title: Spectroscopic identification of reactive porphyrin motions.
abstract: Nuclear resonance vibrational spectroscopy (NRVS) reveals the vibrational dynamics of a Mössbauer probe nucleus. Here, (57)Fe NRVS measurements yield the complete spectrum of Fe vibrations in halide complexes of iron porphyrins. Iron porphine serves as a useful symmetric model for the more complex spectrum of asymmetric heme molecules that contribute to numerous essential biological processes. Quantitative comparison with the vibrational density of states (VDOS) predicted for the Fe atom by density functional theory calculations unambiguously identifies the correct sextet ground state in each case. These experimentally authenticated calculations then provide detailed normal mode descriptions for each observed vibration. All Fe-ligand vibrations are clearly identified despite the high symmetry of the Fe environment. Low frequency molecular distortions and acoustic lattice modes also contribute to the experimental signal. Correlation matrices compare vibrations between different molecules and yield a detailed picture of how heme vibrations evolve in response to (a) halide binding and (b) asymmetric placement of porphyrin side chains. The side chains strongly influence the energetics of heme doming motions that control Fe reactivity, which are easily observed in the experimental signal.
authors: Department of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston, Massachusetts 02115, USA.
authors: Alexander
authors: A
authors: Barabanschikov
authors: Alexander
authors: A
authors: Demidov
authors: Minoru
authors: M
authors: Kubo
authors: Paul M
authors: PM
authors: Champion
authors: J Timothy
authors: JT
authors: Sage
authors: Jiyong
authors: J
authors: Zhao
authors: Wolfgang
authors: W
authors: Sturhahn
authors: E Ercan
authors: EE
authors: Alp
mesh_terms: D003198:Computer Simulation; D004583:Electrons; D008958:Models, Molecular; D011166:Porphyrins / Q000737:chemistry*; D013057:Spectrum Analysis / Q000379:methods; D013696:Temperature
chemical_list: D011166:Porphyrins