Formation of Metallo-6 A -((2-(bis(2-aminoethyl)amino)ethyl)amino)-6 A -deoxy-β-cyclodextrins and Their Complexation of Tryptophan in Aqueous Solution (original) (raw)

1996, Inorganic Chemistry

A pH titration study shows that 6 A -((2-(bis(2-aminoethyl)amino)ethyl)amino)-6 A -deoxy--cyclodextrin ( CDtren) forms binary metallocyclodextrins, [M( CDtren)] 2+ , for which log(K/dm 3 mol -1 ) ) 11.65 ( 0. 06, 17.29 ( 0.05, and 12.25 ( 0.03, respectively, when M 2+ ) Ni 2+ , Cu 2+ , and Zn 2+ , where K is the stability constant in aqueous solution at 298.2 K and I ) 0.10 mol dm -3 (NaClO 4 ). The ternary metallocyclodextrins [M( CDtren)Trp] + , where Trpis the tryptophan anion, are characterized by log(K/dm 3 mol -1 ) ) 8.2 ( 0.2 and 8.1 ( 0.2, 9.5 ( 0.3 and 9.4 ( 0.2, and 8.1 ( 0.1 and 8.3 ( 0.1, respectively, where the first and second values represent the stepwise stability constants for the complexation of (R)-and (S)-Trp -, respectively, when M 2+ ) Ni 2+ , Cu 2+ , and Zn 2+ . From comparisons of stabilities and UV-visible spectra, the binary and ternary metallocyclodextrins appear to be six-coordinate when M 2+