SPECTROSCOPIC AND ELECTRONIC-STRUCTURE STUDIES OF MET-HEMERYTHRIN MODEL COMPLEXES - A DESCRIPTION OF THE FERRIC-OXO DIMER BOND
SPECTROSCOPIC AND ELECTRONIC-STRUCTURE STUDIES OF MET-HEMERYTHRIN MODEL COMPLEXES - A DESCRIPTION OF THE FERRIC-OXO DIMER BOND
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DOI：
10.1021/ic00107a024
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发表时间：
1995-02-01
影响因子：
4.6
通讯作者：
SOLOMON, EI
中科院分区：
文献类型：
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作者：
BROWN, CA;REMAR, GJ;SOLOMON, EI
理论和光谱技术的结合已被用来探测电子结构的mu-oxo非血红素铁二聚体复合物模型中发现的氧载体hemerythrin的活性位点。变温电子吸收（包括单晶极化和取向平均），变温磁圆二色性（MCD），和变温共振拉曼光谱已被用来分配所有的光谱特征存在于这些复合物。这些光谱研究的补充高自旋和对称性破缺SCF-X α-SW计算。总之，在这些复合物中的高度共价键合的描述已经产生。Fe-氧代二聚体单元的独特UV/维斯吸收光谱由低能量强的氧代-> Fe 3+配体到金属电荷转移（LMCT）跃迁主导。这些转变出现在低得多的能量比预期的，由于存在非常大的激发态反铁磁交换的LMCT过渡桥氧，stoup。这些氧代LMCT跃迁的不同自旋分量可以从它们在上面列出的不同光谱中表现出的大的温度依赖性来识别。观察到的激发态分裂已被分析，使用最近开发的价键构型相互作用（VBCI）模型来描述这种桥接配体电荷转移激发态反铁磁性和探测特定的超交换途径在地面和激发态。该VBCI模型表明了一种反向的电荷转移有序方案，其中Fe（III）-O-Fe（III）平面中的π CT跃迁能量最低。这些转变的低能量和Fe（III）-O-Fe（III）键的高共价性也是相对于单体Fe 3+络合物的配体场转变的较高强度的来源。用田边模型分析了（6）A（1）→（4）A（1）-跃迁的配位场激发态分裂，该跃迁是铁磁性的.并证明了混合π/σ（Fe d（yz）- Fe d（z2））磁交换途径的重要性。分析了Fe（III）-O-Fe（III）单元中Fe-氧代键的性质，其强度主要是由于氧代p（z）轨道与铁的4s和4p轨道的强σ键相互作用。高稳定性的mu-氧代铁二聚体键提供了显着的洞察不同的双核非血红素蛋白hemerythrin，甲烷单加氧酶和核糖核苷酸还原酶之间的O-2反应性的差异。
A combination of theoretical and spectral techniques have been used to probe the electronic structure of mu-oxo non-heme Fe dimer complexes which model the active site found in the oxygen carrier hemerythrin. Variable temperature electronic absorption (including single crystal polarized and orientationally averaged), variable temperature magnetic circular dichroism (MCD), and variable temperature resonance Raman spectroscopies have been used to assign all of the spectral features present in these complexes. These spectral studies are complemented by both high spin and broken symmetry SCF-X alpha-SW calculations. Together, a description of the highly covalent bonding in these complexes has been generated. The unique UV/vis absorption spectra of the Fe-oxo dimer unit is dominated by low energy intense oxo --> Fe3+ ligand to metal charge-transfer (LMCT) transitions. These transitions appear at much lower energy than expected due to the presence of very large excited-state antiferromagnetic exchange in the LMCT transitions from the bridging oxo,stoup. The different spin components of these oxo LMCT transitions can be identified from their large temperature dependence exhibited in the different spectroscopies listed above. The observed excited state splittings have been analyzed using a recently developed valence bond configuration interaction (VBCI) model to describe this bridging-ligand charge-transfer excited state antiferromagnetism and probe specific superexchange pathways in the ground and excited states. This VBCI model indicates an inverted charge-transfer ordering Scheme with the in the Fe(III)-O-Fe(III) plane pi CT transition lowest in energy. The low energy of these transitions and the high covalency of the Fe(III)-O-Fe(III) bond are also sources of the higher intensity of the ligand field transitions relative to those of monomeric Fe3+ complexes. The ligand field excited-state splitting for the (6)A(1) --> (4)A(1)-transition, which is ferromagnetic, is analyzed using the Tanabe model. of exchange and demonstrates the importance of a mixed pi/sigma (Fe d(yz) - Fe d(z2)) magnetic exchange pathway. The nature of the Fe-oxo bond in the Fe(III)-O-Fe(III) unit is analyzed and its' strength is mainly due to strong sigma bonding interactions of the oxo p(z) orbital with the 4s and 4p orbitals of the iron. The high stability of the mu-oxo iron dimer bond provides significant insight into differences in the O-2 reactivity among the different binuclear non-heme proteins hemerythrin, methane monooxygenase, and ribonucleotide reductase.