From extended solids to nano-scale actinide clusters

Selected highlights of more than a decade of research efforts concerning the structural chemistry of actinyl materials at the University of Notre Dame is reviewed, with an emphasis on complex topological arrangements of polyhedra to form extended structures and frameworks. Earlier work focused on structures of uranyl minerals and synthetic compounds, with increasing emphasis on neptunyl materials and the importance of cation–cation interactions in their structural details and properties. Much of the research over the past 5 years has examined a growing family of nano-scale clusters of uranyl peroxide polyhedra containing from 16 to 60 polyhedra. These clusters contain topological squares, pentagons and hexagons, and six have adopted fullerene topologies with 12 pentagons and an even number of hexagons.     

Predictive modeling of positive mode IMS gas-phase ionization: is 2nd-order Møller-Plesset perturbation theory adequate?

Low level ab initio Quantum Chemistry (QC) is shown to be a promising technique for predicting the relative ordering of a wide variety of potential analyte, dopant, and interferent molecules, by their proton affinities (PA). Computed PAs, using a single level of chemical theory, are summarized for 53 compounds and when compared to literature reference data have a mean unsigned error of ∼9.5 kJ/mol. Where applicable, multiple conformations of the protonated species were explored. In these cases, the Boltzmann weighted PA is reported. Finally, examples are shown in which QC modeling is used to predict potential fragmentation products initiated by the positive mode ionization.     

Three-dimensional numerical modeling of geoacoustic scattering from seafloor topography

A three-dimensional (3-D), second-order finite-difference method was used to create synthetic seismograms for wave propagation in heterogeneous media in order to investigate the scattering of elastic and acoustic energy due to topography on the seafloor. The method uses a fully staggered grid in Cartesian coordinates as developed by Virieux [Geophysics 51, 889-901 (1986)]. Numerical results were generated for two models: a linear fault scarp on the seafloor, and a flat seafloor containing a rectangular channel. Wave-front snapshots allow the scattering and focusing of different wave modes with direction to be visualized. Compressional and shear wave backscattering from the sides of the features can be seen together with the trapped compressional wave energy propagating inside the channel. The results illustrate the effects of out of the plane scattering due to simple seafloor topographic features.     

Instrumental neutron activation analysis of high-purity gallium,arsenic, and gallium arsenide

Instrumental neutron activation analysis (INAA) has been applied to obtain useful data on impurity concentrations in ultra-pure materials whose matrix elements are strongly activated and create severe interference for several weeks after irradiation. An analytical procedure has been developed and used to determine Sc, Fe, Co, Zn, Se, Zr, Ag, In, Sn, Sb, Te, and Hg in high-purity gallium, arsenic, and gallium arsenide. Detection limits ranged from 50 ng/g for iron to 0.001 ng/g for scandium. Problems of contamination control, blank level, and standardization are discussed.     

Enantioselective Synthesis of Spiroindenes by Enol‐Directed Rhodium(III)‐Catalyzed C?H Functionalization and Spiroannulation

Chiral cyclopentadienyl rhodium complexes promote highly enantioselective enol‐directed C(sp²)‐H functionalization and oxidative annulation with alkynes to give spiroindenes containing all‐carbon quaternary stereocenters. High selectivity between two possible directing groups, as well as control of the direction of rotation in the isomerization of an O‐bound rhodium enolate into the C‐bound isomer, appear to be critical for high enantiomeric excesses.