EFFECTS OF AMPHIPHILIC TOPOLOGY ON SELF-ASSOCIATION IN SOLUTION, AT THE AIR-WATER-INTERFACE, AND IN THE SOLID-STATE

The self-association of sodium carboxylates 1a-5a in aqueous solution has been studied by H-1 NMR and dye solubilization. Amphiphile 1a, the derivative of 1,6-methano[10]annulene bearing a carboxylate on the br idge carbon, is an example of a ''contrafacial amphiphile'', a rigid m olecule with distinct polar and nonpolar faces. Amphiphiles 2a and 3a, the sodium salts of 2-naphthylacetic and 1-naphthylacetic acids, resp ectively, are isomers of la with more conventional amphiphilic archite ctures. Amphiphiles 4a and 5a are derivatives of 1a with extended nonp olar surfaces. Concentration-dependent H-1 NMR data indicate that self -association of 1a-5a is weak and occurs in a stepwise fashion. Up to its aqueous solubility limit of 0.54 M, contrafacial amphiphile la doe s not solubilize the hydrophobic dye orange OT, but conventional isome rs 2a and 3a solubilize the dye above 0.33 and 0.50 M, respectively. C ontrafacial amphiphile 4a also does not solubilize orange OT, but 5a d oes solubilize the dye. The properties of isomers 1a-3a were compared also at the air-water interface. via tensiometry. Between zero and 0.1 5 M, naphthyl derivatives 2a and 3a cause a significant lowering of su rface tension, but contrafacial amphiphile la has little effect on sur face tension up to 0.35 M. Crystal structures of carboxylic acids 1b, 4b, and 5b show that the aromatic face of the 1,6-methano[10]annulene unit that is anti to the bridge engages in ''herringbone'' interaction s with neighboring aromatic surfaces, which is similar to the behavior of conventional hydrocarbon aromatic moieties. The solid state packin g patterns observed for 1b-3b allow a speculative rationalization of t he differences in surface activity among 1a-3a.