Less Symmetrical Dicopper(II) Complexes as Catechol Oxidase Models—An Adjacent Thioether Group Increases Catecholase Activity

Abstract

Three new unsymmetrical compartmental dinucleating ligands, 4-bromo-2-(4-methylpiperazin-1-ylmethyl)-6-[{2-(1-piperidyl)ethyl}aminomethyl]phenol (HL1), 4-bromo-2-(4-methylpiperazin-1-ylmethyl)-6-[{2-(morpholin-4-yl)ethyl}aminomethyl]phenol (HL2), and 4-bromo-2-(4-methylpiperazin-1-ylmethyl)-6-[{2-(thiomorpholin-4-yl)ethyl}aminomethyl]phenol (HL3), have been synthesized in order to model the active site of type 3 copper proteins. The dicopper(II) complexes of these ligands give first hints about the influence of a thioether group close to the metal site. The bromophenol-based ligands have one piperazine arm and one other bidentate arm in positions 2 and 6 of the phenolic ring, respectively. With each ligand a dinuclear copper(II) complex was prepared and structurally characterized. The copper ions were found to have square pyramidal environments and a mixture of endogenous phenoxo and exogenous acetate bridging. The influence of a heteroatom in one arm of the ligand on catecholase activity and speciation in solution was studied by UV/Vis spectroscopy, ESI-MS experiments and, DFT calculations.

A dicopper complex with distant metal centers. Structure, magnetic properties, electrochemistry and catecholase activity

“…As can be seen from data in Table 3, in both solvent mixtures an increase in pH causes a slight improvement in catalyst performance, while a much more noticeable enhancement is observed when solvent is changed from MeCN/H 2 O to MeOH/ H 2 O; at pH 7.5 catalytic efficiency is 20 times better in the latter than in the former. The k cat /K M value obtained for this complex in MeOH/H 2 O pH=8.0 is better than most of the dinuclear copper complexes whose catecholase activity has been reported recently [20,21,25,27,43], suggesting the action of a mechanism that depends on other factors different from the Cu-Cu distance.…”

Copper(II) Complexes of N‐Methylated Derivatives of ortho‐ and meta‐Xylyl‐Bridged Bis(1,4,7‐triazacyclononane) Ligands: Synthesis, X‐ray Structure and Reactivity as Artificial Nucleases

“…[31] Structurally similar molecules to C m but which have a Cu 2 (µ 2 -ac)(µ-O) binding motif show Cu···Cu distances around 3.3-3.6 Å. [32][33][34][35][36] These compounds show promise as catalysts for catechol oxidation, [32,36] and also as model systems for the tyrosinase active site. [34] The C m complex has some structural similarities to the active site of the hydrolase enzyme, methane mono-oxygenase, [37][38][39][40][41][42] which features a dicarboxalatobridged diiron core, but with an additional water-derived ligand bridging the two iron(III) centres.…”

Investigation of 3d-transition metal acetates in the oxidation of substituted dioxolene and phenols

“…The structural and functional aspects of CO have been elucidated with the help of several model systems [24,49,68,71,81,82,84,[100][101][102]. In addition the search for the mimics leads to several alternate mechanisms of oxidation [20][21][22]46,[103][104][105].…”