Electron Transfer Reagents Research Articles

Activation of Intact Electron-Transfer Products of Polypeptides and Proteins in Cation Transmission Mode Ion/Ion Reactions

Cationic peptide electron-transfer products that do not fragment spontaneously are exposed to ion trap collisional activation immediately upon formation while they pass through a high-pressure collision cell (Q2), where the electron-transfer reagent anions are stored. Radial ion acceleration, which is normal to the ion flow, is implemented by applying an auxiliary dipolar alternating current to a pair of opposing rods of the Q2 quadrupole array at a frequency in resonance with the surviving electron-transfer products. Collisional cooling of cations in the pressurized Q2 ensures efficient overlap of the positive and negative ions for ion/ion reactions and also gives rise to relatively long residence times (milliseconds) for ions in Q2, making it possible to fragment ions via radial excitation during their axial transmission. The radial activation for transmission mode electron-transfer ion/ion reactions has been demonstrated with a doubly protonated tryptic peptide, a triply protonated phosphopeptide, and [M + 7H]7+ ions of ubiquitin. In all cases, significant increases in fragment ion yields and structural information from electron-transfer dissociation (ETD) were observed, suggesting the utility of this method for improving transmission mode ETD performance for relatively low charge states of peptides and proteins.

New Modes of Reactivity in the Threshold of the Reduction Potential in Solution. Alkylation of Lithium PAH (Polycyclic Aromatic Hydrocarbon) Dianions by Primary Fluoroalkanes: A Reaction Pathway Complementing the Classical Birch Reductive Alkylation

Some of the most highly reduced organic species in solution, such as the dianions of PAHs (polycyclic aromatic hydrocarbons) display unexpected reactivity patterns when they react with an appropriate counterpart. As seen before in their reaction with propene and other alkenes, PAHs(-2) apparently react with fluoroalkanes in a nucleophilic fashion in spite of being generally regarded as powerful electron-transfer reagents in their reactions with haloalkanes. This methodology complements the current methodologies on reductive alkylation of polycyclic arenes by allowing access to a new set of regioisomers, the regiochemistry of which can be easily predicted by simple MO calculations.

Effects of Cation Charge-Site Identity and Position on Electron-Transfer Dissociation of Polypeptide Cations

The effect of cation charge site on gas-phase ion/ion reactions between multiply protonated model peptides and singly charged anions has been examined. Insights are drawn from the quantitative examination of the product partitioning into competing channels, such as proton transfer (PT) versus electron transfer (ET), electron transfer followed by dissociation (ETD) versus electron transfer without dissociation (ET, no D), and fragmentation of backbone bonds versus fragmentation of side chains. Peptide cations containing protonated lysine, arginine, and histidine showed similar degrees of electron transfer, which were much higher than the peptide having fixed-charge sites, that is, trimethyl ammonium groups. Among the four types of cation charge sites, protonated histidine showed the highest degree of ET, no D, while no apparent intact electron-transfer products were observed for peptides with protonated lysine or arginine. All cation types showed side chain losses with arginine yielding the greatest fraction and lysine the smallest. The above trends were observed for each electron-transfer reagent. However, proton transfer was consistently higher with 1,3-dinitrobeznene anions, as was the fraction of side-chain losses. The partitioning of products among the various electron-transfer channels provides evidence for several of the mechanisms that have been proposed to account for electron-transfer dissociation and electron-capture dissociation. The simplest picture to account for all of the observations recognizes that several mechanisms can contribute to the observed products. Furthermore, the identity of the anionic reagent and the positions of the charge sites can affect the relative contributions of the competing mechanisms.

Photon enhanced aggregation of single walled carbon nanotube dispersions

The authors describe a photon enhanced aggregation of dispersed single walled carbon nanotubes in the presence of electron transfer reagents. A recently synthesized metallodendrimer strongly and specifically binds to the ends of the nanotubes. Upon optical excitation, of the metal to ligand charge transfer absorption, of various ruthenium complexes, the nanotubes rapidly coagulate. The electron transfer mechanism is consistent with observed photon enhancement process. These results support a directed self-assembly paradigm for nanostructured materials.

Fischer Carbene Complexes: Beautiful Playgrounds to Study Single Electron Transfer (SET) 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, please click on HTML or PDF.

Ytterbium(II) Complex Bearing a Diaminobis(phenolate) Ligand: Synthesis, Structure, and One-Electron-Transfer and ε-Caprolactone Polymerization Reactions

The first divalent ytterbium complex supported by a diaminobis(phenolate) ligand, YbL(THF)2.0.5C7H8 (1; THF = tetrahydrofuran), was synthesized in good yield by the amine elimination reaction of Yb[N(SiMe3)2]2(THF)2 with H2L (L = [Me2NCH2CH2N(CH2-2-OC6H2-3,5-But2)2]) in a 1:1 molar ratio. X-ray structural determination shows complex 1 to be a THF-solvated monomer, which adopts a distorted octahedral coordination geometry around the Yb atom. Complex 1 can react with PhNCO and PhCCH, as a single electron-transfer reagent, to give the corresponding reduction coupling product [(YbLOCNPh)(THF)]2.4THF (2) and the alkynide complex YbLCCPh(DME) (3; DME = 1,2-dimethoxyethane). Complexes 2 and 3 have been characterized by X-ray crystal structural analysis. In complex 2, the dianionic oxamide ligand resulting from the reductive coupling of two phenyl isocyanate molecules coordinates to two Yb atoms in a mu,eta4 fashion. Complex 3 has a monomeric structure with a Yb-C(terminal phenylacetynide) bond length of 2.374(3) A. Complex 1 is also a highly efficient catalyst for ring-opening polymerization of epsilon-caprolactone.

Fischer Carbene Complexes: Beautiful Playgrounds To Study Single Electron Transfer (SET) Reactions

The knowledge of the reactivity of Fischer carbene complexes in electron transfer processes is still in the early stage of development, but interesting advances are foreseeable in this young branch of metal-carbene chemistry. Although these compounds have a dual reactivity (which makes them good substrates for oxidation and reduction processes), their behavior towards chemical electron transfer (ET) reagents was unknown until very recently. This article covers the progress accomplished in the reactivity of these compounds towards chemical ET reagents (C(8)K or SmI(2)), as well as the use of nonconventional sources of electrons, such as electrospray ionization (ESI) to induce ET processes. Special emphasis will be made on the effect of the structure of the starting carbene in the outcome of the reaction and in discussing the different mechanisms proposed.

Facile Regiocontrolled Synthesis of Trialkyl‐Substituted Pyrazines.

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, please click on HTML or PDF.

Use of tris(2,2'-bipyridine)osmium as a photoluminescence-following electron-transfer reagent for postcolumn detection in capillary high-performance liquid chromatography.

The photoluminescence-following electron-transfer (PFET) technique, developed in our laboratory, is a sensitive chromatographic detection method for oxidizable analytes. Because the oxidations are homogeneous, the technique avoids the problem of electrode fouling. A liquid-phase oxidant reacts with the electrochemically active analytes after separation, becoming capable of photoluminescence. Laser-induced photoluminescence is measured to quantitate the analytes. Thus, the electrochemical properties of the oxidant determine the detection selectivity, and the spectroscopic properties define the sensitivity. The properties of tris(2,2'-bipyridine)osmium (1) were investigated for use as the liquid-phase oxidant in the PFET system. The redox potential of the complex is less positive than that of tris(2,2'-bipyridine)ruthenium (2); thus, on-line generation of 1(3+) by reaction with PbO2, and selective oxidation of catechols by 1(3+), was possible. The mild oxidizing power of 1(3+) led to a lower background signal (compared to 2(3+)) when mixed with acidic mobile phases. Photoluminescence from 1(2+) was much weaker than that from 2(2+); nonetheless, the system achieved subnanomolar detection limits for dopamine, 3-methoxytyramine, and serotonin. Dopamine and 3-methoxytyramine in rat brain striatal dialysates were determined before and after the injection of nomifensine. The pH of the mobile phase can govern the detection selectivity, since oxidation of most organics is accompanied by proton transfer. Reaction of 1 with catechols showed pH-dependent sensitivity resulting from pH-dependent reaction rate changes. Since the reaction rate is also temperature dependent, increased temperature at the mixer resulted in higher sensitivity. However, the noise level also increased at elevated temperature; thus, the detection limit did not improve.

Effect of Sodium Naphthalenide, a Key SET Reagent, on Trifluoroacetyl Derivatives.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Facile Regiocontrolled Synthesis of Trialkyl-Substituted Pyrazines

[reaction: see text] Alpha-nitro ketones can be transformed selectively into trialkyl-substituted pyrazines via reaction with alpha-amino ketones using octyl viologen as an electron-transfer reagent. The new synthetic method, and the optimal reaction conditions that allow for the regiochemical control, are described.

Effect of sodium naphthalenide, a key SET reagent, on trifluoroacetyl derivatives

Aromatic trifluoroacetyl derivatives on treatment with single electron transfer (SET) reagent, sodium naphthalenide, yield symmetrical defluorinated dimers, whereas for aliphatic trifluoroacetyl compounds the reaction usually fails. Investigations have been made for different substituents as well as for similar types of chloro and bromo compounds to establish the scope of the reaction.

Effect of Sodium Naphthalenide, a Key SET Reagent, on 3-Substituted Indoles.

For Abstract see ChemInform Abstract in Full Text.

Development of Radical Reactions with Zirconocene Complexes as Electron Transfer Reagents.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Chemical Methods for Ether‐Bond Cleavage by Electron‐Transfer Reagents

AbstractFor Abstract see ChemInform Abstract in Full Text.

Development of Radical Reactions with Zirconocene Complexes as Electron Transfer Reagents

Abstract Bis(cyclopentadienyl)zirconium chloride hydride (Schwartz reagent) proved to be an efficient radical chain carrier for radical reduction of organic halides. Treatment of 1-bromoadamantane with Cp2Zr(H)Cl in THF at 25 °C in the presence of triethylborane furnished adamantane quantitatively. Radical cyclization of 2-haloalkyl allyl ethers afforded five-membered products under the same reaction conditions. Reduction with Cp2Zr(H)Cl generated in situ from Cp2ZrCl2 and sodium bis(2-methoxyethoxy)aluminium hydride (Red-Al) also proceeded smoothly. Moreover, the reduction could function by using a catalytic amount of Cp2ZrCl2. A zirconocene–olefin complex also induced reductive radical cyclization of 2-haloalkyl allyl ethers in THF. This complex served as a single electron transfer reagent to promote the radical cyclization. Furthermore, the cyclization reaction in DME afforded 3-tetrahydrofuranylmethylzirconium efficiently.

A novel method for the synthesis of alkoxyamine initiators for nitroxide-mediated radical polymerization using Mn(OAc)3 as electron-transfer reagent

O -substituted hydroxylamines which are known to initiate and promote nitroxide-mediated radical polymerization were synthesized in high yield by a novel and facile synthetic approach. Using the favorable Mn(OAc)3 as electron transfer agent in the in situ generation of benzylic radicals and their trapping by nitroxide radicals provides a new powerful and more economic way to the desired alkoxyamine initiators for this controlled, living radical polymerization. TEMPO, TIPNO and the protected tris-hydroxy derivative of TIPNO were used to synthesize the appropriate alkoxyamines.

Effect of Sodium Naphthalenide, a Key Set Reagent, on 3-Substituted Indoles

Action of the single electron transfer (SET) reagent sodium naphthalenide on 3-substituted indoles revealed that indoles with electron-donating substituents do not respond whereas indoles with electron-withdrawing substituents easily react, yielding several products depending upon the substituent.

First Fluorescent Photoinduced Electron Transfer (PET) Reagent for Hydroperoxides

A novel fluorescent reagent for hydroperoxides, 4-(2-diphenylphosphinoethylamino)-7-nitro-2,1,3-benzoxadiazole (1), was developed on the basis of the method for designing photoinduced electron transfer (PET) reagents having a benzofurazan skeleton. Compound 1 was quantitatively reacted with hydroperoxides to give its fluorescent derivative, 2. In acetonitrile, the Phi value (0.44) of 2 was 31 times greater than that of 1. The long excitation (458 nm) and emission (520 nm) wavelengths of 2 are suitable for the determination of hydroperoxides, especially in biosamples. [structure: see text]

A comparison of electron transfer reagents in the reductive opening of epoxides: reasons for the superiority of titanocene based complexes

Several commonly used electron transfer reagents were compared in their reactivity towards three epoxides. These substrates were designed to allow for a distinction between competing courses of the reaction. It was found that titanocene reagents were clearly superior due to their low Lewis acidity, high reduction tendency towards epoxides, and low reduction tendency towards the pivotal β-metal oxy radical intermediates.