Purification and Characterization of a Chymosin from Rhizopus microsporus var. rhizopodiformis

Purification and characterization of a chymosin from Rhizopus microsporus var. rhizopodiformis were investigated in the present study. A newly isolated R. microsporus var. rhizopodiformis F518 produced a high level of milk-clotting activity (1,001 SU/mL). A chymosin from the fungus was purified 3.66-fold with a recovery yield of 33.2 %. The enzyme appeared as a single protein band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) with a molecular mass of 37.0 kDa. It was optimally active at 60 °C and was stable up to 40 °C. The purified enzyme was an acid protease with an optimum pH of 5.2 and retained 80 % of residual activity within pH 2.0–8.0. The inhibition of 96 and 100 % by pepstatin A at 0.01 and 0.02 mM, respectively, revealed that the enzyme is an aspartic protease. Thus, high milk-clotting activity of the chymosin with good stability will strengthen the potential use of the chymosin as a substitute for calf rennet in cheese manufacturing.     

TiCl3-Mediated Synthesis of 2,3,3-Trisubstituted Indolenines: Total Synthesis of (+)-1,2-Dehydroaspidospermidine, (+)-Condyfoline,and (−)-Tubifoline

2,3,3-Trisubstituted indolenine constitutes an integral part of many biologically important monoterpene indole alkaloids. We report herein an unprecedented access to this skeleton by a TiCl₃-mediated reductive cyclization of tetrasubstituted alkenes bearing a 2-nitrophenyl substituent. The proof of concept is demonstrated firstly by accomplishing a concise total synthesis of (+)-1,2-dehydroaspidospermidine featuring a late-stage application of this key transformation. A sequence of reduction of nitroarene to nitrosoarene followed by 6π-electron-5-atom electrocyclization and a 1,2-alkyl shift of the resulting nitrone intermediate was proposed to account for the reaction outcome. A subsequent total synthesis of (+)-condyfoline not only illustrates the generality of the reaction, but also provides a mechanistic insight into the nature of the 1,2-alkyl shift. The exclusive formation of (+)-condyfoline indicates that the 1,2-alkyl migration follows a concerted Wagner–Meerwein pathway, rather than a stepwise retro-Mannich/Mannich reaction sequence. Conditions for almost quantitative conversion of (+)-condyfoline to (−)-tubifoline by way of a retro-Mannich/1,3-prototropy/transannular cyclization cascade are also documented.     

A ratiometric fluorescent probe with high sensitivity and selectivity for phosgene sensing in solution and gas

Phosgene has attracted wide attention because of its important applications and value in modern industry, agriculture, and other fields, though it easily leaks and is difficult to detect. In this work, we designed and synthesized a naphthalimide-based fluorescent probe, which is easy to prepare, stable, and able to discriminate between phosgene, acetyl chloride, oxalyl chloride, thionyl chloride, phosphorus oxychloride, and tosyl chloride. Our results indicate that the probe can react with phosgene selectively and sensitively, showing remarkable ratiometric fluorescence changes. Furthermore, the probe can be made into test strips, which can determine phosgene in air effectively. The present work provides a novel class of naphthalimide-based derivatives with potential application in phosgene sensing in real time simply and safely with further optimization.     

Combustion behavior and thermal stability of TPU composites based on layered yttrium hydroxides and graphene oxide

Journal of Thermal Analysis and Calorimetry - Layered yttrium hydroxides (LYH)- and graphene oxide (GO)-supported layered yttrium hydroxides (GO–LYH) were synthesized by a co-precipitation...     

Irreversible Amide‐Linked Covalent Organic Framework for Selective and Ultrafast Gold Recovery

Design of stable adsorbents for selective gold recovery with large capacity and fast adsorption kinetics is of great challenge, but significant for the economy and the environment. Herein, we show the design and preparation of an irreversible amide‐linked covalent organic framework (COF) JNU‐1 via a building block exchange strategy for efficient recovery of gold. JNU‐1 was synthesized through the exchange of 4,4′‐biphenyldicarboxaldehyde (BA) in mother COF TzBA consisting of 4,4′,4′′‐(1,3,5‐triazine‐2,4,6‐triyl)trianiline (Tz) and BA with terephthaloyl chloride. The irreversible amide linked JNU‐1 gave good stability, unprecedented fast kinetics, excellent selectivity and outstanding adsorption capacity for gold recovery. X‐ray photoelectron spectroscopy along with thermodynamic study and quantum mechanics calculation reveals that the excellent performance of JNU‐1 for gold recovery results from the formation of hydrogen bonds C(N)?H???Cl and coordinate interaction of O and Au. The rational design of irreversible bonds as both inherent linkage and functional groups in COFs is a promising way to prepare stable COFs for diverse applications.     

Photoredox/palladium-cocatalyzed enantioselective alkylation of secondary benzyl carbonates with 4-alkyl-1,4-dihydropyridines

A photoredox/palladium-cocatalyzed enantioselective alkylation of racemic secondary carbonates with 4-alkyl-1,4-dihydropyridines under visible light irradiation has been developed. The present study provides a method for the preparation of optically active diarylalkanes from racemic diarylmethyl carbonates by a dynamic kinetic asymmetric transformation(DYKAT).This photoredox/palladium dual catalysis strategy expands the scope of the asymmetric Pd-catalyzed benzylic substitution reaction and serves as its potential alternative and complement.     

家庭网络设备的远程管理技术

首先阐述了家庭网络设备远程管理的必要性、内容及相关技术问题;然后着重介绍了TR-069规范规定的网络架构、协议层次及远程管理系统的工作流程;最后结合实例分析了远程管理系统运行过程,     

Analysis and optimisation of grooved parallel slider bearings with cavitation

Meccanica - This paper introduces an analytical approach to optimize the textured bearing with cavitation to improve the load support. For this purpose, a grooved parallel slider bearing is...     

基于故事情景链语法的偶动画短片分析与建模

偶动画是动画领域一个重要的分支,与传统手绘动画同步出现,甚至更早。偶动画作品以其独特的拍摄方法和艺术魅力,为众多艺术家和观众所喜爱。偶动画影片设计周期长、工作量大、生产过程复杂、经济风险高,用传统手工工艺制作完成一部5 min的定格动画影片,通常需要数年。本文以丹麦知名动画导演克里多夫·皮拉丹的《柏树山上的风》及德国格里高利·祖坎导演的《龙焰火枪》为例,提出以故事情节(storyline(i)),?i∈1,2,…,n?与情景链（scenario?chain）语法有限集的形式语言表达式分解偶动画电影的故事元素,通过叙事空间（narrative?space）中镜头画面的组接逻辑,形成不同叙事结构,以分析定格动画电影的故事寓意（implied?meaning）,从故事计算的角度将其转化为标准化设计流程,为构建偶动画电影故事建模理论以及辅助智能计算提供思路,方法提高了偶动画电影的设计与制作效率,为多学科协同创作提供了新模式,使普通偶动画爱好者也能参与创作。