New Tetraaza Macrobicyclic Ditopic Receptors for Metal Ions: Synthesis, Redox Response and Kinetics of Phosphate Hydrolysis of Unsymmetrical Macrobicyclic Mono- and Binuclear Nickel(II) Complexes

Abstract

A new series of macrobicyclic ditopic receptors is derived from the precursor compound 3,4:10,11-dibenzo-1,13[N,N 0 -bis{(3-formyl-2-hydroxy-5-methyl)-benzyl}di-aza]-5,9-dioxocyclohexadecane. Using this precursor, mono-and binuclear nickel(II) complexes of type [NiL](ClO 4 ) and [Ni 2 L](ClO 4 ) 2 have been synthesized to undertake electrochemical and catalytic studies on the basis of macrocyclic ring size. The receptor is a tricompartmental macrocycle consisting of ether oxygen, tertiary nitrogen and imine nitrogen atoms. The redox studies of these systems show that the nickel(II) complexes undergo quasi-reversible oneelectron reduction and oxidation. All the nickel(II) complexes have square planar geometry and are EPR silent. Examination of the kinetics of the hydrolysis of 4-nitrophenyl phosphate shows that the catalytic activities of the complexes increase with the macrocyclic ring size of the complexes. As the macrocyclic ring size of the complexes increases, the spectral, electrochemical and catalytic studies of the complexes show considerable variation due to distortion in the geometry around the nickel(II) centre.

Electrochemical, phosphate hydrolysis, DNA binding and DNA cleavage properties of new polyaza macrobicyclic dinickel(ii) complexes

“…This strongly suggests that the coordination geometry around the metal ion in the heterocyclic base free (1 and 4) and heterocyclic base coordinated complexes (2, 3, 5 and 6) might be distorted square planar and distorted octahedral, respectively. 9,12 Interestingly, the absorption maxima (l max ) of complexes 4-6 are higher than those of complexes 1-3. This indicates that the coordination geometry around the Ni II ions is more distorted 13 in the N-methylated polyaza macrobicyclic ligand (L 2 ) than the N-methyl free polyaza macrobicyclic ligand (L 1 ).…”

Structural, magnetic, electrochemical, catalytic, DNA binding and cleavage studies of new macrocyclic binuclear copper(II) complexes

“…For the complex 2b the Cu-O ph -Cu bridge angle is 102.2 (11)°and the observed exchange interaction value was (À2J) 125.5 cm À1 . The possible reason for this low exchange interaction values of unsymmetrical binuclear Cu(II) complexes may be due to the ligand induced two different geometries around the two copper atoms within the molecule [43], deviation from coplanarity [36] with a dihedral angle of 11.7 (9)°and outof-plane displacement (s = 7.64°) of the phenyl ring from the oxygen atom within the Cu 2 O 2 core.…”

“…The same trends were observed for the complexes of ligands 2d-e, which contain aromatic diimines. From the electrochemical studies it can be stated that the complexes containing aromatic diimines get reduced at higher negative potential than that of the complexes containing aliphatic diimine, the higher reduction potential can be attributed due to the greater planarity and electronic properties those are associated with aromatic rings [36].…”

Probing the role of the divalent metal ion in uteroferrin using metal ion replacement and a comparison to isostructural biomimetics

“…Both sets of data show a linear pH dependence of the redox potentials; while the pH dependence of the redox potentials of the derivative is similar to that observed for the native enzyme, the potentials are shifted to approximately 180 mV higher values. Since this potential is thus not likely to be due to the chromophoric Fe(III)/ Fe(II) couple, and since the M(II) site does not have strong electron donors to stabilize Ni(III) [41], it is hypothesized that the observed potential in the derivative is associated with the oxidation of the tyrosinate ligand involved in the formation of the ligand to metal charge transfer (LMCT) complex (Tyr55; Fig. 1).…”