Rjmk. Gebbink et al., Aggregation of a crown ether-based copper amphiphile as a mimic for the superstructure of hemocyanin, J CHEM S DA, (20), 2001, pp. 3056-3064
Citations number
51
Categorie Soggetti
Inorganic & Nuclear Chemistry
Journal title
JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS
Inspired by the alkali metal ion-controlled self-assembly of the oxygen-tra
nsporting dinuclear copper protein hemocyanin, a novel crown ether amphiphi
le (1) has been designed. A diaza-18-crown-6 moiety (diaza-18-crown-6 = 1,1
0-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), resu
lting in an amphiphile that has independent ligand sets for the coordinatio
n of copper ions and alkali metal ions. The copper complex of this amphiphi
le, [Cu-II (1)]( ClO4)(2), forms monolayers at the air-water surface. In th
e presence of certain alkali metal salts, the molecules in the monolayers s
tretch out and form sandwich complexes (2 : 1 amphiphile : metal ion stoich
iometry). This is in contrast to the 1 : 1 complexes which are obtained wit
h amphiphiles that lack the Cu-PY2 part. Electron microscopy experiments re
veal that hollow tubules are generated when [Cu-II (1)](ClO4)(2) is dispers
ed in water. The diameters of these tubes range from 45-55 nm, while their
length can extend up to 5 mum. The presence of an alkali metal salt leads t
o vesicular structures with diameters ranging from 180-210 nm. Based on pow
der X-ray diffraction results, the amphiphile [Cu-II (1)](ClO4)(2) is packe
d 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 (1)](ClO4)(2), E-1/2 = -0.08 V, undergoes
an anodic shift to +0.083 V in the presence of K+ ions. An in situ preparat
ion of [Cu-I (1)](ClO4) did not show binding of molecular oxygen, whereas [
Cu-II (1)](ClO4)(2) reacted with H2O2, leading to degradation of ligand 1.