Biomedical subjects
Publications and source records attributed to Kay Severin.
The assembly of organometallic half-sandwich complexes with bis(dihydroxypyridine) ligands gives hexanuclear structures, which can be regarded as expanded triple-stranded helicates.
A coordination cage with an elusive icosahedral geometry was obtained by K+-induced rearrangement of a hexanuclear [(cymene)Ru(pyridine-3,5-dicarboxylate)]6 complex.
The chelate ligand tris[(1-vinylimidazol-2-yl)methyl]amine (5) was synthesized in five steps from commercially available starting materials. Upon reaction with ZnCl2 or CuCl2 in the presence of NH4PF6, the complexes [Zn5Cl]PF6 (6) and [Cu5Cl]PF6 (7) were obtained. The structure of both complexes was determined by single-crystal X-ray crystallography. Immobilization of 6 and 7 was achieved by co-polymerization with ethylene glycol dimethacrylate. The supported complexes P6-Zn and P7-Cu were found to be efficient catalysts for the hydrolysis of bis(p-nitrophenyl)phosphate (BNPP) at 50 degrees C. At pH 9.5, the heterogeneous catalyst P7-Cu was 56 times more active than the homogeneous catalyst 7. Partitioning effects, which increase the local concentration of BNPP in the polymer, are shown to contribute to the enhanced activity of the immobilized catalyst.
The combination of the air-stable RuIII complex [Cp*RuCl2(PPh3)] with AIBN can be used to catalyze the atom transfer radical addition reactions of polychlorinated compounds and of sulfonyl chlorides to olefins with unprecedented turnover numbers of up to 44 000.
Indicator-displacement assays based on the organometallic complex [{Cp*RhCl2}2] (Cp*=pentamethylcyclopentadienyl) and the dye gallocyanine were used to sense amino sugars and aminoglycosides in buffered aqueous solution by conducting UV-visible spectroscopy. The data of three assays at pH 7.0, 8.0, and 9.0 were sufficient to distinguish between the amino sugars galactosamine, glucosamine, mannosamine and the aminoglycosides kanamycin A, kanamycin B, amikacin, apramycin, paromomycin, and streptomycin. Furthermore, the assays were used to characterize mixtures of aminoglycosides and obtain quantitative information about the respective analytes.
The synthesis of water-soluble, organometallic macrocycles is described. They were obtained by self-assembly in reactions of the half-sandwich complexes [[Ru(C6H5Me)Cl2]2], [[Ru(p-cymene)Cl2]2], [[Rh(Cp)Cl2]2], and [[Ir(Cp*)Cl2]2] with the ligand 5-dimethylaminomethyl-3-hydroxy-2-methyl-4-(1H)-pyridone in buffered aqueous solution at pH 8. The structure of the Ru-(p-cymene) complex was determined by single-crystal X-ray crystallography. Upon mixing, these complexes undergo scrambling reactions to give dynamic combinatorial libraries. In combination with structurally related complexes based on amino-methylated 3-hydroxy-2-(1H)-pyridone ligands, an exchange of metal fragments but no mixing of ligands was observed. This self-sorting behavior was used to construct dynamic combinatorial libraries of macrocycles, in which two four-component sub-libraries are connected by two common building blocks. This type of network topology influences the adaptive behavior of the library as demonstrated in selection experiments with lithium ions as the target.
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Three immobilized Cu(II) complexes were generated by the following: (a) homopolymerization of the N,N',N' '-chelate ligand tris[2-(1-vinylimidazolyl)]phosphine (1) and subsequent metalation with CuCl2; (b) copolymerization of 1 with ethyleneglycol dimethacrylate (EGDMA) und subsequent metalation with CuCl2; or (c) molecular imprinting with the organometallic Mo-complex [Mo(eta3-C4H7)(CO)2(1)](TsO) (5) and EGDMA and subsequent replacement of Mo(II) by Cu(II). All three polymeric Cu complexes were found to efficiently promote the hydrolysis of activated phosphoesters with the relative activity being dependent on the nature of the polymer and the substrate.
A meso-tetraaryl ruthenium porphyrin complex having four polymerizable vinylbenzoxy groups (2) has been synthesized by reaction of pyrrole with 4-(vinylbenzoxy)benzaldehyde and subsequent metalation with [Ru3(CO)12]. The porphyrin complex was immobilized by copolymerization with ethylene glycol dimethacrylate. The resulting polymer P2 was found to catalyze the oxidation of alcohols and alkanes with 2,6-dichloropyridine N-oxide without activation by mineral acids. Under similar conditions, the homogeneous catalyst 2 was completely inefficient. By using diphenylaminomethane and 1-aminoadamantane as coordinatively bound templates during the polymerization procedure, the molecularly imprinted polymers P3 and P4 have been synthesized. Compared with the polymer P2, the imprinted catalysts displayed a significantly increased activity with rate enhancements of up to a factor of 16.
Twenty natural amino acids can be distinguished with high fidelity using an array of indicator displacement assays in combination with a multivariate analysis. The array is easily constructed by mixing of commercially available building blocks at different pH.
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The reaction of [(Et(3)P)PdCl(2)](2) with 2,3-dihydroxypyridine, 5-chloro-2,3,-dihydroxypyridine, or 2-hydroxynicotinic acid in the presence of base gives neutral, metallomacrocyclic compounds in which the heterocycles act as dianionic, bridging ligands. The macrocycles contain four or ten palladium atoms as evidenced by single crystal X-ray analyses.
Experimental data are presented which demonstrate that the target concentration has a strong influence on the outcome of selection experiments with a dynamic mixture of self-assembled receptors.
The reaction of half-sandwich complexes of ruthenium, rhodium, and iridium with amino-substituted 3-hydroxy-2-pyridone ligands in aqueous solution gives monomeric O,O'-chelate complexes. Upon addition of base, the complexes assemble to form trimeric metallamacrocycles, as evidenced by NMR spectroscopy and single-crystal X-ray analyses. The macrocycles are able to act as highly selective receptors for lithium ions. The binding constants depend on the nature of the half-sandwich complex, the ligand, and the pH. With a commercially available (cymene)Ru complex, a receptor with a Li+ binding constant of K(a) = 5.8 (+/-1.0) x 10(4) M(-1) and a Li+-Na+ selectivity of 10 000:1 can be obtained. The fact that the assembly process of the receptor is pH-dependent can be used to detect the presence of lithium ions by a pH measurement. Furthermore, it is possible to transduce the binding of Li+ into a change of color by means of a chemical reaction with FeCl(3). This allows the detection of Li+ in the pharmacologically relevant concentration range of 0.5-1.5 mM by the "naked eye".
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Methods for the synthesis of bimetallic complexes in which two different metal fragments are connected by three chloro or bromo bridges are reported. The reactions are general, fast, and give rise to structurally defined products in quantitative yields. Therefore, they are ideally suited for generating a library of homo- and heterobimetallic complexes in a combinatorial fashion. This is of special interest for applications in homogeneous catalysis. Selected members of this library were synthesized and comprehensively characterized; single-crystal X-ray analyses were performed for 15 new bimetallic compounds.
Numerical simulations are presented that describe the adaptive behavior of simple dynamic combinatorial libraries (DCLs) upon addition of a target. By studying the effect of various parameters such as the network topology, the initial concentrations, the association constants, and the binding affinities, general characteristics of such systems were derived. It is shown that the adaptation may lead to the amplification of molecules with a high affinity to the target, but only for specific boundary conditions. Furthermore, it is demonstrated that the selection process can be refined by using an evolutionary approach. These results are of importance for the design of selection experiments with DCLs.
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