Differences of pH-dependent mechanisms on generation of hydride donors using Ru(II) complexes containing geometric isomers of NAD+ model ligands

NMR and radiolysis studies in aqueous solution

Brian W. Cohen, Dmitry Polyansky, Ruifa Zong, Hui Zhou, Theany Ouk, Diane E. Cabelli, Randolph P. Thummel, Etsuko Fujita

Research output: Contribution to journalArticle

29 Citations (Scopus)

Abstract

The pH-dependent mechanism of the reduction of the nicotinamide adenine dinucleotide (NADH) model complex [Ru(bpy)2(5)]2+ (5 = 3-(pyrid-2′-yl)-4-azaacridine) was compared to the mechanism of the previously studied geometric isomer [Ru(bpy)2(pbn)]2+ (pbn = 2-(pyrid-2′-yl)-1-azaacridine, previously referred to as 2-(pyrid-2′-yl)-benzo[b]-1,5-naphthyridine) in aqueous media. The exposure of [Ru(bpy)2(5)]2+ to CO2 •- leads to the formation of the one-electron reduced species (k = 4.4×109 M-1 s-1). At pH <11.2, the one-electron reduced species can be protonated, k = 2.6×104 s-1 in D2O. Formation of a C-C bonded dimer is observed across the pH range of 5-13 (k = 4.5×108 M-1 s -1). At pH <11, two protonated radical species react to form a stable C-C bonded dimer. At pH > 11, dimerization of two one-electron reduced species is followed by disproportionation to one equivalent starting complex [Ru(bpy)2(5)]2+ and one equivalent [Ru(bpy) 2(5HH)]2+. The structural difference between [Ru(bpy) 2(pbn)]2+ and [Ru(bpy)2(5)]2+ dictates the mechanism and product formation in aqueous medium. The exchange of the nitrogen and carbon atoms on the azaacridine ligands alters the accessibility of the dimerization reactive site, thereby changing the mechanism and the product formation for the reduction of the [Ru(bpy)2(5)] 2+ compound.

Original languageEnglish
Pages (from-to)8034-8044
Number of pages11
JournalInorganic Chemistry
Volume49
Issue number17
DOIs
Publication statusPublished - Sep 6 2010

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Radiolysis
radiolysis
Hydrides
Isomers
NAD
hydrides
isomers
Nuclear magnetic resonance
Ligands
aqueous solutions
nuclear magnetic resonance
ligands
dimerization
nicotinamide
Dimerization
adenines
products
nitrogen atoms
electrons
bis(bipyridyl)ruthenium(II)

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Physical and Theoretical Chemistry

Cite this

Differences of pH-dependent mechanisms on generation of hydride donors using Ru(II) complexes containing geometric isomers of NAD+ model ligands : NMR and radiolysis studies in aqueous solution. / Cohen, Brian W.; Polyansky, Dmitry; Zong, Ruifa; Zhou, Hui; Ouk, Theany; Cabelli, Diane E.; Thummel, Randolph P.; Fujita, Etsuko.

In: Inorganic Chemistry, Vol. 49, No. 17, 06.09.2010, p. 8034-8044.

Research output: Contribution to journalArticle

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abstract = "The pH-dependent mechanism of the reduction of the nicotinamide adenine dinucleotide (NADH) model complex [Ru(bpy)2(5)]2+ (5 = 3-(pyrid-2′-yl)-4-azaacridine) was compared to the mechanism of the previously studied geometric isomer [Ru(bpy)2(pbn)]2+ (pbn = 2-(pyrid-2′-yl)-1-azaacridine, previously referred to as 2-(pyrid-2′-yl)-benzo[b]-1,5-naphthyridine) in aqueous media. The exposure of [Ru(bpy)2(5)]2+ to CO2 •- leads to the formation of the one-electron reduced species (k = 4.4×109 M-1 s-1). At pH <11.2, the one-electron reduced species can be protonated, k = 2.6×104 s-1 in D2O. Formation of a C-C bonded dimer is observed across the pH range of 5-13 (k = 4.5×108 M-1 s -1). At pH <11, two protonated radical species react to form a stable C-C bonded dimer. At pH > 11, dimerization of two one-electron reduced species is followed by disproportionation to one equivalent starting complex [Ru(bpy)2(5)]2+ and one equivalent [Ru(bpy) 2(5HH)]2+. The structural difference between [Ru(bpy) 2(pbn)]2+ and [Ru(bpy)2(5)]2+ dictates the mechanism and product formation in aqueous medium. The exchange of the nitrogen and carbon atoms on the azaacridine ligands alters the accessibility of the dimerization reactive site, thereby changing the mechanism and the product formation for the reduction of the [Ru(bpy)2(5)] 2+ compound.",
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AU - Zong, Ruifa

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AU - Cabelli, Diane E.

AU - Thummel, Randolph P.

AU - Fujita, Etsuko

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