E.P.R. spin trapping has been employed to study radical production during the bactericidal action of three peroxide compounds (peracetic acid, 4-percarboxy-N-isobutyltrimellitimide and magnesium monoperoxyphthalate) upon both Gram negative (Escherichia Coli) and Gram positive (Staphylococcus Aureus) bacteria. Use of the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) has allowed direct detection of both carbon-centred and hydroxyl radicals, which are produced at varying rates for the different bacteria/peracid systems studied. The inhibition of bactericidal action, by DMPO and two antioxidants, Vitamin C and Trolox C, indicates that radicals are the lethal species and evidence is presented which suggests that radical production is internal to the bacterial cell. Hydroxyl radicals are believed to be the lethal species. The effect of added iron chelators and haem protein inhibitors indicates that iron species and haem proteins in particular are involved. A marked variation is found in observed hydroxyl-radical adduct signals with both the nature and concentration of peracid. A strong inverse correlation is found between the concentration of the observed radical adduct signal and the relative strength of the peroxide as a bactericide; use of a stable nitroxide as a radical scavenger confirms that strong bactericides produce radicals at a much faster rate than weak bactericides. Plots of radical generation versus time are correlated with % bacterial kill, offering further evidence that hydroxyl radicals are the lethal species.

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A quantitative study has been made of the formation of hydrogen peroxide when alkaline solutions of tannic acid, gallic acid and a number of other molecules containing the catechol (1,2-dihydroxybenzene) moiety are exposed to air or dioxygen. For gallic acid, from the pH dependence of the initial rates of reaction, it is shown that, over the pH range ca. 7.0-8.5, the predominant reactive species is the dianion. The photochemical production of hydrogen peroxide, using 254 nm radiation, has been studied for a variety of air-saturated solutions of phenolic substances at pH 6.0 or below, where the thermal reaction is negligible, and apparent quantum yields are reported. Appreciable formation of hydrogen peroxide is observed with 1,2-, 1,3and 1,Cbenzene diols.Possible mechanisms for the thermal and photochemical reactions are discussed and it is suggested that benzenediol groups may be involved in the natural photochemical production of hydrogen peroxide in surface waters.

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