Jee Joo-Eun, Eigler Siegfried, Jux Norbert, Zahl Achim, van Eldik Rudi
Institute for Inorganic Chemistry, University of Erlangen-Nürnberg, Erlangen, Germany.
Inorg Chem. 2007 Apr 16;46(8):3336-52. doi: 10.1021/ic061732g. Epub 2007 Mar 22.
The polyanionic, water-soluble, and non-micro-oxo dimer-forming iron porphyrin (hexadecasodium iron 54,104,154,204-tetra-t-butyl-52,56,102,106,152,156,202,206-octakis[2,2-bis(carboxylato)ethyl]-5,10,15,20-tetraphenylporphyrin), (P16-)FeIII, with 16 negatively charged meso substituents on the porphyrin was synthesized and fully characterized by UV-vis and 1H NMR spectroscopy. A single pKa1 value of 9.90 +/- 0.01 was determined for the deprotonation of coordinated water in the six-coordinate (P16-)FeIII(H2O)2 and as attributed to the formation of the five-coordinate monohydroxo-ligated form, (P16-)FeIII(OH). The porphyrin complex reversibly binds NO in aqueous solution to yield the nitric oxide adduct, (P16-)FeII(NO+)(L), where L = H2O or OH-. The kinetics for the reversible binding of NO were studied as a function of pH, temperature, and pressure using the stopped-flow technique. The data for the binding of NO to the diaqua complex are consistent with the operation of a dissociative mechanism on the basis of the significantly positive values of DeltaS and DeltaV, whereas the monohydroxo complex favors an associatively activated mechanism as determined from the corresponding negative activation parameters. The rate constant, kon = 3.1 x 104 M-1 s-1 at 25 degrees C, determined for the NO binding to (P16-)FeIII(OH) at higher pH, is significantly lower than the corresponding value measured for (P16-)FeIII(H2O)2 at lower pH, namely, kon = 11.3 x 105 M-1 s-1 at 25 degrees C. This decrease in the reactivity is analogous to that reported for other diaqua- and monohydroxo-ligated ferric porphyrin complexes, and is accounted for in terms of a mechanistic changeover observed for (P16-)FeIII(H2O)2 and (P16-)FeIII(OH). The formed nitrosyl complex, (P16-)FeII(NO+)(H2O), undergoes subsequent reductive nitrosylation to produce (P16-)FeII(NO), which is catalyzed by nitrite produced during the reaction. Concentration-, pH-, temperature-, and pressure-dependent kinetic data are reported for this reaction. Data for the reversible binding of NO and the subsequent reductive nitrosylation reaction are discussed in reference to that available for other iron(III) porphyrins in terms of the influence of the porphyrin periphery.
合成了具有16个带负电荷的中取代基的聚阴离子、水溶性且不形成微氧代二聚体的铁卟啉（十六钠铁54,104,154,204-四叔丁基-52,56,102,106,152,156,202,206-八[2,2-双（羧基）乙基]-5,10,15,20-四苯基卟啉），(P16-)FeIII，并通过紫外可见光谱和1H NMR光谱对其进行了全面表征。对于六配位的(P16-)FeIII(H2O)2中配位水的去质子化，测定了单个pKa1值为9.90±0.01，这归因于形成了五配位的单羟基配位形式(P16-)FeIII(OH)。该卟啉配合物在水溶液中可逆地结合NO，生成一氧化氮加合物(P16-)FeII(NO+)(L)，其中L = H2O或OH-。使用停流技术研究了NO可逆结合的动力学，该动力学是pH、温度和压力的函数。NO与二水合配合物结合的数据与解离机理一致，这是基于显著正值的ΔS和ΔV，而单羟基配合物有利于缔合活化机理，这是根据相应的负活化参数确定的。在较高pH下，测定的NO与(P16-)FeIII(OH)结合的速率常数kon = 3.1×104 M-1 s-1（25℃），明显低于在较低pH下测定的(P16-)FeIII(H2O)2的相应值，即在25℃下kon = 11.3×105 M-1 s-1。反应活性的这种降低类似于其他二水合和单羟基配位的铁卟啉配合物所报道的情况，并且可以根据在(P16-)FeIII(H2O)2和(P16-)FeIII(OH)中观察到的机理转变来解释。形成的亚硝酰配合物(P16-)FeII(NO+)(H2O)随后进行还原亚硝化反应生成(P16-)FeII(NO)，这是由反应过程中产生的亚硝酸盐催化的。报道了该反应的浓度、pH、温度和压力依赖性动力学数据。关于NO的可逆结合和随后的还原亚硝化反应的数据，根据卟啉外围的影响，参考了其他铁(III)卟啉的可用数据进行了讨论。
