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Structural studies on the stereoisomerism of a natural dye miraxanthin I

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Abstract

The chemical structure of a yellow dye present in Mirabilis jalapa L., miraxanthin I, was characterized by NMR spectroscopy. The extract of M. jalapa was analysed by a high-performance liquid chromatographic system (LC-DAD-FL-ESI-MS/MS) and the presence of miraxanthin I among other betaxanthins was confirmed. This dye was synthesized from previously generated methionine-betaxanthin by oxidation with 10% H2O2. The E/Z stereoisomers of miraxanthin I were found by NMR analysis to occur in a 50 : 33 : 10 : 7 ratio in aqueous solution (7E,9E : 7Z,9E : 7E,9Z : 7Z,9Z configurations, respectively). Comparison of NMR data with chemical shifts obtained from quantum chemical calculations strongly suggests the presence of intramolecular hydrogen bonds which may favour a more rigid structure of the dye. This explains the highest fluorescence quantum yield among betaxanthins. The observed changes in the 1H NMR spectra during the measurements indicate on miraxanthin I hydrolysis for which a mechanism is proposed. The first step during the hydrolysis process is protonation of the nitrogen atom within the central bridge bond system which is observed in the ZE stereoisomer by NMR.

Graphical abstract: Structural studies on the stereoisomerism of a natural dye miraxanthin I

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Publication details

The article was received on 14 Aug 2019, accepted on 25 Oct 2019 and first published on 30 Oct 2019


Article type: Paper
DOI: 10.1039/C9NJ04215F
New J. Chem., 2019, Advance Article

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    Structural studies on the stereoisomerism of a natural dye miraxanthin I

    S. Niziński, Ł. Popenda, M. F. Rode, A. Kumorkiewicz, Z. Fojud, E. Paluch-Lubawa, S. Wybraniec and G. Burdziński, New J. Chem., 2019, Advance Article , DOI: 10.1039/C9NJ04215F

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