Pyrophosphate-based gemini surfactants

Two series of pyrophosphate-based gemini surfactants [diimidazolium (1) and disodium PP'-dialkyl pyrophosphate (2) (a, R = 1-octyl; b, R = 1-dodecyl; c, R = 2-dodecyl)] were synthesized, along with a series of imidazolium monoalkyl phosphate surfactants (3a-c) for comparison. The surfactants were characterized by measurement of their Krafft temperatures (T-k) and critical aggregation concentrations (cac's). The Tk and cac values of the pyrophosphate surfactants a-re lower than those of their conventional phosphate surfactant counterparts. Aggregated surfactants 1 and 3 in D2O were characterized by H-1 and P-31 NMR spectroscopy, and solutions of 1c and 3c in H2O Were characterized by phase-contrast optical microscopy and cryogenic high-resolution scanning electron microscopy (cryo-HRSEM), By optical microscopy, fiberlike aggregates were observed for gemini surfactant le, and both fibers and rod/tubule-like aggregates were observed for its single-chain counterpart 3c. By cryo-HRSEM, lamellar ice was observed for both le and 3c. Also, a single-crystal X-ray diffraction study of 1b was performed, and its cleavable nature was demonstrated.