Redox Processes in the Iron(III)/9,10-Phenanthraquinone System

Abstract

With the use of the model complexes [(PQ)FeCl(CH(3)O)](+), [(phen)FeCl(CH(3)O)](+), and [(PQ)(phen)FeCl(CH(3)O)](+), where PQ is 9,10-phenanthraquinone and phen is 1,10-phenanthroline, the reactivity of phenanthraquinone in complexes with iron(III) is investigated. It is shown that 9,10-phenanthraquinone takes part in redox processes occurring at iron and thereby allows the oxidation of methanolate to formaldehyde. The oxidation is driven by the reduction of iron(III) to iron(II) and 9,10-phenanthraquinone to the semihydroquinone radical or semiquinolate, if the hydrogen atom is transferred from methanolate to chlorine rather than PQ. 1,10-Phenanthroline, on the other hand, acts as an innocent ligand, and the [(phen)FeCl(CH(3)O)](+) complex shows a typical two-state reactivity. The reactivity of [(PQ)(phen)FeCl(CH(3)O)](+) reveals that the hexacoordination of iron energetically facilitates the oxidation of methanolate, and therefore it is proposed that, in the presence of suitable reductants, the mixture of iron(III) and 9,10-phenanthraquinone can lead to the generation of the semihydroquinone radicals, species responsible for the toxicity of PQ. The fragmentation of [(PQ)(phen)FeCl(CH(3)O)](+) also demonstrates a strong binding of phen toward iron(III), which is a reason for using phen as an iron chelator in biochemistry. The structures and reactivities of the complexes are investigated by means of mass spectrometry, infrared multiphoton dissociation spectra, and density functional theory calculations.

Electrospray mass spectrometric studies of nickel(II)-thiosemicarbazones complexes: Intra-complex proton transfer in the gas phase ligand exchange reactions

“…Path-1 apparently leads to thermodynamically more stable products. However, the unpaired d-orbital electron of the transition state metal in the complexes can undergo a spin flip between the low-spin state and the high-spin state [42]. Interestingly, spin flip of the triplet Ni 2+ leads to a more stable state for the both products (CI-1d and CI-2d), in which the singlet state CI-1d-s and CI-2d-s are 21.3 kJ/mol and 71.7 kJ/mol lower in free energy than the corresponding triplet state one, respectively.…”

Infrared Multiphoton Dissociation Spectroscopy with Free‐Electron Lasers: On the Road from Small Molecules to Biomolecules

“…Quinones can accept two electrons stepwise, sequentially forming semiquinones and diol–diates. This behaviour was studied for ortho ‐quinone phenanthraquinone (PQ) in complexes with sodium, copper and iron (Figure ) . The sodium cation can only be in the +I oxidation state.…”

“…This behaviour was studied for ortho-quinone phenanthraquinone (PQ) in complexes with sodium,c oppera nd iron ( Figure 12). [36,37] The sodium cation can only be in the + Io xi-dation state. Accordingly,t he binding in the [(PQ) 2 Na] + complex is dominated by ion-dipole interactions.T he C=Os tretching band of [(PQ) 2 Na] + is found at 1670cm À1 .C opper(I) in the analogousc omplex [(PQ) 2 Cu] + is redox active and can be oxidised.C opper oxidation requires PQ reduction to the semiquinone form.…”

“…The red bar indicates the carbonyl stretchingb ands of the complexes. Adapted with permission from references[36,37].C opyright 2009 American Chemical Society and Copyright2 016 Elsevier.…”

10-Hydroxy-10-(1,3-thiazol-2-ylmethyl)phenanthren-9(10H)-one

“…For general background to and applications of phenanthrenone derivatives, see: Bloom (1961); Kumagai et al (1997); McClellan (1987); Meyer & Spengler (1905); Milko & Roithova (2009); Mustafa et al (1956); Nel et al (2001); Schuetzle et al (1981); Shimada et al (2004); Zhang et al (2004). For ring conformations, see: Cremer & Pople (1975).…”