Effect of configuration and conformation on the spin multiplicity in xylylene type biradicals

The singlet-triplet splitting energy gap DeltaE(S.T) = E-S - E-T is calculated for the ortho-, meta-, and para-xylylenes and their heteroatomic analogous by means of AM1-CI approach. It is shown that when the radical centers R-.(R-.=H2C.-,H2N.+- or HN.-) are twisted sufficiently Tar out of conjugation with the benzene ring, DeltaE(S.T) tends to zero or is negative, i.e, ortho-, meta-, and para-phenylenes turn into weak ferromagnetic or antiferromagnetic coupling unit, while they are strong ferromagnetic (meta-isomers) or antiferromagnetic (ortho-, para-isomers) coupling units under planar conformation. It is suggested that serious twisted conformation is not recommended candidate for the design of novel high-spin molecules with stable high-spin ground states by ortho- or para-phenylene coupling unit.

构型与构象对苯双自由基体系基态自旋多重度及其稳定性的影响

利用AM1-CI方法计算了构象对邻、间、对二取代苯双自由基体系基态自旋多重度及其稳定性的影响. 结果表明单 - 三重态能量差(△ES－T)和部分占据分子轨道的能量劈裂(△EPOMO)随自由基与苯环间的二面角而变化. 当二面角接近90°时, 分子具有平面或近平面构象时强的铁磁或反铁磁耦合单元, 由于具有近简并的高自旋和低自旋基态, 而变成弱的反铁磁或铁磁耦合单元. 由此提出为获得具有稳定高自旋基态的高自旋分子, 实验上应尽量避免选用强烈扭曲的邻、对苯分子构象.

A rule to design high spin molecules with hetero-spin centers

The series of biradicals with m-phenylene coupling unit and hetero-spin centers were calculated compared with those possessing home-spin centers using AM1-CI method. A simple rule was proposed to design high spin molecules with ferromagnetic coupling unit and hetero-spin centers. Two neutral (or charged) hetero-spin centers resulted in high spin ground state, one neutral and another charged hetero-spin centers correspond to low spin ground state. The latter was ascribed to the huge splitting of two partially occupied molecular orbitals.

Using triazine as coupling unit for intramolecular ferromagnetic coupling of multiradicals

Novel high spin tri-, tetra-, pentaradicals, composed of triazine coupling units and cationic amino radical spin centers (+ . NH) under various configurations and linkages, are predicted from AM1-CI calculations. It is found that for charged planar multiradicals the stability of high spin ground states depends on both the molecular configuration and the number of end groups. Generally, cyclic 1,3-bridged charged multiradicals (S less than or equal to 5/2) possess more stable high spin ground states than their isomers under the branched 1,3,5,-bridged configuration. Therefore, it is suggested that in the design of planar high spin molecules with stable high spin ground states, less end groups and all the supposed spin centers and/or the coupling units should be under the same structural situation. (C) 1999 Elsevier Science B.V. All rights reserved.

The intermolecular coupling through space for stacked high spin molecules

Intermolecular ferromagnetic interactions in two stacking models for the dimer of high spin molecules are investigated by means of AM1-CI approach. It is shown that the stability of high spin ground state versus low spin state can be simply traced back to the number and the extent of atoms with reversed signs of pi-spin density in neighboring molecules coupled to each other in shortest distance.

设计具有稳定高自旋基态多自由基体系的结构规则

利用半经验AM1分子轨道方法引入组态相互作用,研究了双自由基体系三重态基态稳定性随分子构象的变化,进一步研究了氯取代基的数量及取代基的位置对基态稳定性的影响。首次发现了影响双自由基及多自由基体系高自旋基态稳定性的自旋分布规律,提出了设计高自旋分子的结构规则。

大分子物质的质谱研究

1. 利用解吸化学电离质谱(DCI-MS)，研究了C_(60)与烷基甲醚和伯醇自身化学电离(self-CI)产物之间的气相离子-分子反应，观察到加成离子[C_(60)C_2H_5O]~+和质子化分子[C_(60)H]~+是C_(60)与烷基甲醚等离子体反应的主要产物；相反，没有检测到C_(60)与伯醇离子体系形成的相应加成产物。利用AM1半经验方法对[C_(60)C_2H_5O]~+的十四种可能结构进行了计算。结果表明最稳定的加成产物是[3+2]环加成产物，并提出了该加成产物的形成途径。2. 使用同样方法研究了C_(60)与丙烯酸甲酯离子体系发生的气相离子-分子反应，观察到加成离子[C_(60)C_3H_3O]~+和质子化分子[C_(60)H]~+为主要产物。利用AM1半经验方法对[C_(60)C_3H_3O]~+的八种可能结构进行了计算，结果表明三种环加成产物为最稳定结构。3. 合成了一系列L7和σ因子肽片段，并利用基质辅助激光解吸电离质谱(MALDI-MS)、电喷雾质谱(ESI-MS)和圆二色(CD)对高效液相色谱(HPLC)提纯的合成肽进行了表征。4. 利用ESI-MS研究了L7和σ合成肽与蛋白质G和蛋白质A的复合物，发现了该复合物产生的最佳条件及其稳定性；并结合亲和色谱，证明了L7和σ合成肽与蛋白质G或蛋白质A形成的复合物是具有特异性的非共价复合物。5. 通过竞争酶联免疫吸附实验（ELISA）、亲和色谱和MALDI-MS的联用，发现L7和σ肽与IgG的Fc片断在蛋白质G和蛋白质A的结合位置不同。6. 利用鸡多克隆抗L7抗体通过免疫键合印迹法发现L7和σ肽之间没有交叉反应性。

Gas-phase ion - Molecule reactions of neutral C-60 with the plasmas of alkyl methyl ethers and primary alcohols

The gas-phase ion-molecule reactions of C-60 with the methoxymethyl ion [CH3O=CH2](+) and the 1-hydroxyethyl ion [CH3CH=OH](+) generated under the self-chemical-ionization (self-CI) conditions of alkyl methyl ethers and primary alcohols were studied in the ion source of a mass spectrometer. The adduct ions [C60C2H5O](+) and protonated molecules [C60H](+) were observed as the major products of C-60 with the plasma of alkyl methyl ethers. On the contrary, the reactions of C-60 With the plasmas of primary alcohols produced few corresponding adduct ions. The AM1 semiempirical molecular orbital calculations were carried out on 14 possible structures. The calculated results showed that the most stable structure among the possible isomers of [C60C2H5O](+) is the [3+2] cycloadduct. According to experimental and theoretical results, the pathway for the formation of the adduct was presented.

Investigation of the structures of the product ions produced via self-CI of acetone

The ion-molecule reactions in acetone were investigated which were induced under the chemical ionization. The structural information of the reaction products were obtained by using collision-induced dissociation (CID) technique performed at ion kinetic energies of 30eV.

A theoretical study on the nonlinear optical second-order properties of azobenzene series molecules

On the basis of AM1 and INDO/CI methods, we devise the program for the calculation of nonlinear second-order optical susceptibilities beta(ijk) and perform systematic theoretical studies on the nonlinear optical second-order properties of azobenzene series molecules, i. e. on the basis of [GRAPHICS] we induced different donors on the left side of phenyl ring, and different accepters on the right side of phenyl ring, and examined the rule of beta variation. The regularity summarized from the calculated results has been explained micromechanically. Finally, a molecule having a big nonlinear second-order optical susceptibility has been designed.

Photocatalytic degradation of CI Acid Blue 80 in aqueous suspensions of titanium dioxide under sunlight

The dye C.I. Acid Blue 80 (AB80) was easily degraded by TiO2-P25 assisted photocatalysis in aqueous dispersion under irradiation of sunlight. The optimal reaction conditions were [TiO2] = 2.0 g/L, pH = 10, [H2O2] = 5 mmol/L. The photocatalytic reaction followed pseudo-first order kinetics. The adsorption of AB80 onto TiO2 was in accord with Langmuir equation.