Use of enzymatic catalysis with E.C. 1.2.3.2 xanthine oxidase for the kinetic determination of V(V) at low concentrations

An enzymatic kinetic method for the determination of V(V) is described, based on the activation of xanthine oxidase-catalysed NADH oxidation, in the presence of xanthine, dithiothreitol and Ag(+) ions. Under these conditions the activating power of V(V) was found to be enhanced. The linear relationship between relative enzyme activity and V(V) concentration allows the enzymatic determination of vanadium in the concentration range 20-500 ng ml , the maximum relative error being +/- 3%, and relative standard deviation less than +/- 2.2%. Possible interferences have been studied.     

A Quasi-Stationary Phase-Field Model with Micro-Movements

This note addresses the global strong solvability of a phase-field system arising in connection with the phase transition theory recently proposed by Frémond. The novelty of this modelization consists in considering the macroscopic effect of the microscopic movements of particles of the system that undergoes the phase transition. In particular, we outline the basic features of this model and deal with the upcoming nonlinear PDE system in the one-dimensional setting by means of an approximation—a priori estimates—passage to the limit procedure.     

Functionalization of corroles: the nitration reaction

The reaction of meso-triarylcorroles with AgNO2 proceeds with concomitant metalation and peripheral substitution to give the corresponding nitro-substituted silverIII corrole complex. The substitution is highly regioselective, giving only the corresponding 3-nitro derivative, among the different possible isomers. The results obtained indicate that the reaction intermediate is the pi-cation radical of the complex, which is then attacked by nitrite ion. This was proven by the reaction of the copper corrole complexes with NaNO2: in this case, the nitration reaction proceeded without the addition of an oxidant, because of the pi-cation radical character of the copper complex. The reaction is also successful in the case of 2,3,17,18-tetraethyl-8,12-diacetoxymethyl-7,13-dimethylcorrole (AMCorH3), with the formation of the meso-substituted silver corrole derivative (NO2)3AMCorAg (fully characterized by X-ray crystallography), the first of its kind to be reported. Two of the corroles are characterized by cyclic voltammetry and spectroelectrochemistry in dichloromethane, and the site of electron transfer is elucidated.     

Sharp $$N^{3/4}$$ Law for the Minimizers of the Edge-Isoperimetric Problem on the Triangular Lattice

We investigate the edge-isoperimetric problem (EIP) for sets of n points in the triangular lattice by emphasizing its relation with the emergence of the Wulff shape in the crystallization problem. By introducing a suitable notion of perimeter and area, EIP minimizers are characterized as extremizers of an isoperimetric inequality: they attain maximal area and minimal perimeter among connected configurations. The maximal area and minimal perimeter are explicitly quantified in terms of n. In view of this isoperimetric characterizations, EIP minimizers \(M_n\) are seen to be given by hexagonal configurations with some extra points at their boundary. By a careful computation of the cardinality of these extra points, minimizers \(M_n\) are estimated to deviate from such hexagonal configurations by at most \(K_t\, n^{3/4}+\mathrm{o}(n^{3/4})\) points. The constant \(K_t\) is explicitly determined and shown to be sharp.     

Attractors for Gradient Flows of Nonconvex Functionals and Applications

This paper addresses the long-time behaviour of gradient flows of nonconvex functionals in Hilbert spaces. Exploiting the notion of generalized semiflows by J. M. Ball, we provide some sufficient conditions for the existence of a global attractor. The abstract results are applied to various classes of nonconvex evolution problems. In particular, we discuss the long-time behaviour of solutions of quasistationary phase field models and prove the existence of a global attractor.     

Crystallization in a One-Dimensional Periodic Landscape

Journal of Statistical Physics - We consider the crystallization problem for a finite one-dimensional collection of identical hard spheres in a periodic energy landscape. This issue arises in...