2007 Fiscal Year Final Research Report Summary
Study on myoglobin models that work in aqueous solution
| Project/Area Number |
17350074
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Functional materials chemistry
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| Research Institution | Doshisha University |
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Principal Investigator |
KANO Koji Doshisha University, Faculty of Technology, Professor (60038031)
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| Project Period (FY) |
2005 – 2007
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| Keywords | myoglobin model / nitric oxide complex / autoxidation mechanism / ligand exchange / cyclodextrin dimer / kinetics / dioxygen complex / NO-myoglobin complex |
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| Research Abstract |
A per-O-methylated β-cyclodextrin dimer, Py2CD, was conveniently prepared via two steps; the Williamson reaction of 3,5-bis(bromomethyl)pyridine and β-cyclodextrin (β-CD) yielding 2A,2'A-O-[3,5-pyridinediylbis(methylene)bis-β-cyclodextrin (bisCD) followed by the O-methylation of all the hydroxy groups of the bisCD. Py2CD formed a very stable 1:1 complex (Fe(III)PCD) with [5,10,15,20-tetrakis(p-sulfonatophenyl)porphinato]iron(III) (Fe^<III>TPPS) in aqueous solution. Fe(III)PCD was reduced with Na_2S_2O_4 to afford the Fe^<II>TPPS/Py2CD complex (Fe(II) PCD). Dioxygen was bound to Fe(II)PCD, the P_<1/2>^<O2> values being 42.4 ± 1.6 and 176 ± 3 Torr at 3 and 25℃, respectively. The k_<on>^<O2> and k_<off>^<O2> values for the dioxygen binding were determined to be 1.3 x 10^7 M^<-1>s^<-1> and 3.8 x 10^3 s^<-1>, respectively, at 25℃. Although the dioxygen adduct was not very stable (K_<O2>=k_<on>^<O2>/k_<off>^<O2> = 3.4 x 10^3 M^<-1>), no autoxidation of the dioxygen adduct of Fe(II)PCD to Fe
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(III)PCD was observed. These results suggest that the encapsulation of Fe^<II>TPPS by Py2CD strictly inhibits not only the extrusion of dioxygen from the cyclodextrin cage, but also the penetration of a water molecule into the cage. The carbon monoxide affinity of Fe(II)PCD was much higher than the dioxygen affinity; the P_<1/2>^<CO> k_<on>^<CO>, k_<off>^<CO>, and K_<CO> values being (1.6 ± 0.2) x 10^<-2> Torr, 2.4 x 10^6 M^<-1>s^<-1>, 4.8 x 10^<-2> s^<-1>, and 5.0 x 10^7 M^<-1>, respectively, at 25℃. Fe(II)PCD also bound nitric oxide. The rate of the dissociation of NO from (NO)Fe(II)PCD ((5.58 ± 0.42) x 10^<-5> s^<-1>) was in good agreement with the maximum rate ((5.12 ± 0.18) x 10^<-5> s^<-1>) of the oxidation of (NO)Fe(II)PCD to Fe(III)PCD and NO_3^-, suggesting that the autoxidation of (NO)Fe(II)PCD proceeds through the ligand exchange between NO and O_2 followed by the rapid reaction of (O_2)Fe(II)PCD with released NO affording Fe(II)PCD and the NO_3^- anion inside the cyclodextrin cage. Less
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