Characterization of Crystalline Muconic Acid Polymorphs

Muconic acid is known to exhibit three isomeric forms, but the cis-trans isomer is largely uncharacterized. Using a combination of X-ray diffraction, solid-state density functional theory, and terahertz spectroscopy, a detailed solid-state structural investigation was performed for cis-trans muconic acid. Two crystalline polymorphs were discovered during this study through their distinct terahertz spectra. Terahertz data also revealed a muconic acid hydrate species present in the bulk samples that is related to the relative stabilities of the two polymorphs. Overall, the measurements and simulations provide new knowledge concerning the isomerization mechanisms of muconic acid.