Paul A. Jelliss

Capping and passivation of aluminum nanoparticles using alkyl-substituted epoxides.

We report here on the synthesis and passivation of small (20-30 nm) aluminum nanoparticles using alkyl-substituted epoxides as capping agents. FTIR and 13C NMR spectroscopy indicate that the epoxides polymerize to form a polyether cap on the surfaces of the aluminum nanoparticles. Nanoparticles capped with epoxyhexane and epoxydodecane are stable in air, but particles capped with epoxyisobutane are pyrophoric. TEM images show spherical Al particles. Powder X-ray diffraction shows the presence of crystalline Al. Titrimetric analysis of the core-shell nanostructures in air reveals that 96% of the total aluminum present is active (unoxidized) aluminum.

Aluminum nanoparticles capped by polymerization of alkyl-substituted epoxides: ratio-dependent stability and particle size.

We report here on the polymerization of epoxide monomers on incipient aluminum nanoparticle cores and the effects of changing the epoxide-capping precursor and the metallic monomer ratio on the resultant stability and particle size of passivated and capped aluminum nanoparticles. When altering the ratio of aluminum to cap monomer precursor, nanoparticles capped with epoxydodecane, epoxyhexane, and epoxyisobutane show a clear decreasing trend in stability with decreasing alkane substituent length. The nanoparticle core size was unaffected by cap ratio or composition. PXRD (powder X-ray diffraction) and DSC/TGA (differential scanning calorimetry/thermal gravimetric analysis) confirm the presence of successfully passivated face-centered cubic (fcc) aluminum nanoparticles. We also report preliminary results from ATR-FTIR (attenuated total reflectance-Fourier transform infrared), (13)C CPMAS (cross-polarization/magic-angle spinning), and (27)Al MAS solid-state NMR (nuclear magnetic resonance) measurements. The most stable aluminum nanoparticle-polyether core-shell nanoparticles are found at an Al:monomer mole ratio of 10:1 with an active Al(0) content of 94%.

Permeability of the Blood-Brain Barrier to a Rhenacarborane

The treatment of brain malignancies with boron neutron capture therapy depends on their ability to cross the blood-brain barrier (BBB). An especially promising class of boron-containing compounds is the rhenacarboranes that, if able to cross the BBB, could act as delivery vehicles as well as a source of boron. Here, we examined the ability of the 3-NO-3,3-κ2-(2,2′-N2C10H6(Me){(CH2)7131I}-4,4′)-closo-3,1,2-ReC2B9H11 (rhenacarborane) labeled with iodine-131 to be taken up into the bloodstream after subcutaneous administration and to cross the BBB. The 131I-rhenacarborane was quickly absorbed from the injection site and reached a steady state in arterial serum of 2.59%/ml of the administered dose. Between 73 and 95% of the radioactivity in serum 6 h after administration represented intact 131I-rhenacarborane. Its octanol/buffer partition coefficient was 1.74, showing it to be lipophilic. Tissue/serum ratios for brain, lung, and liver showed classic patterns for a lipid-soluble substance with high levels immediately achieved and rapid redistribution. For brain, a steady state of approximately 0.107% of the administered dose/gram-brain was rapidly reached, and 71% of the radioactivity in brain 6 h after subcutaneous administration represented intact 131I-rhenacarborane. Steady-state values were 1.53 and 0.89% of the injected dose per gram for lung and liver, respectively. 131I-Rhenacarborane was quickly effluxed from brain by a nonsaturable system after its injection into the lateral ventricle of the brain. In conclusion, these results show that a rhenacarborane was enzymatically resistant and able to cross the BBB by transmembrane diffusion and accumulate in brain in substantial amounts. This supports their use as therapeutic agents for targeting the central nervous system.

Unique properties of a perfluoroalkyl-modified 2,2′-bipyridyl ruthenium complex in a Nafion™ membrane: attenuated leaching of a potential biofuel cell redox mediator

The synthesis and characterization are described for the complex salt [Ru(κ2-2,2′-N2C10H6{(CH2)3(CF2)5CF3}2-4,4′)(κ2-2,2′-N2C10H8)2][PF6]2, where one of the 2,2′-bipyridyl ligands bears terminal bis(perfluoralkyl) chains, the purpose of which is to exploit ‘like-dissolves-like’ intermolecular forces as an anchoring mechanism for the complex in Nafion™ membranes. TBAB-modified-Nafion™ thin films (sulfonic acid protons exchanged for NBun4+ cations) were cast or spin-coated onto electrodes and glass microscope slips, exposed to CH2Cl2 solutions of the complex and then examined by fluorimetry and cyclic voltammetry. Steady state and time-resolved luminescence analysis revealed quite different behavior in comparison with tris-2,2′-bipyridyl ruthenium in unmodified Nafion™ films. Exposure to methanol solutions indicated mitigation of the swelling effect of this solvent along with sustained structural integrity of the mediator complex among the various microenvironmental domains of the TBAB-modified-Nafion™ polymer. The dramatic leaching evident for samples of regular tris-2,2′-bipyridyl ruthenium dications in unmodified and modified Nafion™ films is not apparent for the new [Ru(κ2-2,2′-N2C10H6{(CH2)3(CF2)5CF3}2-4,4′)(κ2-2,2′-N2C10H8)2]2+/TBAB-modified-Nafion™-coated electrodes. Thus CVs of the latter show sustained peak current densities in excess of 1.0 mA cm−2 for the Ru3+/2+ couple and thus decent mediator retention over multiple potential cycles when exposed to mixed methanol–phosphate buffer solutions.

Metal and Metal Carbide Nanoparticle Synthesis Using Electrical Explosion of Wires Coupled with Epoxide Polymerization Capping.

In this study, metal-containing nanoparticles (NPs) were produced using electrical explosion of wires (EEW) in organic solvents. The explosion chamber was constructed from Teflon to withstand the shockwave, allow growth and reaction of the incipient NPs in various organic solvents containing dissolved ligands, and allow a constant flow of argon to maintain an inert environment. A survey of different transition d-block metals was conducted with metals from groups 4-8, affording metal carbide NPs, while metals from groups 9-12 gave elemental metallic NPs. Tungsten carbide phase WC1-x, which has not been previously isolated as a single-phase material, was exclusively formed during EEW. We used polymerization initiation by electron-rich metallic nanoparticles (PIERMEN) as a capping technique for the nascent NPs with an alkyl epoxide employed as the monomers. Transmission electron microscopy showed spherical particles with the metallic core embedded in a polymer matrix with predominantly smaller particles (<50 nm), but also a broad size distribution with some larger particles (>100 nm). Powder X-ray diffraction (PXRD) was used to confirm the identity of the metallic NPs. The capping agents were characterized using ATR-FTIR spectroscopy. No evidence is observed for the formation of crystalline oxides during EEW for any metals used. Differential scanning calorimetry/thermal gravimetric analysis was used to study the NPs behavior upon heating under an air flow up to 800 °C with the product oxides characterized by PXRD. The bifurcation between metal-carbide NPs and metal NPs correlates with the enthalpy of formation of the product carbides. We observed PIERMEN capping of elemental metal NPs only when the metal has negative standard electrode potentials (relative to a bis(biphenyl) chromium(I)/(0) reference electrode).

Deprotonation of the carbaboranenido-7-NH2But-7-CB10H12: crystal structures ofnido-7-NH2But-7-CB10H12 and[NEt3(CH2Ph)][nido-7-NHBut-7-CB10H12]

The crystal structure of nido-7-NH 2 Bu t -7-CB 10 H 12 1 has been determined by X-ray diffraction. The compound crystallises in the orthorhombic space group Pbca [a = 10.507(5), b = 13.805(6), c = 18.093(9) A]. The nido-icosahedral structure was established with two endo-B–H–B and two NH 2 hydrogen atoms located in Fourier-difference maps and refined. The structure determination is also supported by 11 B-{ 1 H}– 11 B-{ 1 H} correlation NMR spectroscopy. A molecular orbital calculation and frontier density analysis of 1 indicated that deprotonation should initially occur at the exo-nitrogen atom. Treatment of 1 with 1 equivalent of LiBu n , followed by addition of [NEt 3 (CH 2 Ph)]Cl, gave [NEt 3 (CH 2 Ph)][nido-7-NHBu t -7-CB 10 H 12 ] 2 as the only product and single crystals were grown for an X-ray diffraction study. The salt crystallises in the monoclinic space group P2 1 /n [a = 10.651(2), b = 11.652(2), c = 20.926(3) A, β = 101.77(2)°]. The 1 H, 13 C-{ 1 H} and 11 B-{ 1 H} NMR spectra of 1 and 2 have also been recorded.

Poly(methyl methacrylate) as an Environmentally Responsive Capping Material for Aluminum Nanoparticles

We present an investigation of the photochemistry of aluminum nanoparticles (Al NPs) capped with poly(methyl methacrylate) (PMMA). Powder X-ray diffraction and Fourier transform infrared spectroscopy with total attenuated reflection confirm the presence of crystalline aluminum cores and the PMMA cap and allow us to confirm the latter’s photodegradation upon exposure to UV light. The PMMA-Al NPs were also characterized by differential scanning calorimetry coupled with thermogravimetric analysis to study the thermal profiles for polymer combustion and metal oxidation exotherms. Transmission electron microscopy confirms that the Al NPs, around 36 nm in diameter, are embedded in the PMMA matrix. Following UV irradiation, the PMMA-Al NPs react considerably faster with alkaline solutions, compared with unphotolyzed samples. Photoactivation of the nanocomposite induces partial decomposition of the PMMA capping layer, exposing the underlying reactive metal cores to the surrounding environment and accelerating its redox reactivity. Photolysis times of 1, 6, 24, and 52 h were investigated to establish a minimum UV exposure time for the activation of the PMMA-Al NPs toward hydrolytic hydrogen gas generation.

Rhenacarborane complexes with nitrosyl and alkylidene ligands. Structures of the complexes [Re{C(OMe)C6H4Me-4}(NO)(CO)(η5-7,8-C2B9H11)] and [Re(NO)(CNBut){η5,σ-7-CN(H)But-7,8-C2B9H10}]

The first examples of rhenacarborane complexes with nitrosyl ligands have been prepared and used to synthesise alkylidene(nitrosyl)rhenacarboranes and a novel complex in which a conjoined carboranyl–iminium group is bound to rhenium both through the η5-C2B3 face of the cage and the iminium carbon atom.