title: The mechanism of the Cu²⁺[12-MCCu(Alaha)-4] metallacrown formation and lanthanum(III) encapsulation.
abstract: A kinetic, calorimetric, mass spectrometry and EPR study has been performed on the formation of the metallacrown Cu(2+)[12-MCCu(Alaha)-4] from Cu(ii) and α-alaninehydroxamic acid (H2L). The acidity range where Cu(2+)[12-MCCu(Alaha)-4] is stable lies between pH 3.5 and 6.0. For pH values below that range the complex CuHL(+) is the prevailing species. This species plays a fundamental role in the formation of Cu(2+)[12-MCCu(Alaha)-4]. Actually, depending on the Cu(II)/H2L ratio and on pH, it can originate a dimer Cu2(HL)2(2+) or a dinuclear complex Cu2L(2+). Both species constitute the nuclei necessary for a further oligomerisation reaction which ends when the crown is formed. The kinetics of Cu(2+)[12-MCCu(Alaha)-4] formation is biphasic. Under conditions of Cu(II) excess the fast phase leads to formation of Cu2L(2+). The slow phase is interpreted in terms of a sequential addition of monomers (CuHL(+)) to the Cu2L(2+) nucleus to form the crown. The interaction of La(III) with Cu(2+)[12-MCCu(Alaha)-4] has also been investigated. The system displays a biphasic behaviour; in the first phase the intermediate complex Cu[12-MCCu(Alaha)-4]La is formed which, in excess of ligand, evolves towards the larger metallacrown La(3+)[15-MCCu(Alaha)-5]. The reaction mechanisms of the two investigated systems are discussed.
authors.affiliation: CEA, DSV, IBEB, Laboratoire des Interactions Protéine Métal, CNRS UMR Biologie Végétale et Microbiologie Environnementale, Université d'Aix-Marseille, Saint-Paul-lez-Durance, France.
authors.forename: Maria R
authors.initials: MR
authors.lastname: Beccia
authors.forename: Begoña
authors.initials: B
authors.lastname: García
authors.forename: Javier
authors.initials: J
authors.lastname: García-Tojal
authors.forename: José M
authors.initials: JM
authors.lastname: Leal
authors.forename: Fernando
authors.initials: F
authors.lastname: Secco
authors.forename: Matteo
authors.initials: M
authors.lastname: Tegoni