Chemical evaluation of eumelanin maturation by tof-sims and alkaline peroxide oxidation hplc analysis

Martin Jarenmark, Peter Sjövall, Shosuke Ito, Kazumasa Wakamatsu, Johan Lindgren

Research output: Contribution to journalArticlepeer-review

2 Citations (SciVal)

Abstract

Residual melanins have been detected in multimillion-year-old animal body fossils; how-ever, confident identification and characterization of these natural pigments remain challenging due to loss of chemical signatures during diagenesis. Here, we simulate this post-burial process through artificial maturation experiments using three synthetic and one natural eumelanin exposed to mild (100C/100 bar) and harsh (250C/200 bar) environmental conditions, followed by chemical analysis employing alkaline hydrogen peroxide oxidation (AHPO) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Our results show that AHPO is sensitive to changes in the melanin molecular structure already during mild heat and pressure treatment (resulting, e.g., in increased C-C cross-linking), whereas harsh maturation leads to extensive loss of eumelanin-specific chemical markers. In contrast, negative-ion ToF-SIMS spectra are considerably less affected by mild maturation conditions, and eumelanin-specific features remain even after harsh treatment. Detailed analysis of ToF-SIMS spectra acquired prior to experimental treatment revealed significant differences between the investigated eumelanins. However, systematic spectral changes upon maturation reduced these dissimilarities, indicating that intense heat and pressure treatment leads to the formation of a com-mon, partially degraded, eumelanin molecular structure. Our findings elucidate the complementary nature of AHPO and ToF-SIMS during chemical characterization of eumelanin traces in fossilized organismal remains.

Original languageEnglish
Article number161
Number of pages16
JournalInternational Journal of Molecular Sciences
Volume22
Issue number1
DOIs
Publication statusPublished - 2021

Subject classification (UKÄ)

  • Analytical Chemistry
  • Geochemistry

Keywords

  • Alkaline hydrogen peroxide oxidation
  • Eumelanin
  • Maturation
  • Principal component analysis
  • Time-of-flight secondary ion mass spectrometry

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