Carbolithiation for the generation of cyclooctadienyl anions and tandem electrocyclization/alkylation to functionalized cis-bicyclo[3.3.0]octenes

A powerful cascade reaction process for the construction of functionalized cis-bicyclo[3.3.0]octenes has been developed. Carbolithiation of 3-methylene-1,4-cyclooctadiene with 1 degrees , 2 degrees , or 3 degrees alkyllithium reagents leads to cyclooctadienyl anions, which undergo disrotatory electrocyclization and subsequent trapping with carbon, oxygen, sulfur, or silicon electrophiles to provide functionalized cis-bicyclo[3.3.0]octenes. Transmetalation of the allyllithium intermediates allowed access to the cuprate manifold of reactivity. The rapid construction of a linear triquinane using this methodology demonstrates the potential for synthetic applications.     

Cavity resonators of metal-coated dielectric nanorods

Metallic nanoparticles bridge the length scale between atoms and crystals, exhibiting mesoscopic properties unique to their size. Thus, they have generated much interest for their potential applications as chemical or biological sensors and particularly as waveguides for light in nanoscale structures. [Y. W. C. Cao, R. C. Jin, and C. A. Mirkin, Science 297, 1536 (2002); H. J. Lezec et al., Science 297, 820 (2002); S. A. Maier, P. G. Kik, and H. A. Atwater, Appl. Phys. Lett. 81, 1714 (2002); J. M. Oliva and S. K. Gray, Chem. Phys. Lett. 379, 325 (2003)]. One important direction of research into the properties of individual metal nanoparticles involves the controlled variation of their geometry, which can yield new and tunable optical properties that simple spherical configurations do not possess. [T. S. Ahmadi, Z. L. Wang, T. C. Green, A. Henglein, and M. A. Ei-Sayed, Science 272, 1924 (1996)]. A prime example of this is the core-shell nanostructure that has a central material surrounded by differing cladding layer.     

Glycopeptide and Oligosaccharide Libraries

Despite the burgeoning interest in the various biological functions and consequent therapeutic potential of the vast number of oligosaccharides found in nature on glycoproteins and cell surfaces, the development of combinatorial carbohydrate chemistry has not progressed as rapidly as expected. The reason for this imbalance is rooted in the difficulty of oligosaccharide assembly and analysis that renders synthesis a rather cumbersome endeavor. Parallel approaches that generate series of analogous compounds rather than real libraries have therefore typically been used. Since generally low affinity is obtained for interactions between carbohydrate receptors and modified oligosaccharides designed as mimetics of natural carbohydrate ligands, glycopeptides have been explored as alternative mimics. Glycopeptides have been proven in many cases to be superior ligands with higher affinity for a receptor than the natural carbohydrate ligand. High-affinity glycopeptide ligands have been found for several types of receptors including the E-, P-, and L-selectins, toxins, glycohydrolases, bacterial adhesins, and the mannose-6-phosphate receptor. Furthermore, the assembly of glycopeptides is considerably more facile than that of oligosaccharides and the process can be adapted to combinatorial synthesis with either glycosylated amino acid building blocks or by direct glycosylation of peptide templates. The application of the split and combine approach using ladder synthesis has allowed the generation of very large numbers of compounds which could be analyzed and screened for binding of receptors on solid phase. This powerful technique can be used generally for the identification and analysis of the complex interaction between the carbohydrates and their receptors.     

Titration of phytic acid

Titrimetric assays for phytic acid by titration with iron(III) or thorium are described. Stannous chloride interferes in both systems, causing negative errors directly proportional to the amount of stannous chloride. The thorium:phytate ratio in the complex formed is 2:1, which is interpreted as resulting from the possession of two chelating centres by phytic acid.     

Anticosmic-shielded ultralow-background germanium detector systems for analysis of bulk environmental samples

A low-level gamma-ray counting system has been developed which reduces system background, relative to other typical low-background systems, by a factor of ten in the energy region below one MeV, and by as much as a factor of forty at higher energies. This germanium-diode gamma-ray spectrometer was constructed for a modest investment above that required for a conventional germanium detector. The techniques involved use: (1) materials of known radiopurity to surround the diode, (2) an active external anticosmic shield to reduce the background continuum due to interactions of cosmic particles with the detector and passive lead shielding, and (3) nitrogen exhausted from the cryogenic dewar to minimize the introduction of ubiquitous radon decay nuclei into the sample counting chamber. A novel method for handling samples prior to counting is presented. Also; some of the difficulties encountered in calibrating a system intended for bulk samples are discussed.Operated for the U.S. Department of Energy by Battelle Memorial Institute under Contract DE-AC06-76RLO 1830.     

Poly(amidoamine-organosilicon) (PAMAMOS) multi-arm star polymers

A new class of hydrophilic core – hydrophobic arms multi-arm star polymers is described: the first such materials to have silicon located in the side arms. They belong to the broad family of radially layered copolymeric amidoamine-organosilicon (PAMAMOS) dendritic macromolecules and may be viewed as nanostructured, covalently bonded, inverse micelles. Two types of hydrophobic, silicon-containing arms have been used, one based on polydimethylsiloxane (PDMS) and another based on predominantly alkyl chains attached by organosilicon chemistry to the hydrophilic polyamidoamine (PAMAM) core. The former polymers are synthesized by a reaction of amine-terminated PAMAMs by mono-functional epoxy PDMS, while the latter are obtained by haloalkylation of the same PAMAMs with a suitable unsaturated silane followed by alkylthiol addition. The Langmuir film behavior of the multi-arm star polymers with PDMS arms is described and rationalized in comparison with that of other hydrophobically modified PAMAM dendrimers reported in the literature. Their uptake of Cu²⁺ from aqueous solutions is also described.     

A tube-excited X-ray fluorescence spectrometer for use in small-diameter boreholes

A portable in-situ x-ray fluorescence analytical system that uses an x-ray tube excitation source and a cooled Si(Li) spectrometer for detecting characteristic emission x rays has been developed for use in small-diameter wells and boreholes. The 15-watt, iron-anode x-ray tube operates up to 30 kV. Three wells at the Sandia National Laboratory Chemical Waste Landfill, lined with 76 thick polyethylene, were logged specifically for Cr contamination. Detection limits below 50 ppm were achieved with counting intervals of 600 seconds and with the Si(Li) detector operating at 450-eV resolution (full width at half maximum [FWHM] for the Mn K-alpha x ray).     

THE CHEMILUMINESCENT NO—O-ATOM REACTION

Abstract— New additional experimental data were obtained to give further information pertinent to the mechanism for the chemiluminescent NO—O-atom reaction. Results were obtained for the change of emission intensities from 10 to 300 microns pressure. Some studies were also made of the effect of various third bodies. The results support a simple two body recombination for the mechanism for the light emission: NO+O + NO₂+ hv .     

The effect of cation size on ion pairing of methyl orange dye with tetraalkylammonium and benzyltrialkylammonium ions in aqueous solution

Formation constants have been measured by a solvent distribution method for the ion pairing of an arene sulfonate, methyl orange dye, with two series of quaternary ammonium ions: R₄N⁺(R=Et,n-Pr,n-Bu, andn-Pent) and C₆H₅CH₂R₃N⁺ (R=Me, Et,n-Pr,n-Bu,n-Pent, andn-Hex). Ion pairing increases dramatically as the length of the R group increases beyond butyl. Using a hard-sphere model for contact ion pairs, it is estimated that coulombic attraction contributes about –kT to the binding free energy and decreases slightly with increasing size of R₄N⁺. Other factors related to solvation effects, of which cosphere overlap predominates, contribute from –2kT to –7kT of binding energy. Plots of logK for association as a function of cation size show an inflection with decreasing slope between R=propyl and R=butyl. Possible causes for the inflection are considered.