Calibration in non-linear NIR spectroscopy using principal component artificial neural networks

Near-infrared (NIR) spectroscopy was used in simultaneous, non-destructive analysis of antipyriine and caffeine citrate tablets. Principal component artificial neural networks (PC-ANNs) were used to construct models for the analytes, using the testing set for external validation. Four pretreated spectra, namely, first-derivative, second-derivative, standard normal variate (SNV) and multiplicative scatter correction (MSC) spectra led to simplified and more robust models than conventional spectra. In PC-ANNs models, the spectra data were analyzed by principal component analysis (PCA) firstly. Then the scores of the principal compounds (PCs) were chosen as input nodes for input layer instead of the spectra data. The artificial neural networks (ANNs) models using the spectra data as input nodes were also established, which were compared with the PC-ANNs models. The result shows the SNV model of PC-ANNs multivariate calibration has the lowest training error and predicting error. The concept of the degree of approximation was introduced and performed as the selective criterion of the optimum network parameters.     

Synthesis and crystal structure of four Pd(II) complexes containing nido or closo carborane diphosphine ligands

Three Pd(II) complexes [Pd₂(μ-Cl)₂{7,8-(PPh₂)₂-7,8-C₂B₉H₁₀}₂] · 0.25CH₂Cl₂ (1), [Pd{7,8-(PPh₂)₂-7,8-C₂B₉H₁₀}₂] · 4CHCl₃ (2) and [PdCl₂(1,2-(PPh₂)₂-1,2-C₂B₁₀H₁₀)] (3) have been synthesized by the reactions of 1,2-(PPh₂)₂-1,2-C₂B₁₀H₁₀ with PdCl₂ in acetonitrile, cyanophenyl and dichloromethane, respectively. A fourth complex, [PdI₂(1,2-(PPh₂)₂-1,2-C₂B₁₀H₁₀)] (4), was obtained by a ligand exchange reaction through the substitution of the Cl⁻ of complex 3 with I⁻. All four complexes have been characterized by elemental analysis, FT-IR, ¹H and ¹³C NMR spectroscopy and X-ray structure determination. Single crystal X-ray determination showed that the carborane cage, nido for 1, 2 and closo for 3, 4, was coordinated bidentately to the Pd atom through the two P atoms, and the geometry at the Pd atom was square-planar in all the complexes.     

Mechanism of flow instability and transition to turbulence

In this paper, a new mechanism of flow instability and turbulence transition is proposed for wall bounded shear flows. It is stated that the total energy gradient in the transverse direction and that in the streamwise direction of the main flow dominate the disturbance amplification or decay. Thus, they determine the critical condition of instability initiation and flow transition under given initial disturbance. A new dimensionless parameter K for characterizing flow instability is proposed which is expressed as the ratio of the energy gradients in the two directions for the flow without energy input or output. It is suggested that flow instability should first occur at the position of K_max which may be the most dangerous position. This speculation is confirmed by Nishioka et al.'s experimental data. Comparison with experimental data for plane Poiseuille flow and pipe Poiseuille flow indicates that the proposed idea is really valid. It is found that the turbulence transition takes place at a critical value of K_max of about 385 for both plane Poiseuille flow and pipe Poiseuille flow, below which no turbulence will occur regardless the disturbance. More studies show that the theory is also valid for plane Couette flows which holds a critical value of K_max of about 370.     

Synthesis,structure characterization,and thermochemistry of the coordination compounds of pyridine-2,6-dicarboxylic acid with several metals (Ca and Co)

Two solid state complexes of pyridine-2,6-dicarboxylate with Ca²⁺ and Co²⁺ ions, Ca₂(DPC)₂(H₂O)₆(H₂DPC)₂(s) and Co(DPC)₂·Co(H₂O)₅·2H₂O(s), were synthesized. X-ray crystallography was applied to characterize the crystal structures of the two complexes. The molecular and cell stacking structures of the two complexes were shown; the crystal data and refinement details were summarized, and the selected bond lengths and angles of the title complexes were listed. Low-temperature heat capacities of the two complexes were measured with an automated adiabatic calorimeter in the temperature ranging from 78 to 380 K. Two polynomial equations of experimental molar heat capacities as a function of the temperature were obtained by the least-squares method. The smoothed molar heat capacities and thermodynamic functions of the complexes were calculated based on the fitted polynomial equations. In addition, thermodynamic properties of the two complexes were compared.     

A novel nitrite sensor fabricated through anchoring nickel-tetrahydroxy-phthalocyanine and polyethylene oxide film onto glassy carbon electrode by a two-step covalent modification approach

In this paper, we present a two-step covalent modification approach to fabricate a novel nitrite sensor through anchoring nickel-tetrahydroxy-phthalocyanine (NiPc(OH)₄) and polyethylene oxide (PEO) onto a glassy carbon electrode (GCE). The surface morphology of the prepared NiPc(OH)₄/PEO composite films under different dry conditions was characterized by scanning electron microscopy (SEM). The electrochemical behavior of NiPc(OH)₄/PEO composite film modified GCE toward the catalytic oxidation of nitrite in pH 7.0 phosphate buffer solution (PBS) was investigated by cyclic voltammetry (CV). After drying under an infrared lamp, the fabricated sensor showed a pronounced electrocatalytic activity improvement toward the oxidation of nitrite and led to a significant decrease in the anodic overpotentials compared with bare GCE, which should be ascribed to the synergistic effect of NiPc(OH)₄ and PEO, as well as the enlarged electrochemical effective surface area after drying. Using differential pulse voltammetry (DPV), the sensor gave a linear response to nitrite over the concentration range of 0.1–5,300 μM, with a detection limit of 0.0522 μM. The nitrite sensor exhibits good sensitivity, selectivity, and stability and has been applied for the determination of nitrite in water samples.     

Oxygen Reduction Reaction in a Droplet on Graphite: Direct Evidence that the Edge Is More Active than the Basal Plane

Carbon‐based metal‐free electrocatalysts for the oxygen reduction reaction (ORR) in alkaline medium have been extensively investigated with the aim of replacing the commercially available, but precious platinum‐based catalysts. For the proper design of carbon‐based metal‐free electrocatalysts for the ORR, it would be interesting to identify the active sites of the electrocatalyst. The ORR was now studied with an air‐saturated electrolyte solution droplet (diameter ca. 15 μm), which was deposited at a specified position either on the edge or on the basal plane of highly oriented pyrolytic graphite. Electrochemical measurements suggest that the edge carbon atoms are more active than the basal‐plane ones for the ORR. This provides a direct way to identify the active sites of carbon materials for the ORR. Ball‐milled graphite and carbon nanotubes with more exposed edges were also prepared and showed significantly enhanced ORR activity. DFT calculations elucidated the mechanism by which the charged edge carbon atoms result in the higher ORR activity.     

Direct Growth of Cobalt Hydroxide Rods on Nickel Foam and Its Application for Energy Storage

The present work reports synthesis of cobalt hydroxide (Co(OH)₂) rods on nickel foam and its supercapacitor application. Hierarchical Co(OH)₂ rods with length of approximately 3.5 μm and diameter of approximately 400 nm were prepared by one‐step, simple, and inexpensive chemical‐bath‐deposition method. The direct growth of Co(OH)₂ rods on the Ni foam gave three dimensional (3D) structure for easy access of electrolyte throughout material surface. Also, well‐adhered interface between Co(OH)₂ rods and Ni‐foam surface gave better conduction channels. Detailed electrochemical study was performed by using cyclic voltammetry and galvanostatic charge/discharge measurements. The results demonstrate that Co(OH)₂ rods on Ni foam are efficient electrodes for supercapacitor application.     

铈对低镍铬锰氮奥氏体不锈钢晶间腐蚀的影响研究

针对不同稀土Ce含量的低镍铬锰氮奥氏体不锈钢,采用电化学动电位再活化法和Cu-CuSO4-16%H2SO4热酸浸泡法研究了两种热处理状态下不同铈含量试样的晶间腐蚀程度。研究结果表明:两种热处理状态下,未添加稀土试样腐蚀最严重。不同稀土含量的试样750℃敏化处理2 h比650℃敏化处理2 h腐蚀程度略重。从两组试验的金相显微组织照片和EPR活化率数据来看,两种热处理状态稀土Ce含量为0.053%时奥氏体不锈钢抗晶间腐蚀能力最强,但当铈含量增加到0.067%时,试样腐蚀又开始恶化。     

A one‐dimensional coordination polymer with a capped [Cu4O4] cubane core assembled from 2‐(hydroxymethyl)pyridine

The one‐dimensional coordination polymer catena‐poly[[[di‐μ₂‐acetato‐tetrakis[μ₃‐(pyridin‐2‐yl)methanolato]tetracopper(II)]‐di‐μ₂‐diacetamidato] acetonitrile monosolvate], {[Cu₄(C₆H₆NO)₄(CH₃COO)₂(C₂N₃)₂]·CH₃CN}_n, has been prepared from the direct reaction of 2‐(hydroxymethyl)pyridine with Cu(OAc)₂·H₂O (OAc⁻ is acetate) in a methanol–acetonitrile mixture. The four Cu centres are bridged by four O atoms from discrete (pyridin‐2‐yl)methanolate ligands and two acetate groups, forming a capped [Cu₄O₄] cubane core. Each core is doubly bridged to each of two adjacent cores by [N(CN)₂]⁻ anions, resulting in one‐dimensional chains. The magnetic properties of the complex were also studied.     

噻唑基温控手性离子液体催化反式肉桂醛和对甲酰基苯甲酸甲酯合成γ-丁内酯

以L-薄荷醇、4-甲基-5-羟乙基噻唑、多聚甲醛、环氧乙烷等为原料,设计合成出一类新型的噻唑基温控手性离子液体催化剂,并将其用于催化反式肉桂醛和对甲酰基苯甲酸甲酯的反应,立体选择性地合成了含有两个手性中心的取代γ-丁内酯.利用催化剂的温控性能,使反应在温控溶剂中进行,可以达到温控相分离催化的效果,实现催化剂的循环使用.选择出最佳温控溶剂为THF/正己烷(体积比为2.5∶2).以1,8-二氮杂双环[5,4,0]十一碳-7-烯(DBU)为碱试剂,在催化剂用量为反应原料的10 mol%,反应温度为35℃,反应时间为16 h的条件下,反式肉桂醛的转化率为95.4%,γ-丁内酯的选择性为80.4%,产物顺反比为3.3∶1,其ee值分别为21.3%和16.1%.考察了催化剂的循环使用性能,结果表明催化剂可循环使用4次,其催化活性基本保持不变.