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.

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.

Hopfgartner, K.

, (1905)

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.

Edgar, G.,Kemp, A. R.

, p. 777 - 777 (1918)

Foster, G. W. A.

, p. 912 - 912 (1906)

Tachiyashiki, Satoshi,Yamatera, Hideo

, p. 9 - 12 (1983)

Anaerobic Oxidation of Cysteine to Cystine by Iron(III). Part 1. The Reaction in Acidic Solution

Jameson, Reginald F.,Linert, Wolfgang,Tschinkowitz, Axel,Gutmann, Viktor

, p. 943 - 946 (1988)

The anaerobic oxidation of cysteine (H2L) by iron(III) has been followed in acidic media by use of a stopped-flow high-speed spectrophotometric method.It is suggested that the species responsible is + which is observable as a transient blue colour on the addition of iron(III) solutions to acidic cysteine solutions.This species exhibits an absorption maximum at 614 nm with a molar absorption coefficient of 1 030 dm3mol-1cm-1.The second-order rate constant for its formation from 2+ and H2L was found to be 1.14E4 dm3mol-1s-1 and the value of log KFeOH 2+> required to fit the data is 2.82.Decomposition to iron(II) and subsequently cystine follows protonation, with an apparent third-order rate constant (including an unknown stability constant) of 1.63E11 dm6mol-2s-1.All measurements were carried out at 25 deg C in solutions of ionic strength 0.10 mol dm-3 (KCl).

Semi-hard magnetic properties of nanoparticles of cobalt ferrite synthesized by the co-precipitation process

Hosni,Zehani,Bartoli,Bessais,Maghraoui-Meherzi

, p. 1295 - 1301 (2017)

The nanoparticles ferromagnetic materials CoFe2O4have been synthesized by the co-precipitation method and annealed at various temperatures from 773 to 1223 K. The influence of the heat treatment on the structural, morphological and magnetic properties of CoFe2O4nanoparticles was investigated. The structure, morphology and magnetic properties of the annealing samples were reached by mean of X-ray diffraction (XRD), scanning electron microscopy (SEM) techniques and measurement of hysteresis loop. The average crystallite size, lattice parameter and X-ray density were calculated from X-ray diffraction data. All samples have the cubic spinel structure with average crystallite sizes increasing from 30 to 178 nm with the temperature. The results show that CoFe2O4nanoparticles prepared by this method have small and more uniform size. The measurements of the hysteresis loop, performed at both 10 K and 300 K, indicate a ferromagnetic behavior of nanoparticles. Also the measurement at 300 K shows that the sample annealed at 1023 K is magnetically harder than the other samples. The coercive fields are 1.58 kOe against the values inferior at 0.61 kOe for the other samples. Indeed, the remanent magnetization is 31.85 emu g?1for the hard magnetic sample against 13.02 and 17.29 emu g?1for the soft magnetic samples annealed at 773 and 1223 K, respectively. The origin of the hard-soft magnetic properties of nanoparticles CoFe2O4is discussed in terms of the co-existence of secondary phases β-Fe2O3, CoO2and the distribution of Fe2+and Co2+ions within the lattice.

ROMP polymer supported manganese porphyrins: Influence of C[dbnd]C bonds along polymer chains on catalytic behavior in oxidation of low concentration Fe2+

Li, Fanfan,Wang, Xuan,Zhang, Yanwu,Zhao, Huanhuan

, (2020/02/22)

One unsaturated polymer support was prepared through ring opening metathesis polymerization (ROMP) of norbornene-2,3-dip-toluene sulfonate initiated by Grubbs 2nd initiator and manganese porphyrins were immobilized on polymer through transesterification reaction. To investigate the effect of C[dbnd]C bonds along polymer chains on the catalytic behavior, the obtained polymer supported catalyst (P-PPIXMnCl) was applied in oxidation of low concentration Fe2+ to mimic catalytic behavior of Ceruloplasmin. In the presence of P-PPIXMnCl, the conversion of Fe2+ reaches to 91.92% and 96.46% at 10 °C and 37.5 °C (body temperature), respectively. Compared to manganese porphyrins, P-PPIXMnCl can dramatically increase oxidation rate of Fe2+ and the catalytic kinetic shows that the oxidation reaction changes from second-order to third-order. Upon hydrogenation of ROMP polymer, the oxidation reaction still conforms to the second-order kinetics. Density functional theory (DFT) calculation shows that the C[dbnd]C bonds along polymer chains play an important role in the coordination with Fe2+ in the catalytic microenvironment. The real time morphology of supported catalysts in aqueous environment characterized by Cryo-TEM indicates that hydrogenation can shrink the morphology of polymer-water skeleton. The catalyst could be recycled six times without any significant loss in activity. The liner heterogeneous catalyst is expected to be used as drugs for treating excessive iron accumulation in the human body.