Synthesis and characterization of a macrocycle containing different functional groups and its non-cyclic counterpart

The macrocycle 9-methyl-3,6,9,12,15,22,31-heptaaza-25,28,38,41-tetraoxa-hex acyclo [31.2.2.(3.6)2.(17.20)8(22.31)]-heptatetraconta-1,17,18,20,33,34-hex aene (L1) containing different functional groups and its non-cyclic counter part bis-[piperazinyl-4-(4-carboxybenzyl)ethyl)]methylamine CL) were synthe sized. The protonation behavior of both compounds, i.e. their basicity cons tants and protonation sequence, was investigated both by potentiometry (25 degreesC, I = 0.15 mol dm(-3), NaCl) and H-1, C-13 NMR spectroscopy. The re sults obtained were log K-1 = 8.48(1), 8.73(1); log K-2 = 7.25(1), 8.20(1); log K-3 = 6.66(1), 6.93(1); log K-4 = 4.01(1), 6.29(1); log K-5 = 3.28, 5. 49(1); log K-6 = 1.7(1) for L and L1, respectively. The complex formation e quilibria between L and El with metal ions such as Ga(III), Co(II), Cu(II), Zn(II) and Cd(II) were investigated by potentiometry using the same experi mental conditions, revealing only mononuclear complexes as well as the pres ence of many protonated species. L forms a less charged and more stable com plex with Ga(III) than does L1. Log K = 15.5(1) for [GaL](+) and 13.8(1) fo r [GaL1](3+), respectively. (C) 2001 Elsevier Science B.V. All rights reser ved.