Az aluminum(III)-ion kolcsonhatasa biologiailag fontos foszfatokkalInteraction of aluminium(III) with biologically important phosphates

In order to obtain information about the Al(III)-phosphate interaction, pH-metric measurements were carried out to assess the complex-forming properties of aluminium(III) with organic phosphates and phosphonates. Special attention was paid to nucleoside 5'-monophosphates. The Al(III)-orthophosphate system is difficult to characterize due to AlPO4 precipitation. To overcome this problem that makes data available in the literature ambiguous, the logarithms of the stability constants of the 1:1 Al(III) complexes of ligands with the same donor groups (lg K-1:1) were plotted against the basicities of the ligands (lg K-PO3H-) The fact that a straight line was obtained indicates that 1:1 complexes of the same bonding mode are formed with organic phosphates, phosphonates and nucleoside 5'-monophosphates. The difference between phosphate and phosphonate groups does not affect the interaction. The corresponding complex of cytidine 5'-monophosphate proved to be of relatively great stability, however, it is only the apparent result of two simultaneous processes. In the case of adenosine 5'-monophosphate, the stability of the 1:1 complex is too great to be accounted for by merely the Al(III)-phosphate interaction. The increase in stability is possibly caused by coordination of the N7 atom and by stacking interaction. The formation constant for the AlHPO4+ species was determined by using the parameters of the log K-PO3H- -log K-1:1 line. Direct pH-metric titrations were performed in order to characterize the stoichiometries and stabilities of the other complexes formed in the Al(III)-orthophosphate system, too. It was established that the Al(III) complexes formed with pyrophosphate and triphosphate are of the same type whereas those of orthophosphate have different structures. The results of pH-metric studies were supported by P-31 NMR measurements.