15438-31-0Relevant academic research and scientific papers
Anaerobic Oxidation of Cysteine to Cystine by Iron(III). Part 2. The Reaction in Basic Solution
Jameson, Reginald F.,Linert, Wolfgang,Tschinkowitz, Axel
, p. 2109 - 2112 (1988)
The anaerobic oxidation of cysteine to cystine (H2L) by iron(III) has been followed over the pH range 8.2-11.6 by use of a stopped-flow high-speed spectrophotometric method (the results obtained below pH 8.6, however, were not reproducible and no attempt was made to establish a rate law over this range).Between pH 8.6 and 11.2 the experimental data were accurately reproduced by assuming that the bis-cysteine complex, 2-, reacts with the mono-cystein complex, , to yield two iron(II) ions, one cystine, and an unoxidised cysteine with a second-order rate constant of 8.36 x 1E3 dm3mol-1s-1.The predominant complex species present in solution is the purple 2- which exhibits an absorption maximum at 545 nm (shoulder at 445 nm) and has a molar absorption coefficient of 3175 dm3mol-1cm-1.The other complex present is also purple and is .The absorption spectrum of this species (obtained over the pH range 5.5-8.0) exhibits a maximum at 503 nm (shoulder at 575 nm) and has a molar absorption coefficient of 1640 dm3mol-1cm-1.The kinetic results were also used to calculate values of this first and second protonation constant for cysteine (log KH1 = 10.34, log KH2 = 8.32) which compare very favourably with previously published values (obtained by potentiometric titration).Finally, a value of log KM2 = 4.76 for the reaction + L2- 2- was also extracted from the kinetic data.All measurements were carried out at 25 deg C in solution of ionic strength 0.10 mol dm-3 (KCl).
Colorimetric studies of the reduction of Fe3+ by coal
Martin,Li,MacPhee
, p. 1970 - 1973 (1993)
The reduction of Fe3+ by coal surfaces has been followed colorimetrically. The kinetics of the reaction in coals with a relatively high O/C ratio are sensitive to mild air oxidation, those having a low O/C ratio are relatively insensitive.
A naphthalene derived Schiff base as a selective fluorescent probe for Fe2+
Santhoshkumar,Velmurugan,Prabhu,Radhakrishnan,Nandhakumar
, p. 1 - 7 (2016)
A naphthalene pyridine Schiff base 1 as a fluorescent chemosensor was developed for the detection of Fe2+ ions in CH3CN-H2O solution. Its binding properties toward various other heavy and transition metal ions including Fe3+ ions were examined. The sensor showed high selectivity and sensitivity towards Fe2+ ions in aqueous media with the lower detection limit of 1.5 × 10-7 M. The fluorescence "turn-on" recognition process follows the ICT process and C=N isomerisation. In addition, determination of Fe2+ in a variety of samples were analyzed which includes commercially available tablets, tomato juice, dark chocolate and tap water.
Reactivity of metal oxides: Thermal and photochemical dissolution of MO and MFe2O4 (M=Ni, Co, Zn)
Garcia Rodenas, Luis A.,Blesa, Miguel A.,Morando, Pedro J.
, p. 2350 - 2358 (2008)
Dissolution rates of NiO, CoO, ZnO, α-Fe2O3 and the corresponding ferrites in 0.1 mol dm-3 oxalic acid at pH 3.5 were measured at 70 °C. The dissolution of simple oxides proceeds through the formation of surface metal oxalate complexes, followed by the transfer of surface complexes (rate-determining step). At constant pH, oxalate concentration and temperature, the trend in the first-order rate constant for the transfer of the surface complexes (kMe; Me=Ni, Co, Zn, Fe) parallels that of water exchange in the dissolved metal ions (k-w). Thus, the most important factor determining the rates of dissolution of metal oxides is the lability of Me-O bonds, which is in turn defined by the electronic structure of the metal ion and its charge/radius ratio. UV (384 nm) irradiation does not increase significantly the dissolution rates of NiO, CoO and ZnO, whereas hematite is highly sensitive to UV light. For ferrites, the reactivity order is ZnFe2O4>CoFe2O4?NiFe2O4. Dissolution is congruent, with rates intermediate between those of the constituent oxides, Fe2O3 and MO (M=Co, Ni, Zn), reflecting the behavior of very thin leached layers with little Zn and Co, but appreciable amounts of Ni. The more robust Ni2+ labilizes less the corresponding ferrite. The correlation between log kM and log k-w is somewhat blurred and displaced to lower kM values. Fe(II), either photogenerated or added as salt, enhances the rate of Fe(III) phase transfer. A simple reaction mechanism is used to interpret the data.
Calorimetric studies on leaching of mechanically activated sphalerite in FeCl3 solution
Xiao, Zhongliang,Chen, Qiyuan,Yin, Zhoulan,Hu, Huiping,Zhang, Pingmin
, p. 5 - 9 (2004)
The thermal behaviors of the leaching of mechanically activated sphalerite were investigated for the first time by calorimetry. The specific granulometric surface area and the structural disorder sphalerite were also analyzed by X-ray diffraction laser particle size analyzer and X-ray powder diffraction (XRD) analysis, respectively. A new method to measure the mechanically activated storage energy of minerals was proposed by designing a thermochemical cycle that made mechanically activated and non-activated mineral reaching the same final state while leaching in FeCl3 solution. The results indicate that the mechanically activated storage energy of sphalerite rises with the increased grinding time and is closely related to the lattice distortions and crystallite sizes. The calorimetric results of the products from sieved in water or ethanol medium and the products from 2 h treatment of mechanically activated sphalerite under pure argon (99.99 vol.%) at different temperatures indicate that the mechanically activated storage energy of sphalerite is caused mainly by changes of the crystal structure, and the reactivity of mechanically activated sphalerite is difficult to lose.
Release of NO from reduced nitroprusside ion. Iron-dinitrosyl formation and NO-disproportionation reactions
Roncaroli, Federico,Van Eldik, Rudi,Olabe, Jose A.
, p. 2781 - 2790 (2005)
The kinetics and mechanism of the thermal decomposition of the one-electron reduction product of [Fe(CN)5NO]2- (nitroprusside ion, NP) have been studied by using UV-vis, IR, and EPR spectroscopy and mass-spectrometric and electrochemical techniques in the pH range of 4-10. The reduction product contains an equilibrium mixture of [Fe(CN)4NO] 2- and [Fe(CN)5NO]3- ions. The first predominates at pH 5NO]3-, which, in turn, is the main component at pH >9-10. Both nitrosyl complexes decay by first-order processes with rate constants around 10-5 s-1 (pH 6-10) related to the dissociation of NO. The decomposition is enhanced at pH 4 by 2 orders of magnitude with protons (and also metal ions) favoring the release of cyanides from the [Fe(CN)4NO]2- ions and the ensuing rapid delivery of NO. At pH 7, an EPR-silent intermediate I1 is detected (VNO, 1695 and 1740 cm-1) and assigned to the trans-[FeII(CN) 4(NO)2]2- ion, an {Fe-(NO)2} 8 species. At pH 6-8, I1 induces a disproportionation process with formation of N2O and the regeneration of nitroprusside in a 1:2 molar ratio. At lower pHs, I1 leads, competitively, to a second paramagnetic (S = 1/2) dinitrosyl intermediate I2, [Fe(CN)2(NO)2]1-, a new member of a series of four-coordinate {Fe(L)2(NO)2} complexes (L = thiolates, imidazole, etc.), described as {Fe(NO)2}9. Other decomposition products are hexacyanoferrate(II) or free cyanide, depending on the pH, and precipitates of the Prussian-Blue type. This study throws light on the conditions favoring rapid release of NO, to promote vasodilatory effects upon NP injection, and describes new processes related to dinitrosyl formation and NO disproportionation, which are also relevant to the diverse biological processes associated with NO and N2O processing.
Electron transfer. Part 165: Oxidations of Ti(II)(aq) with ligated iron(III) and ruthenium(III)
Mukherjee, Ritam,Manivannan,Gould, Edwin S.
, p. 3633 - 3636 (2007)
Titanium(II) solutions, prepared by dissolving titanium wire in triflic acid + HF, contain equimolar quantities of Ti(IV). Treatment of such solutions with excess Fe(III) or Ru(III) complexes yield Ti(IV), but reactions with Ti(II) in excess give Ti(III). Oxidations by (NH3)5Ru(III) complexes, but not by Fe(III) species, are catalyzed by titanium(IV) and by fluoride. Stoichiometry is unchanged. The observed rate law for the Ru(III)-Ti(II)-Ti(IV) reactions in fluoride media points to competing reaction paths differing by a single F-, with both routes involving a Ti(II)-Ti(IV) complex which is activated by deprotonation. It is suggested that coordination of Ti(IV) to TiII(aq) minimizes the mismatch of Jahn-Teller distortions which would be expected to lower the Ti(II,III) self-exchange rate.
Kinetics of Redox Reactions between Complexes of Molybdenum and Iron: The Oxidation of Iron(II) by Molybdenum(VI) and of 3+ by 3+
Millan, Carlos,Diebler, Hartmut
, p. 2397 - 2402 (1988)
In 8 mol dm-3 hydrochloric acid MoVI is reduced to MoV by FeII.Under these conditions, MoVI exists predominantly as MoO2Cl2 and MoV as MoOCl52-.Spectrophotometric studies indicate that the stoicheiometry of the reaction is exactly 1:1 and that the equilibrium is far to the side of the products.Studies of the kinetics of this redox process by stopped-flow techniques revealed that the rate of reaction is first-order in each reactant and that the second-order rate constant is k=(3.6+/-0.1) x 103 dm3 mol-1 s-1 (20 deg C, 8 mol dm-3 HCl).The mechanism of the reaction is not known, but a chloride-bridged inner-sphere process appears plausible.Equilibrium studies of the oxidation of 3+ by Fe3+ in 1 mol dm-3 p-toluenesulphonic acid (Hpts) indicate that a dimeric MoV species, Mo2O42+, is the first stable product.With an excess of Fe3+, this species is oxidized to MoVI.In kinetic studies with Fe3+ in excess, three processes could be observed: (a) the disappearance of Mo3+, (b) the formation of Mo2O42+, and (c) the disappearance of Mo2O42+.Process (a) occurs in the ms range.It is described by the equation -d3+>/dt=k13+>3+>, with k1=(1.30+/-0.05) x 103 dm3+ mol-1 s-1 (25 deg C, 1 mol dm-3 Hpts), and obviously proceeds by an outer-sphere mechanism.Steps (b) and (c) overlap strongly (seconds to minutes).The measured reaction curves for (b) and (c) can be satisfactorily described by two superimposed exponentials of rather similar time constants.The formation of Mo2O42+ from the products of the fast step is discussed in terms of a mechanism which is in approximate though not complete agreement with the experimental data.The second-order rate constant for the oxidation of the intermadiate Mo2O42+ by FeIII which has been evaluated from the reaction curves agrees well with that of a previous study in which Mo2O42+ was oxidized directly.
Photocontrolled electron transfer reaction between a new dyad, tetrathiafulvalene-photochromic spiropyran, and ferric ion
Guo, Xuefeng,Zhang, Deqing,Zhu, Daoben
, p. 212 - 217 (2004)
Photocontrolled electron transfer reaction is important not only for understanding the complicated biological processes such as photosynthesis and respiration but also for the design and studies of molecular electronics. This paper presents the synthesis and spectral and electrochemical studies of a new dyad 1 containing an electroactive unit (tetrathiafulvalene, TTF) and a photochromic unit (spiropyran, SP). Spectral studies showed that the redox states of the TTF unit of dyad 1 in the presence of ferric ions were dependent on the photoswitching process of the spiropyran unit upon UV light irradiation. Electrochemical investigations indicated that the oxidation potential of ferrous ion was largely reduced after coordination with MC (the open form of SP). As a result, the electron-transfer reaction from MC?·Fe2+ to TTF+ì?, which act as electron donor and acceptor, respectively, is thermodynamically favorable. Therefore, the electron-transfer reaction between the TTF unit and ferric ion can be photocontrolled in the presence of the SP unit. The present result shows the possibility to design new electron donor-acceptor supramolecules containing spiropyran units to photoregulate the electron-transfer reaction.
Pulse Radiolytic Studies of the Reactions of HO2/O2- with Fe(II)/Fe(III) Ions. The Reactivity of HO2/O2- with Ferric Ions and Its Implication of the Occurrence of the Haber-Weiss Reaction
Rush, James D.,Bielski, Benon H. J.
, p. 5062 - 5066 (1985)
The reactions between ferrous ion, Fe2+, and the simple complexes of Fe(III), FeOH2+, and FeSO4+ with superoxide and perhydroxyl radicals O2-/HO2 have been studied as a function of pH (1-7) in aqueous sulfate and formate media.The measured rate constants for the various reactions are k17(HO2 + Fe2+) = (1.2 +/- 0.2) X 106 M-1 s-1 (in good agreement with earlier reported values6d); k18(O2- + Fe2+) = (1.0 +/- 0.1) X 107 M-1 s-1; k20(O2- + FeSO4+) ca. k22(O2- + FeOH2+) = (1.5 +/- 0.2) X 108 M-1 s-1.The reduction of FeSO4+ by HO2 is relatively slow, k19(HO2 + FeSO4+) 3 M-1 s-1.At neutral pH the superoxide radical is catlytically decomposed to dioxygen and hydrogen peroxide by trace amounts of Fe(II)/Fe(III), if the overall reaction is completed before Fe(III) can polymerize/precipitate.The corresponding second-order rate constant is kcat = (1.3 +/- 0.2) X 107 M-1 s-1.The results from the kinetic studies of reactions 20 and 22 corroborate the mechanism for the catalytic decomposition of hydrogen peroxide by Fe(II)/Fe(III) advanced by Barb, Baxendale, George, and Hargrave in 1951.2,3
