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1.
A novel topological index based on the Wiener Index is proposed as W = 1/2, summation(n/ij)=S*(ij) the element S*(ij) of the distance matrix is defined either as S*(ij)= square root (E(i)E(j)/R(ij) (atoms i and j are adjacent) or as S*(ij)=(j-i+1)square root (E(i)...xE /R(ij) (atoms i and j are not adjacent), where E(i) and E(j) represent the total energy of the valence electrons of vertexes i and j, respectively, R(ij) is the sum of the distance between the vertexes i and j in a molecular graph. The distance and the energy of the vertexes in a molecule are taken into account in this definition. Hence the application of the index W to multiple bond and heteroatom-containing organic systems and inorganic systems is possible. Good correlation coefficients are achieved not only in the standard formation enthalpy of methyl halides, halogen-silicon, but also in the retention index of gas chromatography of the hydrocarbons.  相似文献   

2.
脂肪醇气相色谱保留指数与结构的相关性研究   总被引:13,自引:2,他引:11  
秦正龙  冯长君 《色谱》2004,22(4):452-455
在分子图的邻接矩阵基础上,构建了一个化合物均价连接性指数mL,mL=∑(Ai·Aj·Ak…)-0.5,其中一阶指数1L及定位基参数β与25种脂肪醇在6种固定相(SE-30,OV-3,OV-7,OV-11,OV-17和OV-25)上的气相色谱保留指数I显著相关,相关系数均大于0.98。所建定量结 构-保留关系(QSRR)模型具有良好的稳定性和预测能力,较好地揭示了脂肪醇在不同固定相上气相色谱保留指数的变化规律。  相似文献   

3.
扩展的距离矩阵指数W~*及其应用研究   总被引:5,自引:0,他引:5  
重新定义了距离矩阵及距离矩阵拓扑指数W~*,该定义考虑分子中每一原子的 性质和成键情况以及分子中每一原子与所有其它原子的结合情况。拓扑指数W~*对 于饱和碳氢体系可还原为Wiener的距离矩阵指数W,同时,W~*还可一般地应用于含 多重键及杂质原子的有机体系和无机体系。本研究用W~*相关的卤代甲烷标准生成 焓、SiX_n(X = F,Cl,Br,I,n = 1~4)体系的标准生成焓,相关系数均在0. 99以上,置信度大于99.9%。并用W~*研究了含苯环的碳氢体系气相色谱保留指数, 含氧原子的醛酮体系的标准生成焓以及卤代苯体系的辛醇/水分配系数。对饱和碳 氢体,W为W~*的特殊形式。  相似文献   

4.
Based on bonding parameters such as Yang's Electronegative Force Gauge Y(i), electronic number of valence layer Z(i), number of combined hydrogen atoms h(i), number of bonding electron b(i), and quantum number such as the highest main quantum number of valence layer n(i), a novel atomic valence delta(i) (Y) is defined and a novel topological index (1)chi(Y) is derived from the atomic valence. The atomic valence is defined as delta(i) (Y) = (Z(i) - h(i))b(i)/n(i) (2)Y(i), while the topological index is expressed as (1)chi(Y) summation operator (i,j=1) (m) (delta(i) (Y)delta(j) (Y))(-1/2). Subsequently, the index (1)chi(Y) is utilized to study the structure-property relationships of complex organic compounds. The results of correlativity showed that the index is highly and extensively correlated with such properties as solubility of phenyl chlorides, gas chromatographic retention index of alkoxyl silanes, and toxicity of heterocyclic nitrogen-containing compounds. Moreover, predicted values are quite consistent with experimental ones when the index is employed to predict the partition coefficient (log P) of fatty alcohols, phenyl chlorides, and barbitals. Compared to the topological indices reported in the literature, the universality and reliability of (1)chi(Y) to the properties of complex organic compounds have been distinctively improved, and its calculating process is simple and convenient.  相似文献   

5.
键连接性指数的建构及其在有机体系中的应用研究   总被引:3,自引:0,他引:3  
杨锋  王振东  孙杰  罗明道  屈松生 《有机化学》2002,22(11):884-888
以化学键为基础建构了键连接性指数及分子键连接性指数,该指数同时考虑顶 点原子的化学特征及键的性质.对于任意化学键,键连接性指数Si=1+△I/R·[( Z1-h1)m2/n1+(Z2-h2)m1/n2],分子键连接性指数S为∑i=1^m√Si或∑i=1^m1/√ Si,其中,Z1,Z2为化学键键连原子的价电子数;n1,n2成键原子的价层最高主量 子数;m1,m2为成键原子的氧化数;h1,h2为与成键原子相连的氢原子个数;△I 为成键原子的电负性差(△I≥0);R为化学键的相对键长.与以顶点为基础的价连 接性指数不同,该指数不仅能方便而有效地应用于饱和碳氢体系亦能有效地应用于 含多重键的不饱和体系及含杂原子的有机体系.研究了饱和碳氢体系标准生成焓, 不饱和碳氢体系和酮、醚、酯体系在水中的溶解度和辛醇/水分配系数,卤代甲烷 体系的标准生成焓,卤代苯体系辛醇/水分配系数,均取得比较满意的结果。  相似文献   

6.
Erythromycin sensitive electrodes have been proposed. Their selectivity toward quaternary ammoniums is described in terms of induction effect and steric hindrance effect: logKil=a_1I-a_2Z/R+a_0, where I is induction effect index, a_1,a_2 and a_0 are coefficients which depend on the electro-active material. A general formula has been suggested to relate the electrode selectivity to the carbon atom number (n) of the alkyl of the quaternary ammonium; logK_(ij)=A/2.7~R-B/(0.80+1.26n)+C, where A, B and C are coefficients which depend on the electro-actlve material, logK_(ij) tends to a limited value C when n increases.  相似文献   

7.
With the new substituted pyrazine ligand pyrazine-2,3-dicarboxylic acid bis[(pyridin-2-ylmethyl)amide], H(2)L, a binuclear complex [Cu(2)(LH)(Cl(3))(H(2)O)].H(2)O (1) and two [2 x 2]G grid complexes, [[Cu(4)(LH)(4)](ClO(4))(4)].5CH(3)OH.4H(2)O (2) and [[Ni(4)(LH)(4)]Cl(4)].5CH(3)CN.13H(2)O (3), have been synthesized and characterized spectroscopically and crystallographically. The ligand H(2)L crystallized in the triclinic space group P1, with a = 4.9882(7) A, b = 12.079(2) A, c = 14.454(2) A, alpha = 107.08(2) degrees, beta = 98.61(2) degrees, gamma = 97.54(2) degrees, V = 808.8(2) A(3), Z = 2, R1 = 0.0747, and R(w) = 0.1829 for 1319 observed reflections [I > 2 sigma(I)]. The molecule is L-shaped with a strong intramolecular bifurcated hydrogen bond in half of the molecule. In the crystal the molecules are linked by an intermolecular hydrogen bond to form a 1D polymer. The binuclear complex [Cu(2)(LH)(Cl(3))(H(2)O)].H(2)O (1) crystallized in the monoclinic space group P2(1)/a, with a = 8.6859(7) A, b = 28.060(2) A, c = 9.5334(9) A, beta = 107.89(1) degrees, V = 2211.2(3) A(3), Z = 4, R1 = 0.039, and R(w) = 0.097 for 1408 observed reflections [I > 2 sigma(I)]. There are two independent copper atoms both having square pyramidal geometry. Both coordinate to a pyrazine, a pyridine, and an amide N atom. Two chlorines complete the coordination sphere of one of the copper atoms, while one chlorine atom and a water molecule complete the coordination sphere of the other. The copper(II) [2 x 2] grid complex [[Cu(4)(LH)(4)](ClO(4))(4)].5CH(3)OH.4H(2)O (2) crystallized in the triclinic space group P1, with a = 17.1515(14) A, b = 17.7507(13) A, c = 19.3333(15) A, alpha = 67.34(1) degrees, beta = 69.79(1) degrees, gamma = 71.50(1) degrees, V = 4980.3(7) A(3), Z = 2, R1 = 0.083, and R(w) = 0.207 for 5532 observed reflections [I > 2 sigma(I)]. The four Cu(II) atoms are octahedrally coordinated by two pyrazine, two pyridine, and two amide N atoms and occupy the corners of a [2 x 2] grid with edge lengths, Cu...Cu, varying from 7.01 to 7.39 A. The nickel(II) [2 x 2] grid complex [[Ni(4)(LH)(4)]Cl(4)].5CH(3)CN.13H(2)O (3) crystallized in the monoclinic space group C2/c, with a = 16.3388(10) A, b = 29.754(2) A, c = 20.857(1) A, beta = 101.845(1) degrees, V = 9923.6(12) A(3), Z = 4, R1 = 0.050, and wR2 = 0.101 for 3391 observed reflections [I > 2 sigma(I)]. Here the complex possesses C(2) symmetry and again each metal atom is octahedrally coordinated to two pyrazine, two pyridine, and two amide N atoms. They occupy the corners of a [2 x 2] grid with an average edge length, Ni.Ni, of 6.97 A. Of the four anions (ClO(4)(-)'s in 2 and Cl(-)'s in 3) required to equilibrate the charges in the grid complexes, two are encapsulated, one above and one below the plane of the four metal atoms. The remaining two anions are located between the "wings" of the ligands. Magnetic susceptibility measurements indicate that the binuclear complex 1 is antiferromagnetic, with a J value of -15.07 cm(-1). This is larger than the J values found for the Cu(II) (2) and Ni(II) (3) grid complexes, which were -5.87 and -2.64 cm(-1), respectively. DFT calculations have been carried out to explain the difference in the J values found for complexes 1 and 2.  相似文献   

8.
The syntheses of macrocyclic species composed of carborane derivatives joined via their carbon vertices by electrophilic mercury atoms are described. The reaction of closo-1,2-Li(2)[C(2)B(10)H(10)(-)(x)()R(x)()] with HgI(2) gives Li(2)[(1,2-C(2)B(10)H(10)(-)(x)()R(x)()Hg)(4)I(2)] [R = Et, x = 2 (5.I(2)Li(2)); R = Me, x = 2 (6.I(2)Li(2)); R = Me, x = 4 (7.I(2)Li(2))]. 6.I(2)(K.[18]dibenzocrown-6)(2) crystallizes in the monoclinic space group C2/m [a = 28.99(2) ?, b = 18.19(1) ?, c = 13.61(1) ?, beta = 113.74(2) degrees, V = 6568 ?(3), Z = 4, R = 0.060, R(w) = 0.070]; 7.I(2)(NBu(4))(2) crystallizes in the monoclinic space group P2(1)/c [a = 12.77(1) ?, b = 21.12(2) ?, c = 20.96(2) ?, beta = 97.87(2) degrees, V = 5600 ?(3), Z = 2, R = 0.072, R(w) = 0.082]. The precursor to 7, closo-8,9,10,12-Me(4)-1,2-C(2)B(10)H(8) (4), is made in a single step by reaction of closo-1,2-C(2)B(10)H(12) with MeI in trifluoromethanesulfonic acid. The free hosts 5, 6, and 7 are obtained by reaction of the iodide complexes with stoichiometric quantities of AgOAc. A (199)Hg NMR study indicates that sequential removal of iodide from 5.I(2)Li(2) and 6.I(2)Li(2) with aliquots of AgOAc solution leads to formation of two intermediate host-guest complexes in solution, presumed to be 5(6)ILi and 5(2)(6)(2).ILi. Crystals grown from a solution of 6.I(2)Li(2) to which 1 equiv of AgOAc solution had been added proved to be an unusual stack structure with the formula 6(3).I(4)Li(4) [tetragonal, I4/m, a = 21.589(2) ?, c = 21.666(2) ?, V = 10098 ?(3), Z = 2, R = 0.058, R(w) = 0.084]. Addition of 2 equiv of NBu(4)Br ion to 5 or 6 gives 5.Br(2)(NBu(4))(2) and 6.Br(2)(NBu(4))(2), respectively, while addition of 1 equiv of KBr to 6 forms 6.BrK. 5.Br(2)(NBu(4))(2) crystallizes in the triclinic space group P&onemacr;, [a = 10.433(1) ?, b = 13.013(1) ?, c = 15.867(2) ?, alpha = 91.638(2) degrees, beta = 97.186(3) degrees, gamma = 114.202(2) degrees, V = 1492 ?(3), Z = 1, R = 0.078, R(w) = 0.104]. The hosts 5 and 6 form 1:1 supramolecular adducts with the polyhedral anions B(10)I(10)(2)(-) and B(12)I(12)(2)(-) in solution.  相似文献   

9.
Natarajan S 《Inorganic chemistry》2002,41(21):5530-5537
Hydro/solvothermal reactions of ZnO, HCl, H(3)PO(4), 1,4-diazacycleheptane (homopiperazine), and H(2)O under a variety of conditions yielded three new organic-inorganic hybrid materials, [C(5)N(2)H(14)][Zn(HPO(4))(2)].xH(2)O (x = approximately 0.46), I, [C(5)N(2)H(14)][Zn(3)(H(2)O)(PO(4))(2)(HPO(4))], II, and [C(5)N(2)H(14)][Zn(2)(HPO(4))(3)].H(2)O, III. While I has a one-dimensional structure, II possesses a two-dimensional layered structure, and III has a three-dimensional structure closely related to the ABW zeolitic architecture. All the compounds consist of vertex linking of ZnO(4), PO(4), and HPO(4) tetrahedral units. The fundamental building unit, single four-membered ring (S4R), is present in all the cases, and the observed differences in their structures result from variations in the connectivity between the S4R units. Thus I has a corner-shared S4R forming an infinite one-dimensional chain, II has two corner-shared chains fused through a 3-coordinated oxygen atom forming a strip and a layer with eight-membered apertures, and III has S4R units connected via oxygen atoms to give rise to channels bound by eight T atoms (T = Zn, P) in all crystallographic directions. Crystal data: I, monoclinic, space group = P2(1)/n (No. 14), a = 8.6053(3) A, b = 13.7129(5) A, c = 10.8184(4) A, beta = 97.946(1) degrees, V = 1264.35(8) A(3), Z = 4; II, monoclinic, space group = P2(1)/c (No. 14), a = 11.1029(1) A, b = 17.5531(4) A, c = 8.2651(2) A, beta = 97.922(2) degrees, V = 1595.42(5) A(3), Z = 4; III, monoclinic, space group = P2(1) (No. 4), a = 8.0310(2) A, b = 10.2475(3) A, c = 10.570(3) A, beta = 109.651(1) degrees, V = 819.24(3) A(3), Z = 2.  相似文献   

10.
<正> Both of the title complexes were produced by oxidative decarbony-lation of NH4 CMO (CO)5I]. The complexes CMo(S2CNC4H8)4]I3 ?C7H8(1) and Mo2S2O2 (S2CNC4H8)2(2) both crystallize in triclinic, space group P1 with cell dimensions for (1) : a=13. 554(4), b=13. 620(4), c= 13. 058 (4) A , α=95. 58 (3), β=105. 38(2), γ=115. 49(2)°,V = 2035(1) A3, Z=2, Dc=1. 89 g. cm-3, final R=0. 054 and Rw = 0. 062 for 2926 observed reflections; and for (2): a = 8.730(2), b=16.592(6), c = 6. 688(2)A, α=97. 67(3), β=98. 10(2), γ=80. 26(2)% V = 939. 2(5) A3, Z = 2, Dc = 2. 05 g. cm-3, final R = 0. 038 and Rw = 0. 046 for 2248 observed reflections. The Mo(V) atom is bonded to eight S atoms in distorted dodecahedron for (1). The Mo atoms in compound (2) are bridged by two S atoms and each Mo atom is coordinated by two S atoms from S2CNC4H8 and one O atom to form distorted tetragonal pyramid.  相似文献   

11.
Two new nickel(II) end-to-end azido-bridged compounds, cis-catena-[NiL(2)(&mgr;-N(3))](n)()(ClO(4))(n)().nH(2)O (1) and [Ni(2)L(4)(&mgr;-N(3))(2)](PF(6))(2) (2), were synthesized and characterized; L is 2-(aminoethyl)pyridine. The crystal structures of 1 and 2 were solved. Complex 1: monoclinic system, space group P2(1)/a, a = 8.637(2) ?, b = 18.9995(7) ?, c = 12.3093(7) ?, beta = 105.92(2) degrees, Z = 4. Complex 2: triclinic system, space group P&onemacr;, a = 9.139(7) ?, b = 10.124(3) ?, c = 12.024(2) ?, alpha = 70.407(14) degrees, beta = 84.19(2) degrees, gamma = 67.67(4) degrees, Z = 1. In the two complexes the nickel atom is situated in a similarly distorted octahedral environment. The two complexes are different; 1 is a one-dimensional helicoidal complex with the two L ligands and the two end-to-end azido bridges in a cis arrangement while complex 2 is a dinuclear system with two end-to-end azido bridges, indicating the extreme importance of the counteranion present (ClO(4)(-) for 1 and PF(6)(-) for 2). The magnetic properties of the two compounds were studied by susceptibility measurements vs temperature. The chi(M) vs T plot for 1 shows the shape for a weakly antiferromagnetically coupled nickel(II) one-dimensional complex without a maximum until 4 K. In contrast, for complex 2 the shape of the chi(M) vs T curve shows a maximum near 40 K, indicating medium antiferromagnetic coupling. From the spin Hamiltonian -J(ij)()S(i)()S(j)(), J values for 1 and 2 were less than -1 and -29.1 cm(-)(1), respectively. The magnetic behavior for 1 and 2 may be explained in terms of the overlap between magnetic orbitals, taking into account the torsion of the Ni(II) atoms and azido-bridging ligands in the two structures.  相似文献   

12.
3,6—二[二甲氨基]二苯并碘六圆氯化物的晶体呈淡黄色六棱柱状。该晶体所属的空间群是P2_1/n,晶胞参数为;a=11.073(2),b=13.766(1),c=11.229(11),β=99.36(5)°,Z=4。在CAD—4四圆衍射仪上用Mo-Kα射线收录了Ⅰ≥3σ(Ⅰ)的独立衍射数据2293个。晶体结构用重原子法解出,晶体结构参数经全矩阵最小二乘方法修正,偏离因子R=0.085。 结构测定结果表明,分子中二苯环不共面,其二面交角约为133°。值得指出的是,围绕对称心成心对称的一对分子呈二聚状态。二聚体中二碘原子、二氯原子及与碘原子毗邻的四个碳原子共处于一个平面。二聚体中I—C1间距有3.074和3.102两种,围绕碘原子的四个键角值为90°左右。在二聚体中碘原子以dsp~2。杂化轨道与周围的二氯原子、二碳原子键合。  相似文献   

13.
由贫硫化合物{Mo_3S_4[S_2P(OEt)_2]_4·H_2O}通过加硫获得了富硫化合物{Mo_3S_7[S_2P(OEt)_2]_3·I}(CH_8C_6H_5).化合物属三斜晶系,空间群PI,晶胞参数为a=10.350(1)A,b=13.931(4)A,c=16.369(3)A,α=103.69(2),β=86.62(1),γ=111.99(2)°,V=2183A~3;z=2,D_c=1.817g·cm~(-3).最终结构偏离因子R为0.042. 簇分子{Mo_3(μ_3-S)(μ-S_2)_3[S_2P(OEt)_2]3·I}属{Mo_3(μ3一Y)(μ-S_2)_3[S_2P(OEt)_2]_3·X}(Y=O,S;X=Cl,I)系列构型.{Mo_3}基本上是一个正三角形,Mo—Mo键长分别为2.721(1),2.724(1),2.725(1)A,Mo的配位多面体为七个硫原子组成的畸变五角双锥,有一个I原子联结着三个(S_2)~(2-)桥基的三个不与Mo共平面的S原子,I—S距离平均为3.169A,比相应的Van der Waals距离(~4.00A)明显地短,显示一定程度的成键作用,簇分子的这一构型是一种较为稳定的结构类型.  相似文献   

14.
We report a conventional ab initio and density functional theory study of the polarizability (alpha(alphabeta)/e(2)a(0) (2)E(h) (-1)) and hyperpolarizability (gamma(alphabetagammadelta)/e(4)a(0) (4)E(h) (-3)) of the sodium dimer. A large [18s14p9d2f1g] basis set is thought to yield near-Hartree-Fock values for both properties: alpha=272.28, Deltaalpha=127.22 and gamma=2157.6 x 10(3) at R(e)=3.078 87 A. Electron correlation has a remarkable effect on the Cartesian components of gamma(alphabetagammadelta). Our best value for the mean is gamma=1460.1 x 10(3). The (hyper)polarizability shows very strong bond-length dependence. The effect is drastically different for the longitudinal and transverse components of the hyperpolarizability. The following first derivatives were extracted from high-level coupled cluster calculations: (dalpha/dR)(e)=54.1, (dDeltaalpha/dR)(e)=88.1e(2)a(0)E(h) (-1), and (dgamma/dR)(e)=210 x 10(3)e(4)a(0) (3)E(h) (-3). We associate the (hyper)polarizability to bonding effects between the two sodium atoms by introducing the differential property per atom Q(diff)/2 identical with (Q[Na(2)(X (1)Sigma(g) (+))]/2-Q[Na((2)S)]). The differential (hyper)polarizability per atom is predicted to be strongly negative for the dimer at R(e), as [alpha(Na(2))/2-alpha(Na)]=-33.8 and [gamma(Na(2))/2-gamma(Na)]=-226.3 x 10(3). The properties calculated with the widely used B3LYP and B3PW91 density functional methods differ significantly. The B3PW91 results are in reasonable agreement with the conventional ab initio values. Last, we observe that low-level ab initio and density functional theory methods underestimate the dipole polarizability anisotropy. Experimental data on this important property are highly desirable.  相似文献   

15.
A new method for molecular structure quantitation is described, in which both electronic and topological attributes are united. The method uses the hydrogen-suppressed skeleton to represent the structure and leads to a graph invariant index for the individual atoms and hydride groups of the molecular skeleton. An intrinsic atom value is calculated for each atom asI = ( + 1)/, in which and are the counts of valence and sigma electrons of atoms in the molecular skeleton, that is, exclusive of bonds to hydrogen atoms. The electrotopological state valueS i for an atomi is defined asS i =I i + I i, where the influence of atom j on atom i, I i, is given as (I i-j j)/r 2;r is the graph separation between atoms i and j, counted as number of atoms, includingi andj. The information in the electrotopological state values is revealed by examples of various types of organic structures, including chain branching and heteroatom variation. The relation of the E-state value to NMR chemical shift is demonstrated for a series of carbonyl compounds.  相似文献   

16.
<正> [{(μ-PhCH2S)Fe2(CO)6}2(u4-S)], Mr = 837.95, triclinic, Pl,a=13.701(3),b=16.542(5), c=17.030(5)A,α=107.69(2),β=90.15(2),γ= 114.49(2)°,V=3309.3A3, Z=4, Dx=1.68 g/cm3,MoKa,λ=0.71069A μ=20.2 cm-1,F(000)=2008, room temperature, final R=0.035 for 4960 independent reflections. The molecule possesses approximate C2 symmetry with the pseudo-twofold axis passing through the unique sulfur atom u4-S(2) and the midpoint of the other two u2-sulfur atoms S(1) and S(3). The unique u4-sulfur atom has a tetrahedral geometry and donates its six valence electrons to the four iron atoms. The average Fe-(μ4-S) distance of 2.247 A is slightly shorter than the average Fe-(μ2-S) distance of 2.265A.  相似文献   

17.
合成了铋(III)苯乙酸-1,10-邻菲罗啉[Bi2(PPA)6·(Phen)2](HPPA=苯乙酸(C8H7O2),Phen=l,10-邻菲罗啉(C12H8N2))三元配合物,并通过元素分析和红外(IR)光谱对其进行了表征,用单晶X-射线衍射测定了配合物的晶体结构.配合物属于三斜晶系,P-1空间群,a=0.9100(6)nm,b=1.2617(8)nm,c=1.3324(9)nm,α=89.757(8)°,β=87.277(8)°,γ=81.155(8)°,V=1.5099(17)nm3,Dc=1.748g·cm-3,μ=5.890mm-1,Z=1,F(000)=780,残差因子R1=0.0484,wR2=0.1090[I>2σ(I)],S=1.002.标题化合物为双核铋(III)配合物,金属中心Bi(III)原子与三个苯乙酸根(PPA)中的6个氧原子、一个1,10-邻菲罗啉分子中的两个氮原子和一个桥连氧原子进行配位,形成九配位的扭曲三帽三方柱配位十四面体,围绕铋原子的价键总数VBi(1)=2.897,两个Bi(III)原子通过两个桥连氧原子连结成中心对称的分子,Bi…Bi间距离为0.4469(2)nm.初步抑菌试验结果显示,配合物对大肠杆菌(E.Coli)、金黄色葡萄球菌(S.Aureus)、枯草芽孢杆菌(B.Subtilis)表现出相似且良好的抑菌效果.  相似文献   

18.
The set of coset representations, CR's, of a group G, [G(/G1), G(/G2), ..., G(/Gs)], where G1 = [I], Gs = G, the marks, m(ij) of subgroup Gj on a given G(/Gi), 1 < or = i < or = s, and the subduction of G(/Gi) by Gj, j < or = i, G(/Gi) precipitates to Gj, are essential tools for the enumeration of stereoisomers and their classification according to their subgroup symmetry (Fujita, S. Symmetry and Combinatorial Enumeration in Chemistry; Springer-Verlag: Berlin, 1991). In this paper, each G(/Gi) is modeled by a set of colored equivalent configurations (called homomers), H = h1, h2, ..., hr, r = G/Gi, such that a given homomer, h(k), remains invariant only under all g epsilon Gi, where g is an element of symmetry. The resulting homomers generate the corresponding set of marks almost by inspection. The symmetry relations among a set H can be conveniently stored in a Cayley-like diagram (Chartrand, G. Graphs as Mathematical Models; Prindle, Weber and Schmidt Incorporated: Boston, MA, 1977; Chapter 10), which is a complete digraph on r vertices so that an arc from vertex v(i) to vertex v(j) is colored with the set Sij of symmetry elements such that h(i)[g(if)]-->h(j),g(ij) epsilon Sij. In addition, each vertex, v(i), is associated with a loop that is colored with a set Sii so that g(ii) epsilon Sii stabilizes h(i). A Cayley-like diagram of a given CR, G[G(/Gi)], leads to graphical generation of G(/Gi) precipitates to Gj for all values of j and also to all m(ij)'s. Several group-theoretical results are rederived and/or became more envisagable through this modeling. The approach is examplified using C2, C3, D2, T, and D3 point groups and is applied to trishomocubane, a molecule that belongs to the D3 point group.  相似文献   

19.
The compounds Y[N(QPPh2)2]3 (Q = S (1), Se (2)) have been synthesized in good yield from the protonolysis reactions between Y[N(SiMe3)2]3 and HN(QPPh2)2 in methylene chloride (CH2Cl2). The compounds are not isostructural. In 1, the Y atom is surrounded by three similar [N(SPPh2)2]- ligands bound eta 3 through two S atoms and an N atom. The molecule possesses D3 symmetry, as determined in the solid state by X-ray crystallography and in solution by 89Y and 31P NMR spectroscopies. In 2, the Y atom is surrounded again by three [N(SePPh2)2]- ligands, but two are bound eta 2 through the two Se atoms and the other ligand is bound eta 3 through the two Se atoms and an N atom. Although a fluxional process is detected in the 31P and 77Se NMR spectra, a triplet is found in the 89Y NMR spectrum of 2 (delta = 436 ppm relative to YCl3 in D2O, 2JY-P = 5 Hz). This implies that on average the conformation of one eta 3- and two eta 2-bound ligands is retained in solution. Crystallographic data for 1: C72H60N3P6S6Y, rhombohedral, R3c, a = 14.927(5) A, c = 56.047(13) A, V = 10815(6) A3, T = 153 K, Z = 6, and R1(F) = 0.042 for the 1451 reflections with I > 2 sigma(I). Crystallographic data for 2: C72H60N3P6Se6Y.Ch2-Cl2, monoclinic, P2(1)n, a = 13.3511(17) A, b = 38.539(7) A, c = 14.108(2) A, beta = 94.085(13) degrees, V = 7241(2) A 3, T = 153 K, Z = 4, and R1(F) = 0.037 for the 8868 reflections with I > 2 sigma(I).  相似文献   

20.
We have developed the finite size scaling method to treat the criticality of Shannon-information entropy for any given quantum Hamiltonian. This approach gives very accurate results for the critical parameters by using a systematic expansion in a finite basis set. To illustrate this approach we present a study to estimate the critical exponents of the Shannon-information entropy S approximately (lambda-lambda(c))(alpha(S) ), the electronic energy E approximately (lambda-lambda(c))(alpha(E) ), and the correlation length xi approximately mid R:lambda-lambda(c)mid R:(-nu) for atoms with the variable lambda=1/Z, which is the inverse of the nuclear charge Z. This was realized by approximating the multielectron atomic Hamiltonian with a one-electron model Hamiltonian. This model is very accurate for describing the electronic structure of the atoms near their critical points. For several atoms in their ground electronic states, we have found that the critical exponents (alpha(E),nu,alpha(S)) for He (Z=2), C (Z=6), N (Z=7), F (Z=9), and Ne (Z=10), respectively, are (1, 0, 0). At the critical points lambda(c)=1/Z(c), the bound state energies become absorbed or degenerate with continuum states and the entropies reach their maximum values, indicating a maximal delocalization of the electronic wave function.  相似文献   

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