Certain Problems of Polymorphism (I)

Diversity in Single- and Multiple-Component Crystals. The Search for and Prevalence of Polymorphs and Cocrystals

“…2 It has been reported that 54-55 elements are allotropic, but this count encompasses allotropes in solid, liquid, and gas phases. 3 Descriptions of the elements in CRC's Handbook of Chemistry and Physics contain references to solid allotropes for 29 elements. 4 Included are commonly cited examples such as carbon (graphite, diamond, fullerenes, amorphous) and phosphorus (stable red form used for matches and unstable white form), along with examples less likely to be encountered by the average scientist.…”

Reversible Phase Transitions in a Buckybowl Monolayer

“…The origin of polymorphism has been attributed to kinetically controlled nucleation and growth, and many thermodynamically unstable polymorphs, such as diamond and cocoa butter in chocolate, are used daily in their metastable form. [5] On the other hand, materials may appear in several thermodynamically stable crystal modifications that can be interconverted reversibly with changing temperature. [6] These so-called enantiotropic phase transitions are equally poorly understood, and there is much debate about the mechanisms involved.…”

Polymorphic Crystallization and Transformation of the Anti-Viral/HIV Drug Stavudine

“…3,4 As a matter of fact, polymorphism is a widespread phenomenon observed for more than half of all active pharmaceutical ingredients. 5 Polymorphs generally have different physical and chemical properties including solubility and melting point resulting in different stability and bioavailability of drug products. 6 Thus, in both theoretical and practical contexts, understanding and controlling the polymorphic outcome of pharmaceutical crystallization is very important.…”