Encapsulation of a highly sensitive EPR active oxygen probe into sonochemically prepared microspheres

High-power ultrasound (20 kHz) was used to encapsulate a solution of perchlorotriphenylmethyl triester (PTM-TE, a stable organic free radical) dissolved in hexamethyldisiloxane (HMDS) into a polymerized shell of bovine serum albumin (BSA). The size distribution of the microspheres was between 0.5 and 3 microm with a maximum at approximately 1.2 microm. The electron paramagnetic resonance spectrum of PTM-TE consists of a single, sharp line which is sensitive to the surrounding concentration of oxygen. It was found that the technique of encapsulating a solution of PTM-TE dissolved in HMDS into the BSA microspheres resulted in an overall loss of EPR signal intensity from the washed suspension of microspheres. However, the encapsulated PTM-TE/HMDS solution remained sensitive to the partial pressure of oxygen in the surrounding environment. The microspheres were found to be useful for determining the partial pressure of oxygen in the muscle and tumor tissue of mice.     

Two-chiral component microemulsion EKC - chiral surfactant and chiral oil. Part 2: diethyl tartrate

In this second study on dual-chirality microemulsions containing a chiral surfactant and a chiral oil, a less hydrophobic and lower interfacial tension chiral oil, diethyl tartrate, is employed (Part 1, Foley, J. P. et al.., Electrophoresis, DOI: 10.1002/elps.200600551). Six stereochemical combinations of dodecoxycarbonylvaline (DDCV: R, S, or racemic, 2.00% w/v), racemic 2-hexanol (1.65% v/v), and diethyl tartrate (D, L, or racemic, 0.88% v/v) were examined as pseudostationary phases (PSPs) for the enantioseparation of six chiral pharmaceutical compounds: pseudoephedrine, ephedrine, N-methyl ephedrine, metoprolol, synephrine, and atenolol. Average efficiencies increased with the addition of a chiral oil to R-DDCV PSP formulations. Modest improvements in resolution and enantioselectivity (alpha(enant)) were achieved with two-chiral-component systems over the one-chiral-component microemulsion. Slight enantioselective synergies were confirmed using a thermodynamic model. Results obtained in this study are compared to those obtained in Part 1 as well as those obtained with chiral MEEKC using an achiral, low-interfacial-tension oil (ethyl acetate). Dual-chirality microemulsions with the more hydrophobic oil dibutyl tartrate yielded, relative to diethyl tartrate, higher efficiencies (100,000-134,000 vs. 80,800-94,300), but lower resolution (1.64-1.91 vs. 2.08-2.21) due to lower enantioselectivities (1.060-1.067 vs. 1.078-1.081). Atenolol enantiomers could not be separated with the dibutyl tartrate-based microemulsions but were partially resolved using diethyl tartrate microemulsions. A comparable single-chirality microemulsion based on the achiral oil ethyl acetate yielded, relative to diethyl tartrate, lower efficiency (78 300 vs. 91 600), higher resolution (1.99 vs. 1.83), and similar enantioselectivities.     

Dual-opposite-injection CZE: theoretical aspects and application to organic and pharmaceutical compounds

Several important figures of merit (migration time, efficiency, resolution, resolution per unit time, and electrophoretic selectivity) are quantitatively compared for the first time for conventional CZE and dual-opposite-injection CZE (DOI-CZE). Aspects of DOI-CZE relevant to the separation of organic and pharmaceutical ions (MW>120 Da) are also discussed. Two new approaches to resolve the codetection of anions and cations, hydrodynamic flow-modified DOI-CZE and polarity reversal in combination with asymmetric detector window positioning, are compared with the method of preliminary transport, a variable procedure within sequential sample introduction, using a six-component sample of organic and pharmaceutical compounds. The advantages of DOI-CZE for the simultaneous analysis of organic/pharmaceutical anions and cations are illustrated in a direct comparison of conventional CZE and DOI-CZE for the separation of a ten-component mixture of pharmaceutical ions (five ionized acids and five ionized bases).     

Review of aqueous chiral electrokinetic chromatography (EKC) with an emphasis on chiral microemulsion EKC

The separation of enantiomers using electrokinetic chromatography (EKC) with chiral microemulsions is comprehensively reviewed through December 1, 2006. Aqueous chiral EKC separations based on other pseudostationary phases such as micelles and vesicles or on other chiral selectors such as CDs, crown ethers, glycopeptides, ligand exchange moeities are also reviewed from both mechanistic and applications perspective for the period of January 2005 to December 1, 2006.     

Photoisomerization and thermal isomerization of arylazoimidazoles

Photoisomerization and thermal isomerization behaviors of an extensive series of arylazoimidazoles are investigated. Absorption spectra are characterized by a structured pipi* absorption band around 330-400 nm with a tail on the lower energy side extending to 500 nm corresponding to an npi* transition. The trans-to-cis photoisomerization occurs on excitation into these absorption bands. The quantum yields are dependent on the excitation wavelength, as observed for azobenzene derivatives, but are generally larger than those of azobenzene. The thermal cis-to-trans isomerization rates are also generally larger than that of azobenzene and are comparable to those of 4-N,N-dimethylaminoazobenzene and 4-nitroazobenzene. Arylazoimidazoles with no substituent on the imidazole nitrogen are unique in that the quantum yield for the trans-to-cis photoisomerization and the rate of thermal cis-to-trans isomerization are particularly large. It is proposed that the fast thermal isomerization is due to an involvement of self-catalyzed and protic molecule-assisted tautomerization to a hydrazone form.     

A simple and selective method for the measurement of leucine and isoleucine from plasma using electrospray ionization tandem mass spectrometry

An analytical method was developed for the rapid and accurate quantification of leucine (LEU) and isoleucine (ILE) from plasma using electrospray ionization tandem mass spectrometry (ESI-MS/MS). The two isomeric amino acids were selectively detected using fragment ions unique to each compound. As a result, the need for chromatographic separation was avoided allowing for faster analysis (3 min). The possibility of any considerable interference between the two transitions was closely monitored, with no significant interference being observed. The presence of interfering compounds in plasma was also evaluated and found to minimal. The method was evaluated based upon linearity, with r2>or=0.995 for both compounds, and accuracy, with no more than 8% deviation from the theoretical value.     

Improved precision in measurements of acoustic impedance spectra using resonance-free calibration loads and controlled error distribution

Resonances and/or singularities during measurement and calibration often limit the precision of acoustic impedance spectra. This paper reviews and compares several established techniques, and describes a technique that incorporates three features that considerably improve precision. The first feature is to minimize problems due to resonances by calibrating the instrument using up to three different acoustic reference impedances that do not themselves exhibit resonances. The second involves using multiple pressure transducers to reduce the effects of measurement singularities. The third involves iteratively tailoring the spectrum of the stimulus signal to control the distribution of errors across the particular measured impedance spectrum. Examples are given of the performance of the technique on simple cylindrical waveguides.     

The Need for Two‐Dimensional Gas Chromatography: Extent of Overlap in One‐Dimensional Gas Chromatograms

The need for two‐dimensional gas chromatography is justified by the extent of peak overlap in one‐dimensional gas chromatograms (GCs) of complex mixtures. Such overlap was predicted long ago by statistical‐overlap theory (SOT). In this paper, SOT is conceptually reviewed and its predictions are shown to be quantitatively accurate. GCs of complex mixtures of polychlorinated biphenyls, pyridine‐ and nitrogen‐containing polynuclear aromatic hydrocarbons, tetrachlorodibenzo‐p‐dioxins and dibenzofurans, fatty acid methyl esters, flavors and fragrances, and naphtha were simulated by commercial GC software on DB‐1, DB‐5, and Stabilwax stationary phases. The numbers of peak maxima in the GCs agreed with predictions of SOT, when the interval of time between successive peaks of pure compounds was described by Poisson statistics. This agreement was realized even though the time intervals actually are deterministic, not statistical. In addition, the numbers of mixture components were predicted with accuracy by regression of peak numbers against SOT. Similar regressions have been reported before, but the theory used here is more sophisticated and its predictions consequently are more accurate. Future directions for finalizing SOT are suggested.     

Kinetics of graft copolymerization of methyl methacrylate onto polychloroprene with tricaprylylmethylammonium chloride as a phase‐transfer catalyst

The phase‐transfer catalyzed graft copolymerization of methyl methacrylate onto polychloroprene was carried out using tricaprylylmethylammonium chloride as a phase‐transfer catalyst in a two‐phase system of an aqueous Na₂S₂O₈ solution and toluene at 55 °C under a nitrogen atmosphere. The initial rate of graft copolymerization was expressed as the combined terms of quaternary onium cation and peroxydisulfate anion in the aqueous phase rather than the fed concentrations of catalyst and Na₂S₂O₈. The observed initial rate of graft copolymerization was used to analyze the graft copolymerization mechanism with a cycle phase‐transfer initiation step in the heterogeneous liquid–liquid system. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3543–3549, 2000     

Relationship between Continuum of Hurst Exponents of Noise-like Time Series and the Cantor Set

In this paper, we have modified the Detrended Fluctuation Analysis (DFA) using the ternary Cantor set. We propose a modification of the DFA algorithm, Cantor DFA (CDFA), which uses the Cantor set theory of base 3 as a scale for segment sizes in the DFA algorithm. An investigation of the phenomena generated from the proof using real-world time series based on the theory of the Cantor set is also conducted. This new approach helps reduce the overestimation problem of the Hurst exponent of DFA by comparing it with its inverse relationship with α of the Truncated Lévy Flight (TLF). CDFA is also able to correctly predict the memory behavior of time series.