title: Ruthenium complexes with hydrophobic ligands that are key factors for the optical imaging of physiological hypoxia.
abstract: The phosphorescence emission of ruthenium complexes was applied to the optical imaging of physiological hypoxia. We prepared three complexes with hydrophobic substituents on the phenanthroline ligand and characterized their emission, which was quenched by molecular oxygen. Among the complexes synthesized in this study, a pyrene chromophore-linked ruthenium complex, Ru-Py, exhibited optimal properties for the imaging of hypoxia; the prolonged lifetime of the triplet excited state of the ruthenium chromophore, which was induced by efficient energy distribution and transfer from the pyrene unit, provided the highest sensitivity towards molecular oxygen. The introduction of hydrophobic pyrene increased the lipophilicity of the complex, leading to enhanced cellular uptake. Consequently, the bright phosphorescence of Ru-Py was seen in the cytoplasm of viable hypoxic cells, whereas the signal from aerobic cells was markedly weaker. Thus, we could clearly discriminate between hypoxic and aerobic cells by monitoring the phosphorescence emission. Furthermore, Ru-Py was applied to optical imaging in live mice. An intramuscular injection of Ru-Py successfully visualized ischemia-based hypoxia, which was constructed by leg banding.
authors.affiliation: Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Katsura Campus, Nishikyo-ku, Kyoto 615-8510, Japan.
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Komatsu
authors.forename: Kazuki
authors.initials: K
authors.lastname: Yoshihara
authors.forename: Hisatsugu
authors.initials: H
authors.lastname: Yamada
authors.forename: Yu
authors.initials: Y
authors.lastname: Kimura
authors.forename: Aoi
authors.initials: A
authors.lastname: Son
authors.forename: Sei-ichi
authors.initials: S
authors.lastname: Nishimoto
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Tanabe
mesh_terms: D000818:Animals; D056831:Coordination Complexes / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D000860:Hypoxia / Q000139:chemically induced*; D008024:Ligands; D008163:Luminescent Measurements / Q000379:methods; D051379:Mice; D015394:Molecular Structure; D061848:Optical Imaging; D010618:Phenanthrolines / Q000737:chemistry*; D010777:Photochemistry; D011721:Pyrenes / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D008024:Ligands; D010618:Phenanthrolines; D011721:Pyrenes; D011725:Pyridines; D012428:Ruthenium