The surface oxidation potential of melanosomes measured by free electron laser-photoelectron emission microscopy

Jacob Garguilo, Lian Hong, Glenn S. Edwards, Robert Nemanich, John D. Simon

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

A technique for measuring the photoionization spectrum and the photoelectron emission threshold of a microscopic structured material is presented. The theoretical underpinning of the experiment and the accuracy of the measurements are discussed. The technique is applied to titanium silicide nanostructures and melanosomes isolated from human hair, human and bovine retinal pigment epithelium cells, and the ink sac of Sepia officinalis. A common photothreshold of 4.5 ± 0.2 eV is found for this set of melanosomes and is attributed to the photoionization of the eumelanin pigment. The relationship between the photoionization threshold and the electrochemical potential referenced to the normal hydrogen electrode is used to quantify the surface oxidation potential of the melanosome. The developed technique is used to examine the effect of iron chelation on the surface oxidation potential of Sepia melanosomes. The surface oxidation potential is insensitive to bound Fe(III) up to saturation, suggesting that the metal is bound to the interior of the granule. This result is discussed in relation to the age-dependent accumulation of iron in human melanosomes in both the eye and brain.

Original languageEnglish (US)
Pages (from-to)692-697
Number of pages6
JournalPhotochemistry and Photobiology
Volume83
Issue number3
DOIs
StatePublished - May 2007
Externally publishedYes

Fingerprint

Melanosomes
Photoionization
Free electron lasers
Photoelectrons
free electron lasers
Microscopy
Microscopic examination
photoelectrons
Lasers
Electrons
microscopy
photoionization
Oxidation
oxidation
Sepia
Iron
pigments
Retinal Pigments
Chelation
Ink

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)
  • Biochemistry
  • Biophysics

Cite this

The surface oxidation potential of melanosomes measured by free electron laser-photoelectron emission microscopy. / Garguilo, Jacob; Hong, Lian; Edwards, Glenn S.; Nemanich, Robert; Simon, John D.

In: Photochemistry and Photobiology, Vol. 83, No. 3, 05.2007, p. 692-697.

Research output: Contribution to journalArticle

Garguilo, Jacob ; Hong, Lian ; Edwards, Glenn S. ; Nemanich, Robert ; Simon, John D. / The surface oxidation potential of melanosomes measured by free electron laser-photoelectron emission microscopy. In: Photochemistry and Photobiology. 2007 ; Vol. 83, No. 3. pp. 692-697.
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