Mechanism of hydride donor generation using a Ru(II) complex containing an NAD+ model ligand: Pulse and steady-state radiolysis studies

Dmitry Polyansky, Diane Cabelli, James Muckerman, Takashi Fukushima, Koji Tanaka, Etsuko Fujita

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Abstract

The mechanistic pathways of formation of the NADH-like [Ru(bpy) 2(pbnHH)]2+ species from [Ru(bpy)2(pbn)] 2+ were studied in an aqueous medium. Formation of the one-electron-reduced species as a result of reduction by a solvated electron (k = 3.0 × 1010 M-1 s-1) or CO 2 •- (k = 4.6 × 109 M-1 s-1) or reductive quenching of an MLCT excited state by 1,4-diazabicyclo[2.2.2]octane (k = 1.1 × 109 M-1 s-1) is followed by protonation of the reduced species (pK a = 11). Dimerization (k7a = 2.2 × 108 M-1 s-1) of the singly reduced protonated species, [Ru(bpy)2(pbnH)]2+, followed by disproportionation of the dimer as well as the cross reaction between the singly reduced protonated and nonprotonated species (k8 = 1.2 × 108 M-1 s-1) results in the formation of the final [Ru(bpy)2(pbnHH)]2+ product together with an equal amount of the starting complex, [Ru(bpy)2(pbn)]2+. At 0.2°C, a dimeric intermediate, most likely a π-stacking dimer, was observed that decomposes thermally to form an equimolar mixture of [Ru(bpy) 2(pbnHH)]2+ and [Ru(bpy)2(pbn)]2+ (pH <9). The absence of a significant kinetic isotope effect in the disproportionation reaction of [Ru(bpy)2(pbnH)] 2+ and its conjugate base (pH > 9) indicates that disproportionation occurs by a stepwise pathway of electron transfer followed by proton transfer.

Original languageEnglish
Pages (from-to)3958-3968
Number of pages11
JournalInorganic Chemistry
Volume47
Issue number10
DOIs
Publication statusPublished - May 19 2008

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Radiolysis
radiolysis
Hydrides
NAD
hydrides
Ligands
ligands
pulses
dimers
octanes
dimerization
electron transfer
Dimers
electrons
Electrons
quenching
protons
products
Proton transfer
Dimerization

ASJC Scopus subject areas

  • Inorganic Chemistry

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Mechanism of hydride donor generation using a Ru(II) complex containing an NAD+ model ligand : Pulse and steady-state radiolysis studies. / Polyansky, Dmitry; Cabelli, Diane; Muckerman, James; Fukushima, Takashi; Tanaka, Koji; Fujita, Etsuko.

In: Inorganic Chemistry, Vol. 47, No. 10, 19.05.2008, p. 3958-3968.

Research output: Contribution to journalArticle

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abstract = "The mechanistic pathways of formation of the NADH-like [Ru(bpy) 2(pbnHH)]2+ species from [Ru(bpy)2(pbn)] 2+ were studied in an aqueous medium. Formation of the one-electron-reduced species as a result of reduction by a solvated electron (k = 3.0 × 1010 M-1 s-1) or CO 2 •- (k = 4.6 × 109 M-1 s-1) or reductive quenching of an MLCT excited state by 1,4-diazabicyclo[2.2.2]octane (k = 1.1 × 109 M-1 s-1) is followed by protonation of the reduced species (pK a = 11). Dimerization (k7a = 2.2 × 108 M-1 s-1) of the singly reduced protonated species, [Ru(bpy)2(pbnH•)]2+, followed by disproportionation of the dimer as well as the cross reaction between the singly reduced protonated and nonprotonated species (k8 = 1.2 × 108 M-1 s-1) results in the formation of the final [Ru(bpy)2(pbnHH)]2+ product together with an equal amount of the starting complex, [Ru(bpy)2(pbn)]2+. At 0.2°C, a dimeric intermediate, most likely a π-stacking dimer, was observed that decomposes thermally to form an equimolar mixture of [Ru(bpy) 2(pbnHH)]2+ and [Ru(bpy)2(pbn)]2+ (pH <9). The absence of a significant kinetic isotope effect in the disproportionation reaction of [Ru(bpy)2(pbnH•)] 2+ and its conjugate base (pH > 9) indicates that disproportionation occurs by a stepwise pathway of electron transfer followed by proton transfer.",
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