Jee Joo-Eun, Wolak Maria, Balbinot Domenico, Jux Norbert, Zahl Achim, van Eldik Rudi
Institute for Inorganic Chemistry, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058 Erlangen, Germany.
Inorg Chem. 2006 Feb 6;45(3):1326-37. doi: 10.1021/ic051339v.
The water-soluble, non-mu-oxo dimer-forming porphyrin, [5,10,15,20-tetrakis-4'-t-butylphenyl-2',6'-bis-(N-methylene-(4''-t-butylpyridinium))porphyrinato]iron(III) octabromide, (P(8+))Fe(III), with eight positively charged substituents in the ortho positions of the phenyl rings, was characterized by UV-vis and 1H NMR spectroscopy and 17O NMR water-exchange studies in aqueous solution. Spectrophotometric titrations of (P(8+))Fe(III) indicated a pKa1 value of 5.0 for coordinated water in (P(8+))Fe(III)(H2O)2. The monohydroxo-ligated (P(8+))Fe(III)(OH)(H2O) formed at 5 < pH < 12 has a weakly bound water molecule that undergoes an exchange reaction, k(ex) = 2.4 x 10(6) s(-1), significantly faster than water exchange on (P(8+))Fe(III)(H2O)2, viz. k(ex) = 5.5 x 10(4) s(-1) at 25 degrees C. The porphyrin complex reacts with nitric oxide to yield the nitrosyl adduct, (P(8+))Fe(II)(NO+)(L) (L = H2O or OH-). The diaqua-ligated (P(8+))Fe(III)(H2O)2 binds and releases NO according to a dissociatively activated mechanism, analogous to that reported earlier for other (P)Fe(III)(H2O)2 complexes. Coordination of NO to (P(8+))Fe(III)(OH)(H2O) at high pH follows an associative mode, as evidenced by negative deltaS(double dagger)(on) and deltaV(double dagger)(on) values measured for this reaction. The observed ca. 10-fold decrease in the NO binding rate on going from six-coordinate (P(8+))Fe(III)(H2O)2 (k(on) = 15.1 x 10(3) M(-1) s(-1)) to (P(8+))Fe(III)(OH)(H2O) (k(on) = 1.56 x 10(3) M(-1) s(-1) at 25 degrees C) is ascribed to the different nature of the rate-limiting step for NO binding at low and high pH, respectively. The results are compared with data reported for other water-soluble iron(III) porphyrins with positively and negatively charged meso substituents. Influence of the porphyrin periphery on the dynamics of reversible NO binding to these (P)Fe(III) complexes as a function of pH is discussed on the basis of available experimental data.
水溶性、不形成μ-氧代二聚体的卟啉[5,10,15,20-四（4'-叔丁基苯基）-2',6'-双（N-亚甲基-（4''-叔丁基吡啶鎓））卟啉铁（III）八溴化物，(P(8+))Fe(III)，在苯环的邻位带有八个带正电荷的取代基，通过紫外可见光谱、1H核磁共振光谱以及水溶液中的17O核磁共振水交换研究对其进行了表征。(P(8+))Fe(III)的分光光度滴定表明，(P(8+))Fe(III)(H2O)2中配位水的pKa1值为5.0。在5＜pH＜12时形成的单羟基配位的(P(8+))Fe(III)(OH)(H2O)有一个弱结合的水分子，该水分子会发生交换反应，k(ex)=2.4×10(6)s(-1)，明显快于(P(8+))Fe(III)(H2O)2上的水交换，即在25℃时k(ex)=5.5×10(4)s(-1)。该卟啉配合物与一氧化氮反应生成亚硝酰加合物(P(8+))Fe(II)(NO+)(L)（L = H2O或OH-）。二水配位的(P(8+))Fe(III)(H2O)2根据解离活化机制结合并释放NO，这与之前报道的其他(P)Fe(III)(H2O)2配合物类似。在高pH下，NO与(P(8+))Fe(III)(OH)(H2O)的配位遵循缔合模式，该反应的负ΔS(double dagger)(on)和ΔV(double dagger)(on)值证明了这一点。从六配位的(P(8+))Fe(III)(H2O)2（k(on)=15.1×10(3)M(-1)s(-1)）到(P(8+))Fe(III)(OH)(H2O)（25℃时k(on)=1.56×10(3)M(-1)s(-1)），观察到NO结合速率下降了约10倍，这分别归因于低pH和高pH下NO结合的限速步骤性质不同。将这些结果与报道的其他带有带正电荷和负电荷的中位取代基的水溶性铁（III）卟啉的数据进行了比较。根据现有实验数据，讨论了卟啉周边对这些(P)Fe(III)配合物与NO可逆结合动力学随pH变化的影响。
