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Title: Conformational change of metal phytates: solid state 1D 13C and 2D 1H-13C NMR spectroscopic investigations

Author
item He, Zhongqi
item ZHONG, JUNYAN - Old Dominion University
item Cheng, Huai

Submitted to: Journal of Food Agriculture and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2013
Publication Date: 2/1/2013
Citation: He, Z., Zhong, J., Cheng, H.N. 2013. Conformational change of metal phytates: solid state 1D 13C and 2D 1H-13C NMR spectroscopic investigations. Journal of Food Agriculture and Environment. 11(1):965-970.

Interpretive Summary: Phytate is an important phosphorous (P) and mineral storage compound in plant seeds, such as cottonseed. It is estimated that over 51 million metric tons of phytate (in K and Mg salts) are produced in crop seeds and fruits globally each year. Cottonseed meal in poultry feed contains about 4.4% (w/w) of phytate. However, up to two-thirds of P bound to phytate is unavailable to poultry. On the other hand, phytate has been reported to be a potential anti-cancer agent. In regards to environmental concern, phytate represents a significant portion of P in animal manure, and its runoff and leaching play a role in eutriphication of surface waters. It is proposed that both the benign and adverse effects of phytate in nutrition and environment are mainly due to its unique structure, where strong chelating ability makes phytate interact with many cations. In this study, we report solid state 1D 13C and 2D 1H-13C NMR spectra of 9 metal phytate compounds. Spectral analysis provides evidence for interconverting conformations that are influenced by different valent cations. Structural information derived from this research improves our understanding of the roles of phytates in metal storage in plants, lability and bioavailability of these organic P compounds in biological systems and the environment, and immobilization of heavy metals in contaminated soils.

Technical Abstract: Phytate is an important phosphorous and mineral storage compound in plant seeds. Both the benign and adverse effects of phytate in nutrition and environment are mainly due to its unique conformational structures, where a strong chelating ability makes phytate interact with many cations (such as Zn2+, Ca2+, Mg2+, and Al3+). However, information is scant on the conformational forms of different solid metal phytate compounds although phytate in solution exists in two conformations: one axial and five equatorial phosphates (1a/5e) structure and an inverted 5a/1e structure. Consequently, we investigated the spectral features of nine representative metal phytate compounds by solid state 1D 13C cross polarization magic angle spinning (CPMAS) and 2D 13C-1H heteronuclear correlation (HETCOR) NMR. A broad peak appeared in all solid 1D NMR spectra of hydrogen monovalent, divalent, and trivalent metal phytate compounds. The spectra of hydrogen monovalent and divalent compounds could be deconvoluted to two separate resonance peaks. 2D HETCOR clearly showed distinct 13C-1H correlations for inositol C-H moieties in hydrogen metal phytates. Based on the known structures of myo-inositol and Na phytate, we interpret the solid NMR structures of hydrogen metal phytates as mixtures of interconverting ring conformations. The observed difference in the 2D HETCOR NMR spectra between hydrogen metal phytates and non-hydrogen metal phytates provides a spectroscopic method to distinguish the two types of phytate compounds from each other.