Cyclopropyl halides. Electron transfer in the lithium aluminum hydride reduction of gemdibromo and monobromocyclopropanes.

The stereochemistry of reduction of mixtures of r-1-bromo-1-deuterio-c- and t-2-phenylcyclopropane and the cyclized products from 1,1-dibromo-2-(3-butenyl cyclopropane upon reduction with lithium aluminum hydride give evidence of a configurationally equilibrated cyclopropyl radical as a reaction intermediate.     

Selective manipulation of steroid hydroxyl groups with boronate esters: Efficient access to antigenic C-3 linked steroid-protein conjugates and steroid sulfate standards for drug detection

The temporary protection of 17alpha-alkyl-5alpha-androstane-3beta,16beta,17beta triols as boronate esters is an efficient method for their regioselective functionalisation. This has been applied to the synthesis of protein-steroid conjugates 7-10 suitable for the development of immunoassays targeting classes of steroids banned from competition in Australian horse racing and other sports. The synthesis of steroids sulfate conjugates 42 and 44 for use as reference standards is also reported.     

Kinetics of AgI precipitation from AgCl as affected by background electrolyte

Iodide retention by AgCl, a potential sorbent in high-level waste (HLW) storage systems, was determined. The kinetics and steady state sorption of iodide were determined in single and mixed electrolytes of NaNO₃, and NaCl at ionic strengths of 25 and 50 mM. Iodide retention involved the conversion of AgCl to AgI. This conversion increased rapidly within 0.02 hours, and retention maxima of 0.92 and 1.0 mol·l·mol⁻¹ Ag occurred for low and high ionic strengths, respectively. These short-term studies indicated that AgCl would be an effective scavenger of I⁻ in HLW containment systems.     

Transport and time dependent small angle X‐ray morphology in metal cation and polymer modified perfluorocarbon ionomers

Transport and absorption in metal cation exchanged and polyvinylpyrrolidone (PVP) modified Nafion® films were studied by various techniques. To understand the microscopic basis for permeation, time resolved small angle X‐ray scattering (SAXS) was used to characterize the ionic domain morphology while films were exposed to vapors of water, dimethyl methylphosphonate (DMMP), or triethyl phosphate. Macroscopic weight uptake studies of DMMP vapor into PVP‐Nafion® were also used to help explain the SAXS absorption studies and DMMP permeation properties. The SAXS results were correlated with macroscopic permeation rates of DMMP, Soman, and water through several different membranes. To provide additional basis for the SAXS derived morphologies, tapping‐mode AFM was also used to image the 3–5 nm diameter ionic domains. A goal for protective suit applications is to find films with a balance of high moisture permeation rate for comfort, and low DMMP permeation. The best balance of properties in this context was found with PVP‐ and zirconyl‐modified films. In another extreme, the permeation rates of both water and DMMP through cesium‐modified Nafion® were low. SAXS studies were used to explain this where the ionic domains of cesium‐modified Nafion® did not “expand” when exposed to DMMP or water vapor. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 284–298, 2009     

Synthesis of amine- and thiol-modified nucleoside phosphoramidites for site-specific introduction of biophysical probes into RNA

For studies of RNA structure, folding, and catalysis, site-specific modifications are typically introduced by solid-phase synthesis of RNA oligonucleotides using nucleoside phosphoramidites. Here, we report the preparation of two complete series of RNA nucleoside phosphoramidites; each has an appropriately protected amine or thiol functional group. The first series includes each of the four common RNA nucleotides, U, C, A, and G, with a 2'-(2-aminoethoxy)-2'-deoxy substitution (i.e., a primary amino group tethered to the 2'-oxygen by a two-carbon linker). The second series encompasses the four common RNA nucleotides, each with the analogous 2'-(2-mercaptoethoxy)-2'-deoxy substitution (i.e., a tethered 2'-thiol). The amines are useful for acylation and reductive amination reactions, and the thiols participate in displacement and oxidative cross-linking reactions, among other likely applications. The new phosphoramidites will be particularly valuable for enabling site-specific introduction of biophysical probes and constraints into RNA.     

Characterization and imaging in optically scattering media by use of laser speckle and a variable-coherence source

We demonstrate the application of laser-speckle statistics formed by a variable-coherence source illuminating a scattering medium, for determining the scattering parameter mu;(s)>(?) of a diffusion model for the medium. Furthermore, we apply this technique to visualize laterally localized inhomogeneities embedded within a highly scattering sample.     

Observation of broadband self-amplified spontaneous coherent terahertz synchrotron radiation in a storage ring

Bursts of coherent synchrotron radiation at far-infrared and millimeter wavelengths have been observed at several storage rings. A microbunching instability has been proposed as the source for the bursts. However, the microbunching mechanism has yet to be elucidated. We provide the first evidence that the bursts are due to a microbunching instability driven by the emission of synchrotron radiation in the bunch. Observations made at the Advanced Light Source are consistent with the values predicted by the proposed microbunching model. These results demonstrate a new instability regime for high energy synchrotron radiation sources and could impact the design of future sources.     

A Screening Assay for the Tetrachlorodibenzo-p-dioxin Receptor using the [125I]iodovaleramide Derivative of Trichlorodibenzo-p-dioxin as the Binding Ligand

Abstract

A relatively simple assay method for the putative cytosolic ‘receptor’ that binds 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds is described. The assay is based on specific binding of [¹²⁵I]dioxin to cytosol ‘receptor’ protein. Saturation is ensured by competition experiments in which unlabeled TCDD and other competitors displace the radiolabeled ligand from specific binding sites. This assay has been applied to estimation of levels of ‘receptor’ in cytosol.