Fluorescence signaling of aromatic oxoanion inclusion within metal-ion activated molecular receptor complexes formed from 2-(9-anthracenylmethylamino)ethyl-appended cyclen

摘要

Our observations that 1-[2-[(9-anthracenylmethylamino)ethyl)-4,7,10-tris[(2S)-2-hydroxy-3-phenoxypropyl]-1,4,7,10-tetraazacyclododecane, L1, complexes Cd(II) to form fluorescent [CdL1]2+ which undergoes a fluorescence change when it acts as an aromatic anion receptor complex has caused us to explore further the potential development of an interesting sequestration/sensor system. Accordingly, three new, octadentate, fluorescent, macrocyclic ligands, 1-[2-[(9-anthracenylmethyl)((2S)-2-hydroxy-3-phenoxypropyl)amino]ethyl]-4,7,10-tris[(2S)-2-hydroxy-3-phenoxypropyl]-1,4,7,10-tetraazacyclododecane, (L2), 1-[2-[(9-anthracenyl-methyl)((2S)-2-hydroxy-3-(4′-methyl)phenoxypropyl)amino]ethyl]-4,7,10-tris[(2S)-2-hydroxy-3-(4′-methyl)phenoxypropyl]-1,4,7,10-tetraazacyclododecane, (L3), and 1-[2-[(9-anthracenylmethyl)((2S)-2-hydroxy-3-(4′-t-butyl)phenoxypropyl)amino]ethyl]-4,7,10-tris[(2S)-2-hydroxy-3-(4′-t-butyl)phenoxypropyl]-1,4,7,10-tetraazacyclododecane, (L4), have been prepared with a view to using their metal complexes to study aromatic anion sequestration. The eight-coordinate Cd(II) complexes of L2 and L3, [CdL2](ClO₄)₂·5H₂O and [CdL3](ClO₄)₂·2H₂O·2Et₂O are both capable of acting as receptors for a range of aromatic oxoanions. This is demonstrated by perturbation of the anthracene derived fluorescence emission intensity as the guest aromatic oxoanion and the receptor complex combine. In 20% aqueous 1,4-dioxane the receptor complex/aromatic oxoanion association constants are in the range of 103.2 M−1 (guest = p-hydroxybenzoate) to 107.3 M−1 (guest = 3,4,5-trihydroxybenzoate).