Stoichiometry and equilibrium constant of the complex of PAMAM-NH2 G4 and 5-fluorouracil

Polyamidoamine dendrimer (PAMAM-NH2 G4) complex with 5-fluorouracil, an oncological drug, was investigated by the technique of equilibrium dialysis at temperatures of 20 degrees C and 45 degrees C. The results obtained were worked out by means of the modified model of two sets of active sites proposed by Bobrovnik. Based on the analysis of the results obtained, it was calculated that at a temperature of 20 degrees C the dendrimer molecule can bind about 12 molecules of the ligand with equilibrium constant K-1 congruent to 55600 and about 37 molecules with equilibrium constant K-2 congruent to 150. At a temperature of 45 degrees C the number of the dendrimer binding sites is similar but the equilibrium constants of binding 5-fluorouracil with both sets of active sites are clearly lower (K-1 congruent to 1820, K-2 congruent to 70). The saturation of both the sets of active sites is of an exothermic character. (C) 2012 Elsevier B.V. All rights reserved.