Crystal polymorphism

Crystal polymorphism is the ability of a substance to crystallize in multiple distinct structures while retaining the same chemical composition. Different forms can have different physical properties and stability.

Nucleation: The initial formation of a stable cluster from which a new phase can grow. Different nuclei can seed competing crystal structures from the same substance.
Pharmaceutical polymorphism: The occurrence of multiple crystal forms of an active pharmaceutical ingredient. Drug polymorphs can differ in solubility, dissolution rate, and bioavailability.
Carbamazepine: An anticonvulsant drug known to crystallize in multiple forms and solvates. Its solid forms provide a well-studied case of pharmaceutical polymorphism.
Allotropy: The ability of a chemical element to exist in different structural forms. It is the elemental counterpart of polymorphism, rather than a phenomenon in compounds alone.
Phase transition: A change between distinct physical states of matter or phases of a system. A polymorph can transform into another when conditions change.
Crystal growth: The enlargement of an ordered solid through the addition of atoms, ions, or molecules. Growth conditions can favor one polymorph over another after nucleation.
Ritonavir: An antiviral drug whose more stable crystal form disrupted production of its original formulation. Its unexpected Form II illustrates how a new polymorph can compromise manufacturing.
Glycine: The simplest amino acid, which crystallizes in several polymorphic forms. Its distinct forms demonstrate polymorphism in a small, flexible molecule.
Pseudopolymorphism: The formation of crystalline solids that differ through incorporated solvent or water molecules. Solvates change composition, unlike true polymorphs of the same chemical substance.
Solubility: The capacity of a substance to dissolve in a specified solvent under specified conditions. Different polymorphs can have different solubilities, affecting performance and processing.

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