Kinetics and mechanism of the reaction of a quasi-aromatic copper(II) complex, [Cu(PnAO)-6H]0, with formaldehyde

The kinetics of the reaction of CH₂O with a quasi-aromatic metal complex (1,1,2,8,9,9-hexamethyl-4,6-dioxa-5-hydro-3,7,10,14-tetraazacyclotetradecane-2,7,10,12-tetraene)copper(II), [Cu(PnAO)-6H]⁰ (AH), have been studied spectrophotometrically under neutral conditions in 1/3(v/v) MeOH–H₂O. The Cu, 2N, 3C quasi-aromatic heterocyclic ring in AH is highly reactive towards CH₂O at the central-aromatic-carbon atom, C(12) and the following reaction mechanism is proposed. The compounds AH, A—CH₂OH and A—CH₂—A were isolated and identified by i.r spectroscopy and by elemental analysis. The kinetic data supported the proposed reaction sequence. All reactions were second order overall. The rate constants and corresponding activation parameters for every step were obtained and are discussed.     

A step-economic and one-pot access to chiral Cα-tetrasubstituted α-amino acid derivatives via a bicyclic imidazole-catalyzed direct enantioselective C-acylation

C^α-Tetrasubstituted α-amino acids are ubiquitous and unique structural units in bioactive natural products and pharmaceutical compounds. The asymmetric synthesis of these molecules has attracted a lot of attention, but a more efficient method is still greatly desired. Here we describe the first sequential four-step acylation reaction for the efficient synthesis of chiral C^α-tetrasubstituted α-amino acid derivatives from simple N-acylated amino acids via an auto-tandem catalysis using a single nucleophilic catalyst. The synthetic efficiency is improved via a direct enantioselective C-acylation; the methodology affords the corresponding C^α-tetrasubstituted α-amino acid derivatives with excellent enantioselectivities (up to 99% ee). This step-economic, one-pot, and auto-tandem strategy provides facile access to important chiral building blocks, such as peptides, serines, and oxazolines, which are often used in medicinal and synthetic chemistry.

The first four-step sequential reaction for the synthesis of C^α-tetrasubstituted chiral α-amino acid derivatives via auto-tandem catalysis has been developed.     

铜在3%NaCl溶液中腐蚀行为的光电化学研究

Cu以其优异的导电性、导热性和易加工性广泛用于工农业生产中．自然Cu的腐蚀和防腐成为人们很关注的问题．人们已经注意到，Cl-对Cu的腐蚀有影响，并进行过一些研究．但目前使用光电化学方法研究这一问题的文章尚不多见，特别是利用测量开路光电压及其瞬态波形这一现场的、无损的、灵敏的监测方法研究户对Cu电极腐蚀全过程的文章尚未见到．本文正是利用如上方法及XPS，AES方法，研究了Cl-对Cu电极腐蚀的全过程，取得了一些有意义的结果．1实验方法Cu电极用99．99％（质量分数）的Cu制成，面积约为39mm2；电极底部由Cu导线焊接引出，…     

Determination of the single component and competitive adsorption isotherms of the 1-indanol enantiomers by the inverse method

The inverse method of isotherm determination consists in calculating the numerical values of the coefficients of an isotherm model that give a set of chromatographic profiles in best possible agreement with the set of experimental profiles available. This method was applied to determine the adsorption isotherms of the 1-indanol enantiomers on a cellulose tribenzoate chiral stationary phase. Both single-component and competitive isotherms were determined by using no more than one or two overloaded band profiles. The isotherms determined from the overloaded band profiles agreed extremely well with the isotherms determined by frontal analysis. Several isotherm models were used and tested. The best-fit isotherm was selected by means of statistical evaluation of the results. The results show that the adsorption is best characterized with a model describing heterogeneous adsorption with bimodal adsorption energy distribution.     

用带误差项的Ishikawa迭代过程逼近φ-强增生算子的零点

本文使用新的分析技巧研究了一致光滑Ｂａｎａｃｈ空间中φ 强增生算子的零点逼近问题，所得结果改进和扩展了近期许多相应的结果     

高能工业CT用新型X射线源焦斑测量

 为了获得较高的空间分辩率，设计了一种新型小束斑驻波电子直线加速器，该加速器取消了加速腔中的鼻锥结构，而在耦合腔中设置鼻锥结构。用狭缝法代替小孔法测得X射线源的焦斑尺寸为1.4mm。讨论了射线源焦点对成像质量的影响，分析了在高能条件下小孔法不适合用于焦点测量的物理原因，用4种测量方法测量了该高能X射线源的参数，测得该系统的成像极限分辩率为2.5 lp/mm，最后对实验结果进行了分析。     

Controlling theoretically total absorption in hybrid-cavity resonator with one graphene monolayer outside cavity

Total absorption is realized theoretically in a graphene-outside-cavity resonator. The structure is composed of the FP-Fano hybrid resonance cavity. Changing the thickness of grating exciting Fano resonance, the absorption-mode number can be tuned effectively. For the focused double-mode absorption, the resonances behave insensitively with the variation of chemical potential of graphene. Varying the geometry of grating can control the coupling extent of two modes. Also, by manipulating the period number of two-side multilayers around graphene, the absorption, shift and number of modes are governed.     

Cooling Characteristics During Bath Quenching of Test Probe Using Inverse Heat Transfer

It is of engineering importance to accurately predict the surface cooling characteristics in bath quenching of metals and alloys. In this investigation, the surface cooling characteristics in quenching of Wolfson probe are estimated with reasonable accuracy by solving an inverse heat conduction problem. Regularization method is used for smoothening the input temperature measurements at probe center, for superior inversion estimates. The reverse pool-boiling curve is captured on bath quenching characteristic, plotted as cooling velocity versus surface temperature. The prime advantage is the bypassing of convection coefficients, which are uncertain in pool boiling.     

A study of fluorescence properties of citrinin in β-cyclodextrin aqueous solution and different solvents

Citrinin (CIT) is a nephrotoxic mycotoxin initially isolated from filamentous fungus Penicilliu citrinum. It was later isolated from several other species, such as Aspergillus and Monascus. It has a conjugated, planar structure that gives it a natural fluorescence ability, which can be used to develop sensitive methods for detecting CIT in food. In this paper, we used the spectro?uorescence technique to study the effects of pH value, β-cyclodextrin (β-CD) and organic solvents on the CIT fluorescence intensity. The results show that lower pH value, aceitc acid, β-CD and acetonitrile can induce a higher fluorescence intensity of CIT, but methanol or H₂O has a decreasing effect on the fluorescence intensity of CIT. Findings in this study provide a theoretical basis for development of a high sensitivity fluorescence-based trace analysis for CIT detection.