Phosphates oxygen isotope enrichment

Grant et al. described an investigation of the ternary complex of ATP and bis(2-pyridyl)amine (MgATP/BPA), using advanced solid-state NMR methods such as Mg REDOR and Mg MQMAS in Mg-isotopically enriched samples. In the 3QMAS spectrum, the authors detected the presence of two Mg sites with close Mg quadrupole parameters. With help of a REDOR experiment, the assignment of these two sets of parameters to Mg ions either coordinated to water molecules or to phosphate oxygen donors was then possible. 

The guanine moiety has the lowest ionization potential of any of the DNA bases or of the sugar-phosphate backbone. As a result, radiation-produced holes are stabilized as dG for hydrated DNA irradiated at 77 K There is an extensive literature describing the role of dG in the radiation chemistry of DNA as studied by pulse radiolysis, flash photolysis, and product analysis. In order to explicate the oxidative reaction sequence in irradiated DNA and to more firmly identify the relevant radical intermediates, ESR spectroscopy was employed to investigate y-irradiated hydrated DNA (T = 12 2). Some experiments were also performed on hydrated (T = 12 2) DNA in which an electron scavenger [thallium(ni) (TP )] was employed to isolate the oxidative path. Oxygen-17 isotopically enriched water was also used to confirm a proposed water addition step to G and the subsequent transformations that follow These experiments were run in oxygen-free samples under conditions for which indirect effects were unimportant. 

To avoid isotopic dilution at high enrichments of oxygen-18, Anbar and Guttmann (1959) have hydrolyzed phosphorus trichloride in 0 -enriched water, oxidized the phosphite in solution with bromine, then added sufficient metallic sodium to make the solution alkaline, and precipitated the phosphate with barium chloride. The free acid may be obtained in solution by shaking with a cation exchange resin (such as Dowex 50). 

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