Influence and role of metal ions in enzymatic catalysis with e.c. 1.2.3.2. xanthine oxidase Application to trace analysis

The effect of metal ions on the reductive half-reaction of xanthine oxidase (XOD) in the catalytic conversion of xanthine into uric acid has been studied spectrophotometrically in Tris-HCl buffer at pH 7.4, 37 +/- 0.1 degrees and ionic strength 0.04M. Some metal ions display inhibitor properties, the sequence of inhibiting efficiency being Ag(I) > Hg(II) > Cu(II) > Cr(VI) > V(V) > Au(III) > Tl(I) and for these the I(50) values were determined. Only Tl(I), V(V) and Cu(II) showed reversible inhibition and therefore for these the mechanisms were assessed [competitive for V(V) and Tl(I); uncompetitive for Cu(II)]. The conditional inhibition constants (K(i)) were also determined. The effect of EDTA for protection of the enzyme against metal inhibition, and for its reactivation after inhibition, was also investigated. Utilization of the linear relationship between relative enzyme activity and inhibitor concentration allowed sensitive and selective (though not specific) determination of Ag(I) and Hg(II) (10(-9)-10(-8)M), and of Cu(II) and Cr(VI) (10(-7)-10(-6)M), the maximum relative error being +/- 4%. For a few metal ions, e.g., Ag(I) and Cr(VI), in the presence of EDTA, a certain specificity is observed.     

A macroscopic model for magnetic shape-memory single crystals

A rate-independent model for the quasi-static magneto-elastic evolution of a magnetic shape-memory single crystal is presented. In particular, the purely mechanical Souza–Auricchio model for shape-memory alloys is here combined with classical micro-magnetism by suitably associating magnetization and inelastic strain. By balancing the effect of conservative and dissipative actions, a nonlinear evolution PDE system of rate-independent type is obtained. We prove the existence of so-called energetic solutions to this system. Moreover, we discuss several limits for the model corresponding to parameter asymptotics by means of a rigorous Γ-convergence argument.     

A phenomenological model for microstructure-dependent inelasticity in shape-memory alloys

Degradation in shape-memory alloy response is a crucial concern for a variety of innovative applications. Under cyclic loadings, these materials generally experience permanent inelastic deformations. The onset of plasticization is known to be very sensitive to the microstructure of the polycrystalline specimen. Moving from recent experimental findings (Malard et al. in Funct Mater Lett 2:45–54, 2009; Acta Mater 59:1542–1556, 2011), we present a phenomenological model for permanent inelastic effects in shape-memory alloys taking into account the polycrystalline microstructure. In particular, the mechanical response under cyclic loadings is investigated in connection with the mean crystal grain size. Formulated within the variational frame of generalized standard materials, the model consists in an extension of the model in Auricchio et al. (Int J Plast 23:207–226, 2007) to the case of microstructure-dependent parameters. The mathematical setting is discussed and numerical simulations showing the capability of the model to reproduce experiments are presented.     

Finite plasticity in $$\varvec{P}^\top \! \varvec{P}$$. Part I: constitutive model

We address a finite-plasticity model based on the symmetric tensor \(\varvec{P}^\top \! \varvec{P}\) instead of the classical plastic strain \(\varvec{P}\). Such a structure arises by assuming that the material behavior is invariant with respect to frame transformations of the intermediate configuration. The resulting variational model is lower dimensional, symmetric and based solely on the reference configuration. We discuss the existence of energetic solutions at the material-point level as well as the convergence of time discretizations. The linearization of the model for small deformations is ascertained via a rigorous evolution-\(\Gamma \)-convergence argument. The constitutive model is combined with the equilibrium system in Part II where we prove the existence of quasistatic evolutions and ascertain the linearization limit (Grandi and Stefanelli in 2016).     

Separation of N1- and N8-acetylspermidine isomers by reversed-phase column liquid chromatography after derivatization with dansyl chloride

The separation of dansyl derivatives of N1- and N8-acetylspermidine by reversed-phase column liquid chromatography is reported. The influence of organic solvents on the retention of acetylspermidines was studied. Best resolutions were achieved using a C18 column and a ternary mobile phase composed of water, methanol and acetonitrile. The precolumn derivatization method permitted the detection of picomole quantities. A method for the determination of acetylspermidines in rat tissues is described.     

Structure result for steady-state solutions of a one-dimensional Frémond model of SMA

This paper deals with the complete characterization of solutions to an elliptic system of variational inequalities. The latter model arises in the study of the long-time behavior of shape memory materials and is suitable of describing a variety of experimentally observed phenomena.     

Determinazione di alcuni composti ossiantrachinonici a mezzo di titolazione in solventi non acquosi

Riassunto E stato applicato il metodo di titolazione potenziometrica con metilato sodico a composti fenolici aventi formula simile come l'1–8 diossiantrachinone, l'1–8 diossi-3-metilantrachinone e l'1–8 diossi-3-metil antrone, di notevole importanza farmaceutica.Come solvente si è usata la piridina e come rivelatori del punto di equivalenza una coppia di elettrodi vetro-antimonio non essendo possibile usare indicatori data la forte colorazione delle soluzioni.

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Summary Potentiometric titration with sodium methylate was used ton determine derivatives whose constitution is similar to that of 1,8-dihydroxyanthraquinone, 1,8-dihydroxy-3-methylanthraquinone and l,8-dihydroxy-3-methylanthrone.The solvent is pyridine. The change point was determined by means of an electrode pair: glass electrode-antimony electrode, since the intense self-color of the solutions excludes the use of indicators.

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Zusammenfassung Die potentiometrische Titration mit Natriummethylat wurde zur Bestimmung von Derivaten herangezogen, deren Zusammensetzung dem 1,8-Dihydroxyanthrachinon, dem 1,8-Dihidroxy-3-methylanthrachinon und dem 1,8-Dihidroxy-3-methylanthron ähnlich ist.Als Lösungsmittel wird Pyridin verwendet. Der Umschlagspunkt wird mit Hilfe eines Elektrodenpaares Glaselektrode-Antimonelektrode festgestellt, da die starke Eigenfärbung der Lösungen den Gebrauch von Indikatoren ausschließt.

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Résumé Le titrage potentiométrique par le méthylate de sodium a été appliqué au dosage de dérivés dont la composition est semblable à celles de la 1, 8-dihydroxyanthraquinone, de la 1,8-dihydroxy-3-méthylanthraquinone et de la l,8-dihydroxy-3-méthylanthrone. On utilise la pyridine comme solvant.Le point final de titrage est déterminé à l'aide d'un système électrode de verre: électrode d'antimoine car la forte coloration des solutions interdit l'emploi d'indicateurs.