阳极溶出催化伏安法的理论研究 Ⅰ.可逆电极溶出

本文推导了玻璃碳电极上可逆溶出催化过程的理论电流方程、峰电流及峰电势方程,得知溶出催化伏安法所得的峰电流比溶出伏安法的峰电流提高了数十倍,从而进一步提高了溶出伏安法的灵敏度。本文还用碲的溶出催化实验验证理论方程。所得实验结果均与理论方程相吻合。     

Quantitative investigations on moving chelation boundary within a continuous EDTA-based sample sweeping system in capillary electrophoresis

Recently, the EDTA-based sweeping of metal ion that combines chelate formation and in-line sample pre-concentration was advanced. However, the moving chelation boundary (MCB) existing in the sweeping system has not been investigated for the quantitative illumination of the mechanism of metal ion sweeping yet. In this paper, the model of MCB was developed from the EDTA-based sweeping. The theoretical studies were performed for boundary movements and controllable sweeping of metal ion. The theoretical studies show that the sweeping system contains the MCB boundary and chelate boundary, and the difference between the MCB and chelate boundary velocities plays a key role in the stacking efficiency of metal ion. To demonstrate the validity of the theoretical conclusion, the experiments of continuous EDTA-based sweeping were performed with CE and a home-made apparatus of a large tube. The home-made apparatus consisted of a glass tube used for the run of continuous EDTA-based sweeping and two peristaltic pumps used for the supply of solution. The experimental results were in accordance with the theoretical conclusions above. The developed theory holds evident for significance for the mechanism of controllable stacking of metal ions in EDTA-based sweeping system in CE.     

Separation of aromatic acids by wide-bore electrophoresis with nanoparticles prepared by electrospray as pseudostationary phase

A model mixture of six aromatic acids has been separated using a laboratory-made wide-bore electrophoretic device with aminopropyl-modified nanoparticles used as pseudostationary phase. Optimization of preparation of nanoparticles by an electrospray (ES) method is described. With the optimized electrophoretic method, 30 mmol/L acetate running buffer, pH 4.5, containing 1.0 mg/mL of nanoparticles as an additive was used, and 3.0 kV applied potential, improved resolution was achieved. The average theoretical plate number obtained was above 5.0 x 10(4) theoretical plates per meter with the highest value achieved in certain runs exceeding 1.0 x 10(5) theoretical plates per meter, which was better than previously reported results (approximately 6.7 x 10(4) theoretical plates per meter). Furthermore, repeatabilities of 2, 6.5, and 6% were obtained for the migration time, peak areas, and peak height, respectively. Additionally, sample capacity and sensitivity were improved by hundredfold using the novel wide-bore electrophoresis system compared to traditional CE.     

The equilibrium structures, vibrational spectra, NLO and directional properties of transition dipole moments of diguanidinium arsenate monohydrate and diguanidinium phosphate monohydrate. The theoretical DFT calculations

For diguanidinium arsenate monohydrate and diguanidinium phosphate monohydrate the energies were minimized and the theoretical vibrational frequencies and potential energy distribution (PED) were calculated by density functional method. The 6-31++G(d,p) basis set was used. The assignment of the bands has been made on the basis of the calculated PED. For calculated equilibrium geometries two methods for determination of direction of transition dipole moments (TDM) were used. The oriented gas model was used for calculation of "static" TDM and from the other side the "dynamic" approximation of TDM by analysis of changes in internal coordination during characteristic vibrations was performed. The restricted Hartree-Fock (RHF) methods were used for calculation of the hyperpolarizability for both investigated molecules. The theoretical results are compared with experimental value of beta.     

Alpha and deuteron induced reactions on vanadium

The stacked foil technique was used in combination with γ-ray spectroscopy to obtain excitation functions for the production of different nuclei using natural vanadium as target and 85 MeV α-particles and 46.5 MeV deuterons as projectiles. The data are compared with theoretical predictions provided by an equilibrium and pre-equilibrium reaction model. In most cases the theoretical predictions seriously under-estimated the measured cross sections.     

开放式声化学反应体系中的反应动力学

采用气液传质的双膜理论建立了开放体系中声化学反应的动力学模型，同时用声源频率为500 kHz，声强为3 W·cm^-2的超声波在开放式声化学反应器内引发被空气饱和溶解的KI纯水溶液中的声化学反应，并检测反应过程中溶液的电导率，pH值改变及KI溶液中I₂的析出量，结果表明，它们与超声辐照时间之间呈线性关系，与理论模型吻合。     

Theoretical estimation of pyrolysis temperatures in electrothermal sample atomization

Based on thermodynamic simulation, a method was proposed for revealing element species at the stage of pyrolysis and estimation of theoretical pyrolysis temperature corresponding to the given analyte losses. The experimental and theoretical pyrolysis temperatures for 43 elements were compared to take into account the loss rates. It was found that, at various levels of analyte losses (0.1,1, and 10%), these temperatures exhibit a linear relationship with a correlation coefficient of no less than 0.66. The developed approach provides the prediction of pyrolysis temperatures in electrothermal atomization and can be used for the selection of a type of chemical modifier. The relationships found are important for the theoretical estimation of the efficiency of chemical modifiers.     

Modeling the effects of column packing quality and residence time changes on protein monomer/aggregate separation

The packing quality of chromatography columns used for the purification of protein therapeutics is routinely monitored to ensure consistent and reproducible performance. In this work, we used established chromatography models to determine the effect of column packing quality and fluid residence time on the separation of protein therapeutic monomer and aggregate species using a hydrophobic interaction chromatography adsorbent (Phenyl Sepharose Fast Flow). The relationship between the number of theoretical plates, fluid residence time, and column separation performance was quantified using modeling simulations. The simulations showed the separation depended on both the fluid residence time and the number of theoretical plates. However, when the number of theoretical plates was increased to ≥150, the simulations predicted that the separation performance of the column was not significantly improved. The approach described here could be used as a method to quantify acceptable height equivalent of a theoretical plate values for columns, and serve as a tool to understand how column packing quality impacts a given chromatographic separation prior to column scale-up, as well as during the monitoring of column lifetime in the manufacturing of large scale protein therapeutics.     

热动力学的研究(Ⅳ)——等浓度二级反应的热动力学研究法

本文根据热动力学的基础理论, 讨论了等浓度二级反应的无量纲参数法, 并用以研究了苯甲酸乙酯皂化反应的热动力学。实验测得的速度常数在误差范围内与文献值很好符合。     

Experimental and theoretical study on the structure and vibrational spectra of β-2-aminopyridinium dihydrogenphosphate

Experimental and theoretical vibrational spectra of β-2-aminopyridinium dihydrogenphosphate (β-2APDP) have been investigated. The FT-IR spectrum of β-2APDP was recorded in the region 4000-400 cm(-1). The optimized molecular structure and theoretical vibrational frequencies of β-2APDP have been investigated using ab initio Hartree-Fock (HF) and density functional B3LYP method with 6-311++G(d,p) basis set. The optimized geometric parameters (bond lengths and bond angles) and theoretical frequencies have been compared with the corresponding experimental data and it is found that they agree well with each other. All the assignments of the theoretical frequencies were performed by potential energy distributions using VEDA 4 program. Furthermore, the used scale factors were obtained from the ratio of the frequency values of the strongest peaks in the experimental and theoretical IR spectra. From the results it was concluded that the B3LYP method is superior to the HF method for the vibrational frequencies.     

X射线荧光光谱理论强度计算中激发因子的选择

激发因子是X射线荧光强度理论计算中的重要参数。对目前常用的四种激发因子算法进行了较为详细的比较,并设计了一种评价激发因子算法的实验方法,即用人工合成试样测定了八对能量接近的X射线特征谱线的强度比,然后根据不同的激发因子算法用理论方法计算出这些谱线对的强度比值,以两者的接近程度来判断这四种激发因子算法的适用性。结果表明,使用NRLXRF程序修改版中的激发因子算法计算出来的理论强度比与实测值之间的相对偏差最小。     

(E)-4-((4-chlorobenzylidene)amino)-N-(thiazole-2yl) benzenesulfonamide: Synthesis,characterization and electronic structure theory and docking studies

Spectroscopic methods (NMR, UV–vis) were utilized to get an understanding of the molecular structure of the (E)-4-((4-chlorobenzylidene)amino)-N-(thiazole-2yl) benzenesulfonamide (4CLBTH). The DFT/B3LYP/cc-pVDZ, were used in the theoretical study of the compound. Calculations using DFT can produce geometrical parameters such as bond lengths and bond angles. The GIAO method was utilized in DMSO to calculate the ¹H and ¹³C NMR for TMS. These results were then compared to the observed data. The UV–Vis spectrum of 4CLBTH was computed by using the B3LYP with the cc-pVDZ basis set. Using theoretical calculations, an investigation into the FMO analysis and the MEP were carried out. The theoretical findings and the experimental findings are in reasonable agreement with one another. The molecular docking was investigated by the autodock suite and visualised using the discovery studio visualizer. The multiwfn software was used to calculate the wavefunction studies.     

Vibrational spectra and ab initio analysis of tert-butyl,trimethylsilyl, and trimethylgermyl derivatives of 3,3-dimethylcyclopropene II. 3,3-Dimethyl-1,2-bis(trimethylsilyl)cyclopropene

The IR and Raman spectra of 3,3-dimethyl-1,2-bis(trimethylsilyl)cyclopropene (I) (synthesised using standard procedures) were measured in the liquid phase. Total geometry optimisation was performed at the HF/6-31G* level. The HF/6-31G*//HF/6-31G* quantum mechanical force field (QMFF) was calculated and used to determine the theoretical fundamental vibrational frequencies, their predicted IR intensities, Raman activities, and Raman depolarisation ratios. Using Pulay's scaling method and the theoretical molecular geometry, the QMFF of I was scaled by a set of scaling factors used previously for 3,3-dimethyl-1,2-bis(tert-butyl)cyclopropene (17 scale factors for a 105-dimensional problem). The scaled QMFF obtained was used to solve the vibrational problem. The quantum mechanical values of the Raman activities were converted to differential Raman cross sections. The figures for the experimental and theoretical Raman and IR spectra are presented. Assignments of the experimental vibrational spectra of I are given. They take into account the calculated potential energy distribution and the correlation between the estimations of the experimental IR and Raman intensities and Raman depolarisation ratios and the corresponding theoretical values (including Raman cross sections) calculated using the unscaled QMFF.     

X-ray emission spectroscopy of nitrogen-rich compounds

Nonresonant X-ray emission spectroscopy was used to compare the nitrogen-rich compounds ammonium nitrate, trinitrotoluene, and cyclotrimethylene-trinitramine. They are representative of crystalline and molecular structures of special importance in industrial and military applications. The spectral signature of each substance was analyzed and correlated with features in the electronic structure of the systems. This analysis was accomplished by means of theoretical simulations of the emission spectra and a detailed examination of the molecular orbitals and densities of states. We find that the two theoretical methods used (frozen-orbital density functional theory and real-space Green's function simulations) account semiquantitatively for the observed spectra and are able to predict features arising from distinct chemical complexes. A comparison of the calculations and the data provides insight into the electronic contributions of specific molecular orbitals, as well as the features due to bandlike behavior. With some additional refinements, these methods could be used as an alternative to reference compounds.     

Bubble nucleation in polymeric liquids. I. Bubble nucleation in concentrated polymer solutions

Laser light scattering, with the aid of Mie's scattering theory, was used to investigate bubble nucleation in concentrated polymer solutions. Solutions with 40, 50 and 60 wt % polystyrene in toluene were used. A test solution in a high-pressure optical cell made of strain-free quartz was heated to a predetermined temperature under pressure. Upon release of the pressure in the cell, both scattered and transmitted light fluxes were measured with photomultipliers, and the variation of system pressure with time was measured using a piezoelectric pressure transducer. The measurement of the light scattering flux and control of the experiment were performed by means of a microcomputer with a general-purpose data acquisition interface. Data reduction was done using the same microcomputer. The critical bubble size was determined by obtaining a one-to-one correspondence between the extrema of the experimental and theoretical scattering curves. While the Mie scattering theory is for monodisperse particles, the experimental scattering curves indicated that the bubbles had a distribution of sizes. Therefore, the log-normal distribution function was used to represent the size distribution; and theoretical scattering curves were computed by varying the breadth parameter in the log-normal distribution function, until we had a one-to-one correspondence between the extrema of the experimental and theoretical scattering curves. In this way, we were able to determine (a) the size distribution of bubbles in the optical cell, (b) the critical bubble size, (c) the total number of bubbles nucleated, and (d) the critical pressure for bubble nucleation, as functions of temperature, the initial equilibrium pressure in the optical cell, and the concentration of the polymer solution.     

Study of the interaction between cyclodextrins and liposome membranes: effect on the permeability of liposomes

We wanted to compare and understand the effect of the most currently used cyclodextrins on a model membrane. We studied the influence of most currently used cyclodextrins on the release of a fluorescent marker encapsulated in the inner cavity of SUV liposomes. It was shown that the observed effect on calcein release can be directly related to the affinity of cyclodextrins for both lipid components of liposomes, cholesterol and phosphatidylcholine. From this relationship, we were able to determine, for each cyclodextrin, a theoretical concentration giving rise to 50% or 100% calcein release. This theoretical concentration was confirmed experimentally.     

Theoretical modeling and experimental analysis of direct contact membrane distillation

A two-dimensional mathematical model was theoretically developed to predict the temperature polarization profile of direct contact membrane distillation (DCMD) processes. A concurrent flat-plate device was designed to verify the theoretical prediction of pure water productivity on saline water desalination. The numerical results from the temperature polarization profile were obtained using the finite difference technique to reduce the two-dimensional partial differential equations into an ordinary differential equations system. The resultant simultaneous linear equations system was solved with the fourth-order Runge-Kutta method. The results show theoretical prediction agreement with the measured values from the experimental runs. A combination of the Knudsen flow and Poiseuille flow models in the present mathematical formulation for membrane coefficient estimation was used to establish theoretical agreement. The influence of the inlet saline water temperature and volumetric flow rate on the pure water productivity as well as the hydraulic dissipated energy are also delineated.     

Experimental investigation and modeling of thermal conductivity of CuO–water/EG nanofluid by FFBP-ANN and multiple regressions

The purpose of this study is to predict the thermal conductivity of copper oxide (CuO) nanofluid by using feed forward backpropagation artificial neural network (FFBP-ANN). Thermal conductivity of CuO nanofluid is measured experimentally using transient hot-wire technique in temperature range of 20–60 °C and in volume fractions of 0.00125, 0.0025, 0.005 and 0.01% for neural network training and modeling. In addition, in order to evaluate accuracy of modeling in predicting the coefficient of nanofluid thermal conductivity, indices of root-mean-square error, coefficient of determination (R ²) and mean absolute percentage error have been used. FFBP-ANN with two input parameters (volume fraction and nanofluid temperature) and one output parameter (nanofluid thermal conductivity) in addition to two hidden layers and one outer layer which purelin, logsig and tansig functions are used was considered as the most optimum structure for modeling with neuron number of 4–10–1. In this study, among common methods of theoretical modeling of nanofluid thermal conductivity, theoretical method of Maxwell and also multivariate linear regression model was used for explaining the importance of modeling and predicting the results using neural network. According to this research, the results of indices and predictions show high accuracy and certainty of ANN modeling in comparison with empirical results and theoretical models.     

Stability of Magnetically Levitated Liquid Bridges of Arbitrary Volume Subjected to Axial and Lateral Gravity

The paramagnetic fluid composed of manganese chloride tetrahydrate dissolved in water was used to form bridges held between two parallel collinear rods. Magnetic levitation was used to control the effective gravity felt by the bridges. Their stability was studied as a function of Bond number and volume of the supported liquid. Data are compared with theoretical predictions for liquid bridges as well as with experimental results, where available. Copyright 1999 Academic Press.     

Structural and spectroscopical study of glutamic acid in the nonzwitterionic form

The molecular structure of glutamic acid in the non-zwitterionic form has been optimized by using the semiempirical MNDO and AMI methods and an ab initio calculation at the 4–31G level. The results were compared with previous reported data for other amino acids. The ab initio optimized structure was used as the starting point for a further force field calculation, and vibrational frequencies and theoretical assignments were thus obtained. In order to compare these results with experiments, the FT-IR spectrum of glutamic acid in an argon matrix was recorded and the measured frequencies were successfully compared with theoretical values, which were previously scaled by using a set of scaling factors.