New class of tridentate 3N ligands and copper(II) complexes: A model for type-2 copper site of phenoxazinone synthase

Abstract

A new series of copper(II) complexes [Cu(L)Cl2] 1–5, where L is dimethyl-(2-{[(pyridin-2-ylmethyl)-amino]-methyl}-phenyl)-amine (L1); dimethyl-{2-[(2-pyridin-2-yl-ethylamino)-methyl]-phenyl}-amine (L2); 2-((3-(dimethylamino) propylamino)-methyl)-N,N-dimethylbenzenamine (L3); 2-((2-(dimethylamino) ethylamino) methyl)-N,N-dimethylbenzenamine (L4) and (2-{[(1H-benzimidazole-2-ylmethyl)-amino]-methyl}-phenyl)-dimethylamine (L5) have been synthesized and characterized as the model for type 2 copper site in phenoxazinone synthases. The molecular structure of 1 exhibits nearly a perfect square pyramidal geometry (τ, 0.01). The complexes showed Cu(II)/Cu(I) redox potentials around −0.128 to −0.215 V in water. The electronic spectra of 1–5 exhibited d-d transitions around 620–643 nm in water. All the complexes exhibit almost similar electron paramagnetic resonance (EPR) parameter (g||, 2.21–2.27; A||, 161–175 × 10−4 cm−1) corresponds to square-based geometry. The complexes have catalyzed the conversion of substrate 2-aminophenol into 2-aminophenoxazine-3-one using molecular oxygen. The formation was accomplished by appearance of a new absorption band at 433 nm with the reaction rate of 6.14–9.89 × 10−3 s−1 in water.