G. Giorgio Bombi

The speciation of aluminum in aqueous solutions of aluminum carboxylates. Part I. X-ray molecular structure of Al[OC(O)CH(OH)CH3]3

Abstract The crystal structure of tris(2-hydroxypropanoate-(L))aluminum(III) was determined by X-ray crystallography and refined to R=0.044. The molecular structure is uncomplicated and contains monomeric [Al(lact)3]entities, in which the metal atom is surrounded by a distorted octahedral {O6} coordination sphere where the oxygen atoms of the carboxylate and of the hydroxyl group are the donating sites. The major source of the geometrical distortion is in the OAlO angles of the metallo-organic ring (c83°. The AlO distances range from 1.86 to 1.91 A. All hydroxyl hydrogen atoms are involved in very tight intermolecular hydrogen bonds (c. 2.50 A) which involve the carbonyl groups of adjacent Al(lact)3 unities. The solid state IR spectrum of Al(lact)3 is interpreted in terms of monohapto ‘end on’ coordination of the carboxylate donating site to AlIII.

An apparatus for voltammetry at solid microelectrodes with periodic renewal of the diffusion layer

Summary An apparatus for voltammetric measurements at a platinum spherical microelectrode with periodic renewal of the “diffusion layer” and interrupted polarization is described. The voltammograms obtained give two curves, corresponding to the instantaneous values of the current at two different times after the beginning of each polarization period. It is suggested that the ratio between these two current values can be used as a preliminary diagnostic criterion for assessing the nature of an electrode process.

Titration of acidic cations in molten nitrates with electrolytically generated oxide ions

Abstract The feasibility of the titration of acidic cations in molten sodium nitrate-potassium nitrate with electrolytieally generated oxide ions has been tested. Quantitative data are given for the titration of zinc and cadmium ions.

Crystal and molecular structures of diaqua(nitrilotriacetato)aluminium(III) and di-µ-hydroxo-bis(nitrilotriacetato)dialuminate(III) dianion

The crystal structures of [Al(nta)(H2O)2]·(CH3)2CO·H2O (1) and [Al(H2O)2][Al2(nta)2(µ-OH)2]-OH·3H2O (2)(nta = nitrilotriacetate) were determined by X-ray crystallography and refined to R= 0.043 [(1)] and 0.045 [(2)]. In both cases the ligating behaviour of nta3– is uncomplicated, i.e. quadridentate and non-bridging, and the geometry around AlIII is distorted octahedral, owing to the geometric requirements of the nta3– ligand. Compound (2) contains dimeric groups in which two Al–nta moieties are joined by two OH bridges; the Al ⋯ Al distance is equal to 2.842(2)A. Both crystal lattices are stabilized by significant intermolecular hydrogen bonds.

Linearity range of Gran plots for the end-point in potentiometric titrations

Simple criteria and procedures to assess which part of a potentiometric titration curve can be used to obtain an appreciably linear Gran plot and an accurate extrapolation to the equivalence volume are discussed for one-step precipitation, complexometric, redox and acid-base titrations. Equations were derived for calculating the limiting values of the experimental parameters that prevent titration errors higher than an assigned value.

Perspective. Analytical validation of a general protocol for the preparation of dose-controlled solutions in aluminium toxicology

Aluminium(III) solutions suitable for careful toxicological investigation both in vivo and in vitro, are prepared from AlCl3·6H2O and from neutral metal complexes, Al(lactate)3, Al2(citrate)2(H2O)6, Al(acetylacetonate)3 and Al(maltolate)3, by dissolving the pure compounds in TRIS-HCl buffer solutions. The metal concentrations in the supernatant liquids are determined spectrophotometrically under reproducible conditions. Al(acetylacetonate)3 and Al(maltolate)3 are detected as molecular entities by using 1H NMR spectroscopy down to concentrations of 200 and 100 µmol l–1, respectively.

Standard electrode potentials of the iodine-iodide system in molten (Li,K)NO3

Summary The standard potentials of the redox couples involving I2, I−, and I3−, and the equilibrium constants of the reactions: I 2 ( g ) ⇌ I 2 ( soln ⁡ . ) I 2 ( g ) + I − ⇌ I 3 − in molten (Li,K)NO3 between 435 and 490°K, have been determined.

Metal–ligand solution equilibria studied by electrospray ionization mass spectrometry: effect of instrumental parameters

Electrospray ionization mass spectrometry (ESI-MS) is being increasingly employed in the study of metal-ligand equilibria in aqueous solution. In the present work, the ESI-MS spectral changes due to different settings of the following instrumental parameters are analyzed: the solution flow rate (F(S)), the nebulizer gas flow rate (F(G)), the sprayer potential (E), and the temperature of the entrance capillary (T). Twenty-eight spectra were obtained for each of six samples containing aluminum(III) and 2,3-dihydroxypyridine at various pH, in the absence or in the presence of a buffer and of sodium ions. Among the considered instrumental parameters, T produced the largest effects on the ionic intensities. F(S) and F(G) affected the ESI-MS spectra to a lower extent than T. In the investigated conditions E had the weakest effects on the spectra.The correlations observed between the ionic intensities and these instrumental parameters were interpreted considering the presence of three kinds of perturbations occurring in the ESI-MS ion source: formation of some dimers in the droplets, different transfer efficiencies from the droplets to the gas phase for different complexes (according to their surface activity), and subsequent partial thermal decomposition of the dimers and of one of the monomeric complexes in the gas phase. Our results show that the evaluation of the effects produced in the ESI-MS spectra by a change of instrumental parameters can allow to identify the perturbations occurring when metal-ligand solutions are studied by ESI-MS.

A neutral lipophilic compound of aluminum(III) as a cause of myocardial infarct in the rabbit.

Intravenous administration of aluminum(III) in the form of the hydrolytically stable and moderately lipophilic complex acetylacetonate in the rabbit a severe pathological picture, the most significant feature of which is the occurrence of a myocardial infarct.

1,6-Dimethyl-4-hydroxy-3-pyridinecarboxylic acid and 4-hydroxy-2-methyl-3-pyridinecarboxylic acid as new possible chelating agents for iron and aluminium

1,6-Dimethyl-4-hydroxy-3-pyridinecarboxylic acid (DQ716) and 4-hydroxy-2-methyl-3-pyridinecarboxylic acid (DQ2) were evaluated for possible application to iron (Fe) and aluminium (Al) chelation therapy. Metal/ligand solution chemistry, electrochemistry, cytotoxicity, octanol/water partitioning (D(o/w)), and chelation efficiency, were studied. The Fe(iii)/DQ716, Fe(iii)/DQ2, Al(iii)/DQ716, and Al(iii)/DQ2 solution chemistry was investigated in aqueous 0.6 mol kg(-1) (Na)Cl at 25 degrees C by means of potentiometric titrations, UV-vis spectrophotometry, and (1)H-NMR spectroscopy. DQ716 exhibited the highest coordination efficiency towards Fe(iii) and Al(iii) among all hydroxypyridinecarboxylic acids examined so far, whereas DQ2 complexes were significantly less stable. These results were confirmed by chelation efficiency measurements performed in an octanol-aqueous solution in the presence of those ligands and metals. Partitioning experiments at pH 7.4 showed both DQ716 and DQ2, and their Fe(iii) and Al(iii) complexes, to be hydrophilic. According to the voltammetric data, the free ligands (DQ716 and DQ2) and their metal complexes are not predicted to undergo redox cycling at in vivo conditions. The standard reduction potentials of these complexes, and the kinetics of their formation and dissociation, were obtained. The toxicity of DQ716 and of DQ2 was investigated with human cancer cell lines and normal human fibroblasts. Cytotoxic effects were observed only for DQ2 at 0.1 mM, following 3 d exposure. According to our results, DQ716 has the required favourable properties to be a chelating agent for Fe and Al.