Title
Imaging mass spectrometry analysis of flavonoids in blue viola petals and their enclosure effects on violanin during color expression
Author
Kohtaro Sugahara, Kazunori Kitao, Takehiro Watanabe, Tohru Yamagaki
Year
2018
Journal
analytical chemistry
Abstract
The color expression of anthocyanin pigments in blue flowers is precisely controlled by the pigments’ chemical and physical environmental properties such as pH, metal ions, and the presence of colorless copigments. Despite the large number of known blue flowers, the coloration mechanisms of these have rarely been resolved. Herein, we showed that the blue coloration of Viola cornuta petals is expressed via the copigmentation of various flavonol 3-O-glycosides that are localized in considerable amounts in the blue regions together with violanin, an anthocyanin. By employing quantitative imaging mass spectrometry, we identified the structures and amounts of the flavonols co-localized with violanin in discrete blue-colored regions in the petal. The obtained data allowed an in vitro reconstruction of the color expression that agreed with the raw viola petal visible spectrum. Visible spectral analysis indicated that neither pH elevation in the vacuoles nor coexisting metal ions affected the color development. Eventually, we experimentally revealed that the excess amounts of flavonol 3-O-glycosides enclosed and destructed the levorotatory helical self-assembly of violanin when blue coloration was expressed via copigmentation.
Instrument
J-725
Keywords
Circular dichroism, Cotton effect, Chemical stability, Ligand binding, Organic chemistry, Biochemistry