Examination of small molecule losses in 5-methylpyranopelargonidin MS/MS CID spectra by DFT calculations.

Abstract

Pyranoanthocyanins are formed during food treatment and maturation (e.g. wine, juices), and they can be considered a natural alternative to artificial food colorants. Tandem mass spectrometry (MS/MS) is perhaps the most important technique in analysis of anthocyanin dyes. Knowledge of fragmentation pattern is a key aspect of their successful structural characterization. Polyphenolic compounds are known to lose small molecules during collision-induced dissociation (CID) in MS/MS experiments. However, the specific positions where such losses occur preferentially are unknown. The aim of this communication is to investigate the energetically most preferred places for H2 O and CO losses during the fragmentation of 5-methylpyranopelargonidin molecule by the means of computational chemistry (employing density functional theory) combined with CID MS/MS experiments and infrared multiphoton dissociation spectroscopy. Mechanisms responsible for the fragmentations were investigated, and optimal geometries and transition states were obtained. Cleavage of water as well as carbon monoxide occurs preferentially from the C-ring of flavonoid skeleton. In the most stable structure of 5-methylpyranopelargonidin, B-ring was found to be tilted with respect to the rest of the molecule. Planarization effort of the parent molecule contributes both to its decarbonylation and dehydration.