Characterization of iron, manganese, and copper synthetic hydroxyapatites by electron paramagnetic resonance spectroscopy
2002
Sutter, B. | Wasowicz, T. | Howard, T. | Hossner, L.R. | Ming, D.W.
The incorporation of micronutrients (e.g., Fe, Mn, Cu) into synthetic hydroxyapatite (SHA) is proposed for slow release of these nutrients to crops in NASA's Advanced Life Support (ALS) program for long-duration space missions. Separate Fe(3+) (Fe-SHA), Mn(2+) (Mn-SHA), and Cu(2+) (Cu-SHA) containing SHA materials were synthesized by a precipitation method. Electron paramagnetic resonance (EPR) spectroscopy was used to determine the location of Fe(3+), Mn(2+), and Cu(2+) ions in the SHA structure and to identify other Fe(3+)-, Mn(2+)-, and Cu(2+)-containing phases that formed during precipitation. The EPR parameters for Fe(3+) (g = 4.20 and 8.93) and for Mn(2+) (g = 2.01, A = 9.4 mT, D = 39.0 mT and E = 10.5 mT) indicated that Fe(3+) and Mn(2+) possessed rhombic ion crystal fields within the SHA structure. The Cu(2+) EPR parameters (g(z) = 2.488, A(z) = 5.2 mT) indicated that Cu(2+) was coordinated to more than six oxygens. The rhombic environments of Fe(3+) and Mn(2+) along with the unique Cu(2+) environment suggested that these metals substituted for the 7 or 9 coordinate Ca(2+) in SHA. The EPR analyses also detected poorly crystalline metal-oxyhydroxides or metal-phosphates associated with SHA. The Fe-, Mn-, and Cu-SHA materials are potential slow release sources of Fe, Mn, and Cu for ALS and terrestrial cropping systems.
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