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Organisationseinheit der BAM
Bromotricarbonyl{15-[2-(methylsulfanyl)ethylsulfanyl]pentadecanoic acid-kappa2S,S'}rhenium(I)
(2006)
The title compound, [ReBr(C18H36O2S2)(CO)3], was synthesized and characterized as a non-radioactive surrogate of a novel Tc-containing fatty acid derivative prepared according to the tricarbonyl/dithioether design with the objective of developing new Tc-based radiopharmaceuticals for the non-invasive diagnosis of myocardial metabolism. The Re chelate contains the metal in the oxidation state +1 and is attached to the terminal position of a fatty acid. The complex formation was accomplished by a ligand exchange reaction using [NBu4]2[Re(CO)3Br3] as starting material.
The Keggin type polyoxotungstate [Ti2W10PO40]7- forms stable associates with the biopolymer chitosan in the nanometer size range. The cluster compound crystallizes from aqueous solution as K4H3[Ti2W10PO40] · 15H2O having a tetragonal structure. Both, the cluster compound and the chitosan/[Ti2W10PO40] associates show a high hydrolytic stability at pH 7.4. The associates formed between the cluster anion [Ti2W10PO40]7- with the polyaminosaccharide chitosan have been characterized by photon correlation spectroscopy, scanning electron microscopy, filtration, centrifugation and zeta potential measurements. The size of the associates formed is in the range of ca. 5×101 to 5×102 nm. These particles have a defined stoichiometry with 56 cluster anions bound per molecule chitosan. The isoelectric point determined by zeta potential measurements was found for a cluster anion to chitosan molar ratio of 5.5, indicating the charge neutralization between protonated chitosan and [Ti2W10PO40]7- anions. Cellular uptake studies with [Ti2W10PO40]7- using tumor cell lines FaDu (human squamous carcinoma) and HT-29 (human adenocarcinoma) showed that the tungsten amount inside the cells is remarkably enhanced in the presence of chitosan.
The CuII complex of H4TETP (H4TETP = 1,4,8,11-tetraazatetradecane-1,4,8,11-tetrapropionic acid) is five-coordinate with a distorted square-pyramidal structure (τ = 0.45; i.e. the geometry is nearly half-way between square-pyramidal and trigonal-bipyramidal) and a relatively long Cu–N and a short Cu–O bond; the comparison between powder and solution electronic spectroscopy, the frozen solution EPR spectrum and ligand-field-based calculations (angular overlap model, AOM) indicate that the solution and solid state structures are very similar, i.e. the complex has a relatively low 'in-plane' and a significant axial ligand field with a dx²-y² ground state. The ligand-enforced structure is therefore shown to lead to a partially quenched Jahn–Teller distortion and to a relatively low complex stability, lower than with the corresponding acetate-derived ligand H4TETA. This is confirmed by potentiometric titration and by the biodistribution with 64Cu-labeled ligands which show that the uptake in the liver is significantly increased with the H4TETP-based system.
Hydrated actinide(IV) ions undergo hydrolysis and further polymerization and precipitation with increasing pH. The resulting amorphous and partly crystalline oxydydroxides AnOn(OH)4-2n·xH2O can usually be observed as colloids above the An(IV) solubility limit. The aging process of such colloids results in crystalline AnO2. The presence of carboxylates in the solution prevents the occurrence of such colloids by formation of polynuclear complexes through a competing reaction between hydrolysis and ligation. The majority of recently described carboxylates reveals a hexanuclear core of [An6(µ3-O)4(µ3-OH)4]12+ terminated by 12 carboxylate ligands. We found that the An(IV) carboxylate solution species remain often preserved in crystalline state. The An(IV) carboxylates show An–An distances which are ~ 0.03 Å shorter than the An–An distances in AnO2 like colloids. The difference in the distances could be used to identify such species in solution.
Structure determination of two asymmetrically substituted oxadiazoles from powder diffraction data
(2008)
The crystal structures of the 1,3,4 oxadiazole compounds N,N-dimethyl-N-[4-(1,3,4-oxadiazol-2-yl)phenyl]amine (1) and 2-methyl-5-phenyl-1,3,4-oxadiazole (2) have been determined. In case of 1 no adequate crystals were available; therefore the structure was solved at room temperature from X-ray powder diffraction data using the method of simulated annealing. This solution is compared to a second one obtained by applying the molecular replacement method. Subsequent Rietveld refinements combined with the so called two stage method based on the data collected to 1.6 Å resolution yielded an Rwp value of 7.27% for 1. Compound 1 crystallizes in the orthorhombic space group P212121 with lattice parameters of a = 7.599(4) Å, b = 6.004(2) Å, c = 21.736(3) Å. The crystal structure of 2 was solved by means of single crystal structure analysis (monoclinic space group P21/c, a = 8.010(3) Å, b = 10.783(4) Å, c = 19.234(7) Å, β = 90.794(9)°).
A systematic structural investigation of R-phenyl-substituted 2,2':6',2"-terpyridines, a family of mono- and bifunctional charge transfer (CT)-operated fluorescent reporters for protons and metal ions, is presented. These molecules are equipped with non-binding and analyte coordinating donor substituents R (R = CF3, H, OMe, OH, DMA, A15C5 equaling monoaza-15-crown-5) of various donor strength and display CT-controlled spectroscopic properties and communication of analytereceptor interactions. The crystal structures of the neutral fluorescent probes are compared to the structures of their terpyridine-alkylated or -protonated counterparts that represent model systems for acceptor protonation or cation coordination. The aim is here a better understanding of the complexation-induced structural and spectroscopic changes and the identification of common packing motifs of bpb-R thereby taking into account the importance of terpyridine building blocks for the construction of supramolecular systems and coordination arrays revealing ππ interactions.
Uranium(IV) sulfate in an aqueous solution and the solid state has been investigated with extended X-ray absorption fine structure (EXAFS) and X-ray diffraction (XRD). The coordination polyhedron comprises monodentate sulfate, bidentate sulfate, and water molecules. The coordination modes of sulfate in solution have been determined from the U-S distances with EXAFS. The U-S distance of 3.67 ± 0.02 Å indicates monodentate sulfate, and the U-S distance of 3.08 ± 0.02 Å indicates bidentate coordination. The obtained sulfur coordination numbers of a solution with a [SO42-]/[U4+] ratio of 40 suggest species with compositions of [U(SO4,bid)2(SO4,mon)2·nH2O]4- and [U(SO4,bid)3 (SO4,mon)2·mH2O]6-. Charge-compensating countercations or ion pairing with Na+ and NH4+ could not be detected with EXAFS. One of the solution species, [U(SO4)5H2O]6-, has been conserved in a crystal. The corresponding crystal structure of Na1.5(NH4)4.5[U(SO4)5·H2O]·H2O [space group P1, a = 9.4995(16) Å, b = 9.8903(16) Å, c = 12.744(2) Å, α = 93.669(2)°, β = 103.846(2)°, γ = 109.339(2)°] has been determined by single-crystal XRD. Two monomeric uranium(IV) sulfate complexes and three sodium units are linked in alternating rows and form a one-dimensoinal ribbon structure parallel to the a axis.