Processing of cyclopropylarenes by toluene dioxygenase: isolation and absolute configuration of metabolites

Several arenes possessing a cyclopropyl substituent were subjected to enzymatic oxidation with toluene dioxygenase. The absolute configuration of metabolites was established by chemical means.     

Enantiomeric separations of amino acids with inductively coupled plasma carbon emission detection

A chiral crown ether column with a pH 1.9 perchloric acid buffered aqueous mobile phase is used to separate amino acid enantiomers by high performance liquid chromatography. An inductively coupled plasma atomic emission spectrometer coupled to the chromatographic system is used as a detector by monitoring the carbon atomic emission line at 193.09 nm. Seven underivatized amino acids are separated and detected resulting in an average mass detection limit of 5 ng (2.5 ng carbon). The chiral crown ether column resolves compounds with a primary amino group near the chiral center by forming a complex between the crown ether and an ammonium ion moiety from the sample. The -form amino acid always elutes faster than its antipode. The carbon emission detector provides nearly identical sensitivities and similar detection limits for any compounds with comparable mass percents of carbon. Quantification is performed on unknown ratios of amino acids using an internal standard without the need for a calibration curve. Summing the calculated amounts of and amino acid and comparing to the known mixture quantity results in an average error of 1.0% for the seven amino acids separated.     

Determination of calcium, iron and magnesium in rabbit arteries by inductively coupled plasma atomic emission spectrometry

Regional variations in arterial concentrations of Ca, Mg and Fe may influence susceptibility to atherosclerosis. However, investigation of such hypotheses requires the availability of a sensitive, reliable method for the determination of elements in small arterial samples. These biologically important elements are determined in rabbit arteries by inductively coupled plasma atomic emission spectrometry (ICP-AES). Arterial samples (aorta and iliac arteries) are collected from 4- and 6- to 7-month-old rabbits fed rabbit chow. Closed-vessel microwave acid digestion is used to prepare the samples. The accuracy of the method is tested with a NIST bovine liver (1577b) standard reference material, and the amount of each metal found is within the reported uncertainty in the certified concentration. Also, the recovery from artery samples spiked with 0.5 μg of each metal is nearly 100% (96-105% Ca, 93-105% Fe, and 92-104% Mg). The simultaneous multielement detection of Ca, Fe and Mg at levels more than 1000-fold higher than the detection limit, in arterial samples weighing as little as 5 mg, suggests that this method may be applicable to very small clinical samples or arterial samples from very small animals.     

Resonant transfer of excitation between two molecules using Maxwell fields

The matrix element for the resonant transfer of excitation between two molecules possessing electric and magnetic multipole moments of arbitrary order is calculated using quantum electrodynamical response theory. A prerequisite of the method is the functional form for the lth order linear electric and magnetic multipole dependent electric displacement and magnetic field operators in the neighborhood of a molecule, whose derivation is also given. The initially unexcited species is viewed as a test body accepting energy resonantly via coupling to the Maxwell fields of the excited multipole source molecule. The generalized electric-electric multipole contribution to the matrix element is shown to agree with an earlier calculation using time-dependent perturbation theory. As an application involving both electric and magnetic terms, the rate of excitation transfer between two chiral molecules is computed and found to depend on the handedness of each species.     

The global attractivity of a higher order rational difference equation

This paper studies global asymptotic stability for positive solutions to the equation

     

Protein determination by microchip capillary electrophoresis using an asymmetric squarylium dye: noncovalent labeling and nonequilibrium measurement of association constants

In response to a growing interest in the use of smaller, faster microchip (mu-chip) methods for the separation of proteins, advancements are proposed that employ the asymmetric squarylium dye Red-1c as a noncovalent label in mu-chip CE separations. This work compares on-column and precolumn labeling methods for the proteins BSA, beta-lactoglobulin B (beta-LB), and alpha-lactalbumin (alpha-LA). Nonequilibrium CE of equilibrium mixtures (NECEEM) represents an efficient method to determine equilibrium parameters associated with the formation of intermolecular complexes, such as those formed between the dye and proteins in this work, and it allows for the use of weak affinity probes in protein quantitation. In particular, nonequilibrium methods employing both mu-chip and conventional CE systems were implemented to determine association constants governing the formation of noncovalent complexes of the red luminescent squarylium dye Red-1c with BSA and beta-LB. By our mu-chip NECEEM method, the association constants K(assoc) for beta-LB and BSA complexes with Red-1c were found to be 3.53 x 10(3) and 1.65 x 10(5) M(-1), respectively, whereas association constants found by our conventional CE-LIF NECEEM method for these same protein-dye systems were some ten times higher. Despite discrepancies between the two methods, both confirmed the preferential interaction of Red-1c with BSA. In addition, the effect of protein concentration on measured association constant was assessed by conventional CE methods. Although a small decrease in K(assoc) was observed with the increase in protein concentration, our studies indicate that absolute protein concentration may affect the equilibrium determination less than the relative concentration of protein-to-dye.     

The isomorphism problem for quantum affine spaces,homogenized quantized Weyl algebras,and quantum matrix algebras

Bell and Zhang have shown that if A and B are two connected graded algebras finitely generated in degree one that are isomorphic as ungraded algebras, then they are isomorphic as graded algebras. We exploit this result to solve the isomorphism problem in the cases of quantum affine spaces, quantum matrix algebras, and homogenized multiparameter quantized Weyl algebras. Our result involves determining the degree one normal elements, factoring out, and then repeating. This creates an iterative process that allows one to determine relationships between relative parameters.     

Going-down pairs of commutative rings

Résumé  D'après D. E. Dobbs, Houston J. Math. 23 (1997), 1–11, nous disons que l'anneau (commutatif)A est un anneau-“going-down” siA/P est un domaine-“going-down” pour chaque idéal premier deA. Etant donné une extension,R⊆T, nous disons que (R, T) est une paire d'anneaux-“going-down” (respectivement, une paire “going-down”) siS est un anneau-“going-down” pour chaque anneau tels queR⊆S⊆T (resp., si “going-down” est satisfait par chaque extension d'anneauxA⊆B tels queR⊆A⊆B⊆T). On montre que siR est un anneau de la dimension 0 (au sens de Krull), alors (R, T) est une paire d'anneaux-“going-down” si et seulement sitr.deg. _R/(P∩R) T/P≤1 pour chaque idéal premier minimalP deT. Des résultats partiels sont obtenus quandR n'est pas de dimension 0. En outre, si (R, T) est une paire d'anneaux-“going-down” tel queT ait un seul idéal premier minimal, alors (R, T) est une paire “going-down”. Des résultats dans l'esprit ci-dessus sont également obtenus pour quelques autres types de paires.

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This paper is taken from the author's doctoral dissertation of May 2000, written under the direction of Professor David E. Dobbs of the University of Tennessee, Knoxville.     

Quantum interference in carbon nanotubes

We present magnetotransport properties of a multiwalled carbon nanotube. We have developed a technique using electron beam lithography to connect a carbon nanotube with a small contact resistance. The temperature dependence of the nanotube is thermally activated down to 30 mK but with multiple energy gap. At low temperature, the magnetoconductance can be analysed in terms of quantum interferences. Both weak localisation and universal conductance fluctuations have been observed. The phase coherence length extracted from the weak localisation is consistent with the amplitude of the conductance fluctuations.