Hydroquinone Form Research Articles

A Comparative Study of Phase I and II Hepatic Microsomal Biotransformation of Phenol in Three Species of Salmonidae: Hydroquinone, Catechol, and Phenylglucuronide Formation.

The in vitro biotransformation of phenol at 11 °C was studied using pre-spawn adult rainbow (Oncorhynchus mykiss) (RBT), brook (Salvelinus fontinalis) (BKT), and lake trout (Salvelinus namaycush) (LKT) hepatic microsomal preparations. The incubations were optimized for time, cofactor concentration, pH, and microsomal protein concentration. Formation of Phase I ring-hydroxylation and Phase II glucuronidation metabolites was quantified using HPLC with dual-channel electrochemical and UV detection. The biotransformation of phenol over a range of substrate concentrations (1 to 180 mM) was quantified, and the Michaelis-Menten kinetics constants, Km and Vmax, for the formation of hydroquinone (HQ), catechol (CAT), and phenylglucuronide (PG) were calculated. Species differences were noted in the Km values for Phase I enzyme production of HQ and CAT, with the following rank order of apparent enzyme affinity for substrate: RBT > BKT = LKT. However, no apparent differences in the Km for Phase II metabolism of phenol to PG were detected. Conversely, while there were no apparent differences in Vmax between species for HQ or CAT formation, the apparent maximum capacity for PG formation was significantly less in LKT than that observed for RBT and BKT. These experiments provide a means to quantify metabolic activation and deactivation of xenobiotics in fish, to compare activation and deactivation reactions across species, and to act as a guide for future predictions of new chemical biotransformation pathways and rates in fish. These experiments provided the necessary rate and capacity (Km and Vmax) inputs that are required to parameterize a fish physiologically based toxicokinetic (PB-TK) model for a reactive chemical that is readily biotransformed, such as phenol. In the future, an extensive database of these rate and capacity parameters on important fish species for selected chemical structures will be needed to allow the effective use of predictive models for reactive, biotransformation chemicals in aquatic toxicology and environmental risk assessment.

Electrochemical Behavior of Quinones Classically Used for Bioenergetical Applications: Considerations and Insights about the Anodic Side

AbstractQuinones are electrochemical probes which are used for a large range of applications including bioenergetics. One electrochemical feature of quinones is their possible slow electron transfer kinetics. In this article we compared several quinones towards electron transfer kinetics and the ability of anodic pretreatment to increase electron transfer rate constant. Rotating disk electrode and chronoamperometry measurements were used to revisit their electrochemical behavior. Additionally, the number of electrons exchanged as a function of the characteristic time was used as a proxy to investigate kinetic limitations. A model was suggested to rationalize our results. Beyond a classification of quinones regarding the kinetic and thermodynamic ability of the hydroquinone form to be re‐oxidized, some intrinsic physicochemical properties were identified from our model (such as a time dependency of the exchanged number of electrons) to characterize such important redox mediators.

Bridging population pharmacokinetic and semimechanistic absorption modeling of APX3330.

APX3330 ((2E)-2-[(4,5-dimethoxy-2-methyl-3,6-dioxo-1,4-cyclohexadien-1-yl)methylene]-undecanoic acid), a selective inhibitor of APE1/Ref-1, has been investigated in treatment of hepatitis, cancer, diabetic retinopathy, and macular edema. APX3330 is administered orally as a quinone but is rapidly converted to the hydroquinone form. This study describes the pharmacokinetics of APX3330 and explores effect of food on absorption. Total plasma quinone concentrations of APX3330 were obtained following oral administration from studies in healthy Japanese male subjects (single dose-escalation; multiple-dose; food-effect) and patients with cancer patients. Nonlinear mixed effects modeling was performed using Monolix to estimate pharmacokinetic parameters and assess covariate effects. To further evaluate the effect of food on absorption, a semi-physiologic pharmacokinetic model was developed in Gastroplus to delineate effects of food on dissolution and absorption. A two-compartment, first order absorption model with lag time best described plasma concentration-time profiles from 49 healthy Japanese males. Weight was positively correlated with apparent clearance (CL/F) and volume. Administration with food led to an 80% higher lag time. CL/F was 41% higher in the cancer population. The semi-physiologic model indicates a switch from dissolution-rate control of absorption in the fasted-state to gastric emptying rate determining absorption rate in the fed-state. Oral clearance of APX3330 is higher in patients with cancer than healthy Japanese males, possibly due to reduced serum albumin in patients with cancer. Delayed APX3330 absorption with food may be related to higher conversion to the more soluble but less permeable hydroquinone form in the gastrointestinal tract. Future work should address pharmacokinetic differences between APX3330 quinone and hydroquinone forms.

Research on the reaction path of chlorobenzene oxidation by electrochemical-sodium persulfate system

Chlorobenzene (CB) is an important organic chemical material that is volatile and difficult to degrade, and has received much attention because of its strong ozone generation potential. An electrochemical-sodium peroxydisulfate (PDS) system was constructed and the oxidation reaction path of chlorobenzene in this system was analyzed. The effects of current density, PDS concentration, initial pH, CB blow-off gas ratio and temperature on the oxidation and mineralization rate of chlorobenzene in the system were investigated respectively. At a current density of 168 A/m2, a PDS concentration of 0.5 mol/L, an initial pH of 10, a CB blow-off gas ratio of 20% and a reaction temperature of 60 °C, the CB conversion and mineralization rates were able to reach more than 90%. The results of electron paramagnetic resonance (EPR) experiments using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and 2,2,6,6-tetramethyl-4-piperidone hydrochloride (TEMP) as spin trapping agents indicate the presence of ⦁OH, · SO4− and 1O2 in the system. The signal of ·O2− was also captured after the quenching of ⦁OH, which further indicates the presence of 1O2. And the results of active substance quenching experiments showed that the active species that mainly contributed to the oxidation of chlorobenzene included ⦁OH, · SO4− and 1O2, and their contributions to the oxidation of chlorobenzene were 25.0%, 31.7% and 22.2%, respectively. The Liquid Chromatograph Mass Spectrometer (LC-MS) characterization results showed that the formation of chlorophenol and hydroquinone and their ring-opening reactions were the most critical processes in the oxidative decomposition of chlorobenzene, and the reaction pathways for the oxidation of chlorobenzene by ⦁OH, · SO4− and 1O2 were proposed by these characterization results.

Redox-crippled MitoQ potently inhibits breast cancer and glioma cell proliferation: A negative control for verifying the antioxidant mechanism of MitoQ in cancer and other oxidative pathologies

Mitochondria-targeted coenzyme Q10 (Mito-ubiquinone, Mito-quinone mesylate, or MitoQ) was shown to be an effective antimetastatic drug in patients with triple-negative breast cancer. MitoQ, sold as a nutritional supplement, prevents breast cancer recurrence. It potently inhibited tumor growth and tumor cell proliferation in preclinical xenograft models and in vitro breast cancer cells. The proposed mechanism of action involves the inhibition of reactive oxygen species by MitoQ via a redox-cycling mechanism between the oxidized form, MitoQ, and the fully reduced form, MitoQH2 (also called Mito-ubiquinol). To fully corroborate this antioxidant mechanism, we substituted the hydroquinone group (-OH) with the methoxy group (-OCH3). Unlike MitoQ, the modified form, dimethoxy MitoQ (DM-MitoQ), lacks redox-cycling between the quinone and hydroquinone forms. DM-MitoQ was not converted to MitoQ in MDA-MB-231 cells. We tested the antiproliferative effects of both MitoQ and DM-MitoQ in human breast cancer (MDA-MB-231), brain-homing cancer (MDA-MB-231BR), and glioma (U87MG) cells. Surprisingly, DM-MitoQ was slightly more potent than MitoQ (IC50 = 0.26 μM versus 0.38 μM) at inhibiting proliferation of these cells. Both MitoQ and DM-MitoQ potently inhibited mitochondrial complex I-dependent oxygen consumption (IC50 = 0.52 μM and 0.17 μM, respectively). This study also suggests that DM-MitoQ, which is a more hydrophobic analog of MitoQ (logP: 10.1 and 8.7) devoid of antioxidant function and reactive oxygen species scavenging ability, can inhibit cancer cell proliferation. We conclude that inhibition of mitochondrial oxidative phosphorylation by MitoQ is responsible for inhibition of breast cancer and glioma proliferation and metastasis. Blunting the antioxidant effect using the redox-crippled DM-MitoQ can serve as a useful negative control in corroborating the involvement of free radical-mediated processes (e.g., ferroptosis, protein oxidation/nitration) using MitoQ in other oxidative pathologies.

Products of Bisphenol A Degradation Induce Cytotoxicity in Human Erythrocytes (In Vitro).

The aim of this work has been to study the possible degradation path of BPA under the Fenton reaction, namely to determine the energetically favorable intermediate products and to compare the cytotoxicity of BPA and its intermediate products of degradation. The DFT calculations of the Gibbs free energy at M06-2X/6-311G(d,p) level of theory showed that the formation of hydroquinone was the most energetically favorable path in a water environment. To explore the cytotoxicity the erythrocytes were incubated with BPA and three intermediate products of its degradation, i.e., phenol, hydroquinone and 4-isopropylphenol, in the concentrations 5-200 μg/mL, for 1, 4 and 24 h. BPA induced the strongest hemolytic changes in erythrocytes, followed by hydroquinone, phenol and 4-isopropylphenol. In the presence of hydroquinone, the highest level of RONS was observed, whereas BPA had the weakest effect on RONS generation. In addition, hydroquinone decreased the level of GSH the most. Generally, our results suggest that a preferable BPA degradation path under a Fenton reaction should be controlled in order to avoid the formation of hydroquinone. This is applicable to the degradation of BPA during waste water treatment and during chemical degradation in sea water.

Depolarized Mitochondrial Membrane Potential and Protection with Duroquinone in Isolated Perfused Lungs from Rats Exposed to Hyperoxia

ObjectiveDissipation of mitochondrial membrane potential (Δψm) is a hallmark of mitochondrial dysfunction, which plays a key in the pathogenesis of Acute Respiratory Distress Syndrome (ARDS). Our objective was to use a previously developed experimental‐computational approach to estimate tissue Δψm in isolated perfused lungs of rats exposed to hyperoxia as a rat model of human ARDS, and to evaluate the ability of the ubiquinone analog duroquinone (DQ) to reverse any hyperoxia‐induced depolarization of lung Δψm.MethodsRats were exposed to hyperoxia (>95% O2) or normoxia (room air) for 48 hrs, after which lungs were excised and connected to a ventilation‐perfusion system. The experimental protocol consisted of measuring the concentration of the fluorescent dye rhodamine 6G (R6G) during three single‐pass phases: loading, washing, and uncoupling, in which the lungs were perfused with and without R6G, and with the mitochondrial uncoupler FCCP, respectively. For normoxic lungs, the protocol was repeated with 1) rotenone (mitochondrial complex I inhibitor), 2) rotenone and either DQ or its vehicle (DMSO), and 3) rotenone, glutathione (GSH), and either DQ or DMSO added to the perfusate. Hyperoxic lungs were studied with and without DQ and GSH added to the perfusate. A physiologically‐based pharmacokinetic (PBPK) computational model was used to estimate lung Δψm from R6G data.ResultsFigure 1 shows that for hyperoxic lungs, R6G venous effluent concentrations tended to be higher during the loading phase, but significantly lower during the uncoupling phase compared to normoxic lungs, consistent with less uptake of R6G by hyperoxic lungs due to partial depolarization of Δψm. Figure 1 also shows that adding DQ to perfusate during the three phases almost completely reversed differences in R6G concentrations between normoxic and hyperoxic lungs. The PBPK computational model analysis of the R6G data show that exposure to hyperoxia depolarized lung tissue Δψm from ‐140 ± 9 (SE, n = 5) mV to ‐107 ± 9 (n = 5) mV, and complex I inhibition depolarized lung Δψm from ‐140 ± 9 (n = 5) to ‐57 ± 2 (n = 4) mV. Computational model analysis results also demonstrate the efficacy of DQ to fully reverse both rotenone‐induced and hyperoxia‐induced lung Δψm depolarization, consistent with the ability of the lungs to reduce DQ to its hydroquinone form (DQH2), which in turn bypasses mitochondrial complexes I and II to reduce mitochondrial complex III and restores Δψm.ConclusionsThis study demonstrates hyperoxia‐induced Δψm depolarization in isolated perfused lungs, and the utility of this approach for assessing the impact of potential therapies such as exogenous quinones that target mitochondria in isolated perfused lungs.

S1-State Decay Dynamics of Benzenediols (Catechol, Resorcinol, and Hydroquinone) and Their 1:1 Water Clusters.

The S1-state decaying rates of the three different benzenediols, catechol, resorcinol, and hydroquinone, and their 1:1 water clusters have been state-specifically measured using the picosecond time-resolved parent ion transients obtained by the pump (excitation) and probe (ionization) scheme. The S1 lifetime of catechol is found to be short, giving τ ∼ 5.9 ps at the zero-point level. This is ascribed to the H-atom detachment from the free OH moiety of the molecule. Consistent with a previous report (J. Phys. Chem. Lett. 2013, 4, 3819-3823), the S1 lifetime gets lengthened with low-frequency vibrational mode excitations, giving τ ∼ 9.0 ps for the 116 cm-1 band. The S1 lifetimes at the additional vibronic modes of catechol are newly measured, showing the nonnegligible mode-dependent fluctuations of the tunneling rate. When catechol is complexed with water, the S1 lifetime is enormously increased to τ ∼ 1.80 ns at the zero-point level while it shows an unusual dip at the intermolecular stretching mode excitation (τ ∼ 1.03 ns at 146 cm-1). Otherwise, it is shortened monotonically with increasing the internal energy, giving τ ∼ 0.67 ns for the 856 cm-1 band. Two different asymmetric or symmetric conformers of resorcinol give the respective S1 lifetimes of 4.5 or 6.3 ns at their zero-point levels according to the estimation from our transients taken within the temporal window of 0-2.7 ns. When resorcinol is 1:1 complexed with H2O, the S1 decaying rate is slightly accelerated for both conformers. The S1 lifetimes of trans and cis forms of hydroquinone are measured to be more or less same, giving τ ∼ 2.8 ns at the zero-point level. When H2O is complexed with hydroquinone, the S1 decaying process is facilitated for both conformers, slightly more efficiently for the cis conformer.

Spectroscopic Identification on CO2 Separation from CH4 + CO2 Gas Mixtures Using Hydroquinone Clathrate Formation

The formation of hydroquinone (HQ) clathrate and the guest behaviors of binary (CH4 + CO2) gas mixtures were investigated by focusing on an application to separate CO2 from landfill gases. Spectroscopic measurements show that at two experimental pressures of 20 and 40 bar, CO2 molecules are preferentially captured in HQ clathrates regardless of the gas composition. In addition, preferential occupation by CO2 is observed more significantly when the formation pressure and the CH4 concentration are lower. Because the preferential occupation of CO2 is found with binary (CH4 + CO2) gas mixtures regardless of the composition of the feed gas, a clathrate-based process can be applied to CO2 separation or concentration from landfill gases or (CH4 + CO2) mixed gases.

Surface plasmon resonance-induced visible light photocatalytic TiO2 modified with AuNPs for the quantification of hydroquinone

The impregnation of size-controlled gold nanoparticles (AuNPs) on an anatase TiO2 structure (AuNPs@TiO2) was studied for the photoelectrochemical detection of hydroquinone (HQ) under visible light illumination integrated into a flow injection analysis (FIA) setup. The crystalline form of TiO2 was preserved during synthesis and the homogeneous distribution of AuNPs over the TiO2 structure was confirmed. Its photoelectrocatalytic activity was improved due to the presence of AuNPs, preventing charge recombination in TiO2 and improving its light absorption ability by the surface plasmon resonance effect (SPR). The FIA system was used in order to significantly reduce the electrode fouling during electroanalysis through periodic washing steps of the electrode surface. During the amperometric detection process, reactive oxygen species (ROS), generated by visible light illumination of AuNPs@TiO2, participate in the oxidation process of HQ. The reduction of the oxidized form of HQ, i.e. benzoquinone (BQ) occurs by applying a negative potential and the measurable amperometric response will be proportional to the initial HQ concentration. The influencing parameters on the response of the amperometric photocurrent such as applied potential, flow rate and pH were investigated. The linear correlation between the amperometric response and the concentration of HQ was recorded (range 0.0125 – 1.0 µM) with a limit of detection (LOD) of 33.8 nM and sensitivity of 0.22 A M−1 cm−2. In this study, we illustrated for the first time that the impregnation of AuNPs in TiO2 allows the sensitive detection of phenolic substances under green laser illumination by using a photoelectrochemical flow system.

Synthesis, inhibitory activity and in silico docking of dual COX/5-LOX inhibitors with quinone and resorcinol core

Based on the significant anti-inflammatory activity of natural quinone primin (5a), series of 1,4-benzoquinones, hydroquinones, and related resorcinols were designed, synthesized, characterized and tested for their ability to inhibit the activity of cyclooxygenase (COX-1 and COX-2) and 5-lipoxygenase (5-LOX) enzymes. Structural modifications resulted in the identification of two compounds 5b (2-methoxy-6-undecyl-1,4-benzoquinone) and 6b (2-methoxy-6-undecyl-1,4-hydroquinone) as potent dual COX/5-LOX inhibitors. The IC50 values evaluated in vitro using enzymatic assay were for compound 5b IC50 = 1.07, 0.57, and 0.34 μM and for compound 6b IC50 = 1.07, 0.55, and 0.28 μM for COX-1, COX-2, and 5-LOX enzyme, respectively. In addition, compound 6d was identified as the most potent 5-LOX inhibitor (IC50 = 0.14 μM; reference inhibitor zileuton IC50 = 0.66 μM) from the tested compounds while its inhibitory potential against COX enzymes (IC50 = 2.65 and 2.71 μM for COX-1 and COX-2, respectively) was comparable with the reference inhibitor ibuprofen (IC50 = 4.50 and 2.46 μM, respectively). The most important structural modification leading to increased inhibitory activity towards both COXs and 5-LOX was the elongation of alkyl chain in position 6 from 5 to 11 carbons. Moreover, the monoacetylation in ortho position of bromo-hydroquinone 13 led to the discovery of potent (IC50 = 0.17 μM) 5-LOX inhibitor 17 (2-bromo-6-methoxy-1,4-benzoquinone) while bromination stabilized the hydroquinone form. Docking analysis revealed the interaction of compounds with Tyr355 and Arg120 in the catalytic site of COX enzymes, while the hydrophobic parts of the molecules filled the hydrophobic substrate channel leading up to Tyr385. In the allosteric catalytic site of 5-LOX, compounds bound to Tyr142 and formed aromatic interactions with Arg138. Taken together, we identified optimal alkyl chain length for dual COX/5-LOX inhibition and investigated other structural modifications influencing COX and 5-LOX inhibitory activity.

Effect of quinoid redox mediators during azo dye decolorization by anaerobic sludge: Considering the catalyzing mechanism and the methane production

The effects of quinoid compounds on azo dyes decolorization were studied. Compared with other quinones, menadione was the most effective at aiding azo dye decolorization. Sodium formate was a suitable carbon source for the anaerobic decolorization system. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis indicated that the microbial structure changed in response to varying carbon sources. Phylogenetic analysis showed that the anaerobic sludge was consisted mainly of nine genera. The mechanism studies showed that the biotransformation of menadione to its hydroquinone form was the rate-limiting step in the dye decolorization process. Moreover, study of the electron transfer mechanism of quinone-mediated reduction showed that azo dye decolorization is not a specific reaction. The NADH chain was involved in the decolorization process. The methane production test indicated that azo dyes had an inhibitory effect on methane production. However, supplementation with a redox mediator could recover the inhibited methanogenesis. High-throughput sequencing analysis revealed that the methanogenic archaeal community was altered in the anaerobic sludge with or without azo dyes and the redox mediator.

Degradation of 3,5-dichlorophenol by UV-C photolysis and UV-C-activated persulfate oxidation process in pure water and simulated tertiary treated urban wastewater

ABSTRACT UV-C and UV-C/peroxydisulfate (PS) treatments of 3,5-dichlorophenol (3,5-DCP), a model industrial pollutant, were comparatively investigated in two different water matrices namely distilled water (DW) and simulated treated urban wastewater (SWW). The treatment performance of the selected treatment processes was comprehensively examined by following changes in 3,5-DCP, dissolved organic carbon (DOC), PS consumption, Cl− release, aromatic/aliphatic degradation products and acute toxicities towards the marine photobacterium Vibrio fischeri and freshwater microalga Pseudokirchneriella subcapitata. The treatability of 2 mg/L (12.3 µM) 3,5-DCP in DW was investigated under different operating conditions such as initial PS concentrations (0.00–1.00 mM) and pH values (3–11) at a fixed light intensity (0.5 W/L). Increasing the pH and PS concentration exhibited positive effects on 3,5-DCP degradation. Even 10 mg/L 3,5-DCP was completely degraded with UV-C/PS treatment in 40 min in the presence of 0.03 mM PS at pH 6.3 accompanied with 95% DOC removal that was achieved after 120 min treatment. The second-order rate constant of 3,5-DCP (10 mg/L) with was determined as 1.77×109 M−1s−1 using competition kinetics. Cl− release and formation of hydroquinone were evidences of 3,5-DCP degradation involving . 3,5-DCP (2 mg/L) was also subjected to UV-C and UV-C/PS treatments in SWW. 3,5-DCP (100% after 60 min) and in particular DOC (26% after 120 min treatment) removal efficiencies observed in DW decreased dramatically in SWW. The original and UV-C/PS-treated samples were non-toxic towards Vibrio fischeri; however, Pseudokirchneriella subcapitata toxicity increased from 20% to 47% through 80 min UV-C/PS treatment of 3,5-DCP.

UV-C-activated persulfate oxidation of a commercially important fungicide: case study with iprodione in pure water and simulated tertiary treated urban wastewater.

Recently, the European Food Safety Authority (EFSA) has banned the use of iprodione (IPR), a common hydantoin fungicide and nematicide that was frequently used for the protective treatment of crops and vegetables. In the present study, the treatment of 2mg/L (6.06μM) aqueous IPR solution through ultraviolet-C (UV-C)-activated persulfate (PS) advanced oxidation process (UV-C/PS) was investigated. Baseline experiments conducted in distilled water (DW) indicated that complete IPR removal was achieved in 20min with UV-C/PS treatment at an initial PS concentration of 0.03mM at pH = 6.2. IPR degradation was accompanied with rapid dechlorination (followed as Cl- release) and PS consumption. UV-C/PS treatment was also effective in IPR mineralization; 78% dissolved organic carbon (DOC) was removed after 120-min UV-C/PS treatment (PS = 0.30mM) compared with UV-C at 0.5W/L photolysis where no DOC removal occurred. LC analysis confirmed the formation of dichloroaniline, hydroquinone, and acetic and formic acids as the major aromatic and aliphatic degradation products of IPR during UV-C/PS treatment whereas only dichloroaniline was observed for UV-C photolysis under the same reaction conditions. IPR was also subjected to UV-C/PS treatment in simulated tertiary treated urban wastewater (SWW) to examine its oxidation performance and ecotoxicological behavior in a more complex aquatic environment. In SWW, IPR and DOC removal rates were inhibited and PS consumption rates decreased. The originally low acute toxicity (9% relative inhibition towards the photobacterium Vibrio fischeri) decreased to practically non-detectable levels (4%) during UV-C/PS treatment of IPR in SWW.

A comparison of experimental and theoretical studies of benzoquinone modified poly(thiophene): effect of polymerization techniques on the structure and properties.

The present manuscript reports the synthesis of benzoquinone (BQ) modified polythiophene (PTh) by chemical and microwave-assisted polymerization techniques. The synthesized oligomers were investigated for their spectral, morphological and thermal properties via FTIR, UV-visible, scanning electron microscopy (SEM) and thermogravimetric (TGA) analyses. Theoretical calculations were performed by using Gaussian 09 software via the DFT/B3LYP method with the 6-311G basis set. FTIR confirmed the formation of hydroquinone modified PTh when the polymerization was carried out by magnetic stirring and ultrasonication, while the formation of BQ modified PTh was obtained by microwave irradiation. The electronic transitions obtained via experimental UV-visible studies were also found to be in close agreement with the theoretical spectra. SEM revealed a well-formed morphology comprising needle shaped rods for the oligomer synthesized under microwave irradiation. The TGA-DTA studies revealed low char content for the above oligomer, while the florescence studies revealed intense emission around 450 nm. The highest quantum yield was found to be 0.024, which also showed high singlet oxygen generation tendency as well as a high single oxygen quantum yield of 0.30 and could be utilized to design imaging probes applicable in photodynamic therapy.

New sources of arbutin: Onobrychis nitida and Onobrychis galegifolia

Arbutin (4-Hydroxyphenyl-β-D-glucopyranoside) is a mono glycosidic form of hydroquinone and has been widely used in cosmetics for a long time due to skin whitening and freckle removing properties. In this study, arbutin was isolated from the methanol extract of Onobrychis galegifolia using flash chromatography. The structure of arbutin was elucidated by 1H and 13C -NMR spectroscopy and as well as 2D NMR techniques. In addition, quantitative analysis of arbutin found in O. galegifolia and O. nitida species was done using HPLC-DAD. According to the results, the arbutin content of methanol extracts of O. galegifolia and O. nitida was found 212.02 and 196.46 mg/g extract respectively. In addition, the arbutin content of cold-water extracts of O. galegifolia and O. nitida was found 128.2 and 99.40 mg/g extract. The amount of arbutin in dry weights was calculated for about 5.66% to 6.86%.

Hydroquinone-Based Anion Receptors for Redox-Switchable Chloride Binding

A series of chloride receptors has been synthesized containing an amide hydrogen bonding site and a hydroquinone motif. It was anticipated that oxidation of the hydroquinone unit to quinone would greatly the diminish chloride binding affinity of these receptors. A conformational switch is promoted in the quinone form through the formation of an intramolecular hydrogen bond between the amide and the quinone carbonyl, which blocks the amide binding site. The reversibility of this oxidation process highlighted the potential of these systems for use as redox-switchable receptors. 1H-NMR binding studies confirmed stronger binding capabilities of the hydroquinone form compared to the quinone; however, X-ray crystal structures of the free hydroquinone receptors revealed the presence of an analogous inhibiting intramolecular hydrogen bond in this state of the receptor. Binding studies also revealed interesting and contrasting trends in chloride affinity when comparing the two switch states, which is dictated by a secondary interaction in the binding mode between the amide carbonyl and the hydroquinone/quinone couple. Additionally, the electrochemical properties of the systems have been explored using cyclic voltammetry and it was observed that the reduction potential of the system was directly related to the expected strength of the internal hydrogen bond.

Swapping and Enhancement of Guest Occupancies in Hydroquinone Clathrates Using CH4 and CO2

In this study, we investigated guest behaviors of CO2 and CH4 molecules during the initial formation of hydroquinone (HQ) clathrates and then the swapping reactions of guest-loaded HQ. Two experime...

Kraft Lignin–Tannic Acid as a Green Stabilizer for Oil/Water Emulsion

To overcome hydrophobicity and low charge density of kraft lignin (KL), softwood KL was reacted with tannic acid (TA), a green reagent, under alkaline conditions. The mechanism of this reaction was identified to proceed through three steps: (i) oxidation of TA, (ii) transesterification of ester groups of TA (in hydroquinone form) by lignin, and (iii) phenolic ring opening of TA. The enhancement in the carboxylate group was observed, resulting in KL–TA with a high charge density and water solubility in a wide pH range. The modified lignin was utilized as an emulsifier to stabilize oil (hexadecane) in water (O/W) emulations. Vertical scan analysis revealed the greater stability of the system against phase separation at low pH values. The stability of the emulsion containing KL–TA could be tuned by pH, while the emulsion containing lignosulfonate (LS) was not pH-responsive. The LS-containing emulsion had lower stability than the KL–TA-containing one. The rheological studies of KL–TA emulsions showed that all...

Chemo- and Regioselective Dihydroxylation of Benzene to Hydroquinone Enabled by Engineered Cytochrome P450 Monooxygenase.

Hydroquinone (HQ) is produced commercially from benzene by multi-step Hock-type processes with equivalent amounts of acetone as side-product. We describe an efficient biocatalytic alternative using the cytochrome P450-BM3 monooxygenase. Since the wildtype enzyme does not accept benzene, a semi-rational protein engineering strategy was developed. Highly active mutants were obtained which transform benzene in a one-pot sequence first into phenol and then regioselectively into HQ without any overoxidation. A computational study shows that the chemoselective oxidation of phenol by the P450-BM3 variant A82F/A328F leads to the regioselective formation of an epoxide intermediate at the C3=C4 double bond, which departs from the binding pocket and then undergoes fragmentation in aqueous medium with exclusive formation of HQ. As a practical application, an E. coli designer cell system was constructed, which enables the cascade transformation of benzene into the natural product arbutin, which has anti-inflammatory and anti-bacterial activities.