Absence of phosphate hydrolysis in the nucleotide substitution reaction on cis-[Co(H2O)2(cyclen)] at physiological pH: Importance of hydrogen-bonding and conjugate base-catalysis

The use of classical Werner-type cis-[Co(Cl)₂(tetraamine)]⁺ (tetraamine = cyclen or tren) complexes for their complexation study of biologically relevant ligands has been pursued. These chlorocomplexes are found to be in the chloroaqua/chlorohydroxo forms under the physiological conditions used, their chloride substitution reactivity being dominated by conjugate base pathways, specially when tetraamine = cyclen. Further studies with nucleotides indicate that the substitution processes on cis-[Co(H₂O)₂(tetraamine)]³⁺, up to neutral pH, correspond to a simple reaction producing final stable phosphato bound mononucleotide complexes. These complexes are found to be an equilibrium mixture between monodentate O-phosphato and chelate O-phosphato-N-nucleotide forms. No evidence has been found for hydrolytic cleavage of the phosphato-nucleoside bond, as found in other systems with activated phosphates or higher pH values. A full kinetic profile of the process is proposed for the systems in the 2–7 pH range which is the same for chloride, nucleoside and nucleotide substitutions. The results are indicative of an important degree of outer-sphere hydrogen bonding between the cobaltocomplex and the entering biologically relevant ligands, as expected for these processes.     

Neural coding: computational and biophysical perspectives

While recognizing a face or kicking a ball may seem to be easy tasks for us, they still constitute challenging problems for even the most sophisticated computer algorithms available nowadays. The brain has evolved complex mechanisms to encode behaviorally relevant information. Here we review the types of codes used by the brain, what their constraints are and how they map the sensory environment or the motor output. We start by defining neural codes and briefly describing some of the current tools available to record activity from the brain. We give several examples of coding strategies used by different systems and multiple organisms and discuss how spiking patterns can be read out. Going beyond correlations between physiology and stimuli, we show what is currently known about the direct causal link between neuronal responses and behavioral output or sensory input. Finally, we identify what we consider to be some of the pressing questions in the field.     

A FEM–DtN formulation for a non‐linear exterior problem in incompressible elasticity

In this paper, we combine the usual finite element method with a Dirichlet‐to‐Neumann (DtN) mapping, derived in terms of an infinite Fourier series, to study the solvability and Galerkin approximations of an exterior transmission problem arising in non‐linear incompressible 2d‐elasticity. We show that the variational formulation can be written in a Stokes‐type mixed form with a linear constraint and a non‐linear main operator. Then, we provide the uniqueness of solution for the continuous and discrete formulations, and derive a Cea‐type estimate for the associated error. In particular, our error analysis considers the practical case in which the DtN mapping is approximated by the corresponding finite Fourier series. Finally, a reliable a posteriori error estimate, well suited for adaptive computations, is also given. Copyright © 2003 John Wiley & Sons, Ltd.     

On the Fredholm theory of Wiener-Hopf equations and the coupling method

The Fredholm properties of the Wiener-Hopf operator onL _p(⁺,^m) are investigated using the coupling method for solving operator equations. The theory applies to equations whose kernel is an element ofL ₁(,^mxm). As usual the determinant of the symbol is assumed to have no zeros on the real line. The method of analysis is independent of the realization theory for symbols that are analytic in a strip containing the real axis although in some sense closely related to it. The connection between the two methods is briefly analysed in the paper.     

The direction of elimination in the pyrolysis kinetics of 3-bromobutyronitrile

The gas phase elimination of 3-bromobutyronitrile, examined in a static system and seasoned vessel, follows a first-order rate law. The reaction in the temperature range of 370.0–420.1°C and pressure range of 54–198 torr, is homogeneous and unimolecular. The temperature dependence of the rate coefficient is given by the equation: log k₁ (s^–1)=(13.74±0.25)–(213.7±3.2) kJ mol^–1 (2.303RT)^–1. The cyano substituent has been found to retard the elimination process through its electronwithdrawing resonance effect. Most of the dehydrobromination product is cis-trans-crotonitrile, while very little of allyl cyanide is obtained. This result is rationalized in terms of electronic factors.

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3- , . . 370,0–420,1°C 54–198 . : log k₁ (cek^–1)=(13,74±0,25)–(213,7±3,2)(/)×(2,303 RT)^–1. - . --, . .

     

Antioxidant and Protective Effects of <Emphasis Type="Italic">Schinus terebinthifolius</Emphasis> Raddi Against Doxorubicin-Induced Toxicity

Doxorubicin is an anticancer drug whose toxic effects on non-cancer cells are associated with increased oxidative stress. This study investigated the chemical composition, antioxidant activity of the methanolic extract of Schinus terebinthifolius Raddi leaves (MESL) as well as effects against doxorubicin-induced toxicity in human erythrocytes, K562 human erythroleukemia cells, and mouse hearts. The chemical composition indicated the presence of phenolic compounds, flavonoids, tannins, and ascorbic acid. MESL showed antioxidant activity by scavenging free radicals and inhibiting hemolysis and lipid peroxidation in human erythrocytes incubated with an oxidizing agent, and was able to increase the enzymatic activity of superoxide dismutase and glutathione peroxidase in human erythrocytes, without influencing the activity of enzyme catalase. The increase of oxidative hemolysis and malondialdehyde levels in erythrocytes incubated with doxorubicin was reduced by treatment with MESL. The cytotoxic activity of doxorubicin in erythroleukemia cells treated with MESL was unmodified. Additionally, the extract protected mice against the doxorubicin-induced cardiotoxicity. In conclusion, the MESL exhibits antioxidant activity, reducing doxorubicin-induced oxidative stress without changing the anticancer action of the drug, and protects against doxorubicin-induced cardiotoxicity. Hence, these findings suggest that these effects are via anti-oxidative by inhibiting free radicals, decreased oxidative stress, and increased antioxidant enzyme activity.