Showing papers on "Quinone published in 2019"
TL;DR: In this paper, a highly stable phosphonate-functionalized anthraquinone is introduced as the redoxactive material in a negative potential electrolyte (negolyte) for aqueous redox flow batteries.
Abstract: A highly stable phosphonate-functionalized anthraquinone is introduced as the redoxactive material in a negative potential electrolyte (negolyte) for aqueous redox flow batteries Revised 20 November 2018
176 citations
TL;DR: In this article, the authors studied two mechanisms of nucleophilic addition of water, one reversible and one irreversible, that limit quinone performance in practical flow batteries and quantified the source of the instability of quinones in water, and explored the relationships between chemical structure, electrochemical reduction potential, and decomposition or instability mechanisms.
Abstract: Quinone–hydroquinone pairs have been proposed as biologically-inspired, low-cost redox couples for organic electrolytes for electrical energy storage, particularly in aqueous redox flow batteries. In their oxidized form, quinones are electrophiles that can react with the nucleophilic water solvent resulting in loss of active electrolyte. Here we study two mechanisms of nucleophilic addition of water, one reversible and one irreversible, that limit quinone performance in practical flow batteries. Using a combination of density functional theory and semi-empirical calculations, we have quantified the source of the instability of quinones in water, and explored the relationships between chemical structure, electrochemical reduction potential, and decomposition or instability mechanisms. The importance of these mechanisms was further verified through experimental characterization of a family of alizarin-derived quinones. Finally, ∼140 000 prospective quinone pairs (over 1 000 000 calculations including decomposition products) were analyzed in a virtual screening using the learned design principles. Our conclusions suggest that numerous low reduction potential molecules are stable with respect to nucleophilic addition, but promising high reduction potential molecules are much rarer. This latter fact suggests the existence of a stability cliff for this family of quinone-based organic molecules, which challenges the development of all-quinone aqueous redox flow batteries.
110 citations
TL;DR: In this article, a facile strategy of using ionic liquid (IL) to tackle the dissolution of quinone electrodes was reported, which would promote the development of high-performance SIBs with ionic electrodes and IL electrolyte.
92 citations
TL;DR: A highly efficient enantioconvergent asymmetric 1,8-addition of aza-para-QMs is described, which provides expedient access to chiral tetrasubstituted allenes bearing an adjacent all-carbon quaternary stereocenter with high enantioselectivity and diastereoselectivities.
56 citations
TL;DR: FeS2 /carbon nanotube (CNT) nanocomposites were synthesized and immobilized on the surface of a glassy carbon electrode (GCE) in order to investigate the electrocatalytic conversion of 4-aminophenol (4-AP) into p-quinone in an aqueous medium.
Abstract: FeS2 /carbon nanotube (CNT) nanocomposites were synthesized and immobilized on the surface of a glassy carbon electrode (GCE) in order to investigate the electrocatalytic conversion of 4-aminophenol (4-AP) into p-quinone in an aqueous medium. The reformed electronic properties (in terms of lowering of band-gap energy and charge-transfer resistance), as well as improved surface area, result in an enhanced redox reaction of 4-AP in the presence of FeS2 -CNT NCs compared to that with FeS2 alone. The 4-AP molecules undergo coupled two-proton and two-electron transfer quasi-reversible redox reactions with a symmetry factor of 0.55 and standard rate constant (k°) of 0.8 cm s-1 . Here, quinone imine is generated as an intermediate which is later converted into quinone in an irreversible hydrolysis reaction. The best catalytic performance can be obtained at the pH value of 7.0.
55 citations
TL;DR: Metal-free, base- free, biomimetic, and chemoselective synthesis of 2,4,6-trisubstituted pyridines was developed for the first time under mild conditions.
55 citations
TL;DR: The presence of structural alerts and evidence for the formation of reactive quinones and quinone imines metabolites and their mechanisms of toxicity through cellular effects are discussed in this review.
Abstract: Quinones and quinone imines are highly reactive metabolites (RMs) able to induce dangerous effects in vivo. They are responsible for all kinds of toxicity, for example, cytotoxicity, immunotoxicity, and carcinogenesis. Furthermore, hepatotoxicity of chemicals/drugs in particular can be induced by quinone and quinone imine metabolites. According to their reactivity, quinones and quinone imines react as Michael's acceptors with cell proteins or DNA and, in this way, cause damage to the cells. Quinones and quinone imines also have high redox potential and, due to their semiquinone radicals, are capable of redox cycling and forming reactive oxygen species (ROS). However, the presence of quinones and quinone imines structures in compounds is not always responsible for a toxic effect. The main question, therefore, is what are the main factors responsible for the toxicity of the chemicals and drugs that form RMs. For this reason, the presence of structural alerts and evidence for the formation of reactive quinones and quinone imines metabolites and their mechanisms of toxicity through cellular effects are discussed in this review, together with examples.
48 citations
TL;DR: A visible light photoredox-catalyzed carbon radical-mediated strategy for in situ formation of ortho-quinone methides from 2-vinyl phenols is described, providing access to trifluoromethylated 2,3-dihydrobenzofurans.
44 citations
TL;DR: Vinylidene-quinone methides are highly electrophilic chiral reagents that can be generated in situ from 2-(phenylethynyl)phenols and their specific reactivity has revealed innovative strategies notably for the control of axial chirality.
44 citations
TL;DR: The first highly asymmetric catalytic synthesis of densely functionalized dihydrobenzofurans is reported, which starts from ortho‐hydroxy‐containing para‐quinone methides with allenoates in the presence of a commercially available chiral phosphine catalyst.
Abstract: The first highly asymmetric catalytic synthesis of densely functionalized dihydrobenzofurans is reported, which starts from ortho-hydroxy-containing para-quinone methides. The reaction relies on an unprecedented formal [4+1]-annulation of these quinone methides with allenoates in the presence of a commercially available chiral phosphine catalyst. The chiral dihydrobenzofurans were obtained as single diastereomers in yields up to 90 % and with enantiomeric ratios up to 95:5.
38 citations
TL;DR: In this article, the first-principles density functional theory method is employed with experimental techniques to investigate the redox properties and charge storage performance of seven quinone derivatives and assess their potential as cathodes in sodium-ion batteries.
TL;DR: The results show how low potential quinones may be tailored to provide a catalytic alternative to stoichiometric DDQ, due to their ability to mediate efficient substrate dehydrogenation while also being compatible with facile reoxidation by O2.
TL;DR: In this paper, a spiro-fused 2,3-dihydrobenzofuran derivatives were readily synthesized in high yields with excellent diastereo and enantio-selectivities.
Abstract: We report a practical and scalable method for the highly diastereo- and enantio-selective construction of 2,3-dihydrobenzofurans bearing spiro-structures by means of cyclization reactions between ortho-quinone methides and α-bromoketones through bifunctional phosphonium salt catalysis under mild conditions. A variety of spiro-fused 2,3-dihydrobenzofuran derivatives were readily synthesized in high yields with excellent diastereo- and enantio-selectivities (up to >20 : 1 dr and 97% ee). This protocol represents an alternative facile way for preparing biologically important chiral 2,3-dihydrobenzofurans. Moreover, mechanistic observations indicated that the hydrogen bonding interaction between the Bronsted acid moiety of the phosphonium catalyst and the “CO” unit of the quinone is crucial for stereoinduction.
TL;DR: A simple deoxygenation reagent prepared in situ from commercially available Mo(CO)6 and ortho-quinone has been developed for the synthesis of indoline and indole derivatives.
Abstract: A simple deoxygenation reagent prepared in situ from commercially available Mo(CO)6 and ortho-quinone has been developed for the synthesis of indoline and indole derivatives. The Mo/quinone complex efficiently deoxygenates carbonyl compounds bearing a neighboring dialkylamino group and effects intramolecular cyclizations with the insertion of a deoxygenated carbonyl carbon into a C(sp3)–H bond, in which a carbonyl group acts as a carbene equivalent. The reaction also proceeds with a catalytic amount of Mo/quinone in the presence of disilane as an oxygen atom acceptor.
TL;DR: This intramolecular lp-π interaction markedly enhanced the stability of the QMs and lowered the pKa values of the corresponding phenol/phenolate couples, becoming the first example of such a non-covalent interaction that stabilizes QMs remotely.
Abstract: Ferrociphenols, especially those possessing a heterocycle at the terminus of an aliphatic chain, display strong anticancer activity through a novel redox mechanism that generates active metabolites such as quinone methides (QMs). X-ray crystallography and UV/Vis spectroscopy reveal that the specific lone pair (lp)-π interaction between a carbonyl group of the imide and the quinone motif of the QM plays an important role in the exceptional cytotoxic behaviour of their imido-ferrociphenol precursors. This intramolecular lp-π interaction markedly enhanced the stability of the QMs and lowered the pKa values of the corresponding phenol/phenolate couples. As the first example of such a non-covalent interaction that stabilizes QMs remotely, it not only expands the scope of the lp-π interaction in supramolecular chemistry, but also represents a new mode of stabilization of a QM. This unprecedented application of lp-π interactions in imido-ferrociphenol anticancer drug candidates may also have great potential in drug discovery and organocatalyst design.
TL;DR: It is hypothesized that the quinone redox state acts as a feed-forward controller of the CBB pathway, signaling the amount of ATP available, and the extent of CO2 fixation was predicted to be dependent on the amounts of ATP generated through the electron transport chain.
Abstract: Rhodopseudomonas palustris CGA009 is a purple non-sulfur bacterium that can fix carbon dioxide (CO2) and nitrogen or break down organic compounds for its carbon and nitrogen requirements. Light, inorganic, and organic compounds can all be used for its source of energy. Excess electrons produced during its metabolic processes can be exploited to produce hydrogen gas or biodegradable polyesters. A genome-scale metabolic model of the bacterium was reconstructed to study the interactions between photosynthesis, CO2 fixation, and the redox state of the quinone pool. A comparison of model-predicted flux values with available Metabolic Flux Analysis (MFA) fluxes yielded predicted errors of 5-19% across four different growth substrates. The model predicted the presence of an unidentified sink responsible for the oxidation of excess quinols generated by the TCA cycle. Furthermore, light-dependent energy production was found to be highly dependent on the quinol oxidation rate. Finally, the extent of CO2 fixation was predicted to be dependent on the amount of ATP generated through the electron transport chain, with excess ATP going toward the energy-demanding Calvin-Benson-Bassham (CBB) pathway. Based on this analysis, it is hypothesized that the quinone redox state acts as a feed-forward controller of the CBB pathway, signaling the amount of ATP available.
TL;DR: For phenol and 25 para-substituted phenols, the thermodynamics of the individual reaction steps, including three subsequent hydrogen atom transfers, as well as hydroxyl HO radical addition, leading to final ortho-quinone formation are investigated.
TL;DR: The role of lipid acyl chain unsaturation for permeation and transversal diffusion of polar molecules across biological membranes is highlighted in a multi-component bilayer to mimic the composition of membranes involved in bioenergetic processes.
Abstract: Natural quinones are amphiphilic molecules that function as mobile charge carriers in biological energy transduction. Their distribution and permeation across membranes are important for binding to enzymatic complexes and for proton translocation. Here, we employ molecular dynamics simulations and free energy calculations with a carefully calibrated classical force-field to probe quinone distribution and permeation in a multi-component bilayer trying to mimic the composition of membranes involved in bioenergetic processes. Ubiquinone, ubiquinol, plastoquinone and menaquinone molecules with short and long isoprenoid tails are simulated. We find that penetration of water molecules bound to the polar quinone head increases considerably in the less ordered and porous bilayer formed by di-linoleoyl (18:2) phospholipids, resulting in a lower free energy barrier for quinone permeation and faster transversal diffusion. In equilibrium, quinone and quinol heads localize preferentially near lipid glycerol groups, but do not perform specific contacts with lipid polar heads. Quinone distribution is not altered significantly by the quinone head, tail and lipid composition in comparison to a single-component bilayer. This study highlights the role of lipid acyl chain unsaturation for permeation and transversal diffusion of polar molecules across biological membranes.
TL;DR: In this paper, a transition metal free visible light mediated organo photoredox catalyzed trifluoromethylation of p-quinone methides (p-QMs) to construct fluoro-analogs of dichlorodiphenyltrichloroethane (DDT) is reported using a bench stable, inexpensive Langlois reagent.
TL;DR: This article reports a convenient and practical synthesis of this heterocycle by a silver (I)-catalyzed cycloaddition reaction between in situ generated ortho-quinone methides and N-allenamides.
Abstract: Chromenes represent an important class of six-membered heterocycles and have drawn tremendous attention in recent years. In this article, we report a convenient and practical synthesis of this heterocycle by a silver (I)-catalyzed cycloaddition reaction between in situ generated ortho -quinone methides and N -allenamides. Diverse 4 H -chromenes were synthesized in good to excellent yields under very mild conditions.
TL;DR: An all-organic cell comprising 2,3-dimethyl-1,4-napthoquinone and pyrano[3,2-f]chromene as electroactive elements exhibited a good combination of large cell voltage and stability of the reduced quinone upon the addition of diethyl malonate.
TL;DR: An iron porphyrin complex is synthesized which includes a pendant quinol group which is demonstrated to perform hydrogen atom transfer (HAT) from the qu inol group appended to the p Morphyrin ligand.
TL;DR: In this study, a method compatible with diverse carboxylic acid partners has been developed and employs 4,5-diazafluoren-9-one as a ligand, in combination with a quinone/iron phthalocyanine cocatalyst system to support aerobic catalytic turnover.
Abstract: Palladium-catalyzed allylic C-H oxidation has been widely studied, but most precedents use acetic acid as the coupling partner. In this study, a method compatible with diverse carboxylic acid partners has been developed. Use of a Pd0 precatalyst under aerobic reaction conditions leads to oxidation of Pd0 by O2 in the presence of the desired carboxylic acid to generate a PdII dicarboxylate that promotes acyloxylation of the allylic C-H bond. Good-to-excellent yields are obtained with a roughly 1:1 ratio of the alkene and carboxylic acid reagents. Optimized reaction conditions employ 4,5-diazafluoren-9-one (DAF) as a ligand, in combination with a quinone/iron phthalocyanine cocatalyst system to support aerobic catalytic turnover.