The effect of organic compounds in the oxidation kinetics of Fe(II)

J. Magdalena Santana-Casiano, Melchor González-Dávila, Ma Jesús Rodríguez, Frank J Millero

Research output: Contribution to journalArticle

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Abstract

The oxidation of Fe(II) has been studied in the presence of the natural organic compounds alanine, glutamic acid, cysteine, and two synthetic aminocarboxilates [(ethylenedioxi)diethylenedinitrilo]tetra-acetic acid (EGTA) and (ethylenedinitro)tetra-acetic acid (EDTA), as a function of pH(t) (6-8), ionic strength (0.2-1 m) and temperature (5-35°C), in NaCl solutions, at different Fe(II)-organic compound ratios. Alanine and glutamic acid did not affect the oxidation kinetics of Fe(II). For these compounds, a second order pH dependence is obeyed over the pH range studied, where log k(obs) = - 16.29(0.16) + 2.09(0.02)pH and log k(obs) = - 15.26(1.3) + 1.94(0.18)pH, for the alanine and glutamic acid, respectively. EGTA formed a strong ferrous complex that inhibited the oxidation of Fe(II) and EDTA increased the oxidation of ferrous iron forming a Fe(III)-EDTA complex that showed photoreduction in the presence of light, regenerating Fe(II). In the pH range from 6 to 8.2, the process was not affected by pH. The dependence with ionic strength was described by the equation log k = 15.351 + 0.565I(1/2) - 1.388I. Cysteine modified this behavior as a function of the Fe(II)-cysteine ratios. A Fe(III)-cysteine complex is formed through a one-electron transfer process that involved the thiol group and resulted in the reduction of Fe(III) back to Fe(II), and the oxidation of cysteine to cystine. The Fe(OH)L complex formation and reduction was affected by pH and cysteine concentration. A kinetic model that describes the behavior observed has been developed. (C) 2000 Elsevier Science B.V.

Original languageEnglish (US)
Pages (from-to)211-222
Number of pages12
JournalMarine Chemistry
Volume70
Issue number1-3
DOIs
StatePublished - May 2000

Fingerprint

Organic compounds
Cysteine
organic compound
acetic acid
oxidation
Acetic Acid
kinetics
Oxidation
Kinetics
Alanine
Glutamic Acid
Egtazic Acid
acid
Ionic strength
thiol
Cystine
Sulfhydryl Compounds
effect
Iron
iron

Keywords

  • Amino acids
  • EDTA
  • EGTA
  • Fe(II)
  • Oxidation

ASJC Scopus subject areas

  • Chemistry(all)
  • Oceanography

Cite this

Santana-Casiano, J. M., González-Dávila, M., Rodríguez, M. J., & Millero, F. J. (2000). The effect of organic compounds in the oxidation kinetics of Fe(II). Marine Chemistry, 70(1-3), 211-222. https://doi.org/10.1016/S0304-4203(00)00027-X

The effect of organic compounds in the oxidation kinetics of Fe(II). / Santana-Casiano, J. Magdalena; González-Dávila, Melchor; Rodríguez, Ma Jesús; Millero, Frank J.

In: Marine Chemistry, Vol. 70, No. 1-3, 05.2000, p. 211-222.

Research output: Contribution to journalArticle

Santana-Casiano, JM, González-Dávila, M, Rodríguez, MJ & Millero, FJ 2000, 'The effect of organic compounds in the oxidation kinetics of Fe(II)', Marine Chemistry, vol. 70, no. 1-3, pp. 211-222. https://doi.org/10.1016/S0304-4203(00)00027-X
Santana-Casiano JM, González-Dávila M, Rodríguez MJ, Millero FJ. The effect of organic compounds in the oxidation kinetics of Fe(II). Marine Chemistry. 2000 May;70(1-3):211-222. https://doi.org/10.1016/S0304-4203(00)00027-X
Santana-Casiano, J. Magdalena ; González-Dávila, Melchor ; Rodríguez, Ma Jesús ; Millero, Frank J. / The effect of organic compounds in the oxidation kinetics of Fe(II). In: Marine Chemistry. 2000 ; Vol. 70, No. 1-3. pp. 211-222.
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N2 - The oxidation of Fe(II) has been studied in the presence of the natural organic compounds alanine, glutamic acid, cysteine, and two synthetic aminocarboxilates [(ethylenedioxi)diethylenedinitrilo]tetra-acetic acid (EGTA) and (ethylenedinitro)tetra-acetic acid (EDTA), as a function of pH(t) (6-8), ionic strength (0.2-1 m) and temperature (5-35°C), in NaCl solutions, at different Fe(II)-organic compound ratios. Alanine and glutamic acid did not affect the oxidation kinetics of Fe(II). For these compounds, a second order pH dependence is obeyed over the pH range studied, where log k(obs) = - 16.29(0.16) + 2.09(0.02)pH and log k(obs) = - 15.26(1.3) + 1.94(0.18)pH, for the alanine and glutamic acid, respectively. EGTA formed a strong ferrous complex that inhibited the oxidation of Fe(II) and EDTA increased the oxidation of ferrous iron forming a Fe(III)-EDTA complex that showed photoreduction in the presence of light, regenerating Fe(II). In the pH range from 6 to 8.2, the process was not affected by pH. The dependence with ionic strength was described by the equation log k = 15.351 + 0.565I(1/2) - 1.388I. Cysteine modified this behavior as a function of the Fe(II)-cysteine ratios. A Fe(III)-cysteine complex is formed through a one-electron transfer process that involved the thiol group and resulted in the reduction of Fe(III) back to Fe(II), and the oxidation of cysteine to cystine. The Fe(OH)L complex formation and reduction was affected by pH and cysteine concentration. A kinetic model that describes the behavior observed has been developed. (C) 2000 Elsevier Science B.V.

AB - The oxidation of Fe(II) has been studied in the presence of the natural organic compounds alanine, glutamic acid, cysteine, and two synthetic aminocarboxilates [(ethylenedioxi)diethylenedinitrilo]tetra-acetic acid (EGTA) and (ethylenedinitro)tetra-acetic acid (EDTA), as a function of pH(t) (6-8), ionic strength (0.2-1 m) and temperature (5-35°C), in NaCl solutions, at different Fe(II)-organic compound ratios. Alanine and glutamic acid did not affect the oxidation kinetics of Fe(II). For these compounds, a second order pH dependence is obeyed over the pH range studied, where log k(obs) = - 16.29(0.16) + 2.09(0.02)pH and log k(obs) = - 15.26(1.3) + 1.94(0.18)pH, for the alanine and glutamic acid, respectively. EGTA formed a strong ferrous complex that inhibited the oxidation of Fe(II) and EDTA increased the oxidation of ferrous iron forming a Fe(III)-EDTA complex that showed photoreduction in the presence of light, regenerating Fe(II). In the pH range from 6 to 8.2, the process was not affected by pH. The dependence with ionic strength was described by the equation log k = 15.351 + 0.565I(1/2) - 1.388I. Cysteine modified this behavior as a function of the Fe(II)-cysteine ratios. A Fe(III)-cysteine complex is formed through a one-electron transfer process that involved the thiol group and resulted in the reduction of Fe(III) back to Fe(II), and the oxidation of cysteine to cystine. The Fe(OH)L complex formation and reduction was affected by pH and cysteine concentration. A kinetic model that describes the behavior observed has been developed. (C) 2000 Elsevier Science B.V.

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KW - Oxidation

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