Interactions of Aluminum(III) with Phosphates

Abstract

In order to obtain information about aluminum(III)-phosphate interactions, potentiometric measurements were carried out to characterize the complex forming properties of Al(III) with organic phosphates, phosphonates, and nucleoside-5'-monophosphates. The aluminum(III)-orthophosphate system is difficult to study due to AlPO(4) precipitation. To overcome this problem, the stability constant logarithms of the 1:1 Al(III) complexes of ligands with the same donor groups (log K(1:1)) were plotted against the basicities of the ligands (log K(PO)3(H)). The resulting linear free energy relation (LFER) indicates that organic phosphates, phosphonates, and uridine-, thymidine-, and guanosine 5'-monophosphates similarly bind Al(III). Adenosine and cytidine 5'-monophosphate fall above the LFER owing to the presence of a second microform with the nucleic base protonated and a hydroxide bound to the Al(III). From the LFER the log stability constant for Al(III) binding to HPO(4)(2-) is estimated as 6.13 +/- 0.05. From the weakness of any soluble orthophosphate complexes of Al(III) we confirm the importance of citrate as the main small molecule Al(3+) binder in the blood serum. The study includes investigation of Al(III) binding to di- and triphosphates, which bind metal ion differently than monophosphates. Structures of the complexes were supported by (31)P NMR measurements.

NMR Spectra and Potentiometry Studies of Aluminum(III) Binding with Coenzyme NAD+ in Acidic Aqueous Solutions

“…These results are also in agreement with those of similar complexes, 8,11,12,17 and the situation generally observed for the octahedral complexes of Al, the chemical shifts of which mainly depend on the number of ligands around the cation. 19 Furthermore, the following potentiometry of the Al-NAD + system also substantiates these assignments.…”

“…7 It is well known that Al has a great affinity to phosphate oxygen. The interactions of Al with inorganic phosphate, 8 organophosphates (AMP, ADP, ATP), 9,16 phosphorylated amino acids 10 and gluose-6-phosphate 11 have been well investigated. In the past, the crystalline state of an extended conformation of NAD + was found with Li(I) coordinated to pyrophosphate oxygen and adenine N7′.…”

Solution equilibrium characterization of insulin-mimetic Zn(II) complexes

“…For the tris complex (not shown) no clear relationship could be obtained, probably because of the higher uncertainty in the log K 3 values and the disturbing hydrolytic processes of the Zn(II) complexes. Similar dependence on the charge of the reacting species was found for the LFER of the phosphate complexes [26].…”

Demonstration of the Importance of Metal Ion Speciation in Bioactive Systems

“…Our earlier results 35 have led us to conclude that both the phosphato and citrato complexes of Al ), under model conditions, in the millimolar concentration range, precipitation occurs at pH >3:5, and one is forced to extrapolate from these data to physiological conditions, which are far from the model conditions. 37 Further, there are rather slow oligomerization reactions in the case of Al III -citrate (A 3À ), which are strongly concentration dependent. As first reported by Ö hman and Sjöberg 38 and Ö hman, 39 at mM model concentrations, a trinuclear species [Al 3 …”