Thursday, November 16, 2006 - 9:30 AM
319-3
Solid state spectral features of metal phytate compounds.
Zhongqi He1, C. Wayne Honeycutt1, Tiequan Zhang2, Perry J. Pellechia3, and Wolfgang A. Caliebe4. (1) USDA-ARS, New England Plant, Soil, and Water Laboratory, Orono, ME 04469, (2) Agric. & Agri-Food Canada, 2585 County Road 20, 2585 County Road 20, Harrow, ON N0R 1G0, CANADA, (3) University of South Carolina, Dept. of Chemistry & Biochemsitry, Columbia, SC 29208, (4) Brookhaven National Laboratory, The National Synchrotron Light Source, Upton, NY 11973
Phytate (inositol hexaphosphoric acid, IP6) is a predominant form of organic phosphorus in animal manure, soil, and other organic substances. Whereas many studies have investigated the wet chemistry of IP6, there is little information on the characterization of solid metal IP6 compounds. This information is essential for further understanding and assessing the chemical behavior of IP6 in diverse soil-plant-water ecosystems. In this work, we characterized eight metal phytate compounds and investigated their structural features using Fourier transform infrared spectroscopy (FT-IR), solid state P-31 nuclear magnetic resonance (NMR) spectroscopy, and X-ray absorption near edge structure (XANES) spectroscopy. The absorption features from 900 to 1200 cm-1 in FT-IR could be used to identify these phytates as: (1) light divalent metal (Ca and Mg) compounds with a sharp band and a broad band, (2) heavy divalent metal (Cu and Mn) compounds with splitting broad bands, and (3) trivalent metal (Al and Fe) compounds with a broad band and a shoulder band. Three different types of chemical structures of metal-phytate compounds were present based on FT-IR analysis. In solid state 31P NMR spectra, Na, Ca, and Al phytates, as well as acidic K phytate, possessed distinguishable major isotropic chemical shift bands. Compared to inorganic phosphates, the spectra of metal phytates demonstrated strong spinning side bands. Similarly, differences were observed among the phosphorus K-edge XANES spectra of five metal phytate compounds. Significant differences can be observed in the intensity, position, and width of the white line at approximately 2153eV. This work demonstrated that the advanced spectroscopic technologies evaluated could be used to advance our knowledge of the fate of phytate, particularly as it interacts with metal species in the environment.