Abstract
Artificial photosynthetic reaction centers have been constructed on a protein surface by cofactor reconstitution, which mimic the function of photosynthetic organisms to convert light energy to chemical potential in the form of long-lived charge-separated states. They feature a ruthenium tris(2,2'-bipyridine) moiety as the sensitizer, which is mechanically linked (i.e., in catenane-type) with a cyclobis(paraquat-p-phenylene) unit (BXV4+, acceptor) and covalently linked with a protoheme or Zn-protoporphyrin (donor) located in the myoglobin pocket. Their cofactors 1 and 2, which are tris(heteroleptic) Ru-bipyridine complexes, were synthesized by sequential coordination of the two different functionalized bipyridine ligands with a readily obtainable precursor [Ru(4,4'-dimethyl-2,2'-bipyridine)Cl3](n) followed by metal insertion; this represents a new efficient synthetic method for tris(heteroleptic) Ru(II) complexes of bidentate polypyridine ligands. Reconstitution of apo-myoglobin (Mb) with 1 and 2 affords the two Mb-based artificial triads, Mb(Fe(III)OH2)-Ru2+-BXV4+ and Mb(Zn)-Ru2+-BXV4+. Laser flash photolysis of the Ru(bpy)3 moiety of Mb(Fe(III)OH2)-Ru2+- BXV4+ in an aqueous solution yields an initial charge-separated state, Mb(Fe(III)OH2)-Ru3+-BXV3+(·), via noncovalent electron transfer, followed by dark electron transfer to generate an intermediate consisting of porphyrin cation radical, Mb(Fe(III·)OH2)-Ru2+-BXV3+(·). Mb(Fe(III ·)OH2)-Ru2+-BXV3+ (·) thus generated is subsequently converted, via a proton-coupled process and with a quantum yield of 0.005, into the final charge-separated state, Mb(Fe(IV)=O)-Ru2+-BXV3+ (·), which bears an energy more than 1 eV above the ground state and a lifetime (τ > 2 ms) comparable to that of natural photosynthetic reaction center. Photoexcitation of Mb(Zn)-Ru2+ -BXV4+ also gives rise to a vectorial two-step electron- transfer relay with the intermediate CS state, Mb(Zn)-Ru3+-BXV3+ (·), for the main pathway leading to the final CS state, Mb(Zn+)-Ru2+-BXV3+ (·), in a yield of 0.08. Although the driving forces for the recombination of Mb(Fe(IV)=O)-Ru2+-BXV3+ (·) and Mb(Zn+)-Ru2+-BXV3+ (·) are similar (ΔG ≃ 1.30 eV), the recombination rate of the former is at least 102-103-fold slower than that of the latter. By analogy with a related system reported previously, it was considered that back ET from BXV3+ (·) to Mb(Fe(IV)=O) might be coupled to the protonation of Mb(Fe(IV)=O) and governed by the slow interconversion between the metal-oxo form and the proton-activated species, rendering the CS state Mb(Fe(IV)=O)-Ru2+-BXV3+ (·) specially long-lived. Control experiments clearly demonstrated that partial incorporation of the triads into the protein matrix plays a crucial role in regulating the electron-transfer pathway and stabilizing the charge separation state.
| Original language | English |
|---|---|
| Pages (from-to) | 241-253 |
| Number of pages | 13 |
| Journal | Journal of the American Chemical Society |
| Volume | 122 |
| Issue number | 2 |
| DOIs | |
| Publication status | Published - Jan 19 2000 |
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All Science Journal Classification (ASJC) codes
- Catalysis
- Chemistry(all)
- Biochemistry
- Colloid and Surface Chemistry
Cite this
Construction of artificial photosynthetic reaction centers on a protein surface : Vectorial, multistep, and proton-coupled electron transfer for long- lived charge separation. / Hu, Yi Zhen; Tsukiji, Shinya; Shinkai, Seiji; Oishi, Shigero; Hamachi, Itaru.
In: Journal of the American Chemical Society, Vol. 122, No. 2, 19.01.2000, p. 241-253.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Construction of artificial photosynthetic reaction centers on a protein surface
T2 - Vectorial, multistep, and proton-coupled electron transfer for long- lived charge separation
AU - Hu, Yi Zhen
AU - Tsukiji, Shinya
AU - Shinkai, Seiji
AU - Oishi, Shigero
AU - Hamachi, Itaru
PY - 2000/1/19
Y1 - 2000/1/19
N2 - Artificial photosynthetic reaction centers have been constructed on a protein surface by cofactor reconstitution, which mimic the function of photosynthetic organisms to convert light energy to chemical potential in the form of long-lived charge-separated states. They feature a ruthenium tris(2,2'-bipyridine) moiety as the sensitizer, which is mechanically linked (i.e., in catenane-type) with a cyclobis(paraquat-p-phenylene) unit (BXV4+, acceptor) and covalently linked with a protoheme or Zn-protoporphyrin (donor) located in the myoglobin pocket. Their cofactors 1 and 2, which are tris(heteroleptic) Ru-bipyridine complexes, were synthesized by sequential coordination of the two different functionalized bipyridine ligands with a readily obtainable precursor [Ru(4,4'-dimethyl-2,2'-bipyridine)Cl3](n) followed by metal insertion; this represents a new efficient synthetic method for tris(heteroleptic) Ru(II) complexes of bidentate polypyridine ligands. Reconstitution of apo-myoglobin (Mb) with 1 and 2 affords the two Mb-based artificial triads, Mb(Fe(III)OH2)-Ru2+-BXV4+ and Mb(Zn)-Ru2+-BXV4+. Laser flash photolysis of the Ru(bpy)3 moiety of Mb(Fe(III)OH2)-Ru2+- BXV4+ in an aqueous solution yields an initial charge-separated state, Mb(Fe(III)OH2)-Ru3+-BXV3+(·), via noncovalent electron transfer, followed by dark electron transfer to generate an intermediate consisting of porphyrin cation radical, Mb(Fe(III·)OH2)-Ru2+-BXV3+(·). Mb(Fe(III ·)OH2)-Ru2+-BXV3+ (·) thus generated is subsequently converted, via a proton-coupled process and with a quantum yield of 0.005, into the final charge-separated state, Mb(Fe(IV)=O)-Ru2+-BXV3+ (·), which bears an energy more than 1 eV above the ground state and a lifetime (τ > 2 ms) comparable to that of natural photosynthetic reaction center. Photoexcitation of Mb(Zn)-Ru2+ -BXV4+ also gives rise to a vectorial two-step electron- transfer relay with the intermediate CS state, Mb(Zn)-Ru3+-BXV3+ (·), for the main pathway leading to the final CS state, Mb(Zn+)-Ru2+-BXV3+ (·), in a yield of 0.08. Although the driving forces for the recombination of Mb(Fe(IV)=O)-Ru2+-BXV3+ (·) and Mb(Zn+)-Ru2+-BXV3+ (·) are similar (ΔG ≃ 1.30 eV), the recombination rate of the former is at least 102-103-fold slower than that of the latter. By analogy with a related system reported previously, it was considered that back ET from BXV3+ (·) to Mb(Fe(IV)=O) might be coupled to the protonation of Mb(Fe(IV)=O) and governed by the slow interconversion between the metal-oxo form and the proton-activated species, rendering the CS state Mb(Fe(IV)=O)-Ru2+-BXV3+ (·) specially long-lived. Control experiments clearly demonstrated that partial incorporation of the triads into the protein matrix plays a crucial role in regulating the electron-transfer pathway and stabilizing the charge separation state.
AB - Artificial photosynthetic reaction centers have been constructed on a protein surface by cofactor reconstitution, which mimic the function of photosynthetic organisms to convert light energy to chemical potential in the form of long-lived charge-separated states. They feature a ruthenium tris(2,2'-bipyridine) moiety as the sensitizer, which is mechanically linked (i.e., in catenane-type) with a cyclobis(paraquat-p-phenylene) unit (BXV4+, acceptor) and covalently linked with a protoheme or Zn-protoporphyrin (donor) located in the myoglobin pocket. Their cofactors 1 and 2, which are tris(heteroleptic) Ru-bipyridine complexes, were synthesized by sequential coordination of the two different functionalized bipyridine ligands with a readily obtainable precursor [Ru(4,4'-dimethyl-2,2'-bipyridine)Cl3](n) followed by metal insertion; this represents a new efficient synthetic method for tris(heteroleptic) Ru(II) complexes of bidentate polypyridine ligands. Reconstitution of apo-myoglobin (Mb) with 1 and 2 affords the two Mb-based artificial triads, Mb(Fe(III)OH2)-Ru2+-BXV4+ and Mb(Zn)-Ru2+-BXV4+. Laser flash photolysis of the Ru(bpy)3 moiety of Mb(Fe(III)OH2)-Ru2+- BXV4+ in an aqueous solution yields an initial charge-separated state, Mb(Fe(III)OH2)-Ru3+-BXV3+(·), via noncovalent electron transfer, followed by dark electron transfer to generate an intermediate consisting of porphyrin cation radical, Mb(Fe(III·)OH2)-Ru2+-BXV3+(·). Mb(Fe(III ·)OH2)-Ru2+-BXV3+ (·) thus generated is subsequently converted, via a proton-coupled process and with a quantum yield of 0.005, into the final charge-separated state, Mb(Fe(IV)=O)-Ru2+-BXV3+ (·), which bears an energy more than 1 eV above the ground state and a lifetime (τ > 2 ms) comparable to that of natural photosynthetic reaction center. Photoexcitation of Mb(Zn)-Ru2+ -BXV4+ also gives rise to a vectorial two-step electron- transfer relay with the intermediate CS state, Mb(Zn)-Ru3+-BXV3+ (·), for the main pathway leading to the final CS state, Mb(Zn+)-Ru2+-BXV3+ (·), in a yield of 0.08. Although the driving forces for the recombination of Mb(Fe(IV)=O)-Ru2+-BXV3+ (·) and Mb(Zn+)-Ru2+-BXV3+ (·) are similar (ΔG ≃ 1.30 eV), the recombination rate of the former is at least 102-103-fold slower than that of the latter. By analogy with a related system reported previously, it was considered that back ET from BXV3+ (·) to Mb(Fe(IV)=O) might be coupled to the protonation of Mb(Fe(IV)=O) and governed by the slow interconversion between the metal-oxo form and the proton-activated species, rendering the CS state Mb(Fe(IV)=O)-Ru2+-BXV3+ (·) specially long-lived. Control experiments clearly demonstrated that partial incorporation of the triads into the protein matrix plays a crucial role in regulating the electron-transfer pathway and stabilizing the charge separation state.
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U2 - 10.1021/ja991406i
DO - 10.1021/ja991406i
M3 - Article
AN - SCOPUS:0033963393
VL - 122
SP - 241
EP - 253
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 2
ER -