Synthesis, Physicochemical Characterization, and Interaction with DNA of Long-Alkyl-Chain Gemini Pyridinium Surfactants

Pyridinium gemini surfactants with hexadecyl chains linked to nitrogen atoms and a tuned aliphatic spacer that bridges the two pyridinium polar heads in 2,2’-positions have been synthesized and characterized. A multitechnique approach allowed us to study the aggregation behavior, using conductivity, surface tension, and fluorescence. Graphs of the specific conductivity (k) versus the surfactant molar concentration (C), and graphs of the molar conductivity (L) versus C0.5 suggest pre-aggregation phenomena of these amphiphiles at very low concentration. The trends of Amin as a function of the spacer length confirm the hypothesis of a conformational change of the molecule with four methylene groups as spacer owing to stacking interactions between the two pyridinium rings mediated by the counterion. Moreover, the trends of Amin and counterion binding (b) suggest that the spacer must be longer than eight carbon atoms to fold efficiently toward the micellar core. The opportunity to tune the surfactant structure and aggregation properties make those surfactants—particularly the long-chain ones for which the DNA complexing ability was shown by means of atomic force microscopy (AFM) imaging—desirable candidates for gene-delivery experiments.