Collisional spectroscopy in structural characterization of melanins: I. A first study on [C8H7ON](+.) ions originating from pyrolysis of biosynthetic and synthetic tryptophan melanins

The structural investigation of four bio- and synthetic melanins, obtained by the action of polyphenol oxidase from potatoes and Psalliota campestris mushrooms and of tyrosinase from Sepia officinalis on tryptophan, or by means of performic oxidation, has been carried out by thermal decomposition performed in the ion source of a mass spectrometer. The structural characterization of the ionic species [C8H7ON](+.), common and abundant for all the examined compounds, has been obtained by accurate mass measurements and collisional spectroscopy. These mass spectrometric techniques have shown unequivocally for ionic species [C8H7ON](+.) the structure of 2-indolinone.