Solution and Structural Characterization of Iron(II) Complexes with Ortho-Halogenated Phenolates: Insights Into Potential Substrate Binding Modes in Hydroquinone Dioxygenases

Abstract

The new ligand cis,cis-1,3,5-tris-(E)-(tolylideneimino)cyclohexane (TACH-o-tolyl) forms a 1:1 complex with iron(II). Addition of substituted phenolates forms 1:1:1 ligand:iron:phenolate complexes, which have been characterized both in the solid state and in solution. There is complete binding of the phenolate to the complex only when there are ortho-halogens on the phenolate. The tertiary complexes with ortho-halo-substituted phenolates exhibit short Fe-halogen distances, and the complex containing a non-coordinating but similarly sized ortho-methyl phenolate has a significantly different conformation and coordination geometry. Therefore, it is likely that the metal-halogen interaction stabilizes the complexes. The iron(II)-halogen interaction in these complexes may explain the substrate specificity of PcpA and LinE, enzymes that preferentially bind phenols and hydroquinones containing halogen substituents in ortho positions.

Structural, spectroscopic, and electrochemical properties of nonheme Fe(ii)–hydroquinonate complexes: synthetic models of hydroquinone dioxygenases

“…17 The dearth of reported Fe/HQ complexes is partly due to the ability of hydroquinonate (HQate) ligands to adopt a bridging position between metal centers, as demonstrated by structures of diiron(III)-porphyrin and -salen complexes with bridging HQate dianions. 18,19 Recently, Machonkin and Holland described the formation and 1 H NMR characterization of a mononuclear iron(II)-2-methylhydroquinonate complex supported by the 1,3,5-tris(tolylideneimino)cyclohexane ligand; 20 however, this species is unstable and it was not possible to obtain crystals suitable for crystallographic analysis.…”

Mononuclear Iron‐(hydro/semi)quinonate Complexes Featuring Neutral and Charged Scorpionates: Synthetic Models of Intermediates in the Hydroquinone Dioxygenase Mechanism

“…The Fe–N TIP bond lengths of 1a range from 2.11 Å for N3 to 2.22 Å for the pseudo‐axial N5 donor (Table ). The anionic BIHQ ligand exhibits Fe1–O1 and Fe1–N7 distances of 1.91 and 2.15 Å, respectively, typical of phenolate and benzimid‐azole donors in high‐spin ferrous complexes. The observed magnetic moment of µ eff = 4.93 µ B at room temperature (r.t.) is also proof that 1a possesses a high‐spin ( S = 2) Fe II center.…”

Synthesis and characterization of water-soluble, heteronuclear ruthenium(III)/ferrocene complexes and their interactions with biomolecules

“…The NMR spectra are very helpful in the characterization of the complexes even with the paramagnetic ruthenium(III) center, as obtaining routine NMR spectra for paramagnetic compounds are somewhat problematic [37,[39][40][41][42]. Peaks in the spectra corresponding to protons close to the paramagnetic centers have large isotropic shifts and/or severe line broadening associated with them [4,44,46].…”

“…Both ruthenium(III) and organometallic ruthenium(II) species [5][6][7][8][9][10][28][29][30][31][32][33][34][35] have been studied and two ruthenium(III) complexes, NAMI-A and KP1019, [11][12][13][14][15][16][17]27,36] have completed phase I clinical trials. [18][19][20][21][22][23][24][25][37][38][39][40][41][42] In recent years, bioorganometallic compounds (defined as biologically active organometallic species)…”