Navigating the Complex Solid Form Landscape of the Quercetin Flavonoid Molecule

Abstract

Quercetin, a naturally occurring bioflavonoid substance widely used in the nutraceutical and food industries, exists in various solid forms that can have different physicochemical properties, thus impacting this compound’s performance in various applications. In this work, we will clarify the complex solid-form landscape of this molecule. Two elusive isostructural solvates of quercetin were obtained from ethanol and methanol. The obtained crystals were characterized experimentally, but the crystallographic structure could not be solved due to their high instability. Nevertheless, the desolvated structure resulting from a high-temperature treatment (or prolonged storage at ambient conditions) of both these two labile crystals was characterized and solved via powder X-ray diffraction and solid-state nuclear magnetic resonance (SSNMR). This anhydrous crystal structure was compared with another anhydrous quercetin form obtained in our previous work, indicating that, at least, two different anhydrous polymorphs of quercetin exist. Navigating the solid-form landscape of quercetin is essential to ensure accurate control of the functional properties of food, nutraceutical, or pharmaceutical products containing crystal forms of this substance.

Development of Potential Therapeutic Agents from Black Elderberries (the Fruits of Sambucus nigra L.)

“…In addition, elderberries produce further flavonoids, of which the content of quercetin in elderberry wine is as high as 43.35 µg/mL [13]. The structure of quercetin has been confirmed via powder X-ray diffraction and solid-state NMR spectroscopy [75]. Quercetin is a naturally occurring flavonoid used widely in the nutraceutical and food industries [76], and its antitumor and anti-infective properties have been reviewed extensively [29,77,78].…”

Elucidating the Polymorphism of Xanthone: A Crystallization and Characterization Study

“…Different crystal structures of the same compound can exhibit very different physical and mechanical products. Hence, establishing the solid forms landscape of a compound (including polymorphs, solvates, hydrates, co-crystals) and the transformation pathways between each of these forms is an increasingly important part of development of a new product. − Furthermore, tailoring the crystal structure of a compound in order to achieve targeted physicochemical properties is a key challenge for crystal engineers. − …”