Optical absorption measurements and optoelectronic DFT calculations for ethanol solvated quercetin and anhydrous/hydrated quercetin crystals

Navigating the Complex Solid Form Landscape of the Quercetin Flavonoid Molecule

“…The two spectra are fully superposable, suggesting that the two samples contain the very same phase, or that they represent isomorphous phases. Moreover, they very well agree with those collected by Miclaus’ group for the two unstable solvates that they studied . The only difference in our spectra is the absence of any resonance ascribable to the presence of ethanol or methanol in QE or QME, respectively.…”

“…Moreover, they very well agree with those collected by Miclaus' group for the two unstable solvates that they studied. 22 The only difference in our spectra is the absence of any resonance ascribable to the presence of ethanol or methanol in QE or QME, respectively. In this sense, Miclaus' spectra are characterized by two peculiarities: (a) in their QE spectrum, only the methyl signal appears but not the CH 2 one; (b) the intensity of the methylic signal in QME does not fit that of the other signals suggesting the presence of a nonstoichiometric solvate or a very inefficient polarization transfer.…”

“…In 2016, the first structure of anhydrous quercetin (CCDC identifier: NAFZEC) was deposited by Vasisht et al, who solved it using computational analysis of PXRD data, and indicating that quercetin crystallizes in an orthorhombic anhydrous form with four molecules per unit cell, and space group Pna 2 1 . However, the data and lattice parameters for the anhydrous quercetin suggested by Vasisht et al are reported several times in literature to be problematic and present large deviations from further lattice and geometry optimizations of the structure. , In 2016, Miclaus et al reported the presence of two weak and highly unstable methanol and ethanol solvates, which result from quercetin recrystallization from the respective solvents and occur in mixtures with the anhydrous form . It is reported that, in the two solvates, the solvent molecules are weakly hydrogen-bonded to the quercetin molecules and serve as intermediates in the transformation to an anhydrous quercetin form.…”