Photoionization thresholds of melanins obtained from free electron laser-photoelectron emission microscopy, femtosecond transient absorption spectroscopy and electron paramagnetic resonance measurements of oxygen photoconsumption

Tong Ye, Lian Hong, Jacob Garguilo, Anna Pawlak, Glenn S. Edwards, Robert Nemanich, Tadeusz Sarna, John D. Simon

Research output: Contribution to journalArticle

68 Citations (Scopus)

Abstract

Free electron laser-photoelectron emission microscopy (FEL-PEEM), femtosecond absorption spectroscopy and electron paramagnetic resonance (EPR) measurements of oxygen photoconsumption were used to probe the threshold potential for ionization of eumelanosomes and pheomelanosomes isolated from human hair. FEL-PEEM data show that both pigments are characterized by an ionization threshold at 282 nm. However, pheomelanosomes exhibit a second ionization threshold at 326 nm, which is interpreted to be reflective of the benzothiazine structural motif present in pheomelanin and absent in eumelanin. The lower ionization threshold for pheomelanin is supported by femtosecond transient absorption spectroscopy. Unlike photolysis at 350 nm, following excitation of solubalized synthetic pheomelanin at 303 nm, the transient spectrum observed between 500 and 700 nm matches that for the solvated electron, indicating the photoionization threshold for the solubalized pigment is between 350 and 303 nm. For the same synthetic pheomelanin, EPR oximetry experiments reveal an increased rate of oxygen uptake between 338 nm and 323 nm, narrowing the threshold for photoionization to sit between these two wavelengths. These results on the solubalized synthetic pigment are consistent with the FEL-PEEM results on the human melanosomes. The lower ionization potential observed for pheomelanin could be an important part of the explanation for the greater incidence rate of UV-induced skin cancers in red-haired individuals.

Original languageEnglish (US)
Pages (from-to)733-737
Number of pages5
JournalPhotochemistry and Photobiology
Volume82
Issue number3
DOIs
StatePublished - May 2006
Externally publishedYes

Fingerprint

melanin
Photoionization
Free electron lasers
Melanins
Electron Spin Resonance Spectroscopy
Photoelectrons
Absorption spectroscopy
free electron lasers
Paramagnetic resonance
photoionization
Microscopy
Spectrum Analysis
electron paramagnetic resonance
Microscopic examination
absorption spectroscopy
photoelectrons
Lasers
Ionization
Electrons
Oxygen

ASJC Scopus subject areas

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

Cite this

Photoionization thresholds of melanins obtained from free electron laser-photoelectron emission microscopy, femtosecond transient absorption spectroscopy and electron paramagnetic resonance measurements of oxygen photoconsumption. / Ye, Tong; Hong, Lian; Garguilo, Jacob; Pawlak, Anna; Edwards, Glenn S.; Nemanich, Robert; Sarna, Tadeusz; Simon, John D.

In: Photochemistry and Photobiology, Vol. 82, No. 3, 05.2006, p. 733-737.

Research output: Contribution to journalArticle

@article{a964af0663e145d2a1bff88c843583b1,
title = "Photoionization thresholds of melanins obtained from free electron laser-photoelectron emission microscopy, femtosecond transient absorption spectroscopy and electron paramagnetic resonance measurements of oxygen photoconsumption",
abstract = "Free electron laser-photoelectron emission microscopy (FEL-PEEM), femtosecond absorption spectroscopy and electron paramagnetic resonance (EPR) measurements of oxygen photoconsumption were used to probe the threshold potential for ionization of eumelanosomes and pheomelanosomes isolated from human hair. FEL-PEEM data show that both pigments are characterized by an ionization threshold at 282 nm. However, pheomelanosomes exhibit a second ionization threshold at 326 nm, which is interpreted to be reflective of the benzothiazine structural motif present in pheomelanin and absent in eumelanin. The lower ionization threshold for pheomelanin is supported by femtosecond transient absorption spectroscopy. Unlike photolysis at 350 nm, following excitation of solubalized synthetic pheomelanin at 303 nm, the transient spectrum observed between 500 and 700 nm matches that for the solvated electron, indicating the photoionization threshold for the solubalized pigment is between 350 and 303 nm. For the same synthetic pheomelanin, EPR oximetry experiments reveal an increased rate of oxygen uptake between 338 nm and 323 nm, narrowing the threshold for photoionization to sit between these two wavelengths. These results on the solubalized synthetic pigment are consistent with the FEL-PEEM results on the human melanosomes. The lower ionization potential observed for pheomelanin could be an important part of the explanation for the greater incidence rate of UV-induced skin cancers in red-haired individuals.",
author = "Tong Ye and Lian Hong and Jacob Garguilo and Anna Pawlak and Edwards, {Glenn S.} and Robert Nemanich and Tadeusz Sarna and Simon, {John D.}",
year = "2006",
month = "5",
doi = "10.1562/2006-01-02-RA-762",
language = "English (US)",
volume = "82",
pages = "733--737",
journal = "Photochemistry and Photobiology",
issn = "0031-8655",
publisher = "Wiley-Blackwell",
number = "3",

}

TY - JOUR

T1 - Photoionization thresholds of melanins obtained from free electron laser-photoelectron emission microscopy, femtosecond transient absorption spectroscopy and electron paramagnetic resonance measurements of oxygen photoconsumption

AU - Ye, Tong

AU - Hong, Lian

AU - Garguilo, Jacob

AU - Pawlak, Anna

AU - Edwards, Glenn S.

AU - Nemanich, Robert

AU - Sarna, Tadeusz

AU - Simon, John D.

PY - 2006/5

Y1 - 2006/5

N2 - Free electron laser-photoelectron emission microscopy (FEL-PEEM), femtosecond absorption spectroscopy and electron paramagnetic resonance (EPR) measurements of oxygen photoconsumption were used to probe the threshold potential for ionization of eumelanosomes and pheomelanosomes isolated from human hair. FEL-PEEM data show that both pigments are characterized by an ionization threshold at 282 nm. However, pheomelanosomes exhibit a second ionization threshold at 326 nm, which is interpreted to be reflective of the benzothiazine structural motif present in pheomelanin and absent in eumelanin. The lower ionization threshold for pheomelanin is supported by femtosecond transient absorption spectroscopy. Unlike photolysis at 350 nm, following excitation of solubalized synthetic pheomelanin at 303 nm, the transient spectrum observed between 500 and 700 nm matches that for the solvated electron, indicating the photoionization threshold for the solubalized pigment is between 350 and 303 nm. For the same synthetic pheomelanin, EPR oximetry experiments reveal an increased rate of oxygen uptake between 338 nm and 323 nm, narrowing the threshold for photoionization to sit between these two wavelengths. These results on the solubalized synthetic pigment are consistent with the FEL-PEEM results on the human melanosomes. The lower ionization potential observed for pheomelanin could be an important part of the explanation for the greater incidence rate of UV-induced skin cancers in red-haired individuals.

AB - Free electron laser-photoelectron emission microscopy (FEL-PEEM), femtosecond absorption spectroscopy and electron paramagnetic resonance (EPR) measurements of oxygen photoconsumption were used to probe the threshold potential for ionization of eumelanosomes and pheomelanosomes isolated from human hair. FEL-PEEM data show that both pigments are characterized by an ionization threshold at 282 nm. However, pheomelanosomes exhibit a second ionization threshold at 326 nm, which is interpreted to be reflective of the benzothiazine structural motif present in pheomelanin and absent in eumelanin. The lower ionization threshold for pheomelanin is supported by femtosecond transient absorption spectroscopy. Unlike photolysis at 350 nm, following excitation of solubalized synthetic pheomelanin at 303 nm, the transient spectrum observed between 500 and 700 nm matches that for the solvated electron, indicating the photoionization threshold for the solubalized pigment is between 350 and 303 nm. For the same synthetic pheomelanin, EPR oximetry experiments reveal an increased rate of oxygen uptake between 338 nm and 323 nm, narrowing the threshold for photoionization to sit between these two wavelengths. These results on the solubalized synthetic pigment are consistent with the FEL-PEEM results on the human melanosomes. The lower ionization potential observed for pheomelanin could be an important part of the explanation for the greater incidence rate of UV-induced skin cancers in red-haired individuals.

UR - http://www.scopus.com/inward/record.url?scp=33745857675&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=33745857675&partnerID=8YFLogxK

U2 - 10.1562/2006-01-02-RA-762

DO - 10.1562/2006-01-02-RA-762

M3 - Article

C2 - 16542109

AN - SCOPUS:33745857675

VL - 82

SP - 733

EP - 737

JO - Photochemistry and Photobiology

JF - Photochemistry and Photobiology

SN - 0031-8655

IS - 3

ER -