Biomimetic Cu, Zn and Cu2 complexes inserted in mesoporous silica as catalysts for superoxide dismutation.

Abstract Three CuZn-superoxide dismutase (SOD) functional mimics, [CuZn(dien) 2 (μ-Im)](ClO 4) 3 (1), [Cu 2 (dien) 2 (μ-Im)](ClO 4) 3 (2) (Im = imidazole, dien = diethylenetriamine), and [CuZn(salpn)Cl 2 ] (3) (H 2 salpn = 1,3-bis(salicylideneamino)propane), were successfully inserted into the nanochannels of SBA-15 type mesoporous silica with retention of the silica mesostructure. X-ray absorption spectroscopic studies indicate that the encapsulated complexes keep unchanged the first-shell environment of Cu(II) and Zn(II) ions. Magnetic measurements suggest that the nanochannels constrain the geometry of the μ -imidazolate-Cu(II) 2 core modifying the relative orientation of the two copper coordination planes. Confinement imposed by the silica nanochannels upon encapsulation of complexes 1 and 2 leads to stable hybrid materials at physiological pH with enhanced SOD activity relative to the free complexes. Unlike the imidazolato-bridged compounds, insertion of 3 in mesoporous silica leads to a less stable hybrid material exhibiting partial release into the aqueous solution and O 2 •− dismutation rate slower than the free complex. The covalent binding of a mononuclear Cu(dien)Im+ moiety to the mesoporous silica showed lower SOD activity than encapsulated imidazolato-bridged CuZn and Cu 2 complexes. The results emphasize the positive effect of encapsulation on SOD activity of imidazolato-bridged dinuclear complexes. Graphical abstract Image 1 Highlights • Biomimetic hybrid materials as potential therapeutic agents against oxidative stress. • Confinement enhances SOD activity of imidazolato-bridged CuZn and Cu 2 catalysts. • Stable catalytic systems with no significant metal leaching at physiological pH. • Encapsulation keeps the silica mesostructure and catalyst integrity. [ABSTRACT FROM AUTHOR]