Wolfgang Schoefberger

Synthesis and Characterization of a Stable Bismuth(III) A3–Corrole

An efficient metalation procedure for bismuth complexes with meso-substituted corrole ligands is presented. Reaction of 5,10,15-tris-pentafluorophenylcorrole H(3)(TpFPC) with Bi{N(SiMe(3))(3)} converts the free ligand H(3)(TpFPC) to a neutral low-valent species Bi(TpFPC), which has been characterized by different spectroscopic techniques. (Spectro)electrochemical studies were performed in order to describe the redox potentials of the Bi(TpFPC) complex and to ascribe the sites of electron transfer. The first crystal structure of a bismuth corrole is presented and compared to the geometry-optimized molecular structure obtained with density functional theory (DFT) calculations. We show an example of a 4-coordinate metallocorrole with a very large out-of-plane displacement and significant doming. The electronic structure of the novel bismuth corrole system is discussed in detail. Time-dependent DFT results support the proposed assignment of electronic transitions observed for the Bi(TpFPC) derivative. To account for the reactivity we investigated the photocatalytic properties of the Bi(TpFPC) complex.

The Role of 2,6-Diaminopyridine Ligands in the Isolation of an Unprecedented, Low-Valent Tin Complex

Stabilization of the central atom in an oxidation state of zero through coordination of neutral ligands is a common bonding motif in transition-metal chemistry. However, the stabilization of main-group elements in an oxidation state of zero by neutral ligands is rare. Herein, we report that the transamination reaction of the DAMPY ligand system (DAMPY=2,6-[ArNH-CH2 ]2 (NC5 H3 ) (Ar=C6 H3 -2,6-iPr2 )) with Sn[N(SiMe3 )2 ]2 produces the DIMPYSn complex (DIMPY=(2,6-[ArNCH]2 (NC5 H3 )) with the Sn atom in a formal oxidation state of zero. This is the first example of a tin compound stabilized in a formal oxidation state of zero by only one donor molecule. Furthermore, three related low-valent Sn(II) complexes, including a [DIMPYSn(II) Cl](+) [SnCl3 ](-) ion pair, a bisstannylene DAMPY{Sn(II) [N(SiMe3 )2 ]2 }2 , and the enamine complex MeDIMPYSn(II) , were isolated. Experimental results and the conclusions drawn are also supported by theoretical studies at the density functional level of theory and (119) Sn Mössbauer spectroscopy.

Benchmarking of ruthenium initiators for the ROMP of a norbornenedicarboxylic acid ester

Abstract The kinetic study of ring-opening metathesis polymerization (ROMP) of a diester functionalised norbornene derivative, (±)-exo,endo-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid diethyl ester, with a series of ruthenium benzylidene complexes revealed the applicability of these initiators for well defined polymerization reactions. Values for the rate of initiation as well as the rate of propagation of the initiators were determined and correlated to the molecular weight and polydispersity of the isolated polymers. As the only initiator providing an entry to virtually monodisperse polymers the classical “first generation Grubbs-catalyst” was identified, while N-heterocyclic carbene based initiators polymerized with a rate of propagation much higher than the rate of initiation yielding polymers with a broader molecular weight distribution.

Water-Soluble, Biocompatible Polyphosphazenes with Controllable and pH-Promoted Degradation Behavior

The synthesis of a series of novel, water-soluble poly(organophosphazenes) prepared via living cationic polymerization is presented. The degradation profiles of the polyphosphazenes prepared are analyzed by GPC, 31P NMR spectroscopy, and UV–Vis spectroscopy in aqueous media and show tunable degradation rates ranging from days to months, adjusted by subtle changes to the chemical structure of the polyphosphazene. Furthermore, it is observed that these polymers demonstrate a pH-promoted hydrolytic degradation behavior, with a remarkably faster rate of degradation at lower pH values. These degradable, water soluble polymers with controlled molecular weights and structures could be of significant interest for use in aqueous biomedical applications, such as polymer therapeutics, in which biological clearance is a requirement and in this context cell viability tests are described which show the non-toxic nature of the polymers as well as their degradation intermediates and products.

Chain-end-functionalized polyphosphazenes via a one-pot phosphine-mediated living polymerization.

A simple polymerization of trichlorophosphoranimine (Cl3P = N−SiMe3) mediated by functionalized triphenylphosphines is presented. In situ initiator formation and the subsequent polymerization progress are investigated by 31P NMR spectroscopy, demonstrating a living cationic polymerization mechanism. The polymer chain lengths and molecular weights of the resulting substituted poly(organo)phosphazenes are further studied by 1H NMR spectroscopy and size exclusion chromatography. This strategy facilitates the preparation of polyphosphazenes with controlled molecular weights and specific functional groups at the α-chain end. Such well-defined, mono-end-functionalized polymers have great potential use in bioconjugation, surface modification, and as building blocks for complex macromolecular constructs.

Asymmetrically substituted cationic indole- and fluorene porphyrins inhibit tumor proliferation in small intestinal neuroendocrine tumors and medullary thyroid carcinomas.

In this study we demonstrate anticancer activity of novel fully water soluble cationic porphyrins. The two cationic porphyrins 5,10,15-tris(N-methylpyridinium-4-yl)-20-[1-phenyl-4-(3-N-phenylsulfonylindolyl)]-21H,23H-porphyrin chloride (TMPy(3)PhenIndolprot(1)P-Cl(3)) and 5-{5-[2-(9,9-Dimethyl)fluorenyl]-N-methylpyridinium-3-yl}-10,15,20-tris(N-methyl-pyridinium-4-yl)-21H,23H-porphyrin chloride (TMPy(3)PyFluorenyl(1)P-Cl(4)) were prepared and their antiproliferative effects were studied in two human tumor cell lines and a normal human fibroblast cell line. Effects of the novel porphyrin compounds were evaluated in the small intestinal neuroendocrine tumor cell line KRJ-I, the medullary thyroid carcinoma cell line MTC-SK and the normal human fibroblast cell line HF-SAR by cell counting, cell proliferation assays and cell cytotoxicity analyses. TMPy(3)PhenIndolprot(1)P-Cl(3) and TMPy(3)PyFluorenyl(1)P-Cl(4) showed antiproliferative effects in the tumor cell lines MTC-SK and KRJ-I; cell viability was decreased and cytotoxic effects were quantified, while no significant alterations of the human fibroblasts were noted. With the advantage of full water solubility and antiproliferative effects in tumor cell lines, the novel porphyrin compounds TMPy(3)PhenIndolprot(1)P-Cl(3) and TMPy(3)PyFluorenyl(1)P-Cl(4) could be a new therapeutic option in anticancer treatment.

Proisocrinins A-F, brominated anthraquinone pigments from the stalked crinoid Proisocrinus ruberrimus.

New brominated anthraquinone pigments, proisocrinins A-F (1-6), were isolated from the strikingly scarlet-colored stalked crinoid Proisocrinus ruberrimus, which had been collected in the deep sea of the Okinawa Trough, Japan. The structures of the compounds were elucidated by spectroscopic analysis including HRMS, 1D 1H and 13C NMR, and 2D NMR. CD spectroscopy revealed that all compounds are present as optically active enantiomers. This is the first report of tribromo and tetrabromo anthraquinones from a natural source.

A water soluble tri-cationic porphyrin–EDTA conjugate induces apoptosis in human neuroendocrine tumor cell lines

Graphical abstract Highlights ► Synthesis of tri-cationic porphyrin–EDTA conjugate (TMPy3PhenEDTA-P-Cl4). ► Treatment of small-intestinal neuroendocrine tumor cells with TMPy3PhenEDTA-P-Cl4. ► Treatment of medullary thyroid carcinoma cell lines with TMPy3PhenEDTA-P-Cl4. ► Apoptotic cell death on MTC cells after treatment with TMPy3PhenEDTA-P-Cl4.

Backbone assignment and secondary structure of the PsbQ protein from Photosystem II

PsbQ is one of the extrinsic proteins situated on the lumenal surface of photosystem II (PSII) in the higher plants and green algae. Its three-dimensional structure was determined by X-ray crystallography with exception of the residues 14–33. To obtain further details about its structure and potentially its dynamics, we approached the problem by NMR. In this paper we report 1H, 15N, and 13C NMR assignments for the PsbQ protein. The very challenging oligo-proline stretches could be assigned using 13C-detected NMR experiments that enabled the assignments of twelve out of the thirteen proline residues of PsbQ. The identification of PsbQ secondary structure elements on the basis of our NMR data was accomplished with the programs TALOS+, web server CS23D and CS-Rosetta. To obtain additional secondary structure information, three-bond HN-Hα J-coupling constants and deviation of experimental 13Cα and 13Cβ chemical shifts from random coil values were determined. The resulting “consensus” secondary structure of PsbQ compares very well with the resolved regions of the published X-ray crystallographic structure and gives a first estimate of the structure of the “missing link” (i.e. residues 14–33), which will serve as the basis for the further investigation of the structure, dynamics and interactions.

Secondary structure estimation of recombinant psbH, encoding a photosynthetic membrane protein of cyanobacterium Synechocystis sp. PCC 6803

The PsbH protein of cyanobacterium Synechocystis sp. PCC 6803 was expressed as a fusion protein with glutathione-S transferase (GST) in E. coli grown on a mineral medium enriched in 15N isotope. After enzymatic cleavage of the fusion protein, the 1H-15N-HSQC spectrum of PsbH protein in presence of the detergent β-D-octyl-glucopyranoside (OG) was recorded on a Bruker DRX 500 MHz NMR spectrometer equipped with a 5 mm TXI cryoprobe to enhance the sensitivity and resolution. Non-labelled protein was used for secondary structure estimation by deconvolution from circular dichroism (CD) spectra. Experimental results were compared with our results from a structural model of PsbH using a restraint-based comparative modelling approach combined with molecular dynamics and energetic modelling. We found that PsbH shows 34–38% α-helical structure (Thr36-Ser60), a maximum of around 15% of β-sheet, and 12–19% of β-turn.