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Photochemistry of Pheomelanin Building Blocks and Model Chromophores: Excited-State Intra- and Intermolecular Proton Transfer

El Nahhas, Amal LU ; Pascher, Torbjörn LU ; Leone, Loredana; Panzella, Lucia; Napolitano, Alessandra and Sundström, Villy LU (2014) In The Journal of Physical Chemistry Letters 5(12). p.2094-2100
Abstract
Pheomelanins, the epidermal pigments of red-haired people responsible for their enhanced UV susceptibility, contain 1,4-benzothiazines and 1,3-benzothiazole as main structural components. Despite the major role played in pheomelanin phototoxicity, the photoreactivity of these species has so far remained unexplored. Static and time-resolved fluorescence spectroscopy was used to identify excited-state reactions of the two main pheomelanin benzothiazole building blocks, namely, the 6-(2-amino-2-carboxyethyl)-4-hydroxy-1,3-benzothiazole (BT) and the 2-carboxy derivative (BTCA) together with model chromophores lacking some of the ionizable functions. The results show that in aqueous buffer solution the OH at 4-position and the benzothiazole... (More)
Pheomelanins, the epidermal pigments of red-haired people responsible for their enhanced UV susceptibility, contain 1,4-benzothiazines and 1,3-benzothiazole as main structural components. Despite the major role played in pheomelanin phototoxicity, the photoreactivity of these species has so far remained unexplored. Static and time-resolved fluorescence spectroscopy was used to identify excited-state reactions of the two main pheomelanin benzothiazole building blocks, namely, the 6-(2-amino-2-carboxyethyl)-4-hydroxy-1,3-benzothiazole (BT) and the 2-carboxy derivative (BTCA) together with model chromophores lacking some of the ionizable functions. The results show that in aqueous buffer solution the OH at 4-position and the benzothiazole nitrogen atom control the photochemistry of both BT and BTCA via excited-state proton transfer to solvent (ESPT) and excited-state intramolecular proton transfer (ESIPT), while the amino acidic groups of the alanyl chain have a minor influence on the photochemistry. The ESPT and ESIPT produce several different excited-state ionic species with lifetimes ranging from similar to 100 ps to similar to 3 ns. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
The Journal of Physical Chemistry Letters
volume
5
issue
12
pages
2094 - 2100
publisher
The American Chemical Society
external identifiers
  • wos:000337870100008
  • scopus:84903144136
ISSN
1948-7185
DOI
10.1021/jz500720g
language
English
LU publication?
yes
id
bc48f669-3ff4-4758-b947-a618616db091 (old id 4609137)
date added to LUP
2014-08-28 15:41:30
date last changed
2017-06-04 04:08:53
@article{bc48f669-3ff4-4758-b947-a618616db091,
  abstract     = {Pheomelanins, the epidermal pigments of red-haired people responsible for their enhanced UV susceptibility, contain 1,4-benzothiazines and 1,3-benzothiazole as main structural components. Despite the major role played in pheomelanin phototoxicity, the photoreactivity of these species has so far remained unexplored. Static and time-resolved fluorescence spectroscopy was used to identify excited-state reactions of the two main pheomelanin benzothiazole building blocks, namely, the 6-(2-amino-2-carboxyethyl)-4-hydroxy-1,3-benzothiazole (BT) and the 2-carboxy derivative (BTCA) together with model chromophores lacking some of the ionizable functions. The results show that in aqueous buffer solution the OH at 4-position and the benzothiazole nitrogen atom control the photochemistry of both BT and BTCA via excited-state proton transfer to solvent (ESPT) and excited-state intramolecular proton transfer (ESIPT), while the amino acidic groups of the alanyl chain have a minor influence on the photochemistry. The ESPT and ESIPT produce several different excited-state ionic species with lifetimes ranging from similar to 100 ps to similar to 3 ns.},
  author       = {El Nahhas, Amal and Pascher, Torbjörn and Leone, Loredana and Panzella, Lucia and Napolitano, Alessandra and Sundström, Villy},
  issn         = {1948-7185},
  language     = {eng},
  number       = {12},
  pages        = {2094--2100},
  publisher    = {The American Chemical Society},
  series       = {The Journal of Physical Chemistry Letters},
  title        = {Photochemistry of Pheomelanin Building Blocks and Model Chromophores: Excited-State Intra- and Intermolecular Proton Transfer},
  url          = {http://dx.doi.org/10.1021/jz500720g},
  volume       = {5},
  year         = {2014},
}