Showing papers by "Peter S. White published in 2008"

Crystal structure of the gold nanoparticle [N(C8H17)4][Au25(SCH2CH2Ph)18].

Abstract: We report the crystal structure of the thiolate gold nanoparticle [TOA+][Au25(SCH2CH2Ph)18-], where TOA+ = N(C8H17)4+. The crystal structure reveals three types of gold atoms: (a) one central gold atom whose coordination number is 12 (12 bonds to gold atoms); (b) 12 gold atoms that form the vertices of an icosahedron around the central atom, whose coordination number is 6 (five bonds to gold atoms and one to a sulfur atom), and (c) 12 gold atoms that are stellated on 12 of the 20 faces of the Au13 icosahedron. The arrangement of the latter gold atoms may be influenced by aurophilic bonding. Together they form six orthogonal semirings, or staples, of −Au2(SCH2CH2Ph)3− in an octahedral arrangement around the Au13 core.

Scope and mechanism of the iridium-catalyzed cleavage of alkyl ethers with triethylsilane.

Abstract: The cationic iridium pincer complex [(POCOP)Ir(H)(acetone)]+[B(C6F5)4]− {1, POCOP = 2,6-[OP(tBu)2]2C6H3} was found to be a highly active catalyst for the room-temperature cleavage and reduction of a wide variety of unactivated alkyl ethers including primary, secondary, and tertiary alkyl ethers as well as aryl alkyl ethers by triethylsilane. Mechanistic studies have revealed the full details of the catalytic cycle with the catalyst resting state(s) depending on the basicity of the alkyl ether. During the catalytic reduction of diethyl ether, cationic iridium silane complex, [(POCOP)Ir(H)(η1-Et3SiH)]+[B(C6F5)4]− (3), and Et2O are in rapid equilibrium with neutral dihydride, (POCOP)Ir(H)2 (5) and diethyl(triethylsilyl)oxonium ion, [Et3SiOEt2]+[B(C6F5)4]− (7), with 5 + 7 strongly favored. Species 7 has been isolated from the reaction mixture and fully characterized. The turnover-limiting step in this cycle is the reduction of 7 by the neutral dihydride 5. The relative rates of reduction of 7 by dihydride 5 a...

Naturalness and Beyond: Protected Area Stewardship in an Era of Global Environmental Change

Abstract: have begun to question the feasibility of maintaining natural conditions in protected areas. Growing awareness of Native American influence and recognition of the dynamics of natural systems raise questions about what naturalness even is. And with increasing recognition of the potential effects of climate change, there is a dawning awareness that it may not even be desirable to maintain naturalness. Is the concept of naturalness still sufficient to guide protected area stewardship? Should it be reinterpreted or more precisely defined? Are there other concepts that should complement it or take its place (Box 1)? In April 2007 we convened a small workshop to explore this question. In this paper, we share some of what was discussed in that workshop. We examine the various meanings of naturalness and why it is increasingly problematic (as commonly defined) as a central goal for protected area management. We detail the case for and against human intervention in ecosystem processes. We explore how naturalness might be redefined or reinterpreted, and how concepts such as ecological integrity

Synthesis, structure, and electronic properties of a dimer of Ru(bpy)2 doubly bridged by methoxide and pyrazolate.

Abstract: The heterobridged dinuclear complex cis,cis-[(bpy)2Ru(μ-OCH3)(μ-pyz)Ru(bpy)2]2+ (1; bpy = 2,2′-bipyridine; pyz = pyrazolate) was synthesized and isolated as a hexafluorophosphate salt. Its molecular structure was fully characterized by X-ray crystallography, 1H NMR spectroscopy, and ESI mass spectrometry. The compound 1·(PF6)2 (C44H38F12N10OP2Ru2) crystallizes in the monoclinic space group P21/c with a = 13.3312(4) A, b = 22.5379(6) A, c = 17.2818(4) A, β = 99.497(2)°, V = 5121.3(2) A3, and Z = 4. The meso diastereoisomeric form was exclusively found in the crystal structure, although the NMR spectra clearly demonstrated the presence of two stereoisomers in solution (rac and meso forms at approximately 1:1 ratio). The electronic properties of the complex in acetonitrile were investigated by cyclic voltammetry and UV−vis and NIR−IR spectroelectrochemistries. The stepwise oxidation of the RuII−RuII complex into the mixed-valent RuII−RuIII and fully oxidized RuIII−RuIII states is fully reversible on the time...

Frontiers of vegetation science - An evolutionary angle

Abstract: s of presentations at the 51st Annual Symposium of the International Association for Vegetation Science, Stellenbosch, South Africa, September 7-12, 2008.

Reduction of an η2-iminoacyl ligand to η2- iminium enabled by adjacent carbon monoxide ligand replacement with a variable electron donor alkyne ligand in a cationic tungsten(II) bis(acetylacetonate) complex

Abstract: Cationic iminoacyl-carbonyl tungsten complexes of the type [W(CO) (eta (2)-MeNCR)(acac) 2] (+) (acac = acetylacetonate; R = Ph ( 1a), Me ( 1b)) easily undergo thermal substitution of CO with two-electron donors to yield [W(L)(eta (2)-MeNCR)(acac) 2] (+) (L = tert-butylisonitrile [R = Ph ( 2a), Me ( 2b)], 2,6-dimethylphenylisonitrile [R = Me ( 2c)], triphenylphosphine [R = Ph ( 3a), Me ( 3c)], and tricyclohexylphosphine [R = Ph ( 3b)]). Tricyclohexylphosphine complex 3b exhibits rapid, reversible phosphine ligand exchange at room temperature on the NMR time scale. Photolytic replacement of carbon monoxide with either phenylacetylene or 2-butyne occurs efficiently to form [W(eta (2)-alkyne)(eta (2)-MeNCR)(acac) 2] (+) complexes ( 5a- d) with a variable electron donor eta (2)-alkyne paired with the eta (2)-iminoacyl ligand in the W(II) coordination sphere. PMe 3 adds to 1a or 5b to form [W(L)(eta (2)-MeNC(PMe 3)Ph)(acac) 2] (+) [L = CO ( 4), MeCCMe ( 6)] via nucleophilic attack at the iminoacyl carbon. Addition of Na[HB(OMe) 3] to 5b yields W(eta (2)-MeCCMe)(eta (2)-MeNCHPh)(acac) 2, 8, which exhibits alkyne rotation on the NMR time scale. Addition of MeOTf to 8 places a second methyl group on the nitrogen atom to form an unusual cationic eta (2)-iminium complex [W(eta (2)-MeCCMe)(eta (2)-Me 2NCHPh)(acac) 2][OTf] ( 9[OTf], OTf = SO 3CF 3). X-ray structures of 2,6-dimethylphenylisonitrile complex 2c[BAr' 4 ], tricyclohexylphosphine complex 3b[BAr' 4 ], and phenylacetylene complex 5a[BAr' 4 ] confirm replacement of CO by these ligands in the [W(L)(eta (2)-MeNCR)(acac) 2] (+) products. X-ray structures of alkyne-imine complexes 6[BAr' 4 ] and 8 show products resulting from nucleophilic addition at the iminoacyl carbon, and the X-ray structure of 9[BAr' 4 ] reflects methylation at the imine nitrogen to form a rare eta (2)-iminium ligand.

trans-Diaqua­bis(2,2′-bipyridine-κ2 N,N′)ruthenium(II) bis­(trifluoro­methane­sulfonate)

Abstract: The title compound, trans-[Ru(bpy)2(H2O)2](CF3SO3)2 (bpy = 2,2′-bipyridine, C10H8N2), crystallized from the decomposition of an aged aqueous solution of a dimeric complex of cis-Ru(bpy)2 in 0.1 M triflic acid. The RuII ion is located on a crystallographic inversion center and exhibits a distorted octa­hedral coordination with equivalent ligands trans to each other. The Ru—O distance is 2.1053 (16) A and the Ru—N distances are 2.0727 (17) and 2.0739 (17) A. The bpy ligands are bent, due to inter-ligand steric inter­actions between H atoms of opposite pyridyl units across the Ru center. The crystal structure exhibits an extensive hydrogen-bonding network involving the water ligands and the trifluoromethane­sulfonate counter-ions within two-dimensional layers, although no close hydrogen-bond inter­actions exist between different layers.

Functional characters, texture and stress

Abstract: 1Botany Department, University of Otago, P.O. Box 56, Dunedin, New Zealand; E-mail bastow@bastow.ac.nz; 2Department of Environmental Science ‘G. Sarfatti’, University of Siena, Via P.A. Mattioli 4, 53100 Siena, Italy; E-mail chiarucci@unisi.it; 3Instituto Multidisciplinario de Biologia Vegetal, Universidad Nacional de Cordoba, Casilla de Correo, RA-5000 Cordoba, Argentina; E-mail sdiaz@com.uncor.edu; 4Department of Biology, University of North Carolina, Chapel Hill, NC 27599-3280, USA; E-mail peter.white@unc.edu; *Corresponding author.

Invasive species, management for conservation and remote sensing

Abstract: The paper chosen for the award by the Chief Editors of Applied Vegetation Science, from among those published in 2007 is that by Hartman & McCarthy (2007). Exotic (alien, non-indigenous) species are a concern for their impact on native communities, as well as fascinating probes into community structure: natural experiments. Recent research has tried to measure their impact by examining invaded and non-invaded sites. This approach has the flaw that the non-invaded sites may not have been invaded because they were different in the first place. Examining sites before and after an invasion is difficult because invasions are not normally noticed until after they have happened, and anyway there might have been an allogenic environmental change, or one caused by the reaction of the other species. The ideal would be to go backwards in time in both invaded and non-invaded sites. Impossible? But Hartman & McCarthy (2007) did this by dendrochronology. Working in deciduous hardwood forest in Ohio, USA, they shewed that the exotic understorey shrub Lonicera maackii (Rupr.) Herder reduced the growth of native trees in the overstorey.