Marcus Theory of a Parallel Effect on α for Hydride Transfer Reaction between NAD<sup>+</sup> Analogues

Lee, In-Sook Han; Jeoung, and Eun Hee; Kreevoy, Maurice M.

doi:10.1021/ja963768l

Cited by 119 publications

(96 citation statements)

References 20 publications

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“…There are a wide distribution of oxyl radical reactions studied by different physical and spectroscopic techniques and by different research groups over the past 50 years. The broad success of the CR/KSE model is surprising because previous applications of the CR to atom and group transfer reactions (other than electron transfer) have been restricted to limited sets of structurally similar reagents under very similar reaction conditions (6,(14)(15)(16).…”

Section: (Si Text) This Reaction Is Much Slower Than H-atom Abstractmentioning

confidence: 99%

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Predicting organic hydrogen atom transfer rate constants using the Marcus cross relation

Warren

Mayer

2010

Proc. Natl. Acad. Sci. U.S.A.

112

137

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Chemical reactions that involve net hydrogen atom transfer (HAT) are ubiquitous in chemistry and biology, from the action of antioxidants to industrial and metalloenzyme catalysis. This report develops and validates a procedure to predict rate constants for HAT reactions of oxyl radicals (RO • ) in various media. Our procedure uses the Marcus cross relation (CR) and includes adjustments for solvent hydrogen-bonding effects on both the kinetics and thermodynamics of the reactions. Kinetic solvent effects (KSEs) are included by using Ingold's model, and thermodynamic solvent effects are accounted for by using an empirical model developed by Abraham. These adjustments are shown to be critical to the success of our combined model, referred to as the CR/KSE model. As an initial test of the CR/KSE model we measured self-exchange and cross rate constants in different solvents for reactions of the 2,4,6-tri-tert-butylphenoxyl radical and the hydroxylamine 2,2′-6,6′-tetramethylpiperidin-1-ol. Excellent agreement is observed between the calculated and directly determined cross rate constants. We then extend the model to over 30 known HAT reactions of oxyl radicals with OH or CH bonds, including biologically relevant reactions of ascorbate, peroxyl radicals, and α-tocopherol. The CR/KSE model shows remarkable predictive power, predicting rate constants to within a factor of 5 for almost all of the surveyed HAT reactions.free radicals | Marcus theory | proton-coupled electron transfer | reactive oxygen species | oxyl radicals H ydrogen atom transfer (HAT) reactions (Eq. 1) have been a cornerstone of organic and biological chemistry for over a century (1, 2). These reactions are key steps in many important processes, from energy conversion to the chemistry of reactive oxygen species and antioxidants (3). Thus, developing a detailed understanding of the factors that dictate HAT reactivity has long been a goal.A large number of HAT rate constants have been measured in many laboratories with various techniques (4, 5). Rates of HAT reactions have traditionally been understood by using the BellEvans-Polanyi (BEP) relation, which relates the activation energy to the enthalpic driving force (6). Whereas the BEP relation holds well within sets of similar reactions, a comprehensive theoretical understanding of HAT is still emerging (3).Our group has been exploring the use of the Marcus cross relation (CR) Eq. 2 (7), a corollary of the Marcus theory of electron transfer, as the basis for a general model for HAT rates (8)(9)(10)(11)(12). This use of the CR grew out of recognizing HAT as one class of a larger set of reactions in which one electron and one proton are transferred (, termed proton-coupled electron transfer. In this paper, we use "HAT" to refer to any reaction in which H • is transferred from a donor to an acceptor in a single kinetic step (Eq. 1), although other definitions have been used (13).The CR, with respect to HAT reactions, relates the cross rate constant (k XH∕Y• , Eq. 1) to the two degenerate self-exchange rate c...

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Section: (Si Text) This Reaction Is Much Slower Than H-atom Abstractmentioning

confidence: 99%

“…2 has been found to predict HATcross-reaction rate constants within 1-2 orders of magnitude (10). Marcus theory has also been successfully applied to proton transfers (14), hydride transfers (15), and methyl transfers (S N 2 reactions) (6,16), although only within sets of very closely related reactions.…”

mentioning

confidence: 99%

Predicting organic hydrogen atom transfer rate constants using the Marcus cross relation

Warren

Mayer

2010

Proc. Natl. Acad. Sci. U.S.A.

112

137

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“…63 The largest hfc value (3.95 G) is significantly smaller than the value without Mg 2 þ ion (4.60 G) due to the spin delocalization to the Mg nucleus. 13,40,64,68 Such onestep versus multistep pathways have been discussed extensively in hydride transfer reactions of dihydronicotinamide coenzyme (NADH) and analogues, particularly including the effect of metal cations and acids, [69][70][71][72][73][74][75][76][77][78][79] because of the essential role of acid catalysis in the enzymatic reduction of carbonyl compounds by NADH. À bound to both Mg 2 þ and the amide proton without detection of an intermediate without hydrogen bonding.…”

Section: Scheme 29mentioning

confidence: 99%

Proton‐Coupled Electron Transfer in Hydrogen and Hydride Transfer Reactions

Fukuzumi

2010

Physical Inorganic Chemistry

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ET. [7][8][9]12,13 The inner-sphere character in organic ET reactions is established by their high sensitivity to steric effects. 14 As the H DA value increases further, the ET process is coupled with the subsequent PT process. This is generally referred to as proton-coupled electron transfer (PCET). [15][16][17][18][19][20][21][22][23][24] What distinguishes PCET from classic HAT is that the proton and electron are transferred between two different (noninteracting) orbitals. In particular, PCET plays an important role in enzymatic reactions such as those of lipoxygenases, which are mononuclear nonheme iron enzymes. [25][26][27] The key step of the lipoxygenase reactions is PCET from a substrate to ferric hydroxide cofactor (Fe(III)-OH) to produce Fe(II)-OH 2 and a radical intermediate substrate, when an electron goes to the metal center and a proton is transferred to the OH ligand. 28,29 When PCET is a concerted process whereby a proton and an electron are transferred simultaneously, such a PCET process may be merged into the one-step HAT process. 30 Thus, there has been long-standing ambiguity as to the mechanistic borderline where a sequential PCET pathway is changed to a one-step HAT pathway or vice versa. Understanding HAT reactions certainly requires knowledge of the thermodynamics and kinetics of the overall HAT, ET, and PT steps.Considering only the two-electron reduction of A, the reduction and protonation give nine species at different oxidation and protonation states as shown in Scheme 2.3. Each species can have an interaction with a variety of metal ions (M n þ ), and such an interaction can control each ET and protonation step, as well as their combined step (hydrogen transfer) in Scheme 2.3. [31][32][33][34][35] The binding of M n þ to radical anions of electron acceptors results in a substantial increase in the ET rate. 31-35 This is defined herein as metal ion-coupled electron transfer (MCET) in analogy to PCET. 36 The binding of M n þ with A . À can also be combined with other noncovalent interactions such as hydrogen bonding and p-p interaction. 36 The initial PCET and MCET processes are followed by the second PCET and MCET processes to afford AH 2 as the two-electron reduced species of A with two protons. 36 SCHEME 2.3 MECHANISTIC BORDERLINE BETWEEN ONE-STEP HAT AND SEQUENTIAL PCETAmong a variety of hydrogen donors, dihydronicotinamide adenine dinucleotide (NADH) and analogues have attracted particular interest, because NADH is the most important source of hydrogen and hydride ion in biological redox reactions. 37-40 If HAT from NADH and analogues to hydrogen atom acceptors (A) occurs in a one-step manner, NAD . and AH . would be the only detectable radical products. In the case of sequential electron and proton transfer, however, NADH . þ and A . À would also be detected as the intermediates for the hydrogen transfer reaction. The radical intermediates such as NADH . þ , NAD . , and the corresponding analogues are involved in a variety of thermal and photoinduced ET reactions of NADH and analo...

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“…The reference 2-(4-fluorophenyl)benzimidazole was synthesized according to literature methods 14,15 and was characterized using NMR and IR spectroscopy. [4-18 F]Fluorobenzoic acid was synthesized as described previously.…”

Section: 13mentioning

confidence: 99%

Microwave‐assisted cyclocondensation of 1,2‐diaminobenzene with [4‐¹⁸F]fluorobenzoic acid: microwave synthesis of 2‐([4‐¹⁸F]fluorophenyl) benzimidazole

Getvoldsen

Fredriksson

Elander

et al. 2004

Labelled Comp Radiopharmac

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The synthesis of 2‐([4‐18F]fluorophenyl)benzimidazole, which has potential to be used as a building block for many endogenous and pharmaceutical compounds, is reported. A range of solvents and catalysts as well as conventional and microwave heating have been investigated to optimise the reaction conditions. The cyclocondensation of 1,2‐diaminobenzene with radiolabelled [4‐18F]fluorobenzoic acid in neat methanesulphonic and polyphosphoric acids under microwave heating led rapidly to the cyclised phenylbenzimidazole. Copyright © 2004 John Wiley & Sons, Ltd.

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Marcus Theory of a Parallel Effect on α for Hydride Transfer Reaction between NAD⁺ Analogues

Cited by 119 publications

References 20 publications

Predicting organic hydrogen atom transfer rate constants using the Marcus cross relation

Predicting organic hydrogen atom transfer rate constants using the Marcus cross relation

Proton‐Coupled Electron Transfer in Hydrogen and Hydride Transfer Reactions

Microwave‐assisted cyclocondensation of 1,2‐diaminobenzene with [4‐¹⁸F]fluorobenzoic acid: microwave synthesis of 2‐([4‐¹⁸F]fluorophenyl) benzimidazole

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Marcus Theory of a Parallel Effect on α for Hydride Transfer Reaction between NAD+ Analogues

Cited by 119 publications

References 20 publications

Predicting organic hydrogen atom transfer rate constants using the Marcus cross relation

Predicting organic hydrogen atom transfer rate constants using the Marcus cross relation

Proton‐Coupled Electron Transfer in Hydrogen and Hydride Transfer Reactions

Microwave‐assisted cyclocondensation of 1,2‐diaminobenzene with [4‐18F]fluorobenzoic acid: microwave synthesis of 2‐([4‐18F]fluorophenyl) benzimidazole

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Marcus Theory of a Parallel Effect on α for Hydride Transfer Reaction between NAD⁺ Analogues

Microwave‐assisted cyclocondensation of 1,2‐diaminobenzene with [4‐¹⁸F]fluorobenzoic acid: microwave synthesis of 2‐([4‐¹⁸F]fluorophenyl) benzimidazole