Ion-exchange and adsorption of Fe(III) by Sepia melanin

Yan Liu, Lian Hong, Valerie R. Kempf, Kazumasa Wakamatsu, Shosuke Ito, John D. Simon

Research output: Contribution to journalArticle

101 Citations (Scopus)

Abstract

Sepia eumelanin is associated with many metal ions, yet little is known about its metal binding capacity and the chemical nature of the binding site(s). Herein, the natural concentrations of metal ions are presented and the ability to remove metals by exposure of the melanin granules to EDTA is quantified. The results reveal that the binding constants of melanin at pH 5.8 for Mg(II), Ca(II), Sr(II) and Cu(II) are, respectively, 5, 4, 14 and 34 times greater than the corresponding binding constants of these ions with EDTA. By exposing Sepia eumelanin to aqueous solutions of FeCl3, the content of bound Fe(III) can be increased from a natural concentration of ∼180 ppm to a saturation limit of ∼80 000 ppm or 1.43 mmol/g of melanin. Similar saturation limits are found for Mg(II) and Ca(II). Exposure of Sepia melanin granules to aqueous solutions containing Ca(II) results in the stoichiometric replacement of the initially bound Mg(II), arguing that these two ions occupy the same binding site(s) in the pigment. The pH-dependent binding of Mg(II) and Ca(II) suggests coordination of these ions to carboxylic acid groups in the pigment. Mg(II) and Ca(II) can be added to a Fe(III)-saturated melanin sample without affecting the amount of Fe(III) pre-adsorbed, clearly establishing Fe(III) and Mg(II)/Ca(II) occupy different binding sites. Taking recent Raman spectroscopic data into account, the binding of Fe(III) is concluded to involve coordination to o-dihydroxyl groups. The effects of metal ion content on the surface morphology were analyzed. No significant changes were found over the full range of Fe(III) concentration studied, which is supported by the Brunauer-Emmett-Teller surface area analysis. These observations imply the existence of channels within the melanin granules that can serve to transport metal ions.

Original languageEnglish
Pages (from-to)262-269
Number of pages8
JournalPigment Cell Research
Volume17
Issue number3
DOIs
Publication statusPublished - Jun 2004

Fingerprint

Sepia
Ion Exchange
Melanins
ion exchange
melanin
Adsorption
Ion exchange
adsorption
Metals
Ions
metal ions
Metal ions
eumelanin
binding sites
granules
Binding Sites
EDTA (chelating agent)
ions
Pigments
Edetic Acid

Keywords

  • Binding affinity
  • Binding sites
  • Calcium
  • Chelation
  • Chemical composition
  • Eumelanin
  • Fe(III)
  • Ion-exchange
  • Iron
  • Magnesium
  • Mass spectrometry
  • Sepia
  • Surface analysis

ASJC Scopus subject areas

  • Cell Biology
  • Agronomy and Crop Science
  • Plant Science
  • Clinical Biochemistry
  • Developmental Biology

Cite this

Liu, Y., Hong, L., Kempf, V. R., Wakamatsu, K., Ito, S., & Simon, J. D. (2004). Ion-exchange and adsorption of Fe(III) by Sepia melanin. Pigment Cell Research, 17(3), 262-269. https://doi.org/10.1111/j.1600-0749.2004.00140.x

Ion-exchange and adsorption of Fe(III) by Sepia melanin. / Liu, Yan; Hong, Lian; Kempf, Valerie R.; Wakamatsu, Kazumasa; Ito, Shosuke; Simon, John D.

In: Pigment Cell Research, Vol. 17, No. 3, 06.2004, p. 262-269.

Research output: Contribution to journalArticle

Liu, Y, Hong, L, Kempf, VR, Wakamatsu, K, Ito, S & Simon, JD 2004, 'Ion-exchange and adsorption of Fe(III) by Sepia melanin', Pigment Cell Research, vol. 17, no. 3, pp. 262-269. https://doi.org/10.1111/j.1600-0749.2004.00140.x
Liu, Yan ; Hong, Lian ; Kempf, Valerie R. ; Wakamatsu, Kazumasa ; Ito, Shosuke ; Simon, John D. / Ion-exchange and adsorption of Fe(III) by Sepia melanin. In: Pigment Cell Research. 2004 ; Vol. 17, No. 3. pp. 262-269.
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