Spectroscopic and calorimetric studies of formation of the supramolecular complexes of PAMAM G5-NH2 and G5-OH dendrimers with 5-fluorouracil in aqueous solution

The results of spectroscopic measurements (increase in solubility, equilibrium dialysis, H-1 NMR titration) and calorimetric measurements (isothermal titration ITC) indicate exothermic (Delta H < 0) and spontaneous (Delta G < 0) combination of an antitumor drug, 5-fluorouracil, by both cationic PAMAM G5-NH2 dendrimer and its hydroxyl analog PAMAM G5-OH in aqueous solutions at room temperature. PAMAM G5-NH2 dendrimer combines about 70 molecules of the drug with equilibrium constant K congruent to 300, which is accompanied by an increase in the system order (Delta S < 0). Hydroxyl dendrimer, PAMAM G5-OH, combines about 14 molecules of 5-fluorouracil with equilibrium constant K congruent to 100. This process is accompanied by an increase in the system disorder (Delta S > 0). (C) 2015 Elsevier B.V. All rights reserved.