Metallo-β-cyclodextrins of 6A-(2-(2-(2-Aminoethylamino)-ethylamino)ethylamino)-6A-deoxy-β-cyclodextrin and 6A-Deoxy-6A-(1,4,7,10-tetraazacyclododecan-1-yl)-β-cyclodextrin: Their Formation and Complexation of (R)- and (S)-Tryptophan and Tryptophanate in Aqueous Solution

Abstract

The binary metallo-β-cyclodextrins formed by 6^A-(2-(2-(2-aminoethylamino)ethylamino)ethylamino)-6^A-deoxy-β-cyclodextrin, [M(βCDtrien)]²⁺, where M²⁺ = Ni²⁺, Cu²⁺ and Zn²⁺, are characterized by log(K/dm³ mol^-1) = 11.500.02, 10.700.07 and 9.400.01, respectively, in aqueous solution at 298.2 K and I = 0.1 mol dm^-3 (NaClO₄), where K is the stability constant. For those formed by 6^A-deoxy-6^A-(1,4,7,10-tetraazacyclododecan-1-yl)-β-cyclodextrin, [M(βCDcyclen)]²⁺, where M²⁺ = Cu²⁺ and Zn²⁺, log(K/dm³ mol^-1) = 13.610.02 and 11.620.04, respectively. The ternary metallo-β-cyclodextrins formed by [M(βCDtrien)]²⁺ and (R)- and (S)-tryptophanate, [M(βCDtrien)((R)-Trp)]⁺ and [M(βCDtrien)((S)-Trp)]⁺ are characterized by log(K/dm³ mol^-1) = 6.900.04 and 6.790.04, 8.20.3 and 7.90.2, and 6.640.08 and 7.010.07, respectively, where M²⁺ = Ni²⁺, Cu²⁺ and Zn²⁺. For the ternary metallo-β-cyclodextrins formed by [M(βCDcyclen)]²⁺ and (R)- and (S)-tryptophanate, [M(βCDcyclen)((R)-Trp)]⁺ and [M(βCDcyclen)((S)-Trp)]⁺, log(K/dm³ mol^-1) = 6.840.06 and 6.850.06, and 4.950.05 and 4.940.04, respectively, where M²⁺ = Cu²⁺ and Zn²⁺. Other binary and ternary metallo-β-cyclo-dextrins are also formed. Binary complexes formed by the substituted β-cyclodextrins are exemplified by βCDcyclen.(R)-Trp^- and βCDcyclen.(S)-Trp^- for which log(Kd/m³ mol^-1) = 3.690.04 and 3.950.03, respectively. These data are discussed together with those from the literature characterizing other metallo-β-cyclodextrin and substituted β-cyclodextrin systems.