Reinhard Kirmse

1.3-DITHIOL-2-THION-4.5-DITHIOLAT AUS SCHWEFELKOHLENSTOFF UND ALKALIMETALL

Abstract Die Reaktion von Schwefelkohlenstoff mit Natrium oder Kalium fuhrt zur Bildung aquimolarer Mengen von 1.3-Dithiol-2-thion-4.5-dithiolat (1) und Trithiocarbonat. Durch Zugabe von ZnCl2 und NEt4Br last sich (1) stabilisieren. Der entstehende Zink-Komplex ermoglicht die Herstellung von 4.5-Bis(benzoylthio)-1.3-dithiol-2-thion (10), woraus durch Umsetzung mit Basen (1) in quantitativer Ausbeute wieder entsteht. Die Alkylierung von (1) fuhrt zu 4.5-Bis(alkylthio)-1.3-dithiol-2-thionen. (1) is ein neuer, schwefelreicher 1.2-Dithiolat-Ligand. Die Kristallstruktur des Bis-Chelates von (1) mit Ni(II) als (n-Bu4N)2-Salz bestatigt die fur (1) angenommene Struktur. The reaction of carbon disulfide with sodium or potassium in dimethyl formamide yields 1,3-dithiole-2-thione-4,5-dithiolate (1) and trithiocarbonate in equimolar amounts. (1) was stabilized by addition of ZnCl2 and NEt4Br. The resulting zinc complex enables the isolation of 4,5-bis(benzoylthio)-1,3-dithiole-2-thione (10). (1) can be recovered from...

How Metal Ions Affect Amyloid Formation: Cu2+‐ and Zn2+‐Sensitive Peptides

The common feature of proteins involved in many neurodegenerative diseases is their ability to adopt at least two different stable conformations. The conformational transition that shifts the equilibrium from the functional, mostly partially α‐helical structure, to the β‐sheet rich amyloid can be triggered by numerous factors, such as mutations in the primary structure or changes in the environment. We present a set of model peptides that, without changes in their primary structure, react in a predictable fashion in the presence of transition metal ions by adopting different conformations and aggregate morphologies. These de novo designed peptides strictly follow the characteristic heptad repeat of the α‐helical coiled‐coil structural motif. Furthermore, domains that favor β‐sheet formation have been incorporated to make the system prone to amyloid formation. As a third feature, histidine residues create sensitivity towards the presence of transition metal ions. CD spectroscopy, ThT fluorescence experiments, and transmission electron microscopy were used to characterize peptide conformation and aggregate morphology in the presence of Cu2+ and Zn2+. Furthermore, the binding geometry within peptide–Cu2+ complexes was characterized by electron paramagnetic resonance spectroscopy.

In(III), Tl(III) and V(IV) tris-chelates of the heterocyclic dithiolene and diselenolene ligands 1,3-dithiole-2-thione-4,5-dithiolate (dmit), 1,2-dithiole-3-thione-4,5-dithiolate (dmt) and 1,3-diselenole-2-selone-4,5-diselenolate (dsis). Crystal and molecular structure of (Bu4N)2 [V(dmt)3]

Abstract Synthesis and characterization of the first trischelates of the dichalcogenolene ligands 1,3-dithiole-2-thione-4,5-dithiolate (dmit), 1,2-dithiole-3-thione-4,5-dithiolate (dmt)and 1,3-diselenole-2-selone-4,5-diselenolate (dsis) with the central ions In(III), Tl(III) and V(IV) are reported. On (Bu4N)2[V(dmt)3] the first X-ray structure of a dithiolene tris-chelate containing unsymmetric ligand was carried out: the compound crystallizes monoclinic, space group P21/c, with four molecules in the unit cell; a = 16.264(3), b = 17.319(4), c = 21.554(4) A, β = 103.03(2)°. The ligand dmt causes a very low symmetry of the VS6 moiety in [V(dmt)3]2− having pseudo-meridional arrangement of the three ligands. The EPR parameters of the compounds (Bu4N)2[V(dmit)3] and (Bu4N)2[V(dmt)3] measured in liquid and frozen acetonic solution are compared with those of the tris(maleonitriledithiolato)vanadate(IV) anion supporting a geometry of the anion being between octahedral and trigonal prismatic.

Single Crystal and Powder EPR Studies on Copper(II) Bis(di‐n‐butyldiselenocarbamate)

Copper(II) bis(di‐n‐butyldiselenocarbamate) is studied in single crystals, diamagnetically diluted by Ni(II) bis(di‐n‐butyldiselenocarbamate), in polycrystalline samples and in frozen solutions by means of EPR. The EPR spectra show that in the unit cell two magnetic nonequivalent Cu(dbsc)2 molecules are to be found and that 77Se ligand hyperfine splitting can be detected. The principal axes of the g and the copper‐hfs tensor do not coincide. A spin Hamiltonian for this case is given. Contrary to the copper‐hfs and the 77Se‐hfs tensors, which were found to be in agreement with what is expected for a planar complex of approximately D2h symmetry, the behavior of the g tensor is significantly different with respect to analogous CuS4 compounds. This indicates that the electronic structure of the complex differs remarkably from the structure of planar Cu(II) complexes; consequently, the symmetry is C2h. The Se‐hfs data were used to estimate the degree of covalency in the Cu–Se σ bond. This was compared with par...

Tc(NX)Y3(Me2PhP)2 complexes (X = O or S; Y = Cl or Br). Preparation, characterization and EPR studies

Abstract The d 5 -‘low-spin’ Tc(II) complexes tribromonitrosyl-bis(dimethylphenylphosphine)technetium(II) and tribromo-thionitrosyl-bis(dimethylphenylphosphine)technetium(II) were prepared by ligand exchange starting from the analogous chloro compounds. The complexes were characterized chemically and IR, UVVis and EPR spectroscopically. In the room temperature EPR spectra a well-resolved 99 Tc hyperfine splitting is observed inidicating a ground state of the unpaired electron which is well separated from the other orbit states. The general features of the spectra at low temperatures are characteristic for an axially symmetric spin Hamiltonian. Analysis of the 99 Tc and 31 P hfs (hfs = hyperfine splittings) shows a marked covalency of the Tcligand bonds. A comparison is given between the chloro and bromo, as well as between the nitrosyl and thionitrosyl complexes.

Q-Band single-crystal EPR study and molecular orbital calculations of [(C6H5)4As][ReVINCl4/ReVOCl4]

Abstract A Q -band single-crystal EPR study of tetraphenylarsoniumtetrachloro-nitridorhenate(VI), [(C 6 H 5 ) 4 As][Re VI NCl 4 ], diamagnetically diluted by the isoelectronic oxorhenate(V) complex is reported. The EPR spectra are typical of an ion with 5d 1 ( S =1/2) configuration and are influenced by large rhenium hyperfine coupling constants and nuclear quadrupole interactions. They are characterized by well-resolved 185,187 Re hyperfine patterns with almost equal spacings and the occurrence of “forbidden” transitions ( Δm I =±1, Δm I =±2). The 185,187 Re hyperfine parameters as well as the data obtained from density functional theory (DFT) and the extended Huckel theory (EHT) molecular orbital calculations are used to analyze the spin density distribution in the system under study. Thereby, the negative sign found for the spin density at the nitrogen from DFT is mainly determined by spin polarization. In addition, both MO methods are used to calculate the electric field gradient being responsible for the 185,187 Re nuclear quadrupole coupling.

[TcNBr4−pClp]− (p = 1–3) nitridotechnetate(VI) mixed-ligand complexes. An EPR study

Abstract The formation of mixed-ligand complexes of the type [TcNBr 4− p Cl p ] − ( p = 1–3) during the reaction between TcNBr 4 − and TcNCl 4 − is reported. Evidence of the individual mixed-ligand compounds is given by their EPR spectral data. In liquid as well as in frozen solution, a strong dependence of the EPR quantities on the composition of the coordination sphere could be detected. This is shown by a nearly linear dependence of g 0 , g ∥, a 0 Tc and A ∥ Tc on the spin-orbit coupling constants of the equatorial donors.

EPR on trichloro-nitrosyl-bis(dimethylphenylphosphine)technetium(II) TcCl3(NO)(PMe2Ph)2

Abstract The d 5 low-spin Tc(II) complex trichloro-nitrosyl-bis(dimethylphenyl-phosphine)technetium(II) was studied by EPR at 295 ≥ T ≥ 27.2 K. In the room-temperature spectrum well-resolved 99 Tc hyperfine splitting is observed indicating a ground state for the unpaired electron which is well separated from other orbital states. At low temperatures the spectrum can be fitted by an axial spin Hamiltonian. The analysis of the 99 Tc hyperfine splitting shows remarkable covalent interactions with the “in-plane” ligands. The 31 P superhyperfine splitting observed was used to get information about the overall spin density distribution in the molecular orbital of the unpaired electron.

Transition metal complexes of quadridentate pyrazolo-based ligands with two thiolato and two imine donor atoms

Abstract The copper(II), nickel(II) and cobalt(II) complexes of new S 2 N 2 ligands on Schiff bases of 4-benzoyl-3-methyl-1-phenyl-2-pyrazoline-5-thione and various diamines were prepared and characterized. Using different diamines it is possible to control the geometry around the central metal atom. An X-ray structure determination of a Cu(II) S 2 N 2 complex showed the (NCuS, NCuS) dihedral angle to be 52.11° and the following distances: CuS1 2.2274, CuS2 2.2089, CuN13 1.973, CuN23 1.998 A.

Lipophilic technetium complexes. III. Chelate complexes of technetium(V) containing the Tc-nitrido core

Etude de la formation des complexes [TcNL 2 ] 0,−2,+2 . Tres grande stabilite de la triple liaison Tc-N. Spectres IR et RMN