Complexes of 6A-(2-Aminoethylamino)-6A-deoxy-b-cyclodextrin and 6A-[Bis(carboxylatomethyl)amino]-6A-deoxy-b-cyclodextrin with (R)- and (S)-Tryptophanate and (R)- and (S)-Phenylalaninate in Aqueous Solution. A pH Titrimetric and N.M.R. Spectroscopic Study

Abstract

The 1 : 1 host–guest complexes formed by 6^A-(2-aminoethylamino)-6^A-deoxy-β-cyclodextrin and (R)- and (S)-tryptophanate are characterized by log(K/dm³ mol^–1) = 4.83±0.02 and 4.72±0.03, respectively, and for those formed with (R)- and (S)-phenylalaninate log(K/dm³ mol^–1) = 3.82±0.05 and 4.12±0.02, respectively, in aqueous solution at 298.2 K and I = 0.10 mol dm^–3 (NaClO₄), where K is the stability constant. The corresponding values for the analogous complexes formed by 6^A-[bis(carboxylatomethyl)amino]-6^A-deoxy-β-cyclodextrin are 3.4±0.1, 3.3±0.1, 4.02±0.06 and 4.00±0.06, respectively. Host–guest complexes are also formed by the monoprotonated substituted β-cyclodextrins. ¹H n.m.r. spectroscopy (ROESY) indicates that the guests are complexed with their indole and phenyl entities inside the annuli of the substituted β-cyclodextrin hosts.