Biscationic bicephalic (double-headed) amphiphiles with an aromatic spacer and a single hydrophobic tail

We report the synthesis and aggregation studies of a homologous family of biscationic “bicephalic” amphiphiles. Each of has a linear alkoxy chain and two trimethylammonium bromide headgroups connected to a benzene ring. Krafft temperatures (TKTK) in water were determined by differential scanning calorimetry (DSC) and conductivity. Critical micelle concentration (cmc) and ionization degree (α) values were determined by monitoring the conductivity of aqueous solutions as a function of concentration, and confirmed by monitoring the 1H NMR chemical shift of the terminal methyl group as a function of concentration. Values for log(cmc) decrease linearly with increasing chain length, with a smaller dependence on chain length than for single-headed amphiphiles, consistent with literature reports on other bicephalic amphiphiles. Comparison to two related amphiphiles, each with a single headgroup reveals that the addition of a second head group results in an increase in cmc and a decrease of TKTK. These effects are attributed to greater water solubility due to the incorporation of a second, hydrophilic headgroup. The effect on α is also discussed.

A family of novel amphiphiles with two head groups and a single linear hydrophobe (10–18 carbons) has been prepared and studied. Krafft temperature and critical micelle concentrations are reported.Figure optionsDownload as PowerPoint slide