Synthesis, surface adsorption, micellization behavior and antibacterial activity of novel gemini surfactants with morpholinium headgroup and benzene-based spacer

Two series of novel gemini surfactants with morpholinium headgroup and benzene-based rigid spacers (abbreviated as(Mor)m-P-m and (Mor)m-BP-m, where m represents the carbon numbers of hydrophobic chains) were synthesized and characterized by H-1 NMR, ESI-MS, and FT-IR spectra. The effect of lengths of rigid spacer and hydrocarbon chain on their solution properties and antibacterial activities were systematically investigated. Due to the existence of morpholinium, they have a superior surface activity to the classic gemini surfactants. (Mor)mBP-mpossess lower CMC and gamma(cmc) than (Mor)m-P-m, which is assumed to be related to the conformation change of spacer. The possible arrangement models for the adsorptions of (Mor)m-P-m and (Mor)m-BP-m at the air-water interface were proposed by comparing their surface parameters with those of other similar surfactants. The pre-micellar associations occur in aqueous solutions of (Mor)16-P-16, (Mor)14-BP-14 and (Mor)16-BP-16. The thermodynamic parameters indicate the micellar processes are spontaneous, and (Mor)m-BP-mhave stronger aggregation tendency than (Mor)m-P-m. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) show they spontaneously self-assemble into vesicle, and the aggregate size of (Mor)m-BP-m is larger than (Mor)m-P-m. These surfactants showed excellent antibacterial properties against Bacillus subtilis and Escherichia coli. Compared with (Mor)m-P-m, (Mor)m-BP-m exhibit a higher activity. (C) 2021 Elsevier B.V. All rights reserved.