ESR Spectroscopic Study Research Articles

ESR-Study of the Proton Exchange with Aliphatic Amino Acids in Toluene

This paper presents the results of an ESR spectroscopic study of the intermolecular proton exchange kinetics with some isomers of aminocaproic acid, such as 2-aminohexanoic and 6-aminohexanoic acids in the toluene indifferent medium. A stable semiquinone radical, namely 3,6-di-tert-butyl-2-hydroxyphenoxyl, is used as a spin probe. The ESR spectra have been recorded on a RE-1306 spectrometer. The article provides the ob-tained dynamic spectra of the intermolecular proton exchange process. Modeling of the proton exchange ESR spectra has been carried out using a previously developed program, which is based on a four-jump model of this reaction and modified Bloch equations. The kinetic parameters of the process of acid-base interaction of the spin probe with amino acids and the activation barrier of the reaction have been estimated with a mini-mum error based on a comparison of the model spectra with the experimental ones. The obtained data have been analyzed and compared with previous studies. It has been found that the reaction rate of the intermo-lecular proton exchange between 3,6-di-tert-butyl-2-hydroxyphenoxy and studied aliphatic amino acids is comparable to the same with aliphatic carboxylic acids. Hoewever, in our case, there is an increase in the ac-tivation barrier, which apparently is associated with a negative effect on the intramolecular hydrogen bonding process between the amino and the carboxyl groups in the amino acid molecule.

Study on gamma and electron beam sterilization of third generation cephalosporins cefdinir and cefixime in solid state

The effect of gamma radiation from 60Co source and 2 MeV e-beam was studied on two thermolabile cephalosporin antibiotics viz cefdinir and cefixime in solid state. The parameters studied to assess radiolytic degradation were loss of chemical and microbiological potency, change in optical rotation, electronic and vibrational absorption characteristics, thermal behavior and color modification. ESR spectroscopic study, HPLC related impurity profile, thermogram and Raman spectrum are applied in deducing the nature of radiolytic impurities and their formation hypotheses. Cefixime is radiation sensitive, whereas cefdinir has acceptable radiation resistance at 25 kGy dose. The nature of radiolytic related impurities and their concentrations indicates that the lactam ring is not highly susceptible to direct radiation attack, which otherwise is considered very sensitive to stress (thermal, chemical and photochemical).

An Electrochemical and ESR Spectroscopic Study on the Molecular Dynamics of TEMPO in Room Temperature Ionic Liquid Solvents

Slow rotational diffusion of probe molecule TEMPO in several room temperature ionic liquid solvents results in asymmetry in its ESR spectrum (see figure), the severity of which depends on the temperature. In some cases the observed variation may be rationalised using simple hydrodynamic theories, while in others it points to an increased level of ordering within the liquid structure (TEMPO: 2,2,6,6-tetramethylpiperidine-N-oxyl).

The electronic and magnetic properties of iron(III) derivatives of selected substituted meso-tetraphenyl porphyrins: ESR spectroscopic study

The electronic and magnetic behaviour of the nonsolvated ferric complexes of: (a) meso-tetratolyl-, (b) meso-tetra-4-hydroxyphenyl-, (c) meso-tetra-4-carboxyphenyl-, and (d) 5-(4-carboxyphenyl)-10,15,20-tritolyl-porphyrins was studied by ESR spectroscopy in the temperature range between 300 and 4K. The complexes exhibit predominant contribution from the low-spin iron species at high temperature and a drastic shift toward the high-spin iron species at the low-temperature limit. These paramagnetic species are in different proportions at different temperatures, as well as in porphyrins with different substituents. The examined porphyrins obtained as disordered solids contain iron complexes with continuous short-range disorder which is additionally sensitive to change of temperature.

An ESR and Optical Spectroscopic Study of the Mechanism of Photostimulated Reactions in Hydrogen Cyanide γ-Irradiated at 77 K

Changes in the electronic absorption spectra and ESR spectra in the course of photobleaching of radiolyzed solid HCN with light of different wavelengths (236–600 nm) were studied by ESR and optical spectroscopy. Two bands at 270 and 290 nm in the optical spectrum were attributed to the presence of H2C=N⋅ and HC⋅=NH radicals, respectively (the molar absorption coefficients are k270≈ 2.7 × 102l mol–1cm–1and k290≈ 1.5 × 102l mol–1cm–1, respectively). Structureless broad bands with maximums at 313 and 465 nm, which were detected after the exposure of a sample to light with λ ≥ 300 nm, can belong to the cyanide ions (CN–) and H2C=N+cations (the molar absorption coefficients of the ions are kion= (0.4–1.0) × 102l mol–1cm–1). In the photobleaching of γ-irradiated HCN (λ = 236–280 nm), H2C=N+radicals were additionally formed by the photoinduced reaction of electron transfer from the CN–anion to the H2C=N+cation. The amount of these radicals generated in the course of photobleaching is several times greater than that of the same radicals formed in the radiolysis via hydrogen atom addition to the multiple bond of HCN molecules.

Free-Radical Bulk Polymerization of Styrene: ESR and Near-Infrared Spectroscopic Study of the Entire Conversion Range

Free-Radical Bulk Polymerization of Styrene: ESR and Near-Infrared Spectroscopic Study of the Entire Conversion Range

DNA damage by dimethylformamide: role of hydrogen peroxide generated during degradation.

Dimethylformamide (DMF) has been suspected to associate with cancers in exposed workers, whereas there has been inadequate evidence for carcinogenicity in experimental animals. We demonstrated that H(2)O(2) was generated during the degradation of DMF under aerobic conditions, and that the amount of H(2)O(2) was enhanced by exposure to solar light or by the contamination of trace metal. Experiments using (32)P-5'-end-labeled DNA fragments revealed that the degraded DMF induced DNA damage in the presence of Cu(II). However, purified DMF did not induce DNA damage even in the presence of Cu(II). Addition of purified DMF enhanced DNA damage induced by H(2)O(2) in the presence of Cu(II). The degraded DMF caused Cu(II)-mediated DNA cleavage frequently at thymine and cytosine residues. The similar pattern of site-specific DNA damage was observed with purified DMF and H(2)O(2). Bathocuproine and catalase inhibited the DNA damage, indicating the involvement of Cu(I) and H(2)O(2). A typical free hydroxy radical scavenger showed no inhibitory effect on the DNA damage. Addition of purified DMF enhanced about 3-4-fold 8-oxo-7, 8-dihydro-2'-deoxyguanosine formation induced by H(2)O(2) and Cu(II). ESR spectroscopic study demonstrated that carbon-centered radicals and nitrogen-centered radicals were generated in the reaction mixture of DMF, H(2)O(2), and Cu(II). Inhibitory effects of scavengers on radical formation and DNA damage suggest that carbon-centered radicals and/or nitrogen-centered radicals may contribute to the DNA damage. These results suggest that H(2)O(2) generation during DMF degradation is related to the possible carcinogenic activity of DMF.

Oxidative DNA Damage by a Metabolite of Carcinogenic and Reproductive Toxic Nitrobenzene in the Presence of NADH and Cu(II)

The mechanism of DNA damage induced by metabolites of nitrobenzene was investigated in relation to the carcinogenicity and reproductive toxicity of nitrobenzene. Nitrosobenzene, a nitrobenzene metabolite, induced NADH plus Cu(II)-mediated DNA cleavage frequently at thymine and cytosine residues. Catalase and bathocuproine inhibited the DNA damage, suggesting the involvement of H2O2and Cu(I). Typical free hydroxyl radical scavengers showed no inhibitory effects on DNA damage. Nitrosobenzene caused the formation of 8-oxo-7,8-dihydro-2′-deoxyguanosine in calf thymus DNA in the presence of NADH and Cu(II). ESR spectroscopic study has confirmed that nitrosobenzene is reduced by NADH to the phenylhydronitroxide radical even in the absence of Cu(II). These results suggest that nitrosobenzene can be reduced non-enzymatically by NADH, and the redox cycle reaction resulted in oxidative DNA damage due to the copper-oxygen complex, derived from the reaction of Cu(I) with H2O2.

Generation and characterization of alkali metal clusters in Y-FAU zeolites. An ESR and MAS NMR spectroscopic study

Charged and neutral metal clusters of various compositions and sizes can be prepared by controlling the alkali metal content by the decomposition of alkali azides and the composition of the host zeolite by ion-exchange. ESR signals show that electron transfer from alkali metal atoms to alkali metal cations does occur, but in a direction opposite to that predicted by the gas-phase thermochemistry. Alkali metal clusters proved to be very active basic catalytic centers.

ESR spectroscopic study on the addition of PhCONHCHCO2Me radicals to alkenes and spin traps

Using ESR spectroscopy, the rate constants for the addition of PhCONHCHCO2Me radicals to alkenes CH2=CXY (X = Me, Y = Ph; X = H, Y = Ph; X = Me, Y = CO2Me; X = H, Y = CO2Me; X = H, Y = CN) and nitrosodurene were determined at 22 °C. It is shown that a linear dependence exists between the donor-acceptor properties of the substituents at the vinyl group and the rate constants for the addition.

Electrochemical and ESR Spectroscopic Study of 2,7-Disubstituted Phenazines.

Cyclic voltammetry (CV) for 2, 7-disubstituted phenazines (1mM, MeO (1), EtO (2), H (3), Cl (4), Br (5), COOEt (6)) was carried out in acetonitrile containing trifluoroacetic acid (TFA, 1% and 2%) and NaClO4 (0.1M) as a supporting electrolyte under N2 gas. Phenazines showed two cathodic peaks (Epc1 and Epc2) and these peaks had counterparts (Epa1 and Epa2, respectively). Plots of the peak potentials against σp were linear. The first cathodic wave corresponds to the reduction of singly protonated phenazines followed by proton transfer. The second cathodic wave corresponds to the reduction of the cation radical of dihydrophenazines to produce dihydrophenazine as a final product.ESR spectrometry of 1-6 in acetonitrile and in acetonitrile containing 1% TFA was conducted and computer simulation of the spectra was carried out. Splitting due to halogen or o-alkyl substituents was observed. Molecular orbital (MO) calculation of anion radicals generated from 1-6 and cation radicals generated from doubly protonated 1-6 did not give good agreement with the results of ESR spectrometry.

Identification of the 1,3,2,4-Dithiadiazolyl RCNSNS(*) Radical Dimers in Solution, Their Dimeric Concerted Photochemically Symmetry-Allowed Rearrangement to 1,2,3,5-Dithiadiazolyl RCNSSN(*) by the Net Exchange of Adjacent Cyclic Sulfur and Nitrogen Atoms, and the Photolysis of RCNSNS(*).

The 1,3,2,4-dithiadiazolyl RCNSNS(*) radicals undergo an unprecedented concerted rearrangement to the thermodynamically more stable 1,2,3,5-dithiadiazolyl RCNSSN(*) radicals by the net exchange of adjacent cyclic sulfur and nitrogen atoms. The UV-visible spectra of RCNSNS(*) (R = Ph, p-O(2)NC(6)H(4), 3,5-(O(2)N)(2)C(6)H(3), CF(3)) in solution show bands at 250 nm (strong) and 680 nm (very weak) attributable to monomer and two dimer bands at 376 and 480 nm, the positions of which are independent of the substituents, providing direct identification of the radical dimers in solution. The dimerization equilibrium constant (K(298) approximately 0.7 for R = Ph) at room temperature was derived from the enthalpy and entropy changes for the dimerization of PhCNSNS(*) (DeltaH(d) degrees = -19.0 kJ/mol, DeltaS degrees = -66.5 J/mol) estimated by a variable-temperature ESR spectroscopic study. In addition, RCNSNS(*) (R = Bu(t), Ph) undergo an apparent unimolecular photolysis to RCN and possibly SNS(*) (analogue of ONO(*)). The photochemical rearrangement and dissociation (for R = Ph and 3,5-(O(2)N)(2)C(6)H(3)) were shown to proceed by irradiation of the radical dimer (376 and 480 nm) and monomer (250 nm), respectively. Thus, the radical rearrangement reasonably occurs via a concerted dimeric pathway shown by molecular orbital calculations (CNDO) to be photochemically symmetry-allowed. In addition, we propose that the radical dissociation proceeds via a concerted unimolecular photochemically symmetry-allowed process.

First electron spin resonance evidence for the production of semiquinone and oxygen free radicals from orellanine, a mushroom nephrotoxin

Orellanine is the tetrahydroxylated and di- N-oxidized bipyridine toxin from several Cortinarius mushrooms. The mechanism responsible for its lethal nephrotoxicity was unknown until now. Our present ESR spectroscopic study of the redox properties of the toxin is an original contribution to the knowledge of its toxicity. It was achieved in particular by comparison of the properties of orellanine to that of other bipyridine compounds. After a one-electron oxidation (e.g., photochemical oxidation upon visible light), a radical form of orellanine is observed at physiological pH under aerobic or anaerobic conditions. This radical, identified as ortho-semiquinone anion radical, can also be generated by oxidation with biological oxidizing agents or enzymatic systems. Production of superoxide and hydroxyl radicals is shown by the spin-trapping method using DMPO as a spin trap. Bioreducing agents like GSH and cysteine involve in vitro the semiquinone radical and orellanine in a redox cycling process resulting in the production of glutathionyl and oxygen free radicals. This process leads in vitro to a large oxygen consumption and to a dramatic depletion of glutathione level. The formation of an apparently stable ortho-semiquinone anion radical and of reactive oxygen radical species is observed for the first time with a mushroom toxin. It is due to the catechol-like functions borne by the di- N-oxidized bipyridine structure of the toxin and may at least partly explain the toxicity of orellanine.

IR, NMR, and ESR spectroscopic study of isotope labeled poly(p-phenylene) prepared by using Ni(0) complex

13C-and D-labeled poly( p-phenylene)s, PPP's, have been prepared by dehalogenation polycondensation using an Ni(0) complex. A ring deformation vibration of PPP shifts from 1596 to 1543 cm −1 due to the 13C-labeling. Peak-to-peak width in ESR spectra of Na-doped and non-doped PPP increases by 0.13-0.25 mT due to the 13C-labeling, whereas that of the non-doped PPP decreases by 0.14 mT due to the D-labeling.

EPR and optical absorption spectra of reduced buckminsterfullerene

The unambiguous identification of the various redox states of C60 is of importance in many areas of fullerene research, such as charge transfer studies between conducting polymers and C60, or the study of the distribution of charged states in solid‐state‐doped samples. This combined ESR and optical absorption spectroscopic study represents the most complete analysis of the anionic states of buckminsterfullerene, from the monoanion to the hexaanion, so far reported.

ChemInform Abstract: Enantioselective Hydrogen‐Atom Abstraction by Optically Active Amine‐ Boryl Radicals: An ESR Spectroscopic Study.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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.

Enantioselective hydrogen-atom abstraction by optically active amine-boryl radicals: An ESR spectroscopic study

ESR spectroscopy has been used to measure the relative rates of α-hydrogen-atom abstraction from enantiomeric pairs of esters by chiral amine-alkylboryl radicals in solution.

Alkane oxidation on isolated Cu2+ ions in zeolitic matrix: a relation between catalytic activity and Cu2+-site local topography

Catalytic ethane oxidation, with O2, using H-ZSM-5 and H-mordenite containing different discrete types of isolated Cu(II) cations was studied. An ESR spectroscopic study was carried out on copper ion coordination in zeolites. It was shown that the intrinsic activity of Cu(II) ion depends strongly on the Cu2+-site local topography. Covalent-bonded Cu(II) cations in the most coordinatively unsaturated square-planar coordination in H-ZSM-5 demonstrated the highest activity in C2H6 complete oxidation.

Electron Spin Resonance Spectra of Sulfinamidyl Radicals and a Comparison of Hyperfine Splitting Constants with Sulfenamidyl and Sulfonamidyl Radicals

Abstract An ESR spectroscopic study of N-arylsulfinyl- and N-alkylsulfinyl-3,5-di-t-butylphenylaminyls (2) is described. The sulfinamidyls 2, generated by the reaction of the corresponding sulfinamides (7) with di-t-butyl diperoxyoxalate (DBPO) in benzene at 21 or 40°C, give hyperfine splitting (hfs) constants which indicate that the unpaired electron is slightly delocalized onto the sulfinyl group. A comparison of the hfs constants for 2 with those for structurally related sulfenamidyl and sulfonamidyl radicals indicates that the abilities of –SR, –S(O)R, and –S(O2)R to delocalize the unpaired electron are in the order –SR>–S(O)R>–(O2)R. The reaction of 7 with DBPO has been examined on the basis of product analyses. The mechanism accounting for the formation of the isolated products is briefly discussed.

Thermal and photochemical reactions of organotin with aminophenols. ESR and other spectroscopic study of a novel organotin radical complex of 2-amino-4-tert-butylphenol

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThermal and photochemical reactions of organotin with aminophenols. ESR and other spectroscopic study of a novel organotin radical complex of 2-amino-4-tert-butylphenolSandip K. Sur and J. P. ColpaCite this: Organometallics 1989, 8, 12, 2749–2751Publication Date (Print):December 1, 1989Publication History Published online1 May 2002Published inissue 1 December 1989https://doi.org/10.1021/om00114a001RIGHTS & PERMISSIONSArticle Views131Altmetric-Citations4LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (379 KB) Get e-Alerts Get e-Alerts