title: Elucidation of the relationships between H-bonding patterns and excited state dynamics in cyclovalone.
abstract: Cyclovalone is a synthetic curcumin derivative in which the keto-enolic system is replaced by a cyclohexanone ring. This modification of the chemical structure might in principle result in an excited state that is more stable than that of curcumin, which in turn should produce an enhanced phototoxicity. Indeed, although curcumin exhibits photosensitized antibacterial activity, this compound is characterized by very fast excited-state dynamics which limit its efficacy as a photosensitizer. In previous works we showed that the main non-radiative decay pathway of keto-enolic curcuminoids is through excited-state transfer of the enolic proton to the keto-oxygen. Another effective deactivation pathway involves an intermolecular charge transfer mechanism occurring at the phenyl rings, made possible by intramolecular H-bonding between the methoxy and the hydroxyl substituent. In this paper we present UV-Vis and IR absorption spectra data with the aim of elucidating the intramolecular charge distribution of this compound and its solvation patterns in different environments, with particular focus on solute-solvent H-bonding features. Moreover, we discuss steady state and time-resolved fluorescence data that aim at characterizing the excited-state dynamics of cyclovalone, and we compare its decay photophysics to that of curcumin. Finally, because during the characterization procedures we found evidence of very fast photodegradation of cyclovalone, its photostability in four organic solvents was studied by HPLC and the corresponding relative degradation rates were calculated.
authors.affiliation: Department of Science and High Technology, University of Insubria, Via Valleggio, 11, 22100 Como, Italy. marco.lamperti@uninsubria.it.
authors.forename: Marco
authors.initials: M
authors.lastname: Lamperti
authors.affiliation: Department of Science and High Technology, University of Insubria, Via Valleggio, 11, 22100 Como, Italy. angelo.maspero@uninsubria.it.
authors.forename: Angelo
authors.initials: A
authors.lastname: Maspero
authors.affiliation: School of Pharmacy, University of Oslo, P.O. Box 1068 Blindern, 0316 Oslo, Norway. h.h.tonnesen@farmasi.uio.no.
authors.forename: Hanne H
authors.initials: HH
authors.lastname: Tønnesen
authors.affiliation: Institute of Photonics and Nanotechnology, Natl. Research Council, Via Valleggio, 11, 22100 Como, Italy. maria.bondani@uninsubria.it.
authors.forename: Maria
authors.initials: M
authors.lastname: Bondani
authors.affiliation: Department of Health Sciences, University of Milano Bicocca, Via Cadore, 48, 20900 Monza, Italy. luca.nardo@unimib.it.
authors.forename: Luca
authors.initials: L
authors.lastname: Nardo
mesh_terms: D003474:Curcumin / Q000031:analogs & derivatives* / Q000737:chemistry; D004355:Drug Stability; D006860:Hydrogen Bonding; D008968:Molecular Conformation; D055668:Photochemical Processes; D017319:Photosensitizing Agents / Q000737:chemistry*; D011789:Quantum Theory; D026082:Singlet Oxygen / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013055:Spectrophotometry, Infrared; D013481:Superoxides / Q000737:chemistry
chemical_list: D017319:Photosensitizing Agents; C000598259:cyclovalone; D013481:Superoxides; D026082:Singlet Oxygen; D003474:Curcumin