RADIOSENSITIZATION OF THYMINE BY COPPER(II) AND NICKEL(II) COMPLEXES OF METRONIDAZOLE

Aqueous solutions of thymine (10(-3) mol dm(-3)) were irradiated with Co-60 gamma-rays in the absence and presence of metronidazole as well as its Cu(II) and Ni(II) complexes (10(-4) mol dm(-3)) under different conditions. The yields for the loss of thymine and those for the form ation of the products of radiolysis were determined by hplc. The degra dation of thymine when compared with that in the absence of metronidaz ole was not significantly altered. However, it increased significantly when the radiolysis of thymine was carried out in the presence of the Cu(II) and Ni(LI) complexes of metronidazole. All three compounds wer e found to promote the formation of thymine glycol although the increa se was more significant for the metal complexes than for free metronid azole. The higher radiosensitizing efficiency observed with the metal complexes as compared with that for free metronidazole is due to their higher rate of oxidation of the transient thymine-OH radical adduct. The reduction of the sensitizers results in the formation of the nitro -anion radical which in the case of the Cu(II) complex undergoes intra molecular electron transfer to the metal centre leading to the formati on of Cu(I).