Showing papers on "Radical ion published in 2009"
TL;DR: The calculation in this paper gives a detailed explanation on the experimental findings that have been reported in literatures and clarifies the mechanism on the oxidative decomposition of EC.
Abstract: The electrochemical oxidative stability of solvent molecules used for lithium ion battery, ethylene carbonate (EC), propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate in the forms of simple molecule and coordination with anion PF(6)(-), is compared by using density functional theory at the level of B3LYP/6-311++G (d, p) in gas phase. EC is found to be the most stable against oxidation in its simple molecule. However, due to its highest dielectric constant among all the solvent molecules, EC coordinates with PF(6)(-) most strongly and reaches cathode most easily, resulting in its preferential oxidation on cathode. Detailed oxidative decomposition mechanism of EC is investigated using the same level. Radical cation EC(*+) is generated after one electron oxidation reaction of EC and there are five possible pathways for the decomposition of EC(*+) forming CO(2), CO, and various radical cations. The formation of CO is more difficult than CO(2) during the initial decomposition of EC(*+) due to the high activation energy. The radical cations are reduced and terminated by gaining one electron from anode or solvent molecules, forming aldehyde and oligomers of alkyl carbonates including 2-methyl-1,3-dioxolane, 1,3,6-trioxocan-2-one, 1,4,6,9-tetraoxaspiro[4.4]nonane, and 1,4,6,8,11-pentaoxaspiro[4.6]undecan-7-one. The calculation in this paper gives a detailed explanation on the experimental findings that have been reported in literatures and clarifies the mechanism on the oxidative decomposition of EC.
223 citations
TL;DR: This paper contains the first published data reporting antioxidant capacities of amino- and amidothiols measured by the ABTS method, and suggests that, when ABTS is being used as an end point assay, a longer incubation time may be needed to obtain reliable data.
Abstract: The reaction rates of several aminothiol, amidothiol, and phenolic antioxidants with ABTS radical cation were measured. Most compounds had half-lives of less than one minute. However several compounds had considerably longer half-lives. Aminothiol derivatives lacking a free thiol group, such as amifostine and RibCys, displayed longer half-lives. Reaction of these compounds with the ABTS radical cation displayed first order kinetic behavior. Of the phenolic compounds studied, chlorogenic acid and caffeic acid had the longest half-lives. Most phenolics displayed a biphasic kinetc pattern involving fast and slow steps. Some of the aminothiols also displayed this type of behavior. Glutathione disulfide was reactive toward ABTS radical cation and displayed slow kinetics. This suggests that the slow step observed with some of the aminothiols may be due to initial rapid formation of disulfide followed by slow reaction of the disulfide with ABTS radical cation. Some compounds required a considerably longer incuba...
166 citations
TL;DR: Nanosecond transient absorption methods were used to determine accurate oxidation potentials (E(ox) in acetonitrile for benzene and a number of its alkyl-substituted derivatives, and equilibrium constants for dimerization were determined.
Abstract: Nanosecond transient absorption methods were used to determine accurate oxidation potentials (Eox) in acetonitrile for benzene and a number of its alkyl-substituted derivatives. Eox values were obtained from a combination of equilibrium electron-transfer measurements and electron-transfer kinetics of radical cations produced from pairs of benzene and biphenyl derivatives, with one member of the pair acting as a reference. Using a redox-ladder approach, thermodynamic oxidation potentials were determined for 21 benzene and biphenyl derivatives. Of particular interest, Eox values of 2.48 ± 0.03 and 2.26 ± 0.02 V vs SCE were obtained for benzene and toluene, respectively. Because of a significant increase in solvent stabilization of the radical cations with decreasing alkyl substitution, the difference between ionization and oxidation potentials of benzene is ∼0.5 eV larger than that of hexamethylbenzene. Oxidation potentials of the biphenyl derivatives show an excellent correlation with substituent σ+ values...
127 citations
TL;DR: The present investigation provides a new kind of candidates for the high-performance NLO materials.
Abstract: The interesting radical ion pair salts M2˙+TCNQ˙− (M = Li, Na, K) are a particular class of charge transfer complexes with excess electron. The ground states of these complexes are triplet. The C2v symmetry geometrical structures of the M2˙+TCNQ˙− (M = Li, Na, K) with all-real frequencies are obtained at the density functional theory (DFT) B3LYP/6-31+G(d) level. All calculations of electric properties in this paper have been carried out at the restricted open-shell second order Moller–Plesset perturbation theory (ROMP2) level. Owing to existing excess electron (from the polarized alkali metal atoms) these charge transfer complexes exhibit large nonlinear optical (NLO) responses dominated by excess electron transitions.
For these radical ion pair salts M2˙+TCNQ˙−, the static first hyperpolarizabilities (β0) are large. The order of β0 values is 19 203 (M = Li) < 24 140 (M = Na) < 29 065 a.u. (M = K). Specially, the second hyperpolarizability (γ0) of the complexes with excess electron is obtained for the first time. These static second hyperpolarizabilities are also large. The order of γ0 values is 2 213 006 (M = Li) < 3 136 754 (M = Na) < 7 905 623 a.u. (M = K). Among the three structures, K2˙+TCNQ˙− has the largest γ0 value to be 7.9 × 106 a.u. (3982 × 10−36 esu), which is about 9 times larger than that of the intramolecular charge transfer complex σ-arylvinylidene trans-[Ru(4-CCHC6H4CCC6H4NO2)Cl(dppm)2]PF6 [Hurst et al., Organometallics, 2001, 20, 4664]. The present investigation provides a new kind of candidates for the high-performance NLO materials.
123 citations
TL;DR: The calculated results indicate that PC is initially oxidized on the cathode to a radical cation intermediate, PC(*+), and then decomposes through three pathways, generating carbon dioxide CO(2) and radical cations.
Abstract: The detailed oxidative decomposition mechanism of propylene carbonate (PC) in the lithium ion battery is investigated using density functional theory (DFT) at the level of B3LYP/6-311++G(d), both in the gas phase and in solvent. The calculated results indicate that PC is initially oxidized on the cathode to a radical cation intermediate, PC(*+), and then decomposes through three pathways, generating carbon dioxide CO(2) and radical cations. These radical cations prefer to be reduced on the anode or by gaining one electron from PC, forming propanal, acetone, or relevant radicals. The radicals terminate by forming final products, including trans-2-ethyl-4-methyl-1,3-dioxolane, cis-2-ethyl-4-methyl-1,3-dioxolane, and 2,5-dimethyl-1,4-dioxane. Among all the products, acetone is most easily formed. The calculations in this paper give detailed explanations of the experimental findings that have been reported in the literature and clarify the role of intermediate propylene oxide in PC decomposition. Propylene oxide is one of the important intermediates. As propylene oxide is formed, it isomerizes forming a more stabile product, acetone.
106 citations
TL;DR: This work demonstrates that electron hopping through the pi-stacked PDI molecules is fast enough to compete effectively with charge recombination in these systems, making these materials of interest as photoactive assemblies for artificial photosynthesis and organic photovoltaics.
Abstract: Photochemical electron donor−acceptor triads having an aminopyrene primary donor (APy) and a p-diaminobenzene secondary donor (DAB) attached to either one or both imide nitrogen atoms of a perylene-3,4:9,10-bis(dicarboximide) (PDI) electron acceptor were prepared to give DAB-APy-PDI and DAB-APy-PDI-APy-DAB. In toluene, both triads are monomeric, but in methylcyclohexane, they self-assemble into ordered helical heptamers and hexamers, respectively, in which the PDI molecules are π-stacked in a columnar fashion, as evidenced by small- and wide-angle X-ray scattering. Photoexcitation of these supramolecular assemblies results in rapid formation of DAB+•−PDI−• spin-polarized radical ion pairs having spin−spin dipolar interactions, which show that the average distance between the two radical ions is much larger in the assemblies (31 A) than it is in their monomeric building blocks (23 A). This work demonstrates that electron hopping through the π-stacked PDI molecules is fast enough to compete effectively with...
105 citations
TL;DR: The reaction shows radical and charge effects in the activation of methane by metal-free radical cations by selective, direct attack of the incipient methyl radical at the O atom of the intermediate.
Abstract: A precise jab to methane: The SO(2)(*+) radical cation (see figure) effectively activates CH(4) at room temperature through a [H(3)C(*)...HOSO(+)] methyl intermediate isolated in the gas phase by mass spectrometry. Methanol and ionized methyl hydrogen sulfoxylate, CH(3)OSOH(*+), are formed by selective, direct attack of the incipient methyl radical at the O atom of the intermediate. The reaction shows radical and charge effects in the activation of methane by metal-free radical cations.
102 citations
TL;DR: DFT calculations located five isomers of His*+ with an alpha-radical with a captodative structure at the global minimum in a deep potential well and confirmed that this isomer is the experimentally observed "long-lived" isomer.
Abstract: Amino acid and peptide radical cations, M*+, are formed by oxidative dissociations of [Cu(auxiliary ligand)(M)]*2+ and [Metal(III)(salen)(M)]+ complexes. The most easily formed radicals contain either an aromatic or basic amino acid residue. Aromatic amino acids have low ionization energies, are easily oxidized and delocalize the charge and spin over the ring systems; basic amino acids facilitate formation of alpha-radicals that have captodative structures in which the charge and spin are formally separated, although feeding back some of the charge onto the amide or carboxyl group adjacent to the radical center through hydrogen bonding enriches the electron-withdrawing properties and is highly stabilizing. DFT calculations located five isomers of His*+ with an alpha-radical with a captodative structure at the global minimum in a deep potential well. An IRMPD spectrum confirmed that this isomer is the experimentally observed "long-lived" isomer. When both charge and spin are on the peptide backbone, as in [GGG]*+, captodative structures have the lowest energies; the barriers to interconversion between the three isomeric alpha-radicals of [GGG]*+ are high as the charge impedes migration of a hydrogen atom. Dissociation of [GGG]*+ is charge-driven. In peptide radical cations containing a basic amino acid residue the charge is sequestered on the side chain and the radical center, either on the backbone or on another side chain, initiates the fragmentation.
102 citations
TL;DR: Thermodynamic and kinetic calculations have been used to reinterpret the UV-vis data related to the OH radical oxidation of guanosine and a secondary channel yielding the G8OH adduct was found to contribute to the overall reaction by 12% at least.
97 citations
TL;DR: The present calculation demonstrates that the inclusion of the first hydration shell around the G(*+)-C base pair has an important effect on the internal proton-transfer energetics.
Abstract: Upon one-electron oxidation, all molecules including DNA bases become more acidic in nature. For the GC base pair, experiments suggest that a facile proton transfer takes place in the G•+−C base pair from N1 of G•+ to N3 of cytosine. This intrabase pair proton-transfer reaction has been extensively considered using theoretical methods for the gas phase, and it is predicted that the proton transfer is slightly unfavorable, in disagreement with experiment. In the present study, we consider the effect of the first hydration layer on the proton-transfer reaction in G•+−C by the use of density functional theory (DFT) using B3LYP/6-31+G** calculations of the G•+−C base pair in the presence of 6 and 11 water molecules. Under the influence of hydration of 11 waters, a facile proton transfer from N1 of G•+ to N3 of C is predicted. The zero-point energy (ZPE)-corrected forward and backward energy barriers, for the proton transfer from N1 of G•+ to N3 of C, was found to be 1.4 and 2.6 kcal/mol, respectively. The pro...
94 citations
18 Sep 2009
TL;DR: Theoretical model of radiation-induced DNA damage is described in this article, where Kumar and Sevilla present a model of the reaction path of DNA to direct energy deposition in DNA by ionizing radiation.
Abstract: Preface to Series vii Introduction ix Contributors xi 1. Theoretical Modeling of Radiation-Induced DNA Damage 1 Anil Kumar and Michael D. Sevilla 2. Radical Reaction Pathways Initiated by Direct Energy Deposition in DNA by Ionizing Radiation 41 William A. Bernhard 3. Chemical Reactions of the Radical Cations of Nucleobases in Isolated and Cellular DNA. Formation of Single-Base Lesions 69 Jean Cadet, Thierry Douki, Didier Gasparutto, Jean-Luc Ravanat, and J. Richard Wagner 4. Reactivity of Nucleic Acid Sugar Radicals 99 Chryssostomos Chatgilialoglu 5. Pyrimidine Nucleobase Radical Reactivity 135 Marc M. Greenberg 6. Reactivity of 5-Halopyrimidines in Nucleic Acids 163 Ryu Tashiro and Hiroshi Sugiyama 7. Kinetics of Long-Range Oxidative Electron Transfer Through DNA 191 Kiyohiko Kawai and Tetsuro Majima 8. Radical Intermediates During Reductive Electron Transfer Through DNA 211 Reji Varghese and Hans-Achim Wagenknecht 9. Low-Energy Electron Interaction with DNA: Bond Dissociation and Formation of Transient Anions, Radicals, and Radical Anions 239 Leon Sanche 10. Electronic-Affinic Radiosensitizers 295 Peter Wardman 11. Reactions of Reactive Nitrogen Species and Carbonate Radical Anions with DNA 325 Vladimir Shafirovich, Conor Crean, and Nicholas E. Geacintov 12. Principles and Applications of Electrochemical Oxidation of Nucleic Acids 357 H. Holden Thorp and Julie M. Sullivan 13. DNA Damage Due to Diradical-Generating Cyclizations 389 Sean M. Kerwin 14. DNA Damage by Phenoxyl Radicals 421 Richard A. Manderville Index 445
TL;DR: It appears that secondary chemistry in the ionized ILs may be dominated by radical ion reactions, similarly to the previously studied conventional organic liquids, depending on the composition of the IL.
Abstract: Room-temperature ionic liquids (ILs) are a promising class of solvents for applications ranging from photovoltaics to solvent extractions. Some of these applications involve the exposure of the ILs to ionizing radiation, which stimulates interest in their radiation and photo- chemistry. In the case of ILs consisting of 1,3-dialkylimidazolium cations and hydrophobic anions, ionization, charge transfer and redox reactions yield charge-trapped species thought to be radicals resulting from neutralization of the constituent ions. Using computational chemistry methods and the recent results on electron spin resonance (ESR) and transient absorption spectroscopy of the ionized ILs, we argue that electron localization in the imidazolium ILs yields a gauche dimer radical cation with the elongated C(2)−C(2) bond. This species is shown to absorb in the near-infrared and the visible regions and accounts for the observed ESR spectra. We suggest that the excess electron in these aromatic ILs is localized as such a dimer...
TL;DR: A highly efficient charge separation system, D-Pt-A, where D (triphenylamine) and A (naphthalenediimide) are bonded to the Pt moiety through highly twisted phenylene ethynylene linkages is reported.
Abstract: We report a highly efficient charge separation system, D-Pt-A, where D (triphenylamine) and A (naphthalenediimide) are bonded to the Pt moiety through highly twisted phenylene ethynylene linkages. The quantum yields for the formation of the charge-separated state were determined to be nearly unity. The lifetimes of D(+)-Pt-A(-) were approximately 1 micros at room temperature and much longer at low temperature. The spin-correlated radical ion pair was directly observed by means of time-resolved EPR spectroscopy.
TL;DR: In this article, a review of recent studies examining the intramolecular coupling of radical cations derived from enol ethers, vinyl sulfides, and ketene acetals with carbon, oxygen, and nitrogen trapping groups is discussed.
Abstract: Anodic electrochemistry is a powerful tool for generating radical cation intermediates and initiating new cyclization reactions. Like most electrochemical reactions, the transformations involve umpolungs. In this review, recent studies examining the intramolecular coupling of radical cations derived from enol ethers, vinyl sulfides, and ketene acetals with carbon, oxygen, and nitrogen trapping groups are discussed to highlight their synthetic potential. 1 Introduction and Background 2 Arteannuins: A Backdrop for Discovery 3 A Detour: Ketene Acetals as Anodic Olefin Coupling Partners 4 Continuing the Detour: Ineleganolide and a Revised Working Model 5 Extending the Model: Nitrogen Trapping Groups 6 Back to Arteannuins: Completing the Ring Skeleton 7 Lactone Targets and a Couple of Final Points 8 Conclusions.
TL;DR: Transient absorbance analyses of CP24 and CP26 complexes that bind lutein and zeaxanthin in the L1 and L2 domains are reported, suggesting the presence of two charge transfer quenching sites in CP26 involving zexanthin radical cation and luteIn radicalcation species.
TL;DR: It is shown that the symmetry break between the electronic structures in the electronic ground state and in the radical cation state is an intrinsic property of the special pair supermolecule, which is particularly attributable to a modification of the structure of PL.
Abstract: Composed of the two bacteriochlorophyll cofactors, PL and PM, the special pair functions as the primary electron donor in bacterial reaction centers of purple bacteria of Rhodobacter sphaeroides. Under light absorption, an electron is transferred to a bacteriopheophytin and a radical pair is produced. The occurrence of the radical pair is linked to the production of enhanced nuclear polarization called photochemically induced dynamic nuclear polarization (photo-CIDNP). This effect can be used to study the electronic structure of the special pair at atomic resolution by detection of the strongly enhanced nuclear polarization with laser-flash photo-CIDNP magic-angle spinning NMR on the carotenoid-less mutant R26. In the electronic ground state, PL is strongly disturbed, carrying a slightly negative charge. In the radical cation state, the ratio of total electron spin densities between PL and PM is 2:1, although it is 2.5:1 for the pyrrole carbons, 2.2:1 for all porphyrinic carbons, and 4:1 for the pyrrole nitrogen. It is shown that the symmetry break between the electronic structures in the electronic ground state and in the radical cation state is an intrinsic property of the special pair supermolecule, which is particularly attributable to a modification of the structure of PL. The significant difference in electron density distribution between the ground and radical cation states is explained by an electric polarization effect of the nearby histidine.
TL;DR: Two different methods for generating protonated S-nitrosocysteine in the gas phase are described and NO loss is found to be the lowest energy channel for the former ion.
TL;DR: Highly conducting molecular metals with unusual oxidation states (+1, +5/3 and neutral) have been developed on the basis of 2,5-bis( 1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene (BDT-TTP) derivatives and analogous metal derivatives M(dt)2 (M = Ni, Au).
28 Sep 2009
TL;DR: Radical and Radical Ion Reactivity in Nucleic acid chemistry as mentioned in this paper provides the only comprehensive review of the chemistry and biochemistry of nucleic acid radical intermediates with contributions by world leaders in the field.
Abstract: [Book summary] The chemistry and biochemistry of reactive intermediates is central to organic chemistry and biochemistry, and underlies a significant portion of modern synthetic chemistry. Radical and Radical Ion Reactivity in Nucleic Acid Chemistry provides the only comprehensive review of the chemistry and biochemistry of nucleic acid radical intermediates. With contributions by world leaders in the field, the text covers a broad range of topics, including:
• A discussion of the relevant theory
• Ionization of DNA
• Nucleic acid sugar radicals
• Halopyrimidines
• Oxidative, reductive, and low energy electron transfer
• Electron affinity sensitizers
• Photochemical generative of reactive oxygen species
• Reactive nitrogen species
• Enediyne rearrangements
• Phenoxyl radicals
A unique compilation on the cutting edge of our understanding, Radical and Radical Ion Reactivity in Nucleic Acid Chemistry provides an unparalleled resource to student and professional researchers in such fields as organic chemistry, biochemistry, molecular biology, and physical chemistry, as well as the industries associated with these disciplines.
TL;DR: In this paper, the role of transient species in photo-oxidation of poly[2-methoxy-5-(3′,7′-dimethyl octyloxy)-1,4-phenylenevinylene] (MDMO-PPV) was investigated by a combination of quenching and sensitization experiments.
Abstract: Because oxygen cannot be fully eliminated from organic solar cells, the occurrence of oxidative photo-degradation of the device in operating conditions has to be considered. Polyphenylene-vinylene-based photovoltaic devices have a short lifetime that currently limits their applications. In this article, we focus on various transient species that are potentially involved in the initiation step of the photo-oxidation of poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV). The role of the transient species was investigated by a combination of quenching and sensitization experiments. Complementary information was obtained by transient absorption spectroscopy. Results evidenced the fact that 1O2 was not the principal reactive intermediate involved in the photo-oxidation of MDMO-PPV. This result was in contradiction with previous reports. It was shown that the MDMO-PPV•+ radical cation was generated after excitation. The presence of oxygen and the photo-aging favored the formation of the radical cation, suggesting that oxygen and photoproducts act as electron acceptors. The charged radicals formed are likely to evolve and give radicals that initiate the oxidation of the polymer by abstraction of the labile hydrogen in α position of the ether function and by addition on the double bonds. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6044–6052, 2009
TL;DR: Oxidation of the radical leads to a triphosphaallyl cation, which is only stable at low temperatures in solution, whereas the stable triphoselytic anion is formed by reduction.
Abstract: Radically complex: The photolytic reaction of [Cp*P{W(CO)(5)}(2)] (Cp* = C(5)Me(5)) with a diphosphene produces, via a radical intermediate, an air-stable complexed triphosphaallyl radical, in which the unpaired electron is evenly distributed over both terminal P atoms. Oxidation of the radical leads to a triphosphaallyl cation, which is only stable at low temperatures in solution, whereas the stable triphosphaallyl anion is formed by reduction (see picture, Mes* = 2,4,6-tri-tert-butylphenyl).
TL;DR: In this paper, the relationship between the polarization of the radical cation and the chemoselectivity of the reaction probed was examined and a new approach to the synthesis of quaternary carbons was uncovered and the compatibility of ene diol ethers with anodic olefin coupling reactions examined.
TL;DR: In this paper, the early events in the triplet 4-carboxybenzophenone (CB)-induced oxidation of N-acetyl-methionine methyl ester (N-Ac-Met-OCH3) are investigated in aqueous solution.
Abstract: The early events in the triplet 4-carboxybenzophenone (CB)-induced oxidation of N-acetyl-methionine methyl ester (N-Ac-Met-OCH3) are investigated in aqueous solution. Upon electron transfer from the methionine residue of N-Ac-Met-OCH3 to 3CB*, the resulting sulfur radical cation undergoes further reactions: (1) back electron transfer, (2) escape of the radical ions from the solvent cage, or (3) proton transfer and escape of the radicals. The yields and paths of these reactions are shown to depend strongly on the pH of the solution, and, similar to the previously reported results for dipeptides (Met-Gly and Gly-Met), on the structural nature of the methionine substituents. In the experiments performed in this work, low quencher concentrations were used to avoid formation of intermolecular transients (e.g., dimeric sulfur-centered radical cation (S∴S)+). Under these experimental conditions, the one-electron oxidized sulfur does not seem to become stabilized in an (S∴N)+ three-electron bonded intramolecular complex. The proposed mechanism is further supported by the stable products analysis. A detailed mechanism involving characterization of the transients is discussed and compared to that of methionine and methionine-containing dipeptides (Met-Gly and Gly-Met). Moreover, a newly installed transient absorption laser system is described in details.
TL;DR: In this article, the relationship between the NMR chemical shifts and the electronic structures of one-electron oxidized products of iron(III) porphyrins such as iron(3) radical cations or iron(4) polymorphic porphynins was discussed.
TL;DR: Odd-electron a+1 radical ions generated in the 157 nm photodissociation of peptide ions were investigated in an ion trap mass spectrometer and thermal fragments appear to be directed by the radical and they strongly depend on the amino acid side-chain structure.
TL;DR: In this article, the peak oxidation potentials of a series of polysubstituted triphenylamines were found to be highly linearly correlated with their ionization potentials as computed by density functional theory.
TL;DR: The first demonstration of a ferrimagnet is reported by utilizing a large-J(intra) system, nitronyl nitroxide-substituted dihydrophenazine radical cation in combination with tetrabromoferrate (FeBr(4)(-)) as the counteranion.
Abstract: Radical-substituted radical cations are attractive spin building blocks of molecule-based magnets. The introduction of an additional spin as a counteranion provides a unique three-spin system wherein the magnetic interactions between the spins of the radical substituent and the radical cation (Jintra) and those between the spins of the radical cation and the anion (Jinter) play decisive roles in determining the magnetic properties of the system. We report the first demonstration of a ferrimagnet by utilizing a large-Jintra system, nitronyl nitroxide-substituted dihydrophenazine radical cation (NNDPP•+) in combination with tetrabromoferrate (FeBr4−) as the counteranion. On the basis of measurements of dc and ac magnetic susceptibilities and heat capacity, the magnetic properties of NNDPP•+·FeBr4− are elucidated to be those of a three-dimensional long-range-ordered ferrimagnet with Tc = 6.7 K.