ADP-specific sensors enable universal assay of protein kinase activity

Two molecular sensors that specifically recognize ADP in a background of over 100-fold molar excess of ATP are described. These sensors are nucleic-acid based and comprise a general method for monitoring protein kinase activity. The ADP-aptamer scintillation proximity assay is configured in a single-step, homogeneous format while the allosteric ribozyme (RiboReporter) sensor generates a fluorescent signal upon ADP-dependent ribozyme self-cleavage. Both systems perform well when configured for high-throughput screening and have been used to rediscover a known protein kinase inhibitor in a high-throughput screening format.     

Determination of tetrodotoxin and its analogs in the puffer fish <Emphasis Type="Italic">Takifugu oblongus</Emphasis> from Bangladesh by hydrophilic interaction chromatography and mass-spectrometric detection

Tetrodotoxin (TTX) and its analogs (TTXs), widely distributed among marine as well as terrestrial animals, induce dangerous intoxications. These highly potential toxins are also known as the causative agent of puffer fish poisoning. A newly developed highly sensitive method for determination of TTXs based on hydrophilic interaction chromatography and mass-spectrometric detection is presented. TTX, anhydrotetrodotoxin, 11-deoxytetrodotoxin and trideoxytetrodotoxin were determined in separated tissues of Bangladeshi marine puffers, Takifugu oblongus. TTX was predominant in skin, muscle and liver, whereas trideoxytetrodotoxin preponderated in the ovary. The toxicity of the various tissues was determined by a mouse bioassay.     

Criterion for bosonic superfluidity in an optical lattice

We show that the current method of determining superfluidity in optical lattices based on a visibly sharp bosonic momentum distribution n(k) can be misleading, for even a normal Bose gas can have a similarly sharp n(k). We show that superfluidity in a homogeneous system can be detected from the so-called visibility (v) of n(k)--that v must be 1 within O(N(-2/3)), where N is the number of bosons. We also show that the T=0 visibility of trapped lattice bosons is far higher than what is obtained in some current experiments, suggesting strong temperature effects and that these states can be normal. These normal states allow one to explore the physics in the quantum critical region.     

Bounds on the non-local effective elastic properties of composites

The paper deals with the effective linear elastic behaviour of random media subjected to inhomogeneous mean fields. The effective constitutive laws are known to be non-local. Therefore, the effective elastic moduli show dispersion, i.e¹ they depend on the “wave vector” k of the mean field. In this paper the well-known Hashin-Shtrikman bounds (1962) for the Lamé parameters of isotropic multi-phase mixtures are generalized to inhomogeneous mean fields k ≠ 0. The bounds involve two-point correlations of random elastic moduli. In the limit k → ∞ the bounds converge to the exact result. The interest is focussed on composites with cell structures and on binary mixtures. To illustrate the results, numerical evaluations are carried out for a binary cell material composed of nearly spherical grains of equal size.     

Bounds for the non-local effective properties of random media

The paper deals with a random medium subjected to a static scalar field with inhomogeneous mean values. Then, effective linear material parameters show dispersion, i.e. they depend on the “wave vector” k of the mean field. The variational methods of P.H. Dederichs and R. Zeller (1973) are generalized to derive upper and lower bounds for scalar effective material parameters as functions of k. In the limit k → 0 (homogeneous mean fields), bounds of the Hashin-Shtrikman type are reproduced. For k → ∞, the bounds coincide with the exact result. In the general case, a two-point moment of the stochastic material parameter is involved. Especially, composites with cell structure and binary mixtures are considered. Detailed calculations are carried out for effective dielectricity, relating mean electric displacement to the mean electric field (which is mathematically equivalent to electrical and thermal conductivities and other scalar parameters), of a binary system composed of nearly spherical grains of equal size.     

Bounds for the non-local effective properties of random media—II

The paper deals with a random medium subjected to a static field with inhomogeneous mean values. Then, effective linear material parameters show dispersion, i.e. they depend on the ‘wave vector’ k of the mean field. Starting from a variational method previously developed by the authors, upper and lower bounds for k-dependent scalar effective parameters are derived in terms of two-point and three-point correlation functions of the stochastic material parameters. Taking into consideration the three-point correlation function gives a substantial improvement of the generalized Hashin-Shtrikman bounds obtained previously. In particular, composites with cell structure and arbitrary binary systems are considered. In order to illustrate the general results, numerical evaluations are carried out for effective permittivity of a binary cell material composed of nearly spherical grains of equal size.     

Investigation of the quantitative properties of the quadrupole orthogonal acceleration time-of-flight mass spectrometer with electrospray ionisation using 3,4-methylenedioxymethamphetamine

This paper describes the investigation of the potential of a quadrupole orthogonal acceleration time-of-flight mass spectrometer (Q-TOF) equipped with an atmospheric pressure ionisation interface for quantitative measurements of small molecules separated by reversed phase liquid chromatography. To this end, the detection limits and linear dynamic range in particular were studied in an LC/MS/MS experiment using 3,4-methylenedioxymethamphetamine standards and 3,4-methylenedioxyethylamphetamine for internal standardisation. In a second phase, the experiment was repeated with real biological extracts (whole blood, serum, and vitreous humour). A calibration for 3,4-methylenedioxymethamphetamine and its metabolite 3,4-methylenedioxyamphetamine was prepared in each of these matrices again using 3,4-methylenedioxyethylamphetamine as internal standard. The resulting quantitative data were compared with those obtained by liquid chromatography with fluorescence detection for the same extracts. The Q-TOF results revealed excellent sensitivity and a linear dynamic range of nearly four decades (2-10 000 pg on-column, r(2) = 0.9998, 1/x weighting). Furthermore, all the calibration curves prepared in biological material were superimposable, LC/MS/MS and LC-fluorescence, and the quantitative results for actual samples compared very favourably. It was concluded that the Q-TOF achieves a linear dynamic range for quantitative LC/MS/MS work exceeding that of fluorescence detection and at much better absolute sensitivity. Copyright 1999 John Wiley & Sons, Ltd.     

Gas-Phase reactions of O 2 −. with alkyl and aryl esters of benzenedicarboxylic acids

The reactions of O ₂ ^?. with alkyl and aryl esters of benzenedicarboxylic acids have been studied under negative-ion chemical ionization (NICI) conditions via a conventional chemical ionization source. Reaction mechanisms have been elucidated by using ion isolation techniques on a Fourier transform ion cyclotron resonance mass spectrometer. In addition, ¹⁸O ₂ ^?. has been used as the reagent and the products of competitive reactions that involve the mixed esters of benzenedicarboxylic acids have been studied. O ₂ ^?. reactions with the alkyl esters of 1,2- and l,3-benzenedicarboxylic acids are attributed to S_N2 displacement at the O-alkyl carbon. The spectra of mixed alkyl esters show that O ₂ ^?. attack is reduced at sterically hindered alkyl groups. In contrast with the spectra of 1,2- and l,3-benzenedicarboxylic acids, the spectra of 1,4-benzenedicarboxylic acids are dominated by M^?. production. Reactions of O ₂ ^?. with phenyl benzoates and the aryl esters of benzenedicarboxylic acids proceed via addition-elimination pathways. Experiments with mixed alkyl-aryl benzenedicarboxylic acid esters show that the addition-elimination reaction pathway is preferred over O-alkyl S_N2 displacement. The O₂/ Ar-NICI mass spectra show features that can be used to distinguish 1,2-, 1,3-, and 1/4-benzenedicarboxylic acid esters. Molecular and fragment ions provide structural information complementary to that generated under electron ionization and chemical ionization conditions.