Biaryl Anion Radical Formation by Potassium Metal Reduction of Aryl Isocyanates and Triaryl Isocyanurates.

The potassium metal reduction of aryl isocyanates (aryl = phenyl, -tolyl, 3,5-dimethylphenyl, 4-biphenylyl, and 1-naphthyl) in THF with 18-crown-6 or in HMPA results in the formation of the corresponding triaryl isocyanurate anion radicals. Continued exposure to potassium results in loss of the isocyanurate anion radical and the eventual formation of the respective biaryl anion radical. The 1,1'-binaphthyl anion radical is found to undergo a cyclodehydrogenation reaction, which leads to formation of the perylene anion radical.

Characterization of an archaeal inorganic pyrophosphatase from Sulfolobus islandicus using a [P]-NMR-based assay.

Inorganic pyrophosphatase catalyzes the conversion of pyrophosphate to phosphate and is often critical for driving reactions forward in cellular processes such as nucleic acid and protein synthesis. Commonly used methods for quantifying pyrophosphatase enzyme activity employ reacting liberated phosphate with a second molecule to produce absorbance changes or employing a second enzyme in coupled reactions to produce a product with a detectable absorbance. In this investigation, a novel [P]-NMR spectroscopy-based assay was used to quantitatively measure the formation of phosphate and evaluate the activity of inorganic pyrophosphatase from the thermoacidophilic Crenarchaeota Sulfolobus islandicus.

Electron Distribution in 1,2,3-Benzotriazole and 1,2,3-Triazole Anion Radical Isomers: An EPR and DFT Study.

The anion radicals of N1- and N2-alkylbenzotriazoles and alkyltriazoles (alkyl = methyl or isopropyl) have been generated by low-temperature potassium metal reduction in tetrahydrofuran. Electron paramagnetic resonance (EPR) analysis and density functional theory calculations reveal that the electron spin distribution within the triazole ring of these systems is markedly different. The magnitude of the electron-nitrogen couplings along with the calculated spin densities reveals that the N2-alkylbenzotriazole and N2-alkyltriazole anion radicals have significantly greater electron spin residing within the N portion of the triazole ring compared with that of the respective N1 isomers.

Development of a new and reliable assay for choline kinase using P NMR.

Choline kinase catalyzes the conversion of choline to phosphocholine (PC) by transferring a phosphate group from adenosine triphosphate (ATP) as the first step in the biosynthetic pathway for the membrane phospholipid phosphatidylcholine, an essential pathway in the parasitic protozoan. Commonly used methods for kinetically quantifying the enzyme include a radioisotope assay utilizing labeled choline and a coupled spectrophotometric assay with multiple enzymes and substrates that indirectly measures choline kinase activity. When testing potential inhibitors with the coupled assay, results can cast doubt on whether choline kinase is being inhibited or one of the coupled enzymes.

Influence of Annulation on the Electron Spin within the 1,2,3-Triazole Ring in Annulenotriazole Anion Radicals.

The low temperature (-100 °C) single electron reduction of N1-phenylbenzotriazole in liquid ammonia, and the room temperature reduction of N1-phenylcyclooctatetraenotriazole in hexamethylphosphoramide, yields stable solutions of both anion radicals, which were studied via EPR spectroscopy. The amount of electron spin localized within the triazole ring, and how spin is distributed within this ring, is greatly influenced by the size of the annulene ring attached. UB3LYP/6-31++G(d,p) geometry optimizations using DFT methods were carried out for both anion radicals, and the calculated coupling constants (and electron spin densities) are in good agreement with the EPR spectroscopic results.

Tris-[8]annulenyl Isocyanurate Trianion Triradical and Hexa-anion from the Alkali Metal Reduction of [8]Annulenyl Isocyanate.

The solution phase alkali metal reduction of [8]annulenyl isocyanate (C8H7NCO) yields an EPR spectrum, which reveals electron couplings to seven protons and only one nitrogen. Although this strongly suggested that the C8H7NCO anion radical was generated, experiments on the oxidized product reveal the actual reduced species to be tris-[8]annulenyl isocyanurate. Unlike the previously studied phenyl isocyanurate anion radical, the unpaired electron(s) is now localized within an [8]annulenyl moiety.

Experimental and computational studies of the neutral and reduced states of indeno[1,2-b]fluorene.

This study examines the intrinsic structural and optoelectronic properties of the neutral indeno[1,2-b]fluorene skeleton as well as those of the corresponding anion radical and dianion. We report their characterization by analysis of solid-state structures and EPR, NMR, and absorbance spectra. Additionally, 20 popular density functional theory methods are used to evaluate their performance for predicting NMR chemical shifts, EPR hyperfine coupling constants, and low-energy transitions of the absorbance spectrum to act as a guide for future studies.

Phenyl isocyanate anion radicals and their cyclotrimerization to triphenyl isocyanurate anion radicals.

Room-temperature sodium metal reduction of phenyl isocyanate (PhNCO) in hexamethylphosphoramide yields the anion radical (PhNCO(•-)) where the unpaired electron exhibits coupling to one nitrogen and five unique protons. The extent of coupling to the carbon in the NCO group was obtained via the reduction of (13)C-labeled PhN(13)CO. Remarkably, this coupling is over 2 orders of magnitude smaller than that found for the alkyl-substituted analogue.

Beta-amino alcohol derived beta-hydroxy- and beta-(o-diphenylphosphino)benzoyloxy(o-diphenylphosphino)benzamides: an ester-amide ligand structural model for the palladium-catalyzed allylic alkylation reaction.

A commercially available collection of beta-amino alcohols have been converted to their corresponding beta-hydroxy- and beta-(o-diphenylphosphino)benzoyloxy(o-diphenylphosphino)benzamides 11a-f and 12a-f and have been employed in the Tsuji-Trost asymmetric alkylation reaction with 1,3-diphenylpropenyl acetate. With the exception of ligands 11b and 11f, the beta-hydroxybenzoyloxy(o-diphenylphosphino)benzamide ligands 11a-f primarily afforded the (R)-enantiomer of the product. In contrast, the bis(phosphine) ligands 12a-f consistently afforded the (S)-enantiomer.

Reduction of an hexamethylphosphoramide degradation product: a diazabutadiene.

Alkali metal over-reduction of an electron acceptor in the presence of a hydrogen atom donor, in hexamethylphosphoramide (HMPA), results in a radical that is not simply the anion radical of the acceptor. This new species exhibits an enigmatic EPR pattern. Using 15N and 2H labeling studies, the "HMPA degradation product" was found to be the anion radical of N,N'-dimethyl-1,4-diazabutadiene.

Isocyanurate anion radicals via electron-initiated cycloaddition of isocyanates.

Room temperature sodium metal reductions of alkyl isocyanates lead to the rapid electron-initiated formation of alkyl isocyanurate anion radicals, which exhibit EPR coupling to only two equivalent nitrogens. Reduction of (13)C-enriched ethyl isocyanate reveals that the odd electron localizes in the pi system of one carbonyl in the isocyanurate ring. EPR line-width alternation effects indicate that at least two stable conformers are in rapid equilibrium undergoing fast exchange.

Carbaporphyrin ketals as potential agents for a new photodynamic therapy treatment of leishmaniasis.

Dimethyl and diethyl carbaporphyrin ketals inhibit the growth of Leishmania tarentolae promastigotes in vitro. The concentration dependency of the inhibitory effect was tested using the MTT assay. The presence of reactive oxygen species, such as singlet oxygen and superoxide, was detected using electron paramagnetic resonance spectroscopy with selected spin traps and confocal microscopy in cultures exposed to these carbaporphyrin ketals.

Single-electron entrapment of [8]annulyne, biannulenylenes, and an annulenoannulene.

The low-temperature (-100 degrees C) dehydrohalogenation of bromocyclooctatetraene followed by immediate electron-transfer yields a stable solution of the [8]annulyne anion radical. If the unstable [8]annulyne is reacted with itself, cyclobutadiene, or benzyne, the respective bi-[8]annulenylene, [6]annuleno[8]annulene, or [6]-[8]annulenylene can be trapped as their anion radicals via one-electron transfer. These condensation products were all obtained from simple [2 + 2] cycloaddition reactions.

The cyclooctatriene-eta2-ynyl potassium zwitterionic radical: evidence for a potassium organometallic.

Low-temperature (-120 degrees C) dehydrohalogenation of bromocyclooctatetraene (BrC8H7) with either sodium or potassium tert-butoxide followed by alkali metal reduction was used to generate the anion radical of [8]annulyne (C8H6*-) in tetrahydrofuran. EPR analysis at -120 degrees C reveals an extraordinarily large metal splitting when K or Cs (aK of 0.214 G and aCs of 3.

Interannular communication in the radical anions of bis-cyclooctatetraene systems.

[reaction: see text] The room-temperature potassium reduction of 1,2-bis-cyclooctatetraeneoxypropane yields two different regio-spin isomer anion radicals in equilibrium (COT-O-C(Me)HCH(2)CH(2)-O-COT(*)(-) = (*)(-)COT-O-C(Me)HCH(2)CH(2)-O-COT) that is shifted far to the right. The presence of the unreduced ring perturbs the spin density on the reduced ring. Addition of more electrons generates the diradical dianion ((*)(-)COT-O-C(Me)HCH(2)CH(2)-O-COT(*)(-)), and the anion radical on the secondary side splits the degeneracy of the psuedo-ortho protons of the anion radical on the primary side.