Discovery of novel iron clusters in proteins by Mössbauer spectroscopy

Iron clusters are the catalytically active groups of many proteins. The basis building blocks of these clusters are few; they are all variants of three archetypal patterns: [Fe–O–Fe], [2Fe–2S], and [4Fe–4S]. Mössbauer spectroscopy, in conjunction with EPR spectroscopy, susceptometry and EXAFS, plays an important role in characterizing type, number, oxidation states and magnetic properties of such clusters in newly discovered proteins, and in detecting how valency and magnetism vary by passing through the catalytical cycle of these proteins. In this contribution we present the characterization of a novel iron cluster with unusual bridging and terminal ligands and metal coordinations.     

Infrared absorption of silane,ammonia, acetylene and diborane in the range of the CO2 laser emission lines: Measurements and modelling

Absorption spectra of the gases SiH₄, NH₃, C₂H₂ and of SiH₄/Ar and SiH₄/B₂H₆ mixtures have been measured in the spectral range of the CO₂ laser from 9.2 to 10.8 µm. In agreement with literature, silane shows the highest absorption (absorption coefficient = 3.3 × 10^–2 Pa^–1 m^–1). The deviation of the measured absorption behaviour of silane from literature, as far as the pressure dependence is concerned, can be explained by the enhanced spectral energy density in our experiment. This is confirmed by a rate-equation model involving the basic mechanisms of V-V and V-T energy transfer between vibrationally excited silane molecules. In contrast to silane, the absorption coefficient of NH₃ at the 10P(20) laser line is 4.5 × 10^–4 Pa^–1 m^–1 atp = 20 kPa and has its maximum of 4.5 × 10^–3 Pa^–1 m^–1 at the 10R(6) laser line. For C₂H₂ and B₂H₆, is even less ( 2.1 Ò 10^–5 Pa^–1 m^–1 for C₂H₂).     

Polymer/carrier composites as materials and reactors for organic synthesis

In this work new polymer/carrier composites are described which serve as novel materials in flow-through reactors for polymer-supported organic solution-phase synthesis. Monolithic polymer/carrier columns are prepared by a new precipitation polymerization process inside the void pore volume of megaporous glass carrier materials. Chemical functionalization of the internal polymer phase with chlorosulfonic acid or trimethylamine generates small, interconnected ion-exchange resin beads with a diameter of 1-3 microm which can be used for a large variety of organic syntheses. These monolithic rods are incorporated into an appropriate casing and can conveniently be operated in the flow-through mode. Important successful applications are polymer-assisted solution-phase reductions, oxidations and Horner-Emmons olefinations. Additionally, the use of these monolithic columns as catalytic microreactors and their performance in selected reactions are described.     

Ultrafast nuclear dynamics induced by photodetachment of Ag2- and Ag2O2-: oxygen desorption from a molecular silver surface

Femtosecond nuclear dynamics of mass-selected neutral Ag2 and Ag2O2 clusters are investigated with the 'negative ion-to neutral-to positive ion'(NeNePo) technique. For the bare silver dimer, wave packet dynamics occurring in the neutral electronic ground state and in the first excited triplet state are observed after photodetachment from the anion with 3.05 eV photon energy. While the dynamics in the ground state lead to an oscillatory structure in the NeNePo-pump-probe spectra with a vibrational constant of 185 cm-1, the dynamics in the triplet state are assigned to a bound-free transition leading to dissociation. Photodetachment from the Ag2O2- complex results in the desorption of O2. The experimental data clearly show the influence of the desorbing oxygen ligand on the nuclear dynamics of the silver dimer inducing a red shift in the vibrational frequency and an intensity enhancement of the oscillatory signal.     

Is it homogeneous or heterogeneous catalysis? Compelling evidence for both types of catalysts derived from [Rh(eta5-C5Me5)Cl2]2 as a function of temperature and hydrogen pressure

Addressed herein is the 20+ year-old question of whether the true benzene and cyclohexene hydrogenation catalysts derived from the organometallic precursor [Rh(eta5-C5Me5)Cl2]2, 1, are homogeneous or heterogeneous. The methodology employed is that developed earlier (Lin, Y.; Finke, R. G. Inorg Chem. 1994, 33, 4891, "A More General Approach to Distinguishing Homogeneous from Heterogeneous Catalysis..."). The kinetic evidence especially, but also the metal product (nanoclusters plus bulk metal), Hg0 poisoning and other experiments, provide compelling evidence that Rh0 nanoclusters are the true benzene hydrogenation heterogeneous catalyst derived from [Rh(eta5-C5Me5)Cl2]2, 1, at the required more vigorous conditions of 50-100 degrees C and 50 atm H2. However, the same methods reveal that the cyclohexene hydrogenation catalyst derived from 1 at the milder conditions of 22 degrees C and 3.7 atm H2 is a nonnanocluster, homogeneous catalyst, most likely the previously identified complex, [Rh(eta5-C5Me5)(H)2(solvent)] (Gill, D. S.; White, C.; Maitlis, P. M J. C. S. Dalton Trans. 1978, 617). In short, the present results solve the two-decade-old problem of identifying the true benzene and cyclohexene hydrogenation catalysts derived from [Rh(eta5-C5Me5)Cl2]2. Perhaps most significant is the demonstration that the methodology employed has the ability to identify both heterogeneous and homogeneous catalysts from the same catalyst precursor.     

trans‐Bis(benzoato‐O)tetrakis(methanol‐O)iron(II): ligand bulk is not structure‐determining

The title compound, [Fe(C₇H₅O₂)₂(CH₄O)₄], is a centrosymmetric six‐coordinate Fe^II complex coordinated by two axial monodentate benzoate ligands and four methanol ligands in the equatorial plane [Fe—O_benzoate 2.0935 (7) Å, and Fe—O_methanol 2.1310 (7) and 2.1290 (7) Å]. The benzoate ligands adopt monodentate ligation, rather than a bridged polymeric structure, because of strong intra‐ and intermolecular hydrogen bonds to the methanol ligands. This structure is nearly identical to that obtained with a much bulkier carboxyl­ate ligand [Chavez, Que & Tolman (2001). Chem. Commun. pp. 111–112].