Responses of enantioselective characteristics of imidazolinone herbicides and Chiralcel OJ column to temperature variations

Temperature affects not only the chromatographic characteristics of solute but may also alter the conformation of the stationary phase. However, temperature influences on enantioseparation of solute and conformation of chiral stationary phase (CSP) are seldom considered simultaneously. In this study, three temperature programs, a conventional heating procedure, a cyclic van't Hoff program, and a step-temperature program, were employed to evaluate temperature effects on enantioseparation of five imidazolinone herbicides on Chiralcel OJ column and the conformational state of the stationary phase. The van't Hoff plots of retention factor (k'), distribution constant (K) and separation factor (alpha) for imazapyr (1), imazapic (2), imazethapyr (3), and imazamox (4) were linear within 15-50 degrees C. Nonlinear van't Hoff plots of alpha were observed for imazaquin (5) with mobile phase of n-hexane (0.1% TFA)-2-propanol at 70/30 or 60/40 (v/v). The large molecular size of imazaquin (5) and van't Hoff plots of alpha were therefore more sensitive at detecting conformational changes of the stationary phase. Small but irreversible conformational changes occurred at 5-10 degrees C with the solvent ratio of 60/40. During the cyclic van't Hoff program, reversible conformational changes were observed at >or=15 degrees C. A switch was even visible at about 25 degrees C with the solvent ratio of 60/40 during the re-cooling cycle. The cyclic van't Hoff temperature program showed that using OJ column may yield satisfactory results at 15-50 degrees C but not at 相似文献   

Evaluation of triproline and tri-α-methylproline chiral stationary phases: Retention and enantioseparation associated with hydrogen bonding

In this study, to demonstrate preparation strategy and improve understanding of chiral recognition mechanisms, triproline chiral stationary phases (CSPs) were evaluated with a series of analytes classified as having none, one, two or three H-bond donors. The average retention factors and mobile phase strength generally followed none < one < two < three hydrogen bond donors. The average solvent volume ratio (H_r stands for average hexane volume ratio in the mobile phase, Hp_r for heptane, ACN_r for acetonitrile, or H₂O_r for water) normalized chromatographic parameters calculated for di-, tri-, tetra-, penta-, hexa-, and decaproline CSPs facilitated the characterization of properties associated to the H-bond donor categorization. The H_r of triproline CSP were 1.0, 0.96 and 0.88 for analyte of none, one and two hydrogen bond donors with hexane/2-propanol mobile phase, respectively. The number of hydrogen bond donors in an analyte was found to be a primary factor in influencing the retention and enantioseparation in the normal-phase and polar organic modes. Two H-bond acceptor solvents methyl tert-butyl ether and ethyl acetate increased chiral separation on oligoproline CSPs for some compounds. The role of carbon-donor hydrogen bonding at the H atom of proline asymmetric center was implied through testing a tri-α-methylproline stationary phase. On oligoproline CSPs, three factors including adjacent hydrogen bond acceptor and carbon-donor, and a rigid proline residue chain were recognized as important for contributing to the broad enantioselectivity. The α hydrogen atom on chiral center of stationary phase was found to play a crucial role in enantiomeric discrimination.     

Optimization of robustness of network controllability against malicious attacks

As the controllability of complex networks has attracted much attention recently, how to design and optimize the robustness of network controllability has become a common and urgent problem in the engineering field. In this work, we propose a method that modifies any given network with strict structural perturbation to effectively enhance its robustness against malicious attacks, called dynamic optimization of controllability. Unlike other structural perturbations, the strict perturbation only swaps the links and keeps the in- and out-degree unchanged. A series of extensive experiments show that the robustness of controllability and connectivity can be improved dramatically. Furthermore, the effectiveness of our method is explained from the views of underlying structure. The analysis results indicate that the optimization algorithm makes networks more homogenous and assortative.     

Quiescent double barrier regime in the DIII-D tokamak

A new sustained high-performance regime, combining discrete edge and core transport barriers, has been discovered in the DIII-D tokamak. Edge localized modes (ELMs) are replaced by a steady oscillation that increases edge particle transport, thereby allowing particle control with no ELM-induced pulsed divertor heat load. The core barrier resembles those usually seen with a low (L) mode edge, without the degradation often associated with ELMs. The barriers are separated by a narrow region of high transport associated with a zero crossing in the E x B shearing rate.     

Orientational Distribution of Fibres in Sheared Fibre Suspensions

Motion of fibres in sheared fibre suspensions is simulated numerically by using the lattice Boltzmann method. The orientational distributions of the fibres are presented for different Reynolds numbers, Stokes numbers, shear rate and fibre aspect ratio. Some computational results are compared with the experimental data of pipe flow, and the qualitative agreement is achieved. The results show that the orientational distributions are greatly affected by the Reynolds numbers, while relatively insensitive to the fibre aspect ratio. The Stokes number and shear rate have obvious influence on the orientation distribution.     

固-液金属界面上金属间化合物的非平衡生长

钎焊过程是一些液态的低熔点金属合金（钎料）与过渡金属（引线）在钎焊温度下相互作用,冷却后形成电路接头的过程[1],其间,金属间化合物生长和存在的特征,极大地影响钎焊接头的强度,抗蠕变性,抗腐蚀性和可焊性,本文拟以纯液态金属与固体金属的快速反应来观察金属间化合物的生长,从而阐述钎焊过程的特征。     

钢结构格构柱设计理论的力学问题

借助钢结构格构柱设计理论的换算长细比、横向最大剪力以及分肢承载力三个重要力学问题的解决思路和求解技巧的演绎教学,培养学生发现工程中的力学问题、寻找解决力学问题的途径、服务工程设计的能力,引导学生深刻认识力学理论在解决工程问题中的重要作用,进而激发学生学习力学理论的兴趣,实现学生探究、解决工程问题的创新思维、创新能力的培养目标.     

旋量值函数的Plemelj公式

对比于多复变中的Bochner-Martinelli型积分的Plernelj公式,定义了艾米尔特Clifford分析中旋量值函数的Cauchy型积分及Cauchy主值积分,得到了旋量值函数的Plemelj公式,最后给出一些特殊情形的Bochner-Martinelli型积分的Plemelj公式.