Tailoring the local environment around metal ions: a solution chemical and structural study of some multidentate tripodal ligands.

Manganese(ii), copper(ii) and zinc(ii) complexes of four polydentate tripodal ligands (tachpyr (N,N',N''-tris(2-pyridylmethyl)-cis,cis-1,3,5-triaminocyclohexane), trenpyr (tris[2-(2-pyridylmethyl)aminoethyl]amine, tach3pyr (N,N',N''-tris(3-pyridylmethyl)-cis,cis-1,3,5-triaminocyclohexane) and tren3pyr (tris[2-(2-pyridylmethyl)aminoethyl]amine)) were characterized in both solution and solid states. A combined evaluation of potentiometric, UV-VIS, NMR and EPR data allowed the conclusion of both thermodynamic and structural information about the complexes formed in solution. The four tailored polydentate tripodal ligands studied here exhibit a high thermodynamic stability, and a variety of coordination environments/geometries for the studied transition metal ions.

A novel 1,3,5-triaminocyclohexane-based tripodal ligand forms a unique tetra(pyrazolate)-bridged tricopper(ii) core: solution equilibrium, structure and catecholase activity.

Copper(ii) complexes of a polydentate tripodal ligand L × 3HCl (L = N,N',N''-tris(5-pyrazolylmethyl)-cis,cis-1,3,5-triaminocyclohexane) were characterized in both solution and solid states. Combined evaluation of potentiometric, UV-VIS, and EPR data indicated the formation of two mononuclear (CuHL, CuL) and three trinuclear (Cu3H-xL2, x = 2, 3, 4) complexes. The high stability and spectroscopic properties of the CuL species indicate a coordination of two pyrazole rings in addition to the three secondary amino groups of L in a square pyramidal geometry.

On the possible roles of N-terminal His-rich domains of Cu,Zn SODs of some Gram-negative bacteria.

The Cu,Zn superoxide dismutases (Cu,Zn SOD) isolated from some Gram-negative bacteria possess a His-rich N-terminal metal binding extension. The N-terminal domain of Haemophilus ducreyi Cu,Zn SOD has been previously proposed to play a copper(II)-, and may be a zinc(II)-chaperoning role under metal ion starvation, and to behave as a temporary (low activity) superoxide dismutating center if copper(II) is available. The N-terminal extension of Cu,Zn SOD from Actinobacillus pleuropneumoniae starts with an analogous sequence (HxDHxH), but contains considerably fewer metal binding sites.