The equilibria of the ternary systems Cu(II)/ α-Alaha /Eu(III) or Gd(III) were studied in aqueous solution and the stability constants of two 15-MC-5, namely {Ln[Cu5L5H-5]}3+ and {Ln[Cu5L5H-5(OH)]}2+ , were determined. The Ln(III) distribution diagrams evidenced that the metallacrowns are the only species which contain the Ln3+ ions, suggesting that the metallamacrocyclic scaffold is obtained by direct self assembly of the ligand and the metal ions. Moreover, the speciation of these systems demonstrated the possibility for the 15-MC-5 and the 12-MC-4 complexes to coexist in solution as a function of the Ln:Cu:L molar ratios employed, and that the amount both types of MC complexes can be tuned with the pH. ESI-MS experiments performed as a function of pH and of various solvents allowed to find the most suitable conditions for the analysis of the MC in solution and to establish a possible correlation with the speciation diagrams. Finally, simulations based on the stability constants obtained for the 15-MC-5 complexes allowed us to critically re-evaluate on a quantitative ground a number of experimental observations concerning ligand- and metal-exchange processes for 15-MC-5 reported in the last decade. As a major point, it has been established that the Ln3+ metallacrowns are stable both with respect to competing ligands (either α-Alaha itself or EDTA and DOTA), and serum proteins like transferrin. Transmetallation processes involving Zn(II) to replace the encapsulated Ln3+ ions could be excluded, although the presence in solution of other components able to form very insoluble salts (such as phosphate) may affect the metallacrown integrity.
Thermodynamics of Self-assembly of Copper(II) 15-metallacrown-5 of Eu(III) and Gd(III) with (S)-α-Alaninehydroxamic Acid in Aqueous Solution
REMELLI, Maurizio;BACCO, Dimitri;
2010
Abstract
The equilibria of the ternary systems Cu(II)/ α-Alaha /Eu(III) or Gd(III) were studied in aqueous solution and the stability constants of two 15-MC-5, namely {Ln[Cu5L5H-5]}3+ and {Ln[Cu5L5H-5(OH)]}2+ , were determined. The Ln(III) distribution diagrams evidenced that the metallacrowns are the only species which contain the Ln3+ ions, suggesting that the metallamacrocyclic scaffold is obtained by direct self assembly of the ligand and the metal ions. Moreover, the speciation of these systems demonstrated the possibility for the 15-MC-5 and the 12-MC-4 complexes to coexist in solution as a function of the Ln:Cu:L molar ratios employed, and that the amount both types of MC complexes can be tuned with the pH. ESI-MS experiments performed as a function of pH and of various solvents allowed to find the most suitable conditions for the analysis of the MC in solution and to establish a possible correlation with the speciation diagrams. Finally, simulations based on the stability constants obtained for the 15-MC-5 complexes allowed us to critically re-evaluate on a quantitative ground a number of experimental observations concerning ligand- and metal-exchange processes for 15-MC-5 reported in the last decade. As a major point, it has been established that the Ln3+ metallacrowns are stable both with respect to competing ligands (either α-Alaha itself or EDTA and DOTA), and serum proteins like transferrin. Transmetallation processes involving Zn(II) to replace the encapsulated Ln3+ ions could be excluded, although the presence in solution of other components able to form very insoluble salts (such as phosphate) may affect the metallacrown integrity.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
