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ESR Studies of Low-Spin Fe (III) Heme Complexes with Hydrogen-Bonded Axial Ligands. Deuterium Isotope Effect on the Principal g values

具有氢键轴向配体的低自旋 Fe (III) 血红素复合物的 ESR 研究。

基本信息

批准号：
05671791
负责人：
SATO Mitsuo
金额：
$ 1.34万
依托单位：
Teikyo University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1993
资助国家：
日本
起止时间：
1993 至 1994
项目状态：
已结题

项目摘要

The deuterium isotope effect on ESR g values has been determined for the first time for low-spin Fe (III) heme complexes with hydrogen-bonded axial ligands. The ESR observations have been made on frozen solutions of Fe (TPP) (OMe-LOMe) _2^-in CH_2Cl_2-MeOL,where TPP is tetraphenylporphyrin dianion and L=H or D.The principal g avlues (g_X=1.9134, g_Y=2.1654, g_Z=2.4949 for L=H and g_X=1.9146, g_Y=2.1643, g_Z=2.4917 for L=D) are analyzed based on the low-symmetry crystal field model to show that both the d orbital energy splittings and the energies to the excited Kramers doublets are increased from the complex with L=H to the one with L=D by 10-30cm^<-1>. On the other hand, a quantum mechanical calculation using double-minimum potentials for O-L-o vibration has shown that the d orbital energy splittings as well as the excitation energies for L=D become greater in comparison with those for L=H in the case of a weaker L-bond in the electronic ground state than in the excited state, and vice versa. It is thus demonstrated that the L-bonding in Fe (TPP) (OMe-LOMe) _2^- is stronger in the excited states than in the ground state. Qualitatively, this finding is explained in terms of an increased electron density at the iron-bound oxygen atoms on electronic excitation. Such a change in the electron density is consistent with the prediction from the electronic structure generally accepted for low-spin Fe (III) heme complexes.

氘同位素效应的ESR g值已被确定为第一次低自旋铁（III）血红素配合物与氢键轴向配体。本文对Fe（TPP）的冷冻溶液进行了ESR观察（OMe-LOMe）_2^-在CH_2Cl_2-MeOL溶液中，TPP为四苯基卟啉阴离子，L=H或D（g_X=1.9134，g_Y=2.1654，g_Z=2.4949，对于L=H和g_X=1.9146，g_Y=2.1643，g_Z=2.4917（L=D）的分析是基于低-对称晶场模型的计算结果表明，从L=H的配合物到L=D的配合物，d轨道能裂和激发Kramers二重态的能量都增加了10- 30 cm ~ 2<-1>。另一方面，用O-L-o振动的双最小势进行的量子力学计算表明，当L-键在电子基态比激发态弱时，L=D的d轨道能裂和激发能比L=H的大，反之亦然。这表明Fe（TPP）（OMe-LOMe）_2^-在激发态时的L-成键比基态时强。定性，这一发现是解释在电子激发铁结合氧原子的电子密度增加。这种电子密度的变化与普遍接受的低自旋Fe（III）血红素络合物的电子结构预测一致。