Strongly bound citrate stabilizes the apatite nanocrystals in bone
Y.-Y. Hu, A. Rawal, and K. Schmidt-Rohr1
+ Author Affiliations
Ames Laboratory and Department of Chemistry, Iowa State University, Ames, IA 50011
Edited by David A. Tirrell, California Institute of Technology, Pasadena, CA, and approved October 12, 2010 (received for review June 27, 2010)
Published online before print December 2, 2010, doi: 10.1073/pnas.1009219107
PNAS December 2, 2010
Abstract: Nanocrystals of apatitic calcium phosphate impart the organic-inorganic nanocomposite in bone with favorable mechanical properties. So far, the factors preventing crystal growth beyond the favorable thickness of ca. 3 nm have not been identified. Here we show that the apatite surfaces are studded with strongly bound citrate molecules, whose signals have been identified unambiguously by multinuclear magnetic resonance (NMR) analysis. NMR reveals that bound citrate accounts for 5.5 wt% of the organic matter in bone and covers apatite at a density of about 1 molecule per (2 nm)2, with its three carboxylate groups at distances of 0.3 to 0.45 nm from the apatite surface. Bound citrate is highly conserved, being found in fish, avian, and mammalian bone, which indicates its critical role in interfering with crystal thickening and stabilizing the apatite nanocrystals in bone.
A nice summary of the article can also be found in C&E News.