Systematic screening and characterization of novel bufadienolides from toad skin using ultra‐performance liquid chromatography/electrospray ionization quadrupole time‐of‐flight mass spectrometry

During the discovery process of novel compounds, it is of significant importance to differentiate novel from known compounds in crude extracts before starting the time‐consuming process of purification. Bufadienolides are the main active components of the skin of the toad Bufo bufo gargarizans Cantor (toad skin), an important traditional Chinese medicine. The fragmentation behavior and mass spectra profiles of bufadienolides standards were investigated using ultra‐performance liquid chromatography/electrospray ionization quadrupole time‐of‐flight mass spectrometry (UPLC/ESI‐Q‐TOFMS). Several fragmentation rules were summarized and applied to characterize novel and known bufadienolides in toad skin. Characteristic substituent groups could be identified by both diagnostic ions and their relative abundance. Bufadienolide stereoisomers could be differentiated from positional isomers by comparing fragment abundance profiles. This was used to characterize new stereoisomers for known bufadienolides. A total of 39 bufadienolides were screened out using a systematic method developed in our laboratory. In addition to 19 known bufadienolides, 20 putative novel compounds, including 8 stereoisomers, were characterized. UPLC/Q‐TOFMS was demonstrated to be a powerful tool for the characterization of low‐abundance bufadienolides in complex samples. This study provides guidelines for the targeted isolation of novel bufadienolides from natural products. Copyright © 2010 John Wiley & Sons, Ltd.     

生态平衡制约下离散尺度结构种群的最优收获

研究基于扩展Leslie投影矩阵的离散尺度结构种群模型的最优收获问题,约束条件包括生态平衡和开发成本等.运用凸优化理论证明了最优收获策略的存在性,导出了最优收获模式,应用模型参数给出了收获比率.结论显示:最优策略具有两阶段结构.     

Computational and experimental analysis of wound healing processes

Wound healing in epidermis is a complex physiological process in which new cells are created to repair the damaged tissue. The timing of cell division and growth mechanisms in wound healing are influenced by biological, mechanical and medical factors. In this work we aim to provide a numerical model based on the observations realised in in-vitro experiments for the understanding of wound healing. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phenol-formaldehyde resin route to the synthesis of several iron group transition metal phosphides

Abstract

A series of iron, cobalt and nickel metal phosphides of chemical formula Fe_xP, Co₂P and Ni₂P with high specific surface areas of 331.1, 294.2 and 228.0 m² g^?1, respectively, was firstly synthesized by phenol-formaldehyde resin route. It was found that the as-prepared Co₂P and Ni₂P samples synthesized using phenol-formaldehyde resin as a carbon source showed much higher BET surface areas than those prepared using other carbon sources reported before, including cinnamic strong alkali anion exchange resin, p-phenylenediamine and hexamethylenetetramine. This phenol-formaldehyde resin route was proved to be as universal as traditional H₂ reduction method.     

Binding of Ionic Pyrene Derivatives to Polyelectrolytes. A Uv Absorption and Fluorescence Study

Abstract

The binding of pyrenesulfonic acid and pyrenebutyric acid to poly(vinyl benzyl trimethylammonium) chloride was investigated by UV and fluorescence spectroscopy. It was found that the binding constant was 7.5 × 10⁴ and 3.5 × 10⁴M^?1, respectively. The addition of the polyelectrolyte quenches the fluorescence of the pyrene group, and at the same time the typical excimer emission appears. This emission originates in pre-formed ground state aggregates of the pyrene derivatives incorporated into the polyion domain. Similar effects were observed when anionic polyelectrolytes, poly(styrene sulfonic), and poly(vinyl sulfonic) acids were added to cationic pyrene derivatives. The binding constants depend on the length of the aliphatic sidechain of the derivatives.     

Photoreduction of Alkyl Polyviologens and Their Low Molecular Analogs in PVA Matrix

The photoreduction behavior of alkyl viologen compounds in a PVA matrix was investigated. The initial photoreduction of alkyl viologens and related polyviologens follows second-order reaction kinetics, and the respective rate constants, which vary only slightly with alkyl chain length, were determined. While the polymer effect was not remarkable in a PVA matrix, the association behavior of radical cations was similar to that found in a 2-propanol aqueous solution.