Speciation 98: Abstracts

Aluminium is considered to be a toxic element, its effects ranging from environmental damage to human pathologies like dialitic dementia, iron-adequate microcytic anaemia, osteomalacia and possibly Alzheimer desease. Aluminium chelating agents may be used to selectively remove the metal from the body and therefore to reduce its toxicity; the most widely used agent is Desferal, which however has several toxic side effects and a number of drawbacks, especially its orally ineffectiveness and high cost [1]; for this reason, in the last years several possible aluminium chelators have been tested in vitro and in vivo for the replacement of Desferal [2, 3]. Suitable molecules are usually chosen on a chemical basis, i.e. according to their capability to form very stable complexes with the metal, and are subsequently tested to determine their pharmacological and toxicological properties.

The present study involves the determination of stoichiometry and stability constants of the aluminium complexes of two derivatives of pyridine, 2-hydroxynicotinic and 3-hydroxypicolinic acid (H₂L), the structure of which suggests a good ligating capability towards the metal; they have known pharmaceutical properties, and a class of their derivatives are used as active principles in antibacterial drugs [4,5].

The study was conducted at 25^oC and in aqueous (Na)Cl 0.6 m; most of results were obtained from potentiometric titrations. In both cases the most important species present are AlLH, AlL₂H₂ and AlL₃H₃; several deprotonation products were also detected, namely AlL, AlL₂H, AlL₃H₂; for hydroxypicolinic acid AlL₂, AlL₃H and AlL₃ were found in addition. Qualitative and quantitative results have been confirmed in part by two independent techniques, UV spectrophotometry and ¹H NMR spectroscopy.

The affinity of the two ligands towards aluminium is remarkable high and therefore they can be proposed as candidates for pharmacological experimentations.

References

1. Kontoghiorghes G.J., Toxic. letters 1995, 80, 1
2. Graff L., Muller G., Burnel D., Vet. Human Toxic. 1995, 37, 455
3. Yokel R.A., Datta A.K., Jackson E.G., J. Pharm. Exp. Therap. 1991, 257, 100
4. Gleckman R., Alvares S., Joubert D.W., Matthews S.J., Am. J. Hosp. Pharm. 1979, 36, 1071
5. Spear K., Johnson C., Gschwend H.W., PCT Int. Appl. WO 94 20, 527, 1993

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