Leslie G. Butler

Spectroscopic properties and redox chemistry of the phosphorescent excited state of octahydrotetrakis(phosphorus pentoxide)diplatinate(4-) ion (Pt2(P2O5)4H84-)

Binuclear complexes built from square-planar Rh(I) or Ir(I) isocyanide units exhibit rich photophysical and photochemical properties. Extensive studies in our laboratory have established that the lowest electronic excited states of one of these complexes, Rh/sub 2/b/sub 4//sup 2 +/ (b = 1.3-diisocyanopropane) (/sup 1/A/sub 1g/ (D/sub 4h/) ground state; Rh-Rh = 3.24 angstrom), are a spin triplet (/sup 3/A/sub 2u/) and a spin singlet (/sup 1/A/sub 2u/) derived from the dsigma/sup */psigma(1a/sub 2u/2a/sub 1g/) orbital configuration and that the E/sub u/(/sup 3/A/sub 2u/) phosphorescent state (t = 8.5 ..mu..s, CH/sub 3/CN solution, 25 /sup 0/C) undergoes electron-transfer reactions with donors and acceptors. Our decision to begin experiments with the goal of extending this type of photochemistry to analogous Pt(II) complexes was based mainly on reports of an intensely luminescent, phosphite-bridged binuclear species, Pt/sub 2/(P/sub 2/O/sub 5/)/sub 4/H/sub 8//sup 4 -/ (Pt-Pt = 2.93 angstrom). Our experiments have shown that the properties of the lowest electronic excited states of Pt/sub 2/(P/sub 2/0/sub 5/)/sub 4/H/sub 8//sup 4 -/ are entirely analogous to those of Rh/sub 2/b/sub 4//sup 2 -/, and they have provided the first examples of electron-transfer reactions involving excited Pt(II) species and acceptor molecules.

Immobilization of As, Cd, Cr and PB-containing soils by using cement or pozzolanic fixing agents☆

The present work reports leaching data for a soil contaminated with four inorganic model wastes, Cd (II) and Pb (II) nitrates, sodium arsenite, and sodium chromate, at concentrations in the range of 10,000 to 12,200 ppm. Various combinations of Type I portland cement (OPC), Type F fly-ash, blast furnace slag, lime, and silica fume have been used to treat the contaminated soils, which are then leached using a slightly modified EP Tox1 leaching procedure. In no case does fly ash improve performance when mixed with other binding agents. Slag offers superior performance compared to fly ash in any combination tested and has some potential for general utility in practice. In particular, several mixtures including slag are effective in immobilizing lead, which sometimes given problems in solidification with cement. Type I portland is a very versatile and dependable reagent compared to the other agents used. In the cases of As and Cr, the performance of portland alone is superior to that of any other reagent or combination, when comparisons were made at the same dosage level. Cement alone was not among the fixing agents tested for Cd and Pb, but several combinations with cement were included. In every case, inclusion of OPC results in leachate concentrations as low as or lower than the corresponding mixture without OPC.

Characterization and phosphate stabilization of dusts from the vitrification of MSW combustion residues

Abstract The use of soluble PO 4 3− as a heavy metal chemical stabilization agent was evaluated for a dust generated from melting or vitrification of municipal solid waste combustion residues. Vitrification dusts contain high concentrations of volatile elements such as Cl, Na, K, S, Pb, and Zn. These elements are present in the dusts largely as simple salts (e.g. PbCl 2 , ZnSO 4 ) which are highly leachable. At an experimental dose of 0.4 moles of soluble PO 4 3− per kg of residue, the pH-dependent leaching (pH 5,7,9) showed that the treatment was able to reduce equilibrium concentrations by factors of 3 to 100 for many metals; particularly Cd, Cu, Pb and Zn. Bulk and surface spectroscopies showed that the insoluble reaction products are tertiary metal phosphate [e.g. Zn 3 (PO 4 ) 2 ] and apatite [e.g. Pb 5 (PO 4 ) 3 Cl] family minerals. Geochemical thermodynamic equilibrium modeling showed that apatite family and tertiary metal phosphate phases act as controlling solids for the equilibrium concentrations of Ca 2+ , Zn 2+ , Pb 2+ , Cu 2+ , and Cd 2+ in the leachates during pH-dependent leaching. Both end members and ideal solid solutions were seen to be controlling solids. Soluble phosphate effectively converted soluble metal salts into insoluble metal phosphate phases despite the relatively low doses and dry mixing conditions that were used. Soluble phosphate is an effective stabilization agent for divalent heavy metals in melting dusts where leachable metals are present in high concentrations.

Petrographic and spectroscopic characterization of phosphate-stabilized mine tailings from Leadville, Colorado.

The use of soluble PO4(3-) and lime as a heavy metal chemical stabilization agent was evaluated for mine tailings from Leadville, Colorado. The tailings are from piles associated with the Wolftone and Maid of Erin mines; ore material that was originally mined around 1900, reprocessed in the 1940s, and now requires stabilization. The dominant minerals in the tailings are galena (PbS), cerrusite (PbCO3), pyromorphite (Pb5(PO4)3Cl), plumbojarosite (Pb0.5Fe3(SO4)2(OH)6), and chalcophanites ((Pb,Fe,Zn,Mn)Mn2O5 x 2H2O). The tailings were treated with soluble PO4(3-) and lime to convert soluble heavy metals (principally Pb, Zn, Cu, Cd) into insoluble metal phosphate precipitates. The treatment process caused bulk mineralogical transformations as well as the formation of a reaction rind around the particles dominated by Ca and P. Within the mineral grains, Fe-Pb phosphosulfates, Fe-Pb sulfates (plumbojarosite), and galena convert to Fe-Ca-Pb hydroxides. The Mn-Pb hydroxides and Mn-(+/-Fe)-Pb hydroxides (chalcophanites) undergo chemical alteration throughout the grains during treatment. Bulk and surface spectroscopies showed that the insoluble reaction products in the rind are tertiary metal phosphate (e.g. (Cu,Ca2)(PO4)2) and apatite (e.g. Pb5(PO4)3Cl) family minerals. pH-dependent leaching (pH 4,6,8) showed that the treatment was able to reduce equilibrium concentrations by factors of 3 to 150 for many metals; particularly Pb2+, Zn2+, Cd2+, and Cu2+. Geochemical thermodynamic equilibrium modeling showed that apatite family and tertiary metal phosphate phases act as controlling solids for the equilibrium concentrations of Ca2+, PO4(3-) Pb2+, Zn2+, Cd2+, and Cu2+ in the leachates during pH-dependent leaching. Both end members and ideal solid solutions were seen to be controlling solids.

A broadband nuclear magnetic resonance spectrometer: Digital phase shifting and flexible pulse programmer

A simple, low‐cost pulse nuclear magnetic resonance (NMR) spectrometer is described. There are two key features of the instrument: (1) all radio frequency phase shifting is done digitally with a new‐generation frequency synthesizer and (2) the pulse programmer is based on a high‐speed 32‐bit parallel interface card in a desktop computer. The spectrometer is well suited for single‐frequency channel experiments such as nuclear quadrupole resonance and deuterium quadrupole echo NMR experiments. Because the rf phase shifting is done digitally, the spectrometer operates easily over a wide frequency range, here 10–300 MHz. The pulse programmer and other software functions are written in LabView, a graphical programming language.

High resolution three-dimensional visualization and characterization of coronary atherosclerosis in vitro by synchrotron radiation x-ray microtomography and highly localized x-ray diffraction

Human atherosclerotic plaques in both native and bypass arteries have been visualized using microtomography to provide additional information on the nature of coronary artery disease. Plaques contained within arteries removed from three white males aged 51, 55 and 70 are imaged in three-dimensions with monochromatic synchrotron x-ray radiation. Fields of view are 658 x 658 x 517 voxels. with cubic voxels ranging from 12 to 13 microm on a side. X-ray energies range from 11 to 15 keV (bandpass approximately 10 eV). At lower energies, high local absorption tends to generate reconstruction artefacts, while at higher energies the arterial wall is scarcely visible. At all energies, calcifications are clearly visible and differences are observed between plaques in native arteries (lifetime accumulations) versus bypass arteries (plaques developing in the interval between the heart bypass operation and the autopsy). In order to characterize coronary calcification, a microfocused, 50 microm2, 25 keV x-ray beam was used to acquire powder diffraction data from selected calcifications. Also, large calcifications were removed from the native arteries and imaged with 25 keV x-ray energy. Calcifications are composed of hydroxyapatite crystallites and an amorphous phase. In summary, native calcifications are larger and have a higher fraction of hydroxyapatite than calcifications from the bypass arteries.

Proton‐poor, gallium‐ and indium‐loaded zeolite dehydrogenation catalysts

The catalytic (propane dehydrocyclization) and reduction behaviors of near 1:1 cation (Ga, In)/framework‐Al MFI zeolites were examined under conditions where the materials were initially either in fully protonated or zero−protonated states. Reductions at appropriate temperatures proceeded up to ∼100% exchange of protons for reduced univalent cations. Further aqueous exchange of alkali (K+>) or alkaline earth (Ba2+) cations increased the selectivity for dehydrogenation reactions at little or no sacrifice in overall activity.

The 10B and 11B nuclear quadrupole resonance spectra of boric acid

Abstract The 11B and 10B nuclear quadrupole resonance spectra of boric acid have been obtained at 77 K, by means of the technique of double resonance by level crossing. A 92% 10B-enriched material was examined in addition to one of normal isotopic composition. The quadrupole coupling constant and asymmetry parameter for 10B are 5344(2) kHz and 0.0163(5), respectively. The corresponding quadrupole coupling constant for 11B, assuming η = 0.0163, is 2576(8) kHz. The 10B spectrum is characterized by the appearance of transitions that may be classified as “multiple quantum,” in addition to the more highly allowed “single-quantum” transitions. Certain of these, which lie at frequencies higher than that of the one allowed 11B transition, are useful in determining the field gradient parameters. In addition “double transitions,” corresponding to simultaneous changes in spin states at two dipolar-coupled nuclei, have been observed; these involve both 10B and 11B.

Improved algorithm for processing grating-based phase contrast interferometry image sets

Grating-based X-ray and neutron interferometry tomography using phase-stepping methods generates large data sets. An improved algorithm is presented for solving for the parameters to calculate transmissions, differential phase contrast, and dark-field images. The method takes advantage of the vectorization inherent in high-level languages such as Mathematica and MATLAB and can solve a 16 × 1k × 1k data set in less than a second. In addition, the algorithm can function with partial data sets. This is demonstrated with processing of a 16-step grating data set with partial use of the original data chosen without any restriction. Also, we have calculated the reduced chi-square for the fit and notice the effect of grating support structural elements upon the differential phase contrast image and have explored expanded basis set representations to mitigate the impact.

The structure of the cornified claw sheath in the domesticated cat ( Felis catus ): implications for the claw-shedding mechanism and the evolution of cornified digital end organs

The morphology of cornified structures is notoriously difficult to analyse because of the extreme range of hardness of their component tissues. Hence, a correlative approach using light microscopy, scanning electron microscopy, three‐dimensional reconstructions based on x‐ray computed tomography data, and graphic modeling was applied to study the morphology of the cornified claw sheath of the domesticated cat as a model for cornified digital end organs. The highly complex architecture of the cornified claw sheath is generated by the living epidermis that is supported by the dermis and distal phalanx. The latter is characterized by an ossified unguicular hood, which overhangs the bony articular base and unguicular process of the distal phalanx and creates an unguicular recess. The dermis covers the complex surface of the bony distal phalanx but also creates special structures, such as a dorsal dermal papilla that points distally and a curved ledge on the medial and lateral sides of the unguicular process. The hard‐cornified external coronary horn and proximal cone horn form the root of the cornified claw sheath within the unguicular recess, which is deeper on the dorsal side than on the medial and lateral sides. As a consequence, their rate of horn production is greater dorsally, which contributes to the overall palmo‐apical curvature of the cornified claw sheath. The external coronary and proximal cone horn is worn down through normal use as it is pushed apically. The hard‐cornified apical cone horn is generated by the living epidermis enveloping the base and free part of the dorsal dermal papilla. It forms nested horn cones that eventually form the core of the hardened tip of the cornified claw. The sides of the cornified claw sheath are formed by the newly described hard‐cornified blade horn, which originates from the living epidermis located on the slanted face of the curved ledge. As the blade horn is moved apically, it entrains and integrates the hard‐cornified parietal horn on its internal side. It is covered by the external coronary and proximal cone horn on its external side. The soft‐cornified terminal horn extends distally from the parietal horn and covers the dermal claw bed at the tip of the uniguicular process, thereby filling the space created by the converging apical cone and blade horn. The soft‐cornified sole horn fills the space between the cutting edges of blade horn on the palmar side of the cornified claw sheath. The superficial soft‐cornified perioplic horn is produced on the internal side of the unguicular pleat, which surrounds the root of the cornified claw sheath. The shedding of apical horn caps is made possible by the appearance of microcracks in the superficial layers of the external coronary and proximal cone horn in the course of deformations of the cornified claw sheath, which is subjected to tensile forces during climbing or prey catching. These microcracks propagate tangentially through the coronary horn and do not injure the underlying living epidermal and dermal tissues. This built‐in shedding mechanism maintains sharp claw tips and ensures the freeing of the claws from the substrate.