Aggregation o9f a crown ether-based copper amphiphile as a mimic for the superstructure of hemocyanin

摘要

Inspired by the alkali metal ion-controlled self-assembly of the oxygen-transporting dinuclear copper protein hemocyanin, a novel crown ether amphiphile (1) has been designed. A diaza-18-crown-6 moiety (diaza-18-crown-6=1,10-diaza-4,7,13,16-tetraoxacyclooctadecane) is appended with an aliphatic C_16 chain and with a PY2 ligand (PY2=bis[2-(2-pyridyl)ethyl]amine), resulting in an amphiphile that has independent ligand sets for the coordination of copper ions and alkali metal ions. The copper complex of this amphiphile, [Cu~II(1)](ClO_4)_2, forms monolayers at the air-water surface. In the presence of certain alkali metal salts, the molecules in the monolayers stretch out and form sandwich complexes (2:1 amphiphile: metal ion stoichiometry). This is in contrast to the 1:! complexes which are obtained with amphiphiles that lack the Cu-PY2 part. Electron microscopy expriments reveal that hollow tubules are generated when [Cu~II(1)](ClO_4)_2 is dispersed in water. The diameters of these tubes range from 45-55 nm, while their length can extend up to 5 #mu#m. The presence of an alkali metal salt leads to vesicular structures with diameters ranging from 180-210 nm. Based on powder X-ray diffraction results, the amphiphile [Cu~II](ClO_4_2 is packed in strongly intercalated bilayers in both tubes and vesicles with a layer thickness of 4.8 nm. Cyclic voltammetry shows that the midpoint potential of aqueous dispersions of [Cu~II](ClO_4_2, E_1/2=-0.08 V, undergoes an anodic shift to +0.083 V in the presence of K~+ ions. An in situ preparation of [Cu~II](ClO_4_2 did not show binding of molecular oxygen, whereas [Cu~II](ClO_4_2 reacted with H_2O_2 leading to degradation of ligand 1.