排序方式: 共有39条查询结果,搜索用时 31 毫秒
1.
Yamina Boukraa 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2018,92(12):2497-2501
Russian Journal of Physical Chemistry A - The liquid-liquid extraction of cobalt(II) from sulfate media (Na2SO4) with substituted salicylideneanilines (SAN) is investigated. The stoichiometry of... 相似文献
2.
ABSTRACT: The reaction of tetrabutylammonium tribromide (TBABr3) with mono and disubstituted alkynes in methanol at 20°C leads to the formation of mainly the corresponding α,α-dibromo, β,β-dimethoxyalkane and the E-(α,β)-dibromoalkene. The additions are faster using sonication. 相似文献
3.
Wouters J Oudjama Y Ghosh S Stalon V Droogmans L Oldfield E 《Journal of the American Chemical Society》2003,125(11):3198-3199
We have obtained the three-dimensional X-ray crystallographic structure of a C67A mutant Escherichia coli isopentenylpyrophosphate-dimethylallylpyrophosphate isomerase (EC 5.3.3.2) complexed with the bromohydrin of isopentenylpyrophosphate, at 1.93 A resolution. The overall backbone fold is very similar to that obtained previously for the wild-type enzyme in the presence of a divalent metal cation (Mn2+ or Mg2+). However, in the new structure, there are two metal binding sites, not just one. The first metal binding site is occupied by Mn2+, coordinated to three histidine and two glutamate residues, while the second is occupied by Mg2+, coordinated to two bromohydrin-ligand phosphate oxygens, the carbonyl oxygen of A67, a carboxyl oxygen of E87, and two water molecules. The C3 hydroxyl group of the bromohydrin inhibitor is involved in a short hydrogen bond to the carboxyl group of E116, one of the two Mn-bound glutamates. The structure obtained is consistent with a mechanism of action of the enzyme in which the carboxyl group of E116 protonates the double bond in isopentenylpyrophosphate, forming a carbocation, followed by removal of a C2 proton by the thiolate of C67, in the wild-type enzyme. The inhibition of the enzyme by a wide variety of other potent inhibitors is also readily explained on the basis of the bromohydrin inhibitor structure. 相似文献
4.
We analyse the properties of a particular birational mapping of two variables (Cremona transformation) depending on two free parameters ( and ), associated with the action of a discrete group of non-linear (birational) transformations on the entries of a q × q matrix. This mapping originates from the analysis of birational transformations obtained from very simple algebraic calculations, namely taking the inverse of q × q matrices and permuting some of the entries of these matrices. It has been seen to yield weak chaos and integrability. We have found new integrable cases of this Cremona transformation, corresponding to the values of = 0 when
, besides the already known values = 0 and = −1, and also arbitrary when = 0. For these cases, one has a foliation of the parameter space in elliptic curves. We give the equations of these elliptic curves. Based on this very example we show how one can find these integrability cases of the Cremona transformation and actually integrate it using a method based on the systematic study of the finite-order conditions of the Cremona transformation. The method is shown to be efficient and straightforward. The various integrability cases are revisited using many different representations of this very mapping (birational transformations, recursion in one variable, …). 相似文献
5.
Positivity - We study the existence and uniqueness of positive solutions of the nonlinear fractional differential equation $$\begin{aligned} \left\{ \begin{array}{l} ^{C}D^{\alpha }x\left( t\right)... 相似文献
6.
We analyze discrete symmetry groups of vertex models in lattice statistical mechanics represented as groups of birational transformations. They can be seen as generated by involutions corresponding respectively to two kinds of transformations onq×q matrices: the inversion of theq×q matrix and an (involutive) permutation of the entries of the matrix. We show that the analysis of the factorizations of the iterations of these transformations is a precious tool in the study of lattice models in statistical mechanics. This approach enables one to analyze two-dimensionalq
4-state vertex models as simply as three-dimensional vertex models, or higher-dimensional vertex models. Various examples of birational symmetries of vertex models are analyzed. A particular emphasis is devoted to a three-dimensional vertex model, the 64-state cubic vertex model, which exhibits a polynomial growth of the complexity of the calculations. A subcase of this general model is seen to yield integrable recursion relations. We also concentrate on a specific two-dimensional vertex model to see how the generic exponential growth of the calculations reduces to a polynomial growth when the model becomes Yang-Baxter integrable. It is also underlined that a polynomial growth of the complexity of these iterations can occur even for transformations yielding algebraic surfaces, or higher-dimensional algebraic varieties. 相似文献
7.
Rekhila Gharib Gabes Yamina Brahimi Razika Bessekhouad Yassine Mahroua Ousama Trari Mohamed 《Journal of Sol-Gel Science and Technology》2018,85(3):677-683
Journal of Sol-Gel Science and Technology - Benzamide is successfully degraded on the novel heterosystem NiMn2O4/TiO2 under visible light. The nanosized spinel is synthesized by the sol–gel... 相似文献
8.
Audra F. Gushwa Yamina Belabassi Jean-Luc Montchamp Anne F. Richards 《Journal of chemical crystallography》2009,39(5):337-347
Abstract The syntheses and X-ray analyses of triphenylmethyl (trityl=Tr) phosphorus compounds are reported and the structural similarities,
differences and 31P chemical shifts compared. A series of seven trityl-substituted phosphorus-containing compounds have been characterized by
single crystal X-ray diffraction. Ph3CPPh2, 1, a bulky P(III) compound crystallizes in the triclinic space group , a = 7.5624(6) ?, b = 9.5470(8) ?, c = 16.9722(14) ?, α = 83.4720(10)°, β = 80.541(2)°, γ = 68.1580(10)°, the borane complex of 1, 2, Ph3CPPh2(BH3) crystallizes as monoclinic colorless crystals, P21/c, a = 10.0972(12) ?, b = 9.6955(12) ?, c = 25.197(3) ?, β = 90.258(2)°. The analogous methyl substituted, 3, Ph3CPMe2(BH3) is monoclinic, C2/c, a = 15.628(3) ?, b = 12.770(3) ?, c = 18.406(4) ?, β = 103.968(3)°. Compounds 4–7 are trityl substituted P(V) compounds: Ph3CP(Ph)(O)(OH), 4, crystallizes in the triclinic space group , a = 8.9847(18) ?, b = 9.7443(19) ?, c = 12.786(3) ?, α = 72.045(3)°, β = 72.031(3)°, γ = 78.769(3)°. Esterification of 4 affords TrCP(O)(Ph)OBn 5, space group, P21/c, a = 7.9196(5) ?, b = 31.701(2) ?, c = 19.8062(13) ?, β = 99.7750(10)°. A phosphonate diester was also characterized, Ph3CP(O)(OEt)2, 6, triclinic, , a = 7.9521(17) ?, b = 9.2205(19) ?, c = 14.471(3) ?, α = 85.906(4)°, β = 83.031(4)°, γ = 68.283(4)°. Treatment of the trityl H-phosphinic acid, Ph3CPO2H2, with elemental selenium yields yellow crystals of 7, [Ph3CP(O)(OH)Se]2, P21/c, a = 9.0603(4) ?, b = 22.3652(11) ?, c = 16.9134(7) ?, β = 107.035(2)°. In our efforts to isolate a nickel-phosphine complex, two Ni(II) complexes were crystallographically analyzed,
[Ni(OP(H)Ph2)6]2BF4
−
8 and 9. Complex 8 with an uncoordinated BF4
− ion crystallizes as yellow orthorhombic crystals, Pbca, a = 18.8247(12) ?, b = 18.5518(12) ?, c = 21.0976(14) ?, while crystals of 9 are trigonal, , a = b = 13.1545(12) ?, c = 68.461(9) ?.
Graphical Abstract The syntheses and X-ray analyses of triphenylmethyl (trityl=Tr) phosphorus compounds are reported and the structural similarities,
differences and 31P chemical shifts compared.
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9.
We study the spectrum of a semi relativistic three-body hamiltonian. The hyperspherical method proves to be very efficient. We show that the ground states of baryons can be calculated with good accuracy. However, when using the meson potential, together with the colour assumption \(Vqq = \tfrac{1}{2}Vq\bar q\) , baryon Regge slopes come out noticeably too small. We analyze this problem and show that a quarkdiquark structure for baryons cures this defect. Altogether the construction of a global unified potential model for mesons and baryons seems quite hopeful. 相似文献
10.
This paper is devoted to the existence and nonexistence of positive solutions for a semilinear elliptic system involving critical Sobolev exponent and weights. We study the effect of the behavior of weights near their minima on the existence of solutions for the considered problem. 相似文献