Iron Porphyrin-Cyclodextrin Supramolecular Complex as a Functional Model of Myoglobin in Aqueous Solution

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• 作者：Koji Kano ; Hiroaki Kitagishi ; Camille Dagallier ; Masahito Kodera ; Takashi Matsuo ; Takashi Hayashi ; Yoshio Hisaeda ; and Shun Hirota
• 刊名：Inorganic Chemistry
• 出版年：2006
• 出版时间：May 29, 2006
• 年：2006
• 卷：45
• 期：11
• 页码：4448 - 4460
• 全文大小：404K
• 年卷期：v.45,no.11(May 29, 2006)
• ISSN：1520-510X

文摘

The 1:1 inclusion complex of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphinato iron(II) (Fe^IITPPS) and an O-methylated-cyclodextrin dimer having a pyridine linker (1) binds dioxygen reversibly in aqueous solution. The O₂ adduct wasvery stable (t_1/2 = 30.1 h) at pH 7.0 and 25 C. ESI-MS and NMR spectroscopic measurements and molecularmechanics (MM) calculations indicated the inclusion of the sulfonatophenyl groups at the 5- and 15-positions ofFe^IIITPPS or Fe^IITPPS into two cyclodextrin moieties of 1 to form a supramolecular 1:1 complex (hemoCD1 for theFe^IITPPS complex), whose iron center is completely covered by two cyclodextrin moieties. Equilibrium measurementsand laser flash photolysis provided the affinities (7be10001.gif"> and 7be10002.gif">) and rate constants for O₂ and CO binding ofhemoCD1 (7be10003.gif">, 7be10004.gif">, 7be10005.gif">, and k7be10006.gif">). The CO affinity relative to the O₂ affinity of hemoCD1 was abnormally high.Although resonance Raman spectra suggested weak back-bonding of d(Fe) *(CO) and hence a weak CO-Fe bond, the CO adduct of hemoCD1 was very stable. The hydrophobic CO molecule dissociated from CO-hemoCD1 hardly breaks free from a shallow cleft in hemoCD1 surrounded by an aqueous bulk phase leading tofast rebinding of CO to hemoCD1. Isothermal titration calorimetry furnished the association constant (K^O2), H,and S for O₂ association to be (2.71 ± 0.51) × 10⁴ M^-1, -65.2 ± 4.4 kJ mol^-1, and -133.9 ± 16.1 J mol^-1 K^-1,respectively. The autoxidation of oxy-hemoCD1 was accelerated by H⁺ and OH^-. The inorganic anions alsoaccelerated the autoxidation of oxy-hemoCD1. The O₂-Fe^II bond is equivalent to the O₂^--Fe^III bond, which isattacked by the inorganic anions or the water molecule to produce met-hemoCD1 and a superoxide anion.