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141.
142.
Rimocidin. I. Carbon skeleton, partial structure, and absolute configuration at C-27 总被引:1,自引:0,他引:1
A C Cope E P Burrows M E Derieg S Moon W D Wirth 《Journal of the American Chemical Society》1965,87(23):5452-5460
143.
144.
First measurement of the left-right cross section asymmetry in Z boson production by e+e- collisions
Abe K Abt I Acton PD Adolphsen CE Agnew G Alber C Alzofon DF Antilogus P Arroyo C Ash WW Ashford V Astbury A Aston D Au Y Axen DA Bacchetta N Baird KG Baker W Baltay C Band HR Baranko G Bardon O Barrera F Battiston R Bazarko AO Bean A Beer G Belcinski RJ Bell RA Ben-David R Benvenuti AC Berger R Berridge SC Bethke S Biasini M Bienz T Bilei GM Bird F Bisello D Blaylock G Blumberg R Bogart JR Bolton T Bougerolle S Bower GR Boyce RF Brau JE Breidenbach M Browder TE Bugg WM Burgess B Burke D 《Physical review letters》1993,70(17):2515-2520
145.
146.
Hugh D. Burrows Carlos F. G. C. Geraldes Teresa J. T. Pinheiro Robin K. Harris Angelika Sebald 《Liquid crystals》2013,40(6-7):853-860
Abstract 207Pb N.M.R. data are reported for a number of even chain length lead(II) carboxylates (soaps) at various temperatures. At room temperature, the solid lead(II) decanoate and tetradecanoate show similar spectra, with a single metal ion site, and modest shielding anisotropy. As the temperature is increased, the soaps (hexanoate to octadecanoate) all form a highly ordered smectic phase, which gives a very broad 207Pb signal of linewidth comparable to that of the solid phase. At higher temperatures, the hexanoate to dodecanoate soaps form a lamellar L α (smectic A) phase, whilst the longer chain length carboxylates melt directly to the liquid phase. Both the lamellar L α and liquid phase give fairly sharp, isotropic signals, whose chemical shifts and linewidths are strongly temperature dependent. Possible explanations for this effect include paramagnetic contributions to the shielding tensor from low-lying electronic states of Pb(II), and contributions to the observed signal from different coordination species produced in the lead(II) carboxylate system. Although there are discrete changes in chemical shift at the phase transition, the magnitudes observed in all the phases are similar, suggesting that there are no dramatic changes in the metal coordination environment. 相似文献
147.
Ayi A. Ayi Andrew D. Burrows Mary F. Mahon Viorica M. Pop 《Journal of chemical crystallography》2011,41(8):1165-1168
Abstract
Crystals of sodium trihydrogen-1,4-benzenediphosphonate, Na[H3bdp], were prepared from the addition of aqueous sodium hydroxide to an acidified solution of 1,4-benzenediphosphonic acid (H4bdp). These were shown by X-ray crystallography to crystallize in the space group P [`1] \bar{1} , with cell parameters a = 5.7500(3) ?, b = 7.9180(5) ?, c = 10.4420(6) ?, α = 80.398(3)°, β = 76.844(4)° and γ = 81.389(4)°. The crystal structure revealed that the title compound forms a coordination network in which sodium-phosphonate sheets are pillared by the benzene rings into a three-dimensional structure. 相似文献148.
Matti Knaapila Beverly Stewart Vasil M. Garamus M. Luísa Ramos Pedro F. Cruz Rui M. M. Brito Lícinia L. G. Justino Rui Fausto Connor Napierala Michael Forster Hugh D. Burrows Ullrich Scherf 《Journal of Polymer Science.Polymer Physics》2019,57(13):826-837
We report on solution aggregates and backbone conformation of poly(9‐undecyl‐9‐methyl‐fluorene) (PF1‐11) and poly(9‐pentadecyl‐9‐methyl‐fluorene) (PF1‐15), having two different side chains compared with poly(9,9‐dihexylfluorene) (PF6) and poly(9,9‐dioctylfluorene) (PF8) with two identical side chains. In the poor solvent methylcyclohexane (MCH), X‐ray scattering indicates that PF1‐11 and PF1‐15 appear as three‐dimensional aggregates (5–10 nm wide and thick), forming ribbon‐like agglomerates (correlation lengths of 100 nm). PF6 and PF8 appear as two‐dimensional aggregates (>10 nm wide and 2–3 nm thick) involving ribbon‐like agglomerates (correlation lengths much greater than 100 nm). Upon heating, all aggregates undergo a gel–sol transition which occurs at lower temperatures for PF1‐11 and PF1‐15 (<60°C) than for PF6 and PF8 (>80°C). In the good solvent toluene, PF1‐11 and PF1‐15 form networks of cylindrical particles. The mesh size and the cylinder radius are smaller in 24°C toluene (60 nm, 0.5 nm) than in 60°C MCH (300 nm, 1–2 nm). Nuclear magnetic resonance spectra in toluene‐d8 together with density functional theory calculations suggest higher torsion angles between polymer repeat units for PF6, PF8, and PF1‐11 (less planar conformation) and a gauche arrangement of the dihedral angles between the bridge carbon atom and the side chain methylene groups in PF1‐15. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 826–837 相似文献
149.
Unzipping kinetics of duplex DNA containing oxidized lesions in an α-hemolysin nanopore 总被引:1,自引:0,他引:1
Jin Q Fleming AM Burrows CJ White HS 《Journal of the American Chemical Society》2012,134(26):11006-11011
The unzipping kinetics for lesion-containing DNA duplexes was studied in an α-hemolysin (α-HL) nanopore. The lesion of focus was the guanine two-electron oxidation product, 8-oxo-7,8-dihydroguanine (OG), and its further oxidation products, the hydantoins guanidinohydantoin (Gh) and spiroiminodihydantoin (Sp). The voltage-driven unzipping of individual duplex DNA molecules with symmetrical overhangs was carried out by pulling one strand of the duplex through the α-HL channel using an electrical field. Entry from the 3' or 5' end produced distinct current blockages, allowing directional effects on unzipping kinetics to be investigated. We find that the strand dissociation of complementary duplexes or duplexes containing the slightly destabilizing lesion OG follows a first-order kinetic model, while opening of duplexes that contain the highly destabilizing lesions Gh or Sp is described by two sequential first-order reactions, in which the intermediate state is proposed to correspond to the duplex unzipped to the lesion site within the channel. The rate constants for strand separation of the duplexes containing single lesions were obtained from kinetic model fits to histograms of unzipping duration. For all duplexes, the rate constants for strand separation displayed a significant dependence on the direction of entry into the nanopore. For duplexes containing Gh, truncated duplexes were used to assign the measured rate constants for the first and second unzipping steps of symmetrically designed duplexes. 相似文献
150.
Susana L.H. Rebelo Mariette M. Pereira Paula V. Monsanto Hugh D. Burrows 《Journal of molecular catalysis. A, Chemical》2009,297(1):35-43
Oxidative degradation of the herbicides atrazine (1), atraton (2), ametryn (3) and mecoprop (4), was carried out with hydrogen peroxide and metalloporphyrins as catalysts. Two different reaction conditions were studied, the first involving Mn(TDCPP)Cl in an aprotic solvent with buffer (S-I), and the second using Fe(TPFPP)Cl in a protic solvent (S-II). Reaction products were characterized, and based on these it is shown that there are two distinct reaction schemes.In the case of the S-I conditions, it is suggested that the s-triazines were oxidized through hydroxylation of the alkyl side chains followed by dealkylation, while S-II was ineffective for these reactions. In contrast, mecoprop, was oxidized with high efficiency by S-II, leading to decarboxylation and further oxidation, while in the presence of S-I, low substrate conversion was observed, and reaction resulted mainly from oxidation at the benzyl position. Sulfoxidation of ametryn was observed with both systems.The different reactivity shown by the two systems supports the involvement of different reactive species, which we assign to the oxo and hydroperoxy complexes. These routes show similarities with metabolic pathways, with the reactivity pattern of S-I analogous to the reported metabolism of these pollutants with cytochrome P450 enzymes, while S-II catalyses mecoprop decarboxylation via a similar pathway to that seen with peroxidase catalysed reactions. 相似文献