COMPLEXATION OF BENZOIC, 4-METHYLBENZOIC, AND (R)-2-PHENYLPROPANOIC AND (S)-2-PHENYLPROPANOIC ACIDS AND THEIR CONJUGATE BASES BY 3(A)-AMINO-3(A)-DEOXY-(2(A)S,3(A)S)-BETA-CYCLODEXTRIN IN AQUEOUS-SOLUTION

A potentiometric titration study of the complexation of benzoic, 4-methylbenzoic, and (R)- and (S)-2-phenylpropanoic acids and their conjugate bases by 3(A)-amino-3(A)-deoxy-(2(A)S,3(A)S)-beta-cyclodextrin, beta CD3NH(2), in which the amino group may be protonated to produce a singly charged species, beta CD3NH(3)(+), is reported. In aqueous solution at 298 . 2K and I = 0 . 10 mol dm(-3) (KCl), the complexation constants for the complexes indicated have the values (in dm(3) mol(-1)) shown in parentheses: benzoic acid.beta CD3NH(3)(+) (K-HA = 110+/-10); benzoate.beta CD3NH(3)(+) (K-A = 19+/-2); 4-methylbenzoic acid.beta CD3NH(3)(+) (K-HA = 210+/-10); 4-methylbenzoate.beta CD3NH(3)(+) (K-A = 21+/-3); (R)- and (S)-2-phenylpropanoic acid.beta CD3NH(3)(+) (K-RHA = 64+/-8, K-SHA = 57+/-5); (R)- and (S)-2-phenylpropanoate.beta CD3NH(3)(+) (K-RA = 51+/-6, K-SA = 32+/-6); and (R)- and (S)-2-phenylpropanoate.beta CD3NH(2) (K-RA' = 13+/-7; K-SA' is too small to quantify reliably). These complexation constants are substantially less than those for the host-guest complexes formed by the isomeric 6(A)-amino-6(A)-deoxy-beta-cyclodextrin and also for those formed by beta-cyclodextrin. The origins of these differences are discussed.