A_a_1,A_a_2-B_b_1B_b_2缩聚反应的固化理论

本文讨论了A_(a_1),A_(a_2)-B_(b_1)B_(b_2)型缩聚反应的固化理论。给出了溶胶-凝胶分配公式、凝胶化条件、分布函数及适合固化全过程的高分子矩的循环公式和k次矩的解析表示式。     

钛基导电氧化物电极上氧的阳极析出动力学与机理研究

本文通过在碱溶液中Ti/RuO_2+TiO_2(A)和Ti/SnO_2+CuCo_2O_4(B)电极上氧阳极析出动力学的对比研究, 表明这两类电极上氧的极化曲线均有两Tafel区。低极化区的Tafel斜率为0.039V(简称b_1区); 高极化区为0.120V(简称b_2区)。在A电极上b_1区i～a_W·a_(OH~-); b_2区i～a_W(浓碱溶液)或i～a_(OH)~(0.1～0.5)(稀碱溶液),在B电极上b_1区i～a_(OH~-); b_2区i～a_(OH~-)~(0.39)(浓碱溶液);或i～a_(OH~-)(稀碱溶液), 实验结果表明, 虽然这两类电极上氧阳极析出过程都由第二电子转移步骤控制, 但其机理不同, 前者是由水分子参加, 控制步骤为RuO_2·OH_(ads)+H_2O ~(rds)→ RuO(OH)~+_3+e后者则为 (SOH)~(n+)_(ads) ~(rds)→ (SOH)~((n+1)+)_(ads)+e它们与PbO_2、Pt和低碳钢上机理有些不同~[1,2]。     

A_(a_1)B_(b_1)—A_(a_2)B_(b_2)缩聚反应的分布函数和高分子矩

本文用概率统计方法,得到了A_(a1)B_(b1)—A_(a2)B_(b2)缩聚反应的分布函数。应用分布函数定义了高分子各类矩。用直接微商法,得到了计算矩的循环公式。解决了用矩表征这类反应的问题。本文也得到了凝胶化条件。     

液相色谱中保留值变化规律——某些PTH-氨基酸最佳冲洗剂配比的选择

本文根据基本方程Ink′=b_0 b_1cB b_2IncB以及色谱柱的总分高效能指标K_1,计算出多元组份分离时所需的最小相对保留值a_(min)和最难分离物质对的相对保留值a′.由a′必须大于′a_(min)以及最后流出组份k′_(lasl)最小的最佳冲洗剂组成选择原则,建立起以最少的实验数据快速进行最佳冲洗剂组成选择的方法.文中给出了以甲醇、乙醚、已烷作三元冲洗剂,以5对氨基酸作样品,进行最佳冲洗剂组成选择的例子,色谱图表明:理论预测与实验结果吻合。     

Pu（^7Fg）＋H2（X^1∑g^＋,0,0）的分子反应动力学

基于PuH_2分子基态(X~7A_1)的分析势能函数，用准经典的Monte-Carlo轨线法 对Pu(~7Fg)+H_2(X~1∑_g~+，0，0)的分子反应动力学过程进行了计算。结果表明 ：Pu(~7F_g)与H_2(X~1∑_g~+，0，0)碰撞是弹性碰撞。     

药物离子选择性电极响应规律的系统研究——Ⅲ.红霉素电极及其对季铵的选择性规律

本文研究了多种红霉素电极。电极对于季铵的选择性可用诱导效应和空间位阻效应来定量说明,符合方程式logK_(ij)=a_1I-a_2Z/R+a_0,式中I为诱导效应指数,a_1,a_2,a_0为与电活性物有关的系数。建立了阳离子型药物电极K_(ij)对季铵烷基链碳原子数n的关系的一般数学模型:logK_(ij)=A/2.7~n+B/(0.80+1.26n)+C。证明:随着碳原子数增大,logK_(ij)趋于一极限值C。此处A,B,C为与电活性物有关的系数。     

经验基体校正方程系数选择的理论判据及其在赤泥分析中的应用

由于电子计算机在 X 射线荧光分析中的应用,用数学公式来校正元素的基体效应已越来越广泛,其中基本参数法由于一些物理参数尚不确定,且需要复杂的计算,一般计算机不能胜任;α系数法也需要大量的数据处理,一般实验室使用有一定困难。下面两个数学公式:c_i=sum from r=0 to 2 a_(ir)I_i~r+I_i ∑m _(ij)I_j+∑b_(ij)I_j (1)c_i=sum from r=0 to 2 a_(ir)I_i~r(1+∑f_(ij)c_j)+∑b_(ij)C_j (2)只要有一套合适的标准,用小型计算机多重回归法求     

改进单纯形优化技术在曲线拟合中的应用

本文对改良单纯形的扩张因子和缩小因子进行优选,同时将单纯形的整体收缩改为变换形心轴的方向,其收敛速度有明显的提高。笔者用此法拟合直线〔A=a_0+a_1μA〕和非线性曲线〔A=A_∞(1-e~-kt)〕,取得满意的结果。     

CH与H2分子反应动力学及选态反应的理论研究

次甲基作为化学反应源曾引起广泛的兴趣.Schaefer 及其合作者于1977年对反应CH(~4Σ~-)+H_2→CH_2(~3B_1)+H 进行过量子化学研究,但是计算中限制了一些自由度.近年来,由于能量梯度方法的发展,反应途径哈密顿理论和变分过渡态理论的提出,有可能进一步对该反应进行分子反应动力学性质的研究.本文用从头算UHF/6-31G 方法和能量梯度方法首先优化出上述反应(原子编号为CH_a+H_bH_c→H_bCH_a+H_c)的过渡态;再用     

Two new epimeric pairs of iridoid from mangrove plant Scyphiphora hydrophyllacea

Two new epimeric pairs of iridoid scyphiphin A_1(1a),A_2(1b) and scyphiphin B_1(2a),B_2(2b) were isolated from Scyphiphora hydrophyllacea Gaertn.F.Their structures were elucidated by spectroscopic methods.The mixture of scyphiphin B_1 and scyphiphin B_2 showed moderate cytotoxicity against human hepatoma SMMC-7721 cell line in vitro by MTT method.     

凝胶化理论的新概念——一种新的划环方法

本文用分子作为划环单位,与Flory等用官能团作为划环单位不同,得到∑A_(ai)与∑_(bj)型分子间反应凝胶生成的临界条件,用数均官能度或分子的数量分数,不用重均官能度或官能团的数量分数表示,更与Flory的实验结果一致.从理论分析,化学反应是分子反应,用分子比用官能团作为划环单位更合理.     

Synthesis of Bicyclic Imidazoles via [2 + 3] Cycloaddition between Nitriles and Regioselectively Generated α-Imino Gold Carbene Intermediates

The cyclic α-imino gold carbene intermediate B is most likely generated in situ via regioselective nitrene transfer from an azido group to a tethered terminal alkyne in the presence of a gold catalyst and at ambient temperature. This highly electrophilic intermediate can react with a weakly nucleophilic nitrile, which is used as the reaction solvent, to deliver a bicyclic imidazole rapidly in an overall bimolecular [2 + 2 + 1] cycloaddition and in mostly serviceable yield. The competing intramolecular Huisgen reaction, although likely also catalyzed by gold, is minimized by using AuCl(3) as the catalyst.     

H+H2(v=0,1)→H2(v′)+H反应截面的电子非绝热三维量子散射近似计算

本文把电子非绝热一维量子散射反应几率和三维量子散射反应截面的近似公式结合起来, 对于反应物分子(H_2)不同的量子振动态(v=0, 1) 分别计算了H+H_2(v=0)→H_2(v′=0, 1)+H和H+H_2(v=1)→H_2(v′=0, 1)+H的平均反应截面σ_0和σ_1, 并同文献上用电子绝热理论计算的结果作了比较, 表明对这类中性原予-分子反应碰撞的过程, 特别是当反应物分子处于振动激发态时, 电子非绝热效应是存在的。     

8-Phosphabicyclo[3.2.1]octanes—III4: The reaction between oxyallyl cations and phosphole derivatives

The reaction of oxyallyl cations with phosphole sulfide as well as phosphole oxides was investigated and was found to give the expected 8-phosphabicyclo[3.2.1]octanic system (2, 4 and 7) apart from other unexpected products (3 and 5). In the case of the phosphole sulfide (1), the oxyallyl cation is believed to react preferentially with the P=S group, rather than the dienic moiety, leading to a P=S to P=O transformation or to a very particular reaction resulting in 5. This occurs through an intermediate (j) in which a C=S group reacts in a [2 + 4] cycloaddition with the phosphole as a diene. The structure and stereochemistry of the various products were established by the aid of their spectral data in conjunction with spectral data of some related compounds. A formal PhPO elimination is believed to occur through an intermediate phosphinate resulting from Bayer-Villiger like oxidation, which then loses the [PhPO₂] group.Phosphole sulfide (1), previously found to react as a dienophile, was shown to enter a [2 + 4] cycloaddition as a diene with powerful dienophiles like 4-methyl-1,2,4-triazoline-3,5-dione (10).     

Density functional theory investigation of the remarkable reactivity of geminal dizinc carbenoids (RZn)(2)CHI (R = Et or I) as cyclopropanation reagents with olefins compared to mono zinc carbenoids RZnCHI(2), EtCHIZnR (R = Et or I)

Density functional theory calculations for the cyclopropanation reactions of several mono zinc carbenoids and their corresponding gem-dizinc carbenoids with ethylene are reported. The mono zinc carbenoids react with ethylene via an asynchronous attack on one CH2 group of ethylene with a relatively high barrier to reaction in the 20-25 kcal/mol range similar to other Simmons-Smith type carbenoids previously studied. In contrast, the gem-dizinc carbenoids react with ethylene via a synchronous attack on both CH2 groups of ethylene and substantially lower barriers to reaction (about 15 kcal/mol) compared to their corresponding mono zinc carbenoid. Both mono zinc and gem-dizinc carbenoid reactions can be accelerated by the addition of ZnI2 groups as a Lewis acid, and this lowers the barrier by another 1.0-5.1 kcal/mol and 0.0-5.5 kcal/mol, respectively, for addition of one ZnI2 group. Our results indicate that gem-dizinc carbenoids react with C=C bonds with significantly lower barriers to reaction and in a noticeably different manner than Simmons-Smith type mono zinc carbenoids. The three gem-dizinc carbenoids have a substantially larger positive charge distribution than those in the mono zinc carbenoids and, hence, a stronger electrophilic character for the gem-dizinc carbenoids.     

Acylmethyl(aryl)tellurium(IV,II) derivatives: intramolecular secondary bonding and steric rigidity

Electrophilic substitution of acylmethanes (methyl ketones), RCOCH3 (R = i-Pr, 1; Et, 2; Me, 3) with aryltellurium trichlorides, ArTeCl3 (Ar = 1-C10H7, Np, A; 2,4,6-Me3C6H2, Mes, B; 4-MeOC6H4, Anisyl, C) under mild conditions affords the corresponding acylmethyl(aryl)tellurium dichlorides (RCOCH2)ArTeCl2. Reduction of the dichlorides, gives tellurides, (i-PrCOCH2)ArTe, 1A-1C, which give the corresponding dihalides, (i-PrCOCH2)ArTeX2 (X = Cl, 1Aa-1Ca; Br, 1Ab-1Cb; I, 1Ac-1Cc) when reacted in situ with SO2Cl2, Br2 or I2. The unsymmetric tellurides are labile towards disproportionation and attempts to obtain them lead to the isolation of Ar2Te2 except in the case of (i-PrCOCH2)MesTe (1B), which represents an interesting example of a kinetically stable aryl(alkyl)telluride. All the dihalomesityltellurium(IV) derivatives show separate 1H and 13C NMR signals for the ortho methyls irrespective of the sizes of R and X ligands. The telluride, 1B with free rotation about Te-C(mesityl) bond shows, like the unsymmetric diorganotellurium(IV) dihalides, only one 125Te NMR signal. The 1,4-chelating behavior of the acyl ligand among diorganotellurium(IV) compounds is inferred from the X-ray diffraction data for 1Aa, 1Ac, 1Ba, 1Bb, 1cA and 1Cc which are indicative of the presence of intramolecular Te...O secondary bonding interactions (SBIs) at least in the solid state. As a consequence, steric repulsion in case of the mesityltellurium(IV) derivatives, 1Ba and 1Bb, reaches the threshold so as to cause loss of two-fold rotational symmetry of the mesityl group about the Te-C(mesityl) bond axis. Intermolecular C-HO...O H-bonding interactions appears to stabilize such an orientation of the aryl ligand at least in the solid state.     

Ab initio potential energy surface, variational transition state theory, and quasiclassical trajectory studies of the F+CH4-->HF+CH3 reaction

In this work we present a study of the F+CH(4)-->HF+CH(3) reaction (DeltaHdegrees(298 K)=-32.0 kcal mol(-1)) using different methods of the chemical reaction theory. The ground potential energy surface (PES) is characterized using several ab initio methods. Full-dimensional rate constants have been calculated employing the variational transition state theory and using directly ab initio data. A triatomic analytical representation of the ground PES was derived from ab initio points calculated at the second- and fourth-order M?ller-Plesset levels with the 6-311+G(2df,2pd) basis set, assuming the CH(3) fragment to be a 15 a.m.u. pseudoatom in the fitting process. This is suggested from experiments that indicate that the methyl group is uncoupled to the reaction coordinate. A dynamics study by means of the quasiclassical trajectory (QCT) method and employing this analytical surface was also carried out. The experimental data available on the HF internal states distributions are reproduced by the QCT results. Very recent experimental information about the reaction stereodynamics is also borne out by our QCT calculations. Comparisons with the benchmark F+H(2) and analogous Cl+CH(4) reactions are established throughout.     

Synergism of the Bacillus thuringiensis Cry1, Cry2, and Vip3 Proteins in Spodoptera frugiperda Control

The polyphagous caterpillar, Spodoptera frugiperda, has been controlled with either chemical insecticides or transgenic plants such as Bt maize that expresses the cry and/or vip genes of the Bacillus thuringiensis (Bt) bacterium. Despite the efficiency of Bt toxins in lepidopteran control, populations resistant to Bt plants have emerged in different locations around the world. Thus, understanding how combined proteins interact against pests can assist resistance control and management. This work demonstrated the toxicity of Cry1Ab, Cry1Ac, Cry1Ca, Cry1Ea, Cry2Aa, Cry2Ab, Vip3Aa, and Vip3Ca in single and combined assays against S. frugiperda neonatal larvae. All protein mixtures had synergistic action in the control of the larvae. The Vip3Aa + Cry1Ab mixture had the highest toxicity, sequentially followed by Vip3Aa + Cry2Ab, Cry1Ab + Cry2Ab + Vip3Aa, Cry1Ea + Cry1Ca, Cry1Ab + Cry2Ab, Vip3Ca + Cry1Ea, and Vip3Ca + Cry1Ca. Cry1Ab, Cry1Ac, Cry2Ab, and Vip3Aa bound to more than one site on the brush border membrane vesicles (BBMV) of S. frugiperda. The Cry1Ab and Cry1Ac proteins share binding site, while Cry1Ab does not share binding site with the Cry2Aa and Cry2Ab proteins. The Vip3Aa protein does not share receptors with the tested Cry1 and Cry2. The results suggest that combination these tested proteins may increase toxicity against S. frugiperda neonates.

     

Reactions of cationic iron clusters with ammonia, models of nitrogen hydrogenation and dehydrogenation

The gas phase reactivities of small cationic iron clusters, Fen+ (n = 1-20), towards ammonia were investigated using Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Sequential addition of ammonia molecules to the clusters was observed to be the dominating process for n > 4. In the case of n = 4 we observed addition of ammonia accompanied by dehydrogenation. This reaction was modelled using hybrid density functional theory. Clusters with n < 4 do not react with ammonia. Clusters Fen+ (n = 1-20) react with neither N2 nor H2 at around 10(-8) mbar. When dinitrogen was seeded into the expanding helium, mixed clusters of the type FenNm+ were observed. These ions react with H2, either by addition, or by substitution of N2. The clusters with m = 1 were isolated in separate experiments and reacted with H2, which showed that mixed clusters with n = 5-13 add up to 5 molecules of dihydrogen in successive slow reactions.