IR spectroscopy of isolated metal-organic complexes of biocatalytic interest: Evidence for coordination number four for Zn2+(imidazole)4

被引:17
|
作者
Lagutschenkov, Anita [1 ]
Lorenz, Ulrich Joseph [2 ]
Dopfer, Otto [1 ]
机构
[1] Tech Univ Berlin, Inst Opt & Atomare Phys, D-10623 Berlin, Germany
[2] Ecole Polytech Fed Lausanne, Lab Chim Phys Mol, CH-1015 Lausanne, Switzerland
关键词
Metal-ligand complexes; Zn2+; Imidazole; IR spectroscopy; Structure elucidation; Zinc enzyme model; AB-INITIO CALCULATIONS; PHOTON DISSOCIATION SPECTROSCOPY; AROMATIC-HYDROCARBON MOLECULES; BIOMOLECULAR BUILDING-BLOCKS; FREE-ELECTRON LASER; GAS-PHASE; INFRARED-SPECTRA; VIBRATIONAL SPECTROSCOPY; BINDING-ENERGIES; IMIDAZOLE COMPLEXES;
D O I
10.1016/j.ijms.2011.08.019
中图分类号
O64 [物理化学(理论化学)、化学物理学]; O56 [分子物理学、原子物理学];
学科分类号
070203 ; 070304 ; 081704 ; 1406 ;
摘要
The characterization of the interactions of Zn2+ ions with imidazole ligands is vital for understanding the function of a plethora of zinc enzymes at the molecular level. The infrared multiple photon dissociation (IRMPD) spectrum of mass selected Zn2+(imidazole)(4) cations, [ZnIm(4)](2+), was obtained in the 670-1840 cm(-1) fingerprint range by coupling the infrared free electron laser (IR-FEL) at the Centre Laser Infrarouge d'Orsay (CLIO) with a quadrupole ion trap mass spectrometer equipped with an electrospray ionization (ESI) source. The experimental efforts are complemented by quantum chemical calculations for [ZnIm(n)](2+) with n = 1-4 at the B3LYP level using basis sets ranging from cc-pVDZ to aug-cc-pVTZ. By comparison with calculated linear absorption spectra, the transitions observed in the IRMPD spectrum are assigned to vibrational modes of the imidazole ligands. In combination, the experimental data and the calculations provide detailed information about structure, metal-ligand bonding, charge distribution, and binding energy of the [ZnIm(4)](2+) complex in the gas phase. The superior abundance of the n = 4 complex of [ZnIm(n)](2+) in the mass spectra of the ESI source is indicative of the preferred coordination number CN = 4 for Zn2+ interacting with imidazole ligands in both the gas and the liquid phase. Comparison of the IR spectra of [ZnIm(n)](2+) with that of bare Im reveals the impact of the strong Zn2+-Im interaction on the electronic, geometric, and vibrational structure of the aromatic ligands upon sequential filling of the first coordination shell. Comparison with the structural and vibrational properties of the imidazole cation demonstrates that the metal-to-ligand charge transfer in [ZnIm(n)](2+) is dominated by sigma donation, whereas contributions from pi donation are minor. (C) 2011 Elsevier B.V. All rights reserved.
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页码:316 / 329
页数:14
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