Asymmetric additions to dienes catalysed by a dithiophosphoric acid

Chiral Br?nsted acids (proton donors) have been shown to facilitate a broad range of asymmetric chemical transformations under catalytic conditions without requiring additional toxic or expensive metals. Although the catalysts developed thus far are remarkably effective at activating polarized functional groups, it is not clear whether organic Br?nsted acids can be used to catalyse highly enantioselective transformations of unactivated carbon-carbon multiple bonds. This deficiency persists despite the fact that racemic acid-catalysed 'Markovnikov' additions to alkenes are well known chemical transformations. Here we show that chiral dithiophosphoric acids can catalyse the intramolecular hydroamination and hydroarylation of dienes and allenes to generate heterocyclic products in exceptional yield and enantiomeric excess. We present a mechanistic hypothesis that involves the addition of the acid catalyst to the diene, followed by nucleophilic displacement of the resulting dithiophosphate intermediate; we also report mass spectroscopic and deuterium labelling studies in support of the proposed mechanism. The catalysts and concepts revealed in this study should prove applicable to other asymmetric functionalizations of unsaturated systems.     

Overcoming lability of extremely long alkane carbon-carbon bonds through dispersion forces

Steric effects in chemistry are a consequence of the space required to accommodate the atoms and groups within a molecule, and are often thought to be dominated by repulsive forces arising from overlapping electron densities (Pauli repulsion). An appreciation of attractive interactions such as van der Waals forces (which include London dispersion forces) is necessary to understand chemical bonding and reactivity fully. This is evident from, for example, the strongly debated origin of the higher stability of branched alkanes relative to linear alkanes and the possibility of constructing hydrocarbons with extraordinarily long C-C single bonds through steric crowding. Although empirical bond distance/bond strength relationships have been established for C-C bonds (longer C-C bonds have smaller bond dissociation energies), these have no present theoretical basis. Nevertheless, these empirical considerations are fundamental to structural and energetic evaluations in chemistry, as summarized by Pauling as early as 1960 and confirmed more recently. Here we report the preparation of hydrocarbons with extremely long C-C bonds (up to 1.704??), the longest such bonds observed so far in alkanes. The prepared compounds are unexpectedly stable--noticeable decomposition occurs only above 200?°C. We prepared the alkanes by coupling nanometre-sized, diamond-like, highly rigid structures known as diamondoids. The extraordinary stability of the coupling products is due to overall attractive dispersion interactions between the intramolecular H???H contact surfaces, as is evident from density functional theory computations with and without inclusion of dispersion corrections.     

Superconductivity in molecular crystals induced by charge injection

Progress in the field of superconductivity is often linked to the discovery of new classes of materials, with the layered copper oxides being a particularly impressive example. The superconductors known today include a wide spectrum of materials, ranging in complexity from simple elemental metals, to alloys and binary compounds of metals, to multi-component compounds of metals and chalcogens or metalloids, doped fullerenes and organic charge-transfer salts. Here we present a new class of superconductors: insulating organic molecular crystals that are made metallic through charge injection. The first examples are pentacene, tetracene and anthracene, the last having the highest transition temperature, at 4 K. We anticipate that many other organic molecular crystals can also be made superconducting by this method, which will lead to surprising findings in the vast composition space of molecular crystals.     

Heck偶联反应在有机单分子膜上的应用

利用Heck偶联反应成功地改变了自组装单分子有机薄膜的化学结构以及末端基团,薄膜末端的碘苯基团与对卤苯乙烯在标准的Heck反应条件下成功发生了偶联反应.这些薄膜经过了接触角、膜厚以及X射线光电子能谱的详细表征.这种表面修饰的方法有效地改变有机薄膜的表面化学.     

铜催化芳杂环C-H键区域选择性芳基化的研究进展

铜作为一种廉价、新型的芳环C-H键官能团化反应催化剂,近年来一直是有机化学和催化化学的研究热点和难点之一.依据参与反应的底物的不同,综述近年来文献报道的铜催化芳杂环C-H键区域选择性芳基化反应及其机理的最新研究进展.     

~1J_(CH)和~1J_(CC)核自旋偶合常数的最大重迭对称性分子轨道计算

利用AM1级别上最大重迭对称性分子轨道法及自然杂化轨道方法,计算了系列烃类化合物分子中各原子的电荷分布和杂化轨道组成系数,拟合出计算C-H及C-C偶合常数的简单关系式,计算了各种烃类分子中不同的C-H键和C-C键偶合常数,计算值和实验数据相一致,为计算1JCH和1JCC提供了一种简便直观的方法.     

IB族金属催化乙烯选择氧化反应的量子化学研究

采用ＥＨＭＯ方法分别计算了铜，银或金表面吸附氧的位能曲线以及铜或银单独存在时氧与乙烯生成超氧化物中间体的位能面，从而了解铜，金不能催化乙烯选择氧化的原因。     

氟代芳基碳酸酯与氨基甲酸酯中氢键的理论研究

运用 AIM理论在 B97D 水平上计算了2-丁炔-1，4-二基二（2，3，4，5，6-五氟苯基碳酸酯）1，2-丁炔-1，4-二基二（4-氟苯基碳酸酯）2及2-丁炔-1，4-二基二（2，3，4，5，6-五氟苯氨基甲酸酯）3中的分子间有机氟 C -H…F -C 氢键．这些分子间氢键为闭壳相互作用．尽管晶体1中 H…F 距离接近经典氢键，但是该有机氟氢键仍为弱氢键．NBO 分析表明，研究的有机氟 C -H…F -C 氢键存在明显的电荷转移，用电荷转移合理地解释了分子1采取顺式结构．     

Protein-disulphide isomerase and prolyl isomerase act differently and independently as catalysts of protein folding

Two enzymes are now known that catalyse slow steps in protein folding. Peptidyl-prolyl cis-trans isomerase catalyses the cis-trans isomerization of Xaa-Pro peptide bonds in oligopeptides and during the refolding of several proteins. The other enzyme, protein-disulphide isomerase, accelerates the reactivation of reduced proteins, presumably by catalysis of thiol-disulphide exchange reactions. Recent evidence indicates that the beta-subunit of prolyl 4-hydroxylase, an enzyme involved in collagen biosynthesis, is identical with disulphide isomerase. On the basis of this important finding, it was suggested that disulphide isomerase accelerates protein folding, not by 'reshuffling' incorrect disulphide bonds, but in the same way as prolyl isomerase by catalysing proline isomerization which is known to be important for the folding of collagen and other proteins. Here we show that the catalytic activities of these two enzymes are different. Disulphide isomerase accelerates the reformation of native disulphide bonds during protein reoxidation. We find no evidence that this enzyme can catalyse the isomerization of proline peptide bonds, a reaction efficiently accelerated by prolyl isomerase. When both enzymes are present simultaneously during protein folding, they act independently of one another.     

Hyperconjugation not steric repulsion leads to the staggered structure of ethane

Many molecules can rotate internally around one or more of their bonds so that during a full 360 degrees rotation, they will change between unstable and relatively stable conformations. Ethane is the textbook example of a molecule exhibiting such behaviour: as one of its two methyl (CH3) groups rotates once around the central carbon-carbon bond, the molecule will alternate three times between an unstable eclipsed conformation and the preferred staggered conformation. This structural preference is usually attributed to steric effects; that is, while ethane rotates towards an eclipsed structure, the electrons in C-H bonds on the different C atoms are drawing closer to each other and therefore experience increased repulsion, introducing a rotation barrier that destabilizes the eclipsed structure. Stabilization of the staggered structure through rotation-induced weakening of the central C-C bond and hyperconjugation has been considered to be involved, but evaluation of the contributions of these effects to ethane's internal rotation barrier and conformational preference remains difficult. Here we report a series of ethane structure optimizations, where successive removal of different interactions indicates that ethane's staggered conformation is the result of preferential stabilization through hyperconjugation. Removal of hyperconjugation interactions yields the eclipsed structure as the preferred conformation, whereas repulsive forces, either present or absent, have no influence on the preference for a staggered conformation.     

高岭石层间尿素-水体系的分子动力学模拟

用分子动力学（MD）方法对尿素-高岭石和尿素-水-高岭石两个体系进行模拟,计算结果表明,在300K时,高岭石平衡层间距随着尿素分子的增多不断增大,增幅逐渐减小;尿素在水溶液中的摩尔分率在0.58左右时高岭石平衡层间距有最大值。尿素在高岭石片层间成双层分布,分别通过O=C键和N—H键与高岭石表面原子形成氢键。水在层间主体相成三层分布,有部分水分子吸附在高岭石表面上。     

Negative differential resistance in single-walled SiC nanotubes

A two-probe system was established for a finite （7, 0） silicon carbide （SIC） nanotube coupled to Au （111） surfaces via Au-C bonds. Using the non-equilibrium Green function （NEGF） combined with density functional theory （DFT）, the above system was studied for its electronic transport properties. Negative differential resistance （NDR） was observed when the bias voltage was greater than 1.4 V. Because the transport properties of the system were sensitive to the applied bias voltage, NDR might be caused by the fluctuation of the transmission coefficient with the bias voltage.     

Stable silver nanoparticles–aptamer bioconjugates for cellular prion protein imaging

Combining the unique optical properties of metal nanoparticles and the specific recognition of aptamer,aptamer–nanoparticle conjugates have been extensively used in a wide range of applications,particularly multifunctional nanoparticles for cell detection and molecular imaging.Conventional conjugates prepared by chemisorption of monothiol-modified oligonucleotides onto nanoparticle surfaces suffer from a lack of stability when exposed to a variety of small molecules.If silver is used in place of gold,then this lack of stability is even more pronounced.In this study,we reported here the effective and facile strategy of preparing stable silver nanoparticle–aptamer conjugates by in situ generation of strong metal affinity capping ligands,dithiocarbamates modified anti-prion protein aptamer.The conjugates produced are stable and can withstand NaCl concentration at0.25 mol/L.Meanwhile,they could be applied in the cellular prion protein imaging successfully.     

直接键连C-X(X=H, C)的核自旋偶合常数的理论研究

利用建立的PM3级别上的最大重迭对称性分子轨道法和自然杂化轨道方法，计算了系列烃类化合物的杂化轨道和电荷分布，拟合出计算C-H及C-C偶合常数的简单关系式，研究了各种烃类分子中不同的C-Ｈ键和Ｃ-Ｃ键偶合常数，理论计算值和实验数据都较为吻合. 进一步验证了直接键连1JCX(X=C, H)偶合常数主要取决于偶合作用中的Fermi接触相，为从简单价键理论角度解释和计算1JCH和1JCC提供了一种简便直观的方法. 计算结果也表明提出的计算方法是可行的.     

Activation of remote meta-C-H bonds assisted by an end-on template

Functionalization of unactivated carbon-hydrogen (C-H) single bonds is an efficient strategy for rapid generation of complex molecules from simpler ones. However, it is difficult to achieve selectivity when multiple inequivalent C-H bonds are present in the target molecule. The usual approach is to use σ-chelating directing groups, which lead to ortho-selectivity through the formation of a conformationally rigid six- or seven-membered cyclic pre-transition state. Despite the broad utility of this approach, proximity-driven reactivity prevents the activation of remote C-H bonds. Here we report a class of easily removable nitrile-containing templates that direct the activation of distal meta-C-H bonds (more than ten bonds away) of a tethered arene. We attribute this new mode of C-H activation to a weak 'end-on' interaction between the linear nitrile group and the metal centre. The 'end-on' coordination geometry relieves the strain of the cyclophane-like pre-transition state of the meta-C-H activation event. In addition, this template overrides the intrinsic electronic and steric biases as well as ortho-directing effects with two broadly useful classes of arene substrates (toluene derivatives and hydrocinnamic acids).     

Catalytic functionalization of unactivated primary C-H bonds directed by an alcohol

New synthetic methods for the catalytic functionalization of C-H bonds have the potential to revolutionize the synthesis of complex molecules. However, the realization of this synthetic potential requires the ability to functionalize selectively one C-H bond in a compound containing many such bonds and an array of functional groups. The site-selective functionalization of aliphatic C-H bonds is one of the greatest challenges that must be met for C-H bond functionalization to be used widely in complex-molecule synthesis, and processes catalysed by transition-metals provide the opportunity to control selectivity. Current methods for catalytic, aliphatic C-H bond functionalization typically rely on the presence of one inherently reactive C-H bond, or on installation and subsequent removal of directing groups that are not components of the desired molecule. To overcome these limitations, we sought catalysts and reagents that would facilitate aliphatic C-H bond functionalization at a single site, with chemoselectivity derived from the properties of the catalyst and site-selectivity directed by common functional groups contained in both the reactant and the desired product. Here we show that the combination of an iridium-phenanthroline catalyst and a dihydridosilane reagent leads to the site-selective γ-functionalization of primary C-H bonds controlled by a hydroxyl group, the most common functional group in natural products. The scope of the reaction encompasses alcohols and ketones bearing many substitution patterns and auxiliary functional groups; this broad scope suggests that this methodology will be suitable for the site-selective and diastereoselective functionalization of complex natural products.     

羰基极性翻转及合成上的应用

羰基是一极性基团,在有机反应中表现为亲电性,与多种亲核试剂反应可形成碳——碳键或碳与其它原子的键,是筑成有机分子极为重要的官能团。如果它的反应性能够翻转,不仅能与亲核试剂反应,而且还能与亲电试剂反应,羰基在有机合成上的怍用将会进一步扩大.本文介绍几种使羰基极性翻转的方法及其在有机合成上的应用。     

淋湘金矿地球化学特征

陕西旬阳淋湘金矿床产于南秦岭古生界泥盆系地层中,容矿围岩主要为碳酸盐岩和细碎屑岩,金矿体主要受近东西向断裂控制．第Ⅱ、第Ⅲ矿化阶段为金的主要矿化阶段,第Ⅱ～Ⅲ阶段石英包体中N2含量大于21μg/g,而第Ⅳ阶段矿物中的N2含量均小于1μg/g,说明成矿流体中的N2含量减少对金矿化不利;成矿流体的氢氧同位素组成与变质水相当;矿石的硫同位素早期为18.21‰,中晚期为17.83‰～14.01‰;铅具有正常铅同位素特征;不同矿化程度的矿石的稀土元素组成的球粒陨石标准化分配曲线,呈富轻稀土的右倾型,曲线形态基本一致,随着矿化增强其稀土元素含量明显增高．这些矿床地球化学特征表明,成矿金属元素和硫主要来源于造山带围岩地层,属容矿岩石为沉积岩中的浅层渗滤同生热盐水型金矿床,成矿时代为燕山期．     

Aluminum matrix composites reinforced by molybdenum-coated carbon nanotubes

To extend the application of carbon nanotubes (CNTs) and explore novel aluminum matrix composites, CNTs were coated by molybdenum layers using metal organic chemical vapor deposition, and then Mo-coated CNT (Mo-CNT)/Al composites were prepared by the combination processes of powder mixing and spark plasma sintering. The influences of powder mixing and Mo-CNT content on the mechanical properties and electrical conductivity of the composites were investigated. The results show that magnetic stirring is better than mechanical milling for mixing the Mo-CNTs and Al powders. The electrical conductivity of the composites decreases with increasing Mo-CNT content. When the Mo-CNT content is 0.5wt%, the tensile strength and hardness of Mo-CNT/Al reach their maximum values. The tensile strength of 0.5wt% Mo-CNT/Al increases by 29.9%, while the electrical conductivity only decreases by 7.1%, relative to sintered pure Al. The phase analysis of Mo-CNT/Al composites reveals that there is no formation of Al carbide in the composites.     

β-环糊精紫杉醇包合物超分子结构的密度泛函理论研究

本文研究了β-环糊精包裹紫杉醇形成的超分子包合物。用密度泛函（DFT）PBE方法对超分子包合物进行结构优化得到稳定几何结构,分析结构表明β-环糊精与紫杉醇通过O—H…O、C—H…O和C-Ч…π氢键的相互作用,形成稳定的包合物。稳定包合物的结合能为-30．93keal／mol。