Spin states of heme and kinetics of CO and O-2 binding to myoglobinстатья
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:Spin and symmetry of the ground and lower excited states of myoglobin modeled by iron(II)porphyrin with an axial imidazole ligand are calculated for various molecular geometries. Distortions of the heme structure retaining the distance between the iron atom and nitrogen atom N-epsilon invariable are shown to induce spin transition from the quintet state (which is the ground state for the experimental heme geometry where separation of the iron atom and center of plane porphyrin cycle is about 0.5 Angstrom) to the singlet state for distances between the iron atom and ring center less than 0.4 Angstrom. In the vicinity of the transition point, the intermediate spin state (triplet) has an energy commensurate with the representative constant of spin-orbital coupling in iron(II) porphyrinates. On the other hand, a relatively small stretching (by 0.15 Angstrom) of the Fe-N-epsilon bond induces transition to the triplet (E-3(g)) ground state. Correlation between the found set of electronic heme states and the peculiarities of CO and O-2 binding to myoglobin is discussed.