Two new cationic surfactants, n-hexadecyl-3-methylpyridinium bromide and n-heptadecyl-3-methylpyridinium bromide have been synthesized and characterized in solid state by FT-IR, and in solution by 1 H- and 13 C-NMR spectroscopy. The values of critical micelle concentration (CMC) were determined by UV-visible spectroscopy and conductometry. Interaction of synthesized surfactants with two anionic drugs, i.e., diclofenac sodium {[2-(2, 6-Dichloroanilino) phenyl] acetic acid} and ketoprofen [(RS)-2-(3-benzoylphenyl) propionic acid] was studied by UV-visible spectroscopy. Binding constant (K), Gibb's free energy (ΔG) and number of drug molecules (n) per micelle were also calculated. These synthesized surfactants were proved to be efficient in increasing the solubility and bioavailability of drug molecules. In order to check the carrier efficiency of synthesized surfactants against bioactive coordinate, on complexes, interaction of recently reported bioactive zinc complexes was tested with synthesized cationic surfactants by conductometric measurements. Mole fractions (X cmc ) and Gibbs free energy (ΔG cmc ) values were also calculated. Both surfactants were further screened for anti-fungal and anti-bacterial activities.

The synthesis of new cationic surfactants i.e., n‐hexyl‐3‐methylpyridium bromide (a) and n‐octyl‐3‐methylpyridium bromide (b), and their characterization using multinuclear nuclear magnetic resonance spectroscopy (NMR) (1H, 13C) and Fourier‐transform infrared spectroscopy (FT‐IR) spectroscopic techniques were reported. The micellization behavior of the synthesized surfactants was studied using conductometry and ultraviolet–Visible spectroscopy. The critical micelle concentration (CMC) of compounds a and b was found to be 0.41 and 0.35 m mol L−1, respectively. The effect of temperature on the CMC of these compounds was examined in the range of 298–318 K and thermodynamic parameters (ΔG, ΔH, and ΔS) of the micellization process were calculated. The antibacterial study of the synthesized surfactants revealed their strong activity against different bacterial strains. Moreover, the interaction of drugs i.e., flurbiprofen and ketoprofen, with the synthesized surfactants was investigated for gaining insights into the role of micelles as drug‐delivery devices. Drug–surfactant interactions were also confirmed via a conductometric method.

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Two new effective corrosion inhibitors, namely N-(n-octyl)-3-methylpyridinium bromide (Py8) and N-(n-dodecyl)-3-methylpyridinium bromide (Py12), have been presented. The cationic pyridinium-based surfactants were analyzed for the corrosion protection of general purpose steel (EN3B) against a strong corrosive media (3.5% NaCl, pH 1.5). The results of the electrochemical measurements, i.e., Tafel polarization, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) revealed a mixed-type behavior of both inhibitors, and the maximum inhibition efficiency (IE) achieved with Py8 and Py12 was 85% and 82%, respectively. The process of adsorption of synthesized inhibitors followed the Langmuir adsorption isotherm, and a higher value of Kads highlighted the existence of strong interaction between inhibitors and the EN3B mild steel surface. Furthermore, the values of ΔG°ads were calculated to be –32 kJ mol−1 for Py8 and –33 kJ mol−1 for Py12, indicating the coexistence of both physisorbed and chemisorbed molecules. The surface morphology of EN3B mild steel samples was observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), where the reduced surface roughness in the presence of Py8 and Py12 in chloride media further supported the evidence of an efficient inhibition process. Density functional theory (DFT) calculations reveal excellent correlation with the experimental results, with Py8 showing superior corrosion inhibition potential, signifying that the alkyl chain length and intramolecular charge transfer are crucial factors in deciding the inhibition performance of the synthesized cationic surfactants. Furthermore, this study proposes the mechanism for the adsorption of the surfactant-based inhibitors over the EN3B mild steel surface, which leads to the formation of an effective and protective anticorrosive film.