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51.
Abstract —The oxygen dependence of 365 nm inactivation of colony-forming ability of Escherichia coli has been investigated in two series of DNA repair-deficient K12 mutants grown to mid-exponential phase. All strains except a uvr A rec A double mutant are more sensitive to inactivation under O2 and show a lower threshold dose. The inactivation of photoreactivating enzyme in a crude cell extract and DNA repair disruption are both reduced when irradiation is carried out under nitrogen. The rec A gene-dependent synergism between 365 nm and ionising radiation is reversible if cells are incubated in full growth medium before ionising radiation treatment. In a wildtype strain, incubation for 2.5 h in full growth medium after 106 J m-2 365 nm radiation changes a sensitised response to a protection from ionising radiation. Protection is not seen at 1.5 times 106 J m-2 . A tentative model for near UV lethality in logarithmic phase cells is suggested which proposes two classes of lesions. One requires oxygen for it's induction, is rapidly fixed as a lethal event as a result of repair disruption, and is primarily responsible for cell death after aerobic 365 nm irradiation. The other lesion, possibly pyrimidine dimers, may lead to cell death under anaerobic conditions. 相似文献
52.
Thermolysis curves for manganese(II), silver and thorium diliturates were obtained. Manganese diliturate precipitated as the octahydrate and dehydrated in two steps. Silver diliturate formed as a monohydrate from aqueous solutions. Thorium diliturate formed as a hydrate containing 20 moles of water and dehydrated in two steps.Methods for the thermogravimetric determination of manganese(II) and thorium by precipitation as the diliturates are suggested. 相似文献
53.
Khalil A. Abboud Peter N. Nickias Eugene Y.‐X. Chen 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(1):m41-m42
In the structure of bis({N‐[dimethyl(1η5‐2,3,4,6‐tetramethylindenyl)silyl]cyclohexylamido‐1κN}(methyl‐3κC)‐di‐μ3‐methylene‐1:2:3κ3C;1:3:3′κ3C‐tris(pentafluorophenyl‐2κC)titanium) benzene disolvate, [Me2Si(η5‐2,3,4,6‐Me4C9H2)(C6H11N)]Ti[(μ3‐CH2)Al(C6F5)3][AlMe(μ3‐CH2)]2 or [Ti2(C21H7AlF15)2(C21H31NSi)2]·2C6D6, the dimer is located on an inversion center, and the two Ti centers are linked by double Ti(μ3‐CH2)Al(C6F5)3AlMe(μ3‐CH2) heterocycles. The electron‐deficient Ti centers are further stabilized by two α‐agostic interactions between Ti and one H atom of each bridging methylene group. 相似文献
54.
Yalan Ning Megan J. Cooney Eugene Y.-X. Chen 《Journal of organometallic chemistry》2005,690(26):6263-6270
Characteristics of methyl methacrylate (MMA) polymerization using oscillating zirconocene catalysts, (2-Ph-Ind)2ZrX2 (X = Cl, 1; X = Me, 2), mixtures of rac- and meso-zirconocene diastereomers, (SBI)ZrMe2 [3, SBI = Me2Si(Ind)2] and (EBI)ZrMe2 [4, EBI = C2H4(Ind)2], as well as diastereospecific metallocene pairs, rac-4/Cp2ZrMe2 (5) and rac-4/CGCTiMe2 [6, CGC = Me2Si(Me4C5)(t-BuN)], are reported. MMA polymerization using the chloride catalyst precursor 1 activated with a large excess of the modified methyl aluminoxane is sluggish, uncontrolled, and produces atactic PMMA. On the other hand, the polymerization by a 2/1 ratio of 2/B(C6F5)3 or 2/Ph3CB(C6F5)4 is controlled and produces syndiotactic PMMA. Mixtures of diastereomeric ansa-zirconocenes 3 or 4 containing various rac/meso ratios, when activated with B(C6F5)3, yield bimodal PMMA; this behavior is attributed to the meso-diastereomer that, in its pure form, affords bimodal, syndio-rich atactic PMMA. For MMA polymerization using diastereospecific metallocene pairs, rac-4/5 and rac-4/6, the isospecific catalyst site dominates the polymerization events under the conditions employed in this study, and the aspecific and syndiospecific sites are largely nonproductive, thereby forming only highly isotactic PMMA. 相似文献
55.
Jouyban A Khoubnasabjafari M Vaez-Gharamaleki Z Fekari Z Acree WE 《Chemical & pharmaceutical bulletin》2005,53(5):519-523
Applicability of the Jouyban-Acree model for calculating absolute viscosity of binary liquid mixtures with respect to temperature and mixture composition is proposed. The correlation ability of the model is evaluated by employing viscosity data of 143 various aqueous and non-aqueous liquid mixtures at various temperatures collected from the literature. The results show that the model is able to correlate the data with an overall percentage deviation (PD) of 1.9+/-2.5%. In order to test the prediction capability of the model, three experimental viscosities from the highest and lowest temperatures along with the viscosities of neat liquids at all temperatures have been employed to train the model, then the viscosity values at other mixture compositions and temperatures were predicted and the overall PD obtained is 2.6+/-4.0%. 相似文献
56.
Eugene R. Corey Joyce Y. Corey Milton D. Glick 《Journal of organometallic chemistry》1977,129(1):17-25
The structures of 5-methyl-5-phenyl-5H-dibenzo[b,f] silepin (I) and 5-methyl- 5-phenyl-1O,11-dihydro-5H-dibenzo [b,f] silepin (II) have been determined from three-dimensional X-ray data collected by counter methods. I crystallizes in the orthorhombic space group Pnam with a 7.596(3), b 18.102(5) and c 12.190(2) Å; observed and calculated densities (Z = 4) are 1.17 and 1.18 g cm?3, respectively. II crystallizes in the monoclinic space group with a 11.115(3), b 7.920(3), c 20.765(5) Å and β 111.71(2)°; observed and calculated densities (Z = 4) are 1.17 g cm?3. Anisotropic refinement of nonhydrogen atoms, with hydrogen atoms included at fixed ideal locations, gave conventional R-factors of 4.5% (I) and 5.0% (II). Compound I exhibits the boat conformation for the tricyclic framework and is located on a crystallographically required mirror plane. Com- pound II has the expected folded boat conformation. The torsion angle about the 10,11-bond is 0.0° for I, a crystallographic symmetry requirement, and 89.9° for II. Mean SiC bond distances are 1.863 Å(I) and 1.875 Å(II). The dihedral angles between the planar benzo groups are 129.7° (I) and 137.2° (II); introduc- tion of unsaturation at the 10,11-position decreases the dihedral angle in the tri- cyclic system, i.e., the tricyclic system is more bent. 相似文献
57.
58.
The equilibrium structures, binding energies, and vibrational spectra of the clusters CH3F(HF)1 n 3 and CH2F2(HF)1 n 3 have been investigated with the aid of large-scale ab initio calculations performed at the Møller–Plesset second-order level. In all complexes, a strong C–FH–F halogen–hydrogen bond is formed. For the cases n = 2 and n = 3, blue-shifting C–HF–H hydrogen bonds are formed additionally. Blue shifts are, however, encountered for all C–H stretching vibrations of the fluoromethanes in all complexes, whether they take part in a hydrogen bond or not, in particular also for n = 1. For the case n = 3, blue shifts of the ν(C–H) stretching vibrational modes larger than 50 cm−1 are predicted. As with the previously treated case of CHF3(HF)1 n 3 complexes (A. Karpfen, E. S. Kryachko, J. Phys. Chem. A 107 (2003) 9724), the typical blue-shifting properties are to a large degree determined by the presence of a strong C–FH–F halogen–hydrogen bond. Therefore, the term blue-shifted appears more appropriate for this class of complexes. Stretching the C–F bond of a fluoromethane by forming a halogen–hydrogen bond causes a shortening of all C–H bonds. The shortening of the C–H bonds is proportional to the stretching of the C–F bond. 相似文献
59.
Jean Bricmont Jean-Raymond Fontaine Eugene Speer 《Communications in Mathematical Physics》1982,86(3):337-362
We consider two models that are small perturbations of Gaussian or mean field models: the first one is a double well /44 — /22 perturbation of a massless Gaussian lattice field in the weak coupling limit (0, proportional to ). The other consists of a spin 1/2 Ising model with long-range Kac type interactions; the inverse range of the interaction, , is the small parameter. The second model is related to the first one via a sine-Gordon transformation. The lattice
d
has dimensiond3.In both cases we derive an asymptotic estimate to first order (in or 2) on the location of the critical point. Moreover, we prove bounds on the remainder of an expansion in or around the Gaussian or mean field critical points.The appendix, due to E. Speer, contains an extension of Weinberg's theorem on the divergence of Feynman graphs which is used in the proofs.Supported by NSF Grant # MCS 78-01885Supported by NSF Grant # PHY 78-15920 相似文献
60.
Hans-Peter Ros Rolf Kyburz Nigel W. Preston Rex T. Gallagher I. Ralph C. Bick Manfred Hesse 《Helvetica chimica acta》1979,62(2):481-487
The revised structure 1 is put forward for peduncularine, the main alkaloid of Aristotelia peduncularis (Labill.) HOOK. F. (Elaeocarpaceae), on the basis of its spectroscopic properties and those of its degradation products, the Hofmann base 3 and the hydrogenation product 4 . Structure 1 represents the relative configuration of the alkaloid. Peduncularine belongs to the class of indole alkaloids with a monoterpene unit as the aliphatic portion. To our knowledge it constitutes the first example in which an isopropyl group has become detached from the terpene unit and occurs as a substituent on nitrogen. 相似文献