Scientific Publications 2004
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2004. "Probing Cation Antisite Disorder in Gd₂Ti₂O₇ Pyrochlore by Site-Specific Near-Edge X-ray-Absorption Fine Structure and X-ray Photoelectron Spectroscopy." Physical Review. B, Condensed Matter and Materials Physics 70(10):100101(R), 1-4. Abstract Disorder in Gd₂Ti₂O₇ is investigated by near-edge x-ray absorption fine structure (NEXAFS) and x-ray photoelectron spectroscopy (XPS). NEXAFS shows Ti⁺⁴ ions occupy octahedral sites with a tetragonal distortion induced by vacant oxygen sites. O 1s XPS spectra obtained with a charge neutralization system from Gd₂Ti₂O₇ (100) and the Gd₂Ti₂O₇ pyrochlore used in Phys. Rev. Lett. 88, 105901 (2002), both yielded a single peak, unlike the previous result on the latter that found two peaks. The current results give no evidence for an anisotropic distribution of Ti and O. The extra features reported in the aforementioned communication resulted from charging effects and incomplete surface cleaning. Thus, a result confirming the direct observation of simultaneous cation–anion antisite disordering and lending credence to the split vacancy model has been clarified.
2004. "Isolation, Characterization of an Intermediate in an Oxygen Atom-Transfer Reaction, and the Determination of the Bond Dissociation Energy." Journal of the American Chemical Society 126(28):8604-8605. Abstract Redox reactions coupled with the formal loss or gain of an oxygen atom are ubiquitous in chemical processes. Such reactions proceed through the reduction of th edonor center (XO) and the oxidation of the acceptor (Y) molecule. Among many examples of the metal centered oxygen atom transfer (OAT) reactivity, those involving molybdenum complexes have been widely investigated due to their involvement in mononuclear molydenum enzymes. The heat of reaction of the overall atom transfer process can be expressed as a difference between the bond dissociation energies (BDEs) of the oxygen-donor(X) and oxygen-acceptor(Y) bond, i.e., H=DX=o-DY=O.
2004. "From First Principles to Catalytic Performance: Tracking Molecular Transformations." Chemical Engineering Science 59(22-23):4703-4714. Abstract The abstract for this product is not available at this time.
2004. "Mechanistic Insight into the Symmetric Fission of [4Fe-4S] Analogue Complexes and Implications for Cluster Conversions in Iron-Sulfur Proteins." Journal of Physical Chemistry A 108(32):6750 -6757. Abstract Assembly and disassembly of protein-bound iron-sulfur clusters are involved in a wide variety of vital biological processes, ranging from stabilization of protein structures to signaling and sensing of environmental conditions such as changes of Fe or O2 concentrations.
2004. "Synthesis of Colloidal Mn2+:ZnO Quantum Dots and High-TC Ferromagnetic Nanocrystalline Thin Films." Journal of the American Chemical Society 126(30):9387-9398. Abstract Abstract:We report the synthesis of colloidal Mn2+-doped ZnO (Mn2+:ZnO) quantum dots and the preparation of room-temperature ferromagnetic nanocrystalline thin films. Mn2+:ZnO nanocrystals were prepared by a hydrolysis and condensation reaction in DMSO under atmospheric conditions. Synthesis was monitored by electronic absorption and electron paramagnetic resonance (EPR) spectroscopies. Zn(OAc)2 was found to strongly inhibit oxidation of Mn2+ by O2, allowing the synthesis of Mn2+:ZnO to be performed aerobically. Mn2+ ions were removed from the surfaces of as-prepared nanocrystals using dodecylamine to yield high-quality internally doped Mn2+:ZnO colloids of nearly spherical shape and uniform diameter (6.1 ( 0.7 nm). Simulations of the highly resolved X-and Q-band nanocrystal EPR spectra, combined with quantitative analysis of magnetic susceptibilities, confirmed that the manganese is substitutionally incorporated into the ZnO nanocrystals as Mn2+ with very homogeneous speciation, differing from bulk Mn2+:ZnO only in the magnitude of D-strain. Robust ferromagnetism was observed in spin coated thin films of the nanocrystals, with 300 K saturation moments as large as 1.35 íB/Mn2+ and TC > 350 K. A distinct ferromagnetic resonance signal was observed in the EPR spectra of the ferromagnetic films. The occurrence of ferromagnetism in Mn2+:ZnO and its dependence on synthetic variables are discussed in the context of these and previous theoretical and experimental results.
