Expanding the Solid-State Landscape of l‑Phenylalanine: Discovery of Polymorphism and New Hydrate Phases, with Rationalization of Hydration/Dehydration Processes

To date, only one crystal structure of l-phenylalanine has been reported, with no confirmed report of polymorphism of this material. In the present work, we report the discovery of a new polymorph of l-phenylalanine, with the structural properties determined directly from powder X-ray diffraction data. The new polymorph of l-phenylalanine is stable only under rigorously dry conditions. In addition, two new solid hydrate phases of l-phenylalanine have been discovered: a monohydrate and a hemihydrate. The hemihydrate is susceptible to partial water deficiency. The crystal structures of the monohydrate and hemihydrate phases have also been determined directly from powder X-ray diffraction data. On the basis of results from dynamic vapor sorption and other experiments, we demonstrate that the three new solid forms are readily interconvertible as a function of relative humidity

Expanding the Solid-State Landscape of l‑Phenylalanine: Discovery of Polymorphism and New Hydrate Phases, with Rationalization of Hydration/Dehydration Processes

To date, only one crystal structure of l-phenylalanine has been reported, with no confirmed report of polymorphism of this material. In the present work, we report the discovery of a new polymorph of l-phenylalanine, with the structural properties determined directly from powder X-ray diffraction data. The new polymorph of l-phenylalanine is stable only under rigorously dry conditions. In addition, two new solid hydrate phases of l-phenylalanine have been discovered: a monohydrate and a hemihydrate. The hemihydrate is susceptible to partial water deficiency. The crystal structures of the monohydrate and hemihydrate phases have also been determined directly from powder X-ray diffraction data. On the basis of results from dynamic vapor sorption and other experiments, we demonstrate that the three new solid forms are readily interconvertible as a function of relative humidity

Polymorphism in 2‑Chlorobenzamide: Run of the Mill or Not?

Structures of two very similar polymorphic forms of 2-chlorobenzamide have been obtained at low temperature. The metastable α-form is very susceptible to grinding, a property not initially realized considering the polymorphs have been reported in the literature for many years. Systematic milling studies have been carried out in a search for other polymorphic forms and to assess the rate of any polymorphic change(s). No new polymorphs were found, though a computational search for low energy structures suggested a complex crystal-energy landscape. An experimental polymorph screen was also carried out

Are Oxygen and Sulfur Atoms Structurally Equivalent in Organic Crystals?

New guidelines for the design of structurally equivalent molecular crystals were derived from structural analyses of new cocrystals and polymorphs of saccharin and thiosaccharin, aided by a computational study. The study shows that isostructural crystals may be obtained through an exchange of >CO with >CS in the molecular components of the solids, but only if the exchanged atom is not involved in hydrogen bonding