Solvent-induced hydrogen tunnelling in ascorbate proton-coupled electron transfers

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

doi:10.1016/j.tetlet.2011.01.142

Cited by 7 publications

(21 citation statements)

References 47 publications

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“…The kinetic isotope effects observed in almost all ascorbate PCET systems presented here are increased unexpectedly [17][18][19][21][22][23] with regard to the KIE-s observed in particular "neat" water reaction. The only exception is the case of hexacyanoferrate oxidant in more concentrated water solutions of inorganic salts [20] where the observed KIE-s are reduced in magnitude.…”

Section: Kinetic Isotope Effects and Hydrogen Tunnelling In Ascorbatementioning

confidence: 91%

“…In addition, it has been widely used in the study of enzymatic reactions, many of which are PCET reactions [7,55,[64][65][66]69,70]. The temperature-dependences of KIE in PCET reactions vary from significantly temperature-dependent, to temperature-independent KIE-s [7,19,20,[69][70][71]. This wide span of KIE temperature-dependences, observed in a great number of enzymatic but also in solution PCET reactions are usually interpreted with Marcus like full-tunnelling model (see Section 2.3.)…”

Section: Kinetic Isotope Effects In Pcet Reactionsmentioning

confidence: 99%

“…The results of the study of KIE-s and tunnelling in the ascorbate reactions [11,[17][18][19][20][21][22][23]72] can contribute to the better understanding of PCET reactions; moreover, many enzymatic reactions involve PCET. The reactions of ascorbate presented are similar to the reactions catalysed by ascorbate peroxidase enzymes [83], and cytochrome b 561 proteins [84], being thus a good potential reference solution reactions which is of importance for the study of enzyme catalysis.…”

Section: Kinetic Isotope Effects and Hydrogen Tunnelling In Ascorbatementioning

confidence: 99%

“…However, to the best of our knowledge, there are no systematic studies of solvent influences on KIE-s and hydrogen tunnelling in PCET reactions [16]. We have investigated KIE-s and hydrogen tunnelling in the following PCET oxidations of ascorbate: (a) reaction with 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO radical) [17,18], (b) reaction with hexacyanoferrate(III) ions [19][20][21][22] and (c) reaction with ferricinium cation [22] in aqueous solutions containing substantial concentrations of organic solvents or salts. Furthermore, KIE-s and hydrogen tunnelling in reaction of ascorbate with hexacyanoferrate(III) ions have been investigated in a series of fairly diluted aqueous solutions containing small concentrations of the partially hydrophobic solutes [23].…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2020

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Recent experimental studies of kinetic isotope effects (KIE-s) and hydrogen tunnelling comprising three proton-coupled electron transfer (PCET) oxidations of ascorbate monoanion, (a) in aqueous reaction solutions, (b) in the mixed water-organic cosolvent systems, (c) in aqueous solutions of various salts and (d) in fairly diluted aqueous solutions of the various partial hydrophobes are reviewed. A number of new insights into the wealth of the kinetic isotope phenomena in the PCET reactions have been obtained. The modulation of KIE-s and hydrogen tunnelling observed when partially hydrophobic solutes are added into water reaction solution, in the case of fairly diluted solutions is revealed as the strong linear correlation of the isotopic ratios of the Arrhenius prefactors Ah/Ad and the isotopic differences in activation energies ΔEa (D,H). The observation has been proposed to be a signature of the involvement of the collective intermolecular excitonic vibrational dynamics of water in activation processes and aqueous chemistry.

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Section: Kinetic Isotope Effects and Hydrogen Tunnelling In Ascorbatementioning

confidence: 91%

Section: Kinetic Isotope Effects In Pcet Reactionsmentioning

confidence: 99%

Section: Kinetic Isotope Effects and Hydrogen Tunnelling In Ascorbatementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2020

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“…Solvent isotope effects have been reported on the first kinetic step (oxidation of ascorbic acid by ferricyanide; k 1 ) consistent with a PCET reaction. Temperature dependence studies have indicated that: (a) the reaction occurs by quantum mechanical tunnelling [18]; (b) the KIE is temperature dependent, consistent with the promoting motions hypothesis [56,57]; and (c) the temperature dependence is strongly influenced by the solvent composition [57].…”

Section: Model Chemistry (Ascorbate and Ferricyanide)mentioning

confidence: 92%

Does the pressure dependence of kinetic isotope effects report usefully on dynamics in enzyme H‐transfer reactions?

et al. 2015

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The temperature dependence of kinetic isotope effects (KIEs) has emerged as the main experimental probe of enzymatic H‐transfer by quantum tunnelling. Implicit in the interpretation is a presumed role for dynamic coupling of H‐transfer chemistry to the protein environment, the so‐called ‘promoting motions/vibrations hypothesis’. This idea remains contentious, and others have questioned the importance and/or existence of promoting motions/vibrations. New experimental methods of addressing this problem are emerging, including use of mass‐modulated enzymes and time‐resolved spectroscopy. The pressure dependence of KIEs has been considered as a potential probe of quantum tunnelling reactions, because semi‐classical KIEs, which are defined by differences in zero‐point vibrational energy, are relatively insensitive to kbar changes in pressure. Reported combined pressure and temperature (p‐T) dependence studies of H‐transfer reactions are, however, limited. Here, we extend and review the available p‐T studies that have utilized well‐defined experimental systems in which quantum mechanical tunnelling is established. These include flavoproteins, quinoproteins, light‐activated enzymes and chemical model systems. We show that there is no clear general trend between the p‐T dependencies of the KIEs in these systems. Given the complex nature of p‐T studies, we conclude that computational simulations using determined (e.g. X‐ray) structures are also needed alongside experimental measurements of reaction rates/KIEs to guide the interpretation of p‐T effects. In providing new insight into H‐transfer/environmental coupling, combined approaches that unite both atomistic understanding with experimental rate measurements will require careful evaluation on a case‐by‐case basis. Although individually informative, we conclude that p‐T studies do not provide the more generalized insight that has come from studies of the temperature dependence of KIEs.

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The average local ionization energy and Fukui function of l-ascorbate, the local reactivity descriptors of antioxidant reactivity

Brala

Fabijanić

Marković

et al. 2014

Computational and Theoretical Chemistry

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Solvent-induced hydrogen tunnelling in ascorbate proton-coupled electron transfers

Cited by 7 publications

References 47 publications

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

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

Does the pressure dependence of kinetic isotope effects report usefully on dynamics in enzyme H‐transfer reactions?

The average local ionization energy and Fukui function of l-ascorbate, the local reactivity descriptors of antioxidant reactivity

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