Biomedical subjects

Andrea Melchior

Publications and source records attributed to Andrea Melchior.

4 recordsLinked to original sources

PubMed2006

Local diffusion in paramagnetic solutions by NMR relaxometry at one frequency.

The relative diffusion coefficient D of a paramagnetic species and a diamagnetic probe molecule bearing nuclear spins is obtained from their measured relaxation times T1 and T2 (or T1rho). This is achieved by introducing the longitudinal relaxivity, r1, a linear expression of 1/T1, and the mixed relaxivity, rmix, a linear expression of 1/T1 and 1/T2 (or 1/T1rho). Under weak assumptions, D is proportional to (rmix - r1) to the power -2/3 and to rmix to the power -1, with easy-to-determine proportionality factors. The method is noninvasive and easy to use on standard NMR spectrometers and imagers. It is validated through the study of various solutions of a Gd(III)-based contrast agent for magnetic resonance imaging.

Journal Article↗

PubMed2004

Mixed nitrogen/oxygen ligand affinities for bipositive metal ions and dioxygen binding to cobalt(II) complexes.

The complex formation of Co(II) and Cd(II) with mixed N/O ligands in dimethylsulfoxide (dmso) at 298 K is investigated by means of potentiometric, UV-Vis, calorimetric, FT-IR, NMR and electrochemical techniques. The linear and cyclic ligands investigated are: 2,2'-oxydiethylamine (NON), N-(2-hydroxyethyl)-ethylenediamine (NNO), 1,4,10-trioxa-7,13-diaza-cyclopentadecane (2,1) and 1,4,7,10-tetraoxa-13-azacyclopentadecane (2,2). The results are discussed by taking into account the donor strength of donor atoms, strain effects in the formation of chelate rings, steric and inductive effects and the size of the cavity when macrocyclic ligands are concerned. DFT studies are also performed to gain an insight into the stabilization of the lower oxidation state of the CoL2(2+/3+) couple in order to understand the different reactivity of the Co(II) complexes towards dioxygen. The kinetics of dioxygen uptake has been studied by UV-Vis measurements and the results reveal an interesting strong solvent effect, which is active in lowering the rate constant for formation of the initial superoxo complex.

Journal Article↗

PubMed2003

Cobalt(II) dioxygen carriers based on simple diamino ligands: kinetic and ab initio studies.

The kinetics of the oxygenation reaction of CoL2(2+) complexes (L=ethylenediamine (en), N,N'-dimethylethylenediamnine (dmen)) have been investigated in dimethyl sulfoxide (dmso) at 298 K and in a medium adjusted to 0.1 mol dm(-3) with Et4NClO4 by means of a UV-vis spectrophotometric technique. The reaction mechanisms are consistent with the fast formation of superoxo 1:1 initial CoL2-O2 species (L=en, dmen), whereas the dimeric mu-peroxo (CoL2)2O2 adduct is formed only when L=en, in the rate determining step. The kinetic results are discussed taking into account the effects of ligand/solvent substitution. EPR results give information on the electronic structure and the coordination geometry of the Co(II) complexes and further confirm the stoichiometry of the species formed. Ab initio calculations provide insights on the geometrical parameters of all the complexes investigated and allow us to draw some hypotheses about the influence of H.H nonbonded interactions in the eventual formation of the dimeric mu-peroxo (CoL2)2O2 complexes. Solvational effects are also considered. The formation of the (CoL3)2O2 adduct is also proved when L=en by means of O2 volumetric absorption.

Journal Article↗

PubMedDate not supplied

A novel multipurpose Excel tool for equilibrium speciation based on Newton-Raphson method and on a hybrid genetic algorithm.

A new algorithm for simulation of chemical equilibria is developed, based on classical Newton-Raphson method applied to mass balance. This tool, named EST (Equilibrium Speciation Tool), is improved by using a robust Genetic Algorithm. In addition, EST works by using Excel spreadsheets and therefore offers the innovation of a great simplicity and versatility. In fact, it allows the users to simulate, or to obtain from experimental data, desired chemical-physical parameters as well as to interact with other available or freely created Excel tools. The reliability of this utility is here proved by comparison with some published data by other authors, concerning both complicated homogeneous and heterogeneous equilibria. In addiction its flexibility is tested computing thermodynamic parameters by using experimental calorimetric data referred to the complex formation of cobalt(II) with a macrocyclic ligand. A brief review and comparison of the relative robustness and quickness of main numerical methods are also reported.

Algorithms↗