Self-Aggregation, Antibacterial Activity, and Mildness of Cyclodextrin/Cationic Trimeric Surfactant Complexes

Despite efficacious antimicrobial activity, cationic oligomeric surfactants show strong skin irritation potential due to their larger cationic charge numbers and multiple hydrophobic chains. This work reports that the incorporation of α-, β-, and γ-CDs with different cavity sizes can effectively improve the mildness of cationic ammonium trimeric surfactant DTAD with a star-shaped spacer while maintaining its high antibacterial activity. On the basis of the different cavity sizes of CDs and the asymmetry in the spacer of DTAD, the CD/DTAD mixtures form α-CD@DTAD, 2α-CD@DTAD, β-CD@DTAD, and γ-CD@DTAD complexes. Compared to DTAD, these CD/DTAD complexes show much stronger self-assembly ability with much lower critical aggregation concentrations (CAC) and form more diverse aggregates with reduced zeta potential. Just above their CACs, the CD/DTAD complexes form vesicles or solid spherical aggregates of ∼50 nm and then transform into small micelles of ∼10 nm as the concentration increases. The strong self-asse...