Di-maltol-polyamine ligands to form heterotrinuclear metal complexes: solid state, aqueous solution and magnetic characterization

The binding properties of the two ligands (L) N,N'-bis[(3-hydroxy-4-pyron-2-yl)methyl]-N,N'-dimethylethylendiamine (Malten) and 4,10-bis[(3-hydroxy-4-pyron-2-yl)methyl]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane (Maltonis) towards M(II) transition metal ions (M(II) = Cu(II) for Malten and Co(II) for Maltonis, respectively), were investigated in aqueous solution. Each compound contains two 3-hydroxy-2-methyl-4-pyrone units (Maltol) symmetrically spaced by a different polyamine fragment. The formation of only mononuclear complexes was detected and the main species present in a wide range of pH is the neutral [M(II)(H-2L)] complex. This is able to stabilize one hard M(III) metal ion such as Gd(III) and Y(III), giving rise to the formation of new hetero-trinuclear complexes of M(II)-M(III)-M(II) sequence. The trinuclear species having the formula {M(III)[M(II)(H-2L)]2}(3+) (M(II) = Cu(II) and M(III) = Y(III) or Gd(III) for Malten and M(II) = Co(II) and M(III) = Gd(III) for Maltonis) are also formed in a wide range of pH, including pH = 7 and can be isolated in high yield as a perchlorate salt. The crystal structures of all the studied hetero-trinuclear species highlight that such systems are formed thanks to the synergy between the different stereochemical requirement of the transition metal (Cu(II) or Co(II)) and the different donor atoms set of the ligands which preorganize the maltol units for the binding of the hard M(III) metal, otherwise difficult to bind in water, through L/M(II)/M(III) self-assembling. The magnetic properties of the hetero-trinuclear spin systems were investigated; in the M(II)-Gd(III)-M(II) species, Gd(III) interacts with the two 3d ions of this class of compounds by similar coupling mechanism.

Thermodynamics of simple and mixed complexes of copper(II) with adenosine 5'-monophosphate and spermine

Thermodynamic parameters pertinent to the equilibria of ternary system copper(II), adenosine 5'-monophosphate (AMP), and 4,9-diazadodecane-1,12-diamine (Spermine, Spe) were determined by means of potentiometric and calorimetric techniques, together with the corresponding parent binary complex parameters. This system could be considered as a model in the study of more complicated biological systems. In particular, it could give useful evidence in the investigation of the interaction between tetramine and DNA. The experimental results seem to suggest that the major contribution in DNA stabilization by means of tetramines is due to the electrostatic interactions occurring between the protonated nitrogen atoms of the amine molecules and the phosphate groups of nucleotides in the nucleic chains.