Ferrocene derivatives included in a water-soluble cavitand: are they electroinactive?

The formation in aqueous solution of kinetically stable inclusion complexes between a deep-cavity cavitand and several redox active ferrocene derivatives was demonstrated using (1)H NMR spectroscopy. The electrochemical kinetics of the inclusion complexes was strongly attenuated as compared to that observed with the free guests.     

Oxidation of methionine residues in aqueous solutions: free methionine and methionine in granulocyte colony-stimulating factor

The free energy barriers and a mechanism of the oxidation of the amino acid methionine in water and in granulocyte colony-stimulating factor (G-CSF) are analyzed via combined quantum mechanical and molecular mechanical (QM/MM) methods, constrained molecular dynamics, and committor probability calculations. The computed free energy barrier of free methionine amino acid is very close to the measured value (14.7 +/- 1.2 versus 15.5 +/- 0.02 kcal/mol). The reaction coordinate was found to be the difference between the O-O bond of H2O2 and the S-O bond, where the S is the sulfur atom of the methionine residue. It was confirmed by computing the committor probability distribution and the distribution of constrained forces that this coordinate is not coupled to the activation of other degrees of freedom. The computed free energies of the oxidation of methionine residues in G-CSF indicate that the protein environment has insignificant effects on the reaction barriers of oxidation. This result further validates our proposal that the access of solvent to methionine sites, as measured by the two-shell water coordination number, governs the kinetics of the oxidation reaction of methionine groups in a protein molecule. We also found that the number of hydrogen bonds between the distal oxygen of H2O2 and the water molecules near the methionine increases along the reaction coordinate as oxidation progresses, indicating that the charge separation developed during the oxidation by H2O2 is stabilized by specific interactions with water molecules, such as hydrogen bonding.     

Novel one-dimensional structures and solution behaviour of copper(II) bromide and chloride complexes of a new pentapyridyldiamine ligand

Copper(II) bromide and chloride complexes of the new heptadentate ligand 2,6-bis(bis(2-pyridylmethyl)amino)methylpyridine (L) have been prepared. For the bromide complexes, chains of novel, approximately C2-symmetric, chiral [Cu2(L)Br2]2+ 'wedge-shaped' tectons are found. The links between the dicopper tectons and the overall chirality and packing of the chains are dictated by the bromide ion content, not the counter anion. In contrast, the chloride complexes exhibit linked asymmetric [Cu2(L)Cl3]+ tectons with distinct N3CuCl2 and N4CuCl2 centres in the solid. The overall structures of the dicopper bromide and chloride units persist in solution irrespective of the halide. The redox chemistry of the various species is also described.     

Synthesen und NMR‐Untersuchungen von Salzen mit den neuen Anionen [PtXn(CF3)6‐n]2— (n = 0 ‐ 5, X = F,OH, Cl,CN) und die Kristallstrukturanalyse von K2[(CF3)2F2Pt(μ‐OH)2PtF2(CF3)2]·2H2O

Syntheses and NMR Spectroscopic Ivestigations of Salts containing the Novel Anions [PtX_n(CF₃)_6‐n]^2— (n = 0 ‐ 5, X = F, OH, Cl, CN) and Crystal Structure of K₂[(CF₃)₂F₂Pt(μ‐OH)₂PtF₂(CF₃)₂]·2H₂O The first syntheses of trifluoromethyl‐complexes of platinum through fluorination of cyanoplatinates are reported. The fluorination of tetracyanoplatinates(II), K₂[Pt(CN)₄], and hexacyanoplatinates(IV), K₂[Pt(CN)₆], with ClF in anhydrous HF leads after working up of the products to K₂[(CF₃)₂F₂Pt(μ‐OH)₂PtF₂(CF₃)₂]·2H₂O. The structure of the salt is determined by a X‐ray structure analysis, P2₁/c (Nr. 14), a = 11.391(2), b = 11.565(2), c = 13.391(3)Å, β = 90.32(3)°, Z = 4, R₁ = 0.0326 (I > 2σ(I)). The reaction of [Bu₄N]₂[Pt(CN)₄] with ClF in CH₂Cl₂ generates mainly cis‐[Bu₄N]₂[PtCl₂(CF₃)₄] and fac‐[Bu₄N]₂[PtCl₃(CF₃)₃], but in contrast that of [Bu₄N]₂[Pt(CN)₆] with ClF in CH₂Cl₂ results cis‐[Bu₄N]₂[PtX₂(CF₃)₄], [Bu₄N]₂[PtX(CF₃)₅] (X = F, Cl) and [Bu₄N]₂[Pt(CF₃)₆]. In the products [Bu₄N]₂[PtX_n(CF₃)_6‐n] (X = F, Cl, n = 0—3) it is possibel to exchange the fluoro‐ligands into chloro‐ and cyano‐ligands by treatment with (CH₃)₃SiCl und (CH₃)₃SiCN at 50 °C. With continuing warming the trifluoromethyl‐ligands are exchanged by chloro‐ and cyano‐ligands, while as intermediates CF₂Cl and CF₂CN ligands are formed. The identity of the new trifluoromethyl‐platinates is proved by ¹⁹⁵Pt‐ and ¹⁹F‐NMR‐spectroscopy.     

Fast counter-electroosmotic capillary electrophoresis–time-of-flight mass spectrometry of hyaluronan oligosaccharides

Fast capillary electrophoresis–mass spectrometry measurements under counter-electroosmotic analyte migration conditions are presented. Efficient separations of a homologous series of six hyaluronan oligosaccharides (comprising 1–6 hyalobiuronic acid moieties) could be completed in 65 s. Separations were achieved in short-length fused silica capillaries under high electric field strengths of up to 1.25 kV·cm⁻¹. Capillary inner diameters ranging from 5 to 50 μm were investigated, resulting in an optimal value of 15 μm. The influence of capillary dimensions and buffer composition on separation efficiency and sensitivity are discussed. Optimal separations were achieved using a 28 cm × 15 μm capillary, a separation high voltage of 35 kV, a background electrolyte of 25 mM ammonium acetate adjusted to pH 8.5, and negative ionization mode. The optimized method was successfully applied to a bovine testicular hyaluronidase digest of hyaluronan. Only minimal sample pretreatment for protein-containing samples is required. The simple manual injection procedure and fast separations allow for a sample throughput of 35 samples per hour.     

Tetracyanoborate salts M[b(CN)4] with M = singly charged cations: properties and structures

A series of tetracyanoborate salts M[B(CN)4] with the singly charged cations of Li+, Na+, Rb+, Cs+, [NH4]+, Tl+, and Cu+ as well as the THF solvate tetracyanoborates Na[B(CN)4] x THF and [NH4][B(CN)4] x THF were synthesized and their X-ray structures, vibrational spectra, solubilities in water, and thermal stabilities determined and compared with already known M[B(CN)4] salts. Crystallographic data for these compounds are as follows: Na[B(CN)4], cubic, Fd3m, a = 11.680(1) A, Z= 8; Li[B(CN)4], cubic, P43m, a = 5.4815(1) A, Z= 1; Cu[B(CN)4], cubic, P43m, a = 5.4314(7) A, Z= 1; Rb[B(CN)4], tetragonal, /4(1)/a, a = 7.1354(2) A, c= 14.8197(6) A, Z= 4; Cs[B(CN)4], tetragonal, /4(1)/a, a = 7.300(2) A, c = 15.340(5) A, Z= 4; [NH4][B(CN)4], tetragonal, /4(1)/a, a = 7.132(1) A, c = 14.745(4) A, Z= 4; Tl[B(CN)4], tetragonal, /4(1)/a, a = 7.0655(2) A, c = 14.6791(4) A, Z= 4; Na[B(CN)4] x THF, orthorhombic, Pnma, a = 13.908(3) A, b = 9.288(1) A, c = 8.738(1) A, Z= 4; [NH4][B(CN)4] x THF, orthorhombic, Pnma, a = 8.831(1) A, b = 9.366(2) A, c = 15.061(3) A, Z= 4. The cubic Li+, Na+, and Cu+ salts crystallize in a structure consisting of two interpenetrating independent tetrahedral networks of M cations and [B(CN)4]- ions. The compounds with the larger countercations (Rb+, Cs+, Tl+, and [NH4]+) crystallize as tetragonal, also with a network arrangement. The sodium and ammonium salts with the cocrystallized THF molecules are both orthorhombic but are not isostructural. In the vibrational spectra the two CN stretching modes A1 and T2 coincide in general and the band positions are a measure for the strength of the interionic interaction. An interesting feature in the Raman spectrum of the copper salt is the first appearance of two CN stretching modes.     

Infrared spectra of V(n)Bz(n+1) sandwich clusters: a theoretical study of size evolution

Results of density functional theory computations of infrared (IR) spectra of linear sandwich V(n)Bz(n+1), n = 1-6, complexes are presented. It is shown that the systematic changes in the spectra as a function of the complex size can be categorized and understood in terms of responses of the "parent" modes of the Bz molecule and the VBz complex. The analysis presented should be applicable to a broad class of linear sandwich systems.     

NO Chemisorption on Pt(111), Rh/Pt(111), and Pd/Pt(111)

The chemisorption of NO on clean Pt(111), Rh/Pt(111) alloy, and Pd/Pt(111) alloy surfaces has been studied by first principles density functional theory (DFT) computations. It was found that the surface compositions of the surface alloys have very different effects on the adsorption of NO on Rh/Pt(111) versus that on Pd/Pt(111). This is due to the different bond strength between the two metals in each alloy system. A complex d-band center weighting model developed by authors in a previous study for SO2 adsorption is demonstrated to be necessary for quantifying NO adsorption on Pd/Pt(111). A strong linear relationship between the weighted positions of the d states of the surfaces and the molecular NO adsorption energies shows the closer the weighted d-band center is shifted to the Fermi energy level, the stronger the adsorption of NO will be. The consequences of this study for the optimized design of three-way automotive catalysts, (TWC) are also discussed.