Structure–activity relationship of cyclodextrin/biocidal double-tailed ammonium surfactant host–guest complexes: Towards a delivery molecular mechanism?

In aqueous solution, the biocidal double-tailed cationic surfactant, di-n-decyl-dimethyl-ammonium chloride can form inclusion complexes with various cyclodextrins (α-CD, β-CD, γ-CD, HP-α-CD, HP-β-CD and CM-β-CD). A physicochemical study has been performed to investigate the association parameters of these host–guest complexes by combining the use of ammonium and chloride selective electrodes, NMR spectroscopy and molecular modeling. stoichiometries, equilibrium constants and geometries were determined by resorting to a specific algorithm. The antimicrobial activity of the encapsulated ammonium surfactant was compared with that of the free ammonium showing three different behaviors depending on the cyclodextrin. The close relationship between the complex structure and the biocidal activity is used to propose a delivery molecular mechanism.