Determination of neo- and d-chiro-Inositol Hexakisphosphate in Soils by Solution ³¹P NMR Spectroscopy

Abstract

The inositol phosphates are an abundant but poorly understood group of organic phosphorus compounds found widely in the environment. Four stereoisomers of inositol hexakisphosphate (IP6) occur, although for three of these (scyllo, neo, and d-chiro) the origins, dynamics, and biological function remain unknown, due in large part to analytical limitations in their measurement in environmental samples. We synthesized authentic neo- and d-chiro-IP6 and used them to identify signals from these compounds in three soils from the Falkland Islands. Both compounds resisted hypobromite oxidation and gave quantifiable 31P NMR signals at δ = 6.67 ppm (equatorial phosphate groups of the 4-equatorial/2-axial conformer of neo-IP6) and δ = 6.48 ppm (equatorial phosphate groups of the 2-equatorial/4-axial conformer of d-chiro-IP6) in soil extracts. Inositol hexakisphosphate accounted for 46–54% of the soil organic phosphorus, of which the four stereoisomers constituted, on average, 55.9% (myo), 32.8% (scyllo), 6.1% (neo), and 5.2% (d-chiro). Reappraisal of the literature based on the new signal assignments revealed that neo- and d-chiro-IP6 occur widely in both terrestrial and aquatic ecosystems. These results confirm that the inositol phosphates can constitute a considerable fraction of the organic phosphorus in soils and reveal the prevalence of neo- and d-chiro-IP6 in the environment. The hypobromite oxidation and solution 31P NMR spectroscopy procedure allows the simultaneous quantification of all four IP6 stereoisomers in environmental samples and provides a platform for research into the origins and ecological significance of these enigmatic compounds.

Characterization of phosphorus forms in lake macrophytes and algae by solution 31P nuclear magnetic resonance spectroscopy

“…These extractants have included NaAs-SD, H 2 O, weak acid, NaHCO 3 , H 2 SO 4 , NaOH, and NaOH-EDTA. Recoveries varied among these extractants (Makarov et al 2002;He et al 2009;Noack et al 2014;Read et al 2014;Turner et al 2012;Zhang et al 2014). In general, recovery was approximately 5∼8 % with 50 mM H 2 SO 4 and 500 mM NaHCO 3 as the extraction agent in fresh microbial cells (Makarov et al 2002).…”

Identification of inositol hexakisphosphate binding sites in soils by selective extraction and solution 31P NMR spectroscopy

“…The greatest concentrations appear to occur in grassland soils, but IP 6 has also been detected in crop soils, forest soils, and rice paddies (Turner, 2007). Four stereoisomers of IP 6 have been identified in soils; the most abundant is the myo isomer, with smaller amounts of the scyllo, neo and D-chiro isomers (Cosgrove, 1962;Cosgrove and Tate, 1963;Turner, 2007;Turner et al, 2012). myo-Inositol hexakisphosphate is the main P compound in seeds and is also present in manure from monogastric animals, which are not able to digest myo-IP 6 (Cosgrove, 1980;Leytem and Maguire, 2007).…”

The “Other” Inositols and Their Phosphates: Synthesis, Biology, and Medicine (with Recent Advances inmyo‐Inositol Chemistry)

“…A recent stimulus has been provided. [11] As stated in the Introduction the work cited describes effects across a very wide area of biology and biochemistry. As such it is difficult to draw any general conclusions about the roles of the "other" inositols beyond saying that they are very diverse, and too few of these roles are yet known to support the drawing of any wide conclusions.…”

“…The phosphorylated forms of most of the inositol isomers are widespread in the environment where they form a large but poorly understood pool of environmental phosphate that is derived mainly from plants. [11] Some of these phosphorylated inositol isomers have been chemically synthesised and tested in assays against various enzymes and receptors to find possible biological roles.[e.g. 32,80,84,164] Obviously, such derivatives with different stereochemistry or regiochemistry of substitution can merely just act on systems controlled by myo-inositol derivatives, but the hope would be to find unique activities.…”

“…[11] This report and a related commentary highlighted the paucity of our knowledge on the origins and biological functions of the inositol hexakisphosphate stereoisomers, despite the fact that they constitute one of the most prevalent groups of organic phosphates in the environment. [12] By implication also, this lack of knowledge extends to the parent inositol stereoisomers and any polyphosphate or other derivative thereof.…”