Single-crystal diffuse scattering studies on polymorphs of molecular crystals. I. the room-temperature polymorphs of the drug benzocaine

E. J. Chan, T. R. Welberry, D. J. Goossens, A. P. Heerdegen, A. G. Beasley, P. J. Chupas

    Research output: Contribution to journalArticlepeer-review

    21 Citations (Scopus)

    Abstract

    The drug benzocaine (ethyl 4-aminobenzoate), commonly used as a local anaesthetic, is a bimorphic solid at room temperature. Form (I) is monoclinic P21/c, while the metastable form (II) is orthorhombic P212121. Three-dimensional diffuse X-ray scattering data have been collected for the two forms on the 11-ID-B beamline at the Advanced Photon Source (APS). Both forms show strong and highly structured diffuse scattering. The data have been interpreted and analysed using Monte Carlo (MC) modelling on the basis that the scattering is purely thermal in origin and indicates the presence of highly correlated molecular motions. In both forms (I) and (II) broad diffuse streaks are observed in the 0kl section which indicate strong longitudinal displacement correlations between molecules in the 031 directions, extending over distances of up to 50 Å. Streaks extending between Bragg peaks in the hk0 section normal to [100] correspond to correlated motions of chains of molecules extending along a that are linked by N - H⋯O=C hydrogen bonds and which occur together as coplanar ribbon pairs. The main difference between the two forms is in the dynamical behaviour of the ribbon pairs and in particular how they are able to slide relative to each other. While for form (I) a model involving harmonic springs is able to describe the motion satisfactorily, as simple excursions away from the average structure, there is evidence in form (II) of anharmonic effects that are precursors of a phase transition to a new low-temperature phase, form (III), that was subsequently found.

    Original languageEnglish
    Pages (from-to)382-392
    Number of pages11
    JournalActa Crystallographica Section B: Structural Science
    Volume65
    Issue number3
    DOIs
    Publication statusPublished - 2009

    Fingerprint

    Dive into the research topics of 'Single-crystal diffuse scattering studies on polymorphs of molecular crystals. I. the room-temperature polymorphs of the drug benzocaine'. Together they form a unique fingerprint.

    Cite this