Potentiometric Study of Pyocyanine

Bacillus pyocyaneus produces, according to the conditions, different varieties of pigment of which pyoeyanine is best known and easily isolated because of its solubility in chloroform. This pigment is indigo blue at alkaline reaction, wine-red at acid reaction, and is reducible to a leuco compound by various reductants or in the absence of air by the living bacillus itself, and the leucodye is readily reoxidizedfon exposure to the air. It behaves in this respect as any of the reversible organic dyestuff s of the quinone type. The pigment can easily be obtained in a pure crystallized form and has been chemically studied by Ledderhose (l), MacCombie and Scarborough (2), and more recently by Wrede and Strack (3). The latter authors consider it as a methylated oxyphenazine and confirmed this assumption by a synthesis. From freezing point determination in glacial acet,ic acid they conclude that the oxidized form of the dye has double the molecular weight of the reduced form. If this be true also for aqueous solutions, the potential curve obtained on titrating the reduced dye with an oxidant or the oxidized dye with a reductant should show a form considerably different from the one of an ordinary organic dyestuff of the quinone type. In our potentiometric studies, however, we found no difference in the potential curve from the one of an ordinary dye. This at least holds for neutral and alkalihe solutions. To be sure in acid solution there is a striking difference, but not of such a nature as to account for a bimolecular structure. This will be discussed later on. Once the reversible nature of the oxidation and reduction of pyocyanine has been recognized it was suggestive to undertake a