Binary and ternary metallo-beta-cyclodextrins of 6(A)-[bis(carboxylatomethyl) amino]-6(A)-deoxy-beta-cyclodextrin

The binary metallo-beta-cyclodextrins formed by 6(A)-[bis(carboxylatomethyl )amino]-6(A)-deoxy-beta-cyclodextrin ([M(beta CDida)], where M2+ = Co2+, Ni 2+, Cu2+ and Zn2+) are characterized by log(K/dm(3) mol(-1)) = 7.29+/-0.01, 9.74+/-0.02, 8.89+/-0.03 and 6.08+/-0.02, respectively, in aqueous solutio n at 298.2 K and I = 0.10 mol dm(-3) (NaClO4), where K is the stability con stant. The ternary metallo-beta-cyclodextrins formed by [M(beta CDida)] and (R)- and (S)-tryptophanate, [M(beta CDida)(R)-Trp](-) and [M(beta CDida)(S )-Trp](-), are characterized by log(K/dm(3) mol(-1)) = 5.49+/-0.04 and 5.16 +/-0.07, 6.33+/-0.04 and 6.34+/-0.02, 6.91+/-0.02 and 6.99+/-0.01, and 5.34 +/-0.02 and 5.36+/-0.04, respectively, when M2+ = Co2+, Ni2+, Cu2+ and Zn2. For [M(beta CDida)(R)-Trp](-) and [M(beta CDida)(S)-Trp](-), pK(a) values of 8.07+/-0.04 and 8.4+/-0.1, 7.45+/-0.02 and 7.88+/-0.04, 8.46+/-0.09 and 8.40+/-0.01, and 8.92+/-0.05 and 8.7+/-0.2 are found when M2+ = Co2+, Ni2, Cu2+ and Zn2+, respectively, and are attributed to the protolysis of an a qua ligand occupying a sixth coordination site on M2+.