RESUMEN
In this paper we report the results of an investigation performed by potentiometric (H+-glass electrode) and visible spectrophotometric measurements on the interaction of UO2(2+) ion towards some carboxylic ligands (acetate, malonate, succinate, azelate). The measurements were carried out at T= 25 degrees C in different ionic media (KNO3 and NaCl) at different ionic strengths (0.1 < or = I/mol L(-1) < or = 1.0, NaCl; I/mol L(-1) = 0.1, KNO3). The dependence on ionic strength of formation constants was taken into account by using both a simple Debye-Hückel type equation and the SIT (Specific ion Interaction Theory) approach. Different speciation models (depending on concentration of reagents, ionic strength, pH-range) both for different carboxylates and different ionic media have been obtained. Linear combinations between formation constants, stoichiometric coefficients and length of alkyl chain of dicarboxylates have been observed and predicted formation constants at I= 0 mol L(-1) are reported for the interaction of UO2(2+) with HOOC-(CH2)n-COOH with 1 < or = n < or = 7. Finally, a visible absorption spectrum for each complex reaching a significant percentage of formation in solution (KNO3 medium) has been calculated to characterise the compounds found by pH-metric refinement.
Asunto(s)
Ácidos Dicarboxílicos/análisis , Ácidos Dicarboxílicos/química , Óxidos/análisis , Óxidos/química , Uranio/análisis , Uranio/química , Agua/química , Concentración de Iones de Hidrógeno , Hidrólisis , Ligandos , Nitratos/química , Concentración Osmolar , Compuestos de Potasio/química , Potenciometría , Cloruro de Sodio/química , Espectrofotometría UltravioletaRESUMEN
Natural sediments show sequestering properties that can lead to a process of self-purification of aquatic environment from metal pollution. The study of the interaction between metal ions and sediment particles enhances what is known about the distribution and bioavailability of heavy metals in natural systems. Our contribution concerns the characterisation of the sequestering ability of a River Po sediment with regard to calcium(II), magnesium(II), cadmium(II), nickel(II) and copper(II), in fixed experimental conditions, through pH-metric and spectrometric measurements. A batch titration procedure was adopted and, in each solution, after equilibration, both pH and pM (M = Ca(II), Mg(II), Cd(II), Ni(II), Cu(II)) (via Inductively Coupled Plasma - Optical Emission Spectroscopy, ICP-OES) values were measured. The experimental data were first processed with a specific software to evaluate the concentration and protonation constants of the sediment ligand site(s). The speciation model was then assessed, together with the values of complexation constants, for the different sediment/metal cation systems. In order to better characterise the copper(II)-sediment interaction and to obtain more information about the nature of ligand site(s) involved, EPR (Electronic Paramagnetic Resonance) measurements were also made on the dry sediment before and after reaction with copper(II) ions.
Asunto(s)
Sedimentos Geológicos/análisis , Metales Pesados/análisis , Ríos/química , Contaminantes Químicos del Agua/análisis , Disponibilidad Biológica , China , Espectroscopía de Resonancia por Spin del Electrón , Monitoreo del Ambiente , Sedimentos Geológicos/química , Concentración de Iones de Hidrógeno , Modelos Biológicos , Espectrofotometría AtómicaRESUMEN
In this paper copper(II) complex formation in aqueous solution with a series of nucleosides (adenosine or guanosine) or nucleotides 5'-monophosphate is studied by means of potentiometry, visible spectrophotometry and ultraviolet circular dichroism. A chemical model has been formulated for each binary system (at T= 25 degrees C and I = 0.1 M), with particular attention to the interaction in the basic field. A spectrum (both visible absorption and ultraviolet circular dichroism) for each complex with a significant percentage of formation (in the adopted experimental conditions) has been calculated, allowing structural details to be hypothesised. The interaction with deprotonated alcoholic group(s) of the ribose moiety has been found to be fundamental in determining the co-ordination chemistry of each ligand considered while cases of co-operation between the purine and ribose donor(s) were also considered. Confirmations were also obtained by an investigation on the corresponding 2'-deoxy compounds as ligands.