Multielement analysis by neutron activation of tissues from swine administered copper supplemented diets

Instrumental neutron activation analysis was used to determine Co, Cu, Fe, Mg, Mn, Se and Zn in tissues from swine fed copper supplemented diets.     

On the lowering of the electronic energy in model insulators due to surface reconstruction

Shubnikov-de Haas oscillations, piezoresistance, Hall mobility, and transverse “Hall” field due to mobility anisotropy have been studied on n-channel (111) Si inversion layers. The valley degeneracy was found to be 2 between 1.7 and 300 K. Under uniaxial mechanical stress the initially isotropic conductivity became strongly anisotropic. All results can be described by the existence of domains in the inversion layer.     

“Living” Radical Polymerization in Tubular Reactors, 2 – Process Optimization for Tailor‐Made Molecular Weight Distributions

“Living” radical polymerization is a relatively new polymerization process that can be used to prepare resins with controlled structures. In this work, a mathematical model developed previously to describe nitroxide‐mediated “living” radical polymerizations performed in tubular reactors is used for the optimization of the process and obtainment of tailor‐made MWDs. Operating conditions and design variables are determined with the help of optimization procedures in order to produce polymers with specified MWDs. It is shown that bimodal and trimodal MWDs, with given peak locations, can be obtained through proper manipulation of the operating conditions. This indicates that the technique discussed in this work is suitable for detailed design of the MWD of the final polymer.

     

Classification of tight regular polyhedra

A regular polyhedron of type \(\{p, q\}\) has at least 2pq flags, and it is called tight if it has exactly 2pq flags. The values of p and q for which there exist tight orientably regular polyhedra were previously known. We determine for which values of p and q there is a tight non-orientably regular polyhedron of type \(\{p, q\}\). Furthermore, we completely classify tight regular polyhedra in terms of their automorphism groups.     

The Double‐Histidine Cu2+‐Binding Motif: A Highly Rigid,Site‐Specific Spin Probe for Electron Spin Resonance Distance Measurements

The development of ESR methods that measure long‐range distance distributions has advanced biophysical research. However, the spin labels commonly employed are highly flexible, which leads to ambiguity in relating ESR measurements to protein‐backbone structure. Herein we present the double‐histidine (dHis) Cu²⁺‐binding motif as a rigid spin probe for double electron–electron resonance (DEER) distance measurements. The spin label is assembled in situ from natural amino acid residues and a metal salt, requires no postexpression synthetic modification, and provides distance distributions that are dramatically narrower than those found with the commonly used protein spin label. Simple molecular modeling based on an X‐ray crystal structure of an unlabeled protein led to a predicted most probable distance within 0.5 Å of the experimental value. Cu²⁺ DEER with the dHis motif shows great promise for the resolution of precise, unambiguous distance constraints that relate directly to protein‐backbone structure and flexibility.     

Reversible and Selective CO2 to HCO2− Electrocatalysis near the Thermodynamic Potential

Reversible catalysis is a hallmark of energy-efficient chemical transformations, but can only be achieved if the changes in free energy of intermediate steps are minimized and the catalytic cycle is devoid of high transition-state barriers. Using these criteria, we demonstrate reversible CO₂/HCO₂⁻ conversion catalyzed by [Pt(depe)₂]²⁺ (depe=1,2-bis(diethylphosphino)ethane). Direct measurement of the free energies associated with each catalytic step correctly predicts a slight bias towards CO₂ reduction. We demonstrate how the experimentally measured free energy of each step directly contributes to the <50 mV overpotential. We also find that for CO₂ reduction, H₂ evolution is negligible and the Faradaic efficiency for HCO₂⁻ production is nearly quantitative. A free-energy analysis reveals H₂ evolution is endergonic, providing a thermodynamic basis for highly selective CO₂ reduction.     

Biochemical sensor tubing for point-of-care monitoring of intravenous drugs and metabolites

In medical facilities, there is strong motivation to develop detection systems that can provide continuous analysis of fluids in medical tubing used to either deliver or remove fluids from a patient's body. Possible applications include systems that increase the safety of intravenous (IV) drug injection and point-of-care health monitoring. In this work, we incorporated a surface-enhanced Raman scattering (SERS) sensor comprised of an array of closely spaced metal nanodomes into flexible tubing commonly used for IV drug delivery and urinary catheters. The nanodome sensor was fabricated by a low-cost, large-area process that enables single use disposable operation. As exemplary demonstrations, the sensor was used to kinetically detect promethazine (pain medication) and urea (urinary metabolite) within their clinically relevant concentration ranges. Distinct SERS peaks for each analyte were used to demonstrate separate detection and co-detection of the analytes.     

Quick detection of contaminants leaching from polypropylene centrifuge tubes with surface‐enhanced Raman spectroscopy and ultraviolet absorption spectroscopy

Anomalous surface‐enhanced Raman scattering (SERS) peaks were identified for liquid sample stored in polypropylene (PP) centrifuge tubes for months. We observed unexpected Raman peaks during experiments with thiamine hydrochloride aqueous solutions stored in PP tubes for 2 months. In order to identify the contaminants, we have performed SERS experiments on deionized (DI) water stored in PP centrifuge tubes for 2 months and compared them with those from fresh DI water sample. We have also carried out ultraviolet (UV) absorption spectra for both fresh and contaminated water. We believe that the water is contaminated because of chemicals leaching from the PP tube. From the gas chromatography‐mass spectrometry data, the main contaminants were found to be phthalic acid (PA) and its derivatives. Further SERS and UV absorption experiment for PA correlated well with the anomalous peaks identified earlier. We qualitatively confirmed the identification and quantitatively estimated the concentration of the suspect contaminants as between 1 and 10 µM with both SERS and UV absorption spectroscopy. With UV absorption spectroscopy, we precisely estimated the concentration as 2.1 µM . We have shown that the sample in PP tube can be contaminated by the leaching chemicals upon long‐term storage, and suggest SERS and UV absorption spectroscopy as two quick and simple techniques to detect the contamination. Copyright © 2011 John Wiley & Sons, Ltd.     

Recent progress in nitroxide-mediated polymerizations in miniemulsion

Recent developments in nitroxide-mediated polymerizations conducted in emulsion and miniemulsion have advanced the field across a range of both experimental and theoretical fronts. This article reviews progress in bicomponent initiating systems (including use of camphorsulfonic acid to enhance rate), unimolecular initiating systems, miniemulsions not requiring the use of volatile costabilizers, polymerization of acrylates, mathematical modeling and simulation, and theoretical understanding with regards to issues such as compartmentalization, preservation of polymer chain livingness, the role of aqueous phase kinetics and phase partitioning. These topics are discussed and analyzed to present an integrated portrait of the current status of nitroxide-mediated polymerizations in emulsion/miniemulsion and to identify the most pressing concerns, issues, and opportunities. To cite this article: M.F. Cunningham, C. R. Chimie 6 (2003).