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

In the title hydrated molecular salt, C18H23N2 +·C6H4ClO3S−·H2O, which shows moderate biological activity against methicillin-resistant Staphylococcus aureus (MRSA), one ethyl group of the 2-[4-(diethylamino)styryl]-1-methylpyridinium cation is disordered over two orientations in a 0.604 (13):0.396 (13) ratio. The main part of the cation is nearly planar with a dihedral angle of 4.50 (10)° between the pyridinium and benzene rings. In the crystal, the components are linked by O—H⋯O hydrogen bonds and C—H⋯O weak interactions. Aromatic π–π stacking interactions with centroid–centroid separations of 3.7363 (12) and 3.7490 (13) Å also occur.


Comment
As disinfectants, quaternary ammonium compounds (QACs) have been used for hygienic care in both medical and domestic purposes due to their low toxicity and wide-ranging antimicrobial properties for a long time (Domagk, 1935). However, the long-term use of any disinfectants will lead to the resistance phenomena of some bacterial strains that makes these disinfectants to become unpractical for real life usage. The appearance of resistant microganisms against QACs, especially Methicillin-resistant Staphylococcus aureus (MRSA), made the common QACs such as benzalkonium chloride and cetylpridinium chloride to be inadequate for MRSA treatment (Wainwright & Kristiansen, 2003;Brown & Skurray, 2001). Therefore, we decided to develop the novel pyridinium QACs which were expected to overcome this Staphylococcus-resistant phenomenon by modifying the QACs structures and to study their anti-MRSA activity. Among various chromophores employed in the research for chemotherapeutic drug design, tertiary amine seems to be an interesting group to be introduced into the structure (Endo et al., 1987). The title compound (I) was one among many pyridinium QACs synthesized in our laboratory (Chanawanno, Chantrapromma, Anantapong, Kanjana-Opas & Fun, 2010) hoping for a new antibacterial drug candidate and this compound showed moderate activity against MRSA with the MIC value of 150 mg/ml. Herein its crystal structure is reported.
The asymmetric unit of the title compound (I) ( lengths are in normal ranges (Allen et al., 1987) and comparable with a related structures (Fun et al., 2011;Kaewmanee et al., 2010).

Experimental
(E)-2-(4-(diethylamino)styryl)-1-methylpyridinium iodide (compound A, 0.13 g, 0.33 mmol) was prepared by the previous method (Kaewmanee et al., 2010) and then was mixed with silver (I) 4-chlorobenzenesulfonate (Chanawanno, Chantrapromma, Anantapong & Kanjana-Opas, 2010) (0.10 g, 0.33 mmol) in methanol (100 ml). The mixture immediately supplementary materials sup-2 yielded a grey precipitate of silver iodide. After stirring the mixture for 30 min, the precipitate of silver iodide was removed and the resulting solution was evaporated yielding an orange solid of the title compound. Orange plates of (I) were recrystallized from methanol by slow evaporation of the solvent at room temperature after a few weeks, Mp. 446-448 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 0.91 Å from O1 and the deepest hole is located at 0.71 Å from S1.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
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 > 2sigma(F 2 ) is used only for calculating R-factors(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.