- Kinetics of oxidation of ascorbate by tetranuclear cobalt(III) complexes ('hexols') in aqueous solution
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The kinetics of oxidation of L-ascorbic acid (H2A) by cobalt(III) hexols, [Co{CoL4(μ-OH)2}3]6+ [L4 =(NH3)4, (en)2, or tren; en = ethane-1,2-diamine, tren = tris(2-aminoethyl)amine], was studied as a function of pH, L-ascorbic acid concentration, temperature and ionic strength, using stopped-flow and conventional spectrophotometric techniques. The rate of the reaction is first order with respect to the concentration of each reactant and increases as [H+] decreases. The kinetic data indicate involvement of the monoprotonated and deprotonated ascorbate species (HA- and A2-) in the redox process. For L4 = (NH3)4 the rate constants, k2 and k3 are 0.22 ± 0.02 and (5.51 ± 0.09) × 105 dm3 mol-1 s-1 respectively at 25°C, and the corresponding activation parameters are ΔH?2 = 103 ± 7 kJ mol-1, ΔS?2 = 89 ± 22 J K-1 mol-1 and ΔH?3 = 46 ± 3 kJ mol-1 and ΔS?3 = 19 ± 11 J K-1 mol-1. The variations in rate constants and activation parameters for the series of complexes mentioned above are discussed. The Fuoss theory was applied to the redox process to estimate the ion-pair formation constant and the rate constant for the electron transfer.
- Abdur-Rashid, Kamaluddin,Dasgupta, Tara P.,Burgess, John
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- Nanostructured membranes for enzyme catalysis and green synthesis of nanoparticles
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Macroporous membranes functionalized with ionizable macromolecules provide promising applications in high capacity toxic metal capture, nanoparticle syntheses, and catalysis. Our low-pressure membrane approach has good reaction and separation selectivities, which are tunable by varying pH, ionic strength, or pressure. The sustainable green chemistry approach under ambient conditions and the evaluation of a reactive poly(acrylic acid) (PAA)-modified polyvinylidene fluoride (PVDF) membrane is described. Two distinct membrane types were obtained through different methods: 1) a stacked membrane through layer-by-layer assembly for the incorporation of enzymes (catalase and glucose oxidase), providing tunable product yields and 2) Fe/Pd nanoparticles for degradation of pollutants, obtained through an in situ green synthesis. Bioreactor-nanodomain interactions and mixed matrix nanocomposite membranes provide remarkable versatility compared to conventional membranes.
- Smuleac, Vasile,Varma, Rajender,Baruwati, Babita,Sikdar, Subhas,Bhattacharyya, Dibakar
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- Kinetics and mechanism of oxidation of l-ascorbic acid by peroxomonosulphate in acid perchlorate medium. Role of copper (II) as a trace metal-ion catalyst
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The kinetics of oxidation of l-ascorbic acid by peroxomonosulphate (PMS) in presence and absence of Cu(II) catalyst has been studied. The stoichiometry of the reaction is represented by the following:H2A + HSO 5- → A + HSO4- + H2O The order with respect to ascorbic acid and peroxomonosulphate is one each. The rate following law in presence of Cu(II) as catalyst has been suggested: (k2″-kun′ = {k1″K 1′ + K1K2″ K1′/ [H+][CuII].
- Sailani, Riya,Dubey, Sapna,Khandelwal,Sharma,Khan, Perveen
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- A new method for thermal analysis: Ion-attachment mass spectrometry (IAMS)
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In this study, we developed the technique of Li+ ion-attachment mass spectrometry (IAMS), a method that has shown promise in the fields of chemical analysis, plasma diagnostics, chemical process monitoring, and thermal analysis. The experimental setup is such that Li+ ions get attached to chemical species (R) by means of intermolecular association reactions to produce (R + Li)+ adduct ions, which are then transferred to a quadrupole mass spectrometer. Recently, an IAMS system became available commercially in a complete form from the Canon Anelva Corp. IAMS has several notable features. It provides only molecular ions, and it permits direct determination of unstable, intermediary, and/or reactive species. Also, it is highly sensitive because it involves ion-molecule reactions. With regard to its applications for thermal analysis, one of its greatest advantages is that it can be used to directly analyze gaseous compounds because it provides mass spectra only of the molecular ions formed by Li+ ion attachment to any chemical species introduced into the spectrometer, including free radicals. Coupled with evolved gas analysis, IAMS works well for the analysis of nonvolatile, untreated, and complex samples because the simplicity of the ion-attachment spectrum permits the analysis of mixtures electron-impact spectra of which are difficult to interpret.
- Fujii, Toshihiro
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- Characterizing homogeneous chemistry using well-mixed microeddies
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Well-mixed reaction volumes are often sought in engineered microchemical devices and can be an important feature of naturally occurring physicochemical processes such as pitting corrosion. Steady streaming eddies can serve as well-mixed, easily controlled microliter chemical reactors for characterizing homogeneous chemical reactions. Here, steady streaming eddies are produced by oscillating a liquid-filled cuvette around a stationary cylindrical electrode (radius 406 μ, length 1.6 cm) at audible frequencies (75 Hz). Oxidant (ferricyanide) electrochemically dosed at small rates (≤30 nmol/s) from the cylindrical electrode accumulates to millimolar concentrations within the closed streamlines of each eddy, where it mixes and reacts with an antioxidant (vitamin C) present in the bulk solution. The composition in the eddy is controlled by varying the oxidant dosing rate and the bulk antioxidant concentration (≤10 mM), as well as the cuvette oscillation amplitude. A simple algebraic mole balance is combined with Raman spectroscopy measurements of oxidant concentration in the eddy and bulk to determine the reaction rate law and homogeneous rate constant (45 ± 9 M-1 s-1) for the antioxidant properties of vitamin C against ferricyanide. Numerical solutions to the full Navier-Stokes equations and species continuity equations illustrate the distribution of species during the reaction and general limitations to the assumption of a well-mixed eddy.
- Lutz, Barry R.,Chen, Jian,Schwartz, Daniel T.
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- Kinetics and Mechanisms of the Photo-Induced Oxidation of Ascorbic Acid by Molecular Oxygen Catalyzed by Ruthenium(II) Complexes Containing 2,2'-Bipyridine and 2,2'-Bipyrazine
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Hydrogen peroxide was efficiently produced by the irradiation of visible light on aqueous acid solutions containing ascorbic acid, molecular oxygen, and ruthenium(II) complexes: (2+) (x=0-3, bpy=2,2'-bipyridine, and bpz=2,2'-bipyrazine).The formation of hydrogen peroxide and the decay of ascorbic acid were followed by polarography during continuous irradiation by visible light of the solution.The rate constants of the quenching reaction of the excited triplet state of the ruthenium(II) complexes by ascorbate and molecular oxygen obtained from the initial rate method were in good agreement with those obtained from luminescence quenching experiments.The initiation reaction in the photo-induced reaction mechanism changes from the oxidative quenching of *(2+) by molecular oxygen to the reductive quenching of *(2+), *(2+), or *(2+) by ascorbate.Such a change in the mechanism arises from a difference in the redox potentials, E0(Ru(3+)/*Ru(2+)) and E0(*Ru(2+)/Ru(+)), for each ruthenium(II) species containing bpy and bpz.The detailed mechanisms are discussed.
- Tsukahara, Keiichi,Wada, Yuuko,Kimura, Masaru
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- L-Galactono-γ-lactone dehydrogenase activity and vitamin C content in fresh-cut potatoes stored under controlled atmospheres
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L-Galactono-γ-lactone dehydrogenase (GLDH) activity and vitamin C content as ascorbic acid (AA) plus dehydroascorbic acid (DHA) were evaluated in five potato tuber cultivars (Agata, Altesse, Franceline, Manon, and Monalisa). The effect of fresh-cutting and subsequent refrigerated storage of Manon potato under different atmospheres (air, 20% CO2 + air, 100% N2, and vacuum packaging) on GLDH activity and vitamin C content was also determined. GLDH from the five potato tuber cultivars showed typical inhibition kinetics by high substrate concentration in the synthesis of AA from its physiological precursor L-galactonic acid-γ-lactone (GL). GLDH activity was not correlated with the corresponding vitamin C content in any potato tuber cultivar. GLDH from all the cultivars presented a major isoform with isoelectric point (IEP) 5, which changed to IEP = 4.3 after minimal processing. In addition, the GLDH-catalyzed synthesis of AA by the new isoform showed typical Michaelis kinetics, in which the enzyme became more efficient to catalyze the reaction. Whether the change in the isoform pattern was due to either post-translational modifications or de novo synthesis of a new isoenzyme remains unanswered. Fresh-cutting increased GLDH activity from 4.7-fold (vacuum packaging) to 11-fold (air) after 6 days. In addition, 100% of vitamin C content was retained in air and decreased in the rest of atmospheres after this storage period, following the sequence vacuum packaging (89%) > 100% N2 (78%) > 20% CO2 + air (63%). This tendency was correlated with the corresponding GLDH activity detected in each storage atmosphere, except in the case of 20% CO2 + air. Vacuum packaging proved to be the best storage condition, because fresh-cut potatoes did not turn brown and retained 89% of initial vitamin C content.
- Tudela, Juan Antonio,Hernandez, Jose Antonio,Gil, Maria Isabel,Espin, Juan Carlos
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- Kinetic study of the oxidation of ascorbic acid by aqueous copper(II) catalysed by chloride ion
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Two methods of monitoring the chloride-catalysed oxidation of ascorbic acid by aqueous CuII have been developed that allow the reaction conditions to be varied more widely than previously and thereby permit a fuller elucidation of the behaviour and rate law for this system. It has been possible to study the reaction over a wide concentration range from 1.6 to 500 mM Cl- and 4 to 100 mM CuII. For the first time, it is shown that the ascorbic acid (H2asc)-CuII-chloride ion-CuI-dehydroascorbic acid (dha) system comes to equilibrium, under anaerobic conditions, with all species present and is driven towards products by chloride complexation of CuI. The results are consistent with the following reaction scheme (i = 0-2). The full rate law has been elucidated and values for various k1i, k-2i, and k2i/k-1i have been determined. (Chemical Equation Presented).
- Sisley, Margaret J.,Jordan, Robert B.
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- Conducting polyaniline-graphene oxide fibrous nanocomposites: Preparation, characterization and simultaneous electrochemical detection of ascorbic acid, dopamine and uric acid
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Polyaniline/graphene oxide (PANI-GO) fibrous nanocomposites have been prepared and the electrochemical catalytic activity towards the electro-oxidation of ascorbic acid (AA), Dopamine (DA) and Uric acid (UA) has been investigated. The nanocomposites were synthesized via an in situ chemical polymerization method. The morphology, composition, thermal and electrochemical properties of the resulting nanocomposites were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, FT-IR spectroscopy, thermo gravimetric analysis and cyclic voltammetry. The catalytic behavior of PANI-GO nanocomposite modified glassy carbon electrode (GCE) towards AA, DA and UA has been investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV). The PANI-GO/GCE showed excellent catalytic activity towards electrochemical oxidation of AA, DA and UA compared to the bare GCE. The electrochemical oxidation signal of AA, DA and UA are well separated into three distinct peaks with peak potential separation of 343 mV, 145 mV and 488 mV between AA-DA, DA-UA and AA-UA respectively in CV studies and the corresponding peak potential separation in DPV mode are 320 mV, 230 mV and 550 mV. Under the optimized DPV experimental conditions, the peak current of AA, DA and UA give linear response over the range of 25-200 μM (R2 = 0.9955), 2-18 μM (R2 = 0.9932) and 2-18 μM (R2 = 0.9902) with detection limit of 20 μM, 0.5 μM and 0.2 μM at S/N = 3, respectively. The attractive features of PANI-GO provide potential applications in the simultaneous detection of AA, DA and UA. The excellent electrocatalytic behavior of PANI-GO may lead to new applications in electrochemical analysis. The Royal Society of Chemistry 2013.
- Manivel,Dhakshnamoorthy,Balamurugan,Ponpandian,Mangalaraj,Viswanathan
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- Kinetic Studies of the Oxidation of L-Ascorbic Acid by the Peroxodisulfate Ion, and of Copper(II)-catalysis
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Kinetic studies of the oxidation reaction of L-ascorbic acid by the peroxodisulfate ion(S2O82-) are carried out in an aqueous solution over the pH range of 3.4-4.6 at various ionic-strengths from 0.071 to 1.07 M (1 M=1 mol dm-3) with NaClO4, and at four temperatures between 15 and 30 deg C, at an ionic-strength of 1.07 M.The variations in the rate of the oxidation with the hydrogen-ion concentrations are consistent with the reaction schemes involving two pH-related species; ascorbic acid H2A (k1=0.032 M-1 s-1 at 25 deg C, ΔH1=17 kJ mol-1, ΔS1=-220 J deg-1 mol-1) and the ascorbic anion HA- (k2=0.43 M-1 s-1 at 25 deg C, ΔH2=45 kJ mol-1, ΔS2=-102 J deg-1 mol-1).A relationship of log k2=-1.47+2.17 I1/2/(1+I1/2) is found with the ionic-strength (I) at 25 deg C.The reaction rate is greatly catalyzed by the presence of trace amounts of the copper(II) ion; the mechanisms of the copper(II)-catalyzed reaction are discussed.
- Kimura, Masaru,Kobayashi, Akiko,Boku, Keiko
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- Oxidation of Ascorbic Acid in the Presence of Nitrites
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We have shown that ascorbic acid in neutral aqueous media rather rapidly interacts with nitrite ions to form dehydroascorbic acid. If the acidity of solution is sufficiently high (pH value does not exceed much above ～7) and the nitrite concentration is of order of 0.05 M or more, the only mechanism of the reaction under aerobic conditions includes, as the first, rate-limiting reaction step, the nitrosation of ascorbic acid. A second-order reaction kinetics was observed in respect to protons, which determined a sharp acceleration of the ascorbic acid conversion when the acidity of the medium was raised. Hence, a suggestion can be drawn that the presence of nitrites in vegetables under acidic storage strongly increases the decay of vitamin C.
- Myshkin, Anatoli E.,Konyaeva, Vera S.,Gumargalieva, Klara Z.,Moiseev, Yuri V.
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- Controlled synthesis of graphene-Gd(OH)3 nanocomposites and their application for detection of ascorbic acid
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In this report, graphene-gadolinium hydroxide (GR-Gd(OH)3) nanocomposites have been prepared using the hydrothermal process. The crystalline structures of GR-Gd(OH)3 have been determined by X-ray diffraction (XRD) measurements and their morphologies have been revealed by field-emission scanning electron microscopy (FE-SEM) observations. The optical properties of GR-Gd(OH)3 have been examined by UV-vis and Fourier transform infrared (FTIR) measurements which revealed mutual interactions between GR and Gd(OH)3. GR-Gd(OH)3 was used to modify the glassy carbon electrode (GCE) which was subsequently utilized for electro-oxidation of ascorbic acid (AA) by cyclic voltammetry method. It was found that the electro-catalytic behavior of GCE modified by GR-Gd(OH)3 (GCE/GR-Gd(OH)3) was superior to that of the bare GCE. The catalytic oxidation peak current showed a linear dependence on the AA concentration and a linear calibration curve was obtained in the concentration range of 0.1-2.5 mM of AA with the lowest limit of detection (LOD) of 0.06 mM. Simultaneously, the oxidation peaks of AA over GCE/GR-Gd(OH)3 shifted to lower over potential compared to that of GCE modified by Gd(OH)3 (GCE/Gd(OH)3). The results indicate that GR-Gd(OH)3 can be used as a promising electrode modifier, which offers a new promising platform for application of the rare earth compound in electrochemistry and bioelectronics. Synchronously, the controlled synthesis of GR-Gd(OH)3 opens an efficient and facile strategy to design other GR-based, rare earth-containing nanocomposites.
- Ruan, Hong,Liu, Baoyong,Li, Hongguang
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- An efficient copper(III) catalyst in the four electron reduction of molecular oxygen by l-ascorbic acid
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The anionic [CuIII(LH-4)]- complex (L = 8,17-dioxa-1,2,5,6,10,11,14,15-octaaza-tricyclo[13.3.1] eicosane-3,4,12,13- tetrone) is one of the rare copper(III) compounds, which exhibits high stability in basic aqueous solution. This copper(III) compound catalyses the reduction of molecular oxygen by l-ascorbic acid at pH 7.97, in Tris-HCl buffer solution at the ionic strength of 0.1 M (NaCl). Stoichiometry of the reaction (2:1.07 for l-ascorbic acid:dioxygen) indicates formation of water and dehydroascorbic acid as primary products. Based on detailed kinetic measurements, the rate equation-d[AscH-]/dt = kobs[AscH-] 0.5[CuIII(LH-4)][O2]0.5 was obtained. The proposed mechanism includes a fast redox pre-equilibrium between the copper(III) centre and its reduced, copper(II) form, induced by the presence of l-ascorbate. The equilibrium constant K1′ at pH 8 (8.78 ± 3.11 × 10-3) and k values for the forward and backward reactions (1.18 ± 0.68 × 106 and 1.46 ± 0.82 × 108 M-2 s-1, respectively) were determined by stopped-flow technique, following the decrease in absorbance of the copper(III) form at 550 nm. In the presence of molecular oxygen, re-oxidation of the copper(II) form of the catalyst takes place, based on cyclic voltammetry (CV) measurements. The decrease of the Cu(II) → Cu(III) oxidation and the subsequent increase of the Cu(III) → Cu(II) reduction current peaks in the CV spectrum, when argon is exchanged to dioxygen atmosphere, indicate a relatively fast oxidation rate for [Cu II(LH-4)]2-. The determined ΔS ? (-41 ± 2 Jmol-1 K-1) for the catalytic reaction indicate an associative mechanism for the formation of the catalytically active copper-oxygen species that will react with the l-ascorbate to yield dehydroascorbate as product.
- Pap, József S.,Szywriel, ?ukasz,Rowińska-Zyrek, Magdalena,Nikitin, Konstantin,Fritsky, Igor O.,Koz?owski, Henryk
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- Effects of pre-micelles of anionic surfactant SDS on the electron transfer reaction between methylene blue and ascorbic acid
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The effect of pre-micellar cluster of the anionic surfactant sodium dodecyl sulphate (SDS) on the electron transfer reaction between methylene blue (MB) and ascorbic acid (AA) in dilute acid medium has been investigated in the temperature range 298–308?K. The reaction is first order each with respect to MB as well as AA. The reaction involves two parallel paths - one uncatalyzed and the other H+-catalyzed path resulting in the rate law, kobs?=?(k0?+?k1 [H+]) [AA] [MB]. Iodide ion has been found to have a specific accelerating effect on the reaction rate. The reaction appears to take place between undissociated AA molecule and MB+/HMB2?+ cation. Anionic surfactant SDS shows an inhibiting effect on the reaction rate in the pre-micellar region, ultimately leading to a limiting value. The inhibiting effect of SDS has been explained in terms of Piszkiewicz's co-operativity model. The co-operativity index (n) value varies from 1.45 to 1.76 in the studied temperature range. The values of KS (the dissociation constant of the pre-micelle), n and surfactant concentration lead to the fact that the electrostatic binding in the pre-micelle is reasonably strong and most of the MB molecules remain in the pre-micelle cluster before the electron transfer with AA takes place. The formation of pre-micelle is exothermic in nature and thus favored at lower temperature.
- Sen, Pratik K.,Mukherjee, Piyali,Pal, Biswajit
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- Mimicking horseradish peroxidase and oxidase using ruthenium nanomaterials
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Although important progress has been achieved for the study of noble metal-based enzyme-like catalysts, there are rare reports on the enzyme mimicking applications of ruthenium nanoparticles (Ru NPs). In this work, we investigated the horseradish peroxidase (HRP) and oxidase mimetic activity of Ru NPs. Mimicking HRP, Ru NPs could catalyze the oxidation of substrates 3,3,5,5-tetramethylbenzidine (TMB), o-phenylenediamine (OPD) and dopamine hydrochloride (DA) in the presence of exogenously added H2O2 to generate the products with blue, yellow and orange colors, respectively. We also report the first evidence that Ru NPs possess intrinsic oxidase-like activity, which could catalyze the oxidization of TMB and sodium l-ascorbate (NaA) by dissolved oxygen. The HRP-like and oxidase-like activities of Ru NPs were found to be related to the concentrations of Ru NPs. The catalytic mechanism was analyzed by electron spin resonance spectroscopy (ESR), which suggested that the enzyme mimicking activities of the Ru NPs might originate from their characteristic of accelerating electron transfer between substrates and H2O2 or O2. Our findings offer a better understanding of enzyme-mimicking Ru NPs and should provide important insights for future applications.
- Cao, Gao-Juan,Jiang, Xiumei,Zhang, Hui,Croley, Timothy R.,Yin, Jun-Jie
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- Solvent-induced hydrogen tunnelling in ascorbate proton-coupled electron transfers
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The over-the-barrier proton-coupled electron transfer interaction of an ascorbate monoanion with a hexacyanoferrate(III) ion in water entered into a tunnelling regime in water-1,4-dioxane, water-ethanol and water-acetonitrile mixed solvents.
- Karkovi?, Ana,Brala, Cvijeta Jakobu?i?,Pilepi?, Viktor,Ur?i?, Stanko
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- Potential antitumor activity of 2-O-α-D-glucopyranosyl-6-O-(2-pentylheptanoyl)-L-ascorbic acid
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Intravenous administration of high-dose ascorbic acid (AA) has been reported as a treatment for cancer patients. However, cancer patients with renal failure cannot receive this therapy because high-dose AA infusion can have side effects. To solve this problem, we evaluated the antitumor activity of a lipophilic stable AA derivative, 2-O-α-D-glucopyranosyl-6-O-(2-pentylheptanoyl)-L-ascorbic acid (6-bOcta-AA-2G). Intravenous administration of 6-bOcta-AA-2G suppressed tumor growth in colon-26 tumor-bearing mice more strongly than did AA, even at 1/10 of the molar amount of AA. Experiments on the biodistribution and clearance of 6-bOcta-AA-2G and its metabolites in tumor-bearing mice showed that 6-bOcta-AA-2G was hydrolyzed to 6-O-(2-propylpentanoyl)-L-ascorbic acid (6-bOcta-AA) slowly to yield AA, and the results suggested that this characteristic metabolic pattern is responsible for making the antitumor activity of 6-bOcta-AA-2G stronger than that of AA and that the active form of 6-bOcta-AA-2G showing antitumor activity is 6-bOcta-AA. In in vitro experiments, the oxidized form of 6-bOcta-AA as well as 6-bOcta-AA showed significant cytotoxicity, while the oxidized forms of ascorbic acid showed no cytotoxicity at all, suggesting that the antitumor activity mechanism of 6-bOcta-AA-2G is different from that of AA and that the antitumor activity is due to the reduced and oxidized form of 6-bOcta-AA. The findings suggest that 6-bOcta-AA-2G is a potent candidate as an alternative drug to intravenous high-dose AA.
- Miura, Kaori,Haraguchi, Misaki,Ito, Hideyuki,Tai, Akihiro
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- A novel dinuclear Schiff-base copper(II) complex modified electrode for ascorbic acid catalytic oxidation and determination
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A new dinuclear copper salicylaldehyde-glycine Schiff-base complex [Cu 2(Sal-Gly)2(H2O)2] was synthesized and structurally characterized. [Cu2(Sal-Gly)2(H 2O)2] crysta
- Zhang, Zhijun,Li, Xi,Wang, Chenggang,Zhang, Chaocan,Liu, Peng,Fang, Tingting,Xiong, Yan,Xu, Wenjing
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- The fabrication of an Ni6MnO8 nanoflake-modified acupuncture needle electrode for highly sensitive ascorbic acid detection
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The current work describes the use of a steel acupuncture needle as an electrode substrate in order to construct an Ni6MnO8 nanoflake layer-modified microneedle sensor for highly sensitive ascorbic acid detection. For the purpose of constructing the functionalized acupuncture needle, first, a carbon film was layered on the needle surface as the seed layer. Subsequently, a straightforward hydrothermal reaction-calcination process was employed for the growth of Ni6MnO8 nanoflakes on the needle to function as a sensing interface. Electrochemical investigations illustrated the fact that the Ni6MnO8 nanoflake-altered acupuncture needle electrode manifested outstanding efficiency toward the amperometric identification of ascorbic acid. In addition, the electrode manifested elevated sensitivity of 3106 μA mM-1 cm-2, detection limit of 0.1 μM, and a broad linear range between 1.0 μM and 2.0 mM. As demonstrated by the results, the Ni6MnO8 nanoflake-modified acupuncture needle constitutes a potentially fresh platform to construct non-enzymatic ascorbic acid sensors.
- Jia, Hongliang,Zhao, Jianwei,Qin, Lirong,Zhao, Min,Liu, Gang
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- Kinetics and mechanism of oxidation of L-ascorbic acid by platinum(IV) in aqueous acid medium
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The oxidation of l-ascorbic acid (H2A) by platinum(IV) in aqueous acid medium exhibits overall second-order kinetics, being first order with respect to each reactant. Increasing both hydrogen and chloride ion concentrations inhibits the rate. The stoichiometry involves reaction of one platinum(IV) ion with H2A to give dehydroascorbic acid. A reaction mechanism consistent with all the experimental observations is proposed.
- Soni,Sailani, Riya,Khandelwal,Sharma
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- Kinetic Investigation of the Reactions Connected to the System Ascorbate + O2 by Amperometric Detection of H2O2 at a Modified Platinum Electrode
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A Pt electrode modified by an electrochemically produced bilayer polymeric membrane [polypyrrole/poly(o-phenylenediamine)] entrapping the enzyme glucose oxidase proved able to detect (response time of few seconds) amperometrically (at +0.7 V vs Ag/AgCl) very low concentrations of hydrogen peroxide (micromolar range) in the presence of much higher amounts of ascorbate. The currents due to ascorbate, also electroactive at the given potential, were negligible under any conditions due to its almost complete rejection by the electrode-modifying membrane system. The very peculiar properties of the device setup were exploited to undertake a kinetic study of the reactions connected to the system ascorbate + 02, following the concentration of H2O2 produced in the reaction mixture at 27 °C, pH = 7. The reaction between ascorbate and H2O2 was also considered; however, different kinetic models based on the two consecutive reactions proved unable to fit the data. An investigation on the single processes by the same experimental approach was then undertaken, leading to two explanations for the inadequacy of simple kinetic models. First, the presence of metal ion traces in the reaction mixture proved to be responsible for the nonlinear dependence of the rate of both reactions on the ascorbate concentration: a mechanism involving the role of ascorbate-metal complexes as the reactants was hypothesized to explain this result. Second, the influence of the reactivity of dehydroascorbic acid, the product of ascorbate oxidation, on the kinetics was ascertained.
- Zambonin, Carlo G.,Losito, Ilario
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- Kinetics and mechanism of the reduction of sodium chlorite by sodium hydrogen ascorbate in aqueous solution at near neutral pH
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The reduction of chlorite ion by the hydrogen ascorbate ion in a neutral solution safely produces chlorine dioxide. The decrease in absorbance at 268 nm with the presence of dimethyl sulfoxide (DMSO) allows measurement of the ascorbate disappearance in the reaction with excess chlorite. The measured rate constant at 25 ± 0.02°C, 3.67 × 10-4 M DMSO, ionic strength 0.51 M (NaClO4), and in the presence of 3.32 × 10 -9 M ethylenediaminetetraacetic acid is 13.81 ± 1.30 M -1 s-1. Rate constant measurements over the range 15-35°C gave an Arrhenius activation energy of 75.51 ± 4.53 kJ mol-1. This result is the first reported determination of the kinetics of this reaction and is consistent with either electron- or oxygen-transfer mechanisms. Anomalously, reduction of chlorite results in its oxidation, because intermediate hypochlorite oxidizes chlorite.
- Curtin, Maria,Dwyer, Sean,Bukvic, Dino,Doona, Christopher J.,Kustin, Kenneth
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- Determination of dehydroascorbic acid in mouse tissues and plasma by using tris(2-carboxyethyl)phosphine hydrochloride as reductant in metaphosphoric acid/ethylenediaminetetraacetic acid solution
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Ascorbic acid (AA) has a strong anti-oxidant function evident as its ability to scavenge superoxide radicals in vitro. Moreover, AA is an essential ingredient for post-translational proline hydroxylation of collagen molecules. Dehydroascorbic acid (DHA), the oxidized form of AA, is generated from these reactions. In this study, we describe an improved method for assessing DHA in biological samples. The use of 35mM tris(2-carboxyethyl)-phosphine hydrochloride (TCEP) as a reductant completely reduced DHA to AA after 2 h on ice in a 5% solution of metaphosphoric acid containing 1mM ethylenediaminetetraacetic acid (EDTA) at pH 1.5. This method enabled us to measure the DHA content in multiple tissues and plasma of 6-weeks-old mice. The percentages of DHA per total AA differed markedly among these tissues, i.e., from 0.8 to 19.5%. The lung, heart, spleen and plasma had the highest levels at more than 10% of DHA per total AA content, whereas the cerebrum, cerebellum, liver, kidney and small intestine had less than 5% of DHA per total AA content. This difference in DHA content may indicate an important disparity of oxidative stress levels among physiologic sites. Therefore, this improved method provides a useful standard for all DHA determinations.
- Sato, Yasunori,Uchiki, Takayuki,Iwama, Mizuki,Kishimoto, Yuki,Takahashi, Ryoya,Ishigami, Akihito
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- Kinetic study of the oxidation of L-ascorbic acid by chromium (VI)
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The reaction between chromium (VI) and L-ascorbic acid has been studied by spectrophotometry in the presence of aqueous citrate buffers in the pH range 5.69-7.21. The reaction is slowed down by an increase of the ionic strength. At constant ionic strength, manganese(II) ion does not exert any appreciable inhibition effect on the reaction rate. The rate law found is r = Kpkr[Cr(VI)] [L-ascorbic acid] [H+]/(1 + Kp[H+]) where Kp is the equilibrium constant for protonation of chromate ion and kr is the rate constant for the redox reaction between the active forms of the oxidant (hydrogenchromate ion) and the reductant (L-hydrogenascorbate ion). The activation parameters associated with rate constant kr are Ea = 20.4 ± 0.9 kJ mol-1, ΔH≠ = 19 ± 0.9 kJ mol-1, and ΔS≠ = -152 ± 3 J K-1 mol-1. The reaction thermodynamic magnitudes associated with equilibrium constant Kp are ΔH0 = 16.5 ± 1.1 kJ mol-1 and ΔS0 = 167 ± 4J K-1 mol-1. A mechanism in accordance with the experimental data is proposed for the reaction.
- Perez-Benito,Arias
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- Glutathione depletion, pentose phosphate pathway activation, and hemolysis in erythrocytes protecting cancer cells from vitamin C-induced oxidative stress
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The discovery that oxidized vitamin C, dehydroascorbate (DHA), can induce oxidative stress and cell death in cancer cells has rekindled interest in the use of high dose vitamin C (VC) as a cancer therapy. However, high dose VC has shown limited efficacy in clinical trials, possibly due to the decreased bioavailability of oral VC. Because human erythrocytes express high levels of Glut1, take up DHA, and reduce it to VC, we tested how erythrocytes might impact high dose VC therapies. Cancer cells are protected from VC-mediated cell death when co-cultured with physiologically relevant numbers of erythrocytes. Pharmacological doses of VC induce oxidative stress, GSH depletion, and increased glucose flux through the oxidative pentose phosphate pathway (PPP) in erythrocytes. Incubation of erythrocytes with VC induced hemolysis, which was exacerbated in erythrocytes from glucose-6-phosphate dehydrogenase (G6PD) patients and rescued by antioxidants. Thus, erythrocytes protect cancer cells from VC-induced oxidative stress and undergo hemolysis in vitro, despite activation of the PPP. These results have implications on the use of high dose VC in ongoing clinical trials and highlight the importance of the PPP in the response to oxidative stress.
- Zhang, Zhuzhen Z.,Lee, Eunice E.,Sudderth, Jessica,Yue, Yangbo,Zia, Ayesha,Glass, Donald,Deberardinis, Ralph J.,Wang, Richard C.
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- A highly selective and simultaneous determination of ascorbic acid, uric acid and nitrite based on a novel poly-N-acetyl-l-methionine (poly-NALM) thin film
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This paper demonstrates the facile fabrication of an N-acetyl-l-methionine (NALM) polymer film on a glassy carbon electrode (GCE) by an electropolymerization technique. Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and electrochemical techniques such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to characterize the modified electrode. This poly-NALM/GCE not only exhibits strong electrocatalytic activity towards the oxidation of ascorbic acid (AA), uric acid (UA) and nitrite with a shift in oxidation potential towards the less positive side, but also enhances peak current responses at physiological pH (7.2) conditions. Further, the overlapped anodic voltammetric peaks of the three analytes on a bare GC electrode were well-resolved into their independent oxidation peaks at the poly-NALM/GC modified electrode with a peak separation of 160 and 590 mV for AA-UA and UA-nitrite, respectively. Under the optimal experimental conditions, the anodic peak currents of AA, UA and nitrite increased linearly within the concentration ranges 10-1000 μM, 1-600 μM and 1-500 μM with correlation coefficients of 0.990, 0.996 and 0.994, respectively. The detection limits are 0.97, 0.34 and 0.75 μM for AA, UA and nitrite ion, respectively (S/N = 3). The modified electrode was successfully utilized to determine AA, UA and nitrite ion simultaneously in real samples such as human urine and tap water samples.
- Kannan, Ayyadurai,Sivanesan, Arumugam,Kalaivani, Govindasamy,Manivel, Arumugam,Sevvel, Ranganathan
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- Efficient Two-Photon Fluorescence Nanoprobe for Turn-On Detection and Imaging of Ascorbic Acid in Living Cells and Tissues
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Ascorbic acid (AA) serves as a key coenzyme in many metabolic pathways, and its abnormal level is found to be associated with several diseases. Therefore, monitoring AA level in living systems is of great biomedical significance. In comparison with one-photon excited fluorescent probes, two-photon (TP) excited probes are more suitable for bioimaging, as they could afford higher imaging resolution with deeper imaging depth. Here, we report for the first time an efficient TP fluorescence probe for turn-on detection and imaging of AA in living cells and tissues. In this nanosystem, the negatively charged two-photon nanoparticles (TPNPs), which were prepared by modifying the silica nanoparticles with a two-photon dye, could adsorb cobalt oxyhydroxide (CoOOH) nanoflakes which carried positive charge by electrostatic force, leading to a remarkable decrease in their fluorescence intensity. However, the introduction of AA could induce the fluorescence recovery of the nanoprobe because it could reduce CoOOH into Co2+ and result in the destruction of the CoOOH nanoflakes. The nanosystem exhibits a high sensitivity toward AA, with a LOD of 170 nM observed. It also shows high selectivity toward AA over common potential interfering species. The nanoprobe possessed both the advantages of TP imaging and excellent membrane-permeability and good biocompatibility of the silica nanoparticles and was successfully applied in TP-excited imaging of AA in living cells and tissues.
- Meng, Hong-Min,Zhang, Xiao-Bing,Yang, Chan,Kuai, Hailan,Mao, Guo-Jiang,Gong, Liang,Zhang, Wenhan,Feng, Suling,Chang, Junbiao
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- Influence of regioisomerism on stability, formation kinetics and ascorbate oxidation preventive properties of Schiff bases derived from pyridinecarboxylic acids hydrazides and pyridoxal 5′-phosphate
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The reaction between pyridoxal 5′-phosphate and hydrazides of 2-,3-, and 4-pyridinecarboxylic acids were studied in aqueous solution. The stability constants as well as the rate constants of formation of hydrazones derived from nicotinic and picolinic acids hydrazides were determined experimentally at pH values of 1.9; 6.6; 7.0; and 7.4. Isoniazid was found to form the least stable Schiff bases with PLP at every studied pH value. In the acidic medium, nicotinic acid derivative forms the most stable hydrazone. In the pH range of 6.6-7.4, the stability of PLP-NH and PLP-PH hydrazones vary in the opposite way. The rate of PLP-INH and PLP-PH Schiff bases formation decreases significantly in the pH range of 6.6-7.4, while the k1 value of PLP-NH remains nearly constant. The PLP-INH, PLP-NH, and PLP-PH were isolated as solids and characterized by means of NMR, IR-spectroscopy and fluorimetry. The PLPPH compound was found to fluoresce stronger than two other Schiff bases either in the solid phase and the solution. The PLP-INH hydrazone forms the 1:1 coordination compound with copper(II) ions, which stability is lg K ~ 5. Despite the stability of Cu(II)-PLP-INH complex lower than that of Cu(II)-EDTA, Cu(II)-CA complexes, sodium ethylenediaminetetraacetate and citric acid are less effective in preventing the copper-mediated oxidation of ascorbate.
- Gamov,Kiselev,Aleksandriiskii,Sharnin
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- MECHANISM OF NITROSATION OF ASCORBIC ACID BY NITRITE IN NEUTRAL AQUEOUS MEDIA
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The main issues in nitrosation of ascorbic acid by the nitrite ion in aqueous media are discussed.Possible mechanisms of the reaction in aqueous media with different acidities are analyzed on the basis of available published data.The main kinetic characterisatics of nitrosation of ascorbic acid in neutral Tris-HCL and phosphate buffers were obtained, and they are interpreted with due regard for the possible active participation of buffer components in the reaction.
- Myshkin, A. E.,Konyaeva, V. S.,Gumargalieva, K. Z.,Moiseev, Yu. V.
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- Signal-enhanced liquid-crystal DNA biosensors based on enzymatic metal deposition
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No cloudiness with a silver lining: Deposition of metallic silver on a liquid-crystal substrate with attached DNA strands greatly alters the surface topology and induces a homeotropic-to-tiled transition of the LC molecules surrounding them, resulting in an obvious change in appearance from dark to birefringent (see picture; Ag: spheres). This enzymatic silver deposition is an excellent signal-enhancement strategy for LC optical amplification.
- Tan, Hui,Yang, Shengyuan,Shen, Guoli,Yu, Ruqin,Wu, Zhaoyang
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- Kinetics and mechanism of the oxidation of L-ascorbic acid by cis-diaqua cobalt(III) ammine complexes
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The kinetics of oxidation of L-ascorbic acid by cis-diaquacobalt(III) complexes, [CoL4(H2O)2]3+ (L4 = (NH3)4, (en)2 or tren; en = ethane-1,2-diamine, tren = tris(2-aminoethyl)amine] was studied as a fuction of pH, L-ascorbic acid concentration, temperature, ionic strength and methanol content of the solvent using stopped-flow and conventional spectrophotometry. The results indicated that only the ascorbate monoanion, HA-, is involved in the redox process with the cobalt(III) species. The rate constants for the [Co(tren)(H2O)2]3+ and [Co(tren)(H2O)(OH)]2+ species (k2 and k5) are 0.26 ± 0.09 and 1.25 ± 0.03 dm3 mol-1 s-1 respectively at 30°C, and the corresponding activation parameters are ΔH2? = 124 ± 9 kJ mol-1, ΔS2? = 137 ± 30 J K-1 mol-1 and ΔH5? = 82 ± 2 kJ mol-1, ΔS5? = 26 ± 6 J K-1 mol-1. The variations in the rate constants and thermodynamic parameters for the series of complexes is discussed. The Marcus cross-relationship for electron transfer has been applied to the redox process to confirm the outer-sphere mechanism and to estimate the self-exchange rate constant for the [CoL4(H2O)(OH)]2+/+ couple.
- Abdur-Rashid, Kamaluddin,Dasgupta, Tara P.,Burgess, John
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- Catalytic activity of thiacalix[4]arenetetrasulfonate metal complexes on modified anion-exchangers for ascorbic acid oxidation
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The catalysis of ascorbic acid (AsA) oxidation by anion-exchangers modified with metal complexes of thiacalix[4]arenetetrasulfonate (Me-TCAS[4] A-500, Me=Mn3+, Fe3+, Co3+, Ce 4+, Cu2+, Zn2+, Ni2+, and H 2) were investigated. Me-TCAS[4]A-500 (Me=Mn3+, Fe3+, Ce4+, and Cu2+) all exhibited the ability to catalyze the oxidative reaction of AsA to dehydroascorbic acid. However, in the presence of high concentrations of AsA, only Cu 2+-TCAS[4]A-500was capable of complete oxidation of the acid. Moreover, after six repeat uses, Cu2+-TCAS[4]A-500 maintained high and relatively constant catalytic activity. Prior treatment of glucose solutions with Cu2+-TCAS[4]A-500even in the presence of high AsA concentrations, enabled the satisfactory determination of glucose without interference by AsA. Cu2+-TCAS[4]A-500 will therefore be applicable as an artificial substitute for ascorbate oxidase, and may be useful as a means to eliminate AsA interference during the analysis of vital compounds such as glucose and uric acid.
- Odo, Junichi,Hirashima, Tomomi,Hayashida, Tomoko,Miyauchi, Asuka,Minemoto, Mami,Iuchi, Masato,Inoguchi, Masahiko
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- Elucidating the chemical and biochemical applications of Citrus sinensis-mediated silver nanocrystal
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Synthesis of nanoparticles using biodegradable source is safer and echo-friendly. Here, we describe the synthesis of polycrystalline silver nanocrystals using Citrus sinensis acting as both reducing and capping agents. After exposing the silver ions to orange extract, rapid reduction of silver ions led to the formation of stable silver nanocrystals due to the reducing and stabilizing properties of orange fruit juice. The synthesized silver nanocrystals were characterized using various analytical techniques like UV–vis spectroscopy, X-ray diffraction (XRD), dynamic light scattering (DLS), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The biochemical activity of the synthesized nanocrystals was studied in the light of affinity to bovine serum albumin using several biophysical methods like absorbance, fluorescence and circular dichroism spectroscopy. Cytotoxic activity of these nanocrystals was also studied against Hep-2 cell line using fluorescence microscopy. It was also found that the synthesized nanocrystals can sense mercuric ion down to 50 μM in the presence of a number of cations. Furthermore, we established that the silver nanoparticles can effectively catalyse the reduction of methylene blue by ascorbic acid. The present study will enrich our knowledge on the chemical and biochemical activities of green-synthesized silver nanocrystals.
- Siddiqui, Nurunnesa,Masum, Abdulla Al,Uddin, Md. Raihan,Mandal, Sukhendu,Sengupta, Mohana,Islam, Md. Maidul,Mukhopadhyay, Subrata
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- Mechanistic studies on oxidation of l-ascorbic acid by an oxo-bridged diiron complex in aqueous acidic media
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[Fe2(-O)(phen)4(H2O)2] 4+ (1) (Fig. 1, phen = 1,10-phenanthroline) equilibriates with [Fe2(-O)(phen)4(H2O)(OH)]3+ (2) and [Fe2(-O)(phen)4(OH)2]2+ (3) in aqueous solution in the presence of excess phen, where no phen-releasing equilibria from 1, 2 and 3 exist. 1 quantitatively oxidizes ascorbic acid (H2A) to dehydroascorbic acid (A) in the pH range 3.00-5.50 in the presence of excess phen, which buffers the reaction within 0.05 pH units and ensures complete formation of end iron product ferroin, [Fe(phen) 3]2+. The reactive species are 1, 2 and HA- and the reaction proceeds through an initial 1: 1 inner-sphere adduct formation between 1 and 2 with HA-, followed by a rate limiting outer-sphere one electron one proton (electroprotic) transfer from a second HA- to the ascorbate-unbound iron(III). The Royal Society of Chemistry 2007.
- Bhattacharyya, Jhimli,Das, Suranjana,Mukhopadhyay, Subrata
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- Sparks fly between ascorbic acid and iron-based nanozymes: A study on Prussian blue nanoparticles
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Herein we reported Prussian blue nanoparticles (PBNPs) possess ascorbic acid oxidase (AAO)- and ascorbic acid peroxidase (APOD)-like activities, which suppressed the formation of harmful H2O2 and finally inhibited the anti-cancer efficiency of ascorbic acid (AA). This newly revealed correlation between iron and AA could provide new insight for the studies of nanozymes and free radical biology.
- Zhang, Wei,Wu, Yang,Dong, Hai-Jiao,Yin, Jun-Jie,Zhang, Hui,Wu, Hao-An,Song, Li-Na,Chong, Yu,Li, Zhuo-Xuan,Gu, Ning,Zhang, Yu
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- Electrochemical Sensor Constructed Using a Carbon Paste Electrode Modified with Mesoporous Silica Encapsulating PANI Chains Decorated with GNPs for Detection of Ascorbic Acid
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In this work, an electrochemical sensor constructed using a carbon paste electrode (CPE), modified with mesoporous silica encapsulating polyaniline (PANI) decorated with gold nanoparticles (GNPs) for the detection of ascorbic acid (AA), was presented. First of all, PANI latex was synthesized by emulsion polymerization. Then, the acid-catalyzed sol–gel solutions of tetraethyl silicate (TEOS) was prepared in the presence of D-glucose, followed by encapsulation of previously prepared PANI latex into as-prepared sol-gel solution. Upon formation of silica frameworks, electroactive composite powder was obtained. Subsequently, the as-prepared composite powder was subjected to Soxhlet extraction to remove D-glucose and the final product was denoted as PM silica. On the other hand, PGM silica was obtained by immersing PM silica in 5?mL of 0.10?mM HAuCl4 solution for 6?h, which reduced the gold nanoparticles (GNPs) onto the surface of PANI chains located inside the nanochannels of wormhole-like mesoporous silica framework. The redox reactions that mediated between EB form of PANI and aqueous HAuCl4 solution were monitored and confirmed by FTIR spectra. The appearance of GNPs inside the PGM silica was characterized by TEM, XPS, XRD, and BET analyses. PGM silica was found to reveal higher redox capability as compared to that of PM silica based on the electrochemical CV studies. It should be noted that PGM silica-modified CPE was found to exhibit high sensitivity, a relatively low limit of detection, excellent sensing repeatability and a broader linear dynamic range for AA detection than those of bare CPE or PM silica-modified CPE. Moreover, A electrochemical sensor constructed from PGM silica-modified CPE was found to reveal better selectivity for a tertiary mixture of AA/DA/UA as compared to that of PM silica-modified CPE based on a series of studies of differential pulse voltammograms. In this work, the fabricated sensor showed reliable data in detecting AA in the tested commercially available products.
- Hsu, Sheng-Chieh,Cheng, Hsiao-Tung,Wu, Pei-Xuan,Weng, Chang-Jian,Santiago, Karen S.,Yeh, Jui-Ming
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- Purification of crude In(OH)3 using the functionalized ionic liquid betainium bis(trifluoromethylsulfonyl)imide
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The recovery of indium from a crude indium(iii) hydroxide using the ionic liquid betainium bis(trifluoromethylsulfonyl)imide, [Hbet][Tf2N], was investigated. Leaching and solvent extraction were combined in one step using the thermomorphic properties of the [Hbet][Tf2N]-H2O system. During leaching (80 °C) a homogeneous phase was formed. Upon lowering the temperature below the lower critical solution temperature (UCST), the dissolved metals distributed themselves between the two phases. The optimal leaching/extraction conditions were determined to be a leaching time of 3 hours at 80 °C in a 1:1 wt/wt [Hbet][Tf2N]-H2O mixture. Large separation factors (>100) between In(iii) and Al(iii), Ca(ii), Cd(ii), Ni(ii) and Zn(ii) were obtained implying an easy separation. Fe(iii), As(v) and Pb(ii) are co-extracted. The separation factor between indium and iron was improved to >1000 by addition of ascorbic acid to reduce Fe(iii) to Fe(ii). The stripping was done very efficiently by HCl solution. The ionic liquid was regenerated during the stripping step. By combining a prehydrolysis and hydrolysis step, indium(iii) hydroxide with a purity >99% was obtained.
- Deferm, Clio,Luyten, Jan,Oosterhof, Harald,Fransaer, Jan,Binnemans, Koen
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- Kinetics of oxidation of ascorbic acid and 1,4-dihydroxybenzene by semiquinone radical bound to ruthenium(II)
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In 40% (v/v) MeOH-H2O media, containing [H+] (0.001-0.038 mol dm-3), the semiquinone (sq) radical, bound to Ru(II) in [Ru(bpy)2(sq)]+ 1, oxidises ascorbic acid (H2A) to dehydroascorbic acid (A), and 1,4-dihydroxybenzene (H2Q) to p-benzoquinone (Q); 1 is itself reduced to [Ru(bpy)2(Hcat)]+ 2H. The reactions are centred at sq not Ru(II). The sq/cat couple in 1 is reversible and its E1/2 increases with increasing [H+]; rate of chemical reduction of 1 to 2H increases in parallel. Rate increases also with increasing mole percent of D2O in the solvent suggesting a preliminary protonation equilibrium producing 1H, in which a H+ binds to the π-electron cloud of Ru(II)-bound sq. Under the experimental conditions, the kinetically significant species are 1H, H2Q, H2A and HA-. The kinetic activity of HA- ion is only ≈200 times more than that of H2A. This testifies against a purely outer-sphere mechanism and suggests significant electronic interaction between the redox partners. Increased percentage of MeOH in the solvent decreases λmax for the LMCT band; reaction rate for ascorbic acid decreases in parallel.
- Ghosh, Debjani,Shukla, Atindra D.,Banerjee, Rupendranath,Das, Amitava
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- VALENCE CHANGE OF COPPER IN CATALYTIC OXIDATION OF L-ASCORBIC ACID BY MOLECULAR OXYGEN
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The copper(II) chloride-catalyzed oxidation of L-ascorbic acid (AA) by O2 was found to involve both the anaerobic oxidation of AA by copper(II) chloride and the reoxidation steps of copper(I) chloride by O2 in the catalytic cycle, by comparing the rate of copper(II)-catalyzed oxidation of AA by O2 (RAIIO) with those of anaerobic oxidation of AA by copper(II) (RAII) and oxidation of copper(I) by O2 (RIO).
- Ito, Sotaro,Yamamoto, Toshimasa,Tokushige, Yuji
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- Kinetic studies of the reactions of pentacyanoferrate(III) complexes with L-ascorbic acid
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The reduction of Fe(CN)5L2- (L = pyridine, isonicotinamide, 4.4′-bipyridine) complexes by ascorbic acid has been subjected to a detailed kinetic study in the range of pH 1-7.5. The rate law of the reaction is interpreted as a rate determining reaction between Fe(III) complexes and the ascorbic acid in the form of H2A(k0). HA-(k1), and A2- (k2), depending on the pH of the solution, followed by a rapid scavenge of the ascorbic acid radicals by Fe(III) complex. With given Ka1 and Ka2. the rate constants are k0 = 1.8, 7.0, and 4.4 M-1 s -1 ; k1 = 2.4 × 103. 5.8 × 10 3, and 5.3 × 103 M-1 s-1 ; k2 = 6.5 × 108, 8.8 × 108, and 7.9 × 108 M-1 s-1 for L = py, isn, and bpy, respectively, at μ = 0.10 M HClO4/LiClO4, T=25°C. The kinetic results are compatible with the Marcus prediction.
- Lin, L.U.-Ming,Lien, Ming-Huei,Yeh, Andrew
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- Highly sensitive and efficient voltammetric determination of ascorbic acid in food and pharmaceutical samples from aqueous solutions based on nanostructure carbon paste electrode as a sensor
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A square wave voltammetric method for the trace analysis of ascorbic acid was developed in this study. Carbon paste electrode was modified with NiO nanoparticle and 1-butyl-3-methylimidazolium tetrafluoroborate as a binder. Electro-oxidation behavior of ascorbic acid on the modified electrode was studied, which indicated that the nanostructure modified electrode could efficiently promote electrocatalytic oxidation of ascorbic acid. A fast, selective, high sensitive and simple electrochemical strategy was then developed for trace analysis of ascorbic acid using the constructed electrode. The catalytic oxidation signal exhibited a wide linear range from 0.08 to 380.0 μM toward the concentration of ascorbic acid with a sensitivity of 0.0158 μA/μM, and the limit of detection was as low as 0.04 μM. The suggested sensor was also used for quantitative determination of ascorbic acid in food and pharmaceutical samples.
- Pardakhty, Abbas,Ahmadzadeh, Saeid,Avazpour, Sanaz,Gupta, Vinod Kumar
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- Possible Formation of Dehydro-L-ascorbic Acid from 2,3-Diketo-L-gulonic Acid in an Aqueous Solution
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The reaction of 2,3-diketo-L-gulonic acid (DKG), which is one of the important intermediate products in the degradation of L-ascorbic acid (ASA) in both food and biological systems, in an aqueous solution was studied. The formation of a small amount of the γ-lactone, dehydro-L-ascorbic acid (DASA), from DKG was observed. This strongly suggests the chemical possibility of a reverse reaction in DASA hydrolysis which has been long believed to be irreversible.
- Miyake, Noriko,Kurata, Tadao
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- High Recovery of Selenium from Kesterite-Based Photovoltaic Cells
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The use of photovoltaic cells is constantly increasing and, in particular, a new generation of thin-film photovoltaic (PV) cells is under development. The absorber of these new cells, kesterite (CZT(S)Se), is composed of abundant chemical elements. Nonetheless, the development of the recycling process for these elements is indispensable for circular economy. This research is focused on the recovery of selenium by thermal oxidation and subsequent reduction. Thus, recycling of selenium has been firstly studied on synthetic kesterite and then validated in a real sample of kesterite extracted from glass-based PV cells. The best results were obtained in a vertical tubular furnace at 750 °C with an input of 20 mL/min of air. The posterior reduction process of selenium oxide was achieved by ascorbic acid, a common and economic reagent. Real kesterite was extracted from PV cells by thermal treatment at 90 °C for 1 hour to remove the encapsulant and ulterior treatment with HCl for the release of kesterite absorber. Optimal conditions from synthetic kesterite were applied to a real sample, recovering more than 90 % of selenium with a purity of 99.4 %.
- Abás, Elisa,Asensio, Maria Pilar,Laguna, Mariano,Pinilla, Jose Luis
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- Simultaneous voltammetric detection of six biomolecules using a nanocomposite of titanium dioxide nanorods with multi-walled carbon nanotubes
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In this proof-of-concept study, a novel nanocomposite of titanium dioxide nanorods with multi-walled carbon nanotubes (TiO2NRs-MWCNTs) was synthesized using a solvo-thermal method and characterized by transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FTIR). The nanocomposite of TiO2NRs-MWCNTs was utilized to modify the surface of a glassy carbon electrode (GCE) using 1.5% (v/v) Nafion solution for a proof-of-concept study to detect uric acid (UA), xanthine (XA), theophylline (TP) and theobromine (TB) in the presence of ascorbic acid (AA) and dopamine (DA). Simultaneous detection of these six biomolecules was performed using differential pulse voltammetry (DPV) in a wide potential window from -0.3 V to -1.6 V (vs. Ag/AgCl) at pH 4.0. The TiO2NRs-MWCNTs/GCE showed strong, stable and six simultaneous well-separated anodic peaks at 0.13, 0.35, 0.50, 0.85, 1.10 and 1.28 V for AA, DA, UA, XA, TP and TB, respectively. The calibration curves showed linearity to 191.0, 147.0, 537.0, 586.0, 893.0, 1653.0 μM with detection limits of 0.51, 0.06, 0.05, 0.09, 0.56 and 0.75 μM for AA, DA, UA, XA, TP and TB, respectively. The electrochemical performance of the TiO2NRs-MWCNTs/GCE displayed good reproducibility for simultaneous determination of six analytes. Finally, our preliminary results suggested that the TiO2NRs-MWCNTs/GCE can provide a promising platform for rapid quantitative detection of AA, DA, UA, XA, TP and TB in quality control studies of real samples such as pharmaceuticals and food products.
- Imran, Saim,Kerman, Kagan,Noroozifar, Meissam,Patel, Bhargav R.,Weng, Hanyi,Ye, Wanying
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- A novel polyoxometalate-based metal-organic nanotube framework templated by twin-Dawson clusters: Synthesis, structure and bifunctional electrocatalytic properties
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A novel polyoxometalate-based metal-organic framework templated by twin-Dawson clusters, [{Cu3(μ3-O)}2(trz)6Cu2(H2O)13][H1.73P2As1.73W16.27O62]·8.25H2O (1) (trz = 1,2,4-triazole), has been synthesized under hydrothermal conditions. In 1, there are two crystal distinct motifs: a 3D metal-organic nanotube framework and seven-connected Dawson clusters. It is worth mentioning that the 3D framework possesses nanotube-like channels. The twin-H1.73P2As1.73W16.27O62 clusters (abbreviated as P2(As/W)18 clusters) as templates occupy channels of the nanotube framework. To the best of our knowledge, this represents the first metal-organic nanotube framework templated by twin-Dawson clusters. The electrochemical experiments indicate that the 1-based glassy carbon electrode (1-GCE) possesses high catalytic efficiency and high stability toward reduction of inorganic bromate molecules and oxidation of the biological molecule ascorbic acid. The electrocatalytic efficiency towards the reduction of bromate in 1 M H2SO4 solution and oxidation of AA in N2 purged solution is ca. 848.4% and 896.8% (catalytic substrate: 0.5 mM), respectively. The current signal after 100 cycles exhibits almost no loss for 1-GCE.
- Lu, Borong,Li, Shaobin,Zhang, Xiaozhou,Zhang, Deqing,Fan, Linlin,Yan, Eryun,Zhang, Yongjuan,Yu, Liang
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p. 15804 - 15810
(2019/10/19)
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- MnO2 nanoparticle mediated colorimetric turn-off determination of ascorbic acid
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Ascorbic acid (AA) is an esstential micronutrient in the human body and participates in vital processes. It can only be supplemented by external intake, making the determination of AA in food or beverages of significance. In the present work, MnO2 nanoparticle (MnO2 NP) based turn-off colorimetry was established for AA determination on the basis of AA-stimulated inhibition of catalytic oxidation. MnO2 NPs were synthesized through a biotemplating method and displayed effective catalytic oxidation activity for oxidation of TMB, triggering a chromogenic reaction. Interestingly, the introduction of AA induced the decomposition of MnO2 NPs and as a consequence decreased the colour. Therefore, sensitive and selective turn-off colorimetry for AA detection was established and a satisfactory linear range of 0.5-30 μM with a detection limit of 0.28 μM was obtained. This MnO2 NP-based method was activated via a novel sensing principle, complementing and facilitating colorimetry for AA.
- Wang, Qi,Ma, Xulu,Lv, Houhua,Wei, Awen,Wu, Tingxuan,Ding, Lifeng,Ma, Xiang,Ma, Chunlei
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p. 381 - 386
(2020/01/09)
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- Ascorbate Oxidase Mimetic Activity of Copper(II) Oxide Nanoparticles
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Although oxidase mimetic nanozymes have been widely investigated, specific biological molecules have rarely been explored as substrates, particularly in the case of ascorbate oxidase (AAO) mimetic nanozymes. Herein, we demonstrate for the first time that copper(II) oxide nanoparticles (CuO NPs) catalyze the oxidation of ascorbic acid (AA) by dissolved O2 (as a green oxidant) to form dehydroascorbic acid (DHAA), thus functioning as a new kind of AAO mimic. Under neutral conditions, the Michaelis–Menten constant of CuO NPs (0.1302 mm) is similar to that of AAO (0.0840 mm). Furthermore, the robustness of CuO NPs is greater than that of AAO, thus making them suitable for applications under various conditions. As a demonstration, a fluorescence AA sensor based on the AAO mimetic activity of CuO NPs was developed. To obtain a fluorescent product, o-phenylenediamine (OPDA) was used to react with the DHAA produced by the oxidation of AA catalyzed by CuO NPs. The developed sensor was cost-effective and easy to fabricate and exhibited high selectivity/sensitivity with a wide linear range (1.25×10?6 to 1.125×10?4 m) and a low detection limit (3.2×10?8 m). The results are expected to aid in expanding the applicability of oxidase mimetic nanozymes in a variety of fields such as biology, medicine, and detection science.
- Chen, Wei,Deng, Hao-Hua,He, Shao-Bin,Hong, Guo-Lin,Hu, Ai-Ling,Peng, Hua-Ping,Zhuang, Quan-Quan
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- Tandem Functionalization in a Highly Branched Polymer with Layered Structure
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A hyperbranched polymer with multilayer structure was developed to demonstrate the possibility of highly efficient tandem functionalization reactions at different domains within one nanostructured platform. The polymer scaffold was constructed by chain-growth copper-catalyzed azide–alkyne cycloaddition polymerization of three functional monomers with sequential monomer addition in one pot. Subsequent reactions with different monomer units resulted in efficient functionalization of each segment with construction of a highly sophisticated polymer structure by a robust procedure. As a proof of concept, the ability of this polymer structure to quantitatively load six species of guest molecules through three different types of conjugation reactions was demonstrated.
- Cao, Xiaosong,Shi, Yi,Gan, Weiping,Gao, Haifeng
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supporting information
p. 5974 - 5981
(2018/03/26)
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- PdPt bimetallic alloy nanowires-based electrochemical sensor for sensitive detection of ascorbic acid
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One-dimensional (1D) bimetallic nanowire materials have attracted much more attention in electroanalysis because of their unique physical and chemical properties. In this work, we further extended the application field of the PdPt bimetallic alloy nanowires (PdPt BANWs) structure and successfully fabricated a novel PdPt BANWs-based electrochemical sensor for sensitive detection of ascorbic acid (AA). It was found that the PdPt BANWs on the electrode exhibited remarkable electrocatalytic activity toward AA oxidation and could be used for sensitive detection of AA in a wide linear range (0.01-0.97 mM) with a high sensitivity of 467.9 μA mM-1 cm-2. The detection limit is as lower as 0.2 μM (S/N = 3). Moreover, the electrochemical sensor also exhibited good selectivity, reproducibility and stability, and had been successfully applied to detection of AA in serum samples and commercial vitamin C tablets with satisfactory results.
- Jin, Lihua,Zhang, Zaihua,Zhuang, Zhihua,Meng, Zheng,Li, Cong,Shen, Yehua
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p. 42008 - 42013
(2016/05/19)
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- Catalytic Light-Driven Generation of Hydrogen from Water by Iron Dithiolene Complexes
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The development of active, robust systems for light-driven hydrogen production from aqueous protons based on catalysts and light absorbers composed solely of earth abundant elements remains a challenge in the development of an artificial photosynthetic system for water splitting. Herein, we report the synthesis and characterization of four closely related Fe bis(benzenedithiolate) complexes that exhibit catalytic activity for hydrogen evolution when employed in systems with water-soluble CdSe QDs as photosensitizer and ascorbic acid as a sacrificial electron source under visible light irradiation (520 nm). The complex with the most electron-donating dithiolene ligand exhibits the highest activity, the overall order of activity correlating with the reduction potential of the formally Fe(III) dimeric dianions. Detailed studies of the effect of different capping agents and the extent of surface coverage of these capping agents on the CdSe QD surfaces reveal that they affect system activity and provide insight into the continued development of such systems containing QD light absorbers and molecular catalysts for H2 formation.
- Lv, Hongjin,Ruberu, T. Purnima A.,Fleischauer, Valerie E.,Brennessel, William W.,Neidig, Michael L.,Eisenberg, Richard
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p. 11654 - 11663
(2016/10/07)
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- Generation of hydrogen peroxide and hydroxyl radical resulting from oxygen-dependent oxidation of l-ascorbic acid via copper redox-catalyzed reactions
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The generation of hydrogen peroxide (H2O2) and hydroxyl radical (HO?) during the oxidation of l-ascorbic acid (l-AA) by oxygen with copper as a catalyst was investigated to set up the O2/Cu/l-AA process with benzoic acid (BA) as a probe reagent. The high concentration of H2O2 that is generated undergoes an intramolecular two-electron transfer and is further activated by the intermediate cuprous copper [Cu(i)] to yield HO? as a product, resulting in significant degradation of BA. Dehydroascorbic acid, 2,3-diketogulonic acid, and l-xylosone were the predominant detected products of the oxidation of l-AA. However, the generation of H2O2 and degradation of BA were regulated by variations in pH, which results from the contradiction between protonated l-AA that is difficult to chelate with Cu(ii) via electron transfer and hydrogen ions (H+), which are indispensable for the generation of H2O2. Furthermore, the concentration of H2O2 and degradation of BA increased with an increase in the dosage of l-AA. Trace amounts of Cu(ii) are effective for catalyzing the oxidation of l-AA, whereas the generation of H2O2 and degradation of BA increased with an increase in the dosage of Cu(ii). Owing to the formation of Cu(i) chloride complexes or Cu(ii) chloride complexes, the addition of chloride (Cl-) could inhibit the generation of H2O2 and degradation of BA.
- Zhou, Peng,Zhang, Jing,Zhang, Yongli,Liu, Ya,Liang, Juan,Liu, Bei,Zhang, Wei
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p. 38541 - 38547
(2016/06/01)
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- NiCo-embedded in hierarchically structured N-doped carbon nanoplates for the efficient electrochemical determination of ascorbic acid, dopamine, and uric acid
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The development of a highly stable and efficient catalyst for sluggish electrooxidation in the electro-determination for ascorbic acid (AA), dopamine (DA) and uric acid (UA) is extremely important for the long-term operation and commercialization of a biosensor device, but it remains a challenge. Herein, we demonstrated an interesting structure of NiCo alloy nanocrystals embedded in hierarchically structured N-doped carbon nanoplates (NiCo-NPs-in-N/C), which is facilely synthesized via a one-step in situ reduction pyrolysis strategy. The two-dimensional N-doped porous carbon shells not only offered the effective confinement effect of NiCo nanocrystals avoiding detachment, dissolution, migration, and aggregation during catalysis process, but also allowed a fast transport pathway for the access of electrolyte to the NiCo surface. As a result, such an intriguing structure shows superior catalytic activity towards the electrooxidation of AA, DA, and UA. The well-separated voltammetric peaks between AA-DA, DA-UA, and AA-UA at the NiCo-NPs-in-N/C are up to 178, 122, and 300 mV, respectively, which is much better than graphene@N-doped carbon core@shell nanoplate (graphene@N/C) and NiCo alloy. Furthermore, the NiCo-NPs-in-N/C also exhibits good reproducibility and stability. The attractive features of NiCo-NPs-in-N/C make it a promising electrocatalyst for the simultaneous determination of AA, DA, and UA.
- Zhang, Xianglan,Yan, Wenfu,Zhang, Jianan,Li, Yuanyuan,Tang, Wanyu,Xu, Qun
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p. 65532 - 65539
(2015/08/18)
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- Nitric Oxide Is Reduced to HNO by Proton-Coupled Nucleophilic Attack by Ascorbate, Tyrosine, and Other Alcohols. A New Route to HNO in Biological Media?
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The role of NO in biology is well established. However, an increasing body of evidence suggests that azanone (HNO), could also be involved in biological processes, some of which are attributed to NO. In this context, one of the most important and yet unanswered questions is whether and how HNO is produced in vivo. A possible route concerns the chemical or enzymatic reduction of NO. In the present work, we have taken advantage of a selective HNO sensing method, to show that NO is reduced to HNO by biologically relevant alcohols with moderate reducing capacity, such as ascorbate or tyrosine. The proposed mechanism involves a nucleophilic attack to NO by the alcohol, coupled to a proton transfer (PCNA: proton-coupled nucleophilic attack) and a subsequent decomposition of the so-produced radical to yield HNO and an alkoxyl radical. (Graph Presented).
- Suarez, Sebastián A.,Neuman, Nicolás I.,Mu?oz, Martina,álvarez, Lucía,Bikiel, Damián E.,Brondino, Carlos D.,Ivanovi?-Burmazovi?, Ivana,Miljkovic, Jan Lj.,Filipovic, Milos R.,Martí, Marcelo A.,Doctorovich, Fabio
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supporting information
p. 4720 - 4727
(2015/04/27)
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- Biomimetic aerobic oxidative hydroxylation of arylboronic acids to phenols catalysed by a flavin derivative
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Flavin-catalysed oxidative hydroxylation of substituted arylboronic acids by molecular oxygen with the assistance of hydrazine or ascorbic acid resulted in phenols in high yields. This mild organocatalytic protocol is compatible with a variety of functional groups and it is alternatively usable for transformation of alkylboronic acids to alcohols. Reaction takes place also in water and fulfils criteria for a green procedure.
- Kotoucova, Hana,Strnadova, Iveta,Kovandova, Martina,Chudoba, Josef,Dvorakova, Hana,Cibulka, Radek
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supporting information
p. 2137 - 2142
(2014/03/21)
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- Simultaneous determination of ascorbic acid, dopamine, uric acid, and tryptophan by nanocrystalline ZSM-5 modified electrodes
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Nanocrystalline ZSM-5 was prepared by using propyltriethoxysilane as an additive in the conventional ZSM-5 synthesis composition. Materials were characterized by a complementary combination of X-ray diffraction, nitrogen sorption, and Scanning electron microscopy. Transition metal ion exchanged nanocrystalline ZSM-5 (M-Nano-ZSM-5, where M = Cu2+, Ni2+, Co2+, Fe2+, and Mn2+) modified electrodes were constructed for the simultaneous determination of ascorbic acid (AA), dopamine (DA), uric acid (UA), and tryptophan (Trp). Electrochemical studies were carried out by using cyclic voltammetry, linear sweep voltammetry, and chronoamperometry in buffer solution at pH 3.5. Fe-Nano-ZSM-5 modified electrode exhibited excellent electrocatalytic activity with wellseparated oxidation peaks towards AA, DA, UA, and Trp in their simultaneous determination. Among the M-Nano-ZSM-5 and transition metal ion-exchanged ZSM-5 (M-ZSM-5) materials investigated in this study, Fe-Nano-ZSM-5 exhibited the highest catalytic activities towards the oxidation of AA, DA, UA, and Trp with good stability, sensitivity, and selectivity. The analytical performance of this sensor was demonstrated for the simultaneous determination of AA, DA, UA, and Trp in blood serum and UA concentration in urine samples.
- Kaur, Balwinder,Srivastava, Rajendra
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p. 6539 - 6550
(2015/01/09)
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- Catalytic oxidation of ascorbic acid via copper-polypyridyl complex immobilized on glass
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A monolayer of redox-active copper-polypyridyl complexes was prepared on glass and silicon substrates. The monolayer was characterized in detail by a combination of complementary surface analysis techniques. The immobilized complex was utilized for catalytic oxidation of ascorbic acid. The surface bound catalyst was found to be temporally and thermally stable, efficient, as well as partially recyclable. It also showed marked improvement over the performance of the same complex under homogeneous conditions, in terms of the catalytic activity and turnover numbers. Such supported catalyst systems are drawing significant attention as they enable merging of the virtues of homogeneous and heterogeneous catalysis.
- Singh, Vikram,Mondal, Prakash Chandra,Chhatwal, Megha,Jeyachandran, Yekkoni Lakshmanan,Zharnikov, Michael
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p. 23168 - 23176
(2014/06/24)
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- Reactivity of a Ru(iii)-hydroxo complex in substrate oxidation in water
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A mononuclear RuIII-OH complex oxidizes substrates such as hydroquinones in water through a pre-equilibrium process based on adduct formation by hydrogen bonding between the RuIII-OH complex and the substrates. The reaction mechanism switches from hydrogen atom transfer to electron transfer depending on the oxidation potential of substrates. This journal is
- Ohzu, Shingo,Ishizuka, Tomoya,Kotani, Hiroaki,Kojima, Takahiko
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supporting information
p. 15018 - 15021
(2015/02/19)
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- Time resolved growth of membrane stabilized silver NPs and their catalytic activity
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Formation of highly stable metal nanostructures in a Nafion membrane with various aspect ratios has been of considerable research interest in recent years. However, there is a need for a proper understanding of the growth mechanism of such nanostructures in Nafion (sometimes larger than the size of water-sulfonate ionic clusters of the membrane). In this work, the early growth kinetics of silver nanoparticles (NPs) in Nafion-117 ion-exchange membrane during in situl-ascorbic acid reduction of Ag+ ions by time resolved in situ small-angle X-ray scattering (SAXS) using synchrotron radiation with a time resolution of 50 ms are revealed for the first time. The SAXS analyses, corroborated by transmission electron microscopy, showed that the sizes of NPs increase rapidly together with their number density until they attain a certain size that could be accommodated in the ～5 nm water-sulfonate ionic clusters. Further growth takes place either by self-agglomeration of the particles ejected out from the water-sulfonic acid clusters or by continuous reduction of metal ions on the existing NP surfaces (uniformly or on a specific plane) leading to formation of bigger nanostructures with various aspect ratios. The time resolved information of NP growth provides an opportunity for the controlled synthesis of metal NPs with a definite size, shape and size distribution for a specific application. The catalytic properties of Ag NPs formed in the membrane were examined using borohydride reduction of a model dye methylene blue. It was observed that smaller Ag NPs with a mean diameter ～3 nm, confined in the hydrophilic clusters of the Nafion matrix, have reasonably good catalytic activity and a lower lag time for the onset of reduction. This journal is
- Patra, Sabyasachi,Sen, Debasis,Pandey, Ashok K.,Bahadur,Mazumder,Ramagiri, Shobha V.,Bellare, Jayesh R.,Roth,Santoro,Yu,Goswami
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p. 59379 - 59386
(2015/02/19)
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- Kinetics and mechanism of oxidation of l -ascorbic acid by peroxomonophosphate in aqueous acid medium
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The kinetics of oxidation of l-ascorbic acid (H2A) by peroxomonophosphate in acid aqueous medium has been studied. The stoichiometry of the reaction corresponds to the reaction as represented by the equation where A is dehydroascorbic acid. The reaction is second order versus first order with respect to each reactant. The rate is retarded by hydrogen ion concentration. A plausible reaction mechanism has been suggested. The derived rate law (2) from such a mechanism accounts for all experimental observations: Such pH dependence is somewhat different from that observed in the case of metal ion oxidants.
- Soni, Narendra K.,Sailani, Riya,Khandelwal,Sharma
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- The kinetics of redox reaction of gold(III) chloride complex ions with l-ascorbic acid
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The synthesis of gold nanoparticles consists of several stages, i.e. reduction, nucleation and growth. The most important step in particles formation process is the reduction reaction of Au(III) ions to Au(I). The rate of such reaction determines the rate of nuclei formation, i.e. reduction reaction of Au(I) to Au(0) and thus the rate of nanoparticles formation. In this paper, the kinetics and mechanism of redox reaction between gold(III) chloride complex ions and l-ascorbic acid in the aqueous solution have been carried out using spectrophotometric technique. From the experimentally obtained kinetic curves the rate constants of reaction at different conditions of initial concentrations of reactants, pH, temperature, ionic strength and concentration of chloride ions, were determined. It was found that in strong acidic solution (pH 1.3), the values of enthalpy (ΔH?) and entropy (ΔS ?) of activation were 38.5 kJ/mol and -89.5 kJ/mol K, respectively and at higher pH (pH 2.5) the values of ΔH? and ΔS? were 42.0 kJ/mol and -64.5 kJ/mol K, respectively. Using obtained results, the kinetic equation was determined and corresponding mechanism of reaction was suggested. Obtained data can be useful for calculating time of nuclei formation and consequently for better size control and size distribution of particles, e.g. in a microreactor.
- Luty-B?ocho, Magdalena,Pac?awski, Krzysztof,Wojnicki, Marek,Fitzner, Krzysztof
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p. 189 - 196
(2013/06/05)
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- Synthesis of highly stable dispersions of nanosized copper particles using l-ascorbic acid
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Highly stable dispersions of nanosized copper particles with an average particle size less than 2 nm were synthesized using a straightforward, cost-effective, and green method. Nontoxic l-ascorbic acid was utilized as both a reducing agent and capping agent precursor in aqueous medium. The copper particles were characterized by ultraviolet-visible spectroscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy The mechanism of l-ascorbic acid on the reduction and stabilization of copper nanoparticles is also discussed. The Royal Society of Chemistry.
- Xiong, Jing,Wang, Ye,Xue, Qunji,Wu, Xuedong
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experimental part
p. 900 - 904
(2011/06/19)
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- A biomimetic synthesis of (-)-ascorbyl phloroglucinol and studies toward the construction of ascorbyl-modified catechin natural products and analogues
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A method for appending the ascorbyl moiety onto the framework of phenolic natural products has been developed. This reaction proceeds in two steps from l-ascorbic acid and employs acetic acid catalysis. Excellent stereoselectivity is observed during C-C b
- Belapure, Sneha A.,Beamer, Zachary G.,Bartmess, John E.,Campagna, Shawn R.
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experimental part
p. 9265 - 9272
(2011/12/03)
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- Development of submillisecond time-resolved mass spectrometry using desorption electrospray ionization
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Reaction kinetics studied by mass spectrometry (MS) has previously been limited to millisecond time resolution. This paper presents the development of a submillisecond time-resolved mass spectrometric method for fast reaction kinetic study, based on the capability of desorption electrospray ionization (DESI) for direct and fast ionization of a high-speed liquid jet stream. The principle underlying this methodology is that two reactant solutions undergo rapid mixing to produce a free liquid jet which is ionized by DESI at different positions corresponding to different reaction times. Due to the high velocity of the liquid jet, high time resolution can be achieved. In this study, the fast reduction reaction of 2, 6-dichlorophenolindophenol (DCIP) and l-ascorbic acid (L-AA) was chosen as an example to demonstrate this concept, and the reaction rate constant was successfully measured with an unprecedented time resolution of 300 μs. The good agreement of the measured value of (116 ± 3) s -1 with that measured by the stopped-flow optical method (105 ± 2) s-1 validates the feasibility of such a DESI-MS approach. Unlike classical spectroscopic techniques that require either chromophoric substrates or labeling, MS is a general detector with high chemical specificity. Therefore, this time-resolved DESI-MS method should find wide applications in fast (bio)chemical reaction investigations.
- Miao, Zhixin,Chen, Hao,Liu, Pengyuan,Liu, Yan
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experimental part
p. 3994 - 3997
(2012/01/14)
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- Enzymatic activity and thermal stability of metallo proteins in hydrated ionic liquids
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Hydrated choline dihydrogen phosphate (Hy[ch][dhp]) containing 30 wt% water was investigated as a novel protein solvent. The Hy[ch][dhp] dissolved some metallo proteins (cytochrome c, peroxidase, ascorbate oxidase, azurin, pseudoazurin and fructose dehydrogenase) without any modification. These proteins retained the surroundings of the active site after dissolution in Hy[ch][dhp]. Some metallo proteins were found to retain their activity in the Hy[ch][dhp].
- Fujita, Kyoko,Ohno, Hiroyuki
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experimental part
p. 1093 - 1099
(2011/12/16)
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- Application of enzyme labeled antibodies for immunosensors based on electrochemical detection
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In this paper, immunosensors based on electrochemical (potentiometric and amperometric) detection are presented. We developed ISFET type potentiometric immunosensor with urease as a label and a screen-printed amperometric immunosensor with alkaline phosphatase, utilizing ascorbic acid phosphate as a substrate. For the free alkaline phosphatase in concentration range 35-3500 pM, the response of amperometric sensors was at the level from 10 to 80 μA. It was stated that the potentiometric immunosensors can be applied for measurements of the total γ-globulin concentration or for detection of the selected IgG in concentration range 1.37 mg/L-4 g/L.
- Kazimierczak,Pijanowska,Torbicz
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p. 1255 - 1263
(2008/12/20)
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