COMPLEXATION OF PHENYLALANINE AND HISTIDINE BY BETA-CYCLODEXTRIN, 6(A)-(3-AMINOPROPYLAMINO)-6(A)-DEOXY-BETA-CYCLODEXTRIN AND ITS METALLOCYCLODEXTRINS IN AQUEOUS-SOLUTION

A pH titration study shows that for the complexation of phenylalanine anion [(R)- and (S)-Phe(-)] by beta-cyclodextrin (beta CD), log(K-1R/dm(3) mol(-1)) = 2.91 +/- 0.08 and log(K-1S/dm(3) mol(-1)) = 2.83 +/- 0.06, and that by 6(A)-(3-aminopropylamino)-6(A)-deoxy-beta-cyclodextrin (beta CDpn) is characterized by log(K-2R/dm(3) mol(-1)) = 2.51 +/- 0.07 and log(K-2S/dm(3) mol(-1)) = 2.74 +/- 0.05. No complexation of histidine (HisH) by beta CD was detected, but for the complexation of histidine anion (His(-)) by beta CDpnH(+) log(K-3R/dm(3) mol(-1)) = 2.50 + 0.02 and log(K-3S/dm(3) mol(-1)) = 2.37 +/- 0.09; and for the complexation of HisH by beta CDpnH(+) log(K-4R/dm(3) mol(-1)) = 2.31 +/- 0.05 and log(K-4S/dm(3) mol(-1)) = 2.18 +/- 0.05. For the complexation of Phe(-) by the metallocyclodextrin, [M(beta CDpn)](2+), log(K-11R/dm(3) mol(-1)) and log(K-11S/dm(3) mol(-1)) = 3.6 +/- 0.2 and 3.69 +/- 0.06, <3.6 and 4.4 +/- 0.1, 7.2 +/- 0.1 and 6.9 +/- 0.1, 47 +/- 0.1 and 4.7 +/- 0.2, when M(2+) = Co2+, Ni2+, Cu2+ and Zn2+, respectively. For the complexation of His(-) by [Cu(beta CDpn)](2+), log(K-11R/dm(3) mol(-1)) = 8.38 +/- 0.04 and log(K-11S/dm(3) mol(-1)) = 8.42 +/- 0.02, and for the complexation of a second His(-) log(K-12R/dm(3) mol(-1)) = 7.75 +/- 0.05 and log(K-12S/dm(3) mol(-1)) = 7.6 +/- 0.1. The roles of the cyclodextrins, divalent metal ions and amino acids affecting complexation are discussed.