With the intention of doing a study of the CrO:-/Cr,O:-equilibrium in aqueous solution, we have carefully re-examined the Raman spectra of CrO:-, Cr,O:-and CICrO;. Diluting stepwise an aqueous solution of 00:-ion we have showed the non-existence of the HCrO; species which was previously considered to exist in such systems. By studying the effect of pH on the Raman spectra we calculated the constant for the equilibrium: 2 Cr0:-+ 2H'S Cr20:-+H20 to be log (jZ2 = 13.77 k 0.02 (20 "C and KNO, 0.8 M). Using this value of the constant, we were able to establish the distribution diagram of the Cr0:-and Cr20:-species versus pH.

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Using the spin-trapping technique, irradiation with visible light of complexes between DNA and proflavine was shown to generate OH radicals. The characteristic spectra were not obtained when proflavine or DNA were irradiated alone, nor when oxygen was absent. Using DMPO as a spin trap we found that the intensity of the DMPO-OH e.p.r. signal was enhanced when the molar ratio between bound proflavine and the DNA phosphorus increased up to a value of 0.15 demonstrating the efficiency of the intercalated dye molecules. A strong decrease of the e.p.r. signal was observed in the presence of various OH. scavengers like t-butanol, isopropanol or sodium benzoate. The OH. production was also decreased when the irradiation was made in the presence of SOD, ceruloplasmin or catalase and after addition of Chelex 100 resin.

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