ИСТИНА

Polyaminopolycarboxylates are attractive ligands for cationic radionuclides for preparation of radiopharmaceuticals with target delivery to tumor cells. Nowadays beta emitting Y-90 and Lu-177 are used as therapeutic agents, Ac-225/ Bi-213 and Pb-212/Bi- 212 are considered as perspective for alpha and beta therapy. In the present work new data on complexation of azacrown moieties with several tri- and divalent cations are presented. For ligands’ and complexes’ characterization potentiometric titration, solvent extraction, column chromatography and solubility technique were used. Treatment of potentiometric titration data was carried out by HYPERQUAD software. Azacrown ethers under consideration possess different acidity that affects by macrocyclic ring size and addition of carboxylic arms or pyridine fragments. It was found that noticeable binding of such hard cations like Ac3+, Y3+ and Lu3+ could be achieved by ligands with carboxylic pendant arms (L1b and L3), while Cu2+ and Pb2+ are effectively complexed just by macrocyclic cavity of L1a and L2. The highest values of stability constants were determined for Bi3+ (table). It is bound quantitatively even at pH 3 and variation of pH leads to monotonous change in apparent stability constants that could be associated with formation of two types of complexes: BiL+ and BiLOH. Bi3+ as extremely hydrolysable cation possesses affinity to different ligands as OH- and different polyaminopolycarboxylates, so constants of respective complexes are usually higher than analogous complexes with trivalent REE. Presence of pyridine and two nitrogens in macrocyclic cavity of L1a provides the same stability for complex as two carboxylic arms in L3. This means that even without carboxylates strong watersoluble complexes with Bi3+ could be formed. Further attempts to strengthen complex by addition of pyridine groups (L1c) or macrocyclic nitrogen (L2) lead to weakening of complex by 3 and 1,5 orders, respectively. Even carboxylic arms in L1b did not effectively increase the binding. Table. Logarithms of apparent stability constants of complexes in the system Bi-L-OH under pH6,5 L1 L2 L3 a) X=H b) X=CH2COOH c) X=CH2Py 19.6(3) 20.4(3) 16.7(3) 18.2(2) 19.6(3) The work was supported by RFBR project 13-03-01304