Showing papers by "Paul Sabatier University published in 1977"

Non-empirical pseudopotentials for molecular calculations

Abstract: Improved three-parameter atomic pseudopotentials are theoretically determined from lithium to krypton. In view of further molecular calculations, accurate expressions are given for the pseudopotent...

Non-empirical pseudopotentials for molecular calculations: II. Basis set extension and correlation effects on the X2 molecules (X=F, Cl, Br, I)

Abstract: The ability of the atomic pseudopotential proposed in Part I to reproduce the all-electron basis set extension and correlation effects in molecules has been tested on F2 and Cl2 through systematic

Experimental resolution of the retardation time spectrum in polymeric solids by a new method: Thermostimulated creep

Abstract: We propose a new method for the investigation of molecular motion in polymeric solids. In a mechanical step-function experiment, we thermally stimulate the response to a constant stress. The high resolving power of this technique permits detailed study of the complex retardation modes observed in polymers. By using “fractional” loading programs it is possible to differentiate a discrete and a continuous distribution of retardation time. This technique allows us to predict the complex compliance in a very wide frequency range: 104-10−12 Hz for experiments performed between liquid nitrogen temperature and 500°K. In low-density polyethylene, we have shown the existence of a discrete spectrum of mechanical retardation times which has the same fine structure as the spectrum of dielectric relaxation times obtained from the study of depolarization thermocurrent on the same sample. The predicted variation versus temperature and frequency of the loss compliance is compared with that of the dielectric loss...

A new method for the study of molecular motion in polymeric solids: Thermally stimulated creep

Abstract: We propose a new method for the investigation of molecular motion in polymeric solids. In a mechanical step-function experiment, we thermally stimulate the response to a constant stress. The high resolving power of this technique permits detailed study of the complex retardation modes observed in polymers. As an example, we consider the thermally stimulated creep of low density polyethylene. The experimental resolution of the thermally stimulated creep spectra shows the existence of elementary processes well fitted by the assumption of single retardation times.

Production des soldats dans les sociétés sortant d'hibernation chez la fourmiPheidole pallidula (Nyl.) (Formicidae, Myrmicinae)

Abstract: 1o Le recensement des adultes et des nymphes dans la nature dePheidole pallidula montre que le pourcentage des soldats varie en cours d'annee: faible a la sortie de l'hibernation, il s'eleve progressivement et atteint son maximum a l'entree de l'hiver. 2o Il est possible de reproduire ces variations au laboratoire, ce qui permet d'analyser les facteurs regulant l'apparition des soldats a la sortie de l'hibernation. a) L'âge des ouvrieres par rapport a la sortie d'hibernation semble sans effets. En effet, des ouvrieres sorties d'hibernation depuis plusieurs semaines et qui ont deja eleve un couvain d'ouvrieres ne sont pas plus aptes a l'elevage des soldats que celles sortant d'hibernation. b) Malgre une evolution saisonniere de leur taille, les œufs sont bipotentiels: les œufs de printemps et les œufs d'ete sont susceptibles de donner naissance a des soldatset a des ouvrieres. Meme les œufs des reines fondatrices peuvent evoluer en larves de soldats. L'orientation depend des soins donnes aux larves et non d'un facteur blastogenique. c) L'abondance des ouvrieres nourrices, favorise l'eclosion des soldats en plus grand nombre. d) Toujours a la sortie de l'hibernation, la production des soldats est inhibee lorsque le pourcentage des soldats adultes est superieur a environ 4% meme si il y a plusieurs milliers d'ouvrieres nourrices.

Relations polyphénols — croissance: Mise en évidence d'un effet inhibiteur des composés phénoliques sur le transport polarisé de l'auxine

Abstract: Polyphenols and Growth: Inhibition of Polar Auxin Transport by Phenolic Compounds. The possible effects of polyphenols on auxin transport in tomato plants (Lycopersicum esculentum Mill.) were investigated. For this purpose, the phenolic content of the material was stimulated by exogenously supplied quinic acid. After the apical bud had been excised, labelled compounds were applied to the cut surface, and the radioactivity transported to the roots was measured. Quinic acid treatment significantly delayed polar transport of labelled auxins (IAA or NAA). It did not affect the migration rate of sucrose−14C and leucine−3H. A number of evidences seems to demonstrate that the phenolics are responsible for these modifications, since similar results were recorded when the labelled compounds were supplied simultaneously with polyphenols from tomato. Moreover, a decreased polarity of NAA transport could be observed when the plants were submitted to treatments which lead to an increased level of phenols (boron deficiency, infection by Fusarium oxysporum). The data presented in this paper suggest that phenolic compounds could act on growth processes via the regulation of polar auxin transport.

Thermostimulated creep and depolarization thermocurrent in low density polyethylene

Abstract: A new method for the study of orientational movements in polymeric solids is proposed: in a mechanical step-function experiment, we thermally stimulate the response at a constant stress. The great advantage of the thermostimulated creep (TSC) technique is to allow the experimental resolving of the mechanical retardation time spectrum. In low density polyethylene, the existence of a discrete spectrum of mechanical retardation times is demonstrated; it has the same fine structure than the spectrum of dielectric relaxation times deduced from the study of depolarization thermocurrent (DTC) on the same sample.

TSC and dielectric study of multiple relaxations in poly‐L‐proline

Abstract: The thermally stimulated current (TSC) technique has been used to perform a detailed study of the complex relaxation modes observed in poly-L-proline II. Each mechanism has been resolved into elementary processes, each well described by using the assumption of a single relaxation time following an Arrhenius equation. This resolution allows us to predict the complex dielectric constant for temperatures between 77 and 400°K and frequencies between 10−6 and 104 Hz. In the range where experimental results are available, the predicted energy losses are in very good agreement with those measured by DC transient experiments, the pendulum technique without contacting electrodes, and the AC bridge. We discuss the probable origin of the various relaxation modes. The relaxation observed at the highest temperature may be attributed to electrons trapped at the boundaries between paracrystalline and crystalline regions. From the changes in the relaxations caused by bound water, we conclude that there are two types of water interacting with the macromolecular substrate. With increasing water content, the relaxation modes observed may first be due to water tightly bound between two carbonyl groups of adjacent chains and second, to increased stiffness of the poly-L-proline chain from more mobile water.

The PCILO Method

Abstract: By all its basic concepts, the PCILO method(1–5) differs from the standard computational methods of quantum chemistry. Most methods are variational, while PCILO is a perturbation expansion. The large majority of ground-state calculations are performed in the Hartree-Fock independent-particle approximation, using an effective single-particle Hamiltonian, while PCILO works in a basis of N-electron wave functions, at the configuration interaction level, dealing with the total N-electron Hamiltonian. The molecular orbitals are frequently identified with the delocalized, symmetry-adapted MOs resulting from the diagonalization of the single-electron effective Hamiltonian, while the PCILO method refers to localized molecular orbitals describing chemical bonds and lone pairs. The first section of this chapter introduces these tools, and shows their connection with the more popular concepts of quantum chemistry. Section 2 contains the algorithm of the method, and Section 3 is a critical discussion of its validity and possible applications.

Metabolisme du γ-aminobutyrate chez Agaricus bisporus III. La succinate-semialdehyde:NAD(P)+ oxydoreductase

Abstract: Metabolism of γ-Aminobutyrate in Agaricus bisporus. III. The Succinate-Semialdehyde: NAD (P)+ Oxidoreductase. The succinate-semialdehyde:NAD(P)+ oxidoreductase (E.C. 1.2.1.16) is responsible for the second step in the catabolism of γ-aminobutyrate: the irreversible enzymatic conversion of succinic semialdehyde (SSA) to succinate. Succinate semialdehyde dehydrogenase was extracted from mitochondrial fraction of fruit-bodies of Agaricus bisporus Lge. The mitochondrial pellet was sonicated and centrifuged at 110,000 g; the supernatant obtained was designated the “crude extract”. The enzyme was extremely unstable on storage, unless 1 mM EDTA and 20% glycerol were added. Kinetic studies were carried out at 30°C, and the formation of NADH or NADPH was followed by measuring increase of absorbance at 340 nm with a spectrophotometer. The dehydrogenase was completely inactive when the reaction was run in the absence of thiol and was more active with NAD+ than with NADP+. In the “crude extract” the activity with NADP+ had a pH optimum between 8.6 and 9.1 and the Km values for SSA and NADP+ were 2.0 × 10−4M and 1.4 × 10−4M respectively. The pH optimum with NAD+ was found between 8.6 and 8.8 and the Km value for SSA is 4.8 × 10−4M and for NAD+ 2.0 × 10−3M. With NAD+, the kinetic values (pH, Km) of the “crude extract” chromatographed on hydroxylapatite were unchanged. Inhibition by thiamine pyrophosphate (TPP) was uncompetitive with respect to NAD+, those by malate, ATP, ADP and NADPH non-competitive and that by NADH competitive. These results and the fact that activity with NAD+ was lost more slowly than with NADP+ indicate the possibility of at least two mitochondrial succinate-semialdehyde dehydrogenases, even though the activities of this enzyme assayed with NAD+ and NADP+ respectively were not able to be separated from each other by hydroxylapatite column chromatography. Some speculations on the metabolic regulation of this dehydrogenase and considerations on the significance of these results in the physiology of respiration in Agaricus bisporus Lge are given.

Synthèses et caractérisation de germylènes difonctionnels

Abstract: Syntheses and caracterization of bifunctional germylenes Several synthetic methods of bifunctional germylenes GeY2 (Y = RO, PhO, RS, CH3COO, Acac; Y2 = OCH2CH2O, SCH2CH2S) or GeXY (Y = RO, X = Cl; Y = RS, X = Cl; Y = Acac, X = Cl) such as exchange reactions, dechlorhydratation reactions and nucleophilic substitutions from GeCl2 · dioxane are described. Some more synthesis of divalent species GeY2 from Ge(OR)2 by transalcoxylation and from Ge(Cp)2 by cleavage using protic species will be presented. The stability and reactivity of these germylenes are discussed. Difunctionnal germylenes give generally a selfpolycondensation reactions. However, their reactivity in situ shows a effective participation of monomeric species GeY2.

NADH and NADPH Dependent Malate Dehydrogenases of Phaseolus vulgaris

Abstract: French bean (Phaseolus vulgaris L. cv. Contender) leaf extracts catalyse the reduction of oxaloacetate to malate in the presence of NADH and NADPH. Under the experimental conditions used, the optimum pH values are 8 and 6 respectively. After chromatography on diethylaminoethyl cellulose, two principal forms of NADH-MDH (L-malate: NAD+ oxidoreductase, E.C. 1.1.1.37) upon which NADPH activities are superposed, can be characterized. This result is confirmed by electrophoresis on polyacrylamide gel. On the other hand, after filtration on Ultrogel 34, NADH-MDH is eluted as a single peak; once again, NADPH activity is associated with it. When PtCl2−4, a powerful inhibitor of MDH, is added to the reaction medium, the degree of inhibition is the same irrespective of the cofactor employed. When root extracts are submitted to chromatography on diethylaminoethyl cellulose, activity profiles are identical to those obtained with leaves. These results suggest that the NAD dependent enzymes can also utilize NADP to reduce oxaloacetate. After addition of dithiothreitol, another NADPH-MDH activity manifests itself in the leaf extracts; it differs from the foregoing ones in its optimum pH, its chromatographic properties and its response to PtCl2−4 action. Root extracts do not exhibit this activity thus showing a specific localization of this enzyme in the green part of the plant.