490-83-5Relevant articles and documents
Kinetics of oxidation of ascorbate by tetranuclear cobalt(III) complexes ('hexols') in aqueous solution
Abdur-Rashid, Kamaluddin,Dasgupta, Tara P.,Burgess, John
, p. 1393 - 1398 (1996)
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.
Nanostructured membranes for enzyme catalysis and green synthesis of nanoparticles
Smuleac, Vasile,Varma, Rajender,Baruwati, Babita,Sikdar, Subhas,Bhattacharyya, Dibakar
, p. 1773 - 1777 (2011)
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.
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
Sailani, Riya,Dubey, Sapna,Khandelwal,Sharma,Khan, Perveen
, p. 1088 - 1094 (2011)
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].
A new method for thermal analysis: Ion-attachment mass spectrometry (IAMS)
Fujii, Toshihiro
, p. 17 - 25,9 (2012)
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.
Characterizing homogeneous chemistry using well-mixed microeddies
Lutz, Barry R.,Chen, Jian,Schwartz, Daniel T.
, p. 1606 - 1612 (2006)
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.
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
Tsukahara, Keiichi,Wada, Yuuko,Kimura, Masaru
, p. 908 - 915 (1991)
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.
L-Galactono-γ-lactone dehydrogenase activity and vitamin C content in fresh-cut potatoes stored under controlled atmospheres
Tudela, Juan Antonio,Hernandez, Jose Antonio,Gil, Maria Isabel,Espin, Juan Carlos
, p. 4296 - 4302 (2003)
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.
Kinetic study of the oxidation of ascorbic acid by aqueous copper(II) catalysed by chloride ion
Sisley, Margaret J.,Jordan, Robert B.
, p. 3883 - 3888 (1997)
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).
Conducting polyaniline-graphene oxide fibrous nanocomposites: Preparation, characterization and simultaneous electrochemical detection of ascorbic acid, dopamine and uric acid
Manivel,Dhakshnamoorthy,Balamurugan,Ponpandian,Mangalaraj,Viswanathan
, p. 14428 - 14437 (2013)
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.
Kinetic Studies of the Oxidation of L-Ascorbic Acid by the Peroxodisulfate Ion, and of Copper(II)-catalysis
Kimura, Masaru,Kobayashi, Akiko,Boku, Keiko
, p. 2068 - 2073 (1982)
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.
