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311.
Prof. Carl Redshaw Mark Walton Dr. Lucy Clowes Dr. David L. Hughes Dr. Anna‐Marie Fuller Dr. Yimin Chao Dr. Alex Walton Dr. Victor Sumerin Dr. Pertti Elo Dr. Igor Soshnikov Dr. Weizhen Zhao Prof. Wen‐Hua Sun 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(27):8884-8899
The reactions of MCl5 or MOCl3 with imidazole‐based pro‐ligand L1H, 3,5‐tBu2‐2‐OH‐C6H2‐(4,5‐Ph2‐1H‐)imidazole, or oxazole‐based ligand L2H, 3,5‐tBu2‐2‐OH‐C6H2(1H‐phenanthro[9,10‐d])oxazole, following work‐up, afforded octahedral complexes [MX(L1, 2)], where MX=NbCl4 (L1, 1 a ; L2, 2 a ), [NbOCl2(NCMe)] (L1, 1 b ; L2, 2 b ), TaCl4 (L1, 1 c ; L2, 2 c ), or [TaOCl2(NCMe)] (L1, 1 d ). The treatment of α‐diimine ligand L3, (2,6‐iPr2C6H3N?CH)2, with [MCl4(thf)2] (M=Nb, Ta) afforded [MCl4(L3)] (M=Nb, 3 a ; Ta, 3 b ). The reaction of [MCl3(dme)] (dme=1,2‐dimethoxyethane; M=Nb, Ta) with bis(imino)pyridine ligand L4, 2,6‐[2,6‐iPr2C6H3N?(Me)C]2C5H3N, afforded known complexes of the type [MCl3(L4)] (M=Nb, 4 a ; Ta, 4 b ), whereas the reaction of 2‐acetyl‐6‐iminopyridine ligand L5, 2‐[2,6‐iPr2C6H3N?(Me)C]‐6‐Ac‐C5H3N, with the niobium precursor afforded the coupled product [({2‐Ac‐6‐(2,6‐iPr2C6H3N?(Me)C)C5H3N}NbOCl2)2] ( 5 ). The reaction of MCl5 with Schiff‐base pro‐ligands L6H–L10H, 3,5‐(R1)2‐2‐OH‐C6H2CH?N(2‐OR2‐C6H4), (L6H: R1=tBu, R2=Ph; L7H: R1=tBu, R2=Me; L8H: R1=Cl, R2=Ph; L9H: R1=Cl, R2=Me; L10H: R1=Cl, R2=CF3) afforded [MCl4(L6–10)] complexes (M=Nb, 6 a – 10 a ; M=Ta, 6 b – 9 b ). In the case of compound 8 b , the corresponding zwitterion was also synthesised, namely [Ta?Cl5(L8H)+] ? MeCN ( 8 c ). Unexpectedly, the reaction of L7H with TaCl5 at reflux in toluene led to the removal of the methyl group and the formation of trichloride 7 c [TaCl3(L7‐Me)]; conducting the reaction at room temperature led to the formation of the expected methoxy compound ( 7 b ). Upon activation with methylaluminoxane (MAO), these complexes displayed poor activities for the homogeneous polymerisation of ethylene. However, the use of chloroalkylaluminium reagents, such as dimethylaluminium chloride (DMAC) and methylaluminium dichloride (MADC), as co‐catalysts in the presence of the reactivator ethyl trichloroacetate (ETA) generated thermally stable catalysts with, in the case of niobium, catalytic activities that were two orders of magnitude higher than those previously observed. The effects of steric hindrance and electronic configuration on the polymerisation activity of these tantalum and niobium pre‐catalysts were investigated. Spectroscopic studies (1H NMR, 13C NMR and 1H? 1H and 1H? 13C correlations) on the reactions of compounds 4 a / 4 b with either MAO(50) or AlMe3/[CPh3]+[B(C6F5)4]? were consistent with the formation of a diamagnetic cation of the form [L4AlMe2]+ (MAO(50) is the product of the vacuum distillation of commercial MAO at +50 °C and contains only 1 mol % of Al in the form of free AlMe3). In the presence of MAO, this cationic aluminium complex was not capable of initiating the ROMP (ring opening metathesis polymerisation) of norbornene, whereas the 4 a / 4 b systems with MAO(50) were active. A parallel pressure reactor (PPR)‐based homogeneous polymerisation screening by using pre‐catalysts 1 b , 1 c , 2 a , 3 a and 6 a , in combination with MAO, revealed only moderate‐to‐good activities for the homo‐polymerisation of ethylene and the co‐polymerisation of ethylene/1‐hexene. The molecular structures are reported for complexes 1 a – 1 c , 2 b , 5 , 6 a , 6 b, 7 a, 8 a and 8 c . 相似文献
312.
DL Leiske CE Miller L Rosenfeld C Cerretani A Ayzner B Lin M Meron M Senchyna HA Ketelson D Meadows S Srinivasan L Jones CJ Radke MF Toney GG Fuller 《Langmuir : the ACS journal of surfaces and colloids》2012,28(32):11858-11865
Meibum is the primary component of the tear film lipid layer. Thought to play a role in tear film stabilization, understanding the physical properties of meibum and how they change with disease will be valuable in identifying dry eye treatment targets. Grazing incidence X-ray diffraction and X-ray reflectivity were applied to meibum films at an air-water interface to identify molecular organization. At room temperature, interfacial meibum films formed two coexisting scattering phases with rectangular lattices and next-nearest neighbor tilts, similar to the Ov phase previously identified in fatty acids. The intensity of the diffraction peaks increased with compression, although the lattice spacing and molecular tilt angle remained constant. Reflectivity measurements at surface pressures of 18 mN/m and above revealed multilayers with d-spacings of 50 ?, suggesting that vertical organization rather than lateral was predominantly affected by meibum-film compression. 相似文献
313.
Fuller BT Fuller JL Sage NE Harris DA O'Connell TC Hedges RE 《Rapid communications in mass spectrometry : RCM》2004,18(23):2889-2896
Carbon (13C/12C) and nitrogen (15N/14N) stable isotope ratios were longitudinally measured in human hair that reflected the period from pre-conception to delivery in 10 pregnant women. There was no significant change in the delta13C results, but all subjects showed a decrease in delta15N values (-0.3 to -1.1 per thousand) during gestation. The mechanisms causing this decrease in hair delta15N have not been fully elucidated. However, since the delta15N values of dietary nitrogen and urea nitrogen are significantly lower compared to maternal tissues, it is hypothesized that the increased utilization of dietary and urea nitrogen for tissue synthesis during pregnancy resulted in a reduction of the steady state diet to a body trophic level effect by approximately 0.5-1 per thousand. An inverse correlation (R2 = 0.67) between hair delta15N and weight gain was also found, suggesting that positive nitrogen balance results in a reduction of delta15N values independent of diet. These results indicate that delta15N measurements have the ability to monitor not only dietary inputs, but also the nitrogen balance of an organism. A potential application of this technique is the detection of fertility patterns in modern and ancient species that have tissues that linearly record stable isotope ratios through time. 相似文献
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315.
We examine a phenomenon recently predicted by numerical simulations of supernova neutrino flavor evolution: the swapping of supernova nu(e) and nu(mu,tau) energy spectra below (above) energy E(C) for the normal (inverted) neutrino mass hierarchy. We present the results of large-scale numerical calculations which show that in the normal neutrino mass hierarchy case, E(C) decreases as the assumed effective 2x2 vacuum nu(e)<==>nu(mu,tau) mixing angle (approximately theta13) is decreased. In contrast, these calculations indicate that E(C) is essentially independent of the vacuum mixing angle in the inverted neutrino mass hierarchy case. With a good neutrino signal from a future galactic supernova, the above results could be used to determine the neutrino mass hierarchy even if theta13 is too small to be measured by terrestrial neutrino oscillation experiments. 相似文献
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