Gemischtligandkomplexe des Technetiums. XVI. Darstellung und Struktur von (1,2-Dicyanoethen-1,2-dithiolato)bis(dimethylphenylphosphan)nitridotechnetium (V), [TcN(Me2PhP)2(mnt)]

Mixed-Ligand Complexes of Technetiums. XVI Synthesis and Structure of (1,2-Dicyanoethene-1,2-dithiolato)bis(dimethylphenylphosphine)nitridotechnetium(V), [TcN(Me₂PhP)₂(mnt)] [TcN(Me₂PhP)₂(mnt)] is formed from [TcNCl₂(Me₂PhP)₃] and one equivalent of the sodium salt of 1,2-dicyanoethene-1,2-dithiolate (Na₂mnt). The same reaction yields [TcN(mnt)₂]^2?, when a large excess of the ligand and long reaction periods are applied. The complex anion can be isolated as tetraalkylammonium or tetraphenylarsonium salts. [TcN(Me₂PhP)₂(mnt)] crystallizes in the triclinic space group P1 (a = 10.000(5), b = 14.182(6), c = 17.77(1) Å, α = 98.77(3), β = 103.77(3), γ = 104.55(3)°; Z = 4). The coordination sphere is a square pyramid with the sulfur and phosphorus atoms as basal plane. Tc is situated out of this plane by 0.56 Å towards the nitrido ligand.     

Synthese,Strukturen und Reaktivität von [(2,4,6-Ph3C6H2)Te(μ2-O)X]2 (X  Br und I)

Synthesis, Structures, and Reactivity of [(2,4,6-Ph₃C₆H₂)Te(μ₂-O)X]₂ (X ? Br, I) [(2,4,6-Ph₃C₆H₂)Te]₂ reacts with iodine affording the aryltellurenic halide (2,4,6-Ph₃C₆H₂)TeI, which is oxidized by oxygen to yield [(2,4,6-Ph₃C₆H₂)Te(μ₂-O)I]₂. It crystallizes with two molecules of dichloromethane in the monoclinic space group P2₁/c with a unit cell of the dimensions a = 911.3(4); b = 1153.3(2); c = 2244.1(9) pm; β = 93.53(2)°, Z = 2). The analogues bromo compound [(2,4,6-Ph₃C₆H₂)Te(μ₂-O)Br]₂ is obtained by the reaction of [(2,4,6-Ph₃C₆H₂)Te(μ₂-O)I]₂ with NH₄Br. It crystallizes with two molecules of xylene in the monoclinic space group P2₁/n (a = 1067.5(5); b = 1018.4(4); c = 2486.5(8) pm; β = 101.71(2)°; Z = 2). Both compounds are built up by two (2,4,6-Ph₃C₆H₂)TeX units (X ? Br, I) which are linked by two oxgen bridges to form centrosymmetric molecules. The Te? O? Te angles are 102°. Distinct Te? O bond lengths have been found (191.4(2) and 208.6(2) pm in [(2,4,6-Ph₃C₆H₂)Te(μ₂-O)I]₂ and 189.8(4)/208.4(5 pm in the bromo compound).     

Gemischtligand-Komplexe des Rheniums. VI. Darstellung und Strukturen der Rhenium?Thionitrosyl-Komplexe mer-[Re(NS)Cl2(Me2PhP)3] · CH2Cl2 und trans-[Re(NS)Cl3(Me2PhP)2]

Mixed-ligand Complexes of Rhenium. VI. Synthesis and X-Ray Structures of the Rhenium Thionitrosyl Complexes mer-[Re(NS)Cl₂(Me₂PhP)₃] · CH₂Cl₂ and trans-[Re(NS)Cl₃(Me₂PhP)₂] mer-Dichlorotris(dimethylphenylphosphine)(thionitrosyl)rhenium(I), mer-[Re(NS)Cl₂(Me₂PhP)₃], and trans-Trichlorobis(dimethylphenylphosphine)(thionitrosyl)rhenium(II), trans-[Re(NS)Cl₃(Me₂PhP)₂], are formed during the reaction of rhenium(V) mixed-ligand complexes of the general formula [ReN(Cl)(Me₂PhP)₂(R₂tcb)] with disulphur dichloride (HR₂tcb = N-(N,N-dialkylthiocarbamoyl)benzamidine). The chelating ligands are substituted during the reaction. mer-[Re(NS)Cl₂(Me₂PhP)₃] crystallizes monoclinic in the space group P2₁/n. The dimensions of the unit cell are a = 8.854(2); b = 31.295(3); c = 11.981(3) Å; β = 108.14(1)°; Z = 4. A final R value of 0.033 was achieved on the basis of 5 387 reflections with I ≥ 3σ(I). The rhenium atom is coordinated in a distorted octahedral environment. The Me₂PhP ligands are arranged meridionally cis to the linear thionitrosyl group. trans-[Re(NS)Cl₃(Me₂PhP)₂] crystallizes in the monoclinic space group C2/c with an unit cell of the dimensions a = 33.320(9); b = 8.446(1); c = 17.28(5) Å; β = 116.09(1)°, Z = 8. The R value converged at 0.026 on the basis of 5 460 independent reflections. The metal is octahedrally coordinated with the phosphine ligands in trans position to each other. The angle Re? N? S is 175.7(3)°.     

Methodology for the immobilization of enzymes onto mesoporous materials

Cytochrome c and xylanase were adsorbed onto two mesoporous materials, SBA-15 (a pure silicate) and MSE (an organosilicate), with very similar physical properties but differing chemical compositions. A methodical order was developed whereby the influences of surface area, pore size, extent of order, particle size, surface potentials, isoelectric points, pH, and ionic strength on immobilization were explored. In silico studies of cytochrome c and xylanase were conducted before any immobilization experiments were carried out in order to select compatible materials and probe the interactions between the adsorbents and the mesoporous silicates. The stabilities of the mesoporous materials at different pH values and their isoelectric points and zeta potentials were determined. Electrostatic attraction dominated protein interactions with SBA-15, while weaker hydrophobic interactions are more prominent with MSE for both cytochrome c and xylanase. The ability of the immobilized protein/enzyme to withstand leaching was measured, and activity tests and thermostability experiments were conducted. Cytochrome c immobilized onto SBA-15 showed resistance to leaching and an enhanced activity compared to free protein. The immobilized cytochrome c was shown to have higher intrinsic activity but lower thermostability than free cytochrome c. From an extensive characterization of the surface properties of the silicates and proteins, we describe a systematic methodology for the adsorption of proteins onto mesoporous silicates. This approach can be utilized in the design of a solid support for any protein.     

Synthese und Struktur von Re4(μ3-Te)4(TeBr2)4Br8

Synthesis and Structure of Re₄(μ₃-Te)₄(TeBr₂)₄Br₈ Re₄(μ₃-Te)₄(TeBr₂)₄Br₈ is obtained from the elements at 550°C in an evacuated glass ampoule. The diamagnetic compound forms air-stable, metallic lustre black crystals crystallizing in the tetragonal space group I4 with a = 1120.2(2), c = 1393.5(3) pm, and Z = 2. The crystal structure is built up by isolated cluster molecules Re₄(μ₃-Te)₄(TeBr₂)₄Br₈ occupying the centres 4 at 1/2, 1/2, 0 and 0, 0, 1/2. The inner sceleton is formed by a Re₄Te₄ heterocubane unit with short Re? Re distances of 277 and 283 pm, which can be discussed as single bonds. Each Re atom coordinates in addition two Br^? ligands and one TeBr₂ molecule. For Re therefore results the oxidation state +IV. Reaction of Re₄(μ₃-Te)₄(TeBr₂)₄Br₈ with I₂ yields (TeI₄)₄.     

Rhenium(V) and technetium(V) complexes with phosphoraneimine and phosphoraneiminato ligands

Air-stable rhenium(V) nitrido complexes are formed when [ReOCl3(PPh3)2], [NBu4][ReOCl4], or [NBu4][ReNCl4] are treated with an excess of silylated phosphoraneiminates of the composition Me3SiNPPh3 or Ph2P(NSiMe3)CH2PPh2 in CH2Cl2. Complexes of the compositions [ReNCl(Ph2PCH2PPh2NH)2]Cl (1), [ReN(OSiMe3)(Ph2PCH2PPh2NH)2]Cl (2) or [ReNCl2(PPh3)2] (3) were isolated and structurally characterized. The latter compound was also produced during a reaction of the rhenium(III) precursor [ReCl3(PPh3)2(CH3CN)] and Me3SiNPPh3. Nitrogen transfer from the phosphorus to the rhenium atoms and the formation of nitrido ligands were observed in all examples. All products of reactions with an excess of the potentially chelating phosphoraneiminate Me3SiNP(Ph2)CH2PPh2 contain neutral Ph2PCH2PPh2NH ligands. The required protons are supplied by a metal-induced decomposition of the solvent dichloromethane. The Re-N(imine) bond lengths (2.055-2.110 A) indicate single bonds, whereas the N-P bond with lengths between 1.596 A and 1.611 A reflect considerable double bond character. An oxorhenium(V) phosphoraneiminato complex, the dimeric compound [ReOCl2(mu-N-Ph2PCH2PPh2N)]2 (4), is formed during the reaction of [NBu4][ReOCl4] with an equivalent amount of Ph2P(NSiMe3)CH2PPh in dry acetonitrile. The blue neutral complex with two bridging phosphoraneiminato units is stable as a solid and in dry solvents. It decomposes in solution, when traces of water are present. The rhenium-nitrogen distances of 2.028(3) and 2.082(3) A are in the typical range of bridging phosphoraneiminates and an almost symmetric bonding mode. Technetium complexes with phosphoraneimine ligands were isolated from reactions of [NBu4][TcOCl4] with Me3SiNPPh3, and [NBu4][TcNCl4] with Me3SiNP(Ph2)CH2PPh2. Nitrogen transfer and the formation of a five-coordinate nitrido species, [TcNCl2(HNPPh3)2] (5), was observed in the case of the oxo precursor, whereas reduction of the technetium(VI) starting material and the formation of the neutral technetium(V) complex [TcNCl2(Ph2PCH2PPh2NH)] (6) or [TcNCl(Ph2PCH2PPh2NH)2]Cl (7) was observed in the latter case. Both technetium complexes are air stable and X-ray structure determinations show bonding modes of the phosphoraneimines similar to those in the rhenium complexes.     

RADIATION PROTECTION BY SUPEROXIDE DISMUTASE

Abstract— Protection of X-irradiated mice by bovine superoxide dismutase is enhanced when the enzyme is given intravenously both before and after the exposure. With the combined treatment, the LD₅₀₍₃₀₎ dose is increased from 734 ± 8 to 1144 ± 15rad for a dose reduction factor of 1.56 ± 0.04. This protection occurs in a dose range where hematological damage is an important contributor to animal lethality. The proliferative capacity of bone marrow stem cells, X-irradiated in air, is protected by exogenous superoxide dismutase. The enzyme increased the D₀ from 105 ± 6 to 290 ± 34rad, an increase that represents 83% of the oxygen enhancement ratio of 3.3. In N₂ and N₂O, the D₀ of the stem cells is 348 ± 50 and 327 ± 55 rad, respectively, and the enzyme does not significantly change these values.     

Dioxouranium Complexes with Acetylpyridine Benzoylhydrazones and Related Ligands

Acetylpyridine benzoylhydrazone and related ligands react with common dioxouranium(VI) compounds such as uranyl nitrate or [NBu₄]₂[UO₂Cl₄] to form air‐stable complexes. Reactions with 2, 6‐diacetylpyridinebis(benzoylhydrazone) (H₂L^1a) or 2, 6‐diacetylpyridinebis(salicylhydrazone) (H₂L^1b) give yellow products of the composition [UO₂(L¹)]. The neutral compounds contain doubly deprotonated ligands and possess a distorted pentagonal‐bipyramidal structure. The hydroxo groups of the salicylhydrazonato ligand do not contribute to the complexation of the metal. The equatorial coordination spheres of the complexes can be extended by the addition of a monodentate ligand such as pyridine or DMSO. The uranium atoms in the resulting deep‐red complexes have hexagonal‐bipyramidal coordination environments with the oxo ligands in axial positions. The sterical strains inside the hexagonal plane can be reduced when two tridentate benzoylhydrazonato ligands are used instead of the pentadentate 2, 6‐diacetylpyridine derivatives. Acetylpyridine benzoylhydrazone (HL²) and bis(2‐pyridyl)ketone benzoylhydrazone (HL³) deprotonate and form neutral, red [UO₂(L)₂] complexes. The equatorial coordination spheres of these complexes are puckered hexagons. X‐ray diffraction studies on [UO₂(L^1a)(pyridine)], [UO₂(L^1b)(DMSO)], [UO₂(L²)₂] and [UO₂(L³)₂] show relatively short U—O bonds to the benzoylic oxygen atoms between 2.328(6) and 2.389(8) Å. This suggests a preference of these donor sites of the ligands over their imino and amine functionalities (U—N bond lengths: 2.588(7)—2.701(6) Å ).     

Synthese von Nitrenkomplexen mit N-Trimethylsilylanilin. II. Charakterisierung und Kristallstruktur der Rhenium(V)-phenylnitren-Komplexe mer-[Re(NPh)Cl3(NH2Ph)(Ph3P)] und trans-[Re(NPh)(OMe)Cl2(Ph3P)2]

Synthesis of Phenylnitrene Complexes with N-Trimethylsilylaniline. II. Characterization and Crystal Structure of the Rhenium(V) Complexes mer-[Re(NPh)Cl₃(NH₂Ph)(Ph₃P)] and trans-[Re(NPh)(OMe)Cl₂(Ph₃P)₂] Reaction of [ReOCl₃(Ph₃P)₂] with N-trimethylsilylaniline yields mer-[Re(NPh)Cl₃(Ph₃P)₂], which reacts under air with excess of N-trimethylsilylaniline to form [Re(NPh)Cl₃ · (NH₂Ph)(Ph₃P)]. Crystallization from CH₂Cl₂/MeOH affords [Re(NPh)(OMe)Cl₂(Ph₃P)₂] as an additional product. [Re(NPh)Cl₃(NH₂Ph)(Ph₃P)] crystallizes in the monoclinic space group P2₁/n with a = 1 192.3(3); b = 1 918.9(3); c = 1 266.3(3) pm; β = 101.71(1)°; Z = 4. The rhenium atom has a distorted octahedral environment with the Cl atoms in meridional positions. The phenyl nitrene ligand is coordinated with an almost linear arrangement Re? N1? C40 = 166.8(6)° and with a bond distance Re?N = 170.5(6) pm. [Re(NPh)(OMe)Cl₂(Ph₃P)₂] · 1/2CH₂Cl₂ crystallizes in the triclinic space group P1 : a = 1 103.1(4); b = 1 227.9(4); c = 1 711.3(5) pm; α = 70.48(3)°; β = 72.71(3)°; γ = 80.03(3)°; Z = 2. The rhenium atom exhibits a distorted octahedral coordination with the Cl atoms and the phosphine ligands in trans positions. As a consequence of the competition of the nitrene ligand and the trans-coordinated methoxy group the Re?;N bond length is slightly lengthened to 173.2(7) pm, while the Re? O bond length of 193.4(6) pm is short. The bond angles Re? N? C70 and Re? O? C80 are 173.3(7)° and 139.1(7)°, respectively.