Phenoxyl Radical Complexes of Zinc(II)

Abstract

A series of phenoxyl radical complexes of zinc(II) have been generated in solution and, in one instance, isolated as solid material (5) in order to study their spectroscopic features by EPR, resonance Raman, and UV−vis spectroscopy. They serve as model complexes for the active form of the copper containing fungal enzyme galactose oxidase. The complexes [Zn(L1H2)]BF4·H2O (1), [Zn(L2H2)]BF4·H2O (2), [Zn(L2H)] (2a), [Zn(L3)(Ph2acac)] (3), [Zn(L4)(Ph2acac)] (4), and [Zn(L4)(Me-acac)] (6) were synthesized from solutions of Zn(BF4)2·4H2O and the corresponding ligand (L1H3 = 1,4,7-tris(3,5-tert-butyl-2-hydroxybenzyl)-1,4,7-triazacyclononane; L2H3 = 1,4,7-tris(3-tert-butyl-5-methoxy-2-hydroxybenzyl)-1,4,7-triazacyclononane; L3H = 1,4-dimethyl-7-(3,5-di-tert-butyl-2-hydroxybenzyl)-1,4,7-triazacyclononane; L4H = 1,4-dimethyl-7-(3-tert-butyl-5-methoxy-2-hydroxybenzyl)-1,4,7-triazacyclononane, Ph2acac- = 1,3-diphenyl-1,3-propanedionate, and Me-acac- = 3-methyl-2,4-pentanedionate). Complexes 2, 3·0.5 toluene·1n-hexane, and 4 were structurally characterized by single-crystal X-ray crystallography. An electrochemical investigation of these complexes in CH3CN and/or CH2Cl2 solution revealed that the coordinated phenolate ligands undergo reversible one-electron oxidations with formation of coordinated phenoxyl radicals. Synthetically, the microcrystalline, paramagnetic (μeff = 1.7 μB), solid material of [Zn(L4)(Ph2acac)]PF6 (5) was produced by one electron oxidation of 4 by 1 equiv of ferrocenium hexafluorophosphate in dry CH2Cl2. Oxidation of coordinated phenol pendent arms in 1, 2, and 2a occurs at significantly higher potentials and is irreversible. Electronic (UV−vis), electron paramagnetic resonance (EPR), and resonance Raman (RR) spectra of the radicals have been studied in solution and allow the description of the electronic structure of these coordinated phenoxyl radical complexes.

Unique Ligand‐Based Oxidative DNA Cleavage by Zinc(II) Complexes of Hpyramol and Hpyrimol

“…The amount of radical species present could not be determined, most likely due to their decaying or delocalised nature (Figure 13). [40] The radical is expected to originate from the phenolate moiety of the ligand coupled with the dehydrogenation of the Hpyramol ligand. Copper complexes with phenolate ligands are known in the literature as structural/functional models for the active site of the enzyme galactose oxidase.…”

Potential-dependent surface enhanced resonance Raman spectroscopy of cytochromec552 fromThermus thermophilus

“…Details of the experimental set-up have been described elsewhere. 10 The spectra were measured with a resolution of 2.5 cm~1 (0.21 cm~1 per data point increment) using 413 nm radiation from a krypton ion laser as the excitation source. The laser power at the sample was 40 mW in both RR and SERR experiments.…”

New phenoxyl radical complexes of manganese, gallium, indium and iron based on an H2bbpen ligand derivative

“…6 ] were obtained from Aldrich Chemical Co. 3,5-di-tert-butyl-2-hydroxybenzyl chloride was synthesized through the modification of a method described in the literature. 17 Triethylamine (Et 3 N) and ethylenediamine were obtained from Merck. The reagents and solvents used in the syntheses were reagent grade and used without further purification.…”