Enantiospecific electrodeposition of a chiral catalyst

Many biomolecules are chiral--they can exist in one of two enantiomeric forms that only differ in that their structures are mirror images of each other. Because only one enantiomer tends to be physiologically active while the other is inactive or even toxic, drug compounds are increasingly produced in an enantiomerically pure form using solution-phase homogeneous catalysts and enzymes. Chiral surfaces offer the possibility of developing heterogeneous enantioselective catalysts that can more readily be separated from the products and reused. In addition, such surfaces might serve as electrochemical sensors for chiral molecules. To date, chiral surfaces have been obtained by adsorbing chiral molecules or slicing single crystals so that they exhibit high-index faces, and some of these surfaces act as enantioselective heterogeneous catalysts. Here we show that chiral surfaces can also be produced through electrodeposition, a relatively simple solution-based process that resembles biomineralization in that organic molecules adsorbed on surfaces have profound effects on the morphology of the inorganic deposits. When electrodepositing a copper oxide film on an achiral gold surface in the presence of tartrate ion in the deposition solution, the chirality of the ion determines the chirality of the deposited film, which in turn determines the film's enantiospecificity during subsequent electrochemical oxidation reactions.     

手性含氮四齿配体催化苯丙酮的不对称氢转移氢化

利用8-羟基喹啉与手性环己基二胺的反应，合成了对空气和水稳定的手性含氮四齿配体（R，R）-C5N4；进而分别与钌、铑或铱等金属络合物组合，现场生成催化体系，用于苯丙酮的不对称氢转移氢化反应；考察了碱添加量、配体用量和底物与催化剂用量摩尔比对反应性能的影响．结果表明，该配体与RhHCO（PPh3）3的混合体系效果较好，可得到68％ee的对映选择性．     

工业用间二甲苯氨氧化催化剂的表面吸附特征研究

用低温N2吸附及H2O，C6H6和m-C6H4(CH3)2等探针分子静态吸附以及NH3－TPD等方法考察了工业用间二甲苯氨氧化生产间苯二甲腈催化剂VCB1，VCB2和VCM表面吸附特征。结果，VCB1，VCB2和VCM催化剂均具有中孔（15－40nm）结构，反应物分子在孔道中的扩散不构成吸附过程的控制步骤，催化剂对反应组分的吸附能力取决于催化剂表面亲合力。VCM对m-C6H4(CH3)2新合力较强，其表面对H2O和NH3的亲合力弱是该催化剂在使用过程中深度氧化产物较多的可能原因之一，结果为催化剂改性提供了理论依据。     

新型水溶性手性钌催化剂的制备及应用

利用发烟硫酸磺化手性双胺双膦配体[（R．R）-C6P2（NH）2]．合成了PNNP-型水溶性手性双胺双膦配体[（R．R）-C6P2（NH）2（SO3Na）4]，并分别与简单的钌、铑络合物反应，制备水溶性手性钌络合物催化剂[（R，R）-C6P2（NH）2（SO3Na）4RuCl2]和铑络合物催化剂[（R，R）-C6P2（NH）2（SO3Na）4RhCl]．经元素分析、红外光谱和核磁共振等对手性配体及手性Ru络合物进行了结构表征．进而用这些水溶性的钌，铑络合物催化剂或水溶性手性配体与铱络合物[IrHCl2（COD）]2组成的混合催化体系研究了多种芳香酮的不对称转移氢化。结果表明．在以异丙醇作为氢源时．对芳香酮的不对称转移氢化都具有较好的催化活性．与铑，铱催化体系相比，水溶性手性钌络合物催化体系具有更高的活性和对映选择性．对于苯乙酮的氢化．其转化率和对映选择性分别达到91.6％和93．0％e．e．．此外，进一步考察了反应温度和KOH用量对水溶性手性钌络合物催化苯乙酮不对称转移氢化性能的影响，并将水溶性手性钌络合物催化体系应用于多种芳香酮的不对称转移氢化，获得了高的收率和对映选择性，分别可达92．0％和96．4％e．e．．研究结果表明，水溶性手性钌络合物[CR．R）-G6P2（NH）2（SO3Na）4RuCl2]是芳香酮不对称氢转移催化氢化的优良催化剂.     

Amplification of chirality in two-dimensional enantiomorphous lattices

The concept of chirality dates back to 1848, when Pasteur manually separated left-handed from right-handed sodium ammonium tartrate crystals. Crystallization is still an important means for separating chiral molecules into their two different mirror-image isomers (enantiomers), yet remains poorly understood. For example, there are no firm rules to predict whether a particular pair of chiral partners will follow the behaviour of the vast majority of chiral molecules and crystallize together as racemic crystals, or as separate enantiomers. A somewhat simpler and more tractable version of this phenomenon is crystallization in two dimensions, such as the formation of surface structures by adsorbed molecules. The relatively simple spatial molecular arrangement of these systems makes it easier to study the effects of specific chiral interactions; moreover, chiral assembly and recognition processes can be observed directly and with molecular resolution using scanning tunnelling microscopy. The enantioseparation of chiral molecules in two dimensions is expected to occur more readily because planar confinement excludes some bulk crystal symmetry elements and enhances chiral interactions; however, many surface structures have been found to be racemic. Here we show that the chiral hydrocarbon heptahelicene on a Cu111 surface does not undergo two-dimensional spontaneous resolution into enantiomers, but still shows enantiomorphism on a mesoscopic length scale that is readily amplified. That is, we observe formation of racemic heptahelicene domains with non-superimposable mirror-like lattice structures, with a small excess of one of the heptahelicene enantiomers suppressing the formation of one domain type. Similar to the induction of homochirality in achiral enantiomorphous monolayers by a chiral modifier, a small enantiomeric excess suffices to ensure that the entire molecular monolayer consists of domains having only one of two possible, non-superimposable, mirror-like lattice structures.     

硅藻土对诺卡氏菌的吸附作用

研究了吉林长白硅藻土吸附水相中诺卡氏菌的吸附过程,讨论了吸附时间、硅藻土用量、溶液初始pH值和吸附温度等实验条件对吸附效果的影响·实验结果表明,硅藻土对水相中的诺卡氏菌具有较好的吸附效果·该吸附过程进行得较快,在20min左右即可达到吸附平衡;在溶液初始pH值为7 0～9 0内都有较好的吸附效果;温度对吸附过程的影响不大,室温条件下操作即可;在诺卡氏菌浓度一定的条件下,适量增加硅藻土用量可以提高吸附效果·扫描电镜分析结果表明,硅藻土表面的微孔和诺卡氏菌表面的菌丝可能是吸附过程的主要吸附位·     

氧化石墨负载的手性二胺铑催化剂催化芳香酮的不对称氢转移反应

以石墨为原料通过Hummer化学氧化法制备出功能化氧化石墨材料,然后将手性二胺基团嫁接到氧化石墨上,再通过后修饰与金属铑配位制备出非均相催化剂,该催化剂在水介质中温和条件下对芳香酮的不对称氢转移反应显示出高的催化活性和对映选择活性.     

An enantiomerically pure hydrogen-bonded assembly

Chiral molecules have asymmetric arrangements of atoms, forming structures that are non-superposable mirror images of each other. Specific mirror images ('enantiomers') may be obtained either from enantiomerically pure precursor compounds, through enantioselective synthesis, or by resolution of so-called racemic mixtures of opposite enantiomers, provided that racemization (the spontaneous interconversion of enantiomers) is sufficiently slow. Non-covalent assemblies can similarly adopt chiral supramolecular structures, and if they are held together by relatively strong interactions, such as metal coordination, methods analogous to those used to obtain chiral molecules yield enantiomerically pure non-covalent products. But the resolution of assemblies formed through weak interactions, such as hydrogen-bonding, remains challenging, reflecting their lower stability and significantly higher susceptibility to racemization. Here we report the design of supramolecular structures from achiral calix[4]arene dimelamines and cyanurates, which form multiple cooperative hydrogen bonds that together provide sufficient stability to allow the isolation of enantiomerically pure assemblies. Our design strategy is based on a non-covalent 'chiral memory' concept, whereby we first use chiral barbiturates to induce the supramolecular chirality in a hydrogen-bonded assembly, and then substitute them by achiral cyanurates. The stability of the resultant chiral assemblies in benzene, a non-polar solvent not competing for hydrogen bonds, is manifested by a half-life to racemization of more than four days at room temperature.     

Catalytic enantioselective reactions driven by photoinduced electron transfer

Photoinduced electron transfer is an essential step in the conversion of solar energy into chemical energy in photosystems I and II (ref. 1), and is also frequently used by chemists to build complex molecules from simple precursors. During this process, light absorption generates molecules in excited electronic states that are susceptible to accepting or donating electrons. But although the excited states are straightforward to generate, their short lifetimes makes it challenging to control electron transfer and subsequent product formation-particularly if enantiopure products are desired. Control strategies developed so far use hydrogen bonding, to embed photochemical substrates in chiral environments and to render photochemical reactions enantioselective through the use of rigid chiral complexing agents. To go beyond such stoichiometric chiral information transmission, catalytic turnover is required. Here we present a catalytic photoinduced electron transfer reaction that proceeds with considerable turnover and high enantioselectivity. By using an electron accepting chiral organocatalyst that enforces a chiral environment on the substrate through hydrogen bonding, we obtain the product in significant enantiomeric excess (up to 70%) and in yields reaching 64%. This performance suggests that photochemical routes to chiral compounds may find use in general asymmetric synthesis.     

Controlling molecular deposition and layer structure with supramolecular surface assemblies

Selective non-covalent interactions have been widely exploited in solution-based chemistry to direct the assembly of molecules into nanometre-sized functional structures such as capsules, switches and prototype machines. More recently, the concepts of supramolecular organization have also been applied to two-dimensional assemblies on surfaces stabilized by hydrogen bonding, dipolar coupling or metal co-ordination. Structures realized to date include isolated rows, clusters and extended networks, as well as more complex multi-component arrangements. Another approach to controlling surface structures uses adsorbed molecular monolayers to create preferential binding sites that accommodate individual target molecules. Here we combine these approaches, by using hydrogen bonding to guide the assembly of two types of molecules into a two-dimensional open honeycomb network that then controls and templates new surface phases formed by subsequently deposited fullerene molecules. We find that the open network acts as a two-dimensional array of large pores of sufficient capacity to accommodate several large guest molecules, with the network itself also serving as a template for the formation of a fullerene layer.     

Molecular control over Au/GaAs diodes

The use of molecules to control electron transport is an interesting possibility, not least because of the anticipated role of molecules in future electronic devices. But physical implementations using discrete molecules are neither conceptually simple nor technically straightforward (difficulties arise in connecting the molecules to the macroscopic environment). But the use of molecules in electronic devices is not limited to single molecules, molecular wires or bulk material. Here we demonstrate that molecules can control the electrical characteristics of conventional metal-semiconductor junctions, apparently without the need for electrons to be transferred onto and through the molecules. We modify diodes by adsorbing small molecules onto single crystals of n-type GaAs semiconductor. Gold contacts were deposited onto the modified surface, using a 'soft' method to avoid damaging the molecules. By using a series of multifunctional molecules whose dipole is varied systematically, we produce diodes with an effective barrier height that is tuned by the molecule's dipole moment. These barrier heights correlate well with the change in work function of the GaAs surface after molecular modification. This behaviour is consistent with that of unmodified metal-semiconductor diodes, in which the barrier height can depend on the metal's work function.     

草酸电还原过程中的铅阴极表面状态变化研究

在饱和草酸溶液中运用双阶跃计时库仑技术研究草酸电解过程中电极表面吸附过程,以此探讨电极失活问题。研究发现在新鲜铅电极表面表现为产物乙醛酸（R）的吸附,但随着恒电流电解的进行电极表面逐渐地表现为反应物（O）的吸附。反应物的直接吸附不利于电荷转移,电极表面呈现钝化现象,电解电流效率也相应下降．     

煤岩体吸附膨胀变形与吸附热力学的参数关系

采用吸附容量法测试了不同煤样对CO2,CH4,N2的吸附性能参数,基于所提出的孔隙介质截面吸附润湿长度概念和孔隙结构模型、表面物理化学及弹性力学原理,导出了吸附膨胀应力和应变理论计算公式,并讨论了吸附常数、温度、气体压力、煤岩体比表面积、气体分子吸附截面积等参数对它们的影响·这些公式比现有的公式应用范围广,能方便计算不同约束条件下的吸附膨胀应变和应力·研究还表明煤岩体比表面积和气体吸附分子截面积越大,气体吸附量、煤岩体的吸附膨胀应力及应变越大·     

Chiral recognition in dimerization of adsorbed cysteine observed by scanning tunnelling microscopy

Stereochemistry plays a central role in controlling molecular recognition and interaction: the chemical and biological properties of molecules depend not only on the nature of their constituent atoms but also on how these atoms are positioned in space. Chiral specificity is consequently fundamental in chemical biology and pharmacology and has accordingly been widely studied. Advances in scanning probe microscopies now make it possible to probe chiral phenomena at surfaces at the molecular level. These methods have been used to determine the chirality of adsorbed molecules, and to provide direct evidence for chiral discrimination in molecular interactions and the spontaneous resolution of adsorbates into extended enantiomerically pure overlayers. Here we report scanning tunnelling microscopy studies of cysteine adsorbed to a (110) gold surface, which show that molecular pairs formed from a racemic mixture of this naturally occurring amino acid are exclusively homochiral, and that their binding to the gold surface is associated with local surface restructuring. Density-functional theory calculations indicate that the chiral specificity of the dimer formation process is driven by the optimization of three bonds on each cysteine molecule. These findings thus provide a clear molecular-level illustration of the well known three-point contact model for chiral recognition in a simple bimolecular system.     

染料包覆纳米银粒子复合膜的吸收红移

采用Sol Gel法制备出染料包覆纳米银粒子的复合膜 ,用电镜 (TEM )测量了该复合膜中纳米银粒子的尺寸大小及形态 ,实验测出了复合膜的吸收光谱 .结果发现 ,与纯染料溶液相比 ,在用荧光素钠 (FS)包覆纳米银粒子的复合膜中 ,FS分子吸收峰红移约 1 0nm ;而在用罗丹明 6G(Rh6G)包覆纳米银粒子的复合膜中 ,Rh6G分子吸收峰红移较小 .从理论上对这种结果给予分析和解释     

乙烷氧化反应的瞬变应答研究──C_2H_6在Mn_2O_3催化剂上氧化反应的速

本文使用瞬变应答技术，研究了Ｃ２Ｈ６在Ｍｎ２Ｏ３催化剂上的氧化反应。根据产物ＣＯ２分别对反应物Ｃ２Ｈ６和Ｏ２的浓度阶跃变化结果，证实Ｃ２Ｈ６的催化氧化反应，必须经历催化剂表面上Ｏ２（吸附态）和Ｃ２Ｈ６（吸附态）的反应步骤，总反应的ＲＤＳ是催化剂表面上吸附态Ｃ２Ｈ６分子的形成。实验还证实了ＣＯ２不影响Ｃ２Ｈ６氧化反应的速率，而Ｈ２Ｏ对此反应有禁阻作用。     

多道次立-平辊轧制轧件角部金属流动状态有限元模拟

利用显式动力学有限元方法和几何模型更新方法对平立辊、内导角半径50 mm孔型辊8、0 mm孔型辊三种情况下,多道次立-平辊轧制过程进行了模拟,分析了三种立辊情况下,轧件角部金属的流动情况.得出在既定轧制规程下,采用平立辊时,轧件角部金属被翻边至轧件水平面上;采用孔型立辊时,轧件角部金属保留在轧件水平面与侧面的交线上.     

Enantioselective magnetochiral photochemistry

Many chemical and physical systems can occur in two forms distinguished solely by being mirror images of each other. This phenomenon, known as chirality, is important in biochemistry, where reactions involving chiral molecules often require the participation of one specific enantiomer (mirror image) of the two possible ones. In fact, terrestrial life utilizes only the L enantiomers of amino acids, a pattern that is known as the 'homochirality of life' and which has stimulated long-standing efforts to understand its origin. Reactions can proceed enantioselectively if chiral reactants or catalysts are involved, or if some external chiral influence is present. But because chiral reactants and catalysts themselves require an enantioselective production process, efforts to understand the homochirality of life have focused on external chiral influences. One such external influence is circularly polarized light, which can influence the chirality of photochemical reaction products. Because natural optical activity, which occurs exclusively in media lacking mirror symmetry, and magnetic optical activity, which can occur in all media and is induced by longitudinal magnetic fields, both cause polarization rotation of light, the potential for magnetically induced enantioselectivity in chemical reactions has been investigated, but no convincing demonstrations of such an effect have been found. Here we show experimentally that magnetochiral anisotropy--an effect linking chirality and magnetism--can give rise to an enantiomeric excess in a photochemical reaction driven by unpolarized light in a parallel magnetic field, which suggests that this effect may have played a role in the origin of the homochirality of life.     

DNA-based self-assembly of chiral plasmonic nanostructures with tailored optical response

Matter structured on a length scale comparable to or smaller than the wavelength of light can exhibit unusual optical properties. Particularly promising components for such materials are metal nanostructures, where structural alterations provide a straightforward means of tailoring their surface plasmon resonances and hence their interaction with light. But the top-down fabrication of plasmonic materials with controlled optical responses in the visible spectral range remains challenging, because lithographic methods are limited in resolution and in their ability to generate genuinely three-dimensional architectures. Molecular self-assembly provides an alternative bottom-up fabrication route not restricted by these limitations, and DNA- and peptide-directed assembly have proved to be viable methods for the controlled arrangement of metal nanoparticles in complex and also chiral geometries. Here we show that DNA origami enables the high-yield production of plasmonic structures that contain nanoparticles arranged in nanometre-scale helices. We find, in agreement with theoretical predictions, that the structures in solution exhibit defined circular dichroism and optical rotatory dispersion effects at visible wavelengths that originate from the collective plasmon-plasmon interactions of the nanoparticles positioned with an accuracy better than two nanometres. Circular dichroism effects in the visible part of the spectrum have been achieved by exploiting the chiral morphology of organic molecules and the plasmonic properties of nanoparticles, or even without precise control over the spatial configuration of the nanoparticles. In contrast, the optical response of our nanoparticle assemblies is rationally designed and tunable in handedness, colour and intensity-in accordance with our theoretical model.     

L-组氨酸不对称转化的研究

L-组氨酸(L-His)在醛的催化下,在羧酸溶剂中能发生消旋.当反应温度升高时,消旋反应速率加快.L-His用(R)-酒石酸((R)-TA)做拆分试剂,在乙酸溶剂中、水杨醛存在下进行不对称转换,合成了D-组氨酸(D-His)的酒石酸盐,经处理得到D-His.在最佳工艺条件下的收率为95.76%,光学纯度大于99.5%.