Synthesis and Molecular Structure of trans‐[IrCl(NO)(PtBu2H)2]BF4

The synthesis and structural characterization of trans‐[IrCl(NO)(PtBu₂H)₂]BF₄ ( 1 ) is reported. The title compound was prepared in good yield in the reaction of in situ‐prepared trans‐[IrCl(coe)(PtBu₂H)₂] (coe = cis‐cyclooctene) with an appropriate amount of nitrosonium tetrafluoridoborate in dichloromethane at room temperature. Single crystals of 1 were grown from dichloromethane/diethyl ether and were analyzed by X‐ray crystallography.     

Spontaneous Reductive Elimination at Iridium(III) Induced by the Strong π-Acceptor Ligand Trifluorophosphane

The reaction of the cyclometalated five-coordinate 16 VE iridium(III) compound [IrCl(H)(P(tBu)₂C₆H₄-κ²P,C)(P(tBu)₂Ph)] ( 1 ) with the strong π-acceptor ligand trifluorophosphane resulted quickly in the quantitative formation of the new iridium(I) complex trans-[IrCl(PF₃)(P(tBu)₂Ph)₂] ( 2 ). This unexpected spontaneous reductive elimination was already observed in reactions of 1 with the very strong π-acceptor ligands CO and NO⁺. First indications during reactions of 1 with lesser strong π-acceptor ligands like alkyl or arylphosphanes did not show this inversion behavior of the cyclometalation. The title species 2 was characterized by spectroscopic methods and its molecular structure in the crystal was confirmed by X-ray crystallography.     

Stable Sulfur Isotope Effects Related to Local Intense Sulfate Reduction in a Tidal Sandflat (Southern North Sea): Results from Loading Experiments

Abstract

Anoxic sediment surfaces coloured black by iron monosulfides (“black spots”) evolve in tidal sandflats of the Wadden Sea (southern North Sea) as a result of the degradation of buried organic matter. To follow the short- and long-term effects of organic matter burial on pore water and sediment isotopic biogeochemistry, formation of artificial black spots was initiated on the Groninger Plate (site RP63) in the backbarrier tidal flats of Spiekeroog island. Changes in concentrations (DOC, TA, TOC, sulfate, sulfide, TRS, Fe) and isotopic compositions (sulfate, sulfide, TRS, pyrite, TOC) were followed for up to 12 months and compared to reference areas. 13°C ratios of TOC clearly mirror the early diagenetic degradation of organic matter. At least temporarily closed system sulfate reduction is inferred for the artificial black spot from the variation of sulfate concentrations and stable sulfur isotope partitioning, In the interstitial waters of the black spot, 34S/32S values of coexisting dissolved sulfate and sulfide yield fractionation degrees between ?5 and ?25%. On the reference area, 34S/32S are fractionated by ?32 to ?42% as calculated from the isotope composition of solid phase reduced sulfur and pore water sulfate. Sulfur isotope fractionation seems to increase with decreasing sulfate reduction rate. Limiting factor seems to be the availability of DOC. Between the pyrite pool and the dissolved sulfide in the black spot, no significant isotope exchange is observed within 12 months.     

Barium isotope fractionation during experimental formation of the double carbonate BaMn[CO3]2 at ambient temperature

In this study, we present the first experimental results for stable barium (Ba) isotope (¹³⁷Ba/¹³⁴Ba) fractionation during low-temperature formation of the anhydrous double carbonate BaMn[CO₃]₂. This investigation is part of an ongoing work on Ba fractionation in the natural barium cycle. Precipitation at a temperature of 21±1°C leads to an enrichment of the lighter Ba isotope described by an enrichment factor of?0.11±0.06‰ in the double carbonate than in an aqueous barium-manganese(II) chloride/sodium bicarbonate solution, which is within the range of previous reports for synthetic pure BaCO ₃ (witherite) formation.     

Inhibition of amyloid aggregation by formation of helical assemblies

The formation of amyloid aggregates is responsible for a wide range of diseases, including Alzheimer's and Parkinson's disease. Although the amyloid-forming proteins have different structures and sequences, all undergo a conformational change to form amyloid aggregates that have a characteristic cross-β-structure. The mechanistic details of this process are poorly understood, but different strategies for the development of inhibitors of amyloid formation have been proposed. In most cases, chemically diverse compounds bind to an elongated form of the protein in a β-strand conformation and thereby exert their therapeutic effect. However, this approach could favor the formation of prefibrillar oligomeric species, which are thought to be toxic. Herein, we report an alternative approach in which a helical coiled-coil-based inhibitor peptide has been designed to engage a coiled-coil-based amyloid-forming model peptide in a stable coiled-coil arrangement, thereby preventing rearrangement into a β-sheet conformation and the subsequent formation of amyloid-like fibrils. Moreover, we show that the helix-forming peptide is able to disassemble mature amyloid-like fibrils.     

Biosupramolecular nanowires from chlorophyll dyes with exceptional charge-transport properties

Conductive tubes: Self-assembled nanotubes of a bacteriochlorophyll derivative are reminiscent of natural chlorosomal light-harvesting assemblies. After deposition on a substrate that consists of a non-conductive silicon oxide surface (see picture, brown) and contacting the chlorin nanowires to a conductive polymer (yellow), they show exceptional charge-transport properties.     

Ligand exchange reactions between copper(II)- and nickel(II)-chelates of different sulphur- and selenium-containing ligands

A single-crystal E.S.R. and multi-nuclear ENDOR study of the mixed ligand complex tetra-n-butylammonium(maleonitriledithiolato)(monoethyldithiophosphato)cuprate(II), diamagnetically diluted by the corresponding Ni(II) complex, and the crystal structure of the host complex are reported. n-Bu₄N[Ni(mnt)(HEtdtp)].0·7 acetone is triclinic, space group P1, Z = 2 with a = 9·029(2), b = 13·432(4), c = 17·246(5) Å, α = 108·9(1), β = 90·2(1) and γ = 109·4(1)°. The spin-hamiltonian parameters are calculated from the results of an extended Hückel molecular orbital calculation. The experimental g-tensor and the copper and the four sulphur hyperfine coupling tensors are reporduced well. The almost isotropic and unexpectedly large coupling of the phosphorous atom is negative, which can be understood qualitatively from a spin polarization mechanism.

The hyperfine coupling tensors of eight protons, three of the acetone molecule, four of the tetra-n-butylammonium cation and one intramolecular one, could be determined. The E.S.R. linewidths are unusually small for Cu complexes. Unresolved proton hyperfine interactions are found to give the largest contribution.