title: Pentacopper(II) complexes of alpha-aminohydroxamic acids: uranyl-induced conversion of a 12-metallacrown-4 to a 15-metallacrown-5.
abstract: Effects of uranyl on the pentacopper(II) complexes of alpha-leucinehydroxamic acid and alpha-tyrosinehydroxamic acid were studied in water and methanol by means of electrospray ionisation mass spectrometry (ES-MS), absorption spectrophotometry, circular dichroism spectroscopy and proton NMR spectroscopy. All the measurements were consistent with the complete conversion of a 12-metallacrown-4 to a 15-metallacrown-5 upon addition of one equivalent of the uranyl ion. The uranyl ion is accommodated in the cavity formed by five copper(II) ions and five alpha-aminohydroxamate ligands. The 15-metallacrown-5 inclusion complexes have a high affinity for the uranyl ion. Competition studies showed that even in the presence of a large excess of calcium(II), the 15-metallacrown-5 remained stable, and no exchange reactions between calcium(II) and uranyl were observed. Extraction of uranyl from the 15-metallacrown-5 was also not detected in the presence of a large excess of 18-crown-6. Trivalent lanthanide ions can be partially sequestered by the 15-metallacrown-5, however, even these trivalent ions are displaced by uranyl.
authors.affiliation: Department of Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium.
authors.forename: Tatjana N
authors.initials: TN
authors.lastname: Parac-Vogt
authors.forename: Antoine
authors.initials: A
authors.lastname: Pacco
authors.forename: Christiane
authors.initials: C
authors.lastname: Görller-Walrand
authors.forename: Koen
authors.initials: K
authors.lastname: Binnemans