The photochemistry of phosphorus compounds. Part VII. The far-ultraviolet spectroscopy and photochemistry of glycerol 1-phosphate and of glycerol 2-phosphate in aqueous solutions

Abstract

The u.v. absorption of the disodium salts of both glycerol 1- and of glycerol 2-phosphate in aqueous solutions exhibits a weak absorptivity from 300 to 220 nm, which is almost unaffected by changes in temperature or by replacement of water with D₂O as a solvent. Below 220 nm, the absorptivity increases sharply. This steep absorption edge is red-shifted with increasing temperature; in D₂O solution it is shifted towards shorter wavelengths. On the basis of these environmental effects, the weak absorption in the 300–220 nm region is assigned to an internal electronic transition, while the intense absorption band below 220 nm is assigned to a ‘charge-transfer-to-solvent transition’.

The photochemistry of the glycerophosphates was studied by irradiation of aqueous solutions at 253·7 nm. In a nitrogen atmosphere, the quantum yield for release of orthophosphate both from glycerol 1- and from glycerol 2-phosphate was ϕ= 0·01. In an oxygen atmosphere, the quantum yield increased to ϕ= 0·023 and 0·030 for glycerol 1- and glycerol 2-phosphate, respectively. Photolysis of glycerol 1-phosphate in H₂¹⁸O in evacuated ampoules resulted in 98% C–O bond fission. Both in nitrogen and in oxygen atmospheres, an acid- and alkalilabile phosphate ester was formed as an initial product, which disappeared upon further photolysis, and which was identified as dihydroxyacetone phosphate. The yield of hydrogen produced by photolysis of glycerol 1-phosphate in evacuated tubes was only 10% of that equivalent to the orthophosphate released. The main non-volatile products in the photolysis in evacuated tubes of ¹⁴C-labelled glycerol 1-phosphate were glycidol (40% of the orthophosphate released), glyceraldehyde or dihydroxyacetone (10%), and glycollic acid (9%). Glycollic acid and carbon dioxide were released only in traces by photolysis of both glycerol 1- and glycerol 2-phosphate in a nitrogen atmosphere, but evolved readily in an oxygen atmosphere. Glycidol itself in aqueous solutions was found to undergo photolysis to glycollic acid and carbon dioxide, very slowly under nitrogen and in evacuated tubes, but immediately in oxygenated solutions.