title: Controlling the redox properties of a pyrroloquinolinequinone (PQQ) derivative in a ruthenium(II) coordination sphere.
abstract: Ruthenium(ii) complexes of PQQTME, a trimethyl ester derivative of redox-active PQQ (pyrroloquinolinequinone), were prepared using a tridentate ligand, 2,2':6',2''-terpyridine (terpy) as an auxiliary ligand. The characterization of the complexes was performed by spectroscopic methods, X-ray crystallography, and electrochemical measurements. In one complex, the pyridine site of PQQTME binds to the [Ru(II)(terpy)] unit as a tridentate ligand, and a silver(i) ion is coordinated by the quinone moiety in a bidentate fashion. In contrast, another complex includes the [Ru(II)(terpy)] unit at the bidentate quinone moiety of the PQQTME ligand. The difference in the coordination modes of the complexes exhibits a characteristic difference in the stability of metal coordination and also in the reversibility of the reduction processes of the PQQTME ligand. It should be noted that an additional metal-ion-binding to the PQQTME ligand largely raises the 1e(-)-reduction potential of the ligand. In addition, we succeeded in the characterization of the 1e(-)-reduced species of the complexes, where the unpaired electron was delocalized in the π-conjugated system of the PQQTME˙(-) ligand, using UV-Vis absorption and ESR spectroscopies.
authors.affiliation: Department of Chemistry, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571, Japan. kojima@chem.tsukuba.ac.jp.
authors.forename: Hiroumi
authors.initials: H
authors.lastname: Mitome
authors.forename: Tomoya
authors.initials: T
authors.lastname: Ishizuka
authors.forename: Yoshihito
authors.initials: Y
authors.lastname: Shiota
authors.forename: Kazunari
authors.initials: K
authors.lastname: Yoshizawa
authors.forename: Takahiko
authors.initials: T
authors.lastname: Kojima
mesh_terms: D018360:Crystallography, X-Ray; D010084:Oxidation-Reduction; D045542:PQQ Cofactor / Q000737:chemistry* / Q000378:metabolism*; D012428:Ruthenium / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D045542:PQQ Cofactor; D012428:Ruthenium