β‐Diketiminate‐Stabilized Magnesium(I) Dimers and Magnesium(II) Hydride Complexes: Synthesis,Characterization, Adduct Formation,and Reactivity Studies

The preparation and characterization of a series of magnesium(II) iodide complexes incorporating β‐diketiminate ligands of varying steric bulk and denticity, namely, [(ArNCMe)₂CH]^? (Ar=phenyl, (^PhNacnac), mesityl (^MesNacnac), or 2,6‐diisopropylphenyl (Dipp, ^DippNacnac)), [(DippNCtBu)₂CH]^? (^tBuNacnac), and [(DippNCMe)(Me₂NCH₂CH₂NCMe)CH]^? (^DmedaNacnac) are reported. The complexes [(^PhNacnac)MgI(OEt₂)], [(^MesNacnac)MgI(OEt₂)], [(^DmedaNacnac)MgI(OEt₂)], [(^MesNacnac)MgI(thf)], [(^DippNacnac)MgI(thf)], [(^tBuNacnac)MgI], and [(^tBuNacnac)MgI(DMAP)] (DMAP=4‐dimethylaminopyridine) were shown to be monomeric by X‐ray crystallography. In addition, the related β‐diketiminato beryllium and calcium iodide complexes, [(^MesNacnac)BeI] and [{(^DippNacnac)CaI(OEt₂)}₂] were prepared and crystallographically characterized. The reductions of all metal(II) iodide complexes by using various reagents were attempted. In two cases these reactions led to the magnesium(I) dimers, [(^MesNacnac)MgMg(^MesNacnac)] and [(^tBuNacnac)MgMg(^tBuNacnac)]. The reduction of a 1:1 mixture of [(^DippNacnac)MgI(OEt₂)] and [(^MesNacnac)MgI(OEt₂)] with potassium gave a low yield of the crystallographically characterized complex [(^DippNacnac)Mg(μ‐H)(μ‐I)Mg(^MesNacnac)]. All attempts to form beryllium(I) or calcium(I) dimers by reductions of [(^MesNacnac)BeI], [{(^DippNacnac)CaI(OEt₂)}₂], or [{(^tBuNacnac)CaI(thf)}₂] have so far been unsuccessful. The further reactivity of the magnesium(I) complexes [(^MesNacnac)MgMg(^MesNacnac)] and [(^tBuNacnac)MgMg(^tBuNacnac)] towards a variety of Lewis bases and unsaturated organic substrates was explored. These studies led to the complexes [(^MesNacnac)Mg(L)Mg(L)(^MesNacnac)] (L=THF or DMAP), [(^MesNacnac)Mg(μ‐AdN₆Ad)Mg(^MesNacnac)] (Ad=1‐adamantyl), [(^tBuNacnac)Mg(μ‐AdN₆Ad)Mg(^tBuNacnac)], and [(^MesNacnac)Mg(μ‐tBu₂N₂C₂O₂)Mg(^MesNacnac)] and revealed that, in general, the reactivity of the magnesium(I) dimers is inversely proportional to their steric bulk. The preparation and characterization of [(^tBuNacnac)Mg(μ‐H)₂Mg(^tBuNacnac)] has shown the compound to have different structural and physical properties to [(^tBuNacnac)MgMg(^tBuNacnac)]. Treatment of the former with DMAP has given [(^tBuNacnac)Mg(H)(DMAP)], the X‐ray crystal structure of which disclosed it to be the first structurally authenticated terminal magnesium hydride complex. Although attempts to prepare [(^MesNacnac)Mg(μ‐H)₂Mg(^MesNacnac)] were not successful, a neutron diffraction study of the corresponding magnesium(I) complex, [(^MesNacnac)MgMg(^MesNacnac)] confirmed that the compound is devoid of hydride ligands.     

Simulation of loss mechanisms in organic solar cells: A description of the mesoscopic Monte Carlo technique and an evaluation of the first reaction method

In this letter we evaluate the accuracy of the first reaction method (FRM) as commonly used to reduce the computational complexity of mesoscale Monte Carlo simulations of geminate recombination and the performance of organic photovoltaic devices. A wide range of carrier mobilities, degrees of energetic disorder, and applied electric field are considered. For the ranges of energetic disorder relevant for most polyfluorene, polythiophene, and alkoxy poly(phenylene vinylene) materials used in organic photovoltaics, the geminate separation efficiency predicted by the FRM agrees with the exact model to better than 2%. We additionally comment on the effects of equilibration on low-field geminate separation efficiency, and in doing so emphasize the importance of the energy at which geminate carriers are created upon their subsequent behavior.     

Ketene functionalized polyethylene: control of cross-link density and material properties

The functionalization and cross-linking of polyethylene is synthetically challenging, commonly relying on highly optimized radical based postpolymerization strategies. To address these difficulties, a norbornene monomer containing Meldrum's acid is shown to be effectively copolymerized with polyethylene using a nickel α-iminocarbaxamidato complex, providing high-melting, semicrystalline polymers with a tunable incorporation of the functional comonomer. Upon heating the copolymer to common polyethylene processing temperatures, the thermolysis of Meldrum's acid to ketene provides the desired reactive group. This simple and versatile methodology does not require small molecule radical sources or catalysts, and the dimerization of the in situ generated ketenes is shown to provide tunable cross-linking densities in polyethylene. Subsequent rheological and tensile experiments illustrate the ability to tune cross-linked polyethylene properties by comonomer incorporation and elucidate valuable structure/property relationships in these materials. This study illustrates the power of well-defined and synthetically accessible functional groups in polyolefin synthesis and functionalization.     

Conjugation of testosterone modifies the interaction of mono-functional cationic platinum(II) complexes with DNA, causing significant alterations to the DNA helix

Previously a range of androgen conjugates with non-conventional platinum(II) complexes have been synthesised with the aim of enhancing cellular delivery, and which have shown increased cytotoxic activity compared with non-steroidal compounds (M. J. Hannon et al., Dalton Trans., 2010, DOI: 10.1039/c0dt00838a). To further study this, the complexes have been assessed for their ability to bind to and alter the structure of DNA. All platinum(II) complexes studied herein bind to model nucleo-bases and DNA, but to our surprise, testosterone-based complexes caused the DNA helix to undergo significant unwinding and bending, whereas non-steroidal control complexes caused minimal structural alterations. These effects are similar to those cisplatin induces on DNA structure despite the fact that these compounds produce a monofunctional lesion. This ability attributed to interactions between the DNA helix and bulky steroidal skeleton of testosterone, coupled with the enhanced cellular delivery induced by the steroid make the steroid approach an exciting way to explore non-conventional platinum drug delivery.     

Search for a standard model Higgs boson in the H→ZZ→ℓ(+)ℓ(-)νν decay channel with the ATLAS detector

A search for a heavy standard model Higgs boson decaying via H→ZZ→→?(+)?(-)νν, where ?=e, μ, is presented. It is based on proton-proton collision data at √s=7 TeV, collected by the ATLAS experiment at the LHC in the first half of 2011 and corresponding to an integrated luminosity of 1.04 fb(-1). The data are compared to the expected standard model backgrounds. The data and the background expectations are found to be in agreement and upper limits are placed on the Higgs boson production cross section over the entire mass window considered; in particular, the production of a standard model Higgs boson is excluded in the region 340相似文献   

Defining topological features of membrane proteins by nanoelectrospray ionisation mass spectrometry

The D‐galactose‐H⁺ symport protein, GalP, of Escherichia coli is the bacterial homologue of the human glucose transport protein, GLUT1. Here we demonstrate that mass spectrometry can be used to map modification by covalently bound reagents, and also to detect structural changes in the GalP protein that occur upon substrate binding. The small thiol‐group‐specific reagent N‐ethylmaleimide (NEM) was used to modify the cysteine residues in GalP(His)₆ both alone and in the presence of D‐glucose, a known substrate. Employing a mixture of proteolysis and thermal degradation methods, the three cysteine residues were found to undergo sequential reactions with NEM, with Cys374 being modified first, followed by Cys389 and finally Cys19, thus indicating their different accessibilities within the three‐dimensional structure of the protein. Prior binding of the substrate D‐glucose to the protein protected Cys19 and Cys374 against NEM modification, but not Cys389. Cys374 had been expected to be shielded by D‐glucose binding while Cys389 had been expected to be unaffected, consistent with their proposed respective locations in the vicinity of, and distant from, the sugar binding site. However, the inaccessibility of Cys19 was unexpected and suggests a structural change in the protein promoted by D‐glucose binding which changes the proximity of Cys19 with respect to the D‐glucose‐binding site. Copyright © 2010 John Wiley & Sons, Ltd.