Synthesis, characterization and antimicrobial properties of new L-cysteine based chiral aromatic polyamides

In this study, chiral dicarboxylic acid monomer of 2,2′-(1,4-phenylene) bis(4,5-dihydrothiazole-4-carboxylic acid) was first prepared by the reaction of 1,4 -dicyanobenzene and L-cysteine. Afterward, novel optically active and aromatic polyamides (PAs) were synthesized by polycondensation of L-cysteine-based diacid and different aromatic diamines in molten tetrabutylammonium bromide. PAs, which were obtained in good yields, showed high thermal stability as well as inherent viscosities in the range of 0.33–0.40 dL/g. FT-IR, 1 HNMR, elemental analysis, and thermogravimetric analysis were used to characterize the chemical structure of the synthetic polymers. Field emission scanning electron microscopy and X-ray powder diffraction methods were used to determine the surface morphology and crystallinity of the polymers, respectively. In addition, the PAs have been tested against the Escherichia coli and Staphylococcus aureus as known gram-negative and gram-positive bacteria, respectively. The antimicrobial activity of Escherichia coli and Staphylococcus aureus indicated minimum inhibitory concentration and minimum bactericidal concentration of 62–125 and 125–250 μg/mL, respectively, while the corresponding values for Staphylococcus aureus were 62–250 and 125–500 μg/mL, respectively.