2-[(E)-4-(Dimethylamino)styryl]-1-methylpyridinium 4-chlorobenzenesulfonate monohydrate

In the title hydrated molecular salt, C16H19N2 +·C6H4ClO3S−·H2O, the 2-[4-(dimethylamino)styryl]-1-methylpyridinium cation exists in an E configuration with respect to the C=C bond and is slightly twisted, with the dihedral angle between the pyridinium and benzene rings being 9.33 (10)°. In the crystal structure, the packing is stabilized by O—H⋯O hydrogen bonds and weak C—H⋯O interactions, which link the cations, anions and water molecules into chains propagating in [010]. These chains are stacked along the a axis by π–π interactions, with centroid-to-centroid distances of 3.6429 (12) and 3.6879 (12) Å; weak C—H⋯π interactions are also observed.


Comment
Our research group have designed and synthesized some quaternary ammonium compounds including pyridinium derivatives. However, there are very few researches in the area of styryl pyridinium dyes being used as antibacterial agents.
Based on the knowledge gathered since a very long time ago (Armitage et al., 1929;Browning et al., 1922;Wainwright & Kristiansen, 2003), we found that styryl pyridinium compounds possess high activity against both susceptible and methicillin-resistant Staphylococcus aureus (MRSA) . This interesting anti-MRSA activity of the styryl pyridinium compounds trigger an encouragement to perform further investigation of these compounds in order to act against the powerful superbug MRSA which can overcome commonly used antibacterial drugs (Wainwright, 2008). Our bacterial assay results show that the title compound was moderately active against MRSA with the minimum inhibition concentration (MIC) = 37.5 µg/ml. Herein its crystal structure is reported.  (Allen et al., 1987) and angles in (I) are in normal ranges and comparable with a related structure .

Experimental
The title compound was prepared by the reported procedure . Orange blocks of (I) were recrystallized from methanol by slow evaporation of the solvent at room temperature after a few weeks, m.p. 516-517 K.

Refinement
Water H atoms were located in difference maps and refined isotropically. The remaining H atoms were placed in calculated positions with d(C-H) = 0.93 Å, U iso = 1.2U eq (C) for aromatic and CH and 0.96 Å, U iso = 1.5U eq (C) for CH 3 atoms. A rotating group model was used for the methyl groups. The highest residual electron density peak is located at 0.69 Å from C11 and the deepest hole is located at 0.67 Å from S1.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.