Vapor-liquid equilibrium for the systems ethyl formate-methyl ethyl ketone,ethyl formate-toluene and ethyl formate-methyl ethyl ketone-toluene: new unifac parameters for interactions between the groups ACH/HCOO,ACCH2/HCOO and CH2Co/HCOO

Vapor-liquid equilibrium data are presented for the binary systems ethyl formate-methyl ethyl ketone (MEK) at 40°C and 50 °C and ethyl formate-toluene at 48°Cand 51°C and for the ternary system ethyl formate-MEK-toluene at 50°C. The measurements were carried out in a recirculation still similar to that proposed by Röck and Sieg. Vapor pressures of the pure substances were measured and the data correlated using the Antoine equation. The binary data were reduced by means of a maximum-likelihood procedure providing the relevant Margules, NRTL and UNIQUAC parameters.New UNIFAC interaction parameters between the groups ACH/HCOO, ACCH₂/HCOO and CH₂CO/HCOO have been obtained. These parameters have been used to predict the ternary data, and a comparison between the experimental and predicted values is presented.     

Aging of cholinesterases phosphylated by tabun proceeds through O-dealkylation

Human butyrylcholinesterase (hBChE) hydrolyzes or scavenges a wide range of toxic esters, including heroin, cocaine, carbamate pesticides, organophosphorus pesticides, and nerve agents. Organophosphates (OPs) exert their acute toxicity through inhibition of acetylcholinesterase (AChE) by phosphorylation of the catalytic serine. Phosphylated cholinesterase (ChE) can undergo a spontaneous, time-dependent process called "aging", during which the OP-ChE conjugate is dealkylated. This leads to irreversible inhibition of the enzyme. The inhibition of ChEs by tabun and the subsequent aging reaction are of particular interest, because tabun-ChE conjugates display an extraordinary resistance toward most current oxime reactivators. We investigated the structural basis of oxime resistance for phosphoramidated ChE conjugates by determining the crystal structures of the non-aged and aged forms of hBChE inhibited by tabun, and by updating the refinement of non-aged and aged tabun-inhibited mouse AChE (mAChE). Structures for non-aged and aged tabun-hBChE were refined to 2.3 and 2.1 A, respectively. The refined structures of aged ChE conjugates clearly show that the aging reaction proceeds through O-dealkylation of the P(R) enantiomer of tabun. After dealkylation, the negatively charged oxygen forms a strong salt bridge with protonated His438N epsilon2 that prevents reactivation. Mass spectrometric analysis of the aged tabun-inhibited hBChE showed that both the dimethylamine and ethoxy side chains were missing from the phosphorus. Loss of the ethoxy is consistent with the crystallography results. Loss of the dimethylamine is consistent with acid-catalyzed deamidation during the preparation of the aged adduct for mass spectrometry. The reported 3D data will help in the design of new oximes capable of reactivating tabun-ChE conjugates.     

The quantum strip: Liouville theory for open strings

The quantum group structure of 2D gravity recently put forward by one of us (J.-L. G.) is used to study quantum gravity on the strip. The boundary conditions, previously studied by A. Neveu and this author become easy to implement when one introduces the universal family of chiral operators associated withU _q (sl(2)). A general formula for inverse powers of the metric-tensor operator is thereby derived. It contains a new universal matrixA, acting in representation-space, which obeys identities involving theR matrix, the Clebsch-Gordon coefficients, and the co-products ofU _q (sl(2)). The physical meaning of these identities is to ensure that these powers of the metric are local and closed by fusion.     

The quantum group structure of 2D gravity and minimal models II: The genus-zero chiral bootstrap

The chiral operator-algebra of the quantum-group-covariant operators (of vertex type) is completely worked out by making use of the operator-approach suggested by the Liouville theory, where the quantum-group symmetry is explicit. This completes earlier articles along the same line. The relationship between the quantum-group-invariant (of IRF type) and quantum-group-covariant (of vertex type) chiral operator-algebras is fully clarified, and connected with the transition to the shadow world for quantum-group symbols. The corresponding 3-j symbol dressing is shown to reduce to the simpler transformation of Babelon and one of the authors (J.-L. G.) in a suitable infinite limit defined by analytic continuation. The above two types of operators are found to coincide when applied to states with Liouville momenta going to in a suitable way. The introduction of quantum-group-covariant operators in the three dimensional picture gives a generalization of the quantum-group version of discrete three-dimensional gravity that includes tetrahedra associated with 3-j symbols and universalR-matrix elements. Altogether the present work and a previous parallel article gives the concrete realization of Moore and Seiberg's scheme that describes the chiral operator-algebra of two-dimensional gravity and minimal models.Unité Propre du Centre National de La Recherche Scientifique, associée à l'École Normale Supérieure et à l'Université de Paris-Sud     

Liquid chromatography-ion trap tandem mass spectrometry for the characterization of polypeptide antibiotics of the colistin series in commercial samples

A selective reversed-phase liquid chromatography-tandem mass spectrometry method is described for the characterization of related substances in the colistin complex. Mass spectral data were acquired on an LCQ ion trap mass spectrometer equipped with an electrospray ionization probe operated in the positive ion mode. The main advantage of this technique is the characterization of novel related substances without time-consuming isolation and purification procedures. Using this method seven new related substances were partially identified in colistin bulk sample and tablets. Four components were assigned as isomers of the main components of colistin.     

Analytical use of immobilized glucose oxidase

With the aim of immobilizing glucose oxidase (GO) for routine determination of glucose, a covalent bond immobilization method on titanium (IV) chloride activated silica supports was used (1). Several parameters were studied in order to optimize the residual activity upon immobilization and during operation. The immobilized enzyme can be reutilized at 25°C for several h a day alternating with storage (4°C) for at least 3,300 h.