Facile evolution of asymmetric organocatalysts in water assisted by surfactant Brønsted acids

Simple mixing of chiral amines and surfactant Brønsted acids such as p-dodecyl benzenesulfonic acid (DBSA) leads to highly effective and selective organocatalysts in water. The in situ generated catalysts catalyze highly stereoselective desymmetrization of prochiral ketones via direct aldol reactions (up to >16:1 dr, >99% ee) in water using micelle as reaction media. The current strategy was also applied in asymmetric Michael addition leading to a catalytic system with good activity and stereoselectivity.     

Ultrafast dynamics in ZnO thin films irradiated by femtosecond lasers

The damage morphologies, threshold fluences in ZnO films were studied with femtosecond laser pulses. Time-resolved reflectivity and transmissivity have been measured by the pump-probe technique at different pump fluences and wavelengths. The results indicate that two-phase transition is the dominant damage mechanism, which is similar to that in narrow band gap semiconductors. The estimated energy loss rate of conduction electrons is 1.5 eV/ps.     

Preparation of monodisperse nanoparticles containing poly(propylene imine)(NH2)32‐polystyrene

Polypropylenimine dendrimer (DAB‐Am‐32, generation 4.0) was converted into a macroinitiator DAB‐Am‐32‐Cl via reaction with 2‐chloropropionyl chloride. Monodisperse nanoparticles containing poly(propylene imine)(NH₂)₃₂‐polystyrene were prepared by emulsion atom transfer radical polymerization (ATRP) of styrene (St), using the DAB‐Am‐32‐Cl/CuCl/bpy as initiating system. The structure of macroinitiator was characterized by FTIR spectrum, ¹H NMR, and ¹³C NMR. The structure of poly(propylene imine)(NH₂)₃₂‐polystyrene was characterized by FT‐IR spectrum and ¹H NMR; the molecular weight and molecular weight distribution of poly(propylene imine)(NH₂)₃₂‐polystyrene were characterized by gel permeation chromatograph (GPC). The morphology, size and size distribution of the nanoparticles were characterized by photon correlation spectroscopy (PCS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The effects of monomer/macroinitiator ratio and surfactant concentration on the size and size distribution of the nanoparticles were investigated. It was found that the diameters of the nanoparticles were smaller than 100 nm (30–80 nm) and monodisperse; moreover, the particle size could be controlled by monomer/macroinitiator ratios and surfactant concentration. With the increasing of the ratio of St/DAB‐Am‐32‐Cl, the number‐average diameter (D_n), weight‐average diameter (D_w) were both increased gradually. With enhancing the surfactant concentration, the measured D_h of the nanoparticles decreased, while the polydispersity increased. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2892–2904, 2009     

Copula函数中参数极大似然估计的性质

设m维随机变量X＝(X1,X2,…,Xm)的copula函数为C(u1,u2,…,um);α)＝C((F1(x1),F2(x2),…,Fm(xm));α),本文在(X1,X2,…,Xm)的样本空间和(U1,U2,…Um)的样本空间上讨论了m元copula函数中参数α的极大似然估计,得到了边缘分布函数连续时,两样本空间上参数α的极大似然估计和最大后验估计的等价性;而边缘分布函数不连续时,两样本空间上参数α的极大似然估计和最大后验估计的渐近等价性.     

An analytic solution for interlaminar stresses in a fiber-reinforced double-layer cylindrical shell

The present paper investigates the basic characteristics of the interlaminar stresses in a double-layer cylindrical shell with both ends simply-supported under uniform external or internal pressure. The double layer shell is composed of a 0° fiber-reinforced composite layer and an isotropic layer. In this paper, this axisymmetric problem is solved exactly with the three-dimensional theory of elasticity. Both the displacement field and the stress field of each layer of the shell are expressed in Fourier series and Fourier-Bessel series. Then we illustrate the effects of the various parameters, such as geometry, material constants, loading conditions and stacking sequence, on the interlaminar stresses.     

Isothermal titration calorimetry vs. high performance liquid chromatography fingerprint

Chinese Medicine Injections (CMIs) are powerful preparations, but adverse drug reactions can hardly be avoided. Incorrect drug combination is a major cause. Recently, insoluble particulate matter test, pH measurement, and high performance liquid chromatography (HPLC) fingerprint have been recommended as potential strategies for prediction of drug-incompatible reactions. However, these methods were complex to manipulate, subjective to judge, or were of poor relevance and low sensitivity. In this study, a novel application for the detection of compatibility of combination of CMIs based on isothermal titration calorimetry (ITC) has been proposed. Qingkailing Injection (QKL) was selected as a representative drug to blend with Potassium Chloride Injection (KCl) and Calcium Chloride Injection (CaCl₂). The type of reactions between them was intuitively manifested by the thermodynamic parameters including Gibbs free energy change (ΔG), enthalpy change (ΔH), and entropy change (ΔS). The results indicated that when QKL mixed with CaCl₂, ΔG < 0, and |ΔH| > T|ΔS|, which meant chemical changes happened between them and ADRs might happen in clinic. On the contrary, the reactions between QKL and KCl existed solely as physical processes, indicating that it was relatively safe. Meanwhile, HPLC fingerprint was also applied, but no significant difference was found. It is hard to distinguish whether incompatible reactions have happened during HPLC. The study suggested that with the advantages of convenience, sensitivity, and reliability, ITC could serve as an essential tool in the detection of incompatible reactions of drug combination. The described method could be used for early prediction of adverse drug reactions, which would be helpful to ensure the rationality of drug combination.     

Examining the Performance of Two Extraction Solvent Systems on Phenolic Constituents from U.S. Southeastern Blackberries

Two common extraction solvent systems, namely acidified aqueous methanol and acidified aqueous acetone, were used to extract blackberry phenolics, and the antioxidant properties of the recovered extracts were compared. The crude extracts were fractionated into low- and high-molecular-weight phenolics by Sephadex LH-20 column chromatography. The hydrophilic-oxygen radical absorbance capacity (H-ORAC_FL), ferric reducing antioxidant power (FRAP), and the cellular antioxidant activity (CAA) assays were employed as indices to assess antioxidant capacity of the extracts and their respective fractions. The methanolic solvent system displayed a greater efficiency at extracting anthocyanin and flavonol constituents from the blackberries, while the acetonic solvent system was better at extracting flavan-3-ols and tannins. Anthocyanins were the dominant phenolic class found in the blackberries with 138.7 ± 9.8 mg C3G eq./100 g f.w. when using methanol as the extractant and 114.6 ± 3.4 mg C3G eq./100 g f.w. when using acetone. In terms of overall antioxidant capacity of blackberry phenolics, the acetonic solvent system was superior. Though present only as a small percentage of the total phenolics in each crude extract, the flavan-3-ols (42.37 ± 2.44 and 51.44 ± 3.15 mg/100 g f.w. in MLF and ALF, respectively) and ellagitannins (5.15 ± 0.78 and 9.31 ± 0.63 mg/100 g f.w. in MHF and AHF, respectively) appear to account for the differences in the observed antioxidant activity between the two solvent systems.     

Chitosan‐Capped Mesoporous Silica Nanoparticles as pH‐Responsive Nanocarriers for Controlled Drug Release

Herein, we present a straightforward synthesis of pH‐responsive chitosan‐capped mesoporous silica nanoparticles (MSNs). These MCM‐41‐type MSNs could be used as nanocapsules to accommodate guest molecules. Subsequently, (3‐glycidyloxypropyl)trimethoxysilane was grafted onto the surface of the MSNs, which served as a bridge to link between MSNs and chitosan, which is ubiquitous in nature and commercially available. Owing to the pH‐responsive and biocompatible features of chitosan, the loading and release of an anti‐cancer drug, doxorubicin hydrochloride, were carried out in vitro, in which the composite chitosan‐capped MSNs (CS‐MSNs) showed excellent environmental response. As the pH value of the media decreased, the degree of drug release correspondingly increased. Moreover, thanks to the perfect biocompatibility of chitosan, the CS‐MSNs exhibited lower cytotoxicity than that of the naked MSNs in an MTT assay. In addition, the in vitro kill potency against MCF‐7 breast‐cancer cells was enhanced over time, as well as with increasing concentration of the drug‐loaded CS‐MSNs. These results indicate that CS‐MSNs are promising candidates for pH‐responsive drug delivery in cancer therapy.     

Femtosecond laser-induced breakdown of multilayers and gold film

We report single-shot damage threshold as a function of pulse duration (50 - 900 fs) for MgF2/ZnS 800-nm omnidirectional-reflection film, interference filter, and gold film. The results indicate that the damage with ultrashort pulse is nonthermal, which is different from that with long pulse. Additionally,the ablation crater depths of 45° high-reflection film and interference filter are presented. A logarithmic relation between the ablation depth and pulse fluence, which is similar to that of transparent materials, is found.