Hydrogen atom abstraction by a mononuclear ferric hydroxide complex: Insights into the reactivity of lipoxygenase
Hydrogen atom abstraction by a mononuclear ferric hydroxide complex: Insights into the reactivity of lipoxygenase
复制标题
DOI：
10.1021/ic060621e
复制
发表时间：
2006-07-24
影响因子：
4.6
通讯作者：
Stack, T. Daniel P.
中科院分区：
文献类型：
--
作者：
Goldsmith, Christian R.;Stack, T. Daniel P.
脂氧合酶模拟物 [Fe-III(PY5)(OH)](CF3SO3)(2) 是由 [FeII(PY5)(MeCN)](CF3SO3)(2) 与碘代苯反应合成的，低温研究表明 Fe(IV) 氧代物质可能是中间体。通过结合溶液和固态方法（包括 EPR 和红外光谱）来分离和鉴定 Fe(III)-OH 络合物。 [Fe-III(PY5)(OH)](2+) 与弱 X-H 键以与氢原子夺取一致的方式发生反应。该复合物的组成可以与之前报道的 Mn(III)-OH 和 Fe(III)-OMe 脂氧合酶模拟物进行有意义的比较。还原为[Fe-II(PY5)(H2O)](2+)时形成的O-H键的键解离能(BDE)估计为80 kcal mol(-1)，比结构类似的[Mn-II(PY5)(H2O)](2+)络合物低2 kcal mol(-1)，支持了普遍接受的观点，即Mn(III)是热力学上优异的氧化剂协调范围的平等。金属的种类对与 9,10-二氢蒽反应的活化熵有很大影响； [Mn-III(PY5)(OH)](2+) 的 Delta S-双匕首值比 [Fe-III(PY5)(OH)](2+) 或 [FeIII(PY5)(OMe)](2+) 多 10 eu，可能是因为还原为 [Mn-II(PY5)(H2O)](2+) 时结构重组增加。 Mn(III) 还原的更大的焓驱动力与 [MnIII(PY5)(OH)](2+) 比 [Fe-III(PY5)(OH)](2+) 反应更快相关。奇怪的是，[FeIII(PY5)(OMe)](2+) 与底物的反应速度仅为 [FeIII(PY5)(OH)](2+) 的两倍左右，尽管甲醇络合物的焓驱动力大 4 kcal mol(-1)。
The lipoxygenase mimic [Fe-III(PY5)(OH)](CF3SO3)(2) is synthesized from the reaction of [FeII(PY5)(MeCN)](CF3SO3)(2) with iodosobenzene, with low-temperature studies suggesting the possible intermediacy of an Fe(IV) oxo species. The Fe(III)-OH complex is isolated and identified by a combination of solution and solid-state methods, including EPR and IR spectroscopy. [Fe-III(PY5)(OH)](2+) reacts with weak X-H bonds in a manner consistent with hydrogenatom abstraction. The composition of this complex allows meaningful comparisons to be made with previously reported Mn(III)-OH and Fe(III)-OMe lipoxygenase mimics. The bond dissociation energy (BDE) of the O-H bond formed upon reduction to [Fe-II(PY5)(H2O)](2+) is estimated to be 80 kcal mol(-1), 2 kcal mol(-1) lower than that in the structurally analogous [Mn-II(PY5)(H2O)](2+) complex, supporting the generally accepted idea that Mn( III) is the thermodynamically superior oxidant at parity of coordination sphere. The identity of the metal has a large influence on the entropy of activation for the reaction with 9,10-dihydroanthracene; [Mn-III(PY5)(OH)](2+) has a 10 eu more negative Delta S-double dagger value than either [Fe-III(PY5)(OH)](2+) or [FeIII(PY5)(OMe)](2+), presumably because of the increased structural reorganization that occurs upon reduction to [Mn-II(PY5)(H2O)](2+). The greater enthalpic driving force for the reduction of Mn(III) correlates with [MnIII(PY5)(OH)](2+) reacting more quickly than [Fe-III(PY5)(OH)](2+). Curiously, [FeIII(PY5)(OMe)](2+) reacts with substrates only about twice as fast as [FeIII(PY5)(OH)](2+), despite a 4 kcal mol(-1) greater enthalpic driving force for the methoxide complex.