Drying from phosphate-buffered solutions can result in the phosphorylation of primary and secondary alcohol groups of saccharides, hydroxylated amino acids, proteins, and glycoproteins.
Drying (e.g., freeze-drying) aqueous phosphate-buffered solutions of organic compounds containing primary and/or secondary alcohol groups promotes esterification, producing orthophosphate esters. The reaction is accelerated by heat and by pH values < 7 and is affected by residual moisture content. The same preparations as solutions, similarly treated, produced little or no phosphorylated materials. The promotion of esterification in the dry state can, in part, be rationalized in terms of a mass-action effect because of the resulting low-water activity in dried preparations. When metaphosphates are used, esterification proceeds at a greatly increased rate and to a greater extent. Because of the relatively facile interconversion of phosphorus oxyacid salts, it is possible that a "metaphosphate species" may be responsible for the esterification reaction in all cases. We conclude that care should be exercised when hydroxylated organic compounds are dried from phosphate buffers so as to avoid the formation of phosphorylated artifacts.
Tarelli
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Division of Chemistry, National Institute for Biological Standards and Control, Potters Bar, Herts, United Kingdom.
Wheeler
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SF
D000596:Amino Acids / Q000737:chemistry / Q000378:metabolism*; D002021:Buffers; D050260:Carbohydrate Metabolism; D002241:Carbohydrates / Q000737:chemistry; D006023:Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D006900:Hydroxylation; D010766:Phosphorylation; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*
D000596:Amino Acids; D002021:Buffers; D002241:Carbohydrates; D006023:Glycoproteins; D011506:Proteins