Multi-Electron Donor Organic Molecules Containing Hydroquinone Methyl-Ether as Redox Active Units (original) (raw)
Related papers
Scientific Reports, 2013
Benzoquinones (BQ) have important functions in many biological processes. In alkaline environments, BQs can be hydroxylated at quinoid ring proton positions. Very little is known about the chemical reaction leading to these structural transformations as well as about the properties of the obtained hydroxyl benzoquinones. We analyzed the behavior of the naturally occurring 2,6-dimethoxy-1,4-benzoquinone under alkaline conditions and show that upon substitution of methoxy-groups, poly-hydroxyl-derivatives (OHBQ) are formed. The emerging compounds with one or several hydroxyl-substituents on single or fused quinone-rings exist in oxidized or reduced states and are very stable under physiological conditions. In comparison with the parent BQs, OHBQs are stronger radical scavengers and redox switchable earth-alkaline metal ligands. Considering that hydroxylated quinones appear as biosynthetic intermediates or as products of enzymatic reactions, and that BQs present in food or administered as drugs can be hydroxylated by enzymatic pathways, highlights their potential importance in biological systems. Q uinones constitute a broad class of biologically active substances (small molecules) involved in vital cellular processes such as respiration and photosynthesis 1-4 . In addition, there is also an increasing number of quinoid compounds produced mainly by plants and fungi, for which antineoplastic or antibiotic features have been described 5,6 . In the respiratory chain, the prime role of coenzymes Q is to mediate the electron transfer between various redox centers and to translocate protons across the inner mitochondrial membrane by turnover of the quinone/quinol (Q/H 2 Q) redox couple. Because of these redox transitions, in cells, coenzymes Q can act as weak radical scavengers 7 and also as a source of superoxide ( N O 2 -) and related oxidants 8 . For quinones in general, the structure of the quinoid core group and its substituents determines their redoxactivity and chemistry which in case of the biologically and pharmacologically important benzoquinones is still not fully resolved. While the mechanistic pathway of electron transfer of quinones in organic (aprotic) media involving two successive one-electron steps seems to be unanimously defined and accepted, in aqueous solutions, quinone electrochemistry is still controversial 9-13 .
Journal of Agricultural and Food Chemistry, 1998
A series of 2,5-diamino-p-benzoquinone derivatives have been prepared and their physicochemical properties studied. The sensitivity of their photoreduction potential to 3-(3,4-dichlorophenyl)-1,1-dimethylurea, 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, and KCN, as well as the photosystem I (PSI) activity, suggests that the reduction of 2,5-diamino-p-benzoquinone derivatives in the illuminated thylakoid is at the primary electron acceptor of PSI and it is reversible. The half-wave potentials of these compounds to their corresponding radical anions in an aprotic medium such as acetonitrile were found to be comparable with the midpoint potential values of the electron transport carriers at the reducing site of PSI. The strong reductant produced by PSI is really more accessible to the strong lipophilic electron acceptor. These lipophilic p-benzoquinone derivatives can reach the carriers inside the thylakoid membrane more easily than the ionic electron acceptor. The accepting electron properties of these compounds at PSI are similar to those of the bipyridinium herbicides.
An electron spin resonance study of the cation radicals of dimethylhydroquinones
Journal of the American Chemical Society, 1968
The electron spin resonance spectra (esr) of the 2,3-, 2,5-, and 2,6-dimethylhydroquinone cations have been obtained by oxidation of the hydroquinones both in an A~C~~-C H J N O~ solution and in concentrated sulfuric acid. The esr spectrum of the 2,6-dimethylhydroquinone cation exhibits line-width alternation phenomena characteristic of the hindered rotation of the OH groups. However, neither the 2,3-nor the 2,5-dimethylhydroquinone cation radical esr spectra show any sign of an alternating Line-width effect. This behavior is interpreted by assuming that the 2,3-and 2,5-dimethylhydroquinone cations are stabilized in the cis and trans conformations, respectively. Comparison of the hyperfine splittings with molecular orbital calculations and with the hyperfine splittings in the corresponding p-benzosemiquinone anions supports this view. Also, the changes are consistent with the assignments made for the hyperfine splittings in the cis and trans isomers of the unsubstituted hydroquinone cation. revious esr studies on the cation radicals of hydro-
Molecules, 2019
In the search for new quinoid compounds endowed with potential anticancer activity, the synthesis of novel heterodimers containing the cytotoxic 7-phenylaminoisoquinolinequinone and 2-phenylaminonaphthoquinone pharmacophores, connected through methylene and ethylene spacers, is reported. The heterodimers were prepared from their respective isoquinoline and naphthoquinones and 4,4′-diaminodiphenyl alkenes. The access to the target heterodimers and their corresponding monomers was performed both through oxidative amination reactions assisted by ultrasound and CeCl3·7H2O catalysis “in water”. This eco-friendly procedure was successfully extended to the one-pot synthesis of homodimers derived from the 7-phenylaminoisoquinolinequinone pharmacophore. The electrochemical properties of the monomers and dimers were determined by cyclic and square wave voltammetry. The number of electrons transferred during the oxidation process, associated to the redox potential EI1/2, was determined by cont...
Inorganica Chimica Acta, 2008
Two carboxyl substituted quinones and their ethyl esters were prepared by alkylation of 2-methyl-1,4-naphthoquinone (MNQ), also known as menadione or vitamin K 3 . All products were characterized by spectroscopic ( 1 H NMR, 13 C NMR, IR) and electrochemical (cyclic voltammetry) methods, and the crystal structure of the two carboxylic derivatives was also determined. Both carboxyl substituted quinones crystallize in the P 1 system as hydrogen bonded dimers. In MeCN, the cyclic voltammograms of the ester derivatives present two reversible one-electron redox waves very similar to those of the parent quinone, MNQ. However, in the same solvent, the corresponding carboxyl substituted quinones show one cathodic and one anodic additional irreversible waves at more positive potentials and a decrease in current intensity of the two quinone reduction waves accompanied by loss of the quasi-reversible character of the second wave. These results show that the presence of the carboxylic substituent does not greatly modify the redox behaviour of the quinone, except for a small anodic shift of the potentials, but the associated presence of H + ions in solution causes an important perturbation to the system, stabilizing the electrogenerated semiquinones by intermolecular self-protonation and/or hydrogen bonding.
Macromolecular rapid communications, 2018
Multihydroxy-anthraquinone derivatives [i.e., 1,2,4-trihydroxyanthraquinone (124-THAQ), 1,2,7-trihydroxyanthraquinone (127-THAQ), and 1,2,5,8-tetrahydroxyanthraquinone (1258-THAQ)] can interact with various additives [e.g., iodonium salt, tertiary amine, N-vinylcarbazole, and 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine] under household green LED irradiation to generate active species (cations and radicals). The relevant photochemical mechanism is investigated using quantum chemistry, fluorescence, cyclic voltammetry, laser flash photolysis, steady state photolysis, and electron spin resonance spin-trapping techniques. Furthermore, the multihydroxy-anthraquinone derivative-based photoinitiating systems are capable of initiating cationic photopolymerization of epoxides or divinyl ethers under green LED, and the relevant photoinitiation ability is consistent with the photochemical reactivity (i.e., 124-THAQ-based photoinitiating system exhibits highest reactivity and ph...
New triphenylantimony(v) catecholate complexes were synthesized by oxidative addition of sterically hindered obenzoquinones containing electronnwithdrawing substituents in different positions of the carbon ring to triphenylantimony. The complexes were characterized using IR spectroscopy, NMR spectroscopy, and cyclic voltammetry. The oxygenninertness of the complexes is shown by NMR spectroscopy and electrochemical studies. The introduction of electronnwithdrawing substituents to the catecholate ligand shifts the first oxidation potential of the complexes to the electropositive region and thus deactivates the triphenylantimony(v) catecholate complexes in the reaction with molecular oxygen.