Effects of Headgroup Structure on the Incorporation of Anions into Sulfobetaine Micelles. Kinetic and Physical Evidence

Zwitterionic micelles of (tetradecyldialkylammonio) propane-, butane- and pentanesulfonate increase the rate of reaction of Br - with methyl naphthalene-2-sulfonate, MeONs, but this reaction is largely suppressed by addition of NaClO 4 . The NMR line width of 35 Cl in ClO 4 - increases very sharply on incorporation into micelles of tetradecyldimethylammonio propanesulfonate, SB3-14. The 14 N line width of SB3-14 also increases significantly under these conditions, but there is no evidence for strong interactions with 23 Na + . Aggregation numbers, N agg, of SB3-14 increase modestly with increasing [SB3-14], but not with the other surfactants. The increase is greater with added NaClO 4, but NaOH, NaCl, and NaNO 3 have little effect on N agg . Interactions of the anions with the micelles are treated with equations of the form of the Langmuir isotherm, and binding parameters estimated kinetically and conductometrically agree. Second-order rate constants of the reaction of Br - with MeONs at micellar surfaces are similar in sulfobetaine and cationic micelles. The reaction of I - with MeONs is also accelerated by micelles of SB3-14.