M−O Bonding Beyond the Oxo Wall: Spectroscopy and Reactivity of Cobalt(III)‐Oxyl and Cobalt(III)‐Oxo Complexes

Terminal oxo complexes of late transition metals are frequently proposed reactive intermediates. However, they are scarcely known beyond Group 8. Using mass spectrometry, we prepared and characterized two such complexes: [(N4Py)Co^III(O)]⁺ ( 1 ) and [(N4Py)Co^IV(O)]²⁺ ( 2 ). Infrared photodissociation spectroscopy revealed that the Co?O bond in 1 is rather strong, in accordance with its lack of chemical reactivity. On the contrary, 2 has a very weak Co?O bond characterized by a stretching frequency of ≤659 cm^?1. Accordingly, 2 can abstract hydrogen atoms from non‐activated secondary alkanes. Previously, this reactivity has only been observed in the gas phase for small, coordinatively unsaturated metal complexes. Multireference ab‐initio calculations suggest that 2 , formally a cobalt(IV)‐oxo complex, is best described as cobalt(III)‐oxyl. Our results provide important data on changes to metal‐oxo bonding behind the oxo wall and show that cobalt‐oxo complexes are promising targets for developing highly active C?H oxidation catalysts.     

Classification of Raman spectra using the correlation kernel

The classification of Raman spectra can be very useful in a wide range of diagnostic applications including bacterial identification. Before any form of classification can be carried out on the Raman spectra, some form of pre‐processing is commonly applied. This pre‐processing greatly affects the accuracy of the results and introduces user bias and over‐fitting effects. In this paper, we propose using support vector machines with the correlation kernel. The use of the correlation kernel on Raman spectra has not been presented before in any published work. Our results illustrate that the correlation kernel is ‘self‐normalizing’ and produces superior classification performance with minimal pre‐processing, even on highly noisy data obtained using inexpensive equipment. Such effective classification approaches can lead to clinically valuable diagnostic applications of Raman Spectroscopy. Copyright © 2010 John Wiley & Sons, Ltd.     

Gas‐Phase Olefin Polymerization in the Presence of Supported and Self‐Supported Ziegler‐Natta Catalysts

The RPPFM is employed to describe the gas‐phase catalytic polymerization of ethylene in the presence of supported or self‐supported Z‐N catalysts. Numerical simulations are carried out to analyze the effect of the catalyst type on the polymerization rate, particle overheating and the average molecular polymer properties of the polyolefin. It is shown that non‐porous, self‐supported Ziegler‐Natta catalysts exhibit higher particle growth rates and lower particle overheating. The average molecular weight of polyethylene produced by both catalysts is almost identical. Depending on particle size and polymer crystallinity, the average monomer solubility and the effective monomer diffusivity can significantly vary.

     

Effects of Organic Solvents on Immobilized Lipase in Pectin Microspheres

Lipase from Brevibacillus agri 52 was found stable up to 90% diethylenglycol (DEG), glycerol (GLY), and 1,2 propanediol (1,2 PRO) at 37 degrees C for 1 h and the stability was reduced only approximately 20% after 12 h incubation, but in 40% dimethylsulfoxide (DMSO), lipase activity was stable only for 1 h. Inhibition of the biocatalysts with dimethylformamide (DMF) was detected at 20% solvent concentration. In water immiscible systems, the stability of lipase in n-hexane, n-tetradecane and n-heptane resembles the water activity, but in the presence of isobutanol, 1-hexanol, and butylbutirate, the stability was significantly reduced. Lipase 52 precipitates in the presence of 50% acetone or ethanol/water mixtures, but enzymatic activity was partially recovered by adding 20% GLY, DEG, 1,2 PRO, or DMSO to the reaction mixture. Furthermore, by increasing DEG in 70% DMF/DEG mixtures, the lipase activity was protected. Encapsulation of lipase in pectin gels cross-linked with calcium ions brings three to four times more enzymatic activity in 70% water miscible organic solvents compared to aqueous systems.     

Biologically Inspired C−H and C=C Oxidations with Hydrogen Peroxide Catalyzed by Iron Coordination Complexes

The development of catalysts for the selective oxidation of readily available hydrocarbons or organic precursors into oxygenated products is a long‐standing goal in organic synthesis. In the last decade, some iron coordination complexes have shown the potential to fit this role. These catalysts can mimic the O?O activation mode of far more sophisticated iron oxygenase enzymes, generating powerful yet selective oxidants. In this review, we report state‐of‐the‐art C?H and C=C oxidations catalyzed by non‐heme iron complexes and H₂O₂ as the oxidant. Finally, we briefly describe some novel oxidative reactivity and the perspectives of this chemistry.     

Scaling in nonstationary voltammetry representations

Despite the widespread use of voltammetry for a range of chemical, biological, environmental, and industrial applications, there is still a lack of understanding regarding the functionality between the applied voltage and the resulting patterns in the current response. This is due to the highly nonlinear relation between the applied voltage and the nonstationary current response, which casts a direct association nonintuitive. In this Article, we focus on large-amplitude/high-frequency ac voltammetry, a technique that has shown to offer increased voltammetric detail compared to alternative methods, to study heterogeneous electrochemical reaction-diffusion cases using a nonstationary time-series analysis, the Hilbert transform, and symmetry considerations. We show that application of this signal processing technique minimizes the significant capacitance contribution associated with rapid voltammetric measurements. From a series of numerical simulations conducted for different voltage excitation parameters as well as kinetic, thermodynamic, and mass transport parameters, a number of scaling laws arise that are related to the underlying parameters/dynamics of the process. Under certain conditions, these observations allow the determination of all underlying parameters very rapidly, experiment duration typically相似文献