| Project/Area Number |
12304040
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Inorganic chemistry
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| Research Institution | Osaka University |
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Principal Investigator |
UEYAMA Norikazu Osaka University, Osaka University, Graduate School of Science, Professor (80093376)
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| Co-Investigator(Kenkyū-buntansha) |
YAMAMOTO Hitoshi 大阪大学, Graduate School of Science, Associate Professor (20222383)
OKAMURA Taka-aki 大阪大学, Graduate School of Science, Assistant Professor (90252569)
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| Project Period (FY) |
2000 – 2003
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| Project Status |
Completed (Fiscal Year 2003)
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| Budget Amount *help |
¥25,700,000 (Direct Cost: ¥23,300,000、Indirect Cost: ¥2,400,000)
Fiscal Year 2003: ¥260,000 (Direct Cost: ¥200,000、Indirect Cost: ¥60,000)
Fiscal Year 2002: ¥5,070,000 (Direct Cost: ¥3,900,000、Indirect Cost: ¥1,170,000)
Fiscal Year 2001: ¥5,070,000 (Direct Cost: ¥3,900,000、Indirect Cost: ¥1,170,000)
Fiscal Year 2000: ¥15,300,000 (Direct Cost: ¥15,300,000)
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| Keywords | Metal complexes / Hydrogen bond / O-transfer reaction / Mo, W-oxidase model / P450 model complexes / pK_a shift / Formation constant / biominerals / ポリ(カルボキシラート) / 炭酸カルシウム / カルシウム錯体 / 脱プロトン化 / pK_a / 結晶形態 / カルボキシラート / hairpin turn構造 / Kemp酸 / カドミナム錯体 / ナトリウム錯体 / NH-O水素結合 / 蒿高いカルボン酸 / リン酸配位子 / アミド基 / NH-S水素結合 / P-450 / Chloroperoxidase / モリブデン酸化酵素 / タングステン酸化酵素 / プテリン |
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| Research Abstract |
Hydrogen bond to coordinating atom in metal thiolate complexes varies the dπ-pπ M-S bonding character, the property and the reactivity as well as M-O bonding character in metal carboxylate complexes. The following five results were obtained by this project "Regulation of Reactivity by Hydrogen Bond to Coordinating Ligand in Metal Complexes".
1) NH-S hydrogen bond between amide NH and coordinating S in Mo(IV) thiolate complexes contributes to the facilitation of O-atom transfer reaction from organic substrates although the hydrogen bond shifts the redox potential positively. On the contrary, the hydrogen bond decreases the O-transfer reactivity in dioxoMo(VI) complexes.
2) A similar shift of redox potential occurs in P450 model Fe(III) complexes. The hydrogen bond stabilizes the Fe(III) form but not Fe(II) form. The switching mechanism works between Fe(III) and Fe(II) presumably using a hair-pin turn conformation with NH-S hydrogen bond and α-helix without the hydrogen bond in the P450 active site.
3) In the case of metal complexes with coordinating O atom like carboxylate and phenolate, the NH-O hydrogen bond affects the M-O covalency in the neutral form, even the Ca-O bond in Ca complexes.
4) The presence of intramolecularly prelocated amide NH near carboxylic acid, thiol and phenol in ground state prompts their protonation and results in the lowering of pK_a. The lowering shift of the pK_a contributes to the increase of formation constant according to a formula, logβ=logK-pK_a especially working in an aqueous micellar solution.
5) In biominerals, strong Ca-O bonding on the surface of CaCO_3 crystal is due to the pK_a shift and the partially covalent Ca-O bond character.
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