| Abstract
| - In order to evaluate factors that affect the extent of organicanion binding to charged micellar interfaces,the ion exchange constants of four substituted aromatic anions,o-, m-, and p-nitrobenzoate andsalicylate,competing for the tetradecyltrimethylammonium bromide (TTAB) micellarinterface have been determinedat room temperature employing a standard two-site model. The ionexchange constants were calculatedusing the chemical shifts of the protons of the organic anions, thefractional ionization constants, α, andthe critical micellization concentrations (cmc). The cmc valueswere determined by surface tension andconductivity methods, whereas the fractional ionization constants ofthe micellar aggregates were calculatedfrom conductivity data. For all systems, the 1H NMRspectra revealed characteristic changes in chemicalshifts of the aromatic protons at concentrations above the cmc allowingthe fractions of micellar boundorganic anion to be measured. Analyzing 1H NMRspectroscopic data together with the cmc and thefractional ionization constants, the ion-exchange constants of 3.8 foro-nitrobenzoate, of 11 for m-nitrobenzoate, or 3.3 for p-nitrobenzoate, and of 20 forsalicylate were calculated. The ion exchangeconstantsclearly reveal that salicylate and m-nitrobenzoate morereadily replace inorganic bromide at the micellarinterface than the para- and ortho-substitutednitrobenzoates and may provide information for deducingimportant mechanisms controlling the binding of organic ions at chargedinterfaces. Furthermore, thedata reveal that inorganic bromide competes more strongly with ahydrophobic organic anion for bindingto the charged micellar interface than is generallyassumed.
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