Showing papers by "University of Antwerp published in 1984"

Plant Antiviral Agents; VI.1 3-Methoxyflavones as Potent Inhibitors of Viral-Induced Block of Cell Synthesis.

Abstract: An investigation of the constituents responsible for the pronounced antiviral activity observed for extracts of EUPHORBIA GRANTII Oliv. stems has afforded four related 3-methoxyflavones exhibiting remarkable activities against picornaviruses and vesicular stomatitis virus. All compounds were found to be derivatives of 3-methylquercetin. The concentration of 3-methylquercetin (3-MQ) and 3,3'-dimethyl-quercetin (3,3'-DMQ) inhibiting 90 % of polio type 1 and coxsackie B4 viruses in tissue culture was about 0.01 microg/ml, whereas the 50 % cytotoxic concentration was 40 microg/ml. When administered intraperitoneally, 3-MQ protected mice from viremia and lethal infections from coxsac kie B4 virus at a daily dose of 20 mg/kg for a period of nine days. Biochemical studies on the mechanism of action of 3-MQ or 3,3'-DMQ on poliovirus replication suggested that these 3-methoxyflavones are able to protect the host cells from a viral induced shutdown of the cellular protein synthesis. Preliminary structure activity relationship studies have shown the 3-methoxyfunction of the flavones to be essential for the observed antiviral effects.

Conformational transitions and geometry differences between low‐energy conformers of N‐acetyl‐N′‐methyl alanineamide: An ab initio study at the 4‐21G level with gradient relaxed geometries

Abstract: Energy pathways between the αR, β′, C, and β-regions of the conformational energy surface of N-acetyl-N′-methylalanyl amide were obtained by SCF ab initio calculations on the 4-21G level, with gradient geometry optimization at each point. The calculations indicate that no barrier exists at this computational level between αR and β′. The variation of geometry (bond distances and bond angles) with conformation is analyzed in detail, and the most important geometrical parameters that should be treated as variables in both empirical energy calculations and in the fitting of polypeptide chains in proteins by x-ray methods are identified. In addition to the ϕ,ψ correlation discussed previously for the helical state, a correlation of these dihedral angles in the β-region is described.

A Decomposition Methodology for Cyclic Databases

Abstract: A methodology is given to decompose a join dependency defined on a given relation scheme. The methodology works for acyclic as well as for cyclic join dependencies.

Ab initio studies of structural features not easily amenable to experiment: Part 31. Conformational analysis and molecular structures of ethylene glycol

Abstract: The geometries of ten conformations of ethylene glycol have been refined without any geometrical constraints by the ab initio gradient method on the 4-21G level. The two most stable forms found are tGg′ and gGg′ , both of which are stabilized by internal hydrogen bonding. A number of conformationally dependent structural trends are apparent in the optimized local geometries. Bond distances and bond angles in different conformations can vary by up to 0.01–0.02 A and 5°, respectively. The results are found to be consistent with most of the previous investigations of the system.

Incommensurate phase of quartz : III. Study of the coexistence state between the incommensurate and the α-phases by neutron scattering and electron microscopy

Abstract: A detailed study of lock-in transition of the incommensurate phase of quartz has been made by two complementary techniques: elastic neutron diffraction and electron microscopy. The neutron experiment was made on bulk samples (a few cm 3 ) with a simultaneous thermal expansion measurement. The transition from the incommensurate phase to the α-phase is 1st order and in general a single interface sweeps the sample. The modulation wavevector was observed to decrease continuously in the vicinity of this interface. Electron microscopy allows to obtain a direct space picture of this coexistence state on very thin samples (a few 100 nm) and to observe how the incommensurate modulation period increases from 10 nm to macroscopic size with the help of «dislocations» in the incommensurate networks of columnar Dauphine twin domains. (Analogous results obtained on AlPO 4 are also presented). The results of these two experimental techniques are well correlated and are discussed in relation to previous results on the quartz transition mainly from light scattering studies Etude detaillee de la transition d'accrochage de la phase incommensurable du quartz. Experiences de diffusion de neutrons sur des echantillons massifs (quelques cm 3 ) avec mesure simultanee de dilatation thermique. Transition phase incommensurable-phase α d'ordre 1 avec la traversee de l'echantillon par une interface unique, en general observation d'une decroissance continue du vecteur d'onde de la modulation au voisinage de cette interface. Image directe de cette coexistence par microscopie electronique sur les echantillons tres minces. Resultats analogues presentes pour AlPO 4

Ab initio studies of structural features not easily amenable to experiment: Part 39. Conformational analysis of glycine and alanine

Abstract: The NCCO torsional potential energies of glycine and alanine were determined by 4-21G ab initio calculations with geometry gradient optimization at each point. The potential energy of glycine is characterized by minima at 0 and 180°, and by a barrier at approximately 75°. The 180° local minimum is part of an energy plateau extending from approximately 150 to 210°. The alanine NCCO potential is characterized by minima at 0 and 150°, and by asymmetric barriers in the 60–90° and 270–300° regions. The 150° minimum is part of an asymmetrically stepped energy plateau extending from approximately 120 to 240°. It is shown that the qualitative features of the alanine potential can be simulated from the CCCO and NCCO torsions of propanoic acid and glycine. Some quantitative differences between the simulated and the actual potentials may point to cooperative effects in the total system. A similar, qualitative prediction is made for the NCCO potential of α-aminoisobutyric acid from glycine and 2-methyl propanoic acid.

Horizontal Decompositions for Handling Exceptions to Functional Dependencies

Abstract: A new way of treating exceptions to functional dependencies in the Relational Database Model is given It uses a method to subdivide a relation into two subrelations whose union is the given relation This horizontal decomposition induces a new constraint: the afunctional dependency, which is the “opposite” of the well known functional dependency The membership problem for this constraint is solved

A Duality Theorem for Hopf Algebras

Abstract: Let k be a commutative ring. All objects we consider are k objects. Let H be a finite Hopf algebra over k (i.e. is f. g. and projective over k). There is a natural action H*⊗ (R #H) → R #H. In [3] corollary 12.7 S. Montgomery and R. Blatter proved that the natural map (R # H) # H* → End R(R # H) is an algebra isomorphism. We consider R # H as a right as a right R module via the map R → R # H). We will give a different proof using non-commutative Galois theory.

The morphological characterization of particles by automated scanning electron microscopy

Abstract: A method is described for the characterization and the classification according to shape of microscopic objects by automated SEM. The classification is performed by a hierarchical cluster analysis on a set of Fourier coefficients that are calculated from a set of radii, measured between a well defined centroid point and the contour lines of the object. This method is incorporated in existing commercial software for automated X-ray and size analysis of airborne particulate matter (PRC, Tracor Northern). Two examples demonstrate the possibilities and limitations of this method.

Dietary selenium intake in Belgium

Abstract: The estimation of the dietary selenium intake in Belgium has been carried out. Average concentration levels in different food classes, as determined by hydride generation atomic absorption spectrometry are used combined with dietary consumption records or production, importation and exportation statistics. Analysis of duplicate meals has been used as an alternative evaluation method. Dietary intake of selenium in Belgium is discussed and compared with intakes published for other different countries.

Theory of Polaron Mobility

Abstract: Publisher Summary The chapter presents a discussion on the theory of polaron mobility. The Boltzmann equation adapted to the Feynman picture of the polaron is reviewed. The first moment of this equation, which expresses conservation of momentum in the case of slowly varying fields, is calculated. The chapter also discusses the properties of the Feynman polaron model Hamiltonian. The linear ac conductivity is studied in the classical frequency region by solving the Boltzmann equation in the relaxation-time approximation (RTA). From this polaron distribution function, the impedance function is calculated, which in the limit of zero frequency equals the polaron impedance result of Osaka. The chapter also presents a discussion from the first moment of the Boltzmann equation, which is a scalar equation. If one chooses for the polaron distribution function a drifted Maxwellian, the Thornber–Feynman (TF) result is obtained, for the nonlinear dc conductivity. The corresponding electron distribution function is calculated. It is a drifted Maxwellian with an effective electron temperature, which is only a function of the lattice temperature and the parameters of the Feynman polaron model (these parameters are a measure of the effective electron-phonon interaction). The validity of the TF result is discussed. The linear ac conductivity at quantum frequencies is studied. The Feynman–Hellwarth–Iddings–Platzman (FHIP) result for the impedance function is obtained. The polaron mass and mobility are calculated in various approximations.

Ab initio studies of structural features not easily amenable to experiment: Part 37. Structural and conformational investigations of the dicarbonyls glyoxal, biacetyl and oxalic acid

Abstract: The geometries of glyoxal, oxalic acid and biacetyl were determined by the ab initio gradient procedure on the 4-21G level, and the conformational energies of glyoxal and biacetyl were calculated as functions of the OC CO torsional angles. In the case of biacetyl, the results are in agreement with previous observations that, even at elevated temperatures, and in somewhat surprising contrast to oxalyl halides, only the trans form is detected in its vapors by gas electron diffraction. Empirical corrections, rg — re (ab initio), are determined for some bond distances and compared to previous estimates. CC rg bond distances, calculated for the CH3CO and C(O)C(O) bonds in biacetyl from the ab initio results with empirical corrections, agree within the experimental error estimates with the more sophisticated of two contradictory electron diffraction models, and the predicted mean CC bond (rg, 1.520 A) is close to the reported experimental means (rg, 1.522(3) and 1.526(2) A).

Interference of aluminium and pH on the Na-influx in an aquatic insectCorixa punctata (IIIig.)

Abstract: Some investigations concerning the impact of acid precipitation on aquatic biota, assess possible toxic effects of aluminium in relation to low pH. But those studies mainly refer to the survival of fishes under these stress conditions. Experiments with some aquatic invertebrates (crustaceans and insect larvae) on mortality under pH and aluminium-stress indicated that aluminium should be the key additional toxic factor in acid water. In this paper, data are presented on the influence of different aluminium-concentrations in relation with a low pH-value, on the Na-influx and haemolymph Na-concentration in the adult waterbug Corixa punctata (Illig.).