Selective halogenation at the pnictogen atom in Lewis-acid/base-stabilised phosphanylboranes and arsanylboranes

The halogenation of Lewis-acid/base-stabilised phosphanylboranes () and arsanylboranes () with CX(4) (X = Cl, Br) leads selectively to the substitution of both protons at the pentel atom and the new compounds [(CO)(5)W(X(2)PBH(2).NMe(3))] (: X = Cl, : X = Br) and [(CO)(5)W(X(2)AsBH(2).NMe(3))] (: X = Cl, : X = Br), respectively, are obtained. The new products were comprehensively characterised by spectroscopic methods and by X-ray crystallography. While compounds and show an antiperiplanar arrangement of the Lewis acid (W(CO)(5)) and the Lewis base (NMe(3)) in the solid state, a synclinal arrangement in and , respectively, was observed. Computational calculations of the optimised antiperiplanar and synclinal geometries of the compounds and in the gas phase slightly favour the antiperiplanar arrangement of the Lewis acid and the Lewis base for both compounds.     

Synthesis and self-association properties of flexible guanidiniocarbonylpyrrole-carboxylate zwitterions in DMSO: intra- versus intermolecular ion pairing

We have synthesized a new class of flexible zwitterions 6a-e, in which a carboxylate is linked via an alkyl chain with variable length (one to five methylene groups) to a guanidiniocarbonylpyrrole cation. The self-association properties of these zwitterions were determined by NMR dilution studies in DMSO and by ESI-MS experiments. The stability and hence also the size of the aggregates formed via self-assembly is critically dependent on the length and therefore flexibility of the spacer. Whereas the smallest zwitterion 6a forms large aggregates already at low concentrations, the more flexible zwitterions only form small oligomers (6b) or dimers (6c-e) at much larger concentrations. The differences between the five zwitterions can be explained based on the different extent of intramolecular ion pairing within the monomers. Any intramolecular ion pairing, which becomes possible with increasing linker length, stabilizes the monomer and therefore destabilizes any oligomer.     

Investigation into the formation of supramolecular compounds from mixed As/S-ligand complexes [(Cp*Mo)2As2S3] (Cp* = C5Me5) and copper halides

The coordination behavior of [(Cp*Mo)2As2S3] (3) (Cp* = C5Me5) toward Cu(I) halides was investigated. One dimensional polymers of the general formula [(Cp*Mo)2As2S3(CuHal)2]n (Hal = Cl, 4; Br, 5) and an oligomer of composition [{(Cp*Mo)2As2S3}3(CuI)7] (6) formed upon the reaction of 3 with the corresponding copper halide. All of the compounds were characterized by ESI-MS, elemental analysis, and single-crystal X-ray crystallography. The solid-state structures of 4 and 5 are isostructural and contain 1D S-shaped chains. This peculiar folding is achieved by alternating planar and folded Cu2Hal2 rings linked together by the central monosulfide bridge of the middle deck of the organometallic unit. The structure of 6 is characterized by a novel [CuI]7 aggregate, which forms a very flat Cu6I3S3 bowl along with three integrated peripheral [(Cp*Mo)2As2S3] building blocks. In contrast to earlier findings, the middle deck of the organometallic units consists in all structures of two trapezoidal AsS dumbbells and one monosulfide ligand.     

Electrocatalytic hydrogen redox chemistry on gold nanoparticles

Electrocatalytic proton reduction leading to the formation of adsorbed molecular hydrogen on gold nanoparticles of 1-3 and 14-16 nm diameter stabilized by 1-mercapto-undecane-11-tetra(ethyleneglycol) has been demonstrated by cyclic voltammetry using a hanging mercury drop electrode. The nanoparticles were adsorbed to the electrode from aqueous dispersion and formed robust surface layers transferrable to fresh base electrolyte solutions. Unique electrocatalytic proton redox chemistry was observed that has no comparable counterpart in the electrochemistry of bulk gold electrodes. Depending on size, the nanoparticles have a discrete number of electrocatalytically active sites for the two-electron/two-proton reduction process. The adsorbed hydrogen formed is oxidized with the reverse potential sweep. These findings represent a new example of qualitative different behavior of nanoparticles in comparison with the corresponding bulk material.     

Interaction of cephalosporins with outer membrane channels of Escherichia coli. Revealing binding by fluorescence quenching and ion conductance fluctuations

Outer membrane channels in gram-negative bacteria are implicated in the influx of the latest generation of cephalosporins. We have measured the interaction strengths of ceftriaxone, cefpirome and ceftazidime in the two most abundant outer membrane porins of Escherichia coli, OmpF and OmpC, by both ion current fluctuations through single protein channels and fluorescence quenching. Statistical analysis of individual antibiotic entry events in membrane-incorporated porins yielded the kinetic rates and the equilibrium binding constant of each antibiotic-porin pair. Affinity constants were independently obtained by measuring the static quenching of inherent tryptophan fluorescence in the porins in the presence of the antibiotics. Through an empirical inner filter effect correction we have succeeded in measuring the chemical interaction of these strongly absorbing antibiotics, and obtained a qualitative agreement with conductance measurements. The interaction of all three antibiotics is smaller for OmpC than OmpF, and in the case of each porin the interaction strength series ceftriaxone > cefpirome > ceftazidime is maintained.     

Parametrization of multiply differential cross sections

Multiply differential cross sections for two- and three-electron escape are parametrised in terms of generalised tensorial asymmetry parameters. The analysis is based exclusivly on rotational invariance as an exact symmetry for the experimental set up. No approximate assumptions are made on the correlated dynamics of many- electron systems. Results are valid for any atomic and molecular target. The new parameters may be used to describe experimental and theoretical data in a compact way, but also to link e.g. coincidence and non-coincidence measurements with each other.     

Zum Reaktionsverhalten der Tris(dialkylthiophosphinyl)phosphane – Die Kristallstruktur von [Ag{O[P(S)Me2]2}2] [AsF6]

Reactivity of Tris(dialkylthiophosphinyl)phosphines – Crystal Structure of [Ag{O[P(S)Me₂]₂}₂][AsF₆] In contrast to tris(dialkylphosphoryl)phosphines the reaction of tris(dimethylthiophosphinyl)phosphine with transition metal hexafluoroarsenates of the type [M(SO₂)_m [AsF₆]_n (M = Ag, m = 0, n = 1; M = Fe, Cd, m = n = 2) forms no molecular 2 : 1-complexes but polymeric products. The silver polymer is transformed into [Ag{O[P(S)Me₂]₂}₂][AsF₆], which is also formed by the reaction of Ag[AsF₆] with O[P(S)Me₂]₂. It crystallizes in the space group P1 with a = 862.5(2), b = 1 241.4(2), c = 1 254.0(3)pm, α = 80.34(1), β = 101.99(6), γ= 73.75(1)° (at 20°C) and Z = 2. The central silver atom is surrounded by four sulphur atoms in a slighly distorted tetrahedron. The average (Ag? S) and (P? S) bond lengthes are 259.4(2) pm and 194.9(2)pm, respectively.     

Photochemistry of Bacteriochlorophylls in Human Blood Plasma: 1. Pigment Stability and Light-induced Modifications of Lipoproteins

Transmetalated derivatives of bacteriochlorophyll are promising sensitizers in photodynamic therapy. Protocols using short delay times between injection and irradiation cause interest in the photochemistry of these pigments in the blood. Using near-infrared irradiation where these pigments absorb strongly, we have studied the photochemistry of Zn- and Pd-bacteriopheophorbide (WST09), and of the highly polar taurinated Pd-derivative, WST11, in isolated fractions of human blood plasma. The stability of all pigments is increased in blood plasma, compared with monomeric solutions. Pd-bacteriopheophorbide is much more stable than the other two derivatives. It also has a higher capacity for inducing reactive oxygen species, yet the consumption of oxygen is comparable. There is furthermore evidence for photobleaching under anoxic conditions. The generation of hydroperoxides (ROOH) is faster with Pd- than with Zn-complexes; the formation of endoperoxides (ROOR′), measured as thiobarbituric acid reactive substances, is comparable with the two central metals. Formation of both ROOH and ROOR′ is increased in low-density lipoproteins (LDL) compared with high-density lipoproteins (HDL), which is probably related to the higher concentration of target molecules in the former. In HDL, extensive cross-linking is induced among the apolipoproteins; judged from the electrophoretic mobility of LDL and HDL particles, there is also a gross structural change. Photosensitized cross-linking is much less pronounced with high-density proteins.     

Binding,Release and Functionalization of Intact Pnictogen Tetrahedra Coordinated to Dicopper Complexes

The bridging MeCN ligand in the dicopper(I) complexes [(DPFN)Cu₂(μ,η¹ : η¹-MeCN)][X]₂ (X=weakly coordinating anion, NTf₂ ( 1 a ), FAl[OC₆F₁₀(C₆F₅)]₃ ( 1 b ), Al[OC(CF₃)₃]₄ ( 1 c )) was replaced by white phosphorus (P₄) or yellow arsenic (As₄) to yield [(DPFN)Cu₂(μ,η² : η²-E₄)][X]₂ (E=P ( 2 a – c ), As ( 3 a – c )). The molecular structures in the solid state reveal novel coordination modes for E₄ tetrahedra bonded to coinage metal ions. Experimental data and quantum chemical computations provide information concerning perturbations to the bonding in coordinated E₄ tetrahedra. Reactions with N-heterocyclic carbenes (NHCs) led to replacement of the E₄ tetrahedra with release of P₄ or As₄ and formation of [(DPFN)Cu₂(μ,η¹ : η¹-^MeNHC)][X]₂ ( 4 a,b ) or to an opening of one E−E bond leading to an unusual E₄ butterfly structural motif in [(DPFN)Cu₂(μ,η¹ : η¹-E₄^DippNHC)][X]₂ (E=P ( 5 a,b ), E=As ( 6 )). With a cyclic alkyl amino carbene (^EtCAAC), cleavage of two As−As bonds was observed to give two isomers of [(DPFN)Cu₂(μ,η² : η²-As₄^EtCAAC)][X]₂ ( 7 a,b ) with an unusual As₄-triangle+1 unit.     

通过脱碳控制全球平均温度

Establishing a reliable method to predict the global mean temperature (T_e) is of great importance because CO₂ reduction activities require political and global cooperation and significant financial resources. The current climate models all seem to predict that the earth's temperature will continue to increase, mainly based on the assumption that CO₂ emissions cannot be lowered significantly in the foreseeable future. Given the earth's multifactor climate system, attributing atmospheric CO₂ as the only cause for the observed temperature anomaly is most likely an oversimplification; the presence of water (H₂O) in the atmosphere should at least be considered. As such, T_e is determined by atmospheric water content controlled by solar activity, along with anthropogenic CO₂ activities. It is possible that the anthropogenic CO₂ activities can be reduced in the future. Based on temperature measurements and thermodynamic data, a new model for predicting T_e has been developed. Using this model, past, current, and future CO₂ and H₂O data can be analyzed and the associated T_e calculated. This new, esoteric approach is more accurate than various other models, but has not been reported in the open literature. According to this model, by 2050, T_e may increase to 15.5 ℃ under "business-as-usual" emissions. By applying a reasonable green technology activity scenario, T_e may be reduced to approximately 14.2 ℃. To achieve CO₂ reductions, the scenario described herein predicts a CO₂ reduction potential of 513 gigatons in 30 years. This proposed scenario includes various CO₂ reduction activities, carbon capturing technology, mineralization, and bio-char production; the most important CO₂ reductions by 2050 are expected to be achieved mainly in the electricity, agriculture, and transportation sectors. Other more aggressive and plausible drawdown scenarios have been analyzed as well, yielding CO₂ reduction potentials of 1051 and 1747 gigatons, respectively, in 30 years, but they may reduce global food production. It is emphasized that the causes and predictions of the global warming trend should be regarded as open scientific questions because several details concerning the physical processes associated with global warming remain uncertain. For example, the role of solar activities coupled with Milankovitch cycles are not yet fully understood. In addition, other factors, such as ocean CO₂ uptake and volcanic activity, may not be negligible.