title: Mimicking the protein access channel to a metal center: effect of a funnel complex on dissociative versus associative copper redox chemistry.
abstract: The control of metal-ligand exchange in a confined environment is of primary importance for understanding thermodynamics and kinetics of the electron transfer process governing the reactivity of enzymes. This study reveals an unprecedented change of the Cu(II)/Cu(I) binding and redox properties through a subtle control of the access to the labile site by a protein channel mimic. The cavity effect was estimated from cyclic voltammetry investigations by comparison of two complexes displaying the same coordination sphere (tmpa) and differing by the presence or absence of a calix[6]arene cone surrounding the metal labile site L. Effects on thermodynamics are illustrated by important shifts of E(1/2) toward higher values for the calix complexes. This is ascribable to the protection of the labile site of the open-shell system from the polar medium. Such a cavity control also generates specific stabilizations. This is exemplified by an impressively exalted affinity of the calixarene system for MeCN, and by the detection of a kinetic intermediate, a noncoordinated DMF guest molecule floating inside the cone. Kinetically, a unique dissymmetry between the Cu(I) and Cu(II) ligand exchange capacity is highlighted. At the CV time scale, the guest interconversion is only feasible after reduction of Cu(II) to Cu(I). Such a redox-switch mechanism results from the blocking of the associative process at the Cu(II) state, imposed by the calixarene funnel. All of this suggests that the embedment of a reactive redox metal ion in a funnel-like cavity can play a crucial role in catalysis, particularly for metallo-enzymes associating electron transfer and ligand exchange.
authors.affiliation: Laboratoire de Chimie, Electrochimie Moléculaires et Chimie Analytique, CNRS, UMR 6521, Université Européenne de Bretagne à Brest, 6 av. Le Gorgeu, 29238 Brest cedex, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Le Poul
authors.forename: Bénédicte
authors.initials: B
authors.lastname: Douziech
authors.forename: Joceline
authors.initials: J
authors.lastname: Zeitouny
authors.forename: Grégory
authors.initials: G
authors.lastname: Thiabaud
authors.forename: Hélène
authors.initials: H
authors.lastname: Colas
authors.forename: Françoise
authors.initials: F
authors.lastname: Conan
authors.forename: Nathalie
authors.initials: N
authors.lastname: Cosquer
authors.forename: Ivan
authors.initials: I
authors.lastname: Jabin
authors.forename: Corinne
authors.initials: C
authors.lastname: Lagrost
authors.forename: Philippe
authors.initials: P
authors.lastname: Hapiot
authors.forename: Olivia
authors.initials: O
authors.lastname: Reinaud
authors.forename: Yves
authors.initials: Y
authors.lastname: Le Mest
mesh_terms: D003300:Copper / Q000737:chemistry*; D007700:Kinetics; D008024:Ligands; D018716:Molecular Mimicry; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D011506:Proteins / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D011506:Proteins; D003300:Copper