Synthesis and Characterization of [Hg(sulfamethoxazolato)2]·2DMSO and[Cu2(μ‐CH3CO2)4(sulfamethoxazole)2]

[Hg(sulfamethoxazolato)₂]·2DMSO ( 1 ) and [Cu₂(CH₃COO)₄(sulfa‐methoxazole)₂] ( 2 ) can be obtained by the reaction of sulfamethoxazole with mercury acetate or copper acetate in methanol. The structures of the two complexes were characterized by single crystal X—ray diffractometry. Compound 1 consists of sulfamethoxazolato ligands bridging the metal ions building an unidimensional chain. Two solvent dimethylsulfoxide molecules are involved via N‐H···O hydrogen bridges. The mercury atom shows a linear primary coordination arrangement formed by two trans deprotonated sulfonamidic nitrogen atoms. The overall coordination around the metal atom may be regarded as a strongly distorted octahedron when the interactions of mercury with four sulfonamidic oxygen atoms [bond distances of 2.761(4) Å—2.971(4) Å] are also considered to build an equatorial plane and the N1 and N1′ atoms [bond distance of 2.037(5) Å] occupy the apical positions. Compound 2 is a dinuclear complex in which the copper ions are bridged by four syn‐syn acetate ligands which are related by a symmetry centre located in the centre of the complex. Each copper atom presents a nearly octahedral coordination where the equatorial plane is formed by four oxygen atoms and an isoxazolic nitrogen atom and the second copper atom occupy the apical positions.     

Neutron diffraction structure determination of the high-temperature form of lithium tritantalate,HLiTa3O8

The crystal structure of HLiTa₃O₈ has been reexamined by electron and neutron diffraction techniques. Neutron Weissenberg and electron diffraction photographs show that the space group of the compound isPmmn and notPmma as determined previously by X-ray diffraction techniques. There are eight molecules in the unit cell of lattice parametersa = 16.718(2)A?,b = 7.696(1)A?,c = 8.931(1)A?. These values show that thebaxis of the new cell is doubled with respect to the parameter measured by X-rays. The structural refinement was based on 1074 independent reflections measured on a single crystal with a four-circle neutron diffractometer. The positions of all atoms, including the lithium atoms have been determined. The finalR andwRfactors were 0.036 and 0.035, respectively. The eight lithium cations occupy two sets of4fpositions(x,¼, z)of thePmmn space group. The ordering of four lithium ions over two sets of possible positions (4j) of space groupPmma is responsible for the doubling of theb axis. The other four Li⁺ occupy two sets of positions (2d) of space groupPmma. All lithium ions are surrounded by 12 oxygen atoms arranged as cuboctahedra. The large thermal vibrations found for the lithium atoms and the ionic conductivity of HLiTa₃O₈ at high temperatures are consistent with weak LiO bonding.     

Preparation of clarithromycin. Selective 6-O-methylation of the novel erythromycin A 9-O-(2-pyrimidyl)oxime

A new method for the preparation of clarithromycin is described through the highly regioselective O-methylation at C(6)-OH of the novel derivative 9-pyrimidyloxime erythromycin A. The facile synthesis of 6,11-O-dimethyl- and 6,11,12-O-trimethyl erythromycin A is also reported. These compounds are useful as standards to assess clarithromycin purity in quality control processes.     

Addition of p-azido-L-phenylalanine to the genetic code of Escherichia coli

We report the selection of a new orthogonal aminoacyl tRNA synthetase/tRNA pair for the in vivo incorporation of a photocrosslinker, p-azido-l-phenylalanine, into proteins in response to the amber codon, TAG. The amino acid is incorporated in good yield with high fidelity and can be used to crosslink interacting proteins.     

Complex Tellurium Salts with Supramolecular Bidimensional Lattices: Synthesis and X‐ray Characterization of (2‐Br‐C5NH5)2[TeX6] (X = Cl,Br)

The reaction of tellurium(IV) tetrahalides with hydrochloric and hydrobromic acid leads to the formation of (H₃O)₂[TeX₆], which reacts subsequently with (2‐Br‐C₅NH₅)⁺X^‐ to afford (2‐Br‐C₅NH₅)₂[TeCl₆] ( 1 ) and (2‐Br‐C₅NH₅)₂[TeBr₆] ( 2 ). The structure of the complex salts were analysed by X‐ray diffractometry affording the centrosymmetric space groups P2₁/n (monoclinic, 1 ) and P1¯ (triclinic, 2 ). Interionic hydrogen bondings hold their lattices in bidimensional supramolecular arrays not yet described in the literature. The lone electron pair of the AX₆E‐system of the hexahalotellurates [TeX₆]^2‐ (X = Cl, Br) seems to be fully delocalized since only small octahedral deviations were observed for the anionic species. The structures of the title compounds were refined with the Te atoms occupying sites with full point symmetry, approximately m3¯m. In both cases the Te atoms enclose centers of inversion and the octahedrally dynamic structures are enforced and stabilized along the supramolecular lattices by the crystal field of the 2‐Br‐pyridinium cations.     

Preparation and properties of dinitrogen complexes of molybdenum and tungsten with trimethylphosphine as coligand : III. Synthesis and properties of cis-[W(N2)2(PMe3)4], trans-[W(C2H4)2(PMe3)4] and [M(N2)(PMe3)5] (M = Mo,W). The crystal and molecular structure of [Mo(N2)(PMe3)5]

The reduction of [WCl₄(PMe₃)₃] with dispersed sodium, under dinitrogen, gives cis-[W(N₂)₂(PMe₃)₄], while under ethylene trans-[W(C₂H₄)₂(PMe₃)₄] is obtained. The ethylene complex can also be prepared by displacement of the dinitrogen molecules in cis-[W(N₂)₂(PMe₃)₄] by ethylene at room temperature and pressure. Interaction of cis-[M(N₂)₂(PMe₃)₄] complexes (M = Mo, W), with PMe₃, under helium or argon, yields [M(N₂)(PMe₃)₅]. The molybdenum complex crystallizes in the orthorhombic space group Pnma, with a 22.063(6), b 12.106(4), c 9.745(4) Å. The Mo—P distance trans to the dinitrogen ligand (2.483(7) Å) is slightly longer than the average of the other four Mo—P bonds (2.460(5) Å).     

A re-investigation of copper coordination in the octa-repeats region of the prion protein

An aqueous solution spectroscopic (Vis and EPR) study of the copper(II) complexes with the Ac-HGGG-NH2 and Ac-PHGGGWGQ-NH2 polypeptides (generically designated as L) suggests square base pyramids ascribable to [Cu(L)H(-2)] complex species, which contain three nitrogen donor atoms, arising from imidazole and peptide groups, in the equatorial plane and for a pseudo-octahedral geometry in the case of [CuLH-3]- and [Cu(L)H-4]2- which have four nitrogen donor atoms in their equatorial plane. The coordination sphere of the copper complex in the [Cu(L)H(-2)] species, which is present at neutral pH values, is completed by two oxygen donor atoms. ESI-MS spectra ascertained that water molecules are not present in the coordination equatorial plane of this latter species, in comparison with other copper(II) complexes with ligands bearing nitrogen and oxygen donor atoms and surely having equatorial water molecules. This indicates the coordination of a carbonyl oxygen atom in the equatorial plane has to be invoked. However, no direct proof about the involvement of a carbonyl group oxygen donor atom apically linked to copper was obtained, due to the flexibility of these structures at room temperature. Additionally, the low A(ll) value leads one to consider another oxygen atom of a carbonyl group being involved in the apical bond to copper in a fast exchange fashion. This apical interaction, which may also involve a water molecule, is more pronounced in the Cu-Ac-HGGG-NH2 than in the analogous Cu-Ac-PHGGGWGQ-NH2 system, probably because of the presence of tryptophan and proline in the polypeptide sequence.     

Structure of a de novo designed protein model of radical enzymes

The use of side chains as catalytic cofactors for protein mediated redox chemistry raises significant mechanistic issues as to how these amino acids are activated toward radical chemistry in a controlled manner. De novo protein design has been used to examine the structural basis for the creation and maintenance of a tryptophanyl radical in a three-helix bundle protein maquette. Here we report the detailed structural analysis of the protein by multidimensional NMR methods. An interesting feature of the structure is an apparent pi-cation interaction involving the sole tryptophan and a lysine side chain. Hybrid density functional calculations support the notion that this interaction raises the reduction potential of the W degrees /WH redox pair and helps explain the redox characteristics of the protein. This model protein system therefore provides a powerful model for exploring the structural basis for controlled radical chemistry in protein.     

Specific adsorption of azide ions on mercury electrodes from constant ionic strength solutions

The adsorption of azide ions on mercury from aqueous solutions of NaN₃+NaF at constant ionic strength has been studied by measurements of the double layer capacity. Taking into account changes in the structure of the diffuse layer, it was possible to show that the properties of the inner layer are similar to those observed previously in solutions of pure NaN₃, and that the same adsorption isotherm applies to both systems.