Spectroscopic Characteristics and Some Chemical Properties of N-methylphenazinium Methyl Sulfate (phenazine Methosulfate) and Pyocyanine at the Semiquidnoid Oxidation Level.

It has long been known that in acid solution phenazine and related compounds, including N-alkylated derivatives, are oxidized and reduced in distinct l-electron steps, thereby passing through a semiquinoid intermediate (l-4). These semiquinoid forms are stable in acid and have a characteristic green color which readily distinguishes them from the fully oxidized or fully reduced compounds. N-Methylphenazinium methyl sulfate (commonly known as phenazine methosulfate) was introduced as an electron acceptor in electron transfer reactions of mitochondria by Kearney and Singer (5) and has recently been used in the reduced form as an electron donor in studies of the cytochrome c oxidase region of the respiratory chain (6). Electron paramagnetic resonance studies of succinic dehydrogenase in which N-methylphenazinium methyl sulfate acted as an electron acceptor showed free radical formation (7,8) leading to the suggestion that in this system the dye may become reduced in one-electron steps (9). The studies on photosynthetic systems of bacteria and green plants, in which N-methylphenazinium methyl sulfate and pyocyanine function as electron transfer agents, catalyze photophosphorylation, and are photo-oxidized in the presence of ubiquinone (10, II), have also raised the question of a role of stable semireduced intermediates of N-methylphenazinium methyl sulfate as donors or acceptors in biological electron transfer systems. Since evidence for the participation of these intermediates may be obtained from spectroscopic observations, further information on these properties is essential. Also of interest is information on the stability of these free radical forms at pH values used in studying biological systems. These considerations have led to the present investigation of some of the spectroscopic and chemical properties of N-methylphenazinium methyl sulfate and pyocyanine in their intermediate oxidation states.