A practical method for preparing peroxynitrite solutions of low ionic strength and free of hydrogen peroxide

The reaction of ozone (not, vert, similar5% in oxygen) with sodium azide (0.02–0.2 M in water) at pH 12 and 0–4°C is shown to yield concentrated, stable peroxynitrite solutions of up to 80 mM. The product of this reaction is identified based on a broad absorption spectrum with a maximum around 302 nm and by its first-order rate of decomposition (k = 0.40 ± 0.01 s−1 at pH 7.05 and 25°C). These peroxynitrite solutions can be obtained essentially free of hydrogen peroxide (detection limit 1 μM) and only traces of azide (detection limit 0.1 mM). They are low in ionic strength and have a pH of about 12 but without buffering capacity; therefore, they can be adjusted to any pH by addition of buffer. These preparations of peroxynitrite frozen at −20°C show negligible decomposition for about 3 weeks of storage and follow a first-order decomposition with a halfiife of about 7 days at refrigerator temperatures (not, vert, similar5°C). These preparations give reactions that are characteristic of peroxynitrite. For example, at pH 7.0, they react with L-tyrosine to give a 7.3 mol % yield of nitrotyrosine(s), and with dimethyl sulfoxide to give a 8.2 mol % yield of formaldehyde, based on starting peroxynitrite concentration.