Optical properties of isolated hormone oxytocin dianions: ionization, reduction, and copper complexation effects
Laure Joly1, Rodolphe Antoine, Abdul-Rahman Allouche
1LASIM, UMR 5579, CNRS et Université Lyon 1, Villeurbanne, F-69622 Lyon, France.
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.
Related Concept Videos
03:02Colors and Magnetism
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
02:52Stereoisomerism
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...
02:58Crystal Field Theory - Octahedral Complexes
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
01:19Complexation Equilibria: The Chelate Effect
02:46Crystal Field Theory - Tetrahedral and Square Planar Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
01:22EDTA: Chemistry and Properties