Non-Covalent Interaction-Controlled Site-Selective C−H Transformations

Site-selective C−H transformations are important to obtain desired compounds as single products in a highly efficient manner. However, it is generally difficult to achieve such transformations because organic substrates contain many C−H bonds with similar reactivities. Therefore, the development of practical and efficient methods for controlling site selectivity is highly desirable. The most frequently used strategy is “directing group method”. Although this method is highly effective and promotes site-selective reactions, it has several limitations. Our group recently reported other methods to achieve site-selective C−H transformations using non-covalent interactions between a substrate and a reagent or a catalyst and a substrate (non-covalent method). In this personal account, the background of site-selective C−H transformations, our reaction design to achieve site-selective C−H transformations, and recently reported reactions are explained.     

利用VSV标记具有特定投射的特异类型神经元的精细结构

神经元是构成神经系统的基本单位之一，对其精细形态结构的研究是了解神经网络构筑和信息处理方式的基础，然而目前缺乏能够标记具有特定投射特征的特异类型神经元精细结构的有效方法.在糖蛋白基因缺失的水泡性口炎病毒（VSV）毒株基础上突变其核蛋白，我们获得了重组病毒VSV-△G-NR7A-EGFP，并发现该病毒在一定窗口期内可实现神经元形态的快速高亮度标记；我们进一步在此基础上构建了VSV-△G-EnvA-NR7A-EGFP病毒，并基于特定的转基因动物及辅助病毒rAAV-EF1α-Dio-Bfp-Tva，通过控制注射位点，分别实现了有NAc-LH投射特异性的D2R神经元和VTA-NAc投射特异性的多巴胺神经元的标记，展示了一种可用于稀疏、高亮地标记具有特定投射特征的特异类型神经元精细结构的新方法.     

Communication network formation with link specificity and value transferability

We model strategic communication network formation with (i) link specificity: link maintenance lowers specific attention and thus value (negative externality previously ignored for communication) and (ii) value transferability via indirect links for informational but not for social value (positive externality modeled uniformly before). Assuming only social value, the pairwise stable set includes many nonstandard networks under high and particular combinations of complete components under low link specificity. Allowing for social and informational value reduces this set to certain fragmented networks under high and the complete network under low link specificity. These extremes are efficient, whereas intermediate link specificity generates inefficiency.     

The first total synthesis of (−)-bitungolide E

The first total synthesis of (−)-bitungolide E is described. The key steps include a Myers’ alkylation, modified Evans’ syn aldol-reaction, using Crimmins protocol, Sharpless asymmetric epoxidation and ring-closing metathesis reaction.     

羰基还原酶辅酶结合域位点突变对其不对称催化性能的影响

基于同源模型的比较和分析,发现羰基还原酶SCR1辅酶结合域P124和W125位点对辅酶NADPH的结合形成了一定的空间位阻效应.通过对该位点进行小侧基氨基酸的取代突变,该酶的底物专一性和立体选择性均发生了不同程度的改变,表明该位点是酶与辅酶有效结合的关键位点,而且它与辅酶结合的空间效应进一步影响了底物结合域活性中心对不同构型的底物及其对映体产物的亲和作用.在底物专一性方面,野生型酶对2-羟基苯乙酮和2-溴苯乙酮及其衍生物等底物表现出较高的催化活性,而突变株W125A,W125G,P124A/W125A和P124G/W125G对苯乙酮及其部分衍生物和2-辛酮等底物的催化活性均有所提高.对于酶的立体选择性,部分突变株发生了转化产物对映体构型反转的现象,突变株P124A/W125A和P124G/W125G催化还原2-羟基苯乙酮和4-氯乙酰乙酸乙酯均生成了(R)-型产物.     

DFT plus PCM calculation for pairing specificity of Watson–Crick‐type bases in aqueous solutions

This study is aimed at explaining the preference for AT and CG pairings and the possible insertion of other tautomeric DNA base pairs such as G_enolT, that respect energetic and steric requirements including at least two hydrogen bonds and 11 ± 0.5Å distance between the 9‐CH₃ of purine and 5‐CH₃ of pyrimidine. The calculated free energy of formation ΔΔG at the DFT B3LYP/6‐31G*‐PCM/BEM level pointed out the CG and AT pairs as the most favored, followed closely by G_enolT, in good agreement with Michaelis–Menten first order kinetics (CG ≈ AT > G_enolT). Unusual DNA base pairs complexes such as AG (BEM) and CT (PCM) resulted to be stable, but it is very difficult to assume that they are likely to be included in the double strand DNA. The calculated enthalpy and dipole moments of isolated DNA bases agree well with experiment. The free energy of hydration, ΔG_hyd, was found to depend on the electrostatic term, while cavitation‐dispersion components are almost constant. The stability of DNA complexes in water resulted from PCM calculations is markedly influenced by the free energy of hydration. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Broad specificity indirect competitive immunoassay for determination of nitrofurans in animal feeds

A generic hapten of nitrofurans was synthesized by derivatization of 5-nitrofurfural with diamine, and the hapten was coupled to carrier protein to prepare different immunogens and coating antigens by using diazotization method and glutaraldehyde method. The obtained novel polyclonal antibodies from immunized rabbits showed broad cross reactivity among seven nitrofurans. After assessment of four coating antigen/antibody combinations, an indirect competitive immunoassay was developed to simultaneously detect the seven nitrofurans in animal feeds. The limits of detection for these analytes were in the range of 5-16 μg kg⁻¹ depending on the compound. Recoveries from nitrofurans fortified blank feeds at levels of 30 and 100 ng g ⁻¹ were in a range of 82.6-108.4% with coefficients of variation lower than 11.4%. The immunoassay was further validated by a HPLC method and the two methods showed good correlation (r = 0.9924). Therefore, the proposed immunoassay could be used as a practical method to monitor the illicit use of nitrofurans in animal feeds.