Journal
JOURNAL OF CHEMICAL PHYSICS
Volume 143, Issue 16, Pages -Publisher
AMER INST PHYSICS
DOI: 10.1063/1.4933430
Keywords
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Funding
- INTERREG IVA 2 Seas Cross-border Cooperation Programme
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In this paper, structural and dynamical properties of ibuprofen and ketoprofen glass-forming liquids have been investigated by means of molecular dynamics simulations. Molecular mobility of both materials is analyzed with respect to the different inter-molecular linear/cyclic hydrogen bonding associations. For ibuprofen, the dominant organization is found to be composed of small hydrogen bonding aggregates corresponding to cyclic dimers through the carboxyl group. For ketoprofen, the propensity of cyclic dimers is significantly reduced by the formation of hydrogen bonds with the ketone oxygen of the molecule altering the hydrogen bond (HB) associating structures that can be formed and thus molecular dynamics. The issue of the presence/absence of the peculiar low frequency Debye-type process in dielectric relaxation spectroscopy (DRS) data in these materials is addressed. Results obtained from simulations confirm that the Debye process originates from the internal cis-trans conversion of the -COOH carboxyl group. It is shown that the specific intermolecular HB structures associated to a given profen control the main dynamical features of this conversion, in particular its separation from the a-process, which make it detectable or not from DRS. For ibuprofen, the possible role of the -CCCO torsion motion, more local than the -COOH motion since it is less influenced by the intermolecular HBs, is suggested in the microscopic origin of the quite intense secondary.-relaxation process detected from DRS. (C) 2015 AIP Publishing LLC.
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