Radical Ion Reactions Research Articles

Novel Way to Harness Solar Energy: Photo-Redox Catalysis in Organic Synthesis

Visible light-mediated photo-redox catalysis has evolved as one of the exponentially growing fields in organic synthesis. The development of visible light-promoted photocatalytic reactions, which enable rapid and efficient synthesis of fine chemicals, is highly desirable from the viewpoint of cost, safety, availability, and environmental friendliness. The present review highlights the renaissance of interest in synthetic applications of photo-redox reactions. This powerful, enabling technology has led in the development of a remarkably diverse range of organic free radical and radical ion reactions, which have remarkable impact in the field of organic synthesis, materials science and pharmaceutical chemistry.

Kinetics studies and mechanistic considerations on the reactions of superoxide radical ions with dissolved organic matter

Superoxide ion (O2•−) is one of the short lived reactive oxygen species (ROS) formed in aquatic environments. The reactions of O2•− with the model dissolved organic matter (DOM) were studied using a chemiluminescent analysis method under relevant environmental conditions. The reaction of O2•− with DOM produced reduced DOM (DOM•−) by fast one-electron-transfer in the initial stage. This process resulted an initial “loss” in the O2•− decay kinetics. DOM•− is unstable which will continue react with O2•− generating H2O2 to complete a catalytic dismutation cycle. Based on analyzing the observed pseudo-first order O2•− decay rates (kpseudo), the quasi-steady-state concentration of DOM•− is found to be equal to the initial loss of O2•−. Thus, the rate constant for DOM•− with HO2•/O2•− is derived to be (1.1–1.9) × 106 M−1 s−1 in the temperature range of 7.8–41.4 °C. Meanwhile, the apparent rate constant for DOM with O2•− in a flow cell during a short time (2.25 s) is measured as (1.5–3.3) × 103 MC−1 s−1 in the temperature range of 8.2–38.6 °C. These temperature dependent O2•− reaction rate constants present an apparent activation energy of (19.6 ± 2.9) kJ molC−1 for DOM, while that of DOM•− (12.5 ± 3.5 kJ mol−1) is lower. For the pseudo-first order decay rate of O2•−, the catalyzed-dismutation by metal components ranges from 13 to 23%; the contribution by aromatic ketones of DOM is estimated to be 10–13% by using NaBH4 reduction method. The residual contribution might mainly occur at the quinone-like groups, which contributed 64%–77% to the total dismutation. The pH effects on the apparent catalytic rate constants dominate the reaction of O2•− with DOM. The present work suggests that DOM is an important sink for O2•− in aquatic environments. Furthermore, we proposed that the reaction of O2•− with DOM could be a potential source of DOM•− in natural water.

Magnetosensitivity of bacteria E. coli: Magnetic isotope and magnetic field effects.

The biological effects of a 25 Mg nuclear spin and weak magnetic fields have been found and studied by using bacterial cells of Escherichia coli (E. coli) grown on standard M9 nutrient media with different isotopes of magnesium: 24 Mg, 25 Mg, 26 Mg, and a natural mixture of Mg isotopes. Among these isotopes only 25 Mg has a nuclear spin I = 5/2 and nuclear magnetic moment which have been known to affect enzymatic processes in vitro due to hyperfine interactions with uncoupled electrons of substrates. Other non-magnetic magnesium isotopes, 24 Mg and 26 Mg, have neither a nuclear spin (I = 0) nor a nuclear magnetic moment. Bacterial cells grown on 25 Mg-media and enriched with this isotope manifest a higher growth rate and colony-forming units (CFU) compared with cells grown on media containing nonmagnetic 24 Mg and 26 Mg isotopes. Magnetic field dependencies of CFU cells enriched with different magnesium isotopes have been obtained. The observed isotope-dependent differences are explained by intracellular enzymatic ion-radical reactions which are magnetic field and nuclear spin sensitive. Enzymatic synthesis of ATP is considered as the most probable magnetosensitive biochemical process in vivo as far as effectiveness of ATP production is concerned; it determines the viability of cells and was shown in vitro as a nuclear spin-dependent reaction. Bioelectromagnetics. 38:581-591, 2017. © 2017 Wiley Periodicals, Inc.

Degradation of Amaranth Dye Using Zero Valent Iron Nanoparticles: Optimal Conditions and Mechanism

Abstract Reductive and oxidative degradation of amaranth dye using zero valent iron nanoparticles (ZVINP) has been investigated. Effect of various reaction parameters such as the iron dosage, stirring speed, and influence of pH were studied, and an optimum condition deduced. The ideal operational conditions were 1.5–2.5 g/L of ZVINP, 15–30 min of reaction time, stirring speed of 150–200 rpm and pH of 3–9 for an initial dye concentration of 50–70 mg/L. Different mechanisms are suggested for the reactions at lower and higher pHs. At low pH, direct reduction followed by protonation and Fenton reaction is responsible for decoloration and degradation. But at higher pH, in addition to reduction, reactions of superoxide radical and ferryl ions also play a role in the degradation and decoloration. On the other hand, there is no contribution from Fenton reaction at higher pH. With these optimized conditions when applied to a coir factory effluent, a complete decolorization and 34% total organic carbon (TOC) reduct...

Exploiting time-resolved magnetic field effects for determining radical ion reaction rates

The capabilities of the method of time-resolved magnetic field effect in determining the rates of charge transfer reactions between radical ions and molecules on a nanosecond time scale have been investigated. The approach relies on the electron spin coherence in radical pair’s partners generated by ionizing radiation. The spin evolution of the pair is sensitive to the reaction since the latter results in changing magnetic interactions of the unpaired electron. This process can be monitored by magnetic-field-sensitive fluorescence from an irradiated sample that is illustrated using reactions involving alkane radical cations. The accuracy and limitations of the approach are discussed.

Visible light photoredox-controlled reactions of N-radicals and radical ions

Radicals are an important class of versatile and highly reactive species. Compared with the wide applications of various C-centred radicals, however, the N-radical species including N-centred radicals and radical ions remain largely unexplored due to the lack of convenient methods for their generation. In recent years, visible light photoredox catalysis has emerged as a powerful platform for the generation of various N-radical species and methodology development towards the synthesis of diverse N-containing compounds. In this tutorial review, we highlight recent advances in this rapidly developing area with particular emphases put on the working models and new reaction design.

Reaction of N-acetyl- and N-[1-(arylsulfonylimino)ethyl]-1,4-benzoquinone imines with sodium arenesulfinates

N-Acetyl- and N-[1-(arylsulfonylimino)ethyl]-1,4-benzoquinone imines having no substituent in the 2- and/or 6-position of the quinoid ring react with sodium arenesulfinates preferentially according to the 1,4-addition pattern. The presence of an ArSO2N group favors radical ion reaction with formation of 1,6-addition products.

Spin states of multielectron systems and the action of multi-spin bans

Magnetic and spin effects in chemical reactions are caused by the effect of spin bans, which con� trol the elementary acts of radical and ion-radical reactions involving, as a rule, two paramagnetic particles. Any description of spin bans acting in chemical and enzymatic reactions, which is accompanied by transfer of several electrons, as well as in the reactions of high spin molecules, requires knowledge of spin states. It is shown that spin states of multielectron states should be described by a spin density matrix; rules for their construction are given and their properties are described. As a first step, the construction of fourdensity matrix is described in detail. The application of fourand threespin density matrixes is shown for analyzing the formation of superoxide anion in respiratory chains of mitochondria.

Reaction mechanisms: radical and radical ion reactions

Radical reactions endear themselves to organic chemists due to their ability to mediate otherwise difficult transformations (e.g. functionalization of unactivated hydrocarbons), and the associated challenges with predicting and/or controlling their reactivity. This manuscript provides an overview of the most significant developments in organic radical chemistry in 2012, with particular attention paid to the mechanistic attributes identified in these contributions. It is loosely structured to provide the broadest possible coverage, and is organized in sections highlighting (1) radical reactions that are either initiated or mediated by transition metals, (2) reactions not involving any transition metals, and (3) reactions of biological molecules or models thereof that provide insight on the roles of organic radicals in biological processes.

ChemInform Abstract: Radical Cation/Anion and Neutral Radicals: A Comparison

AbstractReview: 120 refs.

Determination of lipoic acid, Trolox methyl ether and tocopherols in human plasma by liquid‐chromatography and ion‐trap tandem mass spectrometry

A method for the simultaneous determination of lipoic acid and/or Trolox methyl ether, along with α-, γ- and δ-tocopherol was developed using liquid chromatography-tandem mass spectrometry with negative electrospray ionization (HPLC-ESI-MS/MS) in an ion-trap mass spectrometer. Detection and quantification were accomplished by a multiple reaction monitoring method, using specific transitions from precursor ion to product ion for each analyte. Chromatographic separation was achieved in a 12 min run using a C(18) -bonded phase and methanol-aqueous ammonium acetate elution gradient. Linear correlations of the chromatographic peak area (r.u. × s(-1) ) to the injected amount (ng) gave the slope values (r.u. × s(-1) × ng(-1) ) 2.34 × 10(4) for α-tocopherol, 5.05 × 10(4) for γ-tocopherol, 1.27 × 10(5) for δ-tocopherol, 8.86 × 10(5) for lipoic acid and 1.23 × 10(5) for Trolox methyl ether. The lower limit of quantification ranged between 0.02 and 1.22 ng for Trolox methyl ether and lipoic acid. MS(3) experiments of γ- and δ-tocopherol suggest ion-radical reactions and dependence of the tocopherol fragmentation pattern on the phenolic ring methylation degree. The method is shown to be applicable to measurement of these metabolites in human serum after extraction.

Reaction mechanisms: radical and radical ion reactions

Radicals and radical ions are involved as intermediates in numerous chemical processes that range from synthesis to reactions in biological systems. Knowledge of the mechanisms by which these different reactions proceed is therefore not only of fundamental importance for the development of new synthetic procedures, but is also crucial for the understanding of, for example, adverse effects of radical induced damage on human health. In the first part an overview on recent developments in synthetic radical chemistry will be given with special emphasis on oxidative and reductive processes under metal and metal-free conditions. Advances in the mechanistic understanding of radical reactions in biological systems will be described in the second part.

ChemInform Abstract: Reaction Mechanisms. Part 1. Radical and Radical Ion Reactions

AbstractReview: 87 refs.

Reaction mechanisms: radical and radical ion reactions

In this chapter the major advances in the chemistry of radicals and radical ions reported in 2010 will be presented from a mechanistic point of view. In the first part recent developments in the area of synthetic methodology, ranging from hydrogen atom transfer, oxidative and reductive processes as well as rearrangement and tandem reactions will be outlined. Advances in the understanding of the role of radicals and radical ions in biological systems will be described in the second part of this report.

ChemInform Abstract: Photoinduced Electron Transfer (PET) in Organic Synthesis

PET processes between ground and excited states of donor-acceptor pairs lead to the formation of radical ion pairs which upon disproportionation gives neutral radicals and/or ions required for synthetic purposes. A host of new reactions has been uncovered, the nature of which is governed by the chemical properties and reactivity profiles of these reactive intermediates. Our objective in this chapter will be to enlist critical examples from the last ten years dealing with the radical ion reactions of synthetic importance initiated by photoexcitation of donor-acceptor pairs.

ChemInform Abstract: Radical Ion Reactions of Carbanions Derived from 4-Nitro-, 2,4-Dinitro-, and 2,4,6-Trinitrotoluenes with Polynitroalkanes.

ChemInform Abstract: Radical Ion Reactions of Carbanions Derived from 4-Nitro-, 2,4-Dinitro-, and 2,4,6-Trinitrotoluenes with Polynitroalkanes.

Reaction mechanisms : Part (i) Radical and radical ion reactions

This chapter examines, from a mechanistic perspective, the major advances in the area of radical and radical ion chemistry reported in 2009. Fundamental classes of radical/radical ion processes are presented (substitution and atom transfer, addition, and fragmentation). The creative design and implementation of multistep (cascading) radical processes in organic synthesis provides new tools for the preparation compounds of incredible structural diversity, and this chapter concludes with some recent examples.

ChemInform Abstract: Reaction Mechanisms. Part 1. Radical and Radical Ion Reactions

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Charge Trapping in Imidazolium Ionic Liquids

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 dimeric ion, and consider the chemical implications of this attribution. We also suggest that three-electron N-N bonding with the formation of a dimer radical anion occurs for amide anions, such as dicyanamide, when the parent anion traps holes; steric hindrance prevents the analogous reaction for bis(triflyl)amide anion. For another anion of practical importance, bis(oxalato)borate, a pathway involving the elimination of CO(2) is suggested. Together, these results indicate the unanticipated tendency of the ILs to localize primary charges as radical ions as opposed to neutral radicals. Thus, 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.

Reaction mechanisms : Part (i) Radical and radical ion reactions

Reaction mechanisms : Part (i) Radical and radical ion reactions