Mechanistic Studies on Trichoacorenol Synthase from Amycolatopsis benzoatilytica

Isotopic labeling experiments performed with a newly identified bacterial trichoacorenol synthase established a 1,5-hydride shift occurring in the cyclization mechanism. During EI-MS analysis, major fragments of the sesquiterpenoid were shown to arise via cryptic hydrogen movements. Therefore, the interpretation of earlier results regarding the cyclization mechanism obtained by feeding experiments in Trichoderma is revised.     

Repurposing the Pummerer Rearrangement: Determination of Methionine Sulfoxides in Peptides

The reversible oxidation of methionine residues in proteins has emerged as a biologically important post-translational modification. However, detection and quantitation of methionine sulfoxide in proteins is difficult. Our aim is to develop a method for specifically derivatizing methionine sulfoxide residues. We report a Pummerer rearrangement of methionine sulfoxide treated sequentially with trimethylsilyl chloride and then 2-mercaptoimidazole or pyridine-2-thiol to produce a dithioacetal product. This derivative is stable to standard mass spectrometry conditions, and its formation identified oxidized methionine residues. The scope and requirements of dithioacetal formation are reported for methionine sulfoxide and model substrates. The reaction intermediates have been investigated by computational techniques and by ¹³C NMR spectroscopy. These provide evidence for an α-chlorinated intermediate. The derivatization allows for detection and quantitation of methionine sulfoxide in proteins by mass spectrometry and potentially by immunochemical methods.     

Environmental Control of Triplet Emission in Donor–Bridge–Acceptor Organometallics

Carbene‐metal‐amides (CMAs) are a promising family of donor–bridge–acceptor molecular charge‐transfer (CT) emitters for organic light‐emitting diodes. A universal approach is demonstrated to tune the energy of their CT emission. A blueshift of up to 210 meV is achievable in solid state via dilution in a polar host matrix. The origin of this shift has two components: constraint of thermally‐activated triplet diffusion, and electrostatic interactions between guest and polar host. This allows the emission of mid‐green CMA archetypes to be tuned to sky blue without chemical modifications. Monte‐Carlo simulations based on a Marcus‐type transfer integral successfully reproduce the concentration‐ and temperature‐dependent triplet diffusion process, revealing a substantial shift in the ensemble density of states in polar hosts. In gold‐bridged CMAs, this shift does not lead to a significant change in luminescence lifetime, thermal activation energy, reorganization energy, or intersystem crossing rate. These discoveries offer new insight into coupling between the singlet and triplet manifolds in CMA materials, revealing a dominant interaction between states of CT character. The same approach is employed using materials which have been chemically modified to alter the energy of their CT state directly, shifting the emission of sky‐blue chromophores into the practical blue range.     

一种袋装产品在线装车机械手设计

针对目前袋装产品在线装车主要靠人工完成,工人劳动强度大、装车效率低、环境恶劣等问题,设计了一种袋装产品在线装车机械手。给出了机械手的总体结构、主要功能和工作原理;重点设计了装有4个缓冲弹簧的双层落袋机构、可以补偿落料装置与货车车帮之间距离误差的摆动机构和落料门宽窄变换机构,减小了袋装产品下落时的冲击力,保证了袋装物料的完整性,实现了车厢空间的最大化利用,可以适应不同规格的袋装产品。对压缩弹簧和关键轴进行受力分析,从实用性和可靠性方面验证了结构设计的合理性。     

葡萄对白粉病与霜霉病的抗性机制

本文结合作者近7年来对葡萄白粉病与霜霉病的抗性研究,对葡萄植物抗白粉病与霜霉病的机制从组织结构生物化学物质两方面进行了综述与探讨。     

纸箱包装机纸板取送机构的设计与研究

针对纸箱包装机纸板取送机构的组成及工作原理,提出采用纸板吸取机构和输送机构的设计方案,介绍各部件的工作原理及分析结构原理,论述设计的合理性和实用性,实现快速输送,满足80箱/min纸箱包装机的供板需求。     

食品中γ-谷氨酰肽的研究进展

γ-谷氨酰肽是指含有γ-谷氨酰残基,能够激活人体钙敏感受体的一类小分子肽。γ-谷氨酰肽在自然界中广泛分布,其本身没有味道或者味道较淡,但添加少量即可增强味道的浓厚感,其凭借这一显著的呈味特性而受到广泛关注。该文对γ-谷氨酰肽的结构特征、呈味机制、制备方法及检测方法进行了综述,以期为γ-谷氨酰肽的深入研究和新型增味产品的研发提供理论参考。     

高含盐废水中TiO2复合光催化剂光降解甲基橙机制及性能

为深入分析盐离子对TiO₂基光催化剂降解有机物污染物过程的影响作用,通过空穴和自由基捕获剂的加入,研究了可见光激发下高含盐废水体系中光降解甲基橙的机制。在此基础上,探索了高含盐废水体系中TiO₂复合光催化剂对污染物降解性能提升的方法。结果表明:可见光激发催化剂形成的光生空穴是有机污染物降解的关键因素,废水体系中盐离子主要干扰体相中光催化反应;当有机污染物被大量吸附于催化剂表面时,盐离子的存在对光催化反应的干扰小;乙二醇热还原处理后的催化剂中Ti³⁺含量的增加,提升了催化剂的可见光响应和光催化活性;接枝于还原氧化石墨烯表面的少量乙二醇促进了催化剂对甲基橙的吸附,从而更有效地抵抗盐离子干扰。     

没食子酸及其衍生物对α-淀粉酶作用机制研究

实验采用碘-淀粉比色法研究没食子酸及其衍生物对α-淀粉酶的影响,结果显示:没食子酸和焦性没食子酸对α-淀粉酶具有明显的促进作用,而没食子酸酚羟基被甲基化后对α-淀粉酶的作用消失,说明酚羟基起到关键作用。当把没食子酸换成水杨酸后,对α-淀粉酶的作用由原来的促进变为抑制,说明没食子酸的三个酚羟基是缺一不可的。在探讨作用机制时发现,没食子酸的三个酚羟基可能是与α-淀粉酶三个催化所必需的酸性氨基酸残基形成稳定氢键、从而起到促进作用,而只有一个羟基的水杨酸与α-淀粉酶形成单键,可以旋转,不利于稳定α-淀粉酶的构象,从而起到抑制作用。根据本实验结果及大量文献资料可以得出以下结论:绝大多数具有酚羟基的化合物都能影响α-淀粉酶的活性,并且其作用机制都可能是通过与α-淀粉酶催化所必需的三个酸性氨基酸残基相结合来实现,其中只有一个酚羟基类的化合物可能只起到抑制作用。     

纤维素酶在染整加工应用中的若干问题(一)

阐述纤维素酶的作用机理，重点讨论了酶处理中的若干问题，包括搅动对纤维素酶处理效果的影响、表面活性剂对酶水解的影响；减量率与纤维素断裂强力和保水性的关系，以及棉织物酶处理后的性能的综合评价等。