Role of magnesium as radiosensitizer in the in vitro radiolysis of aqueous solutions of guanosine-5'-monophosphate disodium.

A combination of Fourier Transform Infrared (FT-IR) spectroscopy and mass spectrometry (MS) was used to investigate the role of Mg2+ ions in gamma-radiolysis of aqueous solutions of guanosine-5'-monophosphate disodium salt. The FT-IR intensity changes together with the mass spectra suggest the interaction of the magnesium atom with the base guanine at the N7 site. The decomposition-limiting yield G(-5'-GMPNa2) in deaerated as well as in nitrous oxide saturated solutions, determined by measuring the absorbance at 253 nm, was found to be 0.6 and 1.2 respectively. Comparison of these values with the corresponding limiting yields of 0.3 and 0.6 that were found in the absence of Mg2+ ions shows the sensitizing role of this ion in the radiolysis of the mononucleotide. This in vitro behaviour may result in more effective local therapy of tumour by gamma-ray irradiation in the presence of Mg2+, due to the 100 per cent sensitization of the radiolysis reaction. It remains to be seen whether this is also true in vivo.