沿直线的垂直方向匀速直线运动的带电直线的电场

本文利用相对论变换关系计算了沿直线的垂直方向匀速运动的带电直线的电场.     

Reductive radical-initiated 1,2-C migration assisted by an azidyl group

We report here a novel reductive radical-polar crossover reaction that is a reductive radical-initiated 1,2-C migration of 2-azido allyl alcohols enabled by an azidyl group. The reaction tolerates diverse migrating groups, such as alkyl, alkenyl, and aryl groups, allowing access to n+1 ring expansion of small to large rings. The possibility of directly using propargyl alcohols in one-pot is also described. Mechanistic studies indicated that an azidyl group is a good leaving group and provides a driving force for the 1,2-C migration.

We report here a novel reductive radical-polar crossover reaction that is a reductive radical-initiated 1,2-C migration of 2-azido allyl alcohols enabled by an azidyl group.

Since the groups of Ryu and Sonoda described the reductive radical-polar crossover (RRPCO) concept in the 1990s,¹ it has attracted considerable attention in modern organic synthesis.² By using this concept, a variety of complex molecules could be assembled in a fast step-economic fashion which is not possible using either radical or polar chemistry alone. However, only two RRPCO reaction modes are known to date: nucleophilic addition and nucleophilic substitution (Fig. 1A). The first RRPCO reaction is the nucleophilic addition of organometallic species, which is generated in situ from the reduction of a strong reducing metal with a carbon-centered radical intermediate and cations (E⁺ = H⁺, I⁺, Br⁺, path 1).³ However, the necessity for a large amount of harmful and strong reducing metals has greatly limited the scope and functional group tolerance of the reaction. Recently, photoredox catalysis has not only successfully overcome the shortcomings of using toxic strong reducing metals in the RRPCO reaction,⁴ but also enabled the development of several new RRPCO reaction types, including the nucleophilic addition with carbonyl compounds or carbon dioxide (path 2),⁵ the cyclization of alkyl halides/tosylates (path 3),⁶ and β-fluorine elimination (path 4).⁷ Although the RRPCO reaction has been greatly advanced by photoredox catalysis, it is still in its infancy, and the development of a novel RRPCO reaction is of great importance.Open in a separate windowFig. 1(A) Reductive radical-polar crossover reactions; (B) this work: reductive radical-initiated 1,2-C migration assisted by an azidyl group.Herein, we wish to report a new type of reductive radical-polar crossover cascade reaction that is the reductive radical-initiated 1,2-C migration under metal-free conditions (Fig. 1B). The development of this approach is not only to further expand the application of the RRPCO reaction, but also to solve the problems associated with the oxidative radical-initiated 1,2-C migration, such as the necessity for an oxidant and/or transition metal for the oxidative termination of the radicals, and also required sufficient ring strain to avoid the generation of epoxy byproducts.⁸ To realize this reaction, a driving force is needed to drive the 1,2-C migration after reductive termination, to avoid the otherwise inevitable protonation of the generated anion.⁹ Inspired by the leaving group-induced semipinacol rearrangement,¹⁰ we envisaged that 2-azidoallyl alcohols¹¹ might be the ideal substrates for the reductive radical-initiated 1,2-C migration because these compounds contain both an allylic alcohol motif, which is vital for the radical-initiated 1,2-C migration, and an azidyl group, a good leaving group,¹² which may facilitate the 1,2-C migration after the reductive termination of the radicals.With the optimal conditions established (ESI, Table S1^†), we then explored the scope of this radical-initiated 1,2-migration. As shown in Table 1, a series of naphthenic allylic alcohols could undergo n+1 ring expansion with minimal impact on the product yield (Table 1, 3aa–aq). Notably, only the alkyl groups were migrated when using benzonaphthenic allylic alcohols in the reaction. These results might be attributed to the aryl group possessing greater steric resistance. The structure of 3an was further verified by single-crystal diffraction. Interestingly, the vinyl azide derived from a pharmaceutical ethisterone was also a viable substrate, affording the migration product 3aq in 57% yield, which highlighted the applicability of this strategy in the late-stage modification of pharmaceuticals. Moreover, the acyclic allylic alcohol with an alkyl chain also successfully delivered the migration product 3ar in 64% yield.Substrate scope of 2-azidoallyl alcohols^ab

尼龙－1010的聚集态结构

用ＷＡＸＤ、ＤＳＣ、方差－范围函数．密度测量等方法，研究了经不同热处理的尼龙－１０１０的聚集态结构．发现退火处理更有利于尼龙－１０１０结晶的生成和稳定，且尼龙－１０１０的结晶，有一个最佳的热处理温度．在该温度附近，尼龙－１０１０的结晶度和微晶尺寸里最大值．     

热致液晶乙基纤维素与尼龙－1010共混物的研究

在自制单螺杆小型挤出机上通过熔融共混的办法，制备了不同配比（５／９５—２５／７５）的ＥＣ／Ｎｙｌｏｎ—１０１０共混物．用ＷＡＸＤ、ＤＳＣ、毛细管流变仪、力学性能测试等方法对共混物进行了研究．发现共混后尼龙－１０１０的形态结构有明显改变，其强度、模量都有提高，在高剪切速率下，共混物粘度大大降低．配比为１５８５时，这些性能的改进尤为明显．     

Neutron activation analysis of extractable organohalogens in milk from China

Instrumental neutron activation analysis (INAA) has been used for the determination of extractable organohalogens (EOX) in milk. The detection limits are 50 ng, 8 ng and 3.5 ng for Cl, Br and I, respectively. The EOX concentrations in milk samples from various regions of China were determined. Meanwhile, organochlorine pesticides residues were detected by gas chromatography. The concentrations of the EOX in the milk samples are decreasing in the order of EOCl >> EOBr > EOI, and EOCl accounts for 95% of the total EOX. The average concentration of EOCl in milk is 4.44 ·g/g expressed as fat weight basis, with the highest value of 17.6 ·g/g from South China. The mean concentrations of total HCH and DDT are 0.038 ·g/g and 0.046 ·g/g, respectively. Organochlorine pesticides account only for 1.6% of the EOCl, indicating the very high proportion of the unknown EOCl in the milk sample. This revised version was published online in August 2006 with corrections to the Cover Date.     

Surface‐Passivated SBA‐15‐Supported Gold Nanoparticles: Highly Improved Catalytic Activity and Selectivity toward Hydrophobic Substrates

Silanol groups on a silica surface affect the activity of immobilized catalysts because they can influence the hydrophilicity/hydrophobicity, matter transfer, or even transition state in a catalytic reaction. Previously, these silanol groups have usually been passivated by using surface‐passivation reagents, such as alkoxysilanes, bis‐silylamine reagents, chlorosilanes, etc., and surface passivation has typically been found in mesoporous‐silicas‐supported molecular catalysts and heteroatomic catalysts. However, this property has rarely been reported in mesoporous‐silicas‐supported metal‐nanoparticle catalysts. Herein, we prepared an almost‐superhydrophobic SBA‐15‐supported gold‐nanoparticle catalyst by using surface passivation, in which the catalytic activity increased more than 14 times for the reduction of nitrobenzene compared with non‐passivated SBA‐15. In addition, this catalyst can selectively catalyze hydrophobic molecules under our experimental conditions, owing to its high (almost superhydrophobic) hydrophobic properties.     

Clickable SBA‐15 to Screen Functional Groups for Adsorption of Antibiotics

Pharmaceutical antibiotics, as emerging contaminants, are usually composed of several functional groups that endow them with the ability to interact with adsorbents through different interactions. This makes the preparation of adsorbents tedious and time‐consuming to screen appropriate functionalized materials. Herein, we describe the synthesis of clickable SBA‐15 and demonstrate its feasibility as a screening material for the adsorption of antibiotics based on similar adsorption trends on materials with similar functional groups obtained by a click reaction and cocondensation/grafting methods.     

可控表面磷原子修饰提升超细W2C纳米颗粒电解水析氢反应性能

研究高活性和稳定性的非贵金属基析氢催化剂对解决当前能源危机和环境污染问题具有重要意义.碳化钨具有与贵金属Pt类似的d带电子结构,因而成为一类新兴的非贵金属析氢催化剂,受到广泛关注.磷掺杂是提高催化剂析氢活性的有效方法之一,然而目前最常见的构筑磷掺杂方法是使用多金属氧酸盐(POMs,如H3PW12O40),其固定的W/P原子比导致W2C中的掺杂浓度难以调控,并且磷掺杂主要是进入碳载体而不是碳化物本身,从而导致无法明确杂原子对其电催化析氢活性的贡献.本文采用植酸(PA)为磷源设计合成了可控磷掺杂W2C纳米颗粒,并探讨了催化剂组分、杂原子掺杂位置与析氢性能之间的关系.深入研究了磷掺杂碳化钨(WCP)的化学结构和析氢活性.与原始的W2C催化剂相比,WCP具有更高的本征活性、更快的电子转移速率和更多的活性位数量,并且在酸性和碱性条件下均表现出较好的析氢性能.特别是过电位为-200 mV时,WCP催化剂的本征活性在酸性和碱性条件下分别为0.07和0.56 H2 s-1,高出纯W2C(0.01和0.05 H2 S-1)数倍.同时,在电流密度为-10 mA cm-2时,优化后的WCP催化剂在酸性和碱性条件下的析氢过电位分别降低了96和88 mV.XPS及EDS元素分析结果表明,随磷源添加量增加,磷掺杂从碳化钨表面逐渐向内部扩散,进一步说明磷取代位置与析氢活性之间的构效关系,高浓度的表面磷取代可以加速质子捕获过程,从而显著提高其析氢活性,而过量的内部磷取代会破坏W2C结构,降低电子转移速率,从而导致析氢性能下降.利用密度泛函理论计算深入研究了WCP具有较好析氢性能的原因,与内部磷取代相比,表面磷取代会使碳化钨表现出更合适的氢吸附自由能,并且更加有效地降低了氢释放势垒,从而优化了析氢反应动力学.综上,本文为元素掺杂工艺提供了新的思路,同时研究了表面异质原子对析氢活性的关键作用,为该类催化材料的构效关系研究提供了新思路.