title: Electronic ground states and vibrational frequency shifts of diatomic ligands in heme adducts.
abstract: DFT calculations were carried out to study heme complexes with diatomic ligand (CO, NO, or O(2)) and trans-imidazole ligand. The optimized electronic ground states of CO, NO, and O(2) adducts are singlet, doublet, and open-shell singlet, respectively. For O(2) adduct, the open-shell singlet is slightly lower in energy than the close-shell singlet. However, important differences are found in optimized structures and vibrational frequencies. Particularly, the trans-imidazole-induced frequency up-shift of the Fe-O(O) stretching mode can be predicted only with the open-shell singlet as ground state. An analysis of normal modes confirms that the up-shifts in the bent (NO and O(2) ) adducts are mainly due to mixing of Fe-X(O) stretching mode with Fe-X-O bending coordinate. Our study of binding mechanism indicates that a secondary source of the upshifts is the diminished weakening of the Fe-X(O) bonds. The Fe-X(O) bond strengths are modulated by σ competition mechanism, which weakens the Fe-X(O) bond and σ-π cooperation mechanism, which only exists in the bent adducts and enforce the Fe-X(O) bond. -
authors.affiliation: School of Chemistry and Chemical Technology, Shanghai Jiao Tong University, Shanghai, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.forename: Huai
authors.initials: H
authors.lastname: Sun
mesh_terms: D002248:Carbon Monoxide / Q000737:chemistry*; D004583:Electrons; D006418:Heme / Q000737:chemistry*; D008024:Ligands; D009569:Nitric Oxide / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D011789:Quantum Theory; D014732:Vibration
chemical_list: D008024:Ligands; D009569:Nitric Oxide; D006418:Heme; D002248:Carbon Monoxide; D010100:Oxygen