Positive heterotropic cooperativity for selective guest binding via electronic communications through a fused zinc porphyrin array

Upon binding with C60 and diamines, such as 4,4′-bipyridine (bpy) and N,N,N′,N′-tetramethylhexane-1,6-diamine (TMHDA), cyclic host 1 possessing two electronically coupled binding sites displays negative homotropic cooperativity and positive heterotropic cooperativity, and their ternary mixtures preferentially form inclusion complexes with hetero-guest pairs 1⊃C60·bpy and 1⊃C60·TMHDA under appropriate conditions. Spectroscopic titration profiles in toluene at 20 °C demonstrated that the association constants (Kassoc) of C60 with monodiamine complexes 1⊃bpy (2.8 × 105 M-1) and 1⊃TMHDA (1.5 × 105 M-1) are 8.5 and 4.5 times greater than that of C60 with guest-free 1 (3.3 × 104 M-1), respectively. On the other hand, mono-C60 complex 1⊃C60 was 6.1 times more accessible than guest-free 1 toward TMHDA. Absorption spectroscopy in the absence of 1 indicated no direct interaction between C60 and diamines. Copyright © 2005 American Chemical Society.