Substituted phenols as ligands III: Crystal and molecular structure of bis(4-formyl-2-methoxyphenolato)bis(pyridine)copper(II) monohydrate

Bis(4-formyl-2-methoxyphenolato)bis(pyridine)copper(II) monohydrate crystallizes in the triclinic system:a = 10·432,b = 9·342,c = 13·799 Å, = 103·75, = 100·53, = 100·81 °,Z = 2, space groupP¯1.The structure was determined by Fourier methods with Cuk diffractometer data, and refined by a combination of block-diagonal and full-matrix least squares toR = 0·068 for 2430 observed reflexions.The copper atoms occupy the special positions 0, 0, 0 and 0,1/2, 1/2; hence, both molecules are centrosymmetric. Both the methoxy and phenolic oxygen atoms of the phenolate ions coordinate to the metal. These, together with coordinated nitrogen atoms from the pyridine molecules, give the copper atoms a six-fold coordination.Hydrogen bonding between a water molecule and the phenolic oxygen atoms of adjacent molecules results in chains of molecules linked approximately along [011].     

Recent advances in low oxidation state aluminium chemistry

The synthesis and isolation of novel low oxidation state aluminium (Al) compounds has seen relatively slow progress over the 30 years since such species were first isolated. This is largely due to the significant challenges in isolating these thermodynamically unstable compounds. Despite challenges with isolation, their reactivity has been widely explored and they have been utilized in a wide range of processes including the activation of strong chemicals bonds, as ligands to transition metals and in the formation of heterobimetallic M–M compounds. As such, attempts to isolate novel low oxidation state Al compounds have continued in earnest and in the last few years huge advances have been made. In this review we highlight the remarkable recent developments in the low oxidation state chemistry of aluminium and discuss the variety of new reactions these compounds have made possible.

Documenting the synthesis and isolation of novel low oxidation state aluminium (Al) compounds, which until recently has seen relatively slow progress over the 30 years since such species were first isolated.     

Numerical simulation of neutron radiation effects in avalanchephotodiodes

A new one-dimensional (1-D) device model developed for the simulation of neutron radiation effects in silicon avalanche photodiodes is described. The model uses a finite difference technique to solve the time-independent semiconductor equations across a user specified structure. The model includes impact ionization and illumination allowing accurate simulation with minimal assumptions. The effect of neutron radiation damage is incorporated via the introduction of deep acceptor levels subject to Shockley-Read-Hall statistics. Preliminary analysis of an EG&G reverse APD structure is compared with experimental data from a commercial EG&G C30719F APD     

Effect of PECVD of SiO2 passivation layers on GaN and InGaP

Thin (200 ) layers of SiO₂ were deposited by plasma enhanced chemical vapor deposition onto GaN and InGaP patterned with transmission line measurement contact pads. The sheet resistance of n-GaN and n- and p-InGaP was measured as a function of N₂O/SiH₄ ratio, rf chuck power, pressure and substrate temperature during the SiO₂ deposition. The sheet resistance ratio before and after the deposition varied from 0.7 to 1.2, reflecting a competition between mechanisms that decrease doping (hydrogen passivation, ion-induced deep traps) and those that increase it (creation of shallow donor states in n-type material through preferential ion of the group V elements, gettering of hydrogen in p-type material). Under most conditions, SiO₂ deposition creates minimal changes to the electrical properties of GaN and InGaP.     

High-speed modulation of 850-nm intracavity contacted shallowimplant-apertured vertical-cavity surface-emitting lasers

GaAs-AlGaAs quantum-well (850 nn) vertical-cavity surface-emitting lasers, with lateral current injection and shallow implanted apertures, show small signal modulation bandwidths of at least 11 GHz and large signal data rates of at least 10 Gb/s. The devices achieved a maximum output power of 2.1 mW, with a threshold current and voltage of 1 mA and 1.71 V, respectively. The shallow implantation step provides photolithographically precise aperture formation (using O⁺ ions), for efficient lateral current injection into the quantum-well active region of the laser, from intracavity contacts. The device aperture was 7 μm in diameter, and the opening in the annular top contact was 13 μm in diameter. The optical spectrum showed several transverse modes     

Potential of fermentation profiling via rapid measurement of amino acid metabolism by liquid chromatography-tandem mass spectrometry

Monitoring amino acid metabolism during fermentation has significant potential from the standpoint of strain selection, optimizing growth and production in host strains, and profiling microbial metabolism and growth state. A method has been developed based on rapid quantification of underivatized amino acids using liquid chromatography-electrospray tandem mass spectrometry (LC-MS-MS) to monitor the metabolism of 20 amino acids during microbial fermentation. The use of a teicoplanin-based chiral stationary phase coupled with electrospray tandem mass spectrometry allows complete amino acid analyses in less than 4 min. Quantification is accomplished using five isotopically labeled amino acids as internal standards. Because comprehensive chromatographic separation and derivatization are not required, analysis time is significantly less than traditional reversed- or normal-phase LC-based amino acid assays. Intra-sample precisions for amino acid measurements in fermentation supernatants using this method average 4.9% (R.S.D.). Inter-day (inter-fermentation) precisions for individual amino acid measurements range from 4.2 to 129% (R.S.D.). Calibration curves are linear over the range 0-300 microg/ml, and detection limits are estimated at 50-450 ng/ml. Data visualization techniques for constructing semi-quantitative fermentation profiles of nitrogen source utilization have also been developed and implemented, and demonstrate that amino acid profiles generally correlate with observed growth profiles. Further, cellular growth events, such as lag-time and cell lysis can be detected using this methodology. Correlation coefficients for the time profiles of each amino acid measured illustrate that while several amino acids are differentially metabolized in similar fermentations, a select group of amino acids display strong correlations in these samples, indicating a sub-population of analytes that may be most useful for fermentation profiling.