Quantitative study on the interaction between ATP and aromatic amines in aqueous solution

The interaction between adenosine-5’-triphosphate (ATP) and some aromatic amines (L), namely 1,2-phenylenediamine, 2-(2,4-diaminophenoxy)ethanol, 4-N-(2-hydroxyethyl)2,4-diaminoanisole, 4,5-diamino-1-N-(2-hydroxyethyl)pyrazole and 1,3-bis(2,4-diaminophenoxy) propane, was studied at T = 298.15 K and I = 0.06 mol L-1 in NaCl aqueous solution. For all the investigated systems, the formation of [(ATP)(L)Hi](i-4) species (i = 1 to n+2; n = maximum protonation degree of amine), with high yields (60-80%) was found. The dependence on ionic strength and on temperature of the complex formation constants was studied using semiempirical equations. The sequestering ability of the aromatic amines toward ATP was defined by calculating the pL50 parameter (the total ligand concentration, as –log CL, able to bind 50% of ATP). The dependence of pL50 on pH, ionic strength and temperature is reported. Moreover, it was found that the overall formation constants are fairly linearly dependent on the number of protons in the complex species. Comparison with the stability of the species of analogous systems, such as ATP – aliphatic amines and pyrophosphate-aliphatic amines, is reported. For all these systems a fairly linear dependence of formation constants on the basicity of amines was found.