Valve turning towards on-cycle in cobalt-catalyzed Negishi-type cross-coupling

Ligands and additives are often utilized to stabilize low-valent catalytic metal species experimentally, while their role in suppressing metal deposition has been less studied. Herein, an on-cycle mechanism is reported for CoCl2bpy2 catalyzed Negishi-type cross-coupling. A full catalytic cycle of this kind of reaction was elucidated by multiple spectroscopic studies. The solvent and ligand were found to be essential for the generation of catalytic active Co(I) species, among which acetonitrile and bipyridine ligand are resistant to the disproportionation events of Co(I). Investigations, based on Quick-X-Ray Absorption Fine Structure (Q-XAFS) spectroscopy, Electron Paramagnetic Resonance (EPR), IR allied with DFT calculations, allow comprehensive mechanistic insights that establish the structural information of the catalytic active cobalt species along with the whole catalytic Co(I)/Co(III) cycle. Moreover, the acetonitrile and bipyridine system can be further extended to the acylation, allylation, and benzylation of aryl zinc reagents, which present a broad substrate scope with a catalytic amount of Co salt. Overall, this work provides a basic mechanistic perspective for designing cobalt-catalyzed cross-coupling reactions.

In situ study of the precursor conversion reactions during solventless synthesis of Co9S8, Ni3S2, Co and Ni nanowires

Synthesis of Co9S8, Ni3S2, Co and Ni nanowires by solventless thermolysis of a mixture of metal(ii) acetate and cysteine in vacuum is reported. The simple precursor system enables the nanowire phase to be tuned from pure metal (Co or Ni) to metal sulfide (Co9S8, Ni3S2) by varying the relative concentration of the metal(ii) acetate. The growth environment facilitates new insights through in situ characterization using field-emission scanning electron microscopy (FESEM) and thermogravimetric analysis with gas chromatography-mass spectrometry (TGA-GC-MS). Direct observation by FESEM shows the temperature at which nanowire growth occurs and suggests adatoms are incorporated into the base of the growing nanowire. TGA-GC-MS reveals the rates of precursor decomposition and identity of the volatilized ligand fragments during heat-up and at the nanowire growth temperature. Our results constitute a new approach for the selective fabrication of high quality Co9S8 and Ni3S2 nanowires and more importantly provides new understanding of precursor decomposition reactions that support symmetry-breaking growth in nanocrystals by heat-up synthesis.

The use of X-ray absorption and synchrotron based micro-X-ray fluorescence spectroscopy to investigate anti-cancer metal compounds in vivo and in vitro

X-ray absorption spectroscopy (XAS) and micro-synchrotron based X-ray fluorescence (micro-SXRF) are element specific spectroscopic techniques and have been proven to be valuable tools for the investigation of changes in the chemical environment of metal centres. XAS allows the determination of the oxidation state, the coordination motif of the probed element, the identity and the number of adjacent atoms and the absorber-ligand distances. It is further applicable to nearly all types of samples independent of their actual physical state (solid, liquid, gaseous) down to μM concentrations. Micro-SXRF can provide information on the distribution and concentration of multiple elements within a sample simultaneously, allowing for the chemical state of several elements within subcellular compartments to be probed. Modern third generation synchrotrons offer the possibility to investigate the majority of the biologically relevant elements. The biological mode of action of metal-based compounds often involves interactions with target and/or transport molecules. The presence of reducing agents may also give rise to changes in the coordination sphere and/or the oxidation state. XAS and micro-SXRF are ideal techniques for investigating these issues. This tutorial review introduces the use of XAS and micro-SXRF techniques into the field of inorganic medicinal chemistry. The results obtained for platinum, ruthenium, gallium, gold and cobalt compounds within the last few years are presented.

Voltammetric determination of cysteine using carbon paste electrode modified with Co(II)-Y zeolite

A novel zeolite modified electrode for use in voltammetric determination of l-cysteine (CySH) was described. The electrode comprises a Co(II)-exchanged zeolite Y as modifier in carbon paste matrix. First, the electrochemical behavior of Co(II) in modified carbon paste electrode was studied. The results demonstrated that diffusion can control the redox process of cobalt cations at the surface of the modified electrode. Then, the behavior of the electrode in the presence of CySH was studied by using cyclic voltammetry and a novel behavior was observed. In high concentration of CySH (above 10 mmol L(-1)), one pair of semi-reversible electrochemical extra peak was observed which was assigned to the processes of oxidation-reduction of CySH at the unmodified and modified electrode. Acidic conditions with respect to the neutral one cause an increase in the electrode response. The modified electrode showed a suitable linear calibration graph in the concentration range of 1.0×10(-9)-1.0×10(-3)mol L(-1) cysteine with a detection limit of 2.37×10(-10)mol L(-1). The influence of potential interfering substances on the peak current was studied and the results showed that the method was highly selective for determination of CySH. Thus, the proposed electrode was used for the determination of CySH in real samples including human blood serum, urine, N-acetylcysteine tablet and powdered poultry feed and the satisfactory results were obtained. Typical features of the sensor can be summarized as: low cost, simple preparation, fast response, good stability and selectivity, wide linear range, low detection limit and high reproducibility.

Aminothiol receptors for decorporation of intravenously administered (60)Co in the rat

This report provides a comparison of the oral decorporation efficacy of L-glutathione (GSH), L-cysteine (Cys), and a liposomal GSH formulation (ReadiSorb) toward systemic (60)Co to that observed following intravenous administration of GSH and Cys in F344 rats. Aminoacid L-histidine (His) containing no thiol functionality was tested intravenously to compare in vivo efficacy of the aminothiol (GSH, Cys) chelators with that of the aminoimidazole (His) chelator. In these studies, (60)Co was administered to animals by intravenous injection, followed by intravenous or oral gavage doses of a chelator repeated at 24-h intervals for a total of 5 doses. The results suggest that GSH and Cys are potent decorporation agents for (60)Co in the rat model, although the efficacy of treatment depends largely on the systemic availability of the chelator. The intravenous route of administration of GSH or Cys was most effective in reducing tissue (60)Co levels and in increasing excretion of radioactivity compared to control animals. Liposomal encapsulation was found to markedly enhance the oral bioavailability of GSH compared to non-formulated GSH. The oral administration of liposomal GSH reduced (60)Co levels in nearly all tissues by 12-43% compared to that observed for non-formulated GSH. Efficacy of oral Cys was only slightly reduced in comparison with intravenous Cys. Further studies to optimize the dosing regimen in order to maximize decorporation efficiency are warranted.

What first principles molecular dynamics can tell us about EXAFS spectroscopy of radioactive heavy metal cations in water

In this paper we show how molecular dynamics simulation can improve comprehension of structure and dynamics of water solvent around heavy cations. In particular, metal-water radial distribution function obtained from molecular dynamics can be used into EXAFS equation to improve the experimental signal fitting. Here we show results on structure and dynamics of Co2+, that is a radiocontaminant cation in its isotopic form 60Co, and lanthanoids(III) that are the chemical analogues of actinides(III) in aqueous solution.