Novel biomimetic iron-catalysts for environmentally benign epoxidations of olefins

A new selective and easily manageable epoxidation method is presented using an inexpensive and efficient FeCl₃·6H₂O and imidazole derivatives as catalysts. Aqueous hydrogen peroxide as an environmentally benign oxidant is utilized. This novel Fe/imidazole system gives moderate to excellent yields toward aromatic mono-, di-, and tri-substituted olefins.     

The twinned crystal structure of μ‐2,2′‐bipyrimidine‐1κ2N1,N1′:2κ2N3,N3′‐bis­{tris­[4,4,4‐trifluoro‐1‐(2‐thienyl)butane‐1,3‐dionato‐κ2O,O′]terbium(III)} ethyl acetate solvate

The title compound, [Tb₂(C₂₄H₁₂F₉O₆S₃)₂(C₈H₆N₄)]·C₄H₈O₂, has two terbium(III) centers bridged by the polyazine ligand 2,2′‐bipyrimidine (bpm), which is distorted from planarity by 7.0 (2)°. The terminal ligand 4,4,4‐trifluoro‐1‐(2‐thienyl)­butane‐1,3‐dione (tta) is bidentate, coordinating through the two O atoms, while the bridging ligand is bis‐bidentate, coordinating through four equivalent N atoms. Both the complex and the ethyl acetate solvent mol­ecules are dis­ordered. The structure was refined as a non‐merohedral twin.     

Mechanisms of exchange modulation in trimethylenemethane-type biradicals: the roles of conformation and spin density

The molecular structures and magnetic properties of six dinitroxide biradicals are described. Five of the dinitroxides are trimethylenemethane-type (TMM-type) biradicals; that is, the intramolecular exchange parameter, J, is modulated by a carbon-carbon double bond. However, the efficacy of the carbon-carbon double bond as an exchange coupler is determined by the molecular conformation. Our results show that the exchange parameters correlate with phenyl-ring torsion angles (phi) via a simple Karplus-Conroy-type relation: J = 44 cos(2) phi - 17. Comparison of these results to those obtained for our isostructural series of bis(semiquinone) biradicals shows that both the magnitude of J and the resistance of ferromagnetic J to bond torsions is proportional to the spin density adjacent to the exchange coupler.     

Darstellung und Charakterisierung von Halogeno(diethyldithiocarbamato) (triethylphosphin)-nickel(II)-Komplexen

The complexes [Ni(PEt ₃)₂ dtc]X (1) and Ni(PEt ₃)Xdtc (2) (dtc=S₂CNEt ₂,X=Cl, Br, I) have been prepared. As conductivity, susceptibility, UV and IR measurements show, the cations [Ni(PEt ₃)₂ dtc]⁺ of1 and the complexes2 at ambient temperature have square-planar structure. We suppose there might exist an equilibrium for2 between square-planar and tetrahedral configuration.

     

Perfluoroalkyl-substituted triazapentadienes and their metal complexes

Triazapentadienides, C(3)F(7)-C(=NR)-N=C(NHR)-C(3)F(7), result from the reaction of primary amines RNH(2) with the fluorinated imine C(3)F(7)-CF=N-C(4)F(9). The aniline derivative (R = Ph) is a weak monoprotic acid in dmso. Its conjugate base exhibits an extensive coordination chemistry. It acts as a bidentate ligand toward the molecular fragments Pd(C(3)H(5)), Rh(c-C(8)H(12)), Ir(c-C(8)H(12)), and Rh(CO)(2). The chelates [C(3)F(7)-C(NPh)-N-C(NPh)-C(3)F(7)](2)M, M = Mg, Mn, Fe, Co, Ni, Cu, Zn, and Pd, were prepared. In the crystallographically characterized Co complex, the metal is 3d(7), S = (3)/(2) and tetrahedrally coordinated. Spin densities at carbon in the C(6)H(5) and C(3)F(7) groups were estimated from the (1)H and (19)F contact shifts. Spin delocalization onto phenyl sp(2) carbons is approximately 10 times greater than onto the fluorinated sp(3) carbons.     

Development of polyphosphate parameters for use with the AMBER force field

Accurate force fields are essential for reproducing the conformational and dynamic behavior of condensed-phase systems. The popular AMBER force field has parameters for monophosphates, but they do not extend well to polyphorylated molecules such as ADP and ATP. This work presents parameters for the partial charges, atom types, bond angles, and torsions in simple polyphosphorylated compounds. The parameters are based on molecular orbital calculations of methyldiphosphate and methyltriphosphate at the RHF/6-31+G* level. The new parameters were fit to the entire potential energy surface (not just minima) with an RMSD of 0.62 kcal/mol. This is exceptional agreement and a significant improvement over the current parameters that produce a potential surface with an RMSD of 7.8 kcal/mol to that of the ab initio calculations. Testing has shown that the parameters are transferable and capable of reproducing the gas-phase conformations of inorganic diphosphate and triphosphate. Also, the parameters are an improvement over existing parameters in the condensed phase as shown by minimizations of ATP bound in several proteins. These parameters are intended for use with the existing AMBER 94/99 force field, and they will permit users to apply AMBER to a wider variety of important enzymatic systems.     

Separations of aldehydes by means of ion-exchange chromatography on bisulfite columns

Mixtures of carbonyl compounds were chromatographed on Dowex-I columns in the bisulfite form. Sodium bisulfite solutions of increasing concentrations were used as eluants. The studied compounds, including acetaldehyde, formaldehyde, 5-hydroxymethylfurfural, furfural and vanillin, were separated completely from each other. The eluate was also analysed quantitatively.     

Fragmentation of doubly-protonated peptide ion populations labeled by H/D exchange with CD(3)OD

Doubly-protonated bradykinin (RPPGFSPFR) and an angiotensin III analogue (RVYIFPF) were subjected to hydrogen/deuterium (H/D) exchange with CD(3)OD in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. A bimodal distribution of deuterium incorporation was present for bradykinin after H/D exchange for 90 s at a CD(3)OD pressure of 4 x 10(-7) Torr, indicating the existence of at least two distinct populations. Bradykinin ion populations corresponding to 0-2 and 5-11 deuteriums (i.e., D(0), D(1), D(2), D(5), D(6), D(7), D(8), D(9), D(10), and D(11)) were each monoisotopically selected and fragmented via sustained off-resonance irradiation (SORI) collision-induced dissociation (CID). The D(0)-D(2) ion populations, which correspond to the slower exchanging population, consistently require lower SORI amplitude to achieve a similar precursor ion survival yield as the faster-reacting (D(5)-D(11)) populations. These results demonstrate that conformation/protonation motif has an effect on fragmentation efficiency for bradykinin. Also, the partitioning of the deuterium atoms into fragment ions suggests that the C-terminal arginine residue exchanges more rapidly than the N-terminal arginine. Total deuterium incorporation in the b(1)/y(8) and b(2)/y(7) ion pairs matches very closely the theoretical values for all ion populations studied, indicating that the ions of a complementary pair are likely formed during the same fragmentation event, or that no scrambling occurs upon SORI. Deuterium incorporation into the y(1)/a(8) pseudo-ion pair does not closely match the expected theoretical values. The other peptide, doubly-protonated RVYIFPF, has a trimodal distribution of deuterium incorporation upon H/D exchange with CD(3)OD at a pressure of 1 x 10(-7) Torr for 600 s, indicating at least three distinct ion populations. After 90 s of H/D exchange where at least two distinct populations are detected, the D(0)-D(7) ion populations were monoisotopically selected and fragmented via SORI-CID over a range of SORI amplitudes. The precursor ion survival yield as a function of SORI amplitude falls into two distinct behaviors corresponding to slower- and faster-reacting ion populations. The slower-reacting population requires larger SORI amplitudes to achieve the same precursor ion survival yield as the faster exchanging population. Total deuterium incorporation into the y(2)/b(5) ion pairs matches closely the theoretical values over all ion populations and SORI amplitudes studied. This result indicates the y(2) and b(5) ions are likely formed by the same mechanism over the SORI amplitudes studied.     

CuTb[B5O10]: Das erste „Metaborat”︁ mit einem [B5O10]5− -Anion

CuTb[B₅O₁₀]: The first “Metaborate” with a [B₅O₁₀]^5? Anion Single crystals of the new compound CuTb[B₅O₁₀] were obtained by a B₂O₃ flux-technique. They crystallize in a so far unknown structure. X-ray investigations on single crystals led to the space group C–I ba2 (Nr. 45); a = 6.294(1) Å; b = 8.406(8) Å; c = 12.733(2) Å; Z = 4. The structure contains [B₅O₁₀]^5? chains isolated from each other. These chains include twelf membered rings of boron and oxygen. Each ring consists of two tetrahedral BO₄ and two planar B₂O₅ groups and is connected with the next one via the BO₄ units. Tb³⁺ is eightfold- and Cu²⁺ elongated octahedraly coordinated by oxygen.     

Selective fluorescence quenching of polycyclic aromatic hydrocarbons by nitromethane within room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate

Recently discovered room temperature ionic liquids (RTILs) show tremendous promise to replace volatile organic compounds (VOCs). Investigation of these RTILs as solvents is in the very early stages. Before the full potential of these RTILs is realized, much more information about them as solvent systems must be obtained. The applicability of one such RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM PF₆), as a solvent toward analysis for polycyclic aromatic hydrocarbons (PAHs) is explored. The steady-state emission behavior of six PAHs along with the fluorescence quenching by nitromethane within BMIM PF₆ is investigated. The steady-state emission of six PAHs showed a bathochromic shift in BMIM PF₆ compared to acetonitrile, indicating possibly a more dipolar environment. Further, the nitromethane quenching of PAH emission strongly suggests a selective nature as the emission from alternant PAHs are quenched while that from nonalternant PAHs is not. The PAH-nitromethane quenching behavior within BMIM PF₆ is compared with that observed in the polar aprotic solvent acetonitrile, and a polar and similar viscosity (to BMIM PF₆) solvent system, 90 wt.% glycerol in water. It is observed that the PAH-nitromethane quenching within BMIM PF₆ and 90 wt.% glycerol in water is less efficient than in acetonitrile. This observation is suggested to arise from solvent viscosity.