June 11, 2010, University of Ottawa
Calcium is an important component in diverse materials and biochemicals. However, NMR spectroscopy of the only spin-active calcium isotope, Ca-43, is notoriously challenging due to its low natural abundance (0.14 %), low resonance frequency, and quadrupolar nature. Recently, researchers from the University of Ottawa, the NRC Steacie Institute for Molecular Sciences (SIMS-NRC), and Dalhousie University have independently reported advances in studies of inorganic polymorphs and cement-based materials using Ca-43 solid-state NMR spectroscopy.
"In spite of the great complexity of the calcium silicate chemistry involved in the hydration of Portland cement, we have shown that Ca-43 solid-state NMR provides useful new insights into cement chemistry", says Igor Moudrakovski (SIMS-NRC) of his collaboration with the Institute for Research in Construction (SIMS-IRC). Josef Zwanziger (Dalhousie) and his academic and industrial partners have similarly applied Ca-43 NMR in their project on the development, optimization and commercialization of high performance cement based composite materials.
Zwanziger explains, "we are trying to understand the nature of the composite-cement interface, and the mechanisms of toughening and strengthening in concrete composites. Calcium NMR is one of the many tools which is shedding light on the nature of the interface." At the University of Ottawa, David Bryce and his research group have demonstrated the utility of calcium NMR in understanding polymorphism in solids. This work has implications for understanding biomaterials as well as inorganic materials.
Because Ca-43 NMR in solid state requires a very strong magnetic field for sensitivity reasons, all these experiments were carried out at the National Ultrahigh-Field NMR Facility for Solids (www.nmr900.ca), a national user facility managed by the University of Ottawa and housed on NRC's Ottawa campus, which houses Canada's only 21.1 T (900 MHz) NMR spectrometer.
The latest calcium NMR research has been published in PCCP and J. Am. Chem. Soc., and a perspective on the state of the field is now available in Dalton Transactions (Bryce, 2010).
David L. Bryce "Calcium Binding Environments Probed by 43Ca NMR Spectroscopy," Dalton Transactions (2010) online. http://dx.doi.org/10.1039/c0dt00416b
Igor Moudrakovski, Rouhollah Alizadeh, James J. Beaudoin, "Natural abundance high field 43Ca solid state NMR in cement science," Physical Chemistry Chemical Physics 12 (2010) 6961-6969. http://dx.doi.org/10.1039/c000353k
David L. Bryce, Elijah B. Bultz, and Dominic Aebi, "Calcium-43 Chemical Shift Tensors as Probes of Calcium Binding Environments. Insight into the Structure of the Vaterite CaCO3 Polymorph by 43Ca Solid-State NMR Spectroscopy," Journal of the American Chemical Society 130 (2008) 9282–9292. http://dx.doi.org/10.1021/ja8017253