Modeling red coral (Corallium rubrum) and African snail (Helixia aspersa) shell pigments: Raman spectroscopy versus DFT studies

Teobald Kupka , Aneta Buczek , Małgorzata A. Broda , Roman Szostak , Lu-Wei Fan , Roman Wrzalik , Leszek Stobiński

Abstract

Pigments from red coral (Corallium rubrum) and African snail (Helixia aspersa) shell were studied non-invasively using Raman spectroscopy with 1064-nm laser beam. The two observed bands because of organic pigments confined in biomineralized CaCO3 matrix at about 1500 and 1100 cm−1 were assigned to ν(C[DOUBLE BOND]C) and ν(C―C), respectively. Both signals originate from polyene(s) of largely unknown structure, containing several conjugated C[DOUBLE BOND]C bonds. The small peak at 1016 cm−1 in the Raman spectrum of coral pigment was assigned to in-plane ―CH3 rocking or structural deformation of polyene chain because of spatial confinement in the mineral matrix. The organic pigments in red coral and snail shell were present in inorganic matrix containing aragonite (shell) and calcite (coral). In addition, using Raman spectroscopy, it was observed that aragonite was replaced by calcite as result of healing damaged parts of snail shell. This is an important finding which indicates a great potential of nondestructive Raman spectroscopy instead of X-ray technique, as a diagnostic tool in environmental studies. To support analysis of the observed Raman spectra detailed calculations using density functional theory (DFT with B3LYP and BLYP density functionals) on structure and vibrations of model all-trans polyenes were undertaken. DFT calculated C[DOUBLE BOND]C and C―C stretching frequencies for all-trans polyenes containing from 2 to 14 C[DOUBLE BOND]C units were compared with the observed ν(C[DOUBLE BOND]C) and ν(C―C) band positions of the studied coral and shell. Individual correction factors were used to better match theoretical wavenumbers with observed band positions in red coral and African snail. It was concluded that all-trans polyene pigments of red coral and dark parts of African snail shell contain 11–12 and 14 C[DOUBLE BOND]C double bond units, respectively. However, Raman spectroscopy cannot produce any clear information on the presence and nature of the end-chain substituents in the studied pigments. Copyright © 2016 John Wiley & Sons, Ltd.
Author Teobald Kupka
Teobald Kupka,,
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, Aneta Buczek
Aneta Buczek,,
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, Małgorzata A. Broda
Małgorzata A. Broda,,
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, Roman Szostak
Roman Szostak,,
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, Lu-Wei Fan
Lu-Wei Fan,,
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, Roman Wrzalik
Roman Wrzalik,,
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, Leszek Stobiński LG PW
Leszek Stobiński,,
- WUT Grafen Laboratory
Journal seriesJournal of Raman Spectroscopy, ISSN 0377-0486
Issue year2016
Vol47
No8
Pages908-916
Publication size in sheets0.5
Keywords in Englishred coral, African snail, polyenes, Raman spectroscopy, DFT
DOIDOI:10.1002/jrs.4922
URL http://onlinelibrary.wiley.com/doi/10.1002/jrs.4922/epdf
Languageen angielski
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Kupka T. (i in.) - Modeling red coral....pdf 539.84 KB
Score (nominal)30
ScoreMinisterial score [Punktacja MNiSW] = 30.0, 28-11-2017, ArticleFromJournal
Ministerial score (2013-2016) [Punktacja MNiSW (2013-2016)] = 30.0, 28-11-2017, ArticleFromJournal
Publication indicators WoS Impact Factor [Impact Factor WoS]: 2016 = 2.969 (2) - 2016=2.648 (5)
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