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 K_ads 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.

New Bioactive Heteroleptic Copper(II) Carboxylates: Structure, Enzymatic and DNA-Binding Studies

Mono-, di- and tri-nuclear Cu(II) and Zn(II) carboxylate complexes were synthesized and structurally characterized having general formulas [Cu₂(biphenylacetate)₄(DMSO)₂] (1), [Zn(3,4-dichlororophenylacetate)₂(1,10-phenanthroline)(H₂O)] (2) and [Zn₃(3,4-dichlororophenylacetate)₆(2,2-bipyridine)₂] (3). Complex 1 is a dinuclear Cu(II) complex with distorted square pyramidal geometry. Complex 2 is a mononuclear Zn(II) complex with distorted octahedral geometry while 3 is a tri-nuclear Zn(II) complex with octahedral (central Zn) as well as square pyramidal (terminal Zn) geometries. The stability of all complexes was checked by TGA and were found thermally stable. The solubility of the complexes was enhanced by using cationic (CTAB) and anionic (SDS) surfactants. Lower CMC values for SDS revealed good interaction as compared to CTAB. DNA-binding ability of the complexes was determined by UV–vis spectrophotometry and viscometry. All complexes bind with DNA effectively. The binding constant values from spectral analysis are 1.00(±0.02) × 10⁴, 1.34(±0.01) × 10⁵ M⁻¹ and 1.11(±0.01) × 10⁴ M⁻¹ for 1–3, respectively. The DPPH-scavenging assay was performed by UV–vis spectrophotometry. All complexes showed good inhibition against the free radical. IC₅₀ values for 1–3 are 109.98, 167.31 and 153.12 µM, respectively. The complexes were found to possess nice biological relevance. Graphical Abstract

The Schiff base has been synthesized by reacting tranexamic acid with indol-3-carboxyaldehyde in the first step and then with carbon disulfide at room temperature in the second step. The homobimetallic complexes have been synthesized by reaction of Schiff base with R₂SnCl₂ and R₃SnCl in 1 : 2 M ratio under stirring, where R = methyl, n-butyl and phenyl. The ligand and complexes have been characterized by elemental analysis, FT-IR, multinuclear NMR (¹H, ¹³C and ¹¹⁹Sn) and semi-empirical study. IR data reveal the bidentate nature of the ligand. Five- or six-coordinate geometry was confirmed in solution by NMR spectroscopy. The homobimetallic complexes and ligand were tested in vitro against some pathogenic bacteria and fungi to assess their antimicrobial properties. The complexes show biological activities with few exceptions.