A semi-analytical method for free vibration of straight orthotropic beams with rectangular cross-sections

On the basis of the two-dimensional elasticity equations with orthotropy, a semi-analytical method is proposed to analyze free vibration of straight beams with rectangular cross-sections. To this end, the state space method is combined with the differential quadrature method so that state equations with respect to state variables at discrete points are derived. The frequency equation for free vibration of straight orthotropic beams is then formulated. Numerical results are presented and compared with that available in the literature. The present method can be used to analyze either shallow or deep orthotropic beams with arbitrary end conditions.     

The Adsorption and Simulated Separation of Light Hydrocarbons in Isoreticular Metal–Organic Frameworks Based on Dendritic Ligands with Different Aliphatic Side Chains

Three isoreticular metal–organic frameworks, JUC‐100, JUC‐103 and JUC‐106, were synthesized by connecting six‐node dendritic ligands to a [Zn₄O(CO₂)₆] cluster. JUC‐103 and JUC‐106 have additional methyl and ethyl groups, respectively, in the pores with respect to JUC‐100. The uptake measurements of the three MOFs for CH₄, C₂H₄, C₂H₆ and C₃H₈ were carried out. At 298 K, 1 atm, JUC‐103 has relatively high CH₄ uptake, but JUC‐100 is the best at 273 K, 1 atm. JUC‐100 and JUC‐103 have similar C₂H₄ absorption ability. In addition, JUC‐100 has the best absorption capacity for C₂H₆ and C₃H₈. These results suggest that high surface area and appropriate pore size are important factors for gas uptake. Furthermore, ideal adsorbed solution theory (IAST) analyses show that all three MOFs have good C₃H₈/CH₄ and C₂H₆/CH₄ selectivities for an equimolar quaternary CH₄/C₂H₄/C₂H₆/C₃H₈ gas mixture maintained at isothermal conditions at 298 K, and JUC‐106 has the best C₂H₆/CH₄ selectivity. The breakthrough simulations indicate that all three MOFs have good capability for separating C2 hydrocarbons from C3 hydrocarbons. The pulse chromatographic simulations also indicate that all three MOFs are able to separate CH₄/C₂H₄/C₂H₆/C₃H₈ mixture into three different fractions of C1, C2 and C3 hydrocarbons.     

Urea-Induced Dissociation of Nerve Growth Factor from Venom of Chinese Cobra by SEC

The urea-induced dissociation of nerve growth factor from venom of Chinese cobra (_cNGF) was studied by intrinsic fluorescence emission spectra, SEC, urea-gradient polyacrylamide gel electrophoresis, assays of biological activity and thermodynamic parameters. The results showed that when urea concentration was lower than or equal to 4.0 mol L^?1 or higher than or equal to 8.0 mol L^?1, _cNGF existed only in native homodimer form or monomer form, respectively; whereas when urea concentration was higher than 4.0 mol L^?1 and lower than 8.0 mol L^?1, they existed simultaneously in the native homodimer and monomer forms and the former decreased, while the latter increased with the increase in urea concentration. Based on the association–dissociation equilibrium between _cNGF and urea molecules, an equation, which includes two characteristic dissociation parameters K and ?m, was presented to describe the urea-induced dissociation process of _cNGF. As the reaction temperature increased from 15 to 35 °C, positive enthalpy and entropy changes were observed, and the parameter K increased from 2.72 × 10^?13 to 5.18 × 10^?12 (L mol^?1), while the parameters ?m and ?G, respectively, decreased from 10.18 to 8.42 and from ?10.27 to ?18.67 (kJ mol^?1), which means that the urea-induced dissociation of _cNGF was spontaneous and entropy-driven and the higher temperature was favorable for the dissociation process. Using the procedures and equations mentioned in the paper, the urea-induced dissociation of _cNGF is first comprehensively described. Furthermore, this work presents a useful method for people to study the dissociation of dimer or multimer proteins induced by denaturants, inducers, pH, etc.     

Chiral dinaphthylporphyrin with C2 symmetry: synthesis,resolution, and enantio-discrimination by single-crystal X-ray diffraction analysis

An intrinsic chiral dinaphthylporphyrin with C₂ symmetry, namely [5,15-trans-bis(2-hydroxynaphthyl)-10-phenyl-20-(4-hydroxyphenyl)porphyrinato]zinc(??) (ZnDNP), has been designed and synthesized. The molecular structure of ZnDNP was determined by single crystal X-ray diffraction analysis. Resolution of the racemic mixture was achieved with chiral HPLC technique. In particular, the stereostructures of the enantiomers and the specific interactions between the chiral meso-dinaphthylporphyrin with l-Phe-OMe were elucidated in the solid state by single-crystal X-ray diffraction analysis.     

Robust method for the analysis of phytochelatins in rice by high‐performance liquid chromatography coupled with electrospray tandem mass spectrometry based on polymeric column materials

A sensitive and robust high‐performance liquid chromatography coupled with electrospray tandem mass spectrometry method for the identification and quantification of glutathione and phytochelatins from rice was developed. Homogenized samples were extracted with water containing 100 mM dithiothreitol, and solid‐phase extraction using polymer anion exchange resin was employed for sample purification. Chromatography was performed on a polymeric column with acetonitrile and water containing 0.1% formic acid as the mobile phase at the flow rate of 300 μL/min. The limit of quantitation was 6–100 nM. This assay showed excellent linearity for both glutathione and phytochelatins over physiological normal ranges, with correlation coefficients (r) > 0.9976. Recoveries for four biothiols were within the range of 76–118%, within relative standard deviations less than 15%. The intraday precision (n = 7) was 2.1–13.3%, and the interday precision over 15 days was 4.3–15.2%. The optimized method was applied to analyze tissue samples from rice grown using nutrient solutions with three different cadmium concentrations (0, 50, and 100 μM). With increasing cadmium concentrations, the content of phytochelatin 2 and phytochelatin 3 in rice roots increased, in contrast to most phytochelatins, and the content of glutathione in rice stems and roots decreased significantly.     

Influence of nano-alumina on curing kinetics and corrosion resistance of alumina based ceramic coatings

With thermal chemical reaction, the nano-alumina ceramic coatings were prepared on A3 steel. Influence of nano-alumina on curing kinetics was investigated by differential scanning calorimetry (DSC) analysis and thermogravimetric analysis (TGA). It was found that all samples show the outstanding heat resistance. However the temperature and the enthalpy of curing decreased with the increase in a nano-alumina content. A model was established to explain the decrease. The physical combination and the decrease in activation energy are the major reason for the decrease. Also electrochemical tests were conducted to investigate the corrosion behavior of the nano-alumina coatings. Corrosion current densities (i _corr) decreased with the increase in the nano-alumina content. This indicated that nano-alumina improved the corrosion resistance of the ceramic coatings. Because the uniformity of ceramic coatings is improved due to the fact that nano-alumina particles fill the pores and spaces of coatings, and nano-alumina particles provide the high physical combination between particles.

     

Solvothermal growth and morphology study of Cu2Se films

Solvothermal growth of cuprous selenide films on copper substrate has been succeeded by treating copper foil in the mixture of selenium powder and amines or hydrazine. The films were characterized by methods of XRD, SEM, TEM and optical spectra (Cu₂Se, JCPDS 47-1448). Films with hexagonal microcrystals can be obtained in hydrazine/water reaction system. When CTAB (CTAB = cetyltrimethylammonium bromide) is added to the system, the film is composed of thin leaf-like microcrystals. When ethylenediamine (en) is used as solvent, the leaf-like microcrystals are crimped.     

Simultaneous analysis of seven astragalosides in Radix Astragali and related preparations by liquid chromatography coupled with electrospray ionization time-of-flight mass spectrometry

A method has been developed for the qualitative and quantitative analysis of pharmacologically active astragalosides isolated from several species of the genus Astragalus by high performance liquid chromatography coupled with electrospray ionization time-of-flight mass spectrometry. Seven astragalosides in Radix Astragali and their commercial pharmaceutical preparations were analyzed using the developed method. The extracted ion current chromatograms were obtained from the total ion current chromatogram using the m/z of [M+Na]+ ions produced by target compounds for peak determination. The limits of detection and limits of quantification were in the range of 0.10-0.22 ng and 0.22-0.52 ng in full scan mode, respectively. All calibration curves showed good linear regression (r2 > or = 0.9965) within the test range. The overall intra- and inter-day precision was less than 2.86% for peak area and the accuracy was higher than 92.9% on using ginsenoside I as internal standard. The assay was successfully utilized to analyze the major biologically active astragalosides in six samples of Astragalus membranaceus (Fisch.) Bge var. mongholicus (Bge.) Hsiao. and eight commercial preparations. The overall results demonstrate that this method is simple, selective, and suitable for the quality control of Chinese medicine and their preparation in the low nanogram range.     

Asymmetric ring opening reaction of oxabenzonorbornadienes with amines promoted by iridium/NMDPP complex

As an efficient catalyst, the [Ir(COD)Cl]₂/NMDPP complex has been successfully applied to promote the asymmetric ring opening reaction of oxabenzonorbornadienes with various amines, which afforded the corresponding products in good yields (72–98%) with good enantioselectivities (80–90% ee).     

Catalytic reaction mechanism of L-lactate dehydrogenase: an ab initio study

Studies on the catalytic reaction mechanism of L-lactate dehydrogenase have been carried out by using quantum chemical ab initio calculation at HF/6-31G* level. It is found that the interconversion reaction of pyruvate to L-lactate is dominated by the hydride ion H_r transfer, and the transfers of the hydride ionH _r and protonH _r are a quasi-coupled process, in which the energy barrier of the transition state is about 168.37 kJ/mol. It is shown that the reactant complex is 87.61 kJ/mol lower, in energy, than the product complex. The most striking features in our calculated results are that pyridine ring of the model cofactor is a quasi-boat-like configuration in the transited state, which differs from a planar conformation in some previous semiempirical quantum chemical studies. On the other hand, the similarity in the structure and charge between theH _r transfer process and the hydrogen bonding with lower barrier indicates that the H_r transfer process occurs by means of an unusual manner. In addition, in the transition state the electrostatic interaction between the substrate and the active site of LDH is quite strong and the polarization of the carbonyl in the substrate is gradually enhanced accompanying the formation of the transition state. These calculated results are well in accord with the previous experimental studies, and indicate that the charge on the hydride ion H_r is only +0.13e in the transition state, which is in agreement with the reported semiempirical quantum chemical calculations.