Theoretical Analysis of Heteroaromatic Thioaminyl Radicals. Part 2: A Comparison of Ab Initio and Density Functional Methods in the Description of Redox Processes

Kaszyński, Piotr

doi:10.1021/jp0109574

Cited by 47 publications

(34 citation statements)

References 28 publications

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“…However, since Gomberg's synthesis of triphenylmethyl (trityl) radical in 1900, numerous families of persistent and stable radicals have been identified and have been the subject of reviews and books [18,20,66,67]. In general, radical stability arises from steric protection of the radical center, via the addition of bulky substituents, and/or delocalization of the unpaired electron throughout the molecular structure [20,[70][71][72][73][74][75]. Prominent and promising classes of stable organic radicals for energy storage include nitroxides [50,67,76,77], phenoxyls [13,20,[51][52][53][78][79][80][81], and verdazyls [54,82].…”

Section: Organic Radicalsmentioning

confidence: 99%

Engineering radical polymer electrodes for electrochemical energy storage

Nevers

Brushett

Wheeler

2017

Journal of Power Sources

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In principle a wide range of organic materials can store energy in the form of reversible redox conversions of stable radicals. Such chemistry holds great promise for energy storage applications due to high theoretical capacities, high rate capabilities, intrinsic structural tunability, and the possibility of low-cost "green" syntheses from renewable sources. There have been steady improvements in the design of organic radical polymers, in which radicals are incorporated into the backbone and/or as pendant groups. This review highlights opportunities for improved redox molecule and polymer design along with the key challenges (e.g., transport phenomena, solubility, and reaction mechanisms) to transitioning known organic radicals into high-performance electrodes. Ultimately, organic-based batteries are still a nascent field with many open questions. Further advances in molecular design, electrode engineering, and device architecture will be required for these systems to reach their full potential and meet the diverse and increasing demands for energy storage.

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Section: Organic Radicalsmentioning

confidence: 99%

Engineering radical polymer electrodes for electrochemical energy storage

Nevers

Brushett

Wheeler

2017

Journal of Power Sources

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“…The standard free-energy change ΔG ○ (aq) for FH − + H + → FH 2 was computed as −2, −4, and 4 kcal/mol using M06-L/SM6, B3LYP/ SM6, and SCC-DFTB/CHARMM, respectively. The pK a can be calculated from ΔG ○ (aq) using eq 18 (18) The pK a obtained for the N1 proton of lumiflavin hydroquinone using the three methods is 1.5 with M06-L/SM6, 3 with B3LYP/SM6, and −3 with SCC-DFTB/CHARMM.…”

Section: Lumiflavin In Aqueous Solutionmentioning

confidence: 99%

Combined Quantum Mechanical and Molecular Mechanical Simulations of One- and Two-Electron Reduction Potentials of Flavin Cofactor in Water, Medium-Chain Acyl-CoA Dehydrogenase, and Cholesterol Oxidase

et al. 2007

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Flavin adenine dinucleotide (FAD) is a common cofactor in redox proteins, and its reduction potentials are controlled by the protein environment. This regulation is mainly responsible for the versatile catalytic functions of flavoenzymes. In this article, we report computations of the reduction potentials of FAD in medium-chain acyl-CoA dehydrogenase (MCAD) and cholesterol oxidase (CHOX). In addition, the reduction potentials of lumiflavin in aqueous solution have also been computed. Using molecular dynamics and free-energy perturbation techniques, we obtained the free-energy changes for two-electron/two-proton as well as one-electron/one-proton addition steps. We employed a combined quantum mechanical and molecular mechanical (QM/MM) potential, in which the flavin ring was represented by the self-consistent-charge density functional tight-binding (SCC-DFTB) method, while the rest of the enzyme-solvent system was treated by classical force fields. The computed two-electron/two-proton reduction potentials for lumiflavin and the two enzyme-bound FADs are in reasonable agreement with experimental data. The calculations also yielded the pKa values for the one-electron reduced semiquinone (FH*) and the fully reduced hydroquinone (FH2) forms. The pKa of the FAD semiquinone in CHOX was found to be around 4, which is 4 units lower than that in the enzyme-free state and 2 units lower than that in MCAD; this supports the notion that oxidases have a greater ability than dehydrogenases to stabilize anionic semiquinones. In MCAD, the flavin ring interacts with four hydrophobic residues and has a significantly bent structure, even in the oxidized state. The present study shows that this bending of the flavin imparts a significant destabilization (approximately 5 kcal/mol) to the oxidized state. The reduction potential of lumiflavin was also computed using DFT (M06-L and B3LYP functionals with 6-31+G(d,p) basis set) with the SM6 continuum solvation model, and the results are in good agreement with results from explicit free-energy simulations, which supports the conclusion that the SCC-DFTB/MM computation is reasonably accurate for both 1e(-)/1H+ and 2e(-)/2H+ reduction processes. These results suggest that the first coupled electron-proton addition is stepwise for both the free and the two enzyme-bound flavins. In contrast, the second coupled electron-proton addition is also stepwise for the free flavin but is likely to be concerted when the flavin is bound to either the dehydrogenase or the oxidase enzyme.

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“…13 To overcome these as far as possible, several comprehensive molecular studies have been carried out. [16][17][18][19][20][21][22][23] Generally, two pathways for free radical scavenging reactions promoted by ArOH compounds have been considered (Scheme 1), which were summarized by Zhang et al 6 and Wright et al 16 and references therein: (i) the H-atom transfer mechanism; and (ii) the proton concerted electron-transfer mechanism. Concerning the Scheme 1.…”

Section: Introductionmentioning

confidence: 99%

Antioxidant activity of phenolic and related compounds: a density functional theory study on the O–H bond dissociation enthalpy

Giacomelli¹,

Miranda²,

Gonçalves³

et al. 2004

Redox Report

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We report here on calculations at the hybrid DFT/HF (B3-LYP/6-31G(d, p)) level of the O-H bond dissociation enthalpy (O-H BDE) of phenylpropenoic acids (caffeic, ferulic, p-coumaric and cinnamic) and phenolic acids and related compounds (gallic, methylgallate, vanillic and gentisic) in order to gain insight into the understanding of structure-antioxidant activity relationships. The results were correlated and discussed mainly on the basis of experimental data in a companion work (Galato D, Giacomelli C, Ckless K, Susin MF, Vale RMR, Spinelli A. Antioxidant capacity of phenolic and related compounds: correlation among electrochemical, visible spectroscopy methods and structure-antioxidant activity. Redox Report 2001; 6: 243-250). The O-H BDE values showed remarkable dependence on the hydroxyl position in the benzene ring and the existence of additional interaction due to hydrogen bonding. For parent molecules, the experimental antioxidant activity (AA) order was properly obeyed only when intramolecular hydrogen bonding was present in the radicalized structures of o-dihydroxyl moieties. In structurally related compounds, excellent correlation with experimental data was in general observed (0.64 < rho < 0.99). However, it is shown that excellent correlation can also be obtained for this series of compounds considering p-radicalized structures which were not stabilized by intramolecular hydrogen bonding, but this had no physical meaning. These findings suggested that the antioxidant activity evaluation of phenolic and related compounds must take into consideration the characteristics of each particular compound.

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Theoretical Analysis of Heteroaromatic Thioaminyl Radicals. Part 2: A Comparison of Ab Initio and Density Functional Methods in the Description of Redox Processes

Cited by 47 publications

References 28 publications

Engineering radical polymer electrodes for electrochemical energy storage

Engineering radical polymer electrodes for electrochemical energy storage

Combined Quantum Mechanical and Molecular Mechanical Simulations of One- and Two-Electron Reduction Potentials of Flavin Cofactor in Water, Medium-Chain Acyl-CoA Dehydrogenase, and Cholesterol Oxidase

Antioxidant activity of phenolic and related compounds: a density functional theory study on the O–H bond dissociation enthalpy

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