Transfer of Amide and 2-Methoxyethoxy Groups and Sodium Encapsulation in the Reaction of TaCl3[N(TMS)2]2 with Sodium Bis(2-methoxyethoxy)aluminum Hydride: X-ray Structure of [NaAl{N(TMS)2}(OCH2CH2OMe)3]2

Abstract  The reaction between the tantalum compound TaCl₃[N(TMS)₂]₂ and the hydridic reducing agent sodium bis(2-methoxyethoxy)aluminum hydride (Vitride) has been investigated in toluene solution at room temperature and found to afford the dimeric aluminate complex [NaAl{N(TMS)₂}(OCH₂CH₂OMe)₃]₂ as the sole isolable product. The molecular structure of the product establishes the existence of a four-coordinate aluminum atom and the formal transfer of the 2-methoxyethoxy and bis(trimethylsilyl)amide groups to the aluminate product. The aggregation of two NaAl{N(TMS)₂}(OCH₂CH₂OMe)₃ units serves to bind the two sodium cations in a crown-ether fashion through six ancillary oxygen atoms. Index Abstract  The reaction between TaCl₃[N(TMS)₂]₂ and the reducing agent Vitride has been examined and found to furnish the dimeric aluminate complex [NaAl{N(TMS)₂}(OCH₂CH₂OMe)₃]₂ in low yields. X-ray diffraction analysis confirms the attendant transfer of the 2-methoxyethoxy and bis(trimethylsilyl)amide groups to the aluminate product, which exists as a dimer that encapsulates two sodium counter ions via the 2-methoxyethoxy appendages.

Spectroscopic and X-ray Diffraction Data on Three Novel Trimetallic Clusters from Thermally Promoted Ligand Substitution in the Tetrahedrane Clusters MeCCo2MoCp(CO)8 and PhCCo2Mo(η5-C5H4CHO)(CO)8

Abstract  

The reaction between the ethylidyne-substituted cluster MeCCo₂MoCp(CO)₈ (1) and the diphosphine ligand 2,3-bis(diphenylphosphino)maleic anhydride (bma) in refluxing CH₂Cl₂ has been investigated and found to afford the new mixed-metal clusters MeCCo₂MoCp(CO)₆[trans-2,3-bis(diphenylphosphino)succinic anhydride] (2) and Co₂MoCp(CO)₅[μ-C(Me)C=C(PPh₂)C(O)OC(O)](μ-PPh₂) (3), with the latter cluster representing the principal reaction product. Refluxing 1 with bma in either 1,2-dichloroethane or toluene yields only 3. The tetrahedrane cluster PhCCo₂Mo(η⁵-C₅H₄CHO)(CO)₈ (4), which contains a formyl-substituted cyclopentadienyl ring, has also been examined with added bma in refluxing CH₂Cl₂ and found to give only Co₂Mo(η⁵-C₅H₄CHO)(CO)₅[μ-C(Ph)C=C(PPh₂)C(O)OC(O)](μ-PPh₂) (5). All three products have been isolated and characterized spectroscopically in solution, and each molecular structure has been determined by X-ray crystallography. Cluster 2 contains a bridging diphosphine ligand with a succinic anhydride ring that results from the formal reduction of the maleic anhydride platform of the bma ligand, while clusters 3 and 5 each exhibit triangular Co₂Mo cores, whose one face is capped by a 6e- C(R)C=C(PPh₂)C(O)OC(O) [where R = Me (3), Ph (5)] ligand. The observed substitution products are discussed as a function of the capping carbyne group, ancillary polyene ligand, and related derivatives prepared by our groups.     

Validation of the Diagnostic Teacher Assessment of Mathematics and Science (DTAMS) Instrument

The Diagnostic Teacher Assessment in Mathematics and Science (DTAMS) was developed to measure the content knowledge and pedagogical content knowledge of middle‐school teachers. Its reliability and validity were initially established by reviewing national standards for content and use of expert question writing teams and reviewers. DTAMS was administered to approximately 1,600 middle‐school mathematics teachers in 17 states. Subsequent analyses using structural equation modeling and item response theory were performed as part of a multistage validation process. This evaluation contributes to the body of work describing the reliability and validity of these assessments. The results of this study confirm trends in middle‐school mathematics teacher preparation and certification and help explain middle‐school student mathematics achievement levels.     

Shape-controlled crystallisation pathways in dense fluids of ccp-forming hard polyhedra

Emergent directional entropic forces that favour facet-to-facet alignment of neighbouring colloidal particles – arising from multi-body interactions upon crowding – should cause the process by which colloidal crystals form from fluids of hard polyhedra to be different than that from fluids of hard spheres. We compute nucleation-free energy barriers for a family of shapes that all self-assemble the same cubic close-packed (ccp) crystal structure formed by hard spheres and find that changing rhombicuboctahedra into rhombic dodecahedra by successively removing facets that compete with the ccp structure cause a systematic decrease in barrier heights. We show that this decrease arises from the increased prominence of facets aligned with neighbouring shapes in the target crystal, which produce local environments in the fluid that facilitate crystallisation.     

A Photoexcitation‐Induced Twisted Intramolecular Charge Shuttle

Charge transfer and separation are important processes governing numerous chemical reactions. Fundamental understanding of these processes and the underlying mechanisms is critical for photochemistry. Herein, we report the discovery of a new charge‐transfer and separation process, namely the twisted intramolecular charge shuttle (TICS). In TICS systems, the donor and acceptor moieties dynamically switch roles in the excited state because of an approximately 90° intramolecular rotation. TICS systems thus exhibit charge shuttling. TICSs exist in several chemical families of fluorophores (such as coumarin, BODIPY, and oxygen/carbon/silicon–rhodamine), and could be utilized to construct functional fluorescent probes (i.e., viscosity‐ or biomolecule‐sensing probes). The discovery of the TICS process expands the current perspectives of charge‐transfer processes and will inspire future applications.     

Characterization of magnetite nanoparticles for SQUID-relaxometry and magnetic needle biopsy

Magnetite nanoparticles (Chemicell SiMAG-TCL) were characterized by SQUID-relaxometry, susceptometry, and TEM. The magnetization detected by SQUID-relaxometry was 0.33% of that detected by susceptometry, indicating that the sensitivity of SQUID-relaxometry could be significantly increased through improved control of nanoparticle size. The relaxometry data were analyzed by the moment superposition model (MSM) to determine the distribution of nanoparticle moments. Analysis of the binding of CD34-conjugated nanoparticles to U937 leukemia cells revealed 60,000 nanoparticles per cell, which were collected from whole blood using a prototype magnetic biopsy needle, with a capture efficiency of >65% from a 750 μl sample volume in 1 min.     

Magnetic resonance spectroscopy outcomes from a comprehensive magnetic resonance study of children with fetal alcohol spectrum disorders

Magnetic resonance (MR) technology offers noninvasive methods for in vivo assessment of neuroabnormalities. A comprehensive neuropsychological/behavioral, MR imaging (MRI), MR spectroscopy (MRS) and functional MRI (fMRI) assessment was administered to children with fetal alcohol spectrum disorders (FASD) to determine whether global and/or focal abnormalities could be identified and to distinguish diagnostic subclassifications across the spectrum. The four study groups included (1) FAS/partial FAS; (2) static encephalopathy/alcohol exposed (SE/AE); (3) neurobehavioral disorder/alcohol exposed (ND/AE) as diagnosed with the FASD 4-Digit Code; and (4) healthy peers with no prenatal alcohol exposure. Results are presented in four separate reports: MRS (reported here) and neuropsychological/behavioral, MRI and fMRI outcomes (reported separately). MRS was used to compare neurometabolite concentrations [choline (Cho), n-acetyl-aspartate (NAA) and creatine (Cre)] in a white matter region and a hippocampal region between the four study groups. Choline concentration in the frontal/parietal white matter region, lateral to the midsection of the corpus callosum, was significantly lower in FAS/PFAS relative to all other study groups. Choline decreased significantly with decreasing frontal white matter volume and corpus callosum length. These outcomes suggest low choline concentrations may reflect white matter deficits among FAS/PFAS. Choline also decreased significantly with increasing severity of the 4-Digit FAS facial phenotype, increasing impairment in psychological performance and increasing alcohol exposure. NAA and Cre concentrations did not vary significantly. This study provides further evidence of the vulnerability of the cholinergic system in FASD.     

γ‐Irradiation of ultrahigh‐molecular‐weight polyethylene: Electron paramagnetic resonance and nuclear magnetic resonance spectroscopy and imaging studies of the mechanism of subsurface oxidation

The shelf aging of irradiated ultrahigh‐molecular‐weight polyethylene (UHMWPE) causes subsurface oxidation, which leads to failure in UHMWPE orthopedic components, yet the mechanisms causing subsurface oxidation remain unclear. The shelf aging of γ‐irradiated UHMWPE bars has been studied with electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) imaging and with microtoming and Fourier transform infrared microscopy. The bars initially contained only allyl radicals, and upon air exposure, a surface layer of peroxyl radicals formed through the reaction of allyl radicals with oxygen. Importantly, a band of low radical intensity just beneath the peroxyl layer became apparent. NMR imaging showed a zone of altered proton relaxation in this zone. With increasing time, surface peroxyl radicals persisted in comparison with the interior allyl radicals, although oxygen did not appear to penetrate any more deeply into the bar. The area of maximal oxidation and mechanical disruption, measured after 3 years, was at the interface between the zone of exterior peroxyl radicals and the zone of low radical intensity. We present a mechanism involving the intermediacy of sterically strained reactive dialkyl peroxides at this interface to explain subsurface oxidation. We also demonstrate that EPR and NMR imaging provides information that could potentially be used to identify subsurface oxidized UHMWPE components before failure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5929–5941, 2004     

An Iterative Construction Heuristic for the Ore Selection Problem

The ore selection problem involves choosing a processing option for a number of mining blocks that maximises the expected payoff for a given level of financial risk. An innovative neighbourhood search heuristic is proposed for the ore selection problem. This iterative construction heuristic employs a stochastic demolition and reconstruction strategy. Computational experiments with this heuristic for two ore selection problem instances, one involving 2,500 blocks and the other involving 78,000 blocks, are given. These problem instances are made publicly available for use by future workers. Our computational experiments indicate that the proposed heuristic produces better quality solutions faster than a relay hybrid (constructive-simulated annealing) heuristic.