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Thermochemistry and crystal structure of different single and multitailed picrates

Picric acid forms stable ionic salts or charge transfer complexes with many aromatic hydrocarbons, alkalines [1], aliphatic or aromatic amines [2] as the most important functional groups in molecules of biological importance, including proteins [3], vitamines [4] and alkaloides. Picrates are commonly used as a counter-ion in many systems involving cation extraction membrane transport extractability and selectivity, where high efficiency and selectivity towards specific ion are desired. The studies of the picrate interactions may be used for various scientific and commercial applications, from dye and explosive manufacturing to biological monitoring methods. New catanionic salts (dodecyltrimethylammonium, didodecyldimethylammonium, tridodecylmethylammonium and N-dodecylpyridinium picrate) were prepared from cationic surfactants halide salts by mixing with equimolar concentrations of picric acid in heated and stirred solutions. Materials were characterized through elemental analysis and by single crystal X-ray analysis techniques. Thermal transitions all of the compounds were studied using DSC analyses techniques and optical polarizing microscope. Novel crystalline complexes are based on electrostatic interactions of components in polar solvents, primarily between negatively charged phenolic oxygen from picrate anion and differently substituted ammonium surfactant cations. This fact provides interesting analysis of the impact of various surfactant ammonium counterions on the lyotropic and thermal properties of respective picrate complexes. Analysis of the geometry of picrate ions in various crystallochemical environments showed several different crystal structures with different stacking patterns. Data of the observed liquid-solid phase transitions indicate kinetic hindering of solidification for more complex picrate molecules bringing a new insight into picrate polymorphic forms and their thermodynamic relationships. All samples crystallized from the melt exhibit similar zig-zag blade structures, as noticed earlier on dodecylammonium picrate [2]. [1] Harrowfield, J. M., Skelton, B. W., White, A. H., Aust. J. Chem. 48 (1995) 1311-1331. [2] Tomašić, V., Tušek-Božić, LJ., Višnjevac, A., Kojić-Prodić, B., Filipović-Vinceković, N., J. Colloid Interface Sci. 227 (2000) 427–436. [3] Zesławska, E., Jacob, U., Stürzebecher, J., Oleksyn, B.J., Bioorg. Medicinal Chem. Letter 16 (2006) 228–234. [4] Anitha, K., Athimoolan, S., Natarajan, S., Acta Cryst. C62 (2006) 426–428.

thermochemistry; picrates; single-; multitailed surfactants

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