INTERACTION OF HEXAAZAALKANES WITH PHOSPHATE TYPE ANIONS - THERMODYNAMIC, KINETIC, AND ELECTROCHEMICAL CONSIDERATIONS

The interaction of adenosine 5'-triphosphate, pyrophosphate, and hexacyanoferrate(II) anions with the cyclic polyamines 1,4,7,10,13,16-hexaazacyclooctadecane ([18]aneN6) and 1,4,7,13-tetramethyl-1,4,7,10,13,16-hexaazacyclooctadecane (Me4[18]aneN6) and with the open-chain polyamine 1,14-bis(methylamino)-3,6,9,12-tetraazatetradecane (Me2pentaen) has been studied in the pH range 3-10 by potentiometry and cyclic voltammetry at 298.1 K in 0.15 mol dm-3 NaClO4 as well as by P-31 NMR spectroscopy. Me4[18]aneN6 in its protonated forms is the receptor displaying the largest stepwise stability constants for the addition of any one of the three fully deprotonated substrates. Despite this fact, ternary distribution diagrams, P-31 NMR, and competitive cyclic voltammetry with [Fe(CN)6]4- show that Me2pentaen is the best receptor for the considered substrates. Relative selectivities of the three receptors are determined using potentiometric and elecrochemical methods. The kinetics of ATP hydrolysis induced by the three receptors have been followed by monitoring the loss of ATP by P-31 NMR spectroscopy. Me4[18]aneN6 is the receptor inducing at pH 3 the largest rate accelerations. The activation energies for the three processes have been determined. Considerations regarding the nucleophilicity and topologies of the receptors are invoked to explain the observed trend.