Quinones In Solution Research Articles

An Aqueous Analog MAC Machine.

Using ions in aqueous milieu for signal processing, like in biological circuits, may potentially lead to a bioinspired information processing platform. Studies, however, have focused on individual ionic diodes and transistors rather than circuits comprising many such devices. Here a 16×16 array of new ionic transistors is developed in an aqueous quinone solution. Each transistor features a concentric ring electrode pair with a disk electrode at the center. The electrochemistry of these electrodes in the solution provides the basis for the transistor operation. The ring pair electrochemically tunes the local electrolytic concentration to modulate the disk's Faradaic reaction rate. Thus, the disk current as a Faradaic reaction to the disk voltage is gated by the ring pair. The 16×16 array of these transistors performs analog multiply-accumulate (MAC) operations, a computing modality hotly pursued for low-power artificial neural networks. This exploits the transistor's operating regime where the disk current is a multiplication of the disk voltage and a weight parameter tuned by the ring pair gating. Such disk currents from multiple transistors are summated in a global reference electrode to complete a MAC task. This ionic circuit demonstrating analog computing is a step toward sophisticated aqueous ionics.

Evaluation of the effect of temperature on the stability and antimicrobial activity of rifampicin quinone

Rifampicin is an antibiotic used as a first line treatment for tuberculosis, as well as in the treatment of other infectious diseases. Drug quality is essential for drug efficacy. Determining the stability and activity of Rifampicin Quinone in solution is important in its role as a standard against which to determine Rifampicin quality and in its effect on treatment and AMR development. Poor quality medicines, such as antimicrobials not only increase mortality and morbidity, but can also contribute to the development of antimicrobial resistance (AMR). One common marker of poor quality in Rifampicin samples is the presence of the degradation product Rifampicin Quinone. In this study we have found that Rifampicin Quinone in solution undergoes a chemical conversion to Rifampicin that is temperature dependent. This conversion occurs in physiologically relevant temperatures (30−50 °C) and time scales (24−120 h) and was verified using HPLC and LC–MS methods. Additionally, the conversion of Rifampicin Quinone to Rifampicin results in an increase in antimicrobial activity. We believe that ours is the first study reporting the instability of Rifampicin Quinone, and this instability in solution at these temperatures and time scales raises concerns for its use as a standard in quality testing using liquid chromatography methods and in studies of the effect of Rifampicin Quinone on AMR. Due to the use of Rifampicin Quinone as a standard in determining Rifampicin quality, the instability of Rifampicin Quinone also poses public health concerns, as the incorrect determination of medicine quality risks patient health and may promote the development of AMR.

Introduction of protonic potential of Brønsted−Lowry acids and bases to the quantification of the energy of proton translocation and elucidation of oxidative phosphorylation

ATP synthesis in mitochondria is driven by the pH gradient between lipid membranes, and a proton-motive force (PMF) forms along the respiratory electron-transport chain. The reasons for these phenomena remain unclear. In an unbuffered quinone solution, acids induce the formation of new cathodic peaks, whose peak potential is dependent on their pKa. Thus, the protons of acids have a potential defined as “protonic potential.” Herein, the energy of proton translocation was easily quantified by protonic potential. We observed that the redox potential of chemical reactions can be transformed into the protonic potential of Brønsted−Lowry acids and bases in an unbuffered solution. We postulated that in the mitochondrial membrane, the redox potential of the respiratory chain can be transformed to protonic potential and that the PMF originates from the protonic potential difference between compounds. Ultimately, the protonic potential energy derived from redox reactions was stored in the ATP.

Completing a Charge Transport Chain for Artificial Photosynthesis.

A ruthenium polypyridyl chromophore with electronically isolated triarylamine substituents has been synthesized that models the role of tyrosine in the electron transport chain in photosystem II. When bound to the surface of a TiO2 electrode, electron injection from a Ru(II) Metal-to-Ligand Charge Transfer (MLCT) excited state occurs from the complex to the electrode to give Ru(III). Subsequent rapid electron transfer from the pendant triarylamine to Ru(III) occurs with an observed rate constant of ∼1010 s-1, which is limited by the rate of electron injection into the semiconductor. Transfer of the oxidative equivalent away from the semiconductor surface results in dramatically reduced rates of back electron transfer, and a long-lived (τ = ∼165 μs) triarylamine radical cation that has been used to oxidize hydroquinone to quinone in solution.

Unveiling interactions between DNA and cytotoxic 2-arylpiperidinyl-1,4-naphthoquinone derivatives: A combined electrochemical and computational study

Three 2-arylpiperidinyl-1,4-naphthoquinone derivatives were synthesized and evaluated in vitro to determine their cytotoxicity on cancer and normal cell lines. In order to establish their possible action mechanism, the electrochemical behaviour of these quinones was examined using cyclic voltammetry (CV) as technique by using a three-electrode setup: a glassy carbon, Ag/AgCl (in 3 M KCl), and platinum wire as working, reference, and counter electrodes, respectively. Kinetic studies were done to determine the control of the reduction reaction and the number of transferred electrons in the process. Furthermore, the addition of dsDNA to the quinone solutions allowed for the observation of an interaction between each quinone and dsDNA as the current-peaks became lower in presence of dsDNA. Otherwise, motivated to support the aforementioned results, electronic structure calculations at the TPSS-D3/6-31+G(d,p) level of theory were carried out in order to find the most favourable noncovalently bonded complexes between quinones and DNA. Noncovalent complexes formed between DNA and 2-arylpiperidinyl-1,4-naphthoquinones and stabilized by π-stacking interactions along with the well-known hydrogen-bonded complexes were found, with the former being more stable than the latter. These results suggest that the intercalation of these quinone derivatives in DNA is the most likely action mechanism.

Synergistic and Antagonistic Interactions among the Particulate Matter Components in Generating Reactive Oxygen Species Based on the Dithiothreitol Assay.

We assessed the interactions among the particulate matter (PM) components in generating the reactive oxygen species (ROS) based on a dithiothreitol (DTT) assay. We started with the standard solutions of known redox-active substances, i.e., quinones (9,10-phenanthraquinone, 1,2-naphthoquinone, 1,4-naphthoquinone, and 5-hydroxy-1,4-naphthoquinone) and metals [Fe (II), Mn (II), and Cu (II)]. Both DTT consumption and hydroxyl radical (·OH) generation were measured in the DTT assay. The interactions of Fe were additive with quinones in DTT consumption but strongly synergistic in ·OH generation. Cu showed antagonistic interactions with quinones in both DTT consumption and ·OH generation. Mn interacted synergistically with quinones in DTT oxidation but antagonistically in ·OH generation. The nature of the interactions of these metals (Fe, Mn, and Cu) with ambient humic-like substances (HULIS) resembled that with quinones, although the intensity of interactions were weaker in DTT consumption than ·OH generation. Finally, we demonstrated that the DTT consumption capability of ambient PM can be well explained by HULIS, three transition metals (Fe, Mn, and Cu), and their interactions, but ·OH generation involves a contribution (∼50%) from additional compounds (aliphatic species or metals other than Fe, Mn, and Cu) present in the hydrophilic PM fraction. The study highlights the need to account for the interactions between organic compounds and metals, while apportioning the relative contributions of chemical components in the PM oxidative potential.

Photocurrent Generation by Photosynthetic Purple Bacterial Reaction Centers Interfaced with a Porous Antimony-Doped Tin Oxide (ATO) Electrode.

The ability to exchange energy and information between biological and electronic materials is critical in the development of hybrid electronic systems in biomedicine, environmental sensing, and energy applications. While sensor technology has been extensively developed to collect detailed molecular information, less work has been done on systems that can specifically modulate the chemistry of the environment with temporal and spatial control. The bacterial photosynthetic reaction center represents an ideal photonic component of such a system in that it is capable of modifying local chemistry via light-driven redox reactions with quantitative control over reaction rates and has inherent spectroscopic probes for monitoring function. Here a well-characterized model system is presented, consisting of a transparent, porous electrode (antimony-doped tin oxide) which is electrochemically coupled to the reaction center via a cytochrome c molecule. Upon illumination, the reaction center performs the 2-step, 2-electron reduction of a ubiquinone derivative which exchanges with oxidized quinone in solution. Electrons from the electrode then move through the cytochrome to reoxidize the reaction center electron donor. The result is a facile platform for performing redox chemistry that can be optically and electronically controlled in time and space.

Fluorescence quenching studies on the interaction of catechin-quinone with CdTe quantum dots. Mechanism elucidation and feasibility studies

Changes of the photoluminescent properties of QD in the presence of oxidized catechin (CQ) were investigated by absorption, steady-state fluorescence, fluorescence lifetime and dynamic light scattering measurements. Photoluminescence intensity and fluorescence lifetime was decreasing with increasing CQ concentration. Dynamic light scattering technique found the hydrodynamic diameter of QD suspension in water is in range of 45nm, whereas in presence of CQ increased to mean values of 67nm. Calculated from absorption peak position of excition band indicated on average QD size of 3.2nm. Emission spectroscopy and time-resolved emission studies confirmed preservation of electronic band structure in QD–CQ aggregates. On basis of the presented results, the elucidated mechanism of QD fluorescence quenching is a result of the interaction between QD and CQ due to electron transfer and electrostatic attraction.The results of fluorescence quenching of water-soluble CdTe quantum dot (QD) capped with thiocarboxylic acid were used to implement a simple and fast method to determine the presence of native antioxidant quinones in aqueous solutions. Feasibility studies on this method carried out with oxidized catechin showed a linear relation between the QD emission and quencher concentration, in range from 1 up to 200μM. The wide linear range of concentration dependence makes it possible to apply this method for the fast and sensitive detection of quinones in solutions.

The Chemistry behind Quinone Flow Batteries

In order to make flow batteries cost-competitive for large-scale stationary storage, significant reductions must be made in the cost of the redox-active materials. We will show that organic molecules such as quinones offer dramatic cost reductions to the storage medium in comparison with metal-based electrolytes. Quinones also provide the ability to tune the redox and solubility properties of the molecules through the incorporation of various substituent groups onto the aromatic ring.We will report the synthesis, chemical, and electrochemical properties of several substituted quinone molecules. These results indicate that bulk solutions of quinones may be easily prepared and used as electrolyte solutions without purification. The reaction can be modified to affect the reduction potential of the solution, while maintaining rapid and reversible electrochemical kinetics. Finally, the unique electronic structure of quinone molecules is described to explain the origin of the fast, un-catalyzed two-electron redox kinetics.

Heterogeneous Proton Transfer As an Explanation for the Unusually Thick Cyclic Voltammograms and Unusually Small Second Redox Wave of Para-Quinones in Aprotic Solvents

Quinones are well-known to undergo two reversible reductions at glassy carbon electrodes in aprotic solvents, first to a radical anion and then to a dianion, eq 1. Despite 50+ years of voltammetric investigation of this chemistry, two unusual features of quinone voltammetry—that the second redox wave is smaller than the first, and that the area between the two waves is thicker than CV simulations say it should be—was typically ignored until Gupta and Linschitz made note of the difference in height of the redox waves in 1997.1 The current explanation for the unequal wave heights, advanced by Macías-Ruvalcaba and Evans in 2010,2 is that some of the radical anion is trapped in the form of a pi dimer in solution. Macias-Ruvalcaba and Evans hypothesize that this dimer can be reduced at the same potential as the monomer radical anion, but only by 1 e- per dimer, resulting in smaller current than expected. There currently is no explanation in the literature for the thickness between the two waves.In this study, concentration dependence of the CVs of differently substituted quinones showed that radical dimerization cannot be a general explanation for the small second redox wave. In some cases the thickness between the waves appears as its own quasi-reversible wave. Addition of phenols to a quinone solution produces a quasi-reversible wave at the same potential due to hydrogen bonding to the radical anion. The McCreery lab showed that oxide content of the surface of glassy carbon can change its chemistry through the presence of functional groups such as phenols.3 In low concentration duroquinone studies, different surface treatments show that with higher oxide content a new wave grows in that is at the same potential as the wave seen in a 1:1 addition of naphthol to the quinone redox system. This indicates that the odd thickness in quinone CV’s may be due to hydrogen bonding of the quinones to phenolic groups on the glassy carbon surface followed by proton transfer.REFERENCES1. Gupta, J. ;Linschitz, H. Hydrogen Bonding and Protonation Effects in Electrochemistry ofQuinones in Aprotic Solvents. J. Am. Chem. Soc., 1997, 119(27), 6384-6391.2. Macías-Ruvalcaba, N.; Evans, D. Association Reactions of the Anion Radicals of SomeHydroxyquinones: Evidence for the Formation of π and σ–Dimers As Well As a Neutral-AnionRadical Complex. J. Phys. Chem. C, 2010, 114(2), 1285-1292.3. Kuo, T.; McCreery, R.L. Surface Chemistry and Electron-Transfer Kinetics of Hydrogen-Modified Glassy Carbon Electrodes. Anal. Chem. 1999, 71, 1553-1560.

SU‐E‐J‐164: Photodynamic Activity of Alternative Photosensitizers with Mamma Carcinoma Cell Lines (MCF‐7)

Purpose To promote the degree of cytotoxicity and photodynamic activity in photodynamic therapy, the mamma carcinoma cell lines with various photosensitizers like naturally occuring quinones extracted from folklore plants were studied. Methods Photosensitizers viz Cat E, Cat Q, MPTQ and Etoposide VP16, 1 were obtained both photochemically or synthetically. The quinones were dissolved in NaCl solution and stored in the dark. Working solutions of various quinones were prepared SOS from stock solutions. Mamma carcinoma cell lines were grown in the laboratory conditions. Results The percentage of cells damage as the function of optical dose for different photosensitizers was studied, found that cell damage increased as the optical dose increased. Studies of oxygen, glucouse, consumption, intra cellular ATP content and the viability of cell lines after photodynamic treatemnt in presence and absence of different quinones in human breast cancer cell lines were done. Conclusion The degree of cytotoxicity promoted by the alternative sensitizers like naturally occuring quinones extracted from folklore plants to improve the photodynamic therapy efficacy have been studied. The vital bio parameters that are essential for the survival of living cells such as the exclusion capacity of TB, dye uptake ability, cell viability test by vital dye and MTT assay are studied by microscopic quantitative HTS assays. HTS assays are expected to an overall damaging to membrane of the cells. HTS assay is useful modality on studying the morphological information on the status of individual cell because such information study on subcellular fraction cannot be available from the biochemical read outs. The cytotoxic effect and increased photodynamic activity based on different methods studied proved that, naturally occuring quinones takes the following order MPT quinoline tan analoges of natural alkaloids), has greater effect than etoposide an analog of natural podophyllotoxin has greater effect than emodin‐quinone and anthraquinone.

An electrochemical actuator based on reversible changes in volume of poly(acrylic acid) gel induced by quinone redox

An actuator consisting of poly(acrylic acid) gel in contact with p-hydroquinone (QH 2)/ p-benzoquinone (BQ), which was immobilized on a Au-coated conductive film electrode, was developed. The driving force of the actuator was changes in volume of the gel induced by pH change resulting from redox reaction of quinone. The pH decreased upon oxidation of QH 2, which gives rise to collapse of the gel, whereas it increased upon reduction of Q, which results in expansion. The actuator stretched upon oxidation of QH 2 at +1.0 V vs. Ag/AgCl in a 10 mM quinone solution containing 1 × 10 −4 M NaClO 4. It bent at open circuit likely due to diffusion of protons to a bulk solution caused by concentration gradient, but the bending rate increased upon reduction of Q at −0.3 V which consumes protons. The actuator showed repeated stretching/bending at least 9 cycles with increasing its working distance upon successive potential switch between +1.0 and −0.3 V. Energy conversion efficiency was evaluated to be 10 −3%.

Inhibition of polymerization of methyl methacrylate by an ortho-benzoquinone-amine system

The kinetic features of the bulk polymerization of MMA in the presence of sterically hindered ortho-benzoquinones and the tertiary amines N,N-dimethylaniline and N,N-dimethylisopropanolamine have been studied. The irradiation of solutions of quinones and amines in MMA with visible light causes inhibition of the thermal polymerization of MMA, with the effects of quinones and amines being synergistic. The effect of inhibition is enhanced as the steric shielding of carbonyl groups of ortho-benzoquinone by substituents becomes weaker. The dependence of the induction period on the redox potentials of quinones passes through a maximum. It is shown that inhibition involves oxyphenoxyl radicals arising from the interaction of the original quinone with the product of its photoreduction in the presence of amines, pyrocatechol. The inhibiting effect depends on the concentration ratio of quinone and pyrocatechol and the nature of amine. When quinone is in excess with respect to pyrocatechol, additional inhibition of polymerization is observed and the rate of quinone consumption during the induction period is increased.

Determination of Short-chain Fatty Acids in Rat and Human Feces by High-Performance Liquid Chromatography with Electrochemical Detection

A simple method for determining short-chain fatty acids (SCFAs) in rat and human feces was developed using high-performance liquid chromatography with electrochemical detection (HPLC-ECD). A two-channel HPLC-ECD system was fabricated using an ion exclusion column and an electrochemical detector with a glassy carbon working electrode. Aqueous solutions of 0.1 mM HClO(4) and of ethanol containing 2-methyl-1,4-naphthoquinone served as a mobile phase and a quinone solution, respectively. Peak areas for lactic, acetic, propionic, butyric, isovaleric, and valeric acids at a detection potential of -0.9 V vs. an Ag/AgCl electrode showed a linear relationship with the acid amount in the range 0.1 to 40 nmol. Standard acids at 4 nmol were determined ten times with relative standard deviations (RSD) of less than 2.0%. The analytical results of healthy human feces were measured within 35 min. RSD (n = 5) in all SCFAs were less than 2.7%, and recoveries of SCFAs were more than 92%. The present method was characterized by reproducibility with the simple and rapid procedure without derivatization of analytes, and it has the potential for clinical and biomedical applications.

An LC method for monitoring medium-chain fatty acid permeation through CaCo-2 cell monolayers

A simple method was developed for monitoring the permeation of medium-chain fatty acids of C8 (octanoic acid) and C10 (decanoic acid) through CaCo-2 cell monolayers by high-performance liquid chromatography with electrochemical detection (HPLC-ECD). The detection was made based on the electrochemical reduction prepeak of quinone caused by acids, requiring the fabrication of a two-channel HPLC-ECD system. In one channel, acetonitrile-water (7:3, v/v) was used as a mobile phase to separate acids by a C30 column. In the other channel, acetonitrile-water (7:3, v/v) containing 6 mmol/L 3,5-di-t-butyl-1,2-benzoquinone and 20 mmol/L LiClO(4) was used as a quinone solution to detect acids by an electrochemical cell with a glassy carbon working electrode. In this HPLC-ECD system, eluted acids were mixed with the quinone solution in a post column fashion to obtain current signals caused by acids. The peak area was found to be linearly related to the acid amount ranging from 25 to 1,000 pmol (r > 0.992). The detection limits of octanoic acid and decanoic acid were 7.5 and 8.8 pmol, respectively. Octanoic acid and decanoic acid spiked into cell culture media samples were extracted with acetonitrile and their recoveries were more than 89.5% with an RSD of less than 8.2%. This method was applied to the permeation experiment of octanoic acid and decanoic acid with CaCo-2 cell monolayers formed on the Transwell system.

Arsenic Redox Changes by Microbially and Chemically Formed Semiquinone Radicals and Hydroquinones in a Humic Substance Model Quinone

Arsenic is a redox-active metalloid whose toxicity and mobility strongly depends on its oxidation state, with arsenite (As(III)) being more toxic and mobile than arsenate (As(V)). Humic substances (HS) are also redox-active and can potentially react with arsenic and change its redox state. In this study we show that semiquinone radicals produced during microbial or chemical reduction of a HS model quinone (AQDS, 9,10-anthraquinone-2,6-disulfonic acid) are strong oxidants. They oxidize arsenite to arsenate, thus decreasing As toxicity and mobility. This reaction depends strongly on pH with more arsenite (up to 67.3%) being oxidized at pH 11 compared to pH 7 (12.6% oxidation) and pH 3 (0.5% oxidation). In addition to As(III) oxidation by semiquinone radicals, hydroquinones that were also produced during quinone reduction reduced As(V) to As(III) at neutral and acidic pH values (less than 12%) but not at alkaline pH. In order to understand redox reactions between arsenite/arsenate and reduced/oxidized HS, we quantified the radical content in reduced quinone solutions and constructed Eh-pH diagrams that explain the observed redox reactions. The results from this study can be used to better predict the fate of arsenic in the environment and potentially explain the occurrence of oxidized As(V) in anoxic environments.

Bioluminescent monitoring of detoxification processes: Activity of humic substances in quinone solutions

This study deals with application of bioluminescent assay systems to evaluate the detoxifying effect of humic substances (HS) on the solutions of organic oxidizers – quinones. A series of homologous quinones with different redox characteristics: 1,4-benzoquinone, tetrafluoro-1,4-benzoquinone, methyl-1,4-benzoquinone, tetramethyl-1,4-benzoquinone, and 1,4-naphtoquinone, was used. Bioluminescent bacteria Photobacterium phosphoreum, and NADH:FMN-oxidoreductase-luciferase enzyme system isolated from these bacteria were used as assay systems. The toxicity was compared in the presence and in the absence of HS. Variation of complexity of bioassays ( in vivo or in vitro) combined with spectrometric and microscopic methods, provides insight into the process of detoxification in quinone solutions. Two ways of HS effect were studied: the reduction activity of HS and intensification of self-protection of bacterial cells on HS addition.

Production of Reactive Oxygen Species on Photolysis of Dilute Aqueous Quinone Solutions

We have examined the generation of the reactive oxygen species (ROS) superoxide and hydrogen peroxide (H2O2) by irradiation of dilute aqueous solutions of disodium anthraquinone-2-6-disulfonate (AQDS) with simulated sunlight. Irradiating a solution of AQDS in 2 mM NaHCO3 and 0.01 M NaCl produced superoxide and H2O2 at nanomolar concentrations. Experiments in which initial concentrations of dioxygen, H2O2, the superoxide radical trap nitroblue tetrazolium and the electron donor dimethyl sulfoxide were varied suggested that the interaction of solvent water with photo-excited quinone moieties produces dioxygen-reducing radicals, and that these are the primary source of ROS in the system. A kinetic model for ROS production is proposed based on our experimental data.

Sonochemistry of antitumor quinones in argon-saturated aqueous solutions: enhanced ferricytochrome c reduction

Sonolysis of argon-saturated aqueous antitumor quinone solutions resulted in an enhancement in ferricytochrome c (Cyt c) reduction. Partial inhibition of these reduction enhancements by addition of superoxide dismutase evidences the production of superoxide ions. No correlation between quinone hydrophobicity or redox potential is observed in the extent of Cyt c reduction. The semiquinone of the parent quinone as well as other quinone-derived reductants are proposed as the electron shuttle intermediates which reduce Cyt c.

Electrochemical and FTIR spectroscopic characterization of the cytochrome bc1 complex from Paracoccus denitrificans: evidence for protonation reactions coupled to quinone binding.

The cytochrome bc(1) complex from Paracoccus denitrificans and soluble fragments of its cytochrome c(1) and Rieske ISP subunits are characterized by a combined approach of protein electrochemistry and FTIR difference spectroscopy. The FTIR difference spectra provide information about alterations in the protein upon redox reactions: signals from the polypeptide backbone, from the cofactors, and from amino acid side chains. We describe typical modes for conformational changes in the polypeptide and contributions of different secondary structure elements. Signals attributed to the different cofactors can be presented on the basis of selected potential steps. Modes associated with bound quinone are identified by comparison with spectra of quinone in solution at 1656, 1642, and 1610 cm(-1) and between 1494 and 1388 cm(-1), as well as at 1288 and 1262 cm(-1). Signals originating from the quinone bound at the Q(o) site can be distinguished. On the basis of the infrared data, the total quinone concentration is determined to be 2.6-3.3 quinones per monomer, depending on preparation conditions. The balance of evidence supports the double-occupancy model. Interestingly, the amplitude of the band at 1746 cm(-1) increases with quinone content, reflecting a protonation reaction of acidic groups. In this context, the involvement of glutamates and/or aspartates in the vicinity of the Q(o) site is discussed on the basis of recently determined crystal structures.