Interfacial Ca2+ environments in nanocrystalline apatites revealed by dynamic nuclear polarization enhanced 43Ca NMR spectroscopy

Daniel Lee,Danielle Laurencin,Christian Bonhomme,César Leroy,Laure Bonhomme-Coury,Charlène Crevant,Gaël De Paëpe,Florence Babonneau

doi:10.1038/ncomms14104

Abstract

The interfaces within bones, teeth and other hybrid biomaterials are of paramount importance but remain particularly difficult to characterize at the molecular level because both sensitive and selective techniques are mandatory. Here, it is demonstrated that unprecedented insights into calcium environments, for example the differentiation of surface and core species of hydroxyapatite nanoparticles, can be obtained using solid-state NMR, when combined with dynamic nuclear polarization. Although calcium represents an ideal NMR target here (and de facto for a large variety of calcium-derived materials), its stable NMR-active isotope, calcium-43, is a highly unreceptive probe. Using the sensitivity gains from dynamic nuclear polarization, not only could calcium-43 NMR spectra be obtained easily, but natural isotopic abundance 2D correlation experiments could be recorded for calcium-43 in short experimental time. This opens perspectives for the detailed study of interfaces in nanostructured materials of the highest biological interest as well as calcium-based nanosystems in general.

Highlights

The interfaces within bones, teeth and other hybrid biomaterials are of paramount importance but remain difficult to characterize at the molecular level because both sensitive and selective techniques are mandatory
The broad diversity of structural roles played by calcium compounds undoubtedly comes from the ability of Ca2 þ cations to adopt a large variety of coordination environments, with coordination numbers varying from 4 to 9, and many different coordination geometries
Solid-state nuclear magnetic resonance (NMR) has been used to study Ca2 þ environments[1,2,3,4,5], it has only rarely been applied to complex materials because of severe sensitivity drawbacks

Summary

Introduction

The interfaces within bones, teeth and other hybrid biomaterials are of paramount importance but remain difficult to characterize at the molecular level because both sensitive and selective techniques are mandatory.

Results

Conclusion