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Probing heme vibrational anisotropy: an imidazole orientation effect?
Qian Peng1, Ming Li, Chuanjiang Hu
1Department of Chemistry and Biochemistry, University of Notre Dame , Notre Dame, Indiana 46556, United States.
Inorganic Chemistry
|September 12, 2013
Summary
Nuclear Resonance Vibrational Spectroscopy (NRVS) revealed how axial ligands affect iron motion in a high-spin complex. Imidazole orientation has minimal impact, unlike imidazolate or NO ligands, correlating with Fe-ligand bond strength.
Area of Science:
- Inorganic Chemistry
- Solid-State Physics
- Computational Chemistry
Background:
- High-spin iron complexes with porphyrin ligands are crucial in various biological and chemical processes.
- Understanding the influence of axial ligands on metal ion dynamics is key to controlling reactivity.
- Nuclear Resonance Vibrational Spectroscopy (NRVS) offers a powerful tool to probe metal motion within crystalline structures.
Purpose of the Study:
- To investigate the complete iron vibrational spectrum of a five-coordinate high-spin iron complex, [Fe(OEP)(2-MeHIm)].
- To quantify the effects of axial ligand orientation on iron motion using experimental and computational methods.
- To compare the orientational effects of different axial ligands (imidazole, imidazolate, NO) on iron dynamics.
Main Methods:
- Oriented single-crystal Nuclear Resonance Vibrational Spectroscopy (NRVS) measurements in three orthogonal directions.
- Density Functional Theory (DFT) calculations to complement experimental data and model ligand effects.
- Analysis of vibrational spectra to determine iron motion and ligand influence.
Main Results:
- The study obtained the complete iron vibrational spectrum for [Fe(OEP)(2-MeHIm)] using NRVS.
- Experimental data and DFT calculations showed that axial imidazole orientation does not control in-plane iron motion.
- DFT calculations indicated that imidazolate ligands significantly affect in-plane iron motion direction.
- The axial NO ligand exhibited the strongest orientational effect on iron motion.
Conclusions:
- The strength of axial ligand orientational effects on iron motion follows the order: NO > imidazolate > imidazole.
- This order is consistent with the varying strengths of the iron-ligand bonds.
- Axial ligand orientation plays a critical role in dictating metal ion dynamics within porphyrin complexes.
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