F430 Model Chemistry. A Reexamination of the [1,4,7,10,13-Pentaazacyclohexadecane-14,16-dionato(2−)]nickel(II)-Induced Formation of Methane from Methyl Coenzyme-M
F430 Model Chemistry. A Reexamination of the [1,4,7,10,13-Pentaazacyclohexadecane-14,16-dionato(2−)]nickel(II)-Induced Formation of Methane from Methyl Coenzyme-M
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F430 模型化学。[1,4,7,10,13-五氮杂环十六烷-14,16-二酮(2−)]镍(II) 诱导甲基辅酶-M 形成甲烷的重新检验
DOI：
10.1021/ic960263n
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发表时间：
1996
期刊：
影响因子：
--
通讯作者：
A. M. Stolzenberg
中科院分区：
文献类型：
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作者：
Zhong Zhang;J. L. Petersen;A. M. Stolzenberg
报道了大环配体1，4，7，10，13-pentaazacyclohexadecane-14，16-dione，L的镍(II)络合物将CH_3SCH_2CH_2SO_3-裂解为CH_4和HSCH_2CH_2SO_3-的报道。CH3SCH2CH2SO3-，或辅因子甲基辅酶-M，在产甲烷细菌产甲烷的最后一步携带甲基。用未提纯的工业级四乙基五胺合成的L镍配合物，可重现辅因子的裂解。然而，镍络合物的真实样品被发现不能进行切割反应。β(OAc)2由L合成，晶胞参数为P21/c(Z=4)，晶胞尺寸为a=8.234(1)？，b=13.439(2)？，c=18.915(2)？，β=95.370(10)°，Andv=2083.9(5)？3。根据I>；2σ(I)的2754个反射光谱，对晶体结构进行了TOR=0.037。镍原子与L的三个二级氮原子以子午线配位方式配位，其余三个配位分别由一个螯合η2-乙酸酯和一个非螯合η1-乙酸酯占据。无论是中性水溶液中盛行的N3O3八面体形式(可能是以水取代乙酸酯作为供氧体)，还是碱性溶液中盛行的五配位、方形锥体、酰胺配位形式，都不会影响甲基辅酶-M的切割。经复查，由工业级四乙基五胺制备的配体被1，4，7，10-四氮杂环十三烷-11，13-二酮，L‘污染，结晶为三斜空间群P1̄(Z=2)，晶胞尺寸为a=8.658(2)？，b=8.663(2)？，c=8.888(2)？，α=69.11(3)°，β=83.51(3)°，γ=62.49(3)°，ANDV=551.3(2)？3.经1277次反射确定结构为σ=0.045。L的镍配合物NIH-2L‘不裂解甲基辅酶-M。NiL(OAc)2和NiH-2L‘的物理混合物溶液可以再现甲基辅酶-M裂解过程中观察到的UV-−-Vis光谱特征，但不能裂解甲基辅酶-M。导致切割反应的化合物(S)或不纯物质中化合物之间的合作作用尚未被分离或鉴定。然而，根据我们的观察，最初提出的将NIL作为活性络合物的机制是不正确的，不能作为甲基辅酶-M还原酶切割甲基辅酶-M的先例。
The report that the nickel(II) complex of the macrocyclic ligand 1,4,7,10,13-pentaazacyclohexadecane-14,16-dione, L, cleaves CH3SCH2CH2SO3-to CH4and HSCH2CH2SO3-was reexamined. CH3SCH2CH2SO3-, or cofactor methyl coenzyme-M, carries the methyl group in the final step of methanogensis in methanogenic bacteria. The cleavage of the cofactor was reproduced when the nickel complex of L synthesized from unpurified, technical grade tetraethylenepentamine was used. However, authentic samples of the nickel complex were found to be incapable of carrying out the cleavage reaction. NiL(OAc)2prepared from L synthesized from pure tetraethylenepentamine crystallizes in the monoclinic space groupP21/c(Z= 4) with unit cell dimensionsa= 8.234(1) Å,b= 13.439(2) Å,c= 18.915(2) Å, β = 95.370(10)°, andV= 2083.9(5) Å3. The structure was refined toR= 0.037 onFo2on the basis of 2754 reflections withI>2σ(I). The nickel atom is coordinated in a meridional fashion by the three secondary nitrogen atoms of L with the remaining three coordination sites occupied by one chelating η2-acetate and one nonchelating η1-acetate. Neither this N3O3octahedral form, which prevails in neutral aqueous solution (presumably with waters replacing the acetates as the oxygen donors), nor the five-coordinate, square pyramidal, amide coordinated form, which prevails in basic solution, effect cleavage of methyl coenzyme-M. Upon reexamination, the ligand prepared from technical grade tetraethylenepentamine was found to be contaminated with 1,4,7,10-tetraazacyclotridecane-11,13-dione, L‘, which crystallizes in the triclinic space groupP1̄ (Z= 2) with unit cell dimensionsa= 8.658(2) Å,b= 8.663(2) Å,c= 8.888(2) Å, α = 69.11(3)°, β = 83.51(3)°, γ = 62.49(3)°, andV= 551.3(2) Å3. The structure was refined toR= 0.045 onF2on the basis of 1277 reflections withI> 2σ(I). The Ni complex of L‘, NiH-2L‘, does not cleave methyl coenzyme-M. Solutions of physical mixtures of NiL(OAc)2and NiH-2L‘ can reproduce the features of the UV−vis spectra observed during cleavage of methyl coenzyme-M but cannot cleave methyl coenzyme-M. The compound(s) or cooperative interactions between compounds in the impure material that are responsible for the cleavage reaction have not been isolated or identified. Nonetheless, based upon our observations, the originally proposed mechanism that involves NiL as the active complex is incorrect and cannot be taken as a precedent for the cleavage of methyl coenzyme-M by the enzyme methyl coenzyme-M reductase.