The dinuclear copper(II) complex of the hexaaza macrocyclic ligand 3,6,9,17,20,23-hexaaza-tricyclo[23.3.1.111,15]triaconta-1(29), 11(30),12,14,25,27-hexaene as a host for alanine, valine, leucine, norleucine, norvaline and serine anions

The hexaaza macrocyclic ligand 3,6,9,17,20,23-hexaazatricyclo[23.3.1.1(11,15)]triaconta-1(29),11(30),12,14,25,27-hexaene (L), which forms strong dinuclear Cu(II) complexes, can act as a host for several anionic guests. The guests under investigation are the amino acids alanine, valine, leucine, norleucine, norvaline and serine. The host-guest interactions were investigated by conventional potentiometric pH-metry, by spectrophotometric titrations in 2:1:1 molar ratio for Cu(II), L and guest and by IR spectroscopy. In aqueous solution three ternary species are formed as a result of coordinate bonding, Coulombic attraction and hydrogen bond formation between the host aid guest. The stability constants as well as the calculated equilibrium constants for the species are reported. It was found that the norleucine anion has the largest affinity for the dinuclear Cu(II) complex. The large inductive effect and the linear structure of its side chain;is suggested to be responsible. (C) 1999 Elsevier Science Ltd. All rights reserved.