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| Titel |
Synchrotron FT-IR analyses of microstructured biomineral domains: Hints to the biomineralization processes in freshwater cultured pearls. |
| VerfasserIn |
A. L. Soldati, V. Vicente-Vilas, B. Gasharova, D. E. Jacob |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250026052
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| Zusammenfassung |
| Recent investigations in freshwater cultured pearls (bio-carbonate) by micro-Raman
spectroscopy (Wehrmeister et al., 2008; Soldati et al., 2008), Scanning Electron Microscopy
(SEM) and Transmission Electron Microscopy (TEM) imaging (Jacob et al., 2008) show
that the pearl biomineralisation starts with a self assembling process in which an
existing gel matrix of amorphous calcium carbonate (ACC) and organic substances
reorganizes and conglomerates in small domains; these conglomerates then form prisms
and mature nacreous tablets of aragonite or vaterite. Raman spectroscopy shows
that the calcium carbonate polymorphs have decreasing luminescence in the order
ACC>Vaterite>Aragonite, coinciding with decreasing quantities of S and P (related to the
organic matrix) measured by Laser Ablation Inductively Coupled Plasma Mass
Spectroscopy (LA-ICP-MS) and Electron Probe Micro Analyzer (EPMA). Although
little is known about the process of transformation of the ACC gel into vaterite and
aragonite, it is speculated that this probably involves dehydration and change of
the accompanying organic matrix. This is also supported by our laboratory FT-IR
analysis. However, due to the small size of the areas of ACC (about 10 ?m) and the
biogenic crystals an in-situ high spatially resolved IR-method is needed to record how
the water content and organic matrix change in the biomineralisation sequence,
to understand which processes take place in the self-organization. The beamline
IR-1 at the ANKA synchrotron source (Karlsruhe, Germany) was used for this
experiment.
Freshwater cultured pearls from China cultured in Hyriopsis cumingii mussels by tissue
nucleation methods (so-called beadless pearls) as well as by bead implantation methods
(aragonite nucleus) were studied. The pearls were cut in half with a diamond-plated saw
and polished with diamond paste on a copper plate. Micro-Raman spectroscopy
maps (Department of Geosciences, at the Johannes Gutenberg-University, Mainz)
were generated to identify and pre-select those pearls containing ACC. Infrared
absorption spectra were measured using a Ge ATR objective on 100-200 ?m thin
sections and polished pearl sections. Attenuated total reflectance spectroscopy gives
the opportunity to measure the infrared absorption in a reflectance mode directly
without necessity to apply Kramers-Kronig transformation. The spectral range
available is 650-5000 cm-1when using a Ge ATR crystal with the MCT detector at the
ANKA-IR microscope and allowed the detection of the ?4 in-plane bending band
(around 750 cm-1 in vaterite and 710 cm-1 in aragonite), the ?1 symmetric stretching
bands (1070-7085 cm-1 for vaterite4 and 1082-1084 cm-1 in aragonite5), the ?2
out-of-plane bending vibration of the CO3 groups (855 cm-1 for vaterite and 857-877
cm-1 in aragonite) and the ?3 asymmetric stretching (1420-1490 cm-1 in vaterite
and 1480 cm-1 in aragonite) respectively (Sato and Masuda, 1969; Yamoto et al.,
1974).Water was detected by the presence of the O-H stretching at around 3500
cm-1. Proteins and sugars included in the biogenic carbonates were recognized
through the N-H and C-H bands, for example 1717-1575 cm-1 for aspartic acid,
1712-1558 cm-1 for glutamic acid, 1500 to 2000 cm-1 amide I and II (Dauphin et al.,
2006).
References
WEHRMEISTER U., JACOB D.E., SOLDATI A.L., HÄGER T. & HOFMEISTER W.
2007. Vaterite in freshwater cultured pearls from China and Japan. The Journal of
Gemmology; 31: 269-276.
SOLDATI A.L., JACOB D.E., WEHRMEISTER U.& HOFMEISTER W. 2008.
Structural characterization and chemical composition of aragonite and vaterite in freshwater
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DAUPHIN Y. 2006. Structure and composition of steptal nacreous layer of Nautilus
macromphalus L. (Mollusca, Cephalopoda). Zoology 109: 95-95. |
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