四氟乙烯齐聚体的反应 四氟乙烯四、五聚体和芳香胺的反应

前已报道四氟乙烯四聚体(全氟-3,4-甲基己烯-3)(1)、五聚体(全氟-3,4-二甲基-4-乙基己烯-2)(2)和脂肪烷氧以及脂肪胺的亲核反应.本文报道化合物1,2和芳香胺如苯胺、β-萘胺的反应.由于烯烃1、2双键处于分子中间,因而当亲核试剂进攻时,双键容易发生重排,生成的末端基烯烃更具反应性,故导致一取代、二取代、三取代以及环化降解等复杂产物.     

A novel method that improves sensitivity of protein detection in PAGE and Western blot

We have developed a simple and inexpensive method that improves sensitivity of protein and antigen detection in standard PAGE procedures. Our technique uses a sample microloader device with a funnel‐like structure, filled with a 4% stacking gel. When attach to the top of a polyacrylamide slab gel, the proteins in a sample are concentrated by electrophoresis into a small volume as they emerge from the device's narrow outlet. Our microloader has several advantages over previous devices, including simple assembly, high versatility, and absence of cross‐contamination between lanes. Addition of this device to a slab gel results in a fivefold increase in the sensitivity of antigen detection in a Western blot. As a result, less protein is required for loading and signal detection. Our protocol is a straightforward modification of a standard experimental technique, and is especially useful when only limited sample quantities are available.     

Photochromic reactions of diarylethenes in single crystals with intermolecular O--H...N hydrogen-bonding networks

The crystal structures and photochromic performance of a single crystal of a diarylethene derivative possessing carboxyl groups, 1,2-bis(5-carboxyl-2-methyl-3-thienyl)perfluorocyclopentene (1 a), and cocrystals of 1 a with 4,4'-, 2,4'-, and 2,2'-bipyridines were examined. In crystal 1 a, a discrete cyclic structure was observed, in which four 1 a molecules are linked through hydrogen bonds between the carboxyl groups. In the homocrystal, photoreactive and photoinactive conformers of 1 a exist in the ratio of 1:1. In the cocrystals of 1 a with bipyridines, O--HN-type hydrogen bonds between 1 a and pyridyl groups were formed, and all 1 a molecules are fixed in a photoreactive conformation. Both the homocrystal 1 a and the cocrystals showed photochromic performances, and color variation from bluish-violet to cyan was observed, depending on the conformation of the packed diarylethene molecules.     

CALCULATION OF THE YOUNG''''S MODULUS OF AN ADSORBED POLYMER LAYER

Polymer layers adsorbed to a surface or in a confined environment often change their mechanical properties. There is even the possibility of solidification of the confined layer. To judge the stiffness of such a layer, we used the Hertz model to calculate the Young's modulus of the polymer layer in the confinement of AFM experiments with silicon nitride tip with a radius of curvature of R≈50 nm and a glass sphere attached to the cantilever R = 5μm. Since there is no visible indentation of the layer in the AFM experiments, the layer is either penetrated very easily, or the indentation is too small to be seen in a force curve. The latter would be the case for a polymer layer with a Young's modulus above 4×108 Pa in case of an experiment with a silicon nitride tip and 4×105 Pa in case of a glass sphere.     

Controlled Dynamic Helicity of a Folded Macrocycle Based on a Bisterephthalamide with a Twofold Z‐Shaped Structure

Dynamic helicity in a folded macrocycle and control of the helical preference are described. We designed macrocycle 1 with a dual mode of folding through the integration of two flexible units that are arranged twice to form a cyclic structure. As a folding unit, we used a terephthalamide skeleton and a Z‐shaped hydrocarbon: the former acted as a control unit to induce a preference of a particular sense of dynamic helicity and the latter was just a spacer. A terephthalamide unit provided a binding site for capturing a ditopic hydrogen‐bonding guest when it adopted helically folded syn forms (M/P). Thus, only the terephthalamide unit controlled the helical sense of dynamic helicity in a folded macrocycle through the supramolecular transmission of chirality upon complexation with a chiral ditopic guest. In addition, chirality on a host could also contribute to the control of the helical preference in a folded macrocycle, which led to exceptionally enhanced chiroptical signals.     

Solid-phase synthesis of 5-arylhistidines via a microwave-assisted Suzuki-Miyaura cross-coupling

Microwave irradiation efficiently promoted the solid-phase Suzuki-Miyaura reaction of a 5-bromohistidine with various arylboronic acids in the presence of a palladium catalyst. This methodology allowed the synthesis of peptides bearing a histidine residue substituted at position 5 of the imidazole ring with a phenyl, a substituted phenyl, a pyridyl, or a thienyl ring, as well as with the benzene ring of a tyrosine residue.     

Boron/nitrogen substitution of the central carbon atoms of the biphenalenyl diradical π dimer: a novel 2e-12c bond and large NLO responses

On the basis of the famous staggered biphenalenyl diradical π dimer 1, the eclipsed biphenalenyl (1a), with no centrosymmetry, was obtained by rotating a layer of 1 by 60° around its central axis. Furthermore, the central carbon atoms of 1 and 1a were substituted by boron and nitrogen atoms to form 2 and 2a with a novel 2e-12c bond. We found that the novel 2e-12c bond is formed by the electron pair of the occupied orbital of the phenalenyl monomer substituted by the nitrogen atom and the unoccupied orbital of the phenalenyl monomer substituted by the boron atom. As a result of the novel 2e-12c bond, 2 and 2a exhibit a fascinating interlayer charge-transfer transition character, which results in a significant difference in the dipole moments (Δμ) between the ground state and the crucial excited state. The values of Δμ for 2 and 2a are 6.4315 and 6.9253 Debye, clearly larger than the values of 0 and 0.0015 Debye for 1 and 1a. Significantly, the boron/nitrogen substitution effect can greatly enhance the first hyperpolarizabilities (β(0) ) of 2 and 2a with a novel 2e-12c bond compared with 1 and 1a with a traditional 2e-12c bond: 0 and 19 a.u. for 1 and 1a are much lower than 3516 and 12272 a.u. for 2 and 2a. Furthermore, the interaction energies (E(int) )of 2 and 2a are larger than those of 1 and 1a, which could be considered as a signature of reliability for the newly designed dimers. Our present work will be beneficial for further theoretical and experimental studies on the properties of molecules with the novel 2e-12c bond.     

Palladium‐Catalyzed Reductive Coupling Reaction of Terminal Alkynes with Aryl Iodides Utilizing Hafnocene Difluoride as a Hafnium Hydride Precursor Leading to trans‐Alkenes

Herein, we describe a reductive cross‐coupling of alkynes and aryl iodides by using a novel catalytic system composed of a catalytic amount of palladium dichloride and a promoter precursor, hafnocene difluoride (Cp₂HfF₂, Cp=cyclopentadienyl anion), in the presence of a mild reducing reagent, a hydrosilane, leading to a one‐pot preparation of trans‐alkenes. In this process, a series of coupling reactions efficiently proceeds through the following three steps: (i) an initial formation of hafnocene hydride from hafnocene difluoride and the hydrosilane, (ii) a subsequent hydrohafnation toward alkynes, and (iii) a final transmetalation of the alkenyl hafnium species to a palladium complex. This reductive coupling could be chemoselectively applied to the preparation of trans‐alkenes with various functional groups, such as an alkyl group, a halogen, an ester, a nitro group, a heterocycle, a boronic ester, and an internal alkyne.     

Total Synthesis of Tetrodotoxin

A total synthesis of tetrodotoxin was accomplished. A Diels–Alder reaction between a known enone and a siloxy diene gave a tricyclic product, the steric bias of which was used to construct the remaining stereogenic centers. A nitrogen atom was introduced either by a four‐step sequence involving a Curtius rearrangement, or a three‐step sequence featuring a newly developed transformation of a terminal alkyne into a nitrile. Introduction of the guanidine moiety followed by the formation of the heterocyclic system by cascade reactions led to tetrodotoxin.     

Synthesis of aspergillide A from a synthetic intermediate of aspergillide B

The first synthesis of aspergillide A, a cytotoxin produced by a marine-derived fungus, has been achieved from a synthetic intermediate of aspergillide B by using a proline-mediated epimerization of a 2,6-trans-substituted tetrahydropyran-2-acetaldehyde intermediate into the corresponding cis-isomer via a retro-oxy-Michael/oxy-Michael sequence as the key transformation.     

Fast fringe-field switching of vertically aligned liquid crystals between high-haze translucent and haze-free transparent states

We report control of the haze value in a liquid crystal (LC) cell driven by a fringe electric field. When a fringe field is applied to a vertically aligned (VA) cell, a large spatial phase difference with a short grating period is induced in the LC layer. The average grating period of a VA cell driven by a fringe field is a quarter of the pitch of the interdigitated electrodes, which is half of the grating period of a VA cell driven by an in-plane field. Moreover, a sharper spatial phase profile is built around the edges of the interdigitated electrodes, which led to a high haze of 84.3% in the translucent state. The device was haze-free in the transparent state owing to the use of an LC layer without a polymer structure. To increase the haze value of the LC device while retaining a short response time, we developed an LC cell with crossed interdigitated electrodes where a large spatial phase difference is induced with little dependence on the azimuth angle. By applying a fringe electric field to a 20 μm thick LC cell using crossed interdigitated electrodes, we demonstrated a very high haze of 95.4% and a response time of less than 5 ms.     

Crystal engineering of photochromic diarylethene single crystals

Photochromic performance of diarylethene single crystals was controlled by crystal engineering using non-covalent aromatic-aromatic interactions as the directional intermolecular force. A diarylethene derivative with two pentafluorophenyl groups, 1,2-bis(2-methyl-5-pentafluorophenyl-3-thienyl)perfluorocyclopentene (1a), formed stoichiometric co-crystals with benzene (Bz) and naphthalene (Np) by aryl-perfluoroaryl interactions. Face-to-face pi-stacking interactions between the pentafluorophenyl groups of 1a and the aromatic molecules are responsible for 2:1 and 1:1 stoichiometric compositions in 1a/Bz and 1a/Np co-crystals, respectively. The diarylethene underwent thermally stable and photoreversible photochromic reactions in a homo-crystal of 1a and co-crystals 1a/Bz and 1a/Np. The absorption spectra of the photogenerated closed-ring isomers varied depending on the conformation of the diarylethene molecules packed in the crystals. The diarylethene 1a also formed 1:1 stoichiometric co-crystals with different kinds of diarylethenes, 1,2-bis(2-ethyl-5-phenyl-3-thienyl)perfluorocyclopentene (2a) and 1,2-bis[2-methyl-5-(1-naphthyl)-3-thienyl]perfluorocyclopentene (3a). Both co-crystals 1a/2a and 1a/3a showed photochromism. Although 1a, 2a, and 3a underwent efficient photocyclization reactions in their homo-crystals, highly selective photocyclization reactions of 2a or 3a were observed in the co-crystals. The selective reactions were confirmed by HPLC and X-ray crystallography. Excited energy transfers from 1a to 2a and from 1a to 3a are considered to occur and cause the selective reactions.     

Prediction of acidity in acetonitrile solution with COSMO-RS

The COSMO-RS method, a combination of the quantum chemical dielectric continuum solvation model COSMO with a statistical thermodynamics treatment for realistic solvation simulations, has been used for the prediction of pK(a) values in acetonitrile. For a variety of 93 organic acids, the directly calculated values of the free energies of dissociation in acetonitrile showed a very good correlation with the pK(a) values (r(2) = 0.97) in acetonitrile, corresponding to a standard deviation of 1.38 pK(a) units. Thus, we have a prediction method for acetonitrile pK(a) with the intercept and the slope as the only adjusted parameters. Furthermore, the pK(a) values of CH acids yielding large anions with delocalized charge can be predicted with a rmse of 1.12 pK(a) units using the theoretical values of slope and intercept resulting in truly ab initio pK(a) prediction. In contrast to our previous findings on aqueous acidity predictions the slope of the experimental pK(a) versus theoretical DeltaG(diss) was found to match the theoretical value 1/RT ln (10) very well. The predictivity of the presented method is general and is not restricted to certain compound classes. However, a systematic correction of -7.5 kcal mol(-1) is required for compounds that do not allow electron-delocalization in the dissociated anion. The prediction model was tested on a diverse test set of 129 complex multifunctional compounds from various sources, reaching a root mean square deviation of 2.10 pK(a) units.     

Synthesis of well-defined polymers with protected silanol groups by atom transfer radical polymerization and their use for the fabrication of polymeric nanoparticles

Copper-mediated atom transfer radical polymerization (ATRP) of a protected silanol group-holding methacrylate, methacryloxypropyltrimethoxysilane (MOPS), was investigated. In a dry condition using carefully distilled solvent and monomer, the polymerization proceeded in a living fashion providing a low-polydispersity polymer with a predicted molecular weight. The ATRP in conjunction with the sequential monomer addition of methyl methacrylate (MMA) and MOPS afforded a block copolymer of the type PMMA-b-poly(MMA-r-MOPS). The heat treatment of a solution of the block copolymer in the presence of a catalytic amount of ammonia gave a polymeric core-shell nanoparticle with a shell of PMMA moieties and a core of the poly(MMA-r-MOPS) blocks cross-linked via the condensation of the trimethoxysilane groups of the MOPS moieties.     

Structural studies of biarylpyridines fluorophores lead to the identification of promising long wavelength emitters for use in fluorescent chemosensors

Fluorescent chemosensors—molecules whose fluorescence emission changes in response to a reversible binding event—require both a substrate binding domain and a reporting fluorophore. Our approach to chemosensor development is based on a combination of a new signaling mechanism and a modular fluorophore synthesis. The latter feature has facilitated detailed study of the properties of polyarylpyridine fluorophores, and has led to the identification of a visibly-emissive pyridine as a promising lead structure for chemosensor development. The results of this study are described herein.     

New CD derivatives as self-assembling contrast agents for magnetic resonance imaging (MRI)

A way to improve Magnetic Resonance Imaging is to deliver a larger number of Imaging Probe units to the target site. Aiming at this objective, we prepared a self-assembling system consisting of: 1) a β-cyclodextrin (β-CD) bearing a covalently bonded Gd complex (DTPA-Lys); 2) a polypeptide containing a high percentage of tyrosine residues (PLT); 3) a second β-CD derivative bearing a covalently bonded peptide vector (CCK8) that can recognize a specific cell-membrane receptor. Both β-CD derivatives can form stable inclusion complexes with the aromatic moieties of the polypeptide. The formation of a supramolecular adduct having a long reorientational correlation time entailed a marked relaxivity increase (per Gd³⁺ ion), which recommends it as a promising model for detail enhancement procedures at the target site. Out of three different synthetic pathways that could be used for binding a CD to DTPA, the most convenient one involved a micro-wave(MW)-assisted Mannich aminomethylation of a monopropargyl β-CD by the primary amino group of t-butyl-DTPA-Lys.     

Theoretical insights into the role of a counterion in copper-catalyzed enantioselective cyclopropanation reactions

The effect of a coordinating counteranion on the mechanism of Cu(I)-catalyzed cyclopropanation has been investigated extensively for a medium-sized reaction model by means of theoretical calculations at the B3LYP/6-31G(d) level. The main mechanistic features are similar to those found for the cationic (without a counteranion) mechanism, the rate-limiting step being nitrogen extrusion from a catalyst-diazoester complex to generate a copper-carbene intermediate. The cyclopropanation step takes place through a direct carbene insertion of the metal-carbene species to yield a catalyst-product complex, which can finally regenerate the starting complex. However, the presence of the counteranion has a noticeable influence on the calculated geometries of all the intermediates and transition structures. Furthermore, the existence of a preequilibrium with a dimeric form of the catalyst, together with a higher activation barrier in the insertion step, explains the lower yield of cyclopropane products observed experimentally in the presence of chloride counterion. The stereochemical predictions of a more realistic model (made by considering a chiral bis(oxazoline)-copper(i) catalyst) have been rationalized in terms of the lack of significant steric repulsions, and the model shows good agreement with the low enantioselectivities observed experimentally for these kinds of catalytic systems.     

适用于针尖增强拉曼技术的Au针尖的研制

采用针尖增强拉曼光谱技术(TERS)研究了刻蚀电位对Au针尖刻蚀效果的影响, 初步探讨了刻蚀过程的机理. 通过监控刻蚀过程中的振荡电流-时间曲线并与扫描电镜得到的结果比较, 发现可以直接利用电流-时间曲线简单地判断刻蚀后针尖的可能形状, 而无需再借助扫描电镜进行表征. 这不但提高了实验效率, 而且还可以避免针尖在转移和电镜表征过程中可能引入的污染. 研究结果表明, 在体积比为1:1的发烟盐酸和无水乙醇的刻蚀液中, 于2.2 V的电压下, 结合电化学方法控制终点可以得到形状对称尖锐的针尖. 这种针尖不但适合于TERS研究, 而且可用作STM针尖和微纳电极并用于其它针尖增强光学技术.     

Quantitative X-Ray Microanalysis of Heterogeneous Materials Using Monte Carlo Simulations

Monte Carlo simulations are used to obtain new results of x-ray microanalysis of sample types frequently encountered in practical analytical situations such as a vertical layer embedded in a homogeneous matrix and a spherical particulate deposited on a substrate. The simulations show that a 10-nm layer of boron in a steel matrix can be imaged using backscattered electrons and detected using x-ray microanalysis with a field emission scanning electron microscope even with an electron beam energy equals to 20 keV and also that these simulations can be useful to estimate the optimum acceleration voltage to perform such analyses. For a carbon spherical particulate located on the top of a gold substrate, it is shown that x-ray emission and electron backscattering are a strong function of the diameter of the particulate and also of the electron beam energy. Finally, a new method to determine the thickness of a thin film deposited on a substrate is proposed that does not require the measurement of the beam current. That technique can also be used for a spherical particulate deposited on a substrate.     

Convolutive forecasting at a hanging mercury drop electrode

Convolutive forecasting is a procedure which converts a non-steady-state voltammogram into a steady-state voltammogram. The procedure was found to be successful on a range of sphericities generated by varying the size of a hanging mercury drop and the potential sweep rate in a series of cyclic voltammetric experiments. Both theoretical and experimental analyses on a reversible electrochemical system were considered. An expression establishing the relationship between the radius of a spherical electrode and the potential sweep rate was developed to define the limits of the convolutive forecasting algorithm which was used.