ION BINDING AND SELECTIVITY IN ZWITTERIONIC MICELLES

Micelles of 3-(N-hexadecyl-N,W-dimethylammonio)propanesulfonate (HPS) incorporate N-butyl-2,3-naphthalimide (NBN), N-decyl- (DeCP), and N-dodecyl-4-cyanopyridimum (DoCP) ion. Upon incorporation in HPS micelles, the NBN fluorescence emission spectra was comparable to that of the same probe in methanol. The fluorescence of micelle-incorporated NBN was quenched by chloride and bromide ions, suggesting specific ion binding to HPS micelles. HPS micelles increased the rate of alkaline hydrolysis of DoCP and DeCP and decreased the rate of hydrolysis of NBN. Added salts inhibited the micellar modified OH- attack on the three substrates. Salt inhibition, analyzed by using a competitive inhibition scheme, demonstrated that HPS micelles bind bromide better than chloride ion and that both ions can displace OH- from the micellar surface. These data show that both charged and zwitterionic micelles can selectively concentrate ions at the micelle-water interface. © 1990 American Chemical Society.