In mining the CSD we identified a total of 95 families of polymorphs related by proton transfer which were classified into six different categories depending on the type of proton transfer observed and the ionisation of species involved.
Dielectric and electrostatic environments of proteins, as well as structural constraints imposed by protein folding, influence the nature of hydrogen bonds. The effects of these factors on hydrogen bond distances are analyzed.
Salt, cocrystal, and the salt–cocrystal intermediate are observed in the famciclovir–fumaric acid multicomponent system.
Implicit solvation is sufficient for describing the absorption and emission of a series of photoacids in acetone, whereas, explicit solvent effects caused by hydrogen bonding become more relevant in DMSO and water.
This perspective highlights the need for an inclusive regulatory definition and touches upon some fundamental crystal-engineering aspects and considerations useful for the design and development of pharmaceutical co-crystals.