A win-win scenario for antibacterial activity and skin mildness of cationic surfactants based on the modulation of host-guest supramolecular conformation

The commercial cationic surfactants (CSAa) with quaternary ammonium (QA) groups have proved to be broadspectrum bactericide against bacteria, fungi, and viruses. Nevertheless, they inevitably exhibit potent irritation on the skin. In this work, we systematically investigated the regulatory mechanism of the host-guest supramolecular conformation with 8-cyclodextrin (8-CD) on the bactericidal performance and skin irritation of CSAa with different head groups and chain lengths. When the ratio of incorporated 8-CD is not greater than 1:1, the bactericidal efficiency of CSAa@8-CD (n > 12) remained above 90 % due to the free QA groups and hydrophobic fraction that can act on negatively charged bacterial membranes. And once the ratio of 8-CD exceeded 1:1, the 8-CD attracted to the bacterial surface by hydrogen bonding might prevent CSAa@8-CD from acting on bacteria, resulting in a decrement in antibacterial performance. Even so, the antibacterial activity of CSAa with long alkyl chains (n = 16, 18) was independent from the complexation of 8-CD. Accordingly, both the zein solubilization assay and the neutrophil migration assay on zebrafish skin evidenced that 8-CD attenuated the interaction of surfactant with skin model proteins and the inflammatory effect on zebrafish, thereby enhancing skin mildness. In this way, we hope to create a simple but effective brainpower using the host-guest approach to guarantee both bactericidal efficiency and skin mildness without modifying the chemical structure of these commercial biocides.

Automated summary

In this study, the regulatory mechanism of 8-cyclodextrin (8-CD) on the bactericidal performance and skin irritation of commercial cationic surfactants (CSAa) with different properties was investigated. It was found that when the ratio of 8-CD was not greater than 1:1, the bactericidal efficiency of CSAa@8-CD (n > 12) remained high. However, when the ratio of 8-CD exceeded 1:1, the antibacterial performance decreased due to the interaction between 8-CD and bacteria.