Speciation 98: Abstracts

Hydroxyalkylodiphosphonic and alkylodiphosphonic acids are used in medicine as drugs against Paget disease, tumour osteolysis, and osteoporosis, in radiodiagnosis as ligands for ^99mTc, as potentially strong chelating agents in metal extraction and as novel antidepressants.

Vanadium is abundant in living systems, although its role is not well understood. Small amounts of vanadium are necessary for the development cells, plants and animals. In a human body vanadium exists in two major oxidation states: V(V) and V(IV) (inside cells).

We report hereby a spectroscopic (EPR and UV-Vis) and potentiometric study of oxovanadium(IV) complexes with four 1-hydroxyalkane-1,1-diyldiphosphonic acids (Fig. 1).

Co-ordination of oxovandium(IV) starts at a very low pH. Stable monomeric (VOHL or VOL for H₃L³) and trinuclear species ((VO)₃L₃ or (VO)₃H_-3L₃ for H₃L³) are present between pH range 2-9 (Fig. 2). Even though all ligands studied showed similar co-ordination abilities towards VO(IV) ions, we observed small, but distinct, steric effects of alkyl side-chains.

Figure 1.

Figure 2. Species distribution curves for the VO²⁺ - H₄L¹ system; metal concentration 1 mmol dm^-3, ligand concentration 2 mmol dm^-3

Back to the list of abstracts