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141.
142.
An interesting effect in non-newtonian flow in oscillating pipes 总被引:1,自引:0,他引:1
143.
A study of the totally rational (entries and eigenvalues) centralizer of an Abelian group, G, is applied to the problem of determing which strongly regular graphs admit such a G as a egular automorphism group. 相似文献
144.
[reaction: see text]Comprehensive analysis of the enolization of alpha-silyloxyketones by Chx2BCl/R3N has allowed us to design stereoselective Chx2BCl-mediated aldol processes that afford syn or anti aldol products and to disclose a hypothesis that accounts for the subtle effects that determine their enolization. 相似文献
145.
Avelino Martín Miguel Mena Adrin Prez‐Redondo Carlos Ylamos 《Acta Crystallographica. Section C, Structural Chemistry》2011,67(5):m157-m159
The reaction of the imide–nitride complex [{Ti(η5‐C5Me5)(μ‐NH)}3(μ3‐N)] with potassium iodide in pyridine at room temperature affords the adduct di‐μ‐iodido‐1:1′κ4I‐bis{tri‐μ3‐imido‐1:2:3κ3N;1:2:4κ3N;1:3:4κ3N‐μ3‐nitrido‐2:3:4κ3N‐tris[2,3,4(η5)‐pentamethylcyclopentadienyl](pyridine‐1κN)‐tetrahedro‐potassiumtrititanium(IV)}, [K2Ti6(C10H15)6I2N2(NH)6(C5H5N)2] or [(C5H5N)(μ‐I)K{(μ3‐NH)3Ti3(η5‐C5Me5)3(μ3‐N)}]2. The crystal structure contains two [KTi3N4] cube‐type units held together by two bridging I atoms. There is a centre of inversion located in the middle of this unprecedented discrete K2I2 unit. The geometry around K is best described as distorted trigonal prismatic, with three imide groups, two bridging I atoms and one pyridine ligand. 相似文献
146.
采用密度泛函理论广义梯度近似第一性原理计算的方法研究了n型Ga掺杂的纤锌矿结构氧化物ZnO的晶格结构、能带结构和态密度,在此基础上分析了其电性能.计算结果表明,掺杂ZnO氧化物晶格a,b轴增大,c轴略有减小;Ga掺杂ZnO氧化物两能带之间具有0.6eV的直接带隙,需要载流子(电子)跃迁的能隙宽度较未掺杂的ZnO氧化物减小;掺杂体系费米能级附近的态密度大大提高,其能带主要由Gas态、Zns态和Os态电子构成,且他们之间存在着强相互作用,其中Gas态电子对导带贡献最大.电输运性能分析结果表明,Ga掺杂ZnO氧化物导电机构由Znp-Op电子在价带与导带的跃迁转变为Gas-Znd-Os电子在价带与导带的跃迁,这也表明Gas态电子在导电过程中的重要作用;掺杂体系费米能级附近的载流子有效质量较未掺杂体系增大,且价带中的载流子有效质量较大,导带中的载流子有效质量较小. 相似文献
147.
Dipl.‐Chem. Inmaculada Mena Dr. E. A. Jaseer Dr. Miguel A. Casado Dr. Pilar García‐Orduña Prof. Fernando J. Lahoz Prof. Luis A. Oro 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(18):5665-5675
The ready availability of rare parent amido d8 complexes of the type [{M(μ‐NH2)(cod)}2] (M=Rh ( 1 ), Ir ( 2 ); cod=1,5‐cyclooctadiene) through the direct use of gaseous ammonia has allowed the study of their reactivity. Both complexes 1 and 2 exchanged the di‐olefines by carbon monoxide to give the dinuclear tetracarbonyl derivatives [{M(μ‐NH2)(CO)2}2] (M=Rh or Ir). The diiridium(I) complex 2 reacted with chloroalkanes such as CH2Cl2 or CHCl3, giving the diiridium(II) products [(Cl)(cod)Ir(μ‐NH2)2Ir(cod)(R)] (R=CH2Cl or CHCl2) as a result of a two‐center oxidative addition and concomitant metal–metal bond formation. However, reaction with ClCH2CH2Cl afforded the symmetrical adduct [{Ir(μ‐NH2)(Cl)(cod)}2] upon release of ethylene. We found that the rhodium complex 1 exchanged the di‐olefines stepwise upon addition of selected phosphanes (PPh3, PMePh2, PMe2Ph) without splitting of the amido bridges, allowing the detection of mixed COD/phosphane dinuclear complexes [(cod)Rh(μ‐NH2)2Rh(PR3)2], and finally the isolation of the respective tetraphosphanes [{Rh(μ‐NH2)(PR3)2}2]. On the other hand, the iridium complex 2 reacted with PMe2Ph by splitting the amido bridges and leading to the very rare terminal amido complex [Ir(cod)(NH2)(PMePh2)2]. This compound was found to be very reactive towards traces of water, giving the more stable terminal hydroxo complex [Ir(cod)(OH)(PMePh2)2]. The heterocyclic carbene IPr (IPr=1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene) also split the amido bridges in complexes 1 and 2 , allowing in the case of iridium to characterize in situ the terminal amido complex [Ir(cod)(IPr)(NH2)]. However, when rhodium was involved, the known hydroxo complex [Rh(cod)(IPr)(OH)] was isolated as final product. On the other hand, we tested complexes 1 and 2 as catalysts in the transfer hydrogenation of acetophenone with iPrOH without the use of any base or in the presence of Cs2CO3, finding that the iridium complex 2 is more active than the rhodium analogue 1 . 相似文献
148.
Brian?FP?Edwards Roshini?Fernando Philip?D?Martin Edward?Grimley Melissa?Cordes Asmita?Vaishnav Joseph?S?Brunzelle Hedeel?Guy?Evans David?R?EvansEmail author 《BMC biochemistry》2013,14(1):36
Background
Dihydroorotase (DHO) is a zinc metalloenzyme, although the number of active site zinc ions has been controversial. E. coli DHO was initially thought to have a mononuclear metal center, but the subsequent X-ray structure clearly showed two zinc ions, α and β, at the catalytic site. Aquifex aeolicus DHO, is a dodecamer comprised of six DHO and six aspartate transcarbamoylase (ATC) subunits. The isolated DHO monomer, which lacks catalytic activity, has an intact α-site and conserved β-site ligands, but the geometry of the second metal binding site is completely disrupted. However, the putative β-site is restored when the complex with ATC is formed and DHO activity is regained. Nevertheless, the X-ray structure of the complex revealed a single zinc ion at the active site. The structure of DHO from the pathogenic organism, S. aureus showed that it also has a single active site metal ion.Results
Zinc analysis showed that the enzyme has one zinc/DHO subunit and the addition of excess metal ion did not stimulate catalytic activity, nor alter the kinetic parameters. The metal free apoenzyme was inactive, but the full activity was restored upon the addition of one equivalent of Zn2+ or Co2+. Moreover, deletion of the β-site by replacing the His180 and His232 with alanine had no effect on catalysis in the presence or absence of excess zinc. The 2.2 Å structure of the double mutant confirmed that the β-site was eliminated but that the active site remained otherwise intact.Conclusions
Thus, kinetically competent A. aeolicus DHO has a mononuclear metal center. In contrast, elimination of the putative second metal binding site in amidohydrolyases with a binuclear metal center, resulted in the abolition of catalytic activity. The number of active site metal ions may be a consideration in the design of inhibitors that selectively target either the mononuclear or binuclear enzymes.149.
Caballo J García-Castro M Martín A Mena M Pérez-Redondo A Yélamos C 《Inorganic chemistry》2011,50(14):6798-6808
A series of titanium-group 3/lanthanide metal complexes have been prepared by reaction of [{Ti(η(5)-C(5)Me(5))(μ-NH)}(3)(μ(3)-N)] (1) with halide, triflate, or amido derivatives of the rare-earth metals. Treatment of 1 with metal halide complexes [MCl(3)(thf)(n)] or metal trifluoromethanesulfonate derivatives [M(O(3)SCF(3))(3)] at room temperature affords the cube-type adducts [X(3)M{(μ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-N)}] (X = Cl, M = Sc (2), Y (3), La (4), Sm (5), Er (6), Lu (7); X = OTf, M = Y (8), Sm (9), Er (10)). Treatment of yttrium (3) and lanthanum (4) halide complexes with 3 equiv of lithium 2,6-dimethylphenoxido [LiOAr] produces the aryloxido complexes [(ArO)(3)M{(μ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-N)}] (M = Y (11), La (12)). Complex 1 reacts with 0.5 equiv of rare-earth bis(trimethylsilyl)amido derivatives [M{N(SiMe(3))(2)}(3)] in toluene at 85-180 °C to afford the corner-shared double-cube nitrido compounds [M(μ(3)-N)(3)(μ(3)-NH)(3){Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-N)}(2)] (M = Sc (13), Y (14), La (15), Sm (16), Eu (17), Er (18), Lu (19)) via NH(SiMe(3))(2) elimination. A single-cube intermediate [{(Me(3)Si)(2)N}Sc{(μ(3)-N)(2)(μ(3)-NH)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-N)}] (20) was obtained by the treatment of 1 with 1 equiv of the scandium bis(trimethylsilyl)amido derivative [Sc{N(SiMe(3))(2)}(3)]. The X-ray crystal structures of 2, 7, 11, 14, 15, and 19 have been determined. The thermal decomposition in the solid state of double-cube nitrido complexes 14, 15, and 18 has been investigated by thermogravimetric analysis (TGA) and differential thermal analysis (DTA) measurements, as well as by pyrolysis experiments at 1100 °C under different atmospheres (Ar, H(2)/N(2), NH(3)) for the yttrium complex 14. 相似文献
150.