title: Vibrational modeling of copper-histamine complexes: metal-ligand IR modes investigation.
abstract: Recent reports on proteins and related models show that vibrational spectroscopy in the far-infrared domain is a promising technique to characterize metal sphere coordination in proteins. The low-frequency modes are however complex, and there is a need to develop the analysis of metal sites by means of quantum chemical calculations as a support for useful interpretation of the far-IR data. In this study, we determined vibrational properties for systems containing Cu(II)-N(Imidazole) interactions present in many biological complexes by means of quantum chemical calculations and confronted the normal mode description with available experimental data. Analysis of the [Cu(histamine)]2+ complex led us to conclude that the anharmonic contributions are negligible in the far-IR domain. Geometry optimizations and vibrational frequency calculations of [Cu(hm)]2+ and [Cu(hm)2(ClO4)2] complexes were compared using various hybrid DFT functionals and basis sets. These investigations stressed the need of potential energy distribution calculations (PED) to assign the vibrational modes, to obtain an overall description of the vibration modes, and to efficiently compare the methods. Comparison of calculation methods with the B3LYP/6-31+G(d,p) and B3LYP/6-311+G(2d,2p) methods and with available experimental data showed that the B3LYP/6-31G(d,p) level of theory provides accurate predictions of the normal mode frequencies and assignments. These comparisons also enlighten that theoretical investigations of 2H- and 65Cu-labeled [Cu(hm)2(ClO4)2] complexes give with a very good accuracy the band shifts of the labeled copper-histamine derivatives. The theoretical calculations combined with experimental data allowed us to predict and calculate with good accuracy the values and assignments of the low-frequency IR modes, notably those involving metal contribution.
authors.affiliation: Institut Charles Gerhardt, MACS, UMR 5253 CNRS-ENSCM-UM1-UM2, 8, rue de l'Ecole Normale, 34296 Montpellier cedex 5, France.
authors.forename: Bertrand
authors.initials: B
authors.lastname: Xerri
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Flament
authors.forename: Hugo
authors.initials: H
authors.lastname: Petitjean
authors.forename: Catherine
authors.initials: C
authors.lastname: Berthomieu
authors.forename: Dorothee
authors.initials: D
authors.lastname: Berthomieu
mesh_terms: D003300:Copper / Q000737:chemistry*; D006632:Histamine / Q000737:chemistry*; D008024:Ligands; D008956:Models, Chemical; D013055:Spectrophotometry, Infrared; D014732:Vibration
chemical_list: D008024:Ligands; D003300:Copper; D006632:Histamine