Thermal and structural properties of surfactant–picrate compounds
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The novel surfactant–picrate compounds were synthesized and characterized by thermal and XRD analysis. The synthesis, based on the electrostatic interactions of components in polar solvents, was carried out using picric acid and cationic surfactants (dodecyltrimethylammonium, didodecyldimethylammonium, and tridodecylmethylammonium halide). The idea was to investigate the dependence of physico-chemical properties and thermal transitions of picrate–surfactant compounds with raising number of dodecyl chains sited on the same ammoniumm head group. The equimolar mixed aqueous solutions are characterized as lyotropic, strongly promoted by picrate anion. The main crystal structure feature of investigated picrates is layered structure with stacked aromatic rings of one picrate molecule on the top of the other one via strong π…π interactions and connection to the alkylammonium molecules with their nitro groups by C–H…O hydrogen bonds. Surfactant–picrate bilayer-like structures are interrupted with layers of polar heads and picrate counterions and the observed width of such a bilayers are functions of more complex structural behaviors which ensures alternation in space of equal numbers of positive and negative charges. Although some of the surfactants used posses thermotropic porperties, like examined tridodecylmethylammonium chloride, no thermotropic mesomorphism is detected in solid state of investigated surfactant–picrate compounds. The thermodynamic parameters of solid–liquid thermal transitions depend linear on the number of dodecyl chains, and for double- and triple-tailed picrate compounds the marked temporal hysteresis of the melt crystallization is registered.
KeywordsThermal analysis Alkyl chain number Cationic surfactant Picrate Crystal structure
This work was supported by the Ministry of the Science, Education, and Sport of the Republic of Croatia (Project Nos 098-0982915-2949 and 098-1191344-2943). We are grateful to Dr. Ellen Wachtel, Department of Materials and Interfaces, Weizmann Institute of Science, Israel, for carrying out the XRD experiments.
- 6.Goto M, Kanno H, Sugaya E, Osa Y, Takayanagi H. Crystal structure of adenosinium picrate. Anal Sci. 2004;20:39–40.Google Scholar
- 15.Harms K, Wolcado S. XCAD4-CAD4 data reduction. Germany: Universitiy of Marburg; 1995.Google Scholar
- 17.Sheldrick GM. SHELX97: program for the refinement of the crystal structures. Germany: Universitiy of Gottingen; 1997.Google Scholar
- 18.Spek AL. PLATON 98: a multipurpose crystallographic tool 101201 version. Utrecht, The Netherlands: University of Utrecht; 2001.Google Scholar