Dihydrogen Adduct (Co-H₂) Complexes Displaying H-atom and Hydride Transfer

The prototypical reactivity profiles of transition metal dihydrogen complexes (M‐H₂) are well‐characterized with respect to oxidative addition (to afford dihydrides, M(H)₂) and as acids, heterolytically delivering H⁺ to a base and H⁻ to the metal. In the course of this study we explored plausible alternative pathways for H₂ activation, namely direct activation through H‐atom or hydride transfer from the σ‐H₂ adducts. To this end, we describe herein the reactivity of an isostructural pair of a neutral S = ½ and an anionic S = 0 Co‐H₂ adduct, both supported by a trisphosphine borane ligand (P₃^B). The thermally stable metalloradical, (P₃^B)Co(H₂), serves as a competent precursor for hydrogen atom transfer to ᵗBu₃ArO·. What is more, its anionic derivative, the dihydrogen complex [(P₃^B)Co(H₂)]¹⁻, is a competent precursor for hydride transfer to BEt₃, establishing its remarkable hydricity. The latter finding is essentially without precedent among the vast number of M‐H₂ complexes known

Dihydrogen Adduct (Co-H₂) Complexes Displaying H-atom and Hydride Transfer

The prototypical reactivity profiles of transition metal dihydrogen complexes (M‐H₂) are well‐characterized with respect to oxidative addition (to afford dihydrides, M(H)₂) and as acids, heterolytically delivering H⁺ to a base and H⁻ to the metal. In the course of this study we explored plausible alternative pathways for H₂ activation, namely direct activation through H‐atom or hydride transfer from the σ‐H₂ adducts. To this end, we describe herein the reactivity of an isostructural pair of a neutral S = ½ and an anionic S = 0 Co‐H₂ adduct, both supported by a trisphosphine borane ligand (P₃^B). The thermally stable metalloradical, (P₃^B)Co(H₂), serves as a competent precursor for hydrogen atom transfer to ᵗBu₃ArO·. What is more, its anionic derivative, the dihydrogen complex [(P₃^B)Co(H₂)]¹⁻, is a competent precursor for hydride transfer to BEt₃, establishing its remarkable hydricity. The latter finding is essentially without precedent among the vast number of M‐H₂ complexes known

The Role of Central Banks and Competition Policies in the Rescue and Recapitalisation of Financial Institutions During (and in the Aftermath of) the Financial Crisis

Recent years have witnessed a change in focus from considerations of factors which could impede competition, for example over-regulation, to the need to strike a balance between over-regulation and insufficient regulation – in order to provide the right level of safety for consumers (such that they are protected from risky investments). A driving force behind the need for deregulation over the past two decades has been the objective and desire to foster competition. Re-regulation thereafter assumed centre stage in some jurisdictions in response to the need to manage cross sector services' risks more efficiently. Rescue cases involving guarantees (contrasted with restructuring cases) during the recent Financial Crisis, have illustrated the prominent position which the goal of promoting financial stability has assumed over that of the prevention or limitation of possible distortions of competition which may arise when granting State aid. The importance attached to maintaining and promoting financial stability - as well as the need to facilitate rescue and restructuring measures aimed at preventing systemically relevant financial institutions from failure, demonstrate how far authorities are willing to overlook certain competition policies. However increased government and central bank intervention also simultaneously trigger the usual concerns – which include moral hazard and the danger of serving as long term substitutes for market discipline. An interesting observation derives from the relationship between State aid grants, competition, and the potential to induce higher risk taking levels. Whilst the need to promote and maintain financial stability is paramount, safeguards need to be implemented and enforced to ensure that measures geared towards the aim of sustaining system stability (measures such as lender of last resort arrangements and State rescues) do not unduly distort competition as well as induce higher risk taking levels. This paper will draw attention to safeguards which have been provided by the Commission where approval is considered for the grant of State aid to financial institutions whose problems are attributable to inefficiencies, poor asset liability management or risky strategies. Whether the distinction drawn by the Commission – with regards to the preferential grant of recapitalisation packages to fundamentally sound banks (which require less restructuring measures)is justified, will also be considered. How far central banks and governments should intervene and how far distortions of competition should be permitted ultimately depends on how systemically relevant a financial institution is

A mechanistic investigation of the photoinduced, copper-mediated cross-coupling of an aryl thiol with an aryl halide

Photoinduced, copper-catalyzed cross-coupling can offer a complementary approach to thermal (non-photoinduced) methods for generating C–X (X = C, N, O, S, etc.) bonds. In this report, we describe the first detailed mechanistic investigation of one of the processes that we have developed, specifically, the (stoichiometric) coupling of a copper–thiolate with an aryl iodide. In particular, we focus on the chemistry of a discrete [Cu^I(SAr)_2]− complex (Ar = 2,6-dimethylphenyl), applying a range of techniques, including ESI-MS, cyclic voltammetry, transient luminescence spectroscopy, optical spectroscopy, DFT calculations, Stern–Volmer analysis, EPR spectroscopy, actinometry, and reactivity studies. The available data are consistent with the viability of a pathway in which photoexcited [Cu^I(SAr)_2]−* serves as an electron donor to an aryl iodide to afford an aryl radical, which then reacts in cage with the newly generated copper(II)–thiolate to furnish the cross-coupling product in a non-chain process

Photoinduced, Copper-Catalyzed Alkylation of Amines: A Mechanistic Study of the Cross-Coupling of Carbazole with Alkyl Bromides

We have recently reported that a variety of couplings of nitrogen, sulfur, oxygen, and carbon nucleophiles with organic halides can be achieved under mild conditions (−40 to 30 °C) through the use of light and a copper catalyst. Insight into the various mechanisms by which these reactions proceed may enhance our understanding of chemical reactivity and facilitate the development of new methods. In this report, we apply an array of tools (EPR, NMR, transient absorption, and UV–vis spectroscopy; ESI–MS; X-ray crystallography; DFT calculations; reactivity, stereochemical, and product studies) to investigate the photoinduced, copper-catalyzed coupling of carbazole with alkyl bromides. Our observations are consistent with pathways wherein both an excited state of the copper(I) carbazolide complex ([Cu^I(carb)_2]^−) and an excited state of the nucleophile (Li(carb)) can serve as photoreductants of the alkyl bromide. The catalytically dominant pathway proceeds from the excited state of Li(carb), generating a carbazyl radical and an alkyl radical. The cross-coupling of these radicals is catalyzed by copper via an out-of-cage mechanism in which [Cu^I(carb)_2]^− and [Cu^(II)(carb)_3]^− (carb = carbazolide), both of which have been identified under coupling conditions, are key intermediates, and [Cu^(II)(carb)_3]^− serves as the persistent radical that is responsible for predominant cross-coupling. This study underscores the versatility of copper(II) complexes in engaging with radical intermediates that are generated by disparate pathways, en route to targeted bond constructions

Arbovirus infections and viral haemorrhagic fevers in Uganda : a serological survey in Karamoja district, 1984

Présentation des résultats de l'enquête effectuée sur 132 habitants du district de Karamoja en Ouganda, qui ont été examinés pour la recherche d'anticorps contre certains arbovirus dont la fièvre hémorragiqu

Vascular endothelial growth factor-A and Poly(A) binding protein-interacting protein 2 expression in human head and neck carcinomas: correlation and prognostic significance

Vascular endothelial growth factor-A (VEGF-A) has been demonstrated to play an important role in tumour angiogenesis and to influence prognosis in many cancers. However its prognostic value in head and neck squamous cell carcinomas (HNSCCs) remains controversial. Therefore, we investigated the clinical relevance of VEGF-A expression in HNSCCs and analysed whether its expression was associated with PAIP2 protein levels, a VEGF-A mRNA-binding partner that strongly regulates VEGF-A expression in tissue culture. We determined the correlation of VEGF-A and PAIP2 protein levels, quantitatively evaluated in tumour tissue homogenates from 54 patients with HNSCC, to clinicopathological parameters. We showed that VEGF-A expression in HNSCC is correlated to the stage of tumour differentiation (P=0.050) and is an independent prognostic factor for progression-free survival (P=0.001) and overall survival (P=0.0004). In a pharynx carcinoma cell line, we demonstrated by RNA interference that VEGF-A expression is closely controlled by PAIP2. Moreover, in human HNSCCs, VEGF-A expression is significantly correlated to PAIP2 protein levels (P=0.0018). Nevertheless, PAIP2 expression is associated with neither clinicopathological factors nor patient's survival. Our data suggest that, in contrast to PAIP2 protein levels, which are unrelated to tumour prognosis, VEGF-A expression could serve as a prognostic marker in head and neck cancer and may be helpful for targeted therapies

Workshop 1: Surveillance issues of pandemic influenza

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A highly efficient, stable, and rapid approach for ex vivo human liver gene therapy via a FLAP lentiviral vector

Allogenic hepatocyte transplantation or autologous transplantation of genetically modified hepatocytes has been used successfully to correct congenital or acquired liver diseases and can be considered as an alternative to orthotopic liver transplantation. However, hepatocytes are neither easily maintained in culture nor efficiently genetically modified and are very sensitive to dissociation before their reimplantation into the recipient. These difficulties have greatly limited the use of an ex vivo approach in clinical trials. In the present study, we have shown that primary human and rat hepatocytes can be efficiently transduced with a FLAP lentiviral vector without the need for plating and culture. Efficient transduction of nonadherent primary hepatocytes was achieved with a short period of contact with vector particles, without modifying hepatocyte viability, and using reduced amounts of vector. We also showed that the presence of the DNA FLAP in the vector construct was essential to reach high levels of transduction. Moreover, transplanted into uPA/SCID mouse liver, lentivirally transduced primary human hepatocytes extensively repopulated their liver and maintained a differentiated and functional phenotype as assessed by the stable detection of human albumin and antitrypsin in the serum of the animals for months. In conclusion, the use of FLAP lentiviral vectors allows, in a short period of time, a high transduction efficiency of human functional and reimplantable hepatocytes. This work therefore opens new perspectives for the development of human clinical trials based on liver-directed ex vivo gene therapy.info:eu-repo/semantics/publishedVersio