The macrocycle 9-methyl-3,6,9,12,15,22,31-heptaaza-25,28,38,41-tetraoxa-hexacyclo [31.2.2.(3.6)2.(17.20)8(22.31)]-heptatetraconta-1,17,18,20,33,34-hexaene (L1) containing different functional groups and its non-cyclic counterpart bis-[piperazinyl-4-(4-carboxybenzyl)ethyl)]methylamine CL) were synthesized. The protonation behavior of both compounds, i.e. their basicity constants 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 results 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 equilibria 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 experimental conditions, revealing only mononuclear complexes as well as the presence of many protonated species. L forms a less charged and more stable complex with Ga(III) than does L1. Log K = 15.5(1) for [GaL](+) and 13.8(1) for [GaL1](3+), respectively. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 21]
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