Determination and regulation of the migration window in electrokinetic chromatography

The determination of the velocities of the mobile and the pseudostationary phases (the migration (time) window) is mandatory for the determination of physicochemical properties by electrokinetic chromatography (EKC). This review offers a detailed discussion on the definition, the importance, the determination and the regulation of the migration (time) window in EKC. An overview on the theoretical treatment of chromatographic processes in EKC is given defining EKC in comparison to the term capillary electrophoresis. Methods to determine and influence the migration window are discussed with emphasis on measures that have been taken to modify the electroosmotic flow velocity. Pseudostationary phases (or separation carriers) that are taken into consideration are anionic and cationic micelles, mixed micelles, microdroplets (microemulsions), polymeric pseudostationary phases and dendrimers.     

Thermoforming process of semicrystalline polymeric sheets: Modeling and finite element simulations

A micromechanically-based elastic-viscoplastic model for the thermoforming process of semicrystalline polymer materials is proposed and implemented in a finite element code. This model takes into account the temperature and strain rate dependence. In this process the applied temperature is taken uniform throughout the sheet and its variation is due only to the adiabatic heating. The simulations are conducted for isotactic polypropylene using the finite element method. The polymer sheet thickness, the orientation of the polymer molecular chains, and the percent crystallinity show an important dependence on the process temperature (polymer softening) and the geometry of the mold. Based on recent experimental results in the literature, amorphization (decrease of crystallinity) is taken into account. Published in Russian in Vysokomolekulyarnye Soedineniya, Ser. A, 2008, Vol. 50, No. 5, pp. 841–849. This article was submitted by the authors in English.     

Single molecule charge transport: from a quantum mechanical to a classical description

This paper explores charge transport at the single molecule level. The conductive properties of both small organic molecules and conjugated polymers (molecular wires) are considered. In particular, the reasons for the transition from fully coherent to incoherent charge transport and the approaches that can be taken to describe this transition are addressed in some detail. The effects of molecular orbital symmetry, quantum interference, static disorder and molecular vibrations on charge transport are discussed. All of these effects must be taken into account (and may be used in a functional way) in the design of molecular electronic devices. An overview of the theoretical models employed when studying charge transport in small organic molecules and molecular wires is presented.     

Quantum-chemical calculations of thermodynamic parameters of the synthesis of tris(hydroxymethyl)phosphine

Thermodynamic characteristics of the process of tris(hydroxymethyl)phosphine synthesis are calculated by the Hartree-Fock-Roothaan method in the basises LANL2DZ and 6–31G. From the calculated data degrees of accumulation are found of the target product that correlate with experimental data. This fact can be taken into account at the choice of conditions for producing tris(hydroxymethyl)phosphine.     

Microwave assisted ecofriendly recycling of poly (ethylene terephthalate) bottle waste

Glycolysis of poly (ethylene terephthalate) bottle waste was carried out using microwave energy. A domestic microwave oven of 800 W was used with suitable modification for carrying out the reaction under reflux. The catalysts used for the depolymerization in ethylene glycol (EG) were zinc acetate and some simple laboratory chemicals such as sodium carbonate, sodium bicarbonate and barium hydroxide. Comparison of results was made from the point of view of the yield of bis (2-hydroxyethylene) terephthalate (BHET) and the time taken for depolymerization. It was observed that under identical conditions of catalyst concentration and PET:EG ratio, the yield of BHET was nearly same as that obtained earlier by conventional electric heating. However, the time taken for completion of reaction was reduced drastically from 8 h to 35 min. This has led to substantial saving in energy.     

Determination of anethole in serum samples by headspace solid-phase microextraction-gas chromatography-mass spectrometry for congener analysis

A rapid headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) method has been developed for the determination of anethole in serum samples. Anethole is a characteristic marker for the consumption of aniseed spirits. This method enabled the detection of anethole with a limit of detection (LoD) of 3.6 ng/ml and a limit of quantification (LoQ) of 5.3 ng/ml in serum samples with a good degree of precision intraday (2.8%) and interday (4.5%). Experiments were conducted with one volunteer, in which the subject consumed the alcoholic drink ouzo on 3 different days under controlled conditions. At defined intervals, blood samples were taken from the subject. Using these blood samples, the concentration-time profiles for anethole were determined. In blood samples taken from 50 drivers who claimed to have consumed drinks containing anethole (ouzo, raki and the German aniseed liqueur "Küstennebel") before the taking of the blood sample, anethole was detected in the serum in concentrations of between 5.4 and 17.6 ng/ml in 10 cases. This is the first report describing the qualitative and quantitative determination of a beverage-characteristic aroma compound - in this case anethole - in serum samples after consumption of alcoholic beverages.     

失踪的镧系元素

The lanthanides include elements having atomic numbers 57 (lanthanum) through 71 (lutetium). They all behave in a similar way in chemical reactions and play an increasingly important role in production and life. This article imagines a series of changes that have taken place on the earth since the disappearance of lanthanides, which shows their importance in human life.     

A theoretical investigation of the remarkable nuclear spin-spin coupling pattern in [(NC)(5)Pt-Tl(CN)](-).

We address the problem of the interpretation of heavy nucleus spin-spin couplings for systems being studied in solution. Solvation can create counterintuitive features concerning the spin-spin couplings, which are enhanced by relativistic effects due to the presence of heavy nuclei. This should therefore be taken into consideration for the discussion of spectra obtained from solution. Evidence for such solvent effects is provided by a relativistic density functional study of [(NC)(5)Pt-Tl(CN)](-) (I). It is demonstrated that the remarkable experimentally observed spin-spin coupling pattern, e.g., (2)J(Tl-C) > (1)J(Tl-C) and J(Pt-Tl) approximately 57 kHz, is semiquantitatively reproduced by our calculations if both relativistic effects and solvation are taken into account. Solvent effects are very substantial and shift the Pt-Tl coupling by more than 100%, e.g. Relativistic increase of s-orbital density at the heavy nuclei, charge donation by the solvent, and the specific features of the multicenter C-Pt-Tl-C bond are responsible for the observed coupling pattern.     

Differential scanning and titration calorimetric studies of macromolecules in aqueous solution

An enormous amount of detailed information can be obtained concerning macromolecules in aqueous solution using data obtained from differential scanning and titration microcalorimetry. This claim is supported by reference to examples taken from recent work concerned with micelles (e.g. CTAB), vesicles (e.g. DOAB and DDP) and enzymes (e.g. CAT and DNA gyrase).     

The molecular end effect and its critical impact on the behavior of charged-uncharged polymer conjugates during free-solution electrophoresis

Recently two novel techniques using free-solution electrophoresis to separate charged-uncharged polymer conjugates have proven successful: end-labeled free-solution electrophoresis (ELFSE) for DNA sequencing, and free-solution conjugate electrophoresis (FSCE) for molar mass profiling of uncharged polymers. The approach taken to analyze the experimental data was an extension of the theory of Long and co-workers (Long, D., Dobrynin, A. V., Rubinstein, M., Ajdari, A., J. Chem. Phys. 1998, 108, 1234-1244) for the electrophoresis of molecules with varying charge distributions. This theory also predicts that the ends of the polymers play a large role in determining the polymer's overall mobility; however, this aspect of the theory was neglected in previous work. Until now this "end effect" has, to the knowledge of the authors, not been recognized in experimental data. Through a careful investigation of the predicted end effect and a reanalysis of the experimental data, we demonstrate that indeed this effect critically impacts on the behavior of charged-uncharged polymer conjugates during electrophoresis. This work indicates that not only does the end effect need to be taken into account to avoid significant errors in data analysis, but also it provides novel system optimization approaches.     

A chromophoric switch based on pseudorotaxanes

In a three-component system containing dibenzo-24-crown-8 (1), diamino-dibenzo-24-crown-8 (2), and 1,2-bis(4,4(')-dipyridyl)ethane (3(2+)), axle 3(2+) can shuttle between wheels 1 and 2 by acid-base control, accompanying color changes from yellow to red. This system could not only be taken as a chromophoric supramolecular switch, but also exhibit a function as INHIBIT logic gate.     

Application of adsorption calorimetry to the study of heterogeneous catalysis reactions

This survey sets out to show that adsorption calorimeters, and particularly conduction-type calorimeters, can be used to measure catalytic activities and determine (i) rate laws, (ii) probable reaction mechanisms, (iii) the secondary processes which cause catalyst activation or deactivation, and (iv) the site distribution at the catalyst surface. The merits and limitations of the various applications of adsorption calorimetry to the study of heterogeneously catalyzed reactions are critically discussed. Most examples are taken from the author's previous publications.     

Comparative Thermogravimetric Studies of Poly(ether-ketone/sulfone) Imides and Their Parent Polymers: I. Poly(ether-ketone/sulfone) ethylimide

Thermogravimetry (TG) was employed to study the thermal degradation kinetics of poly(etherketone/sulfone)ethylimide (PEK-IE and PES-IE). The corresponding decomposition activation energies and reaction orders were obtained and the comparison was made with their parent polymerspoly(ether-ketone/sulfone) with Cardo group (PEK-C and PES-C). The results show that the degradation activation energies of PEK-IE and PES-IE were lower than that of PEK-C and PES-C; and two stages of the degradation process were found for all the four polymers. For PEK-IE and PES-IE, the activation energies in the first decomposition stage are much lower than that in the second stage and the two stages can be taken as slow induction and fast degradation, whereas for PEK-C and PES-C the activation energies in the first decomposition stage are larger than that in the second stage, and the two stages can both be taken as two fast degradation stages. The decomposition mechanism of the two stages was also speculated.This revised version was published online in November 2005 with corrections to the Cover Date.     

因子分析在速差动力学分析中的应用──肾上腺素和去甲基肾上腺素的同时测定

将一种改进的目标因子分析法(MTFA)用于复杂反应的速差动力学分析体系,采用此法处理实验数据时,引入了一个非零截距因子,采用模拟纯谱运算。可使方法的准确度大大提高。据此建立了一种停流技术进样、速差动力学分析同时测定、因子分析处理实验数据的新方法;对于10^-6mol·L^-1级的肾上腺素-去甲基肾上腺素混合物,比例范围在1:5～5:1之间,测定相对误差小于±10%,用于合成样品中肾上腺素和去甲基肾上腺素的同时测定,获得了满意结果。     

An Alternative Demonstration of Chemical Waves: A Video Clip of a One-Dimensional Wave in the Iodate–Arsenite System

A chemical wave was initiated in a system (glass tube or graduated cylinder) containing a water solution of potassium iodate, potassium hydrogen sulfate, starch, and an excess of potassium arsenite. A large number of photos (329) were taken with a digital camera (one snapshot every 30 seconds). These photos were linked to give a unique video clip. This video clip may be used as a time-saving alternative to the classical demonstration. Similar clips may be made for other long-lasting processes.     

A theoretical investigation on the mechanism of the PtCl2-mediated cycloisomerization of heteroatom-tethered 1,6-enynes

A mechanistic study based on DFT theoretical calculations for the PtCl(2)-catalyzed formation of bicyclic adducts from heteroatom tethered 1,6-enynes is reported. Different reaction pathways have been taken into account and the results are discussed. This analysis clearly reveals that the kinetically preferred pathway involves an initial 6-endo-cyclization from a triggered reactant complex by pi-complexation of Pt(II) onto the alkyne to form a cyclopropyl platina-carbene intermediate, followed by a [1,2]-hydrogen shift.     

On the relationship between the chemical bond energy and the electron energy levels of strongly ionic compounds

The analysis of experimental data suggests that the energy levels of ions in a crystal shift rigidly by an amount equal to the Madelung energy (electrostatic bond energy) maintaining the same separation as in the free ion. This leads to the conclusion that the electrostatic bonding energies of ions in a crystal is taken up partly by the orbital electrons and partly by the nuclear charge.     

Lanthanide complexes as imaging agents anchored on nano-sized particles of boehmite

The synthesis of boehmite nanoparticles modified with lanthanides (Eu, Tb and Gd) is described. Their synthesis, characterization and in vitro assays with HeLa cells were performed. The nuclear magnetic relaxation dispersion (NMRD) profiles of the two chelating moieties were studied. Imaging data from laser scanning confocal fluorescence microscopy and flow cytometry revealed that the nanoscaffolds were taken up by the cells, distributed throughout the cytoplasm and showed no toxicity. This platform could represent an alternative to silica-based inert matrices as imaging vehicles.     

Influence of substrate treatment on self-organized pattern formation by langmuir-blodgett transfer

Mesoscopic stripe patterns can be obtained by Langmuir-Blodgett (LB) transfer of l-alpha-dipalmitoylphosphatidylcholine (DPPC) onto solid substrates. In order to investigate the influence of substrates on the pattern formation, silicon slides treated by different cleaning processes were taken as model systems. A shift in the transfer pressure range for patterning was observed between plasma- and RCA-treated silicon. This can be explained with a model of equivalent states and taking into account the influence of microscale water films on the substrates.     

Symmetry forbidden vibronic spectra and internal conversion in benzene

The spectra of symmetry-forbidden transitions and internal conversion were investigated in the present work. Temperature dependence was taken into account for the spectra simulation. The vibronic coupling, essential in the two processes, was calculated based on the Herzberg-Teller theory within the Born-Oppenheimer approximation. The approach was employed for the symmetry-forbidden absorption/fluorescence, and internal conversion between 1(1)A(1g) and 1(1)B(2u) states in benzene. Vibrational frequencies, normal coordinates, electronic transition dipole moments, and non-adiabatic coupling matrix elements were obtained by ab initio quantum chemical methods. The main peaks, along with the weak peaks, were in good agreement with the observed ones. The rate constant of the 1(1)A(1g)← 1(1)B(2u) internal conversion was estimated within the order of 10(3) s(-1). This could be regarded as the lower limit (about 4.8 × 10(3) s(-1)) of the internal conversion. It is stressed that the distortion effect was taken into account both in the symmetry-forbidden absorption/fluorescence, and the rate constants of internal conversion in the present work. The distortion effects complicate the spectra and increase the rate constants of internal conversion.