Dynamics of metal centers monitored by nuclear inelastic scattering

Abstract

Abstract. Nuclear inelastic scattering of synchrotron radiation has been used now since ten years as a tool for vibrational spectroscopy. This method has turned out especially useful in case of large molecules that contain a Mössbauer active metal center. Recent applications to iron-sulfur proteins, to iron(II) spin crossover complexes and to tin-DNA complexes are discussed. Special emphasis is given to the combination of nuclear inelastic scattering and density functional calculations.

Intermolecular Dynamics in Crystalline Iron Octaethylporphyrin (FeOEP)

“…4,5,17 Normal mode refinement to NRVS data is especially stringent because the computed normal modes must match the measured VDOS in both frequency and Fe amplitude, on an absolute scale. NRVS measurements of heme model compounds have been obtained mostly from polycrystalline material, [8][9][10] and from single crystals in a few special cases. [18][19][20][21] Despite that, all normal mode calculations have assumed an isolated single molecule, neglecting any intermolecular interactions associated with crystal packing.…”

“…The normal modes of vibration in a molecule are determined by the set of interatomic force constants associated with the molecule’s equilibrium structure. Normal mode frequencies are measured with a variety of experimental techniques such as Raman and infrared spectroscopies, − with gas phase, liquid, and even solid specimens, and the experimental spectra are compared to those predicted by empirical force fields , or from density functional theory, − for example, in order to refine the force fields or confirm the validity of the particular density functionals employed. This is typically a highly underdetermined problem, as is clearly seen with empirical force fields: the number of force field components connecting various sets of atoms in the molecule is substantially larger than the number of parameters needed to fit the data.…”

“…Nuclear resonance vibrational spectroscopy (NRVS) is a synchrotron-based technique that measures the Fe-weighted vibrational density of states (VDOS) for iron-containing materials, based on the resonant interaction of 57 Fe nuclei with X-rays. − VDOS spectra have been obtained from a variety of heme proteins and iron-porphyrin complexes, and several have been compared to normal mode calculations. ,, Normal mode refinement to NRVS data is especially stringent because the computed normal modes must match the measured VDOS in both frequency and Fe amplitude, on an absolute scale. NRVS measurements of heme model compounds have been obtained mostly from polycrystalline material, − and from single crystals in a few special cases. − Despite that, all normal mode calculations have assumed an isolated single molecule, neglecting any intermolecular interactions associated with crystal packing.…”