Thin layer cyclic voltammetry: an efficient tool to determine the redox characteristics of large dendrimers

Dendrimers with an electroactive bis(phenanthroline) copper(I) core have been prepared and thin layer cyclic voltammetry (TLCV) found to be an efficient tool to determine their redox characteristics in spite of the slow electron transfer kinetics observed for the largest compounds.     

Main group heteroatoms in transition metal clusters

The class of transition metal cluster compounds which contain individual main group heteroatoms is surveyed. Hydrido-clusters and clusters containing group IV, V, VI and VII atoms are dealt with in turn with reference to their synthesis, structure and reactivity.     

Isothermal and non-isothermal water transport in porous membranes. I. The power balance

A quantitative study of water transport through porous, unselective membranes of various types is presented. Effects produced by hydraulic pressure are compared with those due to a transmembrane temperature gradient. p]The quantities directly determined for five types of porous partitions of different structure are: hydraulic permeability, thermoosmotic permeability, activation energies of both these transport processes and thermal pressure. Experiments have been systematically conducted at temperatures from +20°C to +60°C. From the experimental data, thermohydraulic conductivity, thermal conductivity, heat of transport, ratio of conductive to convective heat fluxes and thermodynamic efficiency of the transport process have been calculated. Each of these quantities is expressed in terms of specific physical properties of system's components. p]These findings provide deeper insight in the fundamental physico-chemical aspects of thermodialysis, and open at the same time promising perspectives of practical applications for this process of direct transformation of thermal into mechanical (and electrochemical) energy.     

Studies on the formation of glutathionylcobalamin: any free intracellular aquacobalamin is likely to be rapidly and irreversibly converted to glutathionylcobalamin

A decade ago Jacobsen and co-workers reported the first evidence for the presence of glutathionylcobalamin (GSCbl) in mammalian cells and suggested that it could in fact be a precursor to the formation of the two coenzyme forms of vitamin B(12), adenosylcobalamin and methylcobalamin (Pezacka et al. Biochem. Biophys. Res. Commun. 1990, 169, 443). It has also recently been proposed by McCaddon and co-workers that GSCbl may be useful for the treatment of Alzheimer's disease (McCaddon et al. Neurology 2002, 58, 1395). Aquacobalamin is one of the major forms of vitamin B(12) isolated from mammalian cells, and high concentrations of glutathione (1-10 mM) are also found in cells. We have now determined observed equilibrium constants, K(obs)(GSCbl), for the formation of GSCbl from aquacobalamin and glutathione in the pH range 4.50-6.00. K(obs)(GSCbl) increases with increasing pH, and this increase is attributed to increasing amounts of the thiolate forms (RS(-)) of glutathione. An estimate for the equilibrium constant for the formation of GSCbl from aquacobalamin and the thiolate forms of glutathione of approximately 5 x 10(9) M(-1) is obtained from the data. Hence, under biological conditions the formation of GSCbl from aquacobalamin and glutathione is essentially irreversible. The rate of the reaction between aquacobalamin/hydroxycobalamin and glutathione for 4.50 < pH < 11.0 has also been studied and the observed rate constant for the reaction was found to decrease with increasing pH. The data were fitted to a mechanism in which each of the 3 macroscopic forms of glutathione present in this pH region react with aquacobalamin, giving k(1) = 18.5 M(-1) s(-1), k(2) = 28 +/- 10 M(-1) s(-1), and k(3) = 163 +/- 8 M(-1) s(-1). The temperature dependence of the observed rate constant at pH 7.40 ( approximately k(1)) was also studied, and activation parameters were obtained typical of a dissociative process (DeltaH++ = 81.0 +/- 0.5 kJ mol(-1) and DeltaS++ = 48 +/- 2 J K(-1) mol(-1)). Formation of GSCbl from aquacobalamin is rapid; for example, at approximately 5 mM concentrations of glutathione and at 37 degrees C, the half-life for formation of GSCbl from aquacobalamin and glutathione is 2.8 s. On the basis of our equilibrium and rate-constant data we conclude that, upon entering cells, any free (protein-unbound) aquacobalamin could be rapidly and irreversibly converted to GSCbl. GSCbl may indeed play an important role in vitamin B(12)-dependent processes.     

Existence globale pour une classe d'équations d'ondes perturbées

In this paper we prove a global well-posedness result for the following Cauchy problem:

where the initial data $\text{(f,g)∈}\text{H}\text{?}{}^1\text{(}\text{R}{}^3\text{)×L}{}^2\text{(}\text{R}{}^3\text{)}$ are compactly supported, 1?α<5, $\text{a}{}_{\mathrm{i}}\text{(t,x)∈L}{}^{\mathrm{\infty }}\text{(}\text{R}{}_{\mathrm{t}}\text{×}\text{R}{}_{\mathrm{x}}{}^3\text{)}$, $\text{V(t,x)∈L}{}^{\mathrm{\infty }}\text{(}\text{R}{}_{\mathrm{t}}\text{;L}{}^3\text{(}\text{R}{}^3{}_{\mathrm{x}}\text{))}$. To cite this article: N. Visciglia, C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

-theory of -pseudo-differential algebras

We are concerned with the so-called -pseudo-differential calculus. We describe the spectrum of the unital and commutative -algebra given by the norm closure of the space of -order pseudo-differential operators modulo compact operators; other related algebras are also considered. Finally, their -theory is computed.

     

Degree complexity for a modified pigeonhole principle

 We consider a modification of the pigeonhole principle, M P H P, introduced by Goerdt in [7]. M P H P is defined over n pigeons and log n holes, and more than one pigeon can go into a hole (according to some rules). Using a technique of Razborov [9] and simplified by Impagliazzo, Pudlák and Sgall [8], we prove that any Polynomial Calculus refutation of a set of polynomials encoding the M P H P, requires degree Ω(log n). We also prove a simple Lemma giving a simulation of Resolution by Polynomial Calculus. Using this lemma, and a Resolution upper bound by Goerdt [7], we obtain that the degree lower bound is tight. Our lower bound establishes the optimality of the tree-like Resolution simulation by the Polynomial Calculus given in [6]. Received: 29 March 2001 / Published online: 2 September 2002 RID="⋆" ID="⋆" A prelimianry version appeared as part of the paper A Study of Proof Search Algorithms for Resolution and Polynomial Calculus published in the Proceedings of the 40-th IEEE Conference on Foundations of Computer Science, 1999 RID="†" ID="†" Partly supported by Project CICYT, TIC 98-0410-C02-01 and Promoción General del Conocimiento PB98-0937-C04-03. RID="††" ID="††" Part of this work was done while the author was a member of the School of Mathematics at Institute for Advanced Study supported by a NSF grant n. 9987845