeßbedingungen auf Glucosinolate in Cruciferen-Gemüse

Zusammenfassung Glucosinolate kommen naturgemäß in Kreuzblütlern vor, wie z. B. inBrassica-Gemüse, welche einen wesentlichen Bestandteil der Nahrung bilden. Glucosinolate werden leicht umgesetzt in eine Reihe physiologisch aktiver Verbindungen unter Einfluß einer endogenen Thioglucosidase, welche aktiv wird, wenn das pflanzliche Gewebe zerstört wird. Die Cruciferen-Gemüse werden roh, aber auch in verarbeiteter Form, gegessen. Der Einfluß der Verarbeitung auf den Abbau der Glucosinolate, sowie auf Art und Menge der gebildeten Reaktionssprodukte, wird besprochen.

     

Ligand-Tuning of the Stability of Pd(II) Conjugates with Cyanocobalamin

Besides the well-known functions performed by vitamin B₁₂ (CblCN) in biochemical processes of the human body, an increasing interest has been raised by the possibility of its use as a transmembrane drug carrier, capable, among others, of enhancing the accumulation of inorganic cytostatics in cancer cells. The present study was aimed at determining the possibility of the formation of CblCN conjugates with Pd(II) complexes. A key aspect was their stability, which we attempted to tune by appropriate choice of ligands. Syntheses, spectroscopic analysis of postreaction systems and kinetic investigations of conjugate formation reactions, have been complemented by DFT modelling. The obtained results showed that ligand charge, geometry and electron affinity may have a significant impact on carrier binding and release leading to the activation of the Pd(II) complex. This provides a rationale to expect that with appropriate composition of the coordination sphere, it will be possible to extend the spectrum of less toxic inorganic chemotherapeutics.     

From Geometry to Activity: A Quantitative Analysis of WO3/Si Micropillar Arrays for Photoelectrochemical Water Splitting

The photoelectrochemical (PEC) activity of microstructured electrodes remains low despite the highly enlarged surface area and enhanced light harvesting. To obtain a deeper understanding of the effect of 3D geometry on the PEC performance, well‐defined WO₃/n‐Si and WO₃/pn‐Si micropillar arrays are fabricated and subjected to a quantitative analysis of the relationship between the geometry of the micropillars (length, pitch) and their PEC activity. For WO₃/n‐Si micropillars, it is found that the photocurrent increases for WO₃/n‐Si pillars, but not in proportion to the increase in surface area that results from increased pillar length or reduced pillar pitch. Optical simulations show that a reduced pillar pitch results in areas of low light intensity due to a shadowing effect. For WO₃/pn‐Si micropillar photoelectrodes, the p–n junction enhances the photocurrent density up to a factor of 4 at low applied bias potential (0.8 V vs RHE) compared to the WO₃/n‐Si. However, the enhancement in photocurrent density increases first and then decreases with reduced pillar pitch, which scales with the photovoltage generated by the p–n junction. This is related to an increased dead layer of the p–n junction Si surface, which results in a decreased photovoltage even though the total surface area increases.     

Investigation of 1 GPa Controlled Clearance Piston Gauge Using Finite Element Analysis

A one GPa controlled clearance piston gauge used as a high pressure standard at KRISS was investigated. In establishing the high pressure standard, the distortion coefficient is one of the most important parameters, but it is not easy to determine. The conventional analysis using a Heydemann–Welch model has a problem when determining a stall pressure, because of the nonlinear characteristic of fall rates with respect to pressure. Some metrological characteristics, such as the distortion coefficient of the piston–cylinder assembly in free deformation (FD) mode and the jacket distortion coefficient and stall pressure in controlled clearance (CC) mode, were investigated using a finite element analysis (FEA). In particular, it was determined that the relation of cubic fall rate to jacket pressure becomes nonlinear above 600 MPa. The FEA results were verified by comparison with a 500 MPa pressure standard and a fall rate measurement of 1 GPa. The most important parameter, the distortion coefficient in the FD and CC mode, was determined to be (7.59 ± 0.24) × 10−7 MPa−1 and (3.35 ± 0.39) × 10−7 MPa−1, respectively. A zero-distortion coefficient was obtained in the FEA when around 17% of the applied pressure was used as the jacket pressure. This value was similar to the experimentally determined result of around 20%.     

Stabilization of the Reductase Domain in the Catalytically Self‐Sufficient Cytochrome P450BM3 by Consensus‐Guided Mutagenesis

The multidomain, catalytically self‐sufficient cytochrome P450 BM‐3 from Bacillus megaterium (P450_BM3) constitutes a versatile enzyme for the oxyfunctionalization of organic molecules and natural products. However, the limited stability of the diflavin reductase domain limits the utility of this enzyme for synthetic applications. In this work, a consensus‐guided mutagenesis approach was applied to enhance the thermal stability of the reductase domain of P450_BM3. Upon phylogenetic analysis of a set of distantly related P450s (>38 % identity), a total of 14 amino acid substitutions were identified and evaluated in terms of their stabilizing effects relative to the wild‐type reductase domain. Recombination of the six most stabilizing mutations generated two thermostable variants featuring up to tenfold longer half‐lives at 50 °C and increased catalytic performance at elevated temperatures. Further characterization of the engineered P450_BM3 variants indicated that the introduced mutations increased the thermal stability of the FAD‐binding domain and that the optimal temperature (T_opt) of the enzyme had shifted from 25 to 40 °C. This work demonstrates the effectiveness of consensus mutagenesis for enhancing the stability of the reductase component of a multidomain P450. The stabilized P450_BM3 variants developed here could potentially provide more robust scaffolds for the engineering of oxidation biocatalysts.     

The FAST module: an add-on unit for driving commercial scanning probe microscopes at video rate and beyond

We present the design and the performance of the FAST (Fast Acquisition of SPM Timeseries) module, an add-on instrument that can drive commercial scanning probe microscopes (SPM) at and beyond video rate image frequencies. In the design of this module, we adopted and integrated several technical solutions previously proposed by different groups in order to overcome the problems encountered when driving SPMs at high scanning frequencies. The fast probe motion control and signal acquisition are implemented in a way that is totally transparent to the existing control electronics, allowing the user to switch immediately and seamlessly to the fast scanning mode when imaging in the conventional slow mode. The unit provides a completely non-invasive, fast scanning upgrade to common SPM instruments that are not specifically designed for high speed scanning. To test its performance, we used this module to drive a commercial scanning tunneling microscope (STM) system in a quasi-constant height mode to frame rates of 100 Hz and above, demonstrating extremely stable and high resolution imaging capabilities. The module is extremely versatile and its application is not limited to STM setups but can, in principle, be generalized to any scanning probe instrument.     

Interdependent Regulation of Polycystin Expression Influences Starvation-Induced Autophagy and Cell Death

Autosomal dominant polycystic kidney disease (ADPKD) is mainly caused by deficiency of polycystin-1 (PC1) or polycystin-2 (PC2). Altered autophagy has recently been implicated in ADPKD progression, but its exact regulation by PC1 and PC2 remains unclear. We therefore investigated cell death and survival during nutritional stress in mouse inner medullary collecting duct cells (mIMCDs), either wild-type (WT) or lacking PC1 (PC1KO) or PC2 (PC2KO), and human urine-derived proximal tubular epithelial cells (PTEC) from early-stage ADPKD patients with PC1 mutations versus healthy individuals. Basal autophagy was enhanced in PC1-deficient cells. Similarly, following starvation, autophagy was enhanced and cell death reduced when PC1 was reduced. Autophagy inhibition reduced cell death resistance in PC1KO mIMCDs to the WT level, implying that PC1 promotes autophagic cell survival. Although PC2 expression was increased in PC1KO mIMCDs, PC2 knockdown did not result in reduced autophagy. PC2KO mIMCDs displayed lower basal autophagy, but more autophagy and less cell death following chronic starvation. This could be reversed by overexpression of PC1 in PC2KO. Together, these findings indicate that PC1 levels are partially coupled to PC2 expression, and determine the transition from renal cell survival to death, leading to enhanced survival of ADPKD cells during nutritional stress.