Electrodeposition of uranium dioxide films

Uranium dioxide films in a hydrated form are electrodeposited unto nickel plates starting with a uranyl nitrate solution in ammonium sulfate. The process is incidental to water splitting which is the dominant electrochemical pathway and as a consequence, the uranium deposition is highly dependent on experimental parameters that require close control such as the pH and concentration of the supporting electrolyte as well as current density, and the cell design. This revised version was published online in July 2006 with corrections to the Cover Date.     

The influence of Mg substitution for Al on the properties of SiMeRE oxynitride glasses

The thermal-mechanical properties of 60Si20Mg20RE (RE: rare earth) oxynitride glasses can be tailored by the substitution of rare earths of decreasing ionic size. The Young’s modulus, hardness, glass transition temperature and viscosity all increase with the substitution La by Gd and Gd by Lu while the thermal expansion coefficients decrease. Compared to the 55Si25Al20RE oxynitride glasses, replacement of Al by Mg lowers the glass transition temperatures and viscosities and raises the thermal expansion coefficients substantially. On the other hand, the Young’s moduli are higher in the Mg-bearing glasses. These behaviors are seen to be a result in changes in the nature of the bonding in the glass structure.     

The Use of Immobilized Cytochrome P4502C9 in PMMA-Based Plug Flow Bioreactors for the Production of Drug Metabolites

Cytochrome P450 enzymes play a key role in the metabolism of pharmaceutical agents. To determine metabolite toxicity, it is necessary to obtain P450 metabolites from various pharmaceutical agents. Here, we describe a bioreactor that is made by immobilizing cytochrome P450 2C9 (CYP2C9) to a poly(methyl methacrylate) surface and, as an alternative to traditional chemical synthesis, can be used to biosynthesize P450 metabolites in a plug flow bioreactor. As part of the development of the CYP2C9 bioreactor, we have studied two different methods of attachment: (1) coupling via the N-terminus using N-hydroxysulfosuccinimide 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide and (2) using the Ni(II) chelator 1-acetato-4-benzyl-triazacyclononane to coordinate the enzyme to the surface using a C-terminal histidine tag. Additionally, the propensity for metabolite production of the CYP2C9 proof-of-concept bioreactors as a function of enzyme attachment conditions (e.g., time and enzyme concentration) was examined. Our results show that the immobilization of CYP2C9 enzymes to a PMMA surface represents a viable and alternative approach to the preparation of CYP2C9 metabolites for toxicity testing. Furthermore, the basic approach can be adapted to any cytochrome P450 enzyme and in a high-throughput, automated process.     

Mass spectrometric analysis reveals O-methylation of pyruvate kinase from pancreatic cancer cells

Pyruvate kinase (PK) is an important glycolytic enzyme that catalyzes the dephosphorylation of phosphoenolpyruvate to pyruvate. Human PK isozyme M2 (PKM2), a splice variant of M1, is overexpressed in many cancer cells, and PKM2 has been investigated as a potential tumor marker for diagnostic assays and as a target for cancer therapy. To facilitate identification and characterization of PK, we studied the enzyme from pancreatic cancer cells and normal pancreatic duct cells by electrophoresis and mass spectrometry, and identified multiple O-methylated residues from PK. These findings advance our knowledge of the biochemical properties of PK and will be important in understanding its biological function in cells.

The Return of the Frequency Sweep: Designing Adiabatic Pulses for Contemporary NMR

Frequency-modulated (FM) pulses that function according to adiabatic principles are becoming increasingly popular in many areas of NMR. Often adiabatic pulses can extend experimental capabilities and minimize annoying experimental imperfections. Here, adiabatic principles and some of the current methods used to create these pulses are considered. The classical adiabatic rapid passage, which is a fundamental element upon which all adiabatic pulses and sequences are based, is analyzed using vector models in different rotating frames of reference. Two methods to optimize adiabaticity are described, and ways to tailor modulation functions to best satisfy specific experimental needs are demonstrated. Finally, adiabatic plane rotation pulses and frequency-selective multiple spin-echo sequences are considered.     

Characterization of a system generating a homogeneous isotropic turbulence field by free synthetic jets

A facility inspired by Hwang and Eaton (2004a, b) for generating a homogeneous isotropic turbulence was built, the objective being to study evaporating droplets in the presence of turbulence. Turbulence was produced by the mixing of six synthetic jets, in ambient atmosphere. Combined PIV and LDA techniques were used to measure the statistical turbulence properties. The turbulence produced was found to be homogeneous isotropic with a small mean flow within a domain having an average size of 50 mm × 50 mm × 50 mm. The rms fluctuations were of the order of 0.9 m/s, corresponding to a Taylor Reynolds number of 240 and an integral length scale of about 40 mm. This apparatus proved to be well suited to the study of the evaporation of droplets in a controlled turbulence field.