Mechanism of the autocatalytic formation of ferrihemoglobin by N,N-dimethylaniline-N-oxide. Structure and ferrihemoglobin forming activity of the purple dye.

The structure of the leuco compound of the purple dye which is formed in mixtrues of N,N-dimethylaniline-N-oxide (DANO) and ferrihemoglobin or ferricytochrome c was elucidated. IR, NMR, mass spectroscopy, and synthesis by oxidation of mixtures of N-methylaniline and 2-dimethylaminophenol showed that the leuco compound is produced by condensation of these two compounds. But only X-ray analysis proved the structure: 2-dimethylamino-4-(N-methylanilino)-phenol. The purple dye was produced from the leuco compound by withdrawal of two electrons and may be considered as resonance hybrid of the p-quinonimine and the o-quinonimine. When DANO was incubated with ferrihemoglobin or ferricytochrome c the oxygen of DANO was used for the production of the dye by oxidation of N-methylaniline and 2-dimethylaminophenol. The amount of N,N-dimethylaniline found in the incubation mixtures corresponded with the amount of purple dye produced. In the absence of molecular oxygen from incubation mixtures of DANO with cytochrome c the purple dye was formed at the same rate as under air. In blood in vitro the purple dye catalytically transferred electrons from ferrohemoglobin to molecuar oxygen. Its ferrihemoglobin-forming activity was lower than that of 4-dimethylaminophenol but higher than that of 2-dimethylaminophenol. The chemical mechanism of the autocatalytic formation of ferrihemoglobin by DANO is described.