Photoinduced electron transfer reaction tuned by donor-acceptor pairs via the rigid, linear spacer heptacyclo[6.6.0.0.0.0.0.0]tetradecane

A new class of donor-{saturated hydrocarbon bridge}-acceptor (D-B-A) dyads were synthesized and utilized on a systematic approach to evaluate the corresponding photoinduced electron transfer (ET) process. Among these dyads heptacyclo[6.6.0.0^2,6.0^3,13.0^4,11. 0^5,9.0^10,14]tetradecane (HCTD) was used as a unique spacer, which possesses a geometry of high symmetry (D_2d), rigidity and linearity. The spectroscopy and dynamics of excited-state ET as functions of donor/acceptor electronic states, orientation as well as solvent properties were analyzed with the aid of theoretical computations. It was observed that the quenching of donor fluorescence (the F₁ band) correlated with the appearance of a broad charge-transfer (CT) emission. Both wavelength and intensity of the CT band varied with solvent-polarity, whereas its rise dynamics complied well with the decay of the F₁ band. In acetonitrile, the CT state decays much faster than the rate of ET (∼63 ps⁻¹) so that the corresponding steady-state emission cannot be resolved. An intriguing effect was observed in the case of benzene-1,2-dithioketals (3a and 3b) where the D and A π-chromophores were aligned in different orientations. The estimated ET rate of 3a (3.9×10¹⁰ s⁻¹) was substantially faster than that of 3b (7×10⁸ s⁻¹). The experimental data were tentatively fitted by a semi-log plot of ET rate constants (k_et) against free energy (ΔG⁰), yielding a value of ∼17.3 cm⁻¹ for the electron-coupling matrix (H_el).     

Thermotropic copolyesters having ordered comonomer sequences and flexible spacers

A series of new copolyesters having ordered comonomer sequences were synthesized via multistep routes and their properties such as glass transition (T_g) and melting temperatures (T_m), crystallization tendency, and mesomorphic properties were compared with those of the corresponding random copolyesters. All of the present copolyesters contain 1,8-octamethylene or 1,10-decamethylene spacers and hydroquinone (HQ) and terephthalic acid (TPA) moieties. In general, both melting and clearing temperatures of the ordered sequence copolyesters were much higher than those of the random counterparts. Crystallization tendency, however, was comparable. All of the present copolyesters are thermotropic and form nematic phase in melts. © 1993 John Wiley & Sons, Inc.     

Effect of the poly(oxytetramethylene)diol spacer length on some properties of liquid crystalline polyurethanes

Previous studies on liquid crystalline polyurethanes prepared from 4,4′-bis(2-hydroxyethoxy)biphenyl (BHBP) and 2,4-tolylene diisocyanate (TDI) were continued. In this article, a series of polyurethanes, which differ in the flexible spacer length and BHBP content is described. Poly(oxytetramethylene)diols of different molecular weights (PTMO, M _n = 250, 650, 1000, 2000) were used as flexible spacers. The polyurethanes were investigated by DSC, polarizing microscopy, x-ray diffractometry, and IR spectroscopy. The molecular weight distribution was determined by GPC. The morphology of the polyurethanes was investigated by the SALS method. Partial replacement of BHBP by 25–75 mol % PTMO and the flexible spacer length influence the liquid crystalline properties, the phase transition temperatures, and the range of mesophase occurrence. © 1993 John Wiley & Sons, Inc.     

Surface chemistry of selected supported metallocene catalysts studied by DR‐FTIR,CPMAS NMR,and XPS techniques

Two supported metallocene catalysts (CS 1: PQ 3030/MAO/Cp₂ZrCl₂ and CS 2: PQ 3030‐BuGeCl₃/MAO/Cp₂ ZrCl₂) were prepared by sequentially loading MAO and Cp₂ZrCl₂ on partially dehydroxylated silica PQ 3030. In catalyst CS 2, ⁿBuGeCl₃ was used to functionalize the silica. These catalysts were characterized by DR‐FTIR spectroscopy, CPMAS NMR spectroscopy, and XPS. Their catalytic performance was evaluated by polymerizing ethylene using the MAO cocatalyst and characterizing the resulting polymers by GPC. Both catalysts produced two metallocenium cations (Cation 1: [Cp₂ZrCl]⁺ and Cation 2: [Cp₂ZrMe]⁺) with comparable equilibrium concentrations and showed varying solid‐state electronic environments. The modified supports (PQ 3030/MAO and PQ 3030‐BuGeCl₃/MAO) acted as weakly coordinating polyanions and stabilized the above cations. BuGeCl₃ did not affect the solid‐state electronic environment. However, it increased the surface cocatalyst to catalyst molar ratio (Al:Zr), acted as a spacer, increased catalyst activity, and enhanced chain‐transfer reactions. The separately fed MAO cocatalyst shifted the equilibrium between Cation 1 and Cation 2 toward the right. Consequently, more Cation 2 was generated, which acted as the effective and active single‐site catalytic species producing monomodal PDI. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis and polymerization of 1-(2,4,6-tricyanophenylthio)-3-[3,5-bis(n,n-dimethylamino)phenoxy]-2-propyl methacrylate; polymer effect on intramolecular charge–transfer interaction

1-[3,5-Bis(N,N-dimethylamino)phenoxy]-ω-(2,4,6-tricyanophenylthio)alkanes ( 1a–c ), where an electron-accepting 2,4,6-tricyanophenylthio group and an electron-donating 3,5-bis(N,N-dimethylamino)phenoxy one are linked with a spacer such as ethylene, trimethylene, and tetramethylene, were prepared in order to examine an effect of the spacer chain length on intramolecular charge–transfer interaction between the 2,4,6-tricyanophenylthio and 3,5-bis(N,N-dimethylamino)phenoxy groups. From the UV-vis spectra measurements of 1a–c , 1-[3,5-bis(N,N-dimethylamino)phenoxy]-3-(2,4,6-tricyanophenylthio)Propane ( 1b ) carrying the trimethylene chain as a spacer was found to have the strongest intramolecular charge–transfer interaction. A new methacrylate-type monomer carrying the 1b unit as a side chain, 1-(2,4,6-tricyanophenylthio)-3-[3,5-bis(N,N-dimethylamino)phenoxy]-2-propyl methacrylate ( 2 ), was prepared successfully in 9.2% total yield in seven steps. The monomer 2 homopolymerized in benzene, tetrahydrofuran, acetone, and dimethyl sulfoxide in the presence of 2,2′-azobis(isobutyronitrile) at 60°C to give polymers [poly( 2 )] with molecular weights of 6,000 to 98,000. An intramolecular charge–transfer interaction in the poly( 2 ) was found to be larger than that in the monomer 2 and to increase with an increase in the degree of polymerization of the poly( 2 ), suggesting that there is an existence of polymer effect other than the polymer effect due to the high local concentration of the donor-acceptor pair. © 1995 John Wiley & Sons, Inc.     

稻属核糖体DNA的限制性片段长度多态性

对稻属13个种和Porteresiacoaretata、Leersiaperrieri及Leersiatisseranti共42份材料进行了核糖体RNA基因（rDNA）的间隔序列长度多态性（RFLP）的分析．共发现20种的间隔序列长度变异类型,其中有些类型具有种的特异性．中国药用野生稻的rDNA变异程度很小,疣粒野生稻的rDNA有变异．Leersiaperrieri和Leersiatisseranti的BamHI酶切转录区片段长度为3．90kb,与稻属的3．80kb．不同．     

Small-angle neutron-scattering study of bis(quaternaryammonium bromide) surfactant micelles in water. Effect of the long spacer chain on micellar structure

The microstructure of the normal micelles formed by dimeric surfactants with long spacers, [Br⁻(CH₃)₂N⁺(C _m H_{2 m +1})-(CH₂) _S  -(C _m H_{2 m +1})N⁺(CH₃)₂Br⁻, m = 10 and s = 8, 10 and 12], has been investigated by small-angle neutron scattering and compared with previously reported results for micelles of the same dimeric surfactants with shorter spacers (m = 10 and s = 2, 3, 4 and 6). It was found that for dimeric surfactants with long spacers (s = 8 and 10), both micellar growth and variation in shape occur to only a small extent, if at all, compared with dimeric surfactants with short spacers. However, for the dimeric surfactant with the longest spacer, s = 12, the extent of micellar growth and shape variation is also large. These results are due to the differences in conformation of dimeric surfactants with short spacers (s = 2–6) compared with that of the surfactants with long spacers (s = 8–12). Received: 15 June 1998 Accepted: 22 July 1998     

象山港黄墩支港菲律宾蛤仔种群COI和ITS1基因序列特征及遗传多样性分析

为了解象山港黄墩支港菲律宾蛤仔种质资源的遗传多样性现状, 采用COI和ITS1分子标记对该种群进行了基因序列特征和遗传多样性分析. 结果表明 在该种群30个个体中扩增得到的COI基因序列长度均为709bp, ITS1序列长度范围在693~729bp(共有746个位点). COI基因序列的位点中有670个保守位点(占94.50%)、39个变异位点(占5.50%); ITS1序列的位点中有保守位点671个(占89.95%)、变异位点62个(占8.31%)和缺失/插入位点13个(占1.74%). COI基因序列的保守性高于ITS1序列. 在COI基因序列中碱基(A+T)的占比(65.84%)高于(C+G), 而ITS1序列中则是碱基(A+T)占比(37.59%)低于(C+G). COI和ITS1序列的遗传距离分析均显示群体内遗传分化不明显. 基于COI基因序列和ITS1序列构建的遗传进化树显示 各科贝类分别相聚, 象山港菲律宾蛤仔位于帘蛤科的分支中, 其COI序列与杂色蛤进化关系最近. 遗传进化树中各种贝类的聚类关系与传统分类学结果相一致, 可作为分类的参考. COI和ITS1序列的平均核苷酸差异数分别为5.497和6.549, 核苷酸多样性指数分别为0.00775和0.00973, 单倍型数目分别为21和28, 单倍型多样性分别为0.963和0.993, 根据COI和ITS1两个序列计算得到的菲律宾蛤仔象山港群体单倍型多样性均大于0.5, 核苷酸多样性指数均大于0.005, 表明该种群遗传多样性丰富, 并处于稳定状态. 本研究结果补充了菲律宾蛤仔遗传多样性方面的研究资料, 并可为象山港菲律宾蛤仔种质资源保护和遗传育种提供理论基础.     

Synthesis and characterization of novel ferroelectric liquid crystal polysiloxane containing undecanoyloxy spacer (I)

A novel side-chain liquid crystal polysiloxane and its corresponding monomer were synthesized by the standard method. We ensured their structures were as expected and their purities were high by ¹H nuclear magnetic resonance and infrared measurements. They were studied by differential scanning calorimetry (DSC) for their thermal analysis and polarizing optical microscopy (POM) with hot stage for their textures and transition temperatures. The results showed good liquid crystal properties and low transition temperatures of the mesophase. X-ray diffractions were done to research their layer structure and SmA and SmC^* phases were assured, in good agreement with the results of the POM and DSC measurements. The optical rotation degree was also measured.     

Synthesis of polymer-supported phosphonium salts and their use as phase transfer catalysts

Spacer-modified polymer supports have been synthesized through the polymeric Grignard reagent method. Phosphonium-active sites were then introduced into these supports and the polymer-supported phosphonium salts were used as phase transfer catalysts for the nucleophilic substitution reactions. Influences of organic solvent, properties of the spacer and temperature on the catalytic activity have been investigated. Based on the experimental results, it was assumed that there might exist a dissolubility equilibrium of the catalytic site between the organic phase and the aqueous phase. With this idea, the results have been reasonably elucidated.