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Science 31 October 2008:
Vol. 322. no. 5902, pp. 724 - 727
DOI: 10.1126/science.1159417
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Reports

Peptides Enhance Magnesium Signature in Calcite: Insights into Origins of Vital Effects

A. E. Stephenson,1* J. J. DeYoreo,2 L. Wu,2,3 K. J. Wu,2 J. Hoyer,4 P. M. Dove1*

Studies relating the magnesium (Mg) content of calcified skeletons to temperature often report unexplained deviations from the signature expected for inorganically grown calcite. These "vital effects" are believed to have biological origins, but mechanistic bases for measured offsets remain unclear. We show that a simple hydrophilic peptide, with the same carboxyl-rich character as that of macromolecules isolated from sites of calcification, increases calcite Mg content by up to 3 mole percent. Comparisons to previous studies correlating Mg content of carbonate minerals with temperature show that the Mg enhancement due to peptides results in offsets equivalent to 7° to 14°C. The insights also provide a physical basis for anecdotal evidence that organic chemistry modulates the mineralization of inorganic carbonates and suggest an approach to tuning impurity levels in controlled materials synthesis.

1 Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, USA.
2 Chemistry and Materials Science Directorate, Lawrence Livermore National Lab, Livermore, CA 94551, USA.
3 Department of Applied Science, University of California–Davis, Davis, CA 95616, USA.
4 Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA.

* To whom correspondence should be addressed. E-mail: dove{at}vt.edu (P.M.D.) and aestephe{at}vt.edu (A.E.S.)

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