东北大平原商品粮基地的农业资源开发对策

东北大平原商品粮基地的农业资源开发对策武志杰（中国科学院沈阳应用生态研究所，沈阳１１００１５）晁岳侠，曾丽娟，王萍（黑龙江省八五三农场）东北大平原覆盖黑龙江、吉林、辽宁（不含朝阳区）和内蒙古呼盟，主要由三江平原、松嫩平原、辽中平原等七个类型区组成。土...

Regioselective Bis-Selenation of Allenes Catalyzed by Palladium Complexes: A Theoretical Study

The reaction mechanism of Pd(O)-catalyzed allene bis-selenation reactions is investigated by using density functional methods. The overall reaction mechanism has been examined. It is found that with the bulkier PMe3 ligand, the rate-determining step is the reductive elimination process, while allene insertion and reductive elimination processes are competitive for the rate-determining step with the PH3 ligand, indicating the importance of the ligand effect. For both cis and trans palladium complexes, allene insertion into the Pd-Se bond of the trans palladium complex using the internal carbon atom attached to the selenyl group is prefer-red among the four pathways of allene insertion processes. The formation of sigma-allyl and pi-allyl palladium complexes is favored over that of the sigma-vinyl palladium species. By using methylallene, the regioselectivity of monosubstituted allene insertion into the Pd-Se bond is analyzed.

A Fully Diarylmethylene-Bridged Triphenylamine Derivative as Novel Host for Highly Efficient Green Phosphorescent OLEDs

A fully diarylmethylene-bridged triphenylamine derivative is efficiently synthesized. It has an almost planar triphenylamine (TPA) skeleton and exhibits excellent thermal and morphological stability. Devices with the novel TPA derivative as host material and Ir(ppy)(3) as triplet emitter show a maximum current efficiency of 83.5 cd/A and a maximum power efficiency of 71.4 Im/W for green electrophosphorescence.

Electron effect of p-substituent on iron(II) and cobalt(II) pyridinebisimine catalyst for ethylene polymerization

A series of 2,6-bis(imino)pyridyl iron and cobalt complexes bearing p-substituent [2,6-(ArN=CMe)(2)C5H3N]-MCl2 (Ar=2,6-Me2C6H3, 2,4,6-Me3C6H2, 2,6-Me-2-4-BrC6H2, 2,6-Me-2-4-ClC6H2, 2,4-Me-2-6-BrC6H2, 2,4-Me-(2)-6-ClC6H2, while M=Fe, Co) have been synthesized and investigated as catalysts for ethylene polymerization in the presence of modified methylaluminoxane as a cocatalyst. The electron effect and positions of the substitueni of pyridinebisimine ligands were observed to affect considerably catalyst activity and polymer property.

Crystallization behavior of a novel poly(aryl ether ketone): PEDEKmK

Isothermal melt and cold crystallization kinetics of PEDEKmK linked by meta-phenyl and biphenyl were investigated by differential scanning calorimetry in two temperature regions. Avrami analysis is used to describe the primary stages of the melt and cold crystallization, with exponent n = 2 and n = 4, respectively. The activation energies are -118 kJ/mol and 510 kJ/mol for crystallization from the melt and the glassy states, respectively. The equilibrium melting point T-m(0) is estimated to be 309 degrees C by using the Hoffman-Weeks approach, which compares favorably with determination from the Thomson-Gibbs method. The lateral and end surface free energies derived from the Lauritzen-Hoffman spherulitic growth rate equation are sigma = 8.45 erg/cm(2) and sigma(e) = 45.17 erg/cm(2), respectively. The work of chain folding q is determined as 3.06 kcal/mol. These observed crystallization characteristics of PEDEKmK are compared with those of the other members of poly(aryl ether ketone) family. (C) 1997 John Wiley & Sons, Inc.

聚芳醚砜环状低聚物的基质辅助激光解吸电离质谱分析

采用基质辅助激光解吸电离飞行时间质谱（ＭＡＬＤＩ－ＴＯＦ－ＭＳ）技术分别对两种合成的聚芳醚砜环状低聚物进行了分析研究，并讨论了低聚物中不同聚合度离子组份的分布规律。实验结果表明，ＭＡＬＤＩ－ＴＯＦ－ＭＳ是分析环状低聚物直观、准确、快速的分析工具。

RAPID-DETERMINATION OF KINETIC-PARAMETERS FOR THE ELECTROCATALYTIC REDUCTION OF DIOXYGEN BY VITAMIN-B12 ADSORBED ON GLASSY-CARBON ELECTRODE

In this paper, the electrochemical behavior of vitamin B-12, ie cyanocobalamin (abbr. VB12) in a weak acidic aqueous solution and adsorbed on glassy carbon (GC) surface (abbr. VB12(ad)/GC) in different pH buffer solutions have been described by using cyclic voltammetry (cv). It is found that VB12 and VB12(ad)/GC exhibit catalytic activity for the electroreduction of O2 according to two reduction peaks at -0.50 and -1.00 V vs. sce; but their electrocatalytic activity is very unstable. Based on the method of hydrodynamic amperometry [B. Miller and S. Bruckenstein, J. electrochem. Soc. 117, 1033 (1970)], some kinetic parameters for the electrocatalytic reduction of O2 by VB12(ad)/GC have been determined rapidly by using a linear rotation-scan method [Rongzhong Jiang and Shaojun Dong, Electrochim. Acta 35, 1451 (1990)]. These kinetic parameters indicate that the reduction of O2 on VB12(ad)/GC gives water predominantly in both potential ranges which correspond to those two reduction peaks. Possible reaction mechanisms have been suggested.

Molecular cloning, characterization and mRNA expression of peroxiredoxin in Zhikong scallop Chlamys farreri

Peroxiredoxin V (PRX V) is known as an atypical 2-cysteine peroxiredoxin that protects the organisms against various oxidative stresses and functions in signal transduction. The cDNA of a PRX V gene (designated as CfPRX) was cloned from scallop Chlamys farreri. The full-length sequence of CfPRX cDNA was of 2,179 bp with a 564 bp open reading frame encoding a peptide of 187 amino acids. Sequence comparison showed that CfPRX shared higher identities with PRX Vs than that with other isoforms of PRX, indicating CfPRX was a member of the PRX V family. Fluorescent real-time quantitative PCR analysis revealed the presence of CfPRX transcripts in gill filaments, adductor muscle, heart, gonad, kidney and hemocytes, and the stimulation of Listonella anguillarum significantly (P < 0.01) enhanced the mRNA expression of CfPRX in hemocyte. These results indicated that CfPRX was a constitutive and inducible acute-phase protein which was involved in the immune resistance to L. anguillarum stimulation.