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

Abstract

Our observations that 1-[2-[(9-anthracenylmethylamino)ethyl)-4,7,10- tris[(2S)-2-hydroxy-3-phenoxypropyl]-1,4,7,10-tetraazacyclododecane, L 1, complexes Cd(II) to form fluorescent [CdL 1] 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, (L 2), 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, (L 3), 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, (L 4), have been prepared with a view to using their metal complexes to study aromatic anion sequestration. The eight-coordinate Cd(II) complexes of L 2 and L 3, [CdL 2](ClO 4) 2•5H 2O and [CdL 3](ClO 4) 2•2H 2O•2Et 2O 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 10 3.2 M -1 (guest = p-hydroxybenzoate) to 10 7.3 M -1 (guest = 3,4,5-trihydroxybenzoate). © 2011 Springer Science+Business Media B.V.