Kinetic Isotope Effects and Hydrogen Tunnelling in PCET Oxidations of Ascorbate: New Insights into Aqueous Chemistry?

Marković, Ana; Brala, Cvijeta Jakobušić; Pilepić, Viktor; Uršić, Stanko

doi:10.3390/molecules25061443

Cited by 8 publications

(5 citation statements)

References 85 publications

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“…When the Δ G is negative, reduction of the nitroxyl radicals by ascorbate occurs spontaneously, whereas no reduction occurs in the case of a positive Δ G . The involvement of hydrogen tunneling at room temperature was reported based on large kinetic isotope effects (KIE, k H / k D ) in the reduction of TEMPO by ascorbate in water ( k H / k D = 24.2) and water–dioxane mixed solvent (1:1 v/v; k H / k D = 31.0) at room temperature ( 87 , 153 ). A large KIE of 12.8 was also observed for the reaction of ascorbate with 2-phenyl-4,4,5,5-tetramethylimiazolione-1-oxide (PTIO • ) in a phosphate buffer solution at ambient temperatures ( 138 ).…”

Section: Chemistry and Redox Properties Of Nitroxyl Radicalsmentioning

confidence: 99%

Nitroxyl Radical as a Theranostic Contrast Agent in Magnetic Resonance Redox Imaging

Matsumoto

Nakanishi

Zhelev

et al. 2022

Antioxidants & Redox Signaling

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Significance: In vivo assessment of paramagnetic and diamagnetic conversions of nitroxyl radicals based on cyclic redox mechanism can be an index of tissue redox status. The redox mechanism of nitroxyl radicals, which enables their use as a normal tissue-selective radioprotector, is seen as being attractive on planning radiation therapy. Recent Advances: In vivo redox imaging using nitroxyl radicals as redox-sensitive contrast agents has been developed to assess tissue redox status. Chemical and biological behaviors depending on chemical structures of nitroxyl radical compounds have been understood in detail. Polymer types of nitroxyl radical contrast agents and/or nitroxyl radical-labeled drugs were designed for approaching theranostics. Critical Issues: Nitroxyl radicals as magnetic resonance imaging (MRI) contrast agents have several advantages compared with those used in electron paramagnetic resonance (EPR) imaging, while support by EPR spectroscopy is important to understand information from MRI. Redox-sensitive paramagnetic contrast agents having a medicinal benefit, that is, nitroxyl-labeled drug, have been developed and proposed. Future Directions: A development of suitable nitroxyl contrast agent for translational theranostic applications with high reaction specificity and low normal tissue toxicity is under progress. Nitroxyl radicals as redoxsensitive magnetic resonance contrast agents can be a useful tool to detect an abnormal tissue redox status such as disordered oxidative stress. Antioxid. Redox Signal. 00, 000-000.

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Section: Chemistry and Redox Properties Of Nitroxyl Radicalsmentioning

confidence: 99%

Nitroxyl Radical as a Theranostic Contrast Agent in Magnetic Resonance Redox Imaging

Matsumoto

Nakanishi

Zhelev

et al. 2022

Antioxidants & Redox Signaling

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“…Theoretical and empirical research on organohydride donors have established quasi-classical and tunneling contributions to the KIE. − From these data, the overall KIE is expected to be dependent on the C–H bond length. In most cases, the quasi-classical contributions remain constant across different combinations of donors and acceptors, but the tunneling contributions to the KIE, and consequently, the total KIE, increase significantly as the C–H bond energy decreases in pure hydride transfer reactions. , However, when the measured KIEs for the reaction between Ru–CO 2+ and BIHs are compared against the hydride transfer reaction free energy changes, which are proportional to the C–H bond hydricity (Δ G H– ), Table , it was observed that as the bond energy decreases, the KIE also decreases.…”

Section: Resultsmentioning

confidence: 99%

Reduction of CO to Methanol with Recyclable Organic Hydrides

Müller,

Ahmad,

Sirlin

et al. 2024

J. Am. Chem. Soc.

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The reaction steps for the selective conversion of a transition metal carbonyl complex to a hydroxymethyl complex that releases methanol upon irradiation with visible light have been successfully quantified in acetonitrile solution with dihydrobenzimidazole organic hydride reductants. Dihydrobenzimidazole reductants have been shown to be inactive toward H 2 generation in the presence of a wide range of proton sources and have been regenerated electrochemically or photochemically. Specifically, the reaction of cis-[Ru-(bpy) 2 (CO) 2 ] 2+ (bpy = 2,2′-bipyridine) with one equivalent of a dihydrobenzimidazole quantitatively yields a formyl complex, cis-[Ru(bpy) 2 (CO)(CHO)] + , and the corresponding benzimidazolium on a seconds time scale. Kinetic experiments revealed a first-order dependence on the benzimidazole hydride concentration and an unusually large kinetic isotope effect, inconsistent with direct hydride transfer and more likely to occur by an electron transfer-proton-coupled electron transfer (EΤ−PCET) or related mechanism. Further reduction/protonation of cis-[Ru(bpy) 2 (CO)(CHO)] + with two equivalents of the organic hydride yields the hydroxymethyl complex cis-[Ru(bpy) 2 (CO)(CH 2 OH)] + . Visible light excitation of cis-[Ru(bpy) 2 (CO)-(CH 2 OH)] + in the presence of excess organic hydride was shown to yield free methanol. Identification and quantification of methanol as the sole CO reduction product was confirmed by 1 H NMR spectroscopy and gas chromatography. The high selectivity and mild reaction conditions suggest a viable approach for methanol production from CO, and from CO 2 through cascade catalysis, with renewable organic hydrides that bear similarities to Nature's NADPH/NADP + .

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“…The isotopic difference, E a (D)– E a (H), (19 kJ mol −1 ) was significantly greater than the difference in zero-point energies of 5.1 kJ mol −1 [ 16 ]. These results indicate that quantum mechanical tunneling plays a role in the hydrogen-transfer reaction from Trolox to DPPH • /β-CD in a phosphate buffer [ 17 , 18 , 19 , 20 ]. ln k H = − E a (H)/( RT ) + ln A H or ln k D = − E a (D)/( RT ) + ln A D …”

Section: Resultsmentioning

confidence: 99%

Tunneling in the Hydrogen-Transfer Reaction from a Vitamin E Analog to an Inclusion Complex of 2,2-Diphenyl-1-picrylhydrazyl Radical with β-Cyclodextrin in an Aqueous Buffer Solution at Ambient Temperature

et al. 2021

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Recently, increasing attention has been paid to quantum mechanical behavior in biology. In this study, we investigated the involvement of quantum mechanical tunneling in the hydrogen-transfer reaction from Trolox, a water-soluble analog of vitamin E (α-tocopherol), to 2,2-diphenyl-1-picrylhydrazyl radical (DPPH•) in a phosphate buffer solution (0.05 M, pH 7.0). DPPH• was used as a reactivity model of reactive oxygen species and solubilized in water using β-cyclodextrin (β-CD). The second-order rate constants, kH and kD, in 0.05 M phosphate buffer solutions prepared with H2O (pH 7.0) and D2O (pD 7.0), respectively, were determined for the reaction between Trolox and DPPH•, using a stopped-flow technique at various temperatures (283–303 K). Large kinetic isotope effects (KIE, kH/kD) were observed for the hydrogen-transfer reaction from Trolox to the β-CD-solubilized DPPH• in the whole temperature range. The isotopic ratio of the Arrhenius prefactor (AH/AD = 0.003), as well as the isotopic difference in the activation energies (19 kJ mol−1), indicated that quantum mechanical tunneling plays a role in the reaction.

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Kinetic Isotope Effects and Hydrogen Tunnelling in PCET Oxidations of Ascorbate: New Insights into Aqueous Chemistry?

Cited by 8 publications

References 85 publications

Nitroxyl Radical as a Theranostic Contrast Agent in Magnetic Resonance Redox Imaging

Nitroxyl Radical as a Theranostic Contrast Agent in Magnetic Resonance Redox Imaging

Reduction of CO to Methanol with Recyclable Organic Hydrides

Tunneling in the Hydrogen-Transfer Reaction from a Vitamin E Analog to an Inclusion Complex of 2,2-Diphenyl-1-picrylhydrazyl Radical with β-Cyclodextrin in an Aqueous Buffer Solution at Ambient Temperature

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