Electron transfer at Au surfaces modified by Tethered Osmium bipyridine–pyridine complexes

Chemically modified electrodes by the osmium complex tethered to Au surfaces by (1) reaction of cysteamine with the aldehyde (X=CHO), (2) mercapto alkanoic acid reaction with amine [X=(CH₂)₂NH₂], and (3) reduction of the diazonium salt of p-aminobenzoic acid and further amidation reaction with the amine derivative of the osmium complex [X=(CH₂)₂NH₂] were performed to explore the electron transfer properties of these redox-modified surfaces. The modified Au surfaces were characterized by infrared reflection absorption spectroscopy and resonant Raman spectroscopy. Cyclic voltammetry was used to study the electrochemical properties of the osmium complexes covalently attached to the surface as a function of the type and length of the tether. Dedicated to the memory of Professor Francisco (Chico) Nart.     

自由基S-腺苷甲硫氨酸酶中超交换作用以及交换增强对Fe4S4介导的SAM活化的调控机制

[4Fe-4S]依赖的自由基S-腺苷甲硫氨酸(SAM)蛋白是氧化还原酶的超家族,它们通过5′-脱氧腺苷自由基中间体催化一系列具有挑战性的转化. 尽管自由基S-腺苷甲硫氨酸酶的结构和功能已得到广泛研究,但这些酶中[4Fe-4S]簇的电子态对反应的依赖性仍不清楚. 本文通过量子力学/分子力学组合计算阐明了丙酮酸-甲酸裂解酶激活酶中[4Fe-4S]簇的电子态对S-腺苷甲硫氨酸活化的调控机制. 计算结果表明,自由基S-腺苷甲硫氨酸酶中S-腺苷甲硫氨酸的活化是由[4Fe-4S]簇中超交换和交换增强作用共同决定. [4Fe-4S]簇中的超交换耦合有利于两个相邻对之间的反铁磁耦合,这使得[4Fe-4S]¹⁺簇的α电子而不是β电子参与S-腺苷甲硫氨酸的活化. 同时在最有利于S-C5′还原裂解的电子态中,Fe4将贡献其α电子参与S-腺苷甲硫氨酸活化,以使Fe4原子获得最大交换相互作用. 这种超交换和交换增强的反应性构成自由基S-腺苷甲硫氨酸酶中[4Fe-4S]簇反应性调控的一般规则.     

STICTION AND ANTI—STICTION IN MEMS AND NEMS

Stiction in microelectromechanical systems (MEMS) has been a major failure mode ever since the advent of surface micromachining in the 80s of the last century due to large surfacearea-to-volume ratio. Even now when solutions to this problem are emerging, such as self-assembled monolayer (SAM) and other measures, stiction remains one of the most catastrophic failure modes in MEMS. A review is presented in this paper on stiction and anti-stiction in MEMS and nanoelectromechanical systems (NEMS). First, some new experimental observations of stiction in radio frequency (RF) MEMS switch and micromachined accelerometers are presented. Second, some criteria for stiction of microstructures in MEMS and NEMS due to surface forces (such as capillary, electrostatic, van der Waals, Casimir forces, etc.) are reviewed. The influence of surface roughness and environmental conditions (relative humidity and temperature) on stiction are also discussed. As hydrophobic films, the self-assembled monolayers (SAMs) turn out able to prevent release-related stiction effectively. The anti-stiction of SAMs in MEMS is reviewed in the last part. The project supported by the Distinguished Young Scholar Fund of NSFC (10225209), key project from the Chinese Academy of Sciences (KJCX2-SW-L2) and National “973” Project (G1999033103)     

建立在硫醇分子电化学替换组装基础上的纳米粒子区域化组装

利用金基底电位变化时硫醇自组装膜的吸脱附性质, 通过改变基底电位和组装溶液, 用电化学方法在金基底上实现了传统自组装技术难以实现的硫醇分子的替换组装; 通过金基底的分区化设计, 用控制电位的组装技术在基底的不同微区内制备了不同末端官能团的硫醇及其衍生物自组装膜; 并在此基础上实现了纳米粒子的区域化组装.     

Surface anchoring of a chiral salen macrocycle on a carboxy‐functionalized platform via a multiple site esterification

This paper reports on the synthesis and surface immobilization of a 40‐membered chiral salen macrocycle via a surface reaction between its hydroxyl‐terminated branches and a carboxy‐functionalized platform using N,N′‐dicyclohexylcarbodiimide (DCC) as activating molecule of the carboxylic group of 11‐mercaptoundecanoic acid, SAM. The peculiarity of this surface reaction at the carboxy‐terminated platform is that a multiple site esterification is obtained, as indicated by time‐of‐flight secondary ion mass spectrometry measurements. Copyright © 2010 John Wiley & Sons, Ltd.     

Exploring the Biosynthetic Potential of TsrM,a B12-dependent Radical SAM Methyltransferase Catalyzing Non-radical Reactions

B₁₂-dependent radical SAM enzymes are an emerging enzyme family with approximately 200,000 proteins. These enzymes have been shown to catalyze chemically challenging reactions such as methyl transfer to sp2- and sp3-hybridized carbon atoms. However, to date we have little information regarding their complex mechanisms and their biosynthetic potential. Here we show, using X-ray absorption spectroscopy, mutagenesis and synthetic probes that the vitamin B₁₂-dependent radical SAM enzyme TsrM catalyzes not only C- but also N-methyl transfer reactions further expanding its synthetic versatility. We also demonstrate that TsrM has the unique ability to directly transfer a methyl group to the benzyl core of tryptophan, including the least reactive position C4. Collectively, our study supports that TsrM catalyzes non-radical reactions and establishes the usefulness of radical SAM enzymes for novel biosynthetic schemes including serial alkylation reactions at particularly inert C−H bonds.     

基于聚多巴胺辅助自组装单分子层技术的PTFE表面修饰及其内皮细胞选择性黏附研究

利用聚多巴胺技术对PTFE进行表面改性,X射线光电子能谱(XPS)、椭偏、接触角以及石英晶体微天平(QCM-D)证实DOPA分子可以在PTFE表面自聚形成反应性的超薄膜功能涂层,并通过聚多巴胺辅助自组装单分子层(SAM)技术构建了活性多肽链段CGREDVDY的界面.细胞黏附实验反映活性链段CGREDVDY的修饰表面具备良好的内皮细胞选择性黏附能力.这种具有内皮细胞选择性黏附能力的界面有望实现材料在复杂生理环境中对内皮细胞的原位诱导,为制备具有血管内皮原位快速愈合功能的新型血液相容性人造血管提供新途径.     

In vitro methylation by methanol: Proteomic screening and prevalence investigation

It is assumed that much more functional importance for protein activity than expected may be granted by methylation that occurs at the side-chain of aspartate or glutamate residue. In vitro methylation mainly comes from the use of methanol in sample preparation prior to MS analysis. In this study, we first performed the methylation site-directed proteomic screening of bovine serum albumin, ovalbumin and 20S proteasome for gel staining using a meaningfully indicative MS-pattern of peak tag (termed as 4P tag) and manual inspection for mass spectral data. As a result, there were 17 proteolytic peptides with 20 modified sites confirmed to be in vitro methylated. Subsequently, the prevalence investigation was performed, focusing on the reaction kinetic behavior of in vitro methylation. This study provided a simple and robust approach for confirmation of in vitro methylation by methanol, as well as the precautious guide for the use of methanol in proteomic study.     

Self-assembled monolayers of flufenaminate anions on mild steel surface formed in aqueous solution

Adsorption of derivative of phenylanthranilic acid - flufenamic acid (FFA) on the “oxide-free” and oxidized surface of mild steel in neutral borate buffer solution was studied by ellipsometry and XPS. Anodic polarization curves reveal that complete suppression of the anodic dissolution of iron is achieved at FFA concentration C_in = 3.8 mM. Besides, adding FFA substantially shifts the pitting potential from 0.06 V to 0.67 V. Ellipsometric studies have shown that at the applied potential −0.65 V, when the surface is free from the oxide layer, FFA forms monomolecular layer. To characterize the surface layers formed after exposing the sample in 5 mM FFA solution the XPS was used to assess the composition and the thickness of the layers. Using the intensities of the Fe 2p, Fe 3p, N 1s, F 1s, O 1s and C 1s and analyzing the angle resolved XPS data the FFA molecules have been shown to form monomolecular layer in which FFA is (vertically or slightly inclined) anchored by iron cations through oxygen atoms of carboxyl group to the surface and the fluorine atoms of CF₃ groups form the utmost layer. Similar orientation is also assumed for FFA molecules adsorbed on the oxidized iron surface. It seems that the layer formed by FFA or similar molecules may serve a robust interface for grafting other substances on such a functionalized surface.