Two-dimensional structure of crystalline self-aggregates of amphiphilic alcohols at the air-water interface as studied by grazing incidence synchrotron x-ray diffraction and lattice energy calculations

J.L. Wang, F. Leveiller, D. Jacquemain, K. Kjær, J. Als-Nielsen, M. Lahav, L. Leiserowitz

    Research output: Contribution to journalJournal articleResearchpeer-review

    Abstract

    The two-dimensional (2D) crystal structures of self-aggregated clusters of amphipbilic alcohols (CnH2n+1OH, n = 23, 30, 31, and C19H39CO2(CH2)nOH, n = 9, 10) on pure water at a temperature of 5 °C have been determined to near-atomic resolution in order to understand the relative abilities of these monolayers to induce ice nucleation. The structures were solved making use of grazing incidence synchrotron X-ray diffraction (GID) data, complemented by lattice energy calculations. The GID data of the different monolayers within each of the two series (CnH2n+1OH, C19H39CO2CnH2nOH) are very similar. The molecules pack in a rectangular unit cell of average dimensions a = 5.0 Å, b = 7.5 Å for the normal alcohols CnH2n+1OH and a = 5.7 Å, b = 7.5 Å for C19H39CO2CnH2nOH. The plane group symmetry is essentially p1g1 for the normal alcohols CnH2n+1OH and essentially p1g1 for the other group. The molecular chains are tilted from the vertical by an average angle of 9°, in the direction of the b axis, for CnH2n+1OH and by 29°, in the direction of the a axis, for the other molecular type. The molecular chains related by glide (g) symmetry are arranged in a herringbone pattern. The fit to the Bragg rod intensity data of CnH2n+1OH permitted a reliable estimate of 0.07 Å2 for the molecular mean-squared motion parallel to the water surface. The a bsolute orientations of the molecules C19H39CO2CnH2nOH were determined by lattice energy calculations. The anisotropic coherence lengths of the crystallites of C19H39CO2CnH2nOH derived from the widths of the two observed Bragg peaks have been correlated with the binding energies of molecules in different directions.
    Original languageEnglish
    JournalJournal of the American Chemical Society
    Volume116
    Issue number4
    Pages (from-to)1192-1204
    ISSN0002-7863
    DOIs
    Publication statusPublished - 1994

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