鉄 ((II) -トリス[2,2'-bi(テトラヒドロピリミジン) ]からTEMPOへの水素原子の移転:マーカス方程式によって予測される活性化の負のエンタルピー
Elizabeth A Mader1, Anna S Larsen, James M Mayer
1Department of Chemistry, University of Washington, Box 351700, Seattle, Washington 98195-1700.
Journal of the American Chemical Society
|July 1, 2004
まとめ
鉄複合体とTEMPOの間の陽子結合電子移転 (PCET) を研究した. この反応は異常な負の活性化エンタルピーを示し,水素原子移転反応に関するマーカス理論の予測を裏付けている.
科学分野:
- 無機化学 無機化学とは
- 化学動力学 化学動力学
- 物理化学 物理化学
背景:
- 陽子結合電子移転 (PCET) は,化学と生物学における基本的な反応機構である.
- PCETの運動学と熱力学を理解することは,新しい触媒とエネルギー貯蔵システムの設計に不可欠です.
- TEMPOのような鉄複合体と窒素酸化物ラジカルは,様々な触媒および酸化還元過程において重要である.
研究 の 目的:
- 鉄 (II) 複合体からテンポ (TEMPO) 複合体への水素原子の移動の運動学と熱力学を調査する.
- 前方および逆のPCET反応の速度定数およびアクティベーションパラメータを決定する.
- このPCET反応の行動を予測するマルカス理論の適用性を評価する.
主な方法:
- 反応をリアルタイムで監視するために,ストップフローUV-VISスペクトロフォトメトリーを使用した.
- 運動データを分析して,298 Kの速度定数を決定した.
- 活性化エンタルピーとエントロピーを含む熱力学的パラメータを計算した.
主要な成果:
- フォワードレート定数 (k1) は260 ± 30 M−1s−1と決定され,リバースレート定数 (k-1) は150 ± 20 M−1s−1.1と決定された.
- 前方反応では異常な負の活性化エンタルピー (ΔH1 = -2.7 ± 0.4 kcal mol−1) が観察されました.
- マーカス理論は,独立に測定された自己交換パラメータを使用して,観測された温度依存性を成功裏に予測しました.
結論:
- この研究は,複雑なPCET反応を分析するためのマーカス理論の有用性を実証しています.
- 負の活性化エンタルピーは,自己交換ではなく,反応の好ましいエンタルピーによって主に駆動されます.
- この研究は,鉄-TEMPOシステムにおける水素原子移転のメカニズムについての洞察を提供します.
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