title: Crystallographic Structure, Intermolecular Packing Energetics, Crystal Morphology and Surface Chemistry of Salmeterol Xinafoate (Form I).
abstract: Single crystals of salmeterol xinafoate (form I), prepared from slow cooled supersaturated propan-2-ol solutions, crystallize in a triclinic P1¯ symmetry with 2 closely related independent salt pairs within the asymmetric unit, with an approximately double-unit cell volume compared with the previously published crystal structure. Synthonic analysis of the bulk intermolecular packing confirms the similarity in packing energetics between the 2 salt pairs. The strongest synthons, as expected, are dominated by coulombic interactions. Morphologic prediction reveals a plate-like morphology, dominated by the {001}, {010}, and {100} surfaces, consistent with experimentally grown crystals. Although surface chemistry of the slow-growing {001} face comprises large sterically hindering phenyl groups, although weaker coulombic interactions still prevail from the alcohol group present on the phenyl and hydroxymethyl groups. The surface chemistry of the faster growing {010} and {100} faces are dominated by the significantly stronger cation/anion interactions occurring between the carboxylate and protonated secondary ammonium ion groups. The importance of understanding the cohesive and adhesive nature of the crystal surfaces of an active pharmaceutical ingredient, with respect to their interaction with other active pharmaceutical ingredient crystals and how that may affect formulation design, is highlighted.
authors.affiliation: Institute of Particle Science and Engineering and School of Chemical and Process Engineering, University of Leeds, Leeds, UK.
authors.forename: Alexandru A
authors.initials: AA
authors.lastname: Moldovan
authors.affiliation: Institute of Particle Science and Engineering and School of Chemical and Process Engineering, University of Leeds, Leeds, UK.
authors.forename: Ian
authors.initials: I
authors.lastname: Rosbottom
authors.affiliation: Institute of Particle Science and Engineering and School of Chemical and Process Engineering, University of Leeds, Leeds, UK. Electronic address: v.ramachandran@leeds.ac.uk.
authors.forename: Vasuki
authors.initials: V
authors.lastname: Ramachandran
authors.affiliation: School of Chemistry, University of Leeds, Leeds, UK.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Pask
authors.affiliation: Institute of Particle Science and Engineering and School of Chemical and Process Engineering, University of Leeds, Leeds, UK.
authors.forename: Oboroghene
authors.initials: O
authors.lastname: Olomukhoro
authors.affiliation: Institute of Particle Science and Engineering and School of Chemical and Process Engineering, University of Leeds, Leeds, UK.
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Roberts
mesh_terms: D001993:Bronchodilator Agents / Q000737:chemistry / Q000378:metabolism; D003460:Crystallization / Q000379:methods; D018360:Crystallography, X-Ray / Q000379:methods; D004735:Energy Transfer / Q000502:physiology; D000068299:Salmeterol Xinafoate / Q000737:chemistry* / Q000378:metabolism*; D013499:Surface Properties; D014961:X-Ray Diffraction / Q000379:methods*
chemical_list: D001993:Bronchodilator Agents; D000068299:Salmeterol Xinafoate
keywords: X-ray diffraction; crystal structure; formulation design; lattice energy; molecular modelling; morphology; polymorphism; pulmonary drug delivery; salmeterol xinafoate; surface chemistry; synthonic engineering