Temperature-Dependent Phase Behavior and the Crystal-Forming Nucleation Process of Ethyl 4-Fluoro-2,3-dihydroxystearate Monolayers
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- 作者：Silke Steffens ; Udo Hö ; weler ; Tim Jö ; dicke ; Jens Oldendorf ; Rainer Rudert ; Gü ; nter Haufe ; Hans-Joachim Galla
- 刊名：Langmuir
- 出版年：2007
- 出版时间：February 13, 2007
- 年：2007
- 卷：23
- 期：4
- 页码：1880 - 1887
- 全文大小：700K
- 年卷期：v.23,no.4(February 13, 2007)
- ISSN：1520-5827
文摘
The phase behavior of enantiomeric compounds as well as mixtures of enantiopure and racemic diastereomers ofethyl 4-fluoro-2,3-dihydroxystearates has been investigated using surface pressure-area isotherms and Brewster anglemicroscopy (BAM). All mixtures exhibit a small plateau region within the surface pressure-area isotherm at 20 
C,whereas the enantiopure compound shows an isotherm behavior similar to that of fatty acids. Corresponding to thefilm balance measurements, the BAM images demonstrate different shapes of the domains within the coexistenceregion of the liquid-condensed/liquid-expanded phase. The domain structures of the monolayers were visualized afterLangmuir-Blodgett transfer on mica sheets by scanning force microscopy (SFM). From the SFM images it becomesobvious that small crystallites are formed for all investigated compounds; however, their molecular assembly is diversefor different enantiomers. Variations in the phase behavior can be correlated with interactions between the polarmolecular moieties and the subphase and altered intermolecular interactions. Molecular modeling calculations wereapplied to elucidate the structural organization of these intermolecular interactions. Ab initio calculations of theminima conformers of (S,S,R)- and (S,S,S)-ethyl 4-fluoro-2,3-dihydroxystearates have been performed to predict withthe HARDPACK program the two-dimensional lattice structure based on the P1 space group. These calculationsshowed that intermolecular hydrogen bridges are crucial for the interactions within and between the molecules.
C,whereas the enantiopure compound shows an isotherm behavior similar to that of fatty acids. Corresponding to thefilm balance measurements, the BAM images demonstrate different shapes of the domains within the coexistenceregion of the liquid-condensed/liquid-expanded phase. The domain structures of the monolayers were visualized afterLangmuir-Blodgett transfer on mica sheets by scanning force microscopy (SFM). From the SFM images it becomesobvious that small crystallites are formed for all investigated compounds; however, their molecular assembly is diversefor different enantiomers. Variations in the phase behavior can be correlated with interactions between the polarmolecular moieties and the subphase and altered intermolecular interactions. Molecular modeling calculations wereapplied to elucidate the structural organization of these intermolecular interactions. Ab initio calculations of theminima conformers of (S,S,R)- and (S,S,S)-ethyl 4-fluoro-2,3-dihydroxystearates have been performed to predict withthe HARDPACK program the two-dimensional lattice structure based on the P1 space group. These calculationsshowed that intermolecular hydrogen bridges are crucial for the interactions within and between the molecules.