title: Optical properties of isolated hormone oxytocin dianions: ionization, reduction, and copper complexation effects.
abstract: Trapped oxytocin (OT) peptide dianions and copper-oxytocin complex dianions are subjected to electron detachment when irradiated by a UV light. Electron photodetachment experiments as a function of the laser wavelength were performed on the native disulfide-containing ring oxytocin, the reduced dithiol oxytocin, and the Cu(II)-oxytocin complex. The electron detachment yield was used to monitor the excited electronic spectrum of the trapped ions. The spectra can be used as a fingerprint of the ionization state of the tyrosine chromophore under different structural environments. In gas-phase oxytocin dianion [OT-2H](2-), the tyrosine is deprotonated while it is neutral for the reduced form of oxytocin [OT(SH)-2H](2-). Optical spectra for the copper complex dianion [OT-4H+Cu](2-) are in favor of a neutral tyrosine in the complex. A structure with the metal cation chelated to four deprotonated amide groups is proposed for this complex.
authors.affiliation: LASIM, UMR 5579, CNRS et Université Lyon 1, Villeurbanne, F-69622 Lyon, France.
authors.forename: Laure
authors.initials: L
authors.lastname: Joly
authors.forename: Rodolphe
authors.initials: R
authors.lastname: Antoine
authors.forename: Abdul-Rahman
authors.initials: AR
authors.lastname: Allouche
authors.forename: Michel
authors.initials: M
authors.lastname: Broyer
authors.forename: Jérôme
authors.initials: J
authors.lastname: Lemoine
authors.forename: Philippe
authors.initials: P
authors.lastname: Dugourd
mesh_terms: D000838:Anions / Q000737:chemistry; D003300:Copper / Q000737:chemistry*; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010121:Oxytocin / Q000737:chemistry*; D014466:Ultraviolet Rays
chemical_list: D000838:Anions; D009942:Organometallic Compounds; D010121:Oxytocin; D003300:Copper