Phase transitions in the antiferroelectric liquid crystal C8 tolane determined by dielectric and electro-optical measurements

Simultaneous dielectric permittivity measurements and analysis of the first and the second harmonic electro-optical responses have been performed on a 26 mum thick planar oriented sample of the antiferroelectric liquid crystal tolane C8, which has a polymorphism similar to that of MHPOBC. Comparison of these measurements for different frequencies and geometries (in the case of the electro-optical experiment) allows one to determine all the transition temperatures. The high frequency dielectric permittivity exhibits its maximum (depending on the frequency) inside the SmA phase, whereas the electro-optical coefficient is a maximum at the transition SmA-SmC_alpha* independent of the frequency. A new method for obtaining the temperature dependence of the relaxation frequency in the SmA phase is proposed.     

Phase transitions in the antiferroelectric liquid crystal C8 tolane determined by dielectric and electro-optical measurements

Simultaneous dielectric permittivity measurements and analysis of the first and the second harmonic electro-optical responses have been performed on a 26 mum thick planar oriented sample of the antiferroelectric liquid crystal tolane C8, which has a polymorphism similar to that of MHPOBC. Comparison of these measurements for different frequencies and geometries (in the case of the electro-optical experiment) allows one to determine all the transition temperatures. The high frequency dielectric permittivity exhibits its maximum (depending on the frequency) inside the SmA phase, whereas the electro-optical coefficient is a maximum at the transition SmA-SmC_alpha* independent of the frequency. A new method for obtaining the temperature dependence of the relaxation frequency in the SmA phase is proposed.     

A cucurbit[6]uril analogue: host properties monitored by fluorescence spectroscopy

This paper describes the host properties of a new cucurbit[6]uril analogue, studied by fluorescence and 1H NMR spectroscopy. This host has an elongated cavity with oval-shaped portals. It is intrinsically fluorescent, and more importantly, this fluorescence is sensitive to guest encapsulation, allowing for the study of the inclusion of nonfluorescent guests by fluorescence spectroscopy. In the case of benzene as guest, significant enhancement of the cucurbit[6]uril analogue host fluorescence was observed upon addition of benzene; this allowed for the determination of the binding constant for 1:1 host-guest complexation, yielding a value of K = 6900 +/- 1100 M(-1). This complexation was also studied by 1H NMR, yielding a similar value of K = 8980 +/- 500 M(-1). The binding of a much larger guest, the dye Nile Red, was also studied, but in this case using guest fluorescence. Significant suppression of the Nile Red fluorescence was observed upon 1:1 complexation with the cucurbit[6]uril analogue, with an extremely large binding constant of 8.2 +/- 0.5 x 10(6) M(-1), indicating a very strong host-guest interaction and an excellent size and shape match. In both cases, binding was much stronger than in the case of the same guests with cucurbit[6]uril itself, and in the case of Nile Red, binding was also much stronger than with modified beta- or gamma-cyclodextrins. This is partly a result of the partial aromatic nature of the host walls, which allow for pi-pi interactions not possible in cucurbiturils or cyclodextrins. The ability to study its inclusion complexes using either host or guest fluorescence, and the very high binding constants observed, illustrates the versatility and potential usefulness of this new host compound.     

Eine Abfangmethode zum Nachweis kurzlebiger Carbenium-Ionen in stark sauren Reaktionsmedien

In a new approach, unstable carbenium ions produced in strong protic media could be trapped by thioethers yielding sulfonium compounds. The method has successfully been applied to the rearrangement reactions of sec-butyl alcohol and pinacol, where carbenium ions could be trapped before their rearrangement. In the case of the pinacol-pinacon rearrangement the carbenium ion 13 has already been discussed but for the first time its existence is proved. Since compound 16 has been found, a new mechanism for the pinacol-pinacon rearrangement is postulated starting with diprotonated pinacol.     

Sigma-pi separation of the electron localization function and aromaticity

The electron localization function (ELF) has been separated in its sigma and pi components. The topological analysis of the new ELFsigma and ELFpi functions has been used to quantify the concept of resonance. The highest bifurcation values of these functions describe in a correct way the aromaticity of classical ring molecules and some new aromatic compounds as B6CO6, Al4(2-), and N5-. In the case of Al4(2-), an important sigma delocalization contribution has been found, which is in agreement with previous interpretation.     

End-point detection in potentiometric titration by continuous wavelet transform

The aim of this work was construction of the new wavelet function and verification that a continuous wavelet transform with a specially defined dedicated mother wavelet is a useful tool for precise detection of end-point in a potentiometric titration. The proposed algorithm does not require any initial information about the nature or the type of analyte and/or the shape of the titration curve. The signal imperfection, as well as random noise or spikes has no influence on the operation of the procedure.The optimization of the new algorithm was done using simulated curves and next experimental data were considered. In the case of well-shaped and noise-free titration data, the proposed method gives the same accuracy and precision as commonly used algorithms. But, in the case of noisy or badly shaped curves, the presented approach works good (relative error mainly below 2% and coefficients of variability below 5%) while traditional procedures fail. Therefore, the proposed algorithm may be useful in interpretation of the experimental data and also in automation of the typical titration analysis, specially in the case when random noise interfere with analytical signal.     

The reliable determination of mercury traces in sea water by subtractive differential pulse voltammetry at the twin gold electrode

In the marine environment, mercury has the greatest toxicological significance among the common metals. By combining several basic principles of advanced voltammetry, a reliable and accurate procedure with a determination limit of 1 ng l^-1 has been developed. The complete method, which is necessary for application to sea water, consists of cathodic deposition under programmed polarization with intermittent short anodic pulses to strip the co-deposited copper usually present in sea water in substantially larger amounts than mercury, subsequent medium exchange to 0.1 M HClO₄–2.5 × 10^-3 M HCl, and differential pulse anodic stripping in the subtractive mode at a twin gold disc electrode system. Construction of the twin electrode (which has its two halves insulated from each other), characteristics of the stages of the voltammetric procedure and its performance are presented. The method is very flexible and can be adapted and simplified for application to other aqueous matrices and natural waters with mercury levels above 100 ng l^-1. The data from a case study yielding a survey of the mercury content in the German North Sea coastal waters demonstrate the significance of this new analytical procedure for research and monitoring tasks in marine trace chemistry.     

Closed capillary method for the diffusion of biological macromolecules

The closed capillary method for the determination of self-diffusion coefficients of trace species in liquids has been further developed for use with biological macromolecules. In this development, a new correction to permit its use with -emitting radioisotopes has been introduced. The improved method has been applied to the case of a human blood lipoprotein.     

Characterizing and Manipulating Individual Molecules by Scanning Tunneling Microscopy

Scanning tunneling microscopy (STM) can provide us the special means to characterize the locally physical and chemical properties of individual molecules, and even help us to manipulate the individual molecules for constructing new molecule-scale devices. Here we have adopted two new types of STM techniques to characterize the encapsulated metal atom inside a fullerene cage, and to construct a molecule-device with strong Kondo effect, respectively. The spatially dI/dV mapping spectra were used to unveil the energy-resolved metal-cage hybrid states of individual Dy@C82 molecule, and the important information about the spatial position of Dy atom inside the cage and the Dy-cage interaction was revealed. The high-voltage pulse by STM tip is controlled to induce the dehydrogenation of Co phthalocyanine molecule and change its adsorption configuration on Au(111) surface, so as to recover Kondo effect that disappears in the case of intact adsorbed molecule.     

Analysis of Non-Competitive Enzyme Inhibitors by Thermometric Titrimetry

Abstract

A new thermometric method for the analysis of non-competitive enzyme inhibitors has been developed. Advantages and basic requirements of the method are discussed. In the case studied, 30 nanograms of silver ions were detected.     

Selective Homogeneous and Heterogeneous Gold Catalysis with Alkynes and Alkenes: Similar Behavior,Different Origin

The development of new sustainable chemical processes requires the implementation of ultra‐selective reaction processes. The enormous selectivity found for gold‐based catalysts when applied in several reactions has opened new frontiers. For instance, the selective activation of alkynes is a common feature for both homogeneous and heterogeneous gold catalysts. Herein, we employ experimental and theoretical methods to assess the similarities and differences in the performance of homogeneous and heterogeneous gold catalysts. Alkynophilicity, the selective activation of alkynes, is found to have a thermodynamic origin in the heterogeneous case and a kinetic one for homogeneous catalysis. Complex enyne rearrangements require the more active homogeneous (single gold) catalyst because it has more electrophilic character than its heterogeneous (nanoparticle) counterpart.     

Novel characterization of proteomics maps by sequential neighborhoods of protein spots

We consider a characterization of proteomics maps based on an alternative kind of neighborhood graphs for the protein spots on 2-D gel. The novel approach considers for every protein spot only the nearest neighborhood consisting of protein spots of higher abundance. The approach has the simplicity and advantages of the recently introduced characterization of proteome maps based on considering the nearest neighborhoods of protein spots, but it also has important additional desirable computational features. The characterization of the nearest neighborhood graphs of 2-D gel proteomics maps is sensitive to the number of spots considered and may lead to changes in the degree of similarity of different maps when the number of points has been changed, thus imposing restrictions on the protocol used for comparison of maps. The novel approach presented in this work is less sensitive to the number of points used in the analysis because graphs are constructed in a stepwise process in which the role of more distant neighbors has been diminished by linking a new spot to the nearest spot that has been already part of the neighborhood graph. In this way a graph with N + 1 spots is obtained from the graph on N spots by adding a single new link, while in the case of the nearest neighborhood graphs adding a new spot introduces novel neighborhoods and generally results in a graph that may differ significantly from the neighborhood graph on N points.     

Continuous separation of biomolecules by the laterally asymmetric diffusion array with out-of-plane sample injection

The laterally asymmetric diffusion array, a biomolecule sorting device, was used to continuously separate a mixture of T2 and T7 coliphage DNA molecules into its constituents. A two-dimensional array of obstacles (in the presence of an average flow v) can be used to rectify the Brownian motion of particles (in this case DNA molecules) so that they diffuse preferentially in one direction, and perpendicular to the direction of the applied field (in this case an electric field). This type of device had not yet been used for actual fractionation of biomolecules, due to difficulties in injection of the sample. Here we show that with a new injection strategy a well-defined, narrow and continuous stream of molecules can be injected into the separation channel, thus enabling this separation technique to be used in a working device. We expect this type of device could now be employed for separation of a variety of different biomolecules, ranging from long dsDNA to small proteins.     

Highly enantioselective phenylacetylene addition to aromatic ketones catalyzed by cinchona alkaloid-aluminum complexes

The catalytic asymmetric addition of phenylacetylene to aromatic ketones is reported. The catalyst, generated from commercially available Cinchona alkaloids and industrially available triethylaluminum, gives the expected tertiary alcohols with good enantiomeric excess (70-89%) and yields (60-83%). No previous case has been reported successfully using triethylaluminum as a Lewis acid in the asymmetric alkynylation of carbonylic derivatives, and thus we provide a new method to obtain optically active tertiary propargyl alcohols.     

糖类物质的毛细管电泳分析

毛细管电泳(CE)是近二十年发展起来的一种新的分离分析技术，它以快速、高效、高灵敏度、所需样品少等优点被广泛应用于各个领域。八十年代末开始应用于糖类物质的分析，并获得了快速发展。本文对毛细管电泳分离分析糖类物质进行了评述，主要集中在多糖的水解、衍生、检测、分析应用及前景等方面。全文引用文献40篇。     

Determination of S-containing drug metabolites from in vitro and in vivo metabolism studies by using LC-ICP/MS

Recently, liquid chromatography coupled to inductively coupled plasma mass spectrometry (LC-ICP/MS) has been introduced to deal with some applications in the field of pharmaceutical, biomedical, and clinical analysis. In the case of drug research, the number of drugs and their metabolites containing detectable elements is quite limited. In this paper, LC-ICP/MS has been demonstrated to be suitable for the determination of S-containing drugs and their metabolites. In order to minimize the interference of polyatomic oxygen (m/z 32), the indirect detection of S, by means of the SO(+) ion (m/z 48), was optimized. For quantification purposes, it has been encountered that the percentage of organic solvent in the mobile phase strongly affects the sensitivity. Here, corrective strategies based on calibration curves established at different solvent concentrations (solvent-zone quantification) and post-column gradient compensation have been proposed to circumvent sensitivity variations. Results obtained have shown that suitable calibration models have been built for any compound regardless of the solvent percentage at which it is eluted from the chromatographic column. To prove the applicability of this methodology, the metabolism of ethacrynic acid and tiotropium bromide has been studied in vitro and in vivo. In the first case, ethacrynic acid does not contain S in its structure, however, the major route of metabolism for this compound consists of the formation of glutathione adduct and its further degradation. In the second case, tiotropium bromide contains two S atoms in its structure.     

Quantum two-state dynamics driven by stationary non-Markovian discrete noise: Exact results

We consider the problem of stochastic averaging of a quantum two-state dynamics driven by non-Markovian, discrete noises of the continuous time random walk type (multistate renewal processes). The emphasis is put on the proper averaging over the stationary noise realizations corresponding, e.g., to a stationary environment. A two-state non-Markovian process with an arbitrary non-exponential distribution of residence times (RTDs) in its states with a finite mean residence time provides a paradigm. For the case of a two-state quantum relaxation caused by such a classical stochastic field we obtain the explicit exact, analytical expression for the averaged Laplace-transformed relaxation dynamics. In the limit of Markovian noise (implying an exponential RTD), all previously known results are recovered. We exemplify new more general results for the case of non-Markovian noise with a biexponential RTD. The averaged, real-time relaxation dynamics is obtained in this case by numerically exact solving of a resulting algebraic polynomial problem. Moreover, the case of manifest non-Markovian noise with an infinite range of temporal autocorrelation (which in principle is not accessible to any kind of perturbative treatment) is studied, both analytically (asymptotic long-time dynamics) and numerically (by a precise numerical inversion of the Laplace-transformed averaged quantum relaxation).     

Fluorescence quenching of carbazole and indole by ethylenetrithiocarbonate

The fluorescence of quenching of carbazoles and indoles by ethylenetrithiocarbonate has been studied. Both steady-state and transient fluorescence experiments were carried out in order to determine rate constants in the case of carbazoles. The results obtained support the charge-transfer mechanism. Ground-state complex formation is assumed to explain the higher rate constants for indole and its derivatives, which appear as positive curvatures in Stem-Volmer plots.     

Activation of DMSO for Swern-type oxidation by 1,1-dichlorocycloheptatriene

A new dimethylsulfoxide activation method employing 1,1-dichlorocycloheptatriene has been developed for a mild Swern-type oxidation of a variety of alcohols. The carbonyl products can be obtained in good to excellent yields from this operationally simple and efficient method. This work is the first report of dimethylsulfoxide activation by a simple chlorinated hydrocarbon reagent, which has the unique ability of equilibrating to its reactive aromatic cationic form.