Speciation 98: Abstracts

Aluminium(III) Speciation in Blood Plasma. Study of Al(III)-Citrate-Phosphate Ternary System

Andrea Lakatos1 Tamás Kiss1, István Bányai2

1 Department of Inorganic and Analytical Chemistry, Jozsef Attila University, P.O.Box 440, H-6701 Szeged, Hungary;
2 Department of Inorganic and Analytical Chemistry, Kossuth University, P.O.Box 21, H-4010 Debrecen, Hungary

Al(III) absorbed in the human body is transported via the blood stream to the different organs. Accordingly, the speciation of Al(III) in blood plasma is an essential question regarding bioavailability of Al(III) for different tissues.. It is agreed that ~80% of plasma Al(III) is bound to transferrin, which is the most significant Al(III) binder. The remaining 20% is carried by low molecular mass biomolecules. The results obtained in different laboratories as concerns the most important low molecular mass Al(III) binders are rather contradictory [1]. Some authors suggest citrate, others propose inorganic phosphate as the main Al(III) binder.

As these two bioligands are simultaneously present in the serum, formation of ternary complexes may be of much greater importance than that of simple binary species.

In the paper our results on time-dependent speciation of the Al(III)-citrate(A)-phosphate(B) ternary system will be presented. Time dependence can give more accurate description of Al(III) speciation since Al(III) is susceptible for very slow complex formation especially if oligomeric species are involved and hence, complexation may not attain the thermodynamic equilibrium in biological fluids.

The potentiometric and parallel 31P NMR results indicate that both at mixing and in equilibrium the ternary complexes predominate. At physiological pH two ternary complexes, AlAB and AlABH-1, and two binary species, AlBH-1 and AlAH-2, are present. Beside the intensive sharp signal of the free ligand 31P NMR shows two broad signals, which may belong to the ternary species and AlBH-1, respectively.

The time-dependent 1H NMR measurements show that phosphate can slowly decompose the very stable structure of the trinuclear species Al3(AH-1)3(OH). This demonstrates the important role of phosphate in Al(III)-binding.

The speciation curves at mol Al(III) concentration (plasma conditions) show that in such diluted solutions the mononuclear species predominate, oligomerization processes are completely suppressed. Intererstingly enough, our results suggest that at neutral pH Al(III) is mostly bound to phosphate.

Acknowledgement. The authors (TK and AL) are thankful to the National Science Research Fund for financial support (Project No. OTKA T23776).

Reference

  1. W.R. Harris, G.Berthon, J.P. Day, C.Exley, T.P. Flaten, W.F.Forbes, T. Kiss, C.Orvig, P.F. Zatta, J. Toxicol. Environ. Health, 48, 543 (1996).

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