Abstract Highly fluorinated gemini surfactants are relevant in pharmaceutical field, owing their ability to deliver genes to the respiratory or to the biliar epithelium, where hydrogenated interfering surfactants are present. We report for the first time the thermodynamic properties of the solutions of 1,1′-Bis(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl)-2,2 n-methylenebispyridinium dichloride (n = 4, 8, 12). The gene delivery ability of the dichlorides and the structure of the DNA nanoparticles are strictly related to their solution enthalpic properties, resulting in a very sensitive probe of the behaviour of the molecule in solution. Dilution enthalpies, density and sound velocities vs. molality for dichlorides and dimethanesulfonates with different spacer length, n, were measured. The evaluation of apparent and partial molar enthalpies as a function of concentration of the dimethanesulfonate suggests that the effect of the counterion is additive and the values obtained for the hydrogenated surfactants can be transferred to the fluorinated ones, allowing the prediction of enthalpic properties in solution. No evidence of the structure change in solution is found in the trends of volumetric properties vs. m. and the group contribution of the single bondCH2 single bond for both the dichlorides and the dimethanesulfonates results additive as well as the effect of the counterion. The adiabatic molar compressibilities seem to be independent from the counterion and show in micellar region a plateau value much greater than in the case of the more traditional hydrogenated gemini surfactants, indicating a less compact structure of the micelles, probably due to the repulsion between hydrogenated and fluorinated moieties of the molecules.
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