Nickelocene chemistry : II. New methylidyne trinickel cluster compounds

The new methylidene trinickel cluster complexes, [RCNi₃(η⁵-C₅H₅₃] (R  CMe₃ or SiMe₃) and [Me₃SiCNi₃(η⁵-C₅H₅)2(η⁵-C₅H₄CH₂SiMe₃)] have been isolated in low yield from reactions between nickelocene and the corresponding alkyllithium reagents, RCH₂Li. The compounds [RCNi₃(η⁵-C₅H₅)₃] (R  Ph, CMe₃ or SiMe₃) have also been obtained by treatment of the σ-alkylnickel complexes [(η⁵-C₅H₅)Ni(CH₂R)(PPh₃)] with n-BuLi in the presence of an excess of nickelocene, but under similar conditions [(η⁵-C₅H₅)Ni(CH₂C_1OH₇-2)-(PPh₃)] (where C_1OH₇-2  2-naphthyl) failed to give [2-C_1OH₇CNi₃(η⁵-C₅H₅)₃]. The attempted synthesis of [(η⁵-C₅H₅)Ni(CH₂CCH)(PPh₃)] from [(η⁵-C₅H₅)-NiBr(PPh₃)] and CHCCH₂MgBr gave only [(η⁵-C₅H₅)Ni(CCMe)(PPh₃)] by an unusual rearrangement reaction.     

Structural properties of ultra-small thorium and uranium dioxide nanoparticles embedded in a covalent organic framework

We report the structural properties of ultra-small ThO₂ and UO₂ nanoparticles (NPs), which were synthesized without strong binding surface ligands by employing a covalent organic framework (COF-5) as an inert template. The resultant NPs were used to observe how structural properties are affected by decreasing grain size within bulk actinide oxides, which has implications for understanding the behavior of nuclear fuel materials. Through a comprehensive characterization strategy, we gain insight regarding how structure at the NP surface differs from the interior. Characterization using electron microscopy and small-angle X-ray scattering indicates that growth of the ThO₂ and UO₂ NPs was confined by the pores of the COF template, resulting in sub-3 nm particles. X-ray absorption fine structure spectroscopy results indicate that the NPs are best described as ThO₂ and UO₂ materials with unpassivated surfaces. The surface layers of these particles compensate for high surface energy by exhibiting a broader distribution of Th–O and U–O bond distances despite retaining average bond lengths that are characteristic of bulk ThO₂ and UO₂. The combined synthesis and physical characterization efforts provide a detailed picture of actinide oxide structure at the nanoscale, which remains highly underexplored compared to transition metal counterparts.

ThO₂ and UO₂ nanoparticles synthesized using a COF-5 template exhibit unpassivated surfaces and provide insight into nanoscale properties of actinides.     

Artificial metalloenzymes: The powerful alliance between protein scaffolds and organometallic catalysts

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Phosphatidylserine/Cholesterol Bilayers Supported on a Polycation/Alkylthiol Layer Pair

1-Stearoyl-2-oleoyl phosphatidylserine (SOPS)/cholesterol bilayers, supported on a polycation/alkylthiol layer pair on a gold surface, were investigated by surface plasmon resonance (SPR) and fluorescence recovery after photobleaching. The substrate was formed by electrostatic adsorbance of a hydrated poly(diallyldimethylammonium chloride) (PDDA) layer on the negatively charged surface of a self-assembled monolayer of 11-mercaptoundecanoic acid (MUA) on gold. Lipid membranes with different SOPS/cholesterol compositions were deposited on the PDDA/MUA layer pair by vesicle fusion. When the cholesterol content was below 20%, single bilayers were deposited. Fluorescence recovery after the bleaching experiments revealed that the SOPS/cholesterol bilayers were mobile at room temperature; lateral diffusion coefficients of a fluorescence probe were approximately 1x10(-9) cm(2)/s. The kinetics of the addition of the ion-channel-forming peptide gramicidin to the supported bilayers was detected by SPR. Copyright 2000 Academic Press.