Correspondence/Rebuttal pubs.acs.org/est
Comment on “Determination of neo- and D-chiro-Inositol Hexakisphosphate in Soils by Solution 31P NMR Spectroscopy”
T
he paper by Benjamin L. Turner, et al.1 is an outstanding treatise on a subject of vital importance to our knowledge of soil organic phosphorus and the environment. It is remarkable how scientific research on soil inositol phosphates and their measurement by 31P NMR spectroscopy has advanced since the 1960s when I first carried out research in this field using 1H NMR spectroscopy. I write to elucidate on the following sentence that appears in the first paragraph of the Introduction: “A report of muco-IP62 was criticized on analytical grounds,3 and this compound does not appear to exist in nature”. In my paper,2 I did not report muco-IP6 in the leaves of velvet mesquite; rather, I reported muco-inositol phosphate of which the number of phosphate groups on the muco-inositol moiety was not determined. Thus, the muco-inositol phosphates isolated from the plant leaves would include any phosphorylated form of muco-inositol; and muco-inositol-1-phosphate was subsequently reported in nature and produced by a NAD+dependent oxido-reductase, which catalysis the isomerization of galactose-6-phosphate to muco-inositol-1-phosphate.4,5 The work reported in my paper2 was the culmination of research carried out during 1967−1970 published in detail in a doctoral dissertation.6 In this research the inositol phosphates were isolated by the method of Anderson7 as a barium salt precipitate, which was washed thoroughly under filtration to remove any nonphosphorylated inositols. The inositol moieties were isolated subsequently by acid hydrolysis to remove the phosphate groups, which was followed by preparative paper chromatography to separate and isolate the inositol stereoisomers. Milligram quantities of each of the isolated inositol diastereomers were collected and recrystallized before subjecting the compounds to spectroscopic analysis including 1H NMR. The criticism3 reported that polysaccharide material could exist in the precipitate fractions isolated by the method of Anderson,7 raising the possibility that some nonphosphorylated inositols may be extracted along with the phosphorylated forms; and that ion-exchange chromatographic separation of inositol phosphate fractions prior to acid hydrolysis would be required to conclude irrefutably that the inositols are isolated in the phosphorylated form. I do not agree with this argument because I filtered and washed thoroughly the organic phosphate fraction (barium phosphate precipitate) obtained by the method of Anderson7 to ensure that no nonphosphorylated inositol would be found in the precipitate. In addition, following acid hydrolysis of the phosphate groups from the barium phosphate precipitate, relatively large (up to 5 mg) samples of each of the inositol diastereomers were separated and isolated by preparative paper chromatography and recrystallized in aqueous acetone or ethanol prior to 1H NMR spectroscopy. The relatively large (∼5 mg) samples of inositol diastereomers, which I isolated from the thoroughly washed barium phosphate precipitate further negates the © 2012 American Chemical Society
argument that traces of nonphosphorylated inositol material could have interfered with the findings of this work. In 1977, I branched off to an altogether different field of research; and many years later found the criticism3 in the scientific literature. At that time I ignored this criticism as trivial; but now feel compelled to defend the work in light of the fact that attention to the criticism was brought to light in this outstanding paper.
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Michael F. L’Annunziata
AUTHOR INFORMATION
Notes
The authors declare no competing financial interest.
REFERENCES
(1) Turner, B. L.; Chessman, A. W.; Godage, H. Y.; Riley, A. M.; Potter, B. V. L. Determination of neo- and D-chiro-inositol hexakisphosphate in soils by solution 31P NMR spectroscopy. Environ. Sci. Technol. 2012, 46, 4994−5005. (2) L’Annunziata., M. F.; Fuller, W. H. Soil and plant relationships of inositol phosphate syereoisomers: The identification of D-chiro- and muco-inositol phosphates in a desert soil and plant system. Soil Sci. Soc. Am. J. 1971, 35, 587−595. (3) Cosgrove, D. J. Inositol Phosphates: Their Chemistry, Biochemistry and Physiology; Elsevier, Amsterdam, 1980, p 197. (4) Adhikari, J.; Majumdar, A. L. L-myo-inositol-1-phosphate synthase from mammalian brain: partial purification and characterization of the fetal and adult enzyme. Ind. J. Biochem. Biophys. 1988, 25, 408−412. (5) Chhetri, D. R.; Mukherjee, A. K.; Adhikari, J. Myo-inositol content in pteridophytes and the isolation and characterization of Lmyo-inositol-1-phosphate synthase from Diplopterygium glaucum. Braz. J. Plant Physiol. 2006, 18, 291−298. (6) L’Annunziata, M. F. Soil-plant Relationships and Spectroscopic Properties of Inositol Srereoisomers; The Identification of D-chiro- and Muco-inositol in a desert Soil-Plant System. Doctoral Dissertation. 1970, The University of Arizona, Tucson, 114 pages, University Microfilms International (UMI), AAT 7104237, http://dissexpress. umi.com/dxweb?sitex=10020:22372:US#results. (7) Anderson, G. The identification and estimation of soil inositol phosphates. J. Sci. Food Agric. 1956, 7, 437−444.
Published: September 27, 2012 11479
dx.doi.org/10.1021/es303314h | Environ. Sci. Technol. 2012, 46, 11479−11479
