Characterization of molecular transport in poly(dimethylsiloxane) microchannels for electrophoresis fabricated with synchrotron radiation-lithography and UV-photolithography

In the present paper, a study was undertaken of molecular transport in ploy(dimethylsiloxane) microchannels that were fabricated by ultraviolet (UV)-photolithography and synchrotron radiation (SR)-lithography characterized and compared for microchip capillary electrophoresis by evaluating in-channel molecular dispersion. A fluorescent tag, sulforhodamine B was used as the probing molecule. It was found that microchannels made by SR-lithography fabrication were superior to those made by UV-photolithography fabrication in terms of molecular transport performance. A deep insight into surface conditions characterized by scanning electron microscopy suggested it was related to the difference in surface roughness. Chromatographic retention in electropherograms further supported such a conclusion, which depended on the phase ratio of the channel surface. The results revealed for PDMS microchannels in this work were in good agreement with the phenomenon found for glass microchannels in the literature.     

Side chain-directed assembly of triangular molecular panels into a tetrahedron vs. open cone

Despite their structural similarity, triangular tetradentate ligands 2b and 2c experience different assembly pathways on complexation with (en)Pd(NO3)2 to give M8L4 tetrahedral (3) and open cone (4) structures, respectively, due to steric restriction by side chains at the corner or on the edge of the ligands.     

New Proof of the Fukui Conjecture by the Functional Asymptotic Linearity Theorem

The present article provides a new proof of the Fukui conjecture concerning the additivity problem of the zero-point vibrational energies of hydrocarbons. This conjecture played a prominent role in the initial development of the repeat space theory (RST), and continues to be of vital significance in the recent development of the theory of the generalized repeat space X _r (q,d). The new proof of the Fukui conjecture has been given here by establishing the functional version of the Asymptotic Linearity Theorem (ALT), the Functional ALT. This enhanced version of the ALT directly implies the validity of the Fukui conjecture; it easily unifies, in a broad perspective, a variety of additivity phenomena in physico-chemical network systems having many identical moieties, and efficiently solves some interpretational problems of the empirical additivity formulae from experimental chemistry. The proof of the functional version of the ALT is based on a new method transferable to the extended theoretical framework of the generalized repeat space X _r (q,d).     

Infrared spectroscopic study on the reaction mechanism of CO hydrogenation over Pd/CeO2

In situ infrared spectroscopy was applied to elucidate the reaction mechanism of CO hydrogenation over Pd/CeO₂. Instead of direct dissociation of CO, a new reaction pathway is proposed for methane formation, involving geminal dicarbonyl intermediates and (HCO)₂(a) intermediates, which may be located on the surface of Pd covered with thin layers of reduced ceria (SMSI effect). Transformation of methane formation sites into methanol formation ones by the oxidation with water vapor formed during the CO?H₂ reaction is proposed, which may be located on the Pd (111) planes adjacent to ceria support.     

Quartz crystal microbalance immunosensor for highly sensitive 2,3,7,8-tetrachlorodibenzo-p-dioxin detection in fly ash from municipal solid waste incinerators

A quartz crystal microbalance (QCM) immunosensor was developed for the detection of 2,3,7,8-tetrachlorodibenzo-p-dioxins (TCDD) in environmental pollutants. An anti-TCDD antibody was immobilized on the gold surface of the QCM via chemical coupling, and its immunologic activity was then maintained by treatment with an artificial stabilizing reagent such as poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate). A competitive immunoreaction with TCDD conjugated ovalbumin (TCDD-ovalbumin) was used to detect TCDD. A calibration curve was obtained through the competitive immunoreaction, and linearity was shown from 100 ng mL(-1) to 0.1 ng mL(-1). Also, the cross-reactivities of the anti-TCDD monoclonal antibody were thoroughly evaluated with several TCDD derivatives. The relationships between GC-MS, ELISA, and QCM were compared using fly ash samples from a municipal solid waste, which were prepared using an accelerated solvent extractor. For 23 samples, the experimental relationship between the TCDD concentration by QCM vs. the TCDD concentration by ELISA was y= 1.07x + 2.70, r= 0.99, and the TCDD concentration by QCM vs. the toxic equivalent quantity (TEQ) value by GC-MS was y= 2.46x - 14.98, r= 0.89.     

Sensitive and high-throughput analyses of purine metabolites by dynamic pH junction multiplexed capillary electrophoresis: a new tool for metabolomic studies.

On-line sample preconcentration by a dynamic pH junction in conjunction with multiplexed capillary electrophoresis (CE) and UV detection represents a sensitive and high-throughput format for future metabolomic research, such as purine analysis. The optimization of purine focusing can be rapidly assessed by systematically altering the sample matrix properties, such as the buffer co-ion, pH and ionic strength using a 96-capillary array format. This method permits focusing of large sample injection volumes, resulting in over a 50-fold improvement in the concentration sensitivity. The limit of detection (S/N = 3) for purine metabolites was less than 8.0 x 10(-8) M under optimum conditions when using UV absorbance. Dynamic pH junction multiplexed CE demonstrated excellent linearity over a hundred-fold concentration range, as well as low inter-capillary precision in terms of normalized migration times and peak areas. The potential for clinically relevant high-throughput analyses of micromolar amounts of purine metabolites in urine was also demonstrated.     

High-sensitivity analyses of metabolites in biological samples by capillary electrophoresis using dynamic pH junction-sweeping

Emerging fields of biochemical research, such as metabolomics, present challenges to current separation technologies because of the large number of metabolites present in a cell and their often low (submicromolar) concentration. Although capillary electrophoresis (CE) holds great promise as the method of choice for high-resolution separations of biological samples, it suffers from poor concentration sensitivity, especially with the use of UV detection. In CE, sweeping and dynamic pH junction represent two complementary on-line focusing techniques that have been used for sensitivity enhancement of hydrophobic and weakly acidic analytes, respectively. However, the application of either the sweeping or dynamic pH junction technique alone might, in some cases, be less effective for the analysis of certain sample mixtures. Recent work in the development of a hyphenated dynamic pH junction-sweeping technique is presented as an effective on-line method of preconcentration suitable for both hydrophilic (anionic) and hydrophobic (neutral) analytes. Sensitive analyses of flavin metabolites by CE with laser-induced fluorescence (LIF) detection is demonstrated in various biological matrixes, including cell extracts of Bacillus subtilis, pooled human plasma, as well as heat-deproteinized flavoenzymes. Enhanced analyte band narrowing and improved sensitivity is achieved for flavins using dynamic pH junction-sweeping compared to either sweeping or dynamic pH junction alone. This results in over a 1200-fold improvement in sensitivity relative to conventional injection methods, giving a limit of detection (LOD, defined as S/N = 3) of about 4.0 x 10(-12) M. Strategies for sensitive and more comprehensive analyses of other cell metabolites, including nucleotides, coenzymes, and steroids, are also discussed when using on-line focusing techniques in conjunction with multiplexed CE and UV detection.     

Effects of ortho-substituents on reactivities,tacticities, and ceiling temperatures of radical polymerizations of phenyl methacrylates

Radical polymerization and copolymerization of some o-alkylphenyl methacrylates were carried out and the effect of the ortho-substituents on the ability to homopolymerize, on the monomer reactivities, and on the ceiling temperatures of the monomers was studied. The effect of the substituent on tacticities and thermal stabilities of the polymers formed was also discussed. The ability to honiopolymerize and the monomer reactivity were considerably decreased by the introduction of the o-substituent. 2,6-Di-tert-butylphenyl methacrylate formed no methanol-insoluble polymer at 60°C. On the basis of the tacticity determined it was noted that the o-substituted phenyl methacrylates preferred syndiotactic addition in the propagation reaction less than did phenyl methacrylate or methyl methacrylate. The polymers formed from the o-substituted monomers were thermally less stable than poly(phenyl methacrylate), and, consistent with this finding, ceiling temperatures of the o-substituted phenyl methacrylates seemed to be lower than that of phenyl methacrylate. The effects observed were characteristic of the o-substituents conformationally close to the carbon-carbon double bond of the monomer or the carbon carrying the unpaired electron of the polymer radical.     

Electrochemical formation of stable ferrocene anion and the formal rate constant of the ferrocene0/− electrode

A reversible cyclic voltammogram for the one-electron reduction of ferrocene in 1,2-dimethoxyethane is recorded under experimental conditions that enable the ferrocene anion to exist for a few minutes. The formal rate constant of the ferrocene^0/? electrode, determined by cyclic voltammetry at ?45°C, ca. 10^?3 cm s^?1, is in striking contrast with that of ferrocene^+/0, > 10^?1 cm s^?1. The distortion of the ferrocene molecule caused by reduction may be a reason for this difference in electron-transfer rate.     

Chiral separation of trimetoquinol hydrochloride and related compounds by micellar electrokinetic chromatography using sodium taurodeoxycholate solutions and application to optical purity determination

The chiral separation of trimetoquinol hydrochloride, which is a bronchodilator (Inolin), and three related compounds by micellar electrokinetic chromatography was investigated using a bile salt as a chiral surfactant. Enantiomers of these compounds, except laudanosoline, were successfully separated within 12 min using a separation tube of effective length 500 mm × 0.05 rum i.d. and a 0.05 M sodium taurodeoxycholate solution of pH 7.0. The observed theoretical plate numbers of the peaks were ca. 150000. Chiral recognition was affected by the structure of bile salts, the pH of the buffer solutions used and the structure of the solutes. Of four kinds of bile salts, successful chiral separation was achieved only using sodium taurodeoxycholate solution under neutral conditions. The method was applied to the optical purity determination of trimetoquinol hydrochloride. The effects of surfactant concentrations and some additives to the micellar solution are briefly described.