Enforcing Termination of Interprocedural Analysis

Interprocedural analysis by means of partial tabulation of summary functions may not terminate when the same procedure is analyzed for infinitely many abstract calling contexts or when the abstract domain has infinite strictly ascending chains. As a remedy, we present a novel local solver for general abstract equation systems, be they monotonic or not, and prove that this solver fails to terminate only when infinitely many variables are encountered. We clarify in which sense the computed results are sound. Moreover, we show that interprocedural analysis performed by this novel local solver, is guaranteed to terminate for all non-recursive programs --- irrespective of whether the complete lattice is infinite or has infinite strictly ascending or descending chains

ADP-ribosylation of arginine

Arginine adenosine-5′-diphosphoribosylation (ADP-ribosylation) is an enzyme-catalyzed, potentially reversible posttranslational modification, in which the ADP-ribose moiety is transferred from NAD+ to the guanidino moiety of arginine. At 540 Da, ADP-ribose has the size of approximately five amino acid residues. In contrast to arginine, which, at neutral pH, is positively charged, ADP-ribose carries two negatively charged phosphate moieties. Arginine ADP-ribosylation, thus, causes a notable change in size and chemical property at the ADP-ribosylation site of the target protein. Often, this causes steric interference of the interaction of the target protein with binding partners, e.g. toxin-catalyzed ADP-ribosylation of actin at R177 sterically blocks actin polymerization. In case of the nucleotide-gated P2X7 ion channel, ADP-ribosylation at R125 in the vicinity of the ligand-binding site causes channel gating. Arginine-specific ADP-ribosyltransferases (ARTs) carry a characteristic R-S-EXE motif that distinguishes these enzymes from structurally related enzymes which catalyze ADP-ribosylation of other amino acid side chains, DNA, or small molecules. Arginine-specific ADP-ribosylation can be inhibited by small molecule arginine analogues such as agmatine or meta-iodobenzylguanidine (MIBG), which themselves can serve as targets for arginine-specific ARTs. ADP-ribosylarginine specific hydrolases (ARHs) can restore target protein function by hydrolytic removal of the entire ADP-ribose moiety. In some cases, ADP-ribosylarginine is processed into secondary posttranslational modifications, e.g. phosphoribosylarginine or ornithine. This review summarizes current knowledge on arginine-specific ADP-ribosylation, focussing on the methods available for its detection, its biological consequences, and the enzymes responsible for this modification and its reversal, and discusses future perspectives for research in this field

Simple techniques for two-dimensional gas chromatography

International audienceThe adaption of the Deans system of double-column gas chromatography for use with a commercial chromatograph is described. Optimization of the carrier gas flow-rates through the two columns is achieved independently in each column. The importance of using an intermediate trap between the two columns is demonstrated. A system for automatic rejection of the major components of the analyzed mixture is described. Quantitative analysis of trace impurities has been performed using a suitable calibration

Levels of PCDDs and PCDFs in human milk from populations in Madrid and Paris

Peer reviewe

A Theoretical Investigation of the Potentialities of the Use of a Multidimensional Column in Chromatography

Two-dimensional column chromatography is a method which combines the advantages of column chromatography (constant, adjustable flow velocity, excellent efficiency, on-line detection) and two-dimensional thin-layer chromatography (successive developments in two perpendicular directions, using two different retention mechanisms). It is shown that by merely keeping constant the solvent flow velocity during the development of a thin-layer plate, a considerable increase in the spot capacity can be achieved, since plate length and particle size can be selected without any prejudicial influence on the solvent velocity which can be kept constant at the value considered as optimum by the analyst. Calculations show that two-dimensional column chromatography can generate peak capacities well in excess of 500, up to several thousands, and that the specifications for the equipment are not too stringent. A 10 × 10 cm column would be 1 mm thick, be well packed with 10-μm particles and be operated at a reduced velocity of 10. Such a packing could be expected to be very homogeneous (A = 0.7) and the reduced plate height would be 1.95. The expected spot capacity is 900, while the pressure drop for a compound with a diffusion constant D = 5 × 10-6, cm2/sec (linear velocity, u, = 0.05 cm/sec) and a solvent with viscosity 1 cP is only 5 atm (flow-rate 3 cm3/min). The sample spot should be about 1 mm in diameter or less. Equipment capable of these performances is under construction. Successful operation of this two-dimensional separation scheme, however, relies on the ability to find two chromatographic systems operating according to widely different mechanisms

DECOMPOSITION OF ACETALDEHYDE IN AIR IN A DIELECTRIC BARRIER DISCHARGE

International audienceAn experimental study of the decomposition of acetaldehyde in a dry air mixture has been carried out using a dielectric barrier discharge. Operating parameters that affect the CH3CHO destruction efficiency include the gas mixture composition, the applied voltage, and the gas residence time in the reactor. The plasma is produced in a narrow gap by a dielectric barrier discharge at low applied voltage, 40 kHz. An isotopic labeling (CD3CHO) is used with gas chromatography-mass spectrometry identification of the formed stabilized species in order to investigate the mechanism of acetaldehyde decomposition, and especially the CH3 center dot radical stability. Additionally, the influence of the plasmagen gas mixture composition on the chemical reaction pathways in the discharge has been studied

Investigation of Selectivity in Reverse Phase Liquid Chromatography . IV- Effects of Stationary and Mobile Phases on Retention of Homologous Series

Extrapolation of log k\u27vs. nc plots for homologous series chromatographed with different mobile phases leads to a common intersection point. Its coordinates depend on the series and the solvent used, and can be rationalized on the basis of the retention model of interaction indices. The existence of this convergence point is reflected in the linear relationship of logagr-logbeta, which permits the optimization of chromatographic separations in the region of solvent compositions where these two parameters can be varied independently