Issue 7, 2012
From the journal:

Physical Chemistry Chemical Physics

From synthetic to biogenic Mg-containing calcites: a comparative study using FTIR microspectroscopy†

Xia Long,a   Michael J. Nasse,bc   Yurong Ma*a  and  Limin Qi*a  

* Corresponding authors

a Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry, Peking University, Beijing, China
E-mail: yurong.ma@pku.edu.cn, liminqi@pku.edu.cn
Fax: +86 1062751708
Tel: +86 1062753269

b Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, USA

c Synchrotron Radiation Center, University of Wisconsin-Madison, Stoughton, USA

Abstract

The formation mechanism of the thermodynamically unstable calcite phase, very high Mg calcite, in biological organisms such as sea urchin or corallina algae has been an enigma for a very long time. In contrast to conventional methods such as KBr pellet Fourier Transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD), FTIR microspectroscopy (FTIRM) provides additional information about a local disorder such as an amorphous phase or the occlusion of Mg ions in the calcite lattice. In this work, we characterise for the first time systematically synthetic and biogenic Mg-containing calcium carbonate samples (especially sea urchin teeth—SUT) in detail by using two FTIRM instruments and compare these samples with KBr pellet FTIR measurements. Furthermore, we present spectra from geogenic calcite and dolomite minerals, recorded with both FTIRM systems, as well as KBr pellet FTIR spectra as references. We analyse the spectra by applying multi-peak curve fitting on the in-plane-bending (ν4) and out-of-plane (ν2) bands. Based on the obtained results we attribute the two singlet bands at ∼860–865 cm−1 and ∼695–704 cm−1 observed in the SUT FTIRM spectra to the existence of amorphous calcium carbonate (ACC), and report for the first time the existence of ACC at the mature end of SUT. In the other three studied biominerals, however, we did not find any ACC. Also, based on the FTIRM results, we observe that not only ν4, but also ν2 shifts to higher wavenumbers if more calcium ions are replaced by magnesium ions in the calcite lattices.

Graphical abstract: From synthetic to biogenic Mg-containing calcites: a comparative study using FTIR microspectroscopy

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Article information

DOI
https://doi.org/10.1039/C2CP22453D
Article type
Paper
Submitted
29 Jul 2011
Accepted
18 Nov 2011
First published
12 Jan 2012

Phys. Chem. Chem. Phys., 2012,14, 2255-2263

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From synthetic to biogenic Mg-containing calcites: a comparative study using FTIR microspectroscopy

X. Long, M. J. Nasse, Y. Ma and L. Qi, Phys. Chem. Chem. Phys., 2012, 14, 2255 DOI: 10.1039/C2CP22453D

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