Aharonov-Bohm oscillation and chirality effect in optical activity of single-wall carbon nanotubes

We study the Aharonov-Bohm effect in the optical phenomena of single-wall carbon nanotubes (SWCN) and also their chirality dependence. Especially, we consider the natural optical activity as a proper observable and derive its general expression based on a comprehensive symmetry analysis, which reveals the interplay between the enclosed magnetic flux and the tubule chirality for arbitrary chiral SWCN. A quantitative result for this optical property is given by a gauge invariant tight-binding approximation calculation to stimulate experimental measurements.

Symmetry restrictions in the chirality dependence of physical properties of single-wall nanotubes

We investigate the chirality dependence of physical properties of nanotubes which are wrapped by the planar hexagonal lattice including graphite and boron nitride sheet, and reveal its symmetry origin. The observables under consideration are of scalar, vector, and tensor types. These exact chirality dependences obtained are useful to verify the experimental and numerical results and propose accurate empirical formulas. Some important features of physical quantities can also be extracted by considering the symmetry restrictions without complicated calculations.

Observation of Three-Quasiparticle Doublet Bands in I-123: Possible Evidence of Chirality

A new band in the odd proton nucleus I-123 is identified via in- beam gamma- ray spectroscopy using the N-14+Cd-116 reaction. This band shows up as doublets with the previously assigned pi g(7/2) circle times (nu h(11/2))(2) band. Possible configurations of the new band are discussed in the framework of the cranked shell model and the geometrical model. It is argued that the new band might be a chiral partner of the previously known pi g(7/2) circle times (nu h(11/2))(2) band.

Synthesis of novel ferrocenylphosphine-amidine ligands with central and planar chirality and their diastereomeric effect in Pd-catalyzed asymmetric allylic alkylation

Some novel ferrocenylphosphine-amidine ligands with central and planar chirality were prepared from (R,S-p)-PPFNH2-R 3 and its diastereomer (S,S-p)-PPFNH2 3a. The efficiency and diastereomeric impact of these ferrocenylphosphine-amidine ligands in the palladium-catalyzed asymmetric allylic substitution was examined, and up to 96% e.e. with 98% yield was achieved by the use of ligand (R,S-p)-4a with a methyl group in the amidino moiety. The results also indicated that (R)-central chirality and (S-p)-planar chirality in these ferrocenylphosphine-amidine ligands were matched for the palladium-catalyzed asymmetric allylic alkylation. (C) 2003 Elsevier Ltd. All rights reserved.

Synthesis of novel P-ketimine bidentate ferrocenyl ligands with central and planar chirality and comparsion in the catalytic activity between P-ketimine and P-aldimine

A series of novel ferrocenylphosphine-ketimine ligands 6 were prepared by reaction of (R,S-p)-PPFNH2-R or (S,S-p)-PPFNH2 with a variety of m-substituted acetophenones. A different catalytic activity was observed between ferrocenylphosphine-ketimine ligands and corresponding aldimine ligands. The efficiency and diastereomeric impact of these ferrocenylphosphine-ketimine ligands in Pd-catalyzed asymmetric allylic alkylation were first investigated, and higher enantioselectivity of over 98% e.e. with 95% yield was obtained by the use of ferrocenylphosphine-ketimine ligands. However, in Rh-catalyzed asymmetric hydrosilylation of aryl ketones, only 42% e.e. was obtained by the use of ferrocenylphosphine-ketimine ligands compared to 90% e.e. with the use of aldimine ligands. (C) 2003 Elsevier Ltd. All rights reserved.

Liquid crystalline phases, microtwinning in crystals and helical chirality transformations in a main-chain chiral liquid crystalline polyester

A main-chain nonracemic chiral liquid crystalline polymer was synthesized from (R)-(-)4'-{w-[2-(p-hydroxy-o-nitrophenyloxy)-1-propyloxy]-1-decyloxyl-4-biphenylcarboxylic acid. This polymer contained 10 methylene units in each chemical repeating unit and was abbreviated PET(R*-10). On the basis of differential scanning calorimetry, wide-angle X-ray diffraction, and polarized light microscopy experiments, chiral smectic C (S-C*) and chiral smectic A (S-A*) phases were identified. Both flat-elongated and helical lamellar crystal morphologies were observed in transmission electron microscopy. Of particular interest was the flat-elongated lamellar crystals were constructed via microtwinning of an orthorhombic cell with dimensions of a = 1.42 nm, b = 1.28 nm, and c = 3.04 nm. On the other hand, the helical lamellar crystals were exclusively left-handed, which was opposite to the right-handed helical crystals grown in PET(R*-9) and PET(R*-11) (having 9 and 11 methylene units, respectively). Note that these three polymers had identical right-handed chiral centers (R*-). Therefore, a single methylene unit difference on the polymer backbones on an atomic length scale substantially changed the chirality of the crystals in the micrometer length scale. Furthermore, aggregates of these helical crystals in PET(R*-10) did not generate banded spherulites in polarized light microscopy. Possible reasons for this change and loss of helical senses (handedness) on different length scales in chirality transferring processes were discussed.

A comparative study of Young's modulus of single-walled carbon nanotube by CPMD, MD, and first principle simulations

Carbon nanotubes (CNTs), due to their exceptional magnetic, electrical and mechanical properties, are promising candidates for several technical applications ranging from nanoelectronic devices to composites. Young's modulus holds the special status in material properties and micro/nano-electromechanical systems (MEMS/NEMS) design. The excellently regular structures of CNTs facilitate accurate simulation of CNTs' behavior by applying a variety of theoretical methods. Here, three representative numerical methods, i.e., Car-Parrinello molecular dynamics (CPMD), density functional theory (DFT) and molecular dynamics (MD), were applied to calculate Young's modulus of single-walled carbon nanotube (SWCNT) with chirality (3,3). The comparative studies showed that the most accurate result is offered by time consuming DFT simulation. MID simulation produced a less accurate result due to neglecting electronic motions. Compared to the two preceding methods the best performance, with a balance between efficiency and precision, was deduced by CPMD.

Density Gradient Ultracentrifugation of Nanotubes: Interplay of Bundling and Surfactants Encapsulation

Density gradient ultracentrifugation (DGU) has emerged as a promising tool to prepare chirality enriched nanotube samples. Here, we assess the performance of different surfactants for DGU. Bile salts (e.g., sodium cholate (SC), sodium deoxycholate (SDC), and sodium taurodeoxycholate (TDC)) are more effective in individualizing Single Wall Carbon Nanotubes (SWNTs) compared to linear chain surfactants (e.g., sodium dodecylbenzene sulfonate (SDBS) and sodium dodecylsulfate (SDS)) and better suited for DGU. Using SC, a narrower diameter distribution (0.69-0.81 nm) is achieved through a single DGU step on CoMoCAT tubes, when compared to SDC and TDC (0.69-0.89 nm). No selectivity is obtained using SDBS. due to its ineffectiveness in debundling. We assign the reduce selectivity of dihydroxy bile salts (S DC and TDC) in comparison with trihydroxy SC to the formation of secondary micelles. This is determined by the number and position of hydroxyl ( OH) groups on the a-side of the steroid backbone. We also enrich CoMoCAT SWNT in the 0.84-0.92 nm range using the Pluronic F98 triblock copolymer. Mixtures of bile salts (SC) and linear chain surfactants (SOS) are used to enrich metallic and semiconducting laser-ablation grown SWNTs. We demonstrate enrichment of a single chirality, (6,5), combining diameter and metallic versus semiconductillg separation on CoMoCAT samples.

硫手性有机小分子催化剂的设计、合成及其在不对称亚胺氢转移还原中的应用

过去十多年，世界手性药物市场需求迅速增长，手性制药工业的发展壮大，已经引起了各国政府、学术界，特别是企业界的高度重视。手性药物中含有大量的手性胺单元，因此研究高效构建手性胺结构单元的方法具有重要的意义和实用价值，而亚胺的不对称还原是合成手性胺最便捷的方法。 手性有机小分子路易斯碱催化三氯氢硅不对称还原亚胺是最近几年才发展起来的一类新的亚胺不对称还原方法。尽管在对映选择性和底物适用范围等方面已经获得了突破性的进展，但是，高性能的路易斯碱催化剂仅局限于N-甲酰氨基酸酰胺一种类型，而且其底物适用范围和催化活性仍不够理想。因此，发展新型催化剂很有必要。 手性硫氧化物作为手性诱导剂的应用已经有数十年的时间，广泛应用在不对称合成及天然产物的全合成中。理论上，硫氧结构单元也可以作为路易斯碱，对硅烷类试剂进行活化，而且硫氧键还有碳氧键难以比拟的先天优势，硫原子自带手性特征，在反应过程中，手性中心离反应位点更近，因此，从手性硫氧化合物出发，极有可能开发出新的高效手性路易斯碱催化剂。最近，Kobayashi和Khiar在亚胺的不对称烯丙基化反应中用手性亚砜活化烯丙基三氯硅烷，获得了较好的ee值，但反应中手性亚砜的用量都需要化学计量以上，因此还不能算做真正意义上的催化剂，进一步的文献调研也未见真正意义上的硫手性有机小分子催化剂。 本文首次成功将硫手性亚磺酰胺衍生物应用于催化三氯氢硅对亚胺的不对称还原，在经过对亚磺酰胺衍生物的多次结构优化，开发出了合成容易，催化活性和立体选择性都很优良，并且有着前所未有的底物普适性的新型手性路易斯碱催化剂。 我们首先尝试将商品化的20mol%叔丁基亚磺酰胺和对甲基亚磺酰胺直接用作催化剂催化三氯氢硅对亚胺的不对称还原，尽管仅获得中等的收率和很低的对映选择性，但证明我们的设计思路是可行的。在此基础上，我们以叔丁基亚磺酰胺为原料和基本骨架，设计合成了一系列的亚磺酰胺类催化剂，通过对催化剂的结构改造，发现当催化剂中存在较强酸性的酚羟基时，催化效果得到大幅提高。随着对催化剂的进一步结构优化，我们找到了一个结构简单，催化效果还不错的催化剂，经过反应条件优化以后，催化反应的收率最高能达到98%，对映选择性最高达93%，并且这个催化剂的底物适应范围比之前报道的催化剂都要广泛。针对酚羟基在催化剂中的重要作用，我们进行了仔细的机理研究后发现，在催化反应中，催化剂极有可能是通过双分子机理去活化三氯氢硅从而实现不对称催化的，而酚羟基的作用就是通过分子间氢键促进双分子催化剂与三氯氢硅的络合。受此启发，我们设计了一系列具有双齿结构的催化剂，通过对双齿催化剂的结构优化，最终筛选出了一个结构更加简单，但催化效果更好的双齿催化剂。10mol%该催化剂催化亚胺还原最高获得95%的收率和96%的ee值。这一结果也进一步验证了我们先前对催化剂机理的推测。 随后，我们还尝试将这些催化剂用于二级胺和芳香酮的直接还原胺化反应中，虽然能获得不错的收率，但对映选择性却很差，我们对反应条件进行了仔细的摸索，仍然没有获得突破。但这些实验为进一步研究二级胺和酮的不对称直接还原胺化反应奠定了良好的基础。 In the past decade, the rapid growth of the global chiral drug market and the significant development of the chiral pharmaceutical industry have attracted a great deal of attention from government, academia and enterprises. Chiral amine is an important structural motif of chiral drugs. Therefore, development of methods for the construction of this motif is of great importance. Catalytic enantioselective reduction of imines represents one of the most straightforward and efficient methods for the preparation of chiral amines. The chiral Lewis base organocatalysts promoted asymmetric reduction of imines by HSiCl3 has recently achieved significant advancements. Although big breakthroughs have been made in terms of substrate generality and enantioselectivity, the highly effective catalysts are limited to N-formyl amino acid amides, of which the efficiency and substrate scope remain unsatisfactory. Therefore, development of novel organocatalysts for this transformation is in great demand. Chiral sulfoxides have been well established as efficient and versatile stereocontrollers and have been extensively used in asymmetric synthesis and total synthesis of natural products. The S=O structural motif of sulfoxide could also behave as Lewis base activator for cholorsilane reagents, which, moreover, could be even better than caboxamide considering that the sulfur atom is chiral and thus the chirality center is closer to the reaction center. There exist great potentials that highly effective novel Lewis base organocatalysts could be developed starting from S-chiral sulfoxides. Recently, several S-chiral sulfoxides were reported by Kobayashi and Khiar to be used as Lewis base catalyst to activate allyltrichlorosilanes in asymmetric allylations and good enantioselectivities were obtained. However, these S-chiral sulfoxides were all used at a more than stoichiometric amount and were thus not authentically catalytic. A careful literature survey further revealed that there has been so far no S-chiral organocatalyst available. In this study, we, for the first time, successfully used S-chiral sulfinamides as Lewis base organocatalysts for the asymmetric reduction of ketimines by HSiCl3. After several rounds of structural optimization, we developed the first example of highly effective S-chiral organocatalysts, which promoted the asymmetric reduction of ketimines with trichlorosilane in high yield and excellent enantioselectivity with unprecedented substrate spectrum. In our initial practice, we examined 20mol% of the commercially available (R)-tert-butanesulfinamide and (S)-toluenesulfinamide as the catalyst in the hydrosilylation of ketimine. Although the product was only furnished in moderate yield and low ee, these results demonstrated that our strategy of catalyst design is on the right way. Next, starting from chiral tert-butanesulfinamide, we prepared a series of tert-butanesulfinamide derivatives via simple reductive amination and examined their catalytic efficiencies in the reduction of ketimine. We found that the catalyst bearing a phenolic hydroxyl group exhibited good reactivity and enantioselectivity. On the basis of which, we obtained a structurally simple and highly effective novel organocatalyst, affording the product in 98% yield and 93% ee under optimal reaction conditions. After careful exploration on the role of phenolic hydroxyl group in the catalyst, we speculated that two molecules of the catalyst be involved in the course of reaction, of which the assembly around the silicon center is facilitated by the intermolecular hydrogen bonding through the phenolic hydroxyl groups. Thus, we incorporated two units of sulfonamide into one molecular and prepared a new type of bissulfinamides organocatalysts and examined their catalytic efficiencies in the reduction of ketimine. After optimizing the structure of these catalysts, we finally obtained a novel organocatalyst which has even simpler molecular structure but showed better efficacies, 10mol% of which afforded up to 97% yield and 96% ee under optimal reaction conditions. These results further proved our speculation about the catalytic mechanism. We also examined the newly developed S-chiral organocatalysts in direct asymmetric reductive amination of secondary amines with aromatic ketone. The product was furnished in good yield but in low ee. No better results could be obtained despite our intense opimization efforts. Nevertheless, these experiments laid excellent foundations for eventual success.

Synthesis and characteristics of the human serum albumin-triazine chiral stationary phase

Human serum albumin (HSA) was successfully bonded to silica with s-triazine as activator. The coupling reaction by this method was rapid and effective. The triazine-activated silica is relatively stable and can be installed for at least 1 month without obvious loss of reactivity when stored below 30 degreesC, pH below 7. It was observed that the amount of bound HSA reached 120 mg/g silica calculated from the UV absorbance difference of the HSA solution. d,l-tryptophan was selected as the probe solute to characterize the properties of HSA bonded s-triazine chiral stationary phase, and separation factor of 9.4 was obtained for d,l-tryptophan. Furthermore, the amount of effective HSA on silica was measured by high-performance frontal analysis, and only 16.8 mg/g silica was responsible for the resolution of d,l-tryptophan. These results indicate that the amount of both the bound and effective HSA on silica with triazine as activator was much higher than those by the Schiff base coupling method. Different kinds of enantiomers were resolved successfully on the aminopropylsilica-bonded HSA s-triazine chiral stationary phase. (C) 2000 Wiley-Liss, Inc.

Interweaving of single-helical and equal double-helical chains with the same helical axis in a 3D metal-organic framework

A novel metal-organic framework with unprecedented interweaving of coaxial single-helical and equal double-helical chains of opposite chirality, which features a super-connective helix simultaneously tangling with eight helices, was reported.

Synthesis of the first rare earth metal bis(alkyl)s bearing an indenyl functionalized N-heterocyclic carbene

Treatment of indenyl-modified imidazolium bromide [C9H7CH2CH2(NCHCHN(C6H2Me3-2,4,6)CH)Br] ((IndH-NHC-H)Br) with rare earth metal tetra(alkyl) lithium (Ln(CH2SiMe3)(4)Li(THF)(4)) or with (trimethylsilylmethyl)lithium (LiCH2SiMe3) and rare earth metal tris(alkyl)s (Ln(CH2SiMe3)(3)(THF)(2)) sequentially afforded the first NHC-stabilized monomeric rare earth metal bis(alkyl) complexes (Ind-NHC)Ln(CH2SiMe3)(2) (1, Ln = Y; 2, Ln = Lu; 3, Ln = Sc) via double-deprotonation reactions. Complexes 1-3 are THF-free isostructural monomers. The monoanionic Ind-NHC species bond to the central metal ion in a eta(5):kappa(1) constrained geometry configuration (CGC) mode, which combine with the two cis-located alkyl moieties to form a tetrahedron ligand core, leading to the chirality of the complexes. Under the presence of activators AlEt3 and [Ph3C][B(C6F5)(4)], complex 2 showed catalytic activity toward the polymerization of isoprene to afford 3,4-regulated polyisoprene (91%).

Synthesis and catalytic application of chiral 1, 1 '-binaphthyl polymers

The synthesis of a new type of polymers with main chain chirality based on BINOL skeleton is described. Titanium-BINOLate catalysts are easily generated from these polymers and applied to the asymmetric reaction of Et2Zn with benzaldehyde. The products are obtained in good yields with moderate enantioselectivities.

Double twist in helical polymer "soft" crystals

In natural and synthetic materials having non-racemic chiral centers, chirality and structural ordering each play a distinct role in the formation of ordered states. Configurational chirality can be extended to morphological chirality when the phase, structures possess low liquid crystalline order. In the crystalline states the crystallization process suppresses the chiral helical morphology due to strong ordering interactions, In this Letter, we report the first observation of helical single lamellar crystals of synthetic non-racemic chiral polymers. Experimental evidence shows that the molecular chains twist along both the long and short axes of the helical lamellar crystals, which is the first time a double-twist molecular orientation in a helical crystal has been observed.