Hydroxyl radical generation via photoreduction of a simple pyridine N-oxide by an NADH analogue

Nakanishi, Ikuo; Nishizawa, Chiho; Ohkubo, Kei; Takeshita, Keizo; Suzuki, Kazuo; Ozawa, Toshihiko; Hecht, Sidney M.; Tanno, Masayuki; Sueyoshi, Shoko; Miyata, Naoki; Okuda, Haruhiro; Fukuzumi, Shunichi; Ikota, Nobuo; Fukuhara, Kiyoshi

doi:10.1039/b509447j

Cited by 12 publications

(9 citation statements)

References 19 publications

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“…45 Decoordinated bpy-N-oxide ligand can potentially engage in such a pathway (Figure 6) producing a highly reactive hydroxyl radical, which may have potential in the biomedical applications, such as cancer treatments. 8,9,46 However, it is an energetically more demanding pathway (Table 2), and we did not observe any indication of O • H radical formation (data not shown). In both pathways, we assumed that (1-NO) is in water solution, where the protons needed for the transformation are readily available.…”

Section: ■ Introductionmentioning

confidence: 65%

Facile Light-Induced Transformation of [Ru^II(bpy)₂(bpyNO)]²⁺ to [Ru^II(bpy)₃]²⁺

et al. 2020

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Ru-based coordination compounds have important applications as photosensitizers and catalysts. [RuII(bpy)2(bpyNO)]2+ (bpy = 2,2′-bipyridine and bpyNO = 2,2′-bipyridine-N-oxide) was reported to be extremely light-sensitive, but its light-induced transformation pathways have not been analyzed. Here, we elucidated a mechanism of the light-induced transformation of [RuII(bpy)2(bpyNO)]2+ using UV–vis, EPR, resonance Raman, and NMR spectroscopic techniques. The spectroscopic analysis was augmented with the DFT calculations. We concluded that upon 530–650 nm light excitation, 3[RuIII(bpyNO–•)(bpy)2]2+ is formed similarly to the 3[RuIII(bpy–•)(bpy)2]2+ light-induced state of the well-known photosensitizer [RuII(bpy)3]2+. An electron localization on the bpyNO ligand was confirmed by obtaining a unique EPR signal of reduced [RuII(bpy)2(bpyNO–•)]+ (g xx = 2.02, g yy = 1.99, and g zz = 1.87 and 14N hfs A xx = 12 G, A yy = 34 G, and A zz = 11 G). 3[RuIII(bpyNO–•)(bpy)2]2+ may evolve via breaking of the Ru–O–N fragment at two different positions resulting in [RuIVO(bpy)2(bpyout)]2+ for breakage at the O-|-N bond and [RuII(H2O)(bpy)2(bpyNOout)]2+ for breakage at the Ru-|-O bond. These pathways were found to have comparable ΔG. A reduction of [RuIVO(bpy)2(bpyout)]2+ may result in water elimination and formation of [RuII(bpy)3]2+. The expected intermediates, [RuIII(bpy)2(bpyNO)]3+ and [RuIII(bpy)3]3+, were detected by EPR. In addition, a new signal with g xx = 2.38, g yy = 2.10, and g zz = 1.85 was observed and tentatively assigned to a complex with the dissociated ligand, such as [RuIII(H2O)(bpy)2(bpyNOout)]3+. The spectroscopic signatures of [RuIVO(bpy)2(bpyout)]2+ were not observed, although DFT analysis and [RuII(bpy)3]2+ formation suggest this intermediate. Thus, [RuII(bpy)2(bpyNO)]2+ has potential as a light-induced oxidizer.

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Section: ■ Introductionmentioning

confidence: 65%

Facile Light-Induced Transformation of [Ru^II(bpy)₂(bpyNO)]²⁺ to [Ru^II(bpy)₃]²⁺

et al. 2020

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“…In addition, the higher content of sulfur in CCox on the carbon surface, presence of N in pyridines and the appearance of pyridine N-oxide after oxidation can lead to the higher catalytic activity of this fabrics compared to that of CC. These groups promote formation of HO• radicals. − The charged pyridine N -oxides can assist the electron transport through the carbon matrix, facilitating the formation of these radicals . The pyridine functionalities, by providing the positive charge to the carbon matrix can also attract strongly CEES and EES, through their heteroatom, leading to their degradation by the formed radicals. , This process of adsorption is expected to be strongest in the pores in which these groups can exist and where CEES or EES are adsorbed relatively strong via dispersive forces.…”

Section: Resultsmentioning

confidence: 99%

Mustard Gas Surrogate Interactions with Modified Porous Carbon Fabrics: Effect of Oxidative Treatment

2017

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Removal of chemical warfare agent (CWA) surrogates by highly porous carbon textiles was investigated. The carbon cloth was modified by oxidation in a mixture of concentrated sulfuric and nitric acid. This process did not affect textile structural integrity. The surface properties of the modified textiles were investigated, and their capabilities to remove 2-chloroethyl ethyl sulfide (CEES) and diethylsulfide (EES), two mustard gas surrogates, were evaluated. The oxidized carbon textiles have a highly active surface that has the ability to form radical species. This enhances the degradation of the surrogates, and so the detoxification efficiency. The reaction products detected suggest differences in degradation mechanisms which depend on the type of fabric surface features. Thus, the oxidized surfaces eliminate CEES mainly through dehydrohalogenation, while the nonoxidized surfaces act via hydrolysis. Only the oxidized carbon has a surface active enough to react with the less reactive surrogate EES, by cleavage of the C-S bond. The surface functional groups promote not only the radical formation but also contribute to a strong adsorption of the CWA surrogates, which enhance the decomposition of these toxic species.

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“…The alternative pathway may involve Hantzsch ester as a hydrogen-atom donor with the N -oxide as an acceptor (Scheme , bottom) . Finally, in further support of our findings, a similar photoreduction of pyridine N -oxide by 1-benzyl-1,4-dihydronicotinamide under UV irradiation was previously reported, wherein the authors demonstrate that the N -oxide was quenching the singlet excited state of the dihydropyridine and afforded the deoxygenated product …”

mentioning

confidence: 99%

“…24 Finally, in further support of our findings, a similar photoreduction of pyridine N-oxide by 1-benzyl-1,4-dihydronicotinamide under UV irradiation was previously reported, wherein the authors demonstrate that the N-oxide was quenching the singlet excited state of the dihydropyridine and afforded the deoxygenated product. 25 In conclusion, we have developed a reductive deoxygenation of heteroaryl N-oxides and the reduction of nitroarenes to the corresponding hydroxylamines via visible-light photoexcitation of Hantzsch ester. These reactions are operationally simple, can be performed under ambient conditions without the exclusion of moisture or air, proceed smoothly in the presence of a variety of functional groups, and do not require the use of an expensive photocatalyst.…”

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confidence: 99%

Catalyst-Free N-Deoxygenation by Photoexcitation of Hantzsch Ester

2020

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A mild and operationally simple protocol for the deoxygenation of a variety of heteroaryl N-oxides and nitroarenes has been developed. A mixture of substrate and Hantzsch ester is proposed to result in an electron donor–acceptor complex, which upon blue-light irradiation undergoes photoinduced electron transfer between the two reactants to afford the products. N-oxide deoxygenation is demonstrated with 22 examples of functionally diverse substrates, and the chemoselective reduction of nitroarenes to the corresponding hydroxylamines is also shown.

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Hydroxyl radical generation via photoreduction of a simple pyridine N-oxide by an NADH analogue

Cited by 12 publications

References 19 publications

Facile Light-Induced Transformation of [Ru^II(bpy)₂(bpyNO)]²⁺ to [Ru^II(bpy)₃]²⁺

Facile Light-Induced Transformation of [Ru^II(bpy)₂(bpyNO)]²⁺ to [Ru^II(bpy)₃]²⁺

Mustard Gas Surrogate Interactions with Modified Porous Carbon Fabrics: Effect of Oxidative Treatment

Catalyst-Free N-Deoxygenation by Photoexcitation of Hantzsch Ester

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Hydroxyl radical generation via photoreduction of a simple pyridine N-oxide by an NADH analogue

Cited by 12 publications

References 19 publications

Facile Light-Induced Transformation of [RuII(bpy)2(bpyNO)]2+ to [RuII(bpy)3]2+

Facile Light-Induced Transformation of [RuII(bpy)2(bpyNO)]2+ to [RuII(bpy)3]2+

Mustard Gas Surrogate Interactions with Modified Porous Carbon Fabrics: Effect of Oxidative Treatment

Catalyst-Free N-Deoxygenation by Photoexcitation of Hantzsch Ester

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Product

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Facile Light-Induced Transformation of [Ru^II(bpy)₂(bpyNO)]²⁺ to [Ru^II(bpy)₃]²⁺

Facile Light-Induced Transformation of [Ru^II(bpy)₂(bpyNO)]²⁺ to [Ru^II(bpy)₃]²⁺