3,4-Dihydropyrimidin-2-(1H)-one-Based Cationic Surfactants: Synthesis, Self-Assembly, and Antimicrobial Activity

3,4-Dihydropyrimidin-2-(1H)-one (DHPM)-based cationic surfactants with alkyl tail lengths of 8, 12, and 16 carbons were synthesized from 4-dimethylaminobenzaldehyde by the green multicomponent reaction and characterized. The self-assembling behavior of the synthesized surfactants was determined by conductometry, tensiometry, and fluorimetry. Surface parameters, including the effectiveness of surface tension reduction, maximum surface excess concentration, minimum area per molecule, surfactant efficiency, and thermodynamic adsorption and micellization parameters, were also calculated. The surface activity of DHPM-based surfactants is found to increase with hydrophobicity, as evidenced by a reduction in critical micelle concentration from 0.067 to 0.040 mM at 298.15 K. Emulsion stability and interfacial tension were significantly influenced by the hydrophobic chain length of the surfactants. The Z-average, polydispersity index, and zeta potential of the micellar solutions were measured by dynamic light scattering, revealing an inverse correlation between the Z-average and surfactant hydrophobicity, which was further supported by transmission electron microscopy. The aggregation number was determined by fluorescence quenching. The antimicrobial efficacy of DHPM-based surfactants was evaluated against six pathogenic microbes, including both gram-positive and gram-negative bacteria and fungi, to assess differences in antimicrobial potency. Molecular docking revealed interactions between surfactant head groups and bacterial cell wall components.