EFFECT OF NITROGEN METHYLATION ON CATION AND ANION COORDINATION BY HEXAAZAMACROCYCLES AND HEPTAAZAMACROCYCLES - CATALYTIC PROPERTIES OF THESE LIGANDS IN ATP DEPHOSPHORYLATION

The stability constants of the complexes formed by ,10-dimethyl-1,4,7, 10,13,16-hexaazacyclooctadecane (L) and rimethyl-1,4,7,10,13,16,19-hep taazacyclohenicosane (L1) with Ni2+, Cu2+, Zn2+, Cd2+ and Pb2+, as wel l as that for the formation of PbL(2+)?+ (L2 = etramethyl-1,4,7,10,13, 16-hexaazacyclooctadecane), were determined by means of potentiometric (pH-metric) titrations in 0.15 mol dm(-3) NaClO4 at 298.1 +/- 0.1 K. The enthalpy changes for the formation of Cu2+ complexes with L and L1 were measured by means of microcalorimetry. These thermodynamic data were compared with those previously reported for L2, 1,4,7,10,13,16-he xaazacyclooctadecane (L3), and 1,4,7,10,13,16,19-heptaazacyclohenicosa ne (L4) evidencing that nitrogen methylation can produce lower or high er complex stability depending on the metal ion and the number of meth ylated nitrogens. The equilibria of complexation of ATP(4-), ADP(3-), AMP(2-), P2O74-, and [Co(CN)(6)](3-) by L and L1 were studied by means of pH-metric titrations in 0.15 mol dm(-3) NaClO4 at 298.1 +/- 0.1 K. The catalytic reactions of ATP dephosphorylation induced by these lig ands in solution were followed by P-31 NMR spectroscopy at different t emperature and pH values. L is the most appropriate receptor, among L- L4, in the recognition of the nucleotide. The catalytic efficiency of hexa- and heptaazaligands increases in the order L < L3 < L2 and L1 < L4, respectively, L4 being the most efficient. Namely, di- and tetrame thylation of L3 produces opposite effects on its catalytic properties.