Lim Booyong S., Holm R. H.
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138.
Inorg Chem. 1998 Sep 21;37(19):4898-4908. doi: 10.1021/ic9801793.
Bovine heart cytochrome c oxidase and related heme copper oxidases are inhibited by cyanide, which binds at the binuclear heme-a(3)/Cu(B) site where dioxygen is reduced to water. To determine the mode of cyanide binding, heme-based binuclear complexes containing iron-cyanide-copper bridges in different oxidation states have been prepared by the reaction of [(py)(OEP)Fe(CN)] with Cu(II,I) precursors and structurally characterized by X-ray methods. Structures of two precursor complexes and two binuclear Cu(I)-CN-Cu(I) species are reported. The assembly (py)(OEP)Fe-CN-Cu(Npy(3)) has a nearly linear Fe(III)-CN-Cu(II) bridge containing low-spin Fe(III). The assemblies (OEP)Fe-NC-Cu(MeNpy(2)) and (OEP-CH(2)CN)Fe-NC-Cu(Npy(3)) exhibit the high-spin bridges Fe(III)-NC-Cu(I) and Fe(II)-NC-Cu(I), respectively. These are the first title bridges in these oxidation states. Bridge atom sequences are obtained from structural refinements of both linkage isomers; those for the reduced bridges are consistent with the soft-acid nature of Cu(I). Cyanide stretching frequencies respond to metal oxidation state and bridge geometry and, using data for solution and solid states, fall into the following ranges: Fe(III)-CN-Cu(II), 2120-2184 cm(-)(1) (11 examples); Fe(III)-NC-Cu(I), 2072-2100 cm(-)(1) (2 examples); Fe(II)-NC-Cu(I), 2099-2107 cm(-)(1) (1 example). These data are compared with nu(CN) values for the enzymes in different oxidation states. A nonlinear Fe(III)-CN-Cu(II) bridge (Cu-N-C = 150-160 degrees ) is consistent with the 2146-2152 cm(-)(1) range found for the fully oxidized enzymes. Bands that can be assigned with some certainty as Fe-CN vibrations in partially and fully reduced enzymes do not appear to correspond to Fe(III)-NC-Cu(I) and Fe(II)-NC-Cu(I) bridges but rather to Fe(II)-CN modes. The current work complements and extends our previous investigation (Scott and Holm, J. Am. Chem. Soc. 1994, 116, 11357) of linear and nonlinear Fe(III)-CN-Cu(II) bridges and is part of an investigation directed at providing a molecular basis of cyanide toxicity. (MeNpy(2) = bis(2-(2-pyridylethyl))methylamine; Npy(3) = tris(2-pyridylmethyl)amine; OEP = octaethylporphyrinate(2-), OEP-CH(2)CN = N-(cyanomethyl)octaethylporphyrinate(1-).)
牛心细胞色素c氧化酶及相关的血红素铜氧化酶会受到氰化物的抑制，氰化物结合在双核血红素-a(3)/Cu(B)位点，在此位点二氧被还原为水。为确定氰化物的结合模式，通过[(py)(OEP)Fe(CN)]与Cu(II,I)前体反应制备了不同氧化态下含有铁-氰-铜桥的基于血红素的双核配合物，并通过X射线方法对其进行了结构表征。报道了两种前体配合物和两种双核Cu(I)-CN-Cu(I)物种的结构。组装体(py)(OEP)Fe-CN-Cu(Npy(3))具有近乎线性的Fe(III)-CN-Cu(II)桥，其中包含低自旋Fe(III)。组装体(OEP)Fe-NC-Cu(MeNpy(2))和(OEP-CH(2)CN)Fe-NC-Cu(Npy(3))分别展示了高自旋桥Fe(III)-NC-Cu(I)和Fe(II)-NC-Cu(I)。这些是这些氧化态下的首个此类桥。桥原子序列通过两种键合异构体的结构精修获得；还原桥的序列与Cu(I)的软酸性质一致。氰化物伸缩频率对金属氧化态和桥几何结构有响应，利用溶液和固态数据，其落入以下范围：Fe(III)-CN-Cu(II)，2120 - 2184 cm(-)(¹)（11个实例）；Fe(III)-NC-Cu(I)，2072 - 2100 cm(-)(¹)（2个实例）；Fe(II)-NC-Cu(I)，2099 - 2107 cm(-)(¹)（1个实例）。这些数据与不同氧化态下酶的ν(CN)值进行了比较。非线性Fe(III)-CN-Cu(II)桥（Cu-N-C = 150 - 160度）与完全氧化酶中发现的2146 - 2152 cm(-)(¹)范围一致。在部分还原和完全还原酶中可较为确定地归属于Fe-CN振动的谱带似乎并不对应于Fe(III)-NC-Cu(I)和Fe(II)-NC-Cu(I)桥，而是对应于Fe(II)-CN模式。当前工作补充并扩展了我们之前对线性和非线性Fe(III)-CN-Cu(II)桥的研究（Scott和Holm，《美国化学会志》1994年，116卷，11357页），并且是旨在提供氰化物毒性分子基础的研究的一部分。（MeNpy(2) = 双(2-(2-吡啶基乙基))甲胺；Npy(3) = 三(2-吡啶基甲基)胺；OEP = 八乙基卟啉(2-)，OEP-CH(2)CN = N-(氰甲基)八乙基卟啉(1-)。）
