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Accession number;02A0304389
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| Title;Photochemical O2 evolution from the Mn4O4 manganese-oxo cubane core: A functional model of the photosynthetic water oxidation complex. |
| Author;
YAGI MASAYUKI
(Niigata Univ., Fac. Education and Human Sci., JPN)
DISMUKES G C
(Princeton Univ.)
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Journal Title;Abstracts. Symposium on Biofunctional Chemistry
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Journal Code:L0836A
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ISSN:
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VOL.16th;NO.;PAGE.66-67(2001)
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| Figure&Table&Reference; |
| Pub. Country;Japan |
| Language;Japanese |
| Abstract;Photosynthesis produces molecular oxygen from water catalyzed by an enzyme whose active site contains a tetramanganese-oxo core of incompletely established structure. The first functional mimic of this core has been synthesized containing a cubical [Mn4O4n+ core, surrounded by six facially-bridging bidentate chelates to the manganese ions (L6Mn4O4; L-=diphenylphosphinate anion). UV light absorption into a Mn-O charge-transfer excited state efficiently releases an O2 molecule if performed in the gas phase and concomitantly releases a bridging L- anion and the cationic species L5Mn4O2+ (presumed Mn4O2-butterfly core type). All species were identified by high resolution mass spectrometry. This reaction proceeds with high quantum efficiency (>50%) and is the only observable reaction channel. The O2 product derive exclusively from the corner oxos of the cube based on photochemistry of the 18O-isotopomer, L6Mn4(18O)4. Neither O2 release nor L- dissociation are observed individually to occur in the excited state, indicating that O-O bond formation and O2 release require dissociation of one of the six L- chelates ("Jack-in-the-Box" mechanism for O2 formation). Thus the [Mn40Jn+ cubane core is an intrinsically reactive core topology that facilitates their photo-rearrangement to an O2 molecule under the control of chelation of the manganese ions by L-. These results may offer insight into the possible nature of the photosynthetic O2-evolving mechanism. (author abst.) |
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