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.     

[Mg(NH2)2]n(n=1—5)团簇的密度泛函理论研究

用密度泛函理论的杂化密度泛函B3LYP方法在6-31G*基组水平上对[MS(NH2)2]n(n=1-5)团簇各种可能的构型进行几何结构优化,预测了各团簇的最稳定结构.对最稳定结构的振动特性、成键特性、电荷特性等进行了理论研究.结果表明:团簇易形成链状结构,Mg-N键长为0.190-0.234 nm,N-H键长为0.101-0.103 nm,H-N-H键角为100.2°-107.5°;团簇中Mg原子的自然电荷在1.585e-1.615e之间,N原子的自然电荷在-1.551 e--1.651 e之间,H原子的自然电荷在0.369e-0.403e之间,-NH2基的自然电荷在-0.784e--0.845e之间,Mg原子和-NH2基之间相互作用呈现较强的离子性.团簇结构及光谱与晶体比较表明,-NH2基在团簇和晶体中均保持其完整性.     

从正常态电阻探讨MgB_2的超导机制

采用化学气相沉积先驱B薄膜两步异位退火法在不同条件下制备了6个MgB2超导薄膜样品,测量了样品的电阻随温度变化关系;结合描述正常态电阻的Bloch-Gruneisen公式,研究了正常态电阻的特性;正常态电阻的测量结果与电子-声子相互作用的描述相符,认为MgB2的超导机制是以声子为媒介的电子-声子相互作用为主。     

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.     

干法刻蚀影响应变量子阱发光的机理研究

采用感应耦合等离子体刻蚀技术对InAsP/InP应变多量子阱和InAsP/InGaAsP应变单量子阱材料的覆盖层进行了不同厚度的干法刻蚀. 实验结果表明，干法刻蚀后量子阱光致荧光强度得到了不同程度的增强. 干法刻蚀过程不仅增加了材料表面粗糙度，同时使其内部微结构发生变化. 采用湿法腐蚀方法去除表面变粗糙对量子阱发光特性的影响，得到干法刻蚀覆盖层20 nm后应变单量子阱微结构变化和其表面粗糙度变化两个因素分别使荧光强度提高1.8倍和1.2倍的结果. 关键词： 干法刻蚀 应变多量子阱 光致发光谱 损伤     

Improving the Molecular Ion Signal Intensity for In Situ Liquid SIMS Analysis

In situ liquid secondary ion mass spectrometry (SIMS) enabled by system for analysis at the liquid vacuum interface (SALVI) has proven to be a promising new tool to provide molecular information at solid–liquid and liquid–vacuum interfaces. However, the initial data showed that useful signals in positive ion spectra are too weak to be meaningful in most cases. In addition, it is difficult to obtain strong negative molecular ion signals when m/z>200. These two drawbacks have been the biggest obstacle towards practical use of this new analytical approach. In this study, we report that strong and reliable positive and negative molecular signals are achievable after optimizing the SIMS experimental conditions. Four model systems, including a 1,8-diazabicycloundec-7-ene (DBU)-base switchable ionic liquid, a live Shewanella oneidensis biofilm, a hydrated mammalian epithelia cell, and an electrolyte popularly used in Li ion batteries were studied. A signal enhancement of about two orders of magnitude was obtained in comparison with non-optimized conditions. Therefore, molecular ion signal intensity has become very acceptable for use of in situ liquid SIMS to study solid–liquid and liquid–vacuum interfaces.

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High performance liquid chromatographic determination of N-nitrosoamines by pre-column fluorescence derivatization with acridone-N-acetyl chloride

A sensitive high performance liquid chromatographic method for the determination of N-nitrosoamines with pre-column fluorescence derivatization has been developed. N-nitrosoamines are first changed into secondary amines using denitrosation reagent, then react with acridone-N-acetyl chloride (ARC-Cl) to produce corresponding secondary amine derivatives, which exhibit a strong fluorescence. Maximum emission for ARC derivatives is 430 nm (lambda(ex) 404 nm). The labelled derivatives are very stable, less than 4% decomposition occurs after heating at 40 degrees C for 24 h. Fluorescence intensities of derivatives are higher in neutral and alkaline than in acidic solutions. This method, in conjunction with a multi-gradient program, offers a baseline resolution of the ARC derivatives from a linear acetonitrile gradient. Separation is carried out on a reverse phase C(18) column. Derivatization and chromatographic conditions are optimized. The relative standard deviation (n=6) at an analytical concentration of 10 pmol of each N-nitroamine is less than 4.5%. The detection limits at the fmol level. The method described is also suitable for analysis of other amino compounds in different biological samples.     

Reactant subspaces and kinetics of chemical reaction networks

This paper studies a chemical reaction network’s (CRN) reactant subspace, i.e. the linear subspace generated by its reactant complexes, to elucidate its role in the system’s kinetic behaviour. We introduce concepts such as reactant rank and reactant deficiency and compare them with their analogues currently used in chemical reaction network theory. We construct a classification of CRNs based on the type of intersection between the reactant subspace R and the stoichiometric subspace S and identify the subnetwork of S-complexes, i.e. complexes which, when viewed as vectors, are contained in S, as a tool to study the network classes, which play a key role in the kinetic behaviour. Our main results on new connections between reactant subspaces and kinetic properties are (1) determination of kinetic characteristics of CRNs with zero reactant deficiency by considering the difference between (network) deficiency and reactant deficiency, (2) resolution of the coincidence problem between the reactant and kinetic subspaces for complex factorizable kinetics via an analogue of the generalized Feinberg–Horn theorem, and (3) construction of an appropriate subspace for the parametrization and uniqueness of positive equilibria for complex factorizable power law kinetics, extending the work of Müller and Regensburger.