Cs2Hg27, das quecksilberreichste Amalgam – ein naher Verwandter der Bergman‐Phasen

Cs₂Hg₂₇, the Mercury‐richest Amalgam with Close Relationship to the Bergman Phases By electrolyzing a solution of cesium iodide in N,N‐dimethylformamide at 2 °C on a mercury cathode the amalgam Cs₂Hg₂₇ can be synthesized. It crystallizes in an own cubic structure type (space group , a = 16.557(4) Å). The structure can be rationalized by a system of concentrical polyhedral spheres, in close analogy to the Bergman phases.     

Synthesis and Characterization of Gd2[Pt2(SO4)4(HSO4)2](HSO4)2

Red single crystals of Gd₂[Pt₂(SO₄)₄(HSO₄)₂](HSO₄)₂ (triclinic, , Z = 1, a = 844.02(9), b = 908.50(9), c = 939.49(8) pm, α = 107.73(1)°, β = 112.10(1)°, γ = 103.53(1)°) were obtained by the reaction of [Gd(NO₃)(H₂O)₇][PtCl₆]·4H₂O with sulfuric acid at 320 °C in a sealed glass ampoule. In the crystal structure, Pt₂ dumbbells are coordinated by four chelating sulfate groups and two monodentate hydrogensulfate ions. Two further HSO₄^? ions are not bonded to the Pt₂ dumbbell. The Gd³⁺ ions are eightfold coordinated by oxygen atoms. The IR data of Gd₂[Pt₂(SO₄)₄(HSO₄)₂](HSO₄)₂ are typical for these type of compounds. The thermal decomposition of the compound leads to elemental platinum and Gd₂O₃.     

Hexachloroplatinates of the Lanthanides: Syntheses and Thermal Decomposition of [M(NO3)2(H2O)6]2[PtCl6]·2H2O (M = La,Pr) and [M(NO3)(H2O)7][PtCl6]·4H2O (M = Gd,Dy)

The reaction of the nitrates M(NO₃)₃·6H₂O (M = La, Pr) and (H₃O)₂PtCl₆ led to yellow single crystals of [M(NO₃)₂(H₂O)₆]₂[PtCl₆]·2H₂O (M = La, Pr) (monoclinic, P2₁/c, Z = 2, La/Pr: a = 697.4(3)/695.5(1), b = 1654.5(1)/1652.5(2), c = 1317.7(6)/1318.5(3) pm, β = 93.97°(7)/93.93°(2), R_all = 0.0169/0.0659) while the reaction of M(NO₃)₃·5H₂O (M = Gd, Dy) and (H₃O)₂PtCl₆ yielded yellow single crystals of [M(NO₃)(H₂O)₇][PtCl₆]·4H₂O (monoclinic, P2₁/n, Z = 4, Gd/Dy: a = 838.72(3)/838.40(2), b = 2131.98(6)/2139.50(7), c = 1142.63(3)/1143.10(3) pm, β = 95.670(4)/95.698(3), R_all = 0.0475/0.0337). The crystal structures consist of octahedral [PtCl₆]^2? anions and complex [M(NO₃)₂(H₂O)₆]₂⁺ and [M(NO₃)(H₂O)₇]²⁺ cations, respectively. The thermal decomposition of both types of compounds leads via various steps to elemental platinum and the oxide chlorides MOCl (M = La, Pr, Gd, Dy).     

Seltenerdhalogenide Ln4X5Z. Teil 1: C und/oder C2 in Ln4X5Z

Rare Earth Halides Ln₄X₅Z. Part 1: C and/or C₂ in Ln₄X₅Z The compounds Ln₄X₅C_n (Ln = La, Ce, Pr; X = Br, I and 1.0 < n < 2.0) are prepared by the reaction of LnX₃, Ln metal and graphite in sealed Ta‐ampoules at temperatures 850 °C < T < 1050 °C. They crystallize in the monoclinic space group C2/m. La₄I₅C_1.5: a = 19.849(4) Å, b = 4.1410(8) Å, c = 8.956(2) Å, β = 103.86(3)°, La₄I₅C_2.0: a = 19.907(4) Å, b = 4.1482(8) Å, c = 8.963(2) Å, β = 104.36(3)°, Ce₄Br₅C_1.0: a = 18.306(5) Å, b = 3.9735(6) Å, c = 8.378(2) Å, β=104.91(2)°, Ce₄Br₅C_1.5: a = 18.996(2) Å, b = 3.9310(3) Å, c = 8.282(7) Å, β = 106.74(1)°, Pr₄Br₅C_1.3: a = 18.467(2) Å, b = 3.911(1) Å, c = 8.258(7) Å, β = 105.25(1)° and Pr₄Br₅C_1.5: a = 19.044(2) Å, b = 3.9368(1) Å, c = 8.254(7) Å, β = 106.48(1)°. In the crystal structure the lanthanide metals are connected to Ln₆‐octahedra centered by carbon atoms or C₂‐groups. The Ln₆‐octahedra are condensed via opposite edges to chains and surrounded by X atoms which interconnect the chains. A part n of isolated C‐atoms is substituted by 1‐n C₂‐groups. The C‐C distances range between 1.26 and 1.40Å. In the ionic formulation (Ln³⁺)₄(X^?)₅(C^4?)_n(C₂^m?)_1?n·e^? with 0 < n < 1 and m = 2, 4, 6 (C₂^2?, C₂^4? C₂^6?), there are 1 < e^? < 5 electrons centered in metal‐metal bonds.     

Das Lanthaniodidethanid o‐La5I9(C2) – Die orthorhombische Hochtemperaturmodifikation

The Lanthanumiodideethanide o‐La₅I₉(C₂) – The Orthorhombic High Temperature Modification o‐La₅I₉(C₂) is synthesized by reaction of LaI₃, La metal and graphite powder in sealed Ta containers at 850 °C < T < 900 °C. It crystallizes in the orthorhombic space group Pbca with a = 8.0247(16) Å, b = 16.887(3) Å, c = 35.886(7) Å. o‐Ce₅I₉(C₂) is isotypic with the lattice parameters a = 7.9284(4) Å, b = 16.714(1) Å, c = 35.530(3) Å. o‐La₅I₉(C₂) transforms at 800 °C to the triclinic low temperature modification t‐La₅I₉(C₂). The transformation is reversible. The La atoms form trigonal bipyramids centered by C₂ groups. These units are connected by iodine atoms above the faces (f), edges (e) and corners according to La₅(C₂)I(f)ⁱI(e)^i?i_2/2I(e)^i?a_7/2I(e)^a?i_7/2. The C‐C distance in the C₂ unit is 1.45(2) Å. The crystals with greenish luster are moisture sensitive.     

Mapping the binding site of thiopeptide antibiotics by proximity-induced covalent capture

Proximity-induced covalent capture (PICC) has been established for the investigation of ligand binding to composite protein/oligonucleotide target complexes. The RNA-induced attachment of the thiopeptides Thiostrepton and Nosiheptide to engineered Cys mutants of the ribosomal protein L11 was highly position selective and allowed mapping of their binding site at amino acid resolution.     

Regioselective Functionalization of 3‐Hydroxy‐pyridine Carboxylates by Neighboring Group Assistance

Regioselective hydrolysis, transesterification, and aminolysis of unactivated, highly substituted pyridine esters were realized under mild conditions by employing neighboring group assisted catalysis. Excellent yields were achieved without active removal of the alcohol byproduct. Regioselective aminolysis had a considerable substrate scope ([hetero]aryl, alkyl and amino acid). A mechanism involving assistance by the deprotonated phenolic OH‐group is suggested for hydrolysis and transesterification.     

Total synthesis of (-)-pseudolaric acid B

We report the enantioselective synthesis of pseudolaric acid B (1a), a diterpene acid isolated from the bark of Pseudolarix kaempferi Gordon, which displays interesting antifungal, antifertility, and cytotoxic activity against multidrug resistant cell lines. Our synthesis utilizes a highly efficient metal-catalyzed [5 + 2] vinylcyclopropane-alkyne intramolecular cycloaddition to construct the polyhydroazulene core of the natural product. Elaboration to the tricyclic scaffold of the pseudolaric acids was completed with an intramolecular alkoxycarbonyl radical cyclization to form the quaternary center and a highly diastereoselective cerium acetylide addition to a methyl ketone for introduction of the acid side chain.     

Characterization of ethyl chloroformate derivative of <Emphasis Type="Italic">β</Emphasis>-methylamino-<Emphasis Type="SmallCaps">l</Emphasis>-alanine

Beta-methylamino-L-alanine (BMAA) is a neurotoxic amino acid that can be produced by cyanobacteria in aqueous environments. To analyze this compound by gas chromatography/mass spectrometry (GC/MS), BMAA must be derivatized to a nonpolar, volatile compound. This can be accomplished by reacting BMAA with ethyl chloroformate. While carrying out electron ionization (EI) mass spectrometric analysis on the (13)C-labeled derivative, it was discovered that the formation of an ion with a peak at m/z 245.12 is the result of [CH(3)CH(2)O.] loss from the amino groups resulting from alpha-cleavage. This differs from previous reports that attributed this peak to alpha-cleavage of the carboxylic ester portion of the BMAA derivative. This finding is important for understanding BMAA derivative mass spectrometric fragmentation patterns and ultimately to properly identifying and quantifying BMAA. Fragmentation pathways for the formation of other major peaks observed in the EI mass spectra are also proposed.