Methylation as an effective way to generate SOD-activity in copper complexes of scorpiand-like azamacrocyclic receptors

Stabilization of polyiodide networks with Cu(ii) complexes of small methylated polyazacyclophanes: shifting directional control from H-bonds to I⋯I interactions

Modulation of hydrogen bonds and iodine–iodine interactions, both covalent and supramolecular, unlocks novel possibilities for the construction of transition metal-polyiodide hybrid networks.

Coordination Chemistry of Cu2+ Complexes of Small N-Alkylated Tetra-azacyclophanes with SOD Activity

A new tetraaza-pyridinophane macrocycle (L1) N-alkylated with two isopropyl and one methyl groups symmetrically disposed has been prepared and its behavior compared with those of the unsubstituted pyridinophane (L3) and the related compound with three methyl groups (L2). The protonation studies show that, first, a proton binds to the central methylated amine group of L1, while, second protonation leads to a reorganization of the protons that are at this stage attached to the lateral isopropylated amines. The X-ray structure of [HL1]⁺ agrees with the UV-vis and NMR studies as well as with the results of DFT calculations. The stability of the Cu²⁺ complexes decreases on increasing the bulkiness of the alkyl substituents of the amine groups. The crystal structures of [CuL1Cl](ClO₄) and [CuL1(H₂O)](ClO₄)₂·H₂O show square pyramidal coordination geometries with the ligands disposed in a bent L-shaped conformation. Kinetic studies indicate that the rates of both complexation and ligand dissociation decrease with the bulkiness of the substituents, so that the stability changes are surely the results of compensating effects, complex formation dominating over complex dissociation. The pH dependence of the rate constants for complex formation cannot be explained by consideration of rapid pre-equilibria involving the different protonated forms of the ligand, and it has been interpreted in terms of a mechanism involving an acid-base equilibrium for a reaction intermediate. NBT SOD studies show that the Cu²⁺ complex of the bulkiest L1 ligand is the one having the highest activity (IC₅₀ = 0.26(5) μM, k_cat = 13.7 × 10⁶ M^-1 s^-1) which can be associated with the poorer σ-donor ability of the tertiary amino groups, and the rigidity of the system, caused by the bulky isopropyl groups.

Enhancement of SOD activity in boehmite supported nanoreceptors

Binuclear Cu²⁺ complexes of a pyridinophane polyamine ligand grafted to boehmite nanoparticles display a remarkable SOD activity enhancement.