Electron spin resonance spin trapping of thiyl,radicals from the decomposition of thionitrites

Alkyl thiyl radicals produced by the homolytic decomposition of thionitrites are detected by ESR spin trapping using 5,5-dimethyl-1-Δ-pyrroline-N-oxide (DMPO).     

Electron paramagnetic resonance spin trapping of glutathiyl radicals by PBN in the presence of cyclodextrins and by PBN attached to beta-cyclodextrin

The reaction of the glutathiyl radical (GS*) with a widely used spin trap N- tert-butyl-alpha-phenylnitrone (PBN) has been studied in the presence of various methylated beta-cyclodextrins and with PBN covalently bound to dimethylated beta-cyclodextrin (PBN-DIMEB) and permethylated beta-cyclodextrin (PBN-TRIMEB). Scavenging rate constants for GS* by PBN were obtained in the presence of randomly methylated cyclodextrin (RAMEB) and PBN-TRIMEB and found to be close to the rate constant previously measured for PBN. RAMEB and 2,6-di- O-Me-beta-cyclodextrin (DIMEB) were found to be the most efficient in the increasing PBN/GS* lifetime, by a factor of 5.5 for RAMEB and 6.8 for DIMEB compared with the lifetime of PBN/GS*. It is concluded that the presence or "attachment of" beta-cyclodextrins does not influence the scavenging rate constant of GS* but it does lead to stabilization of the spin adducts formed.     

Electron spin resonance investigations of human retinal pigment epithelium melanosomes from young and old donors

Electron spin resonance (ESR) examinations of human retinal pigment epithelium melanosomes isolated from eyes of young and old donors were carried out. The examined ESR signal was a single line, which is characteristic for free radicals of eumelanin o-semiquinones. The content of free radicals related to melanosomes dry weight for samples from older donors (ages over 45 years) were higher than for sample from younger donors (between 14 and 22 years). Simultaneously, the content of free radicals calculated for one melanosome is constant and does not depend on age. The homogeneous broadening of the recorded ESR lines shows that there are no isolated spin packets in all investigated melanin samples. Slow spin-lattice (T1 approximately 10(-5) s) and fast spin-spin (T2 approximately 10(-8) s) relaxation processes occur in these samples. Saturation of the ESR lines at low microwave power was measured. High concentration of free radicals in melanosome samples was responsible for the fast spin-spin relaxation process.     

Electron spin resonance of some paramagnetic compounds of iridium(II)

This paper deals with some electronic problems suggested by Malatesta. Electron spin resonance with [IrBr₃(NO)(PPh₃)₂] shows that the electronic configuration of the paramagnetic compound is described by that of the Ir-NO moiety. Specifically the three values of g tensor components demonstrate that the unpaired electron is located in a largely comprised π* (NO) orbital, so that the electronic state of NO is similar to that of gaseous trapped NO. The overlap between Ir and NO orbitals is through the d_π (d_xz or d_yz) metal orbitals, with consequent bent coordination of NO ligand. In conclusion the stability of d⁷ configuration of Ir in this monomeric compound is due to the easy electron transfer between metal and ligand, in agreement with that described in other monomeric Ir(II) compounds.     

Electron spin resonance analysis of superoxide anion radical scavenging activity with spin trapping agent, diphenyl-PMPO.

Recently, a novel electron spin resonance (ESR) spin-trapping agent, 2-(diphenylphosphinoyl)-2-methyl-3,4-dihydro-2H-pyrrole N-oxide (Diphenyl-PMPO), was synthesized. Because it had some advantages in stability and reactivity over conventional spin-trapping agents, we applied it to the ESR analyses of superoxide anion radical scavenging activity (SOSA) of superoxide dismutase (SOD) and of well-known natural antioxidants (green tea, oolong tea, and red wine). At the same time, the results with Diphenyl-PMPO were compared with 5,5-dimethyl-1-pyrroline N-oxide (DMPO). Our results revealed that Diphenyl-PMPO showed higher detectability than DMPO in the SOSA assays of SOD and natural antioxidants, so it could be available for the ESR analyses as an alternative to conventional spin-trapping agents.     

Electron paramagnetic resonance studies of magnetically aligned phospholipid bilayers utilizing a phospholipid spin label

X-band electron paramagnetic resonance (EPR) spectroscopy was used to study the structural and dynamic properties of magnetically aligned phospholipid bilayers utilizing a variety of phosphocholine spin labels (PCSL) as a function oftemperature. 1-Palmitoyl-2-[n-(4,4-dimethyloxazolidine-N-oxyl)stearoyl]-sn-glycero-3-phosphocholine (n-PCSL) in which a nitroxide group was attached to the different acyl chain positions of the phospholipid (n = 5, 7, 12, and 14) were used as an EPR spin probe to investigate magnetically aligned phospholipid bilayers from the plateau (near to the headgroup) region to the end of the acyl chain (center of the bilayers). The addition of certain types of paramagnetic lanthanide ions changes the overall magnetic susceptibility anisotropy tensor of the bicelles, such that the bicelles flip with their bilayer normal either parallel or perpendicular to the magnetic field. The present study reveals for the first time that, in the case of the n-PCSL, the bilayer normal is aligned parallel and perpendicular to the magnetic field in the presence of lanthanide ions having positive delta(chi) (e.g., Tm3+) and negative delta(chi) (e.g., Dy3+), respectively. The magnetic alignment of the bilayers and the corresponding segmental molecular order parameter, S(mol), were investigated as a function of the temperature. The S(mol) values decrease in the following order, 5-PCSL > 7-PCSL > 12-PCSL > 14-PCSL, for the magnetically aligned phospholipid bilayers. Also, the variable temperature study indicates that, by increasing the temperature, the order parameters S(mol) decreased for all the n-PCSLs. The results indicate that magnetically aligned phospholipid bilayers represent an excellent model membrane system for X-band EPR studies.     

Electron paramagnetic resonance spin probe study of carbon dioxide‐induced polymer plasticization

Steady‐state electron paramagnetic resonance (EPR) spectroscopy using nitroxide spin probes has been used to investigate the plasticization of poly(vinyl acetate) and poly(ethyl methacrylate) by carbon dioxide. By varying the CO₂ pressure at constant ambient temperature, the glass transition for each polymer could be depressed to 25 °C. This effect has been quantified by a parameter P_50G, obtained by plotting the EPR spectral width as a function of CO₂ pressure. Certain spin probes showed free volume distribution effects, manifested in the EPR spectra as “double peaks.” Possible reasons for this phenomenon are presented and discussed, and the efficacy of CO₂ as a plasticizer is clearly demonstrated by direct comparison with di‐n‐butyl phthalate. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2097–2108, 2005     

Electron paramagnetic resonance of ultraviolet-irradiated polyolefins

If films of polyolefins are ultraviolet-irradiated at liquid nitrogen temperature, alkyl radicals which can be examined by EPR are produced. No EPR spectra are observed from polyolefins irradiated at room temperature in air. Ultraviolet irradiation of polyolefins containing small alkyl side chains generally produces radicals corresponding to the pendant group or methyl radicals if the side chains contain a methyl branch. For some polymers the radical species could not be identified with certainty. Stabilization studies indicate that an optimum concentration of ultraviolet stabilizer is necessary for maximum stabilization of polyolefins. Preliminary results of EPR studies of the ultraviolet irradiation of various polyolefins are given, and some possible radical species are discussed.     

Electron paramagnetic resonance for everybody--MICROspec-X--a new class of electron paramagnetic resonance spectrometer

The electron paramagnetic resonance spectroscopy is the only method for detecting free radicals. Free radicals have an increased importance in our daily life. A small transportable EPR spectrometer is presented for the popularisation of the EPR method. The technical construction and some applications are illustrated which show the usability of the spectrometer.     

Electron spin resonance of manganese(II) complexes with proteins

Analysis of the spectra arising from complexes of Mn²⁺ with carbonic anhydrase B(CA) and β-galactosidase (β-Gal) indicates that the dominant anisotropic term in the spin hamiltonian is a quadratic zero field splitting (ZFS) interaction of an approximately rhombic symmetry, characterized by a considerable extent of distribution in the ZFS parameters.     

Electron spin dynamics in photoexcited diamagnetic and paramagnetic corroles

Three corroles, which differ by their cavity's core, namely, diamagnetic free-base tris(pentafluorophenyl)corrole and its gallium(III) complex and the paramagnetic oxo-chromium(V) complex, were studied by steady-state and time-resolved electron paramagnetic resonance (EPR) spectroscopy. The magnetic and orientational parameters of the corroles, oriented in a nematic liquid crystal, were determined and interpreted in terms of their structure, geometry, and excited states spin dynamics. It was shown that both diamagnetic corroles, photoexcited to their triplet states, exhibit similar EPR line shapes, which is characterized by a negative zero-field splitting parameter, D, whose origin is due to molecular "stretching". Photoexcited Cr(V)O-corrole exhibits polarized ground-state EPR spectrum in emission mode. This polarization stems from the sequence of photophysical and photochemical reactions, involving the formation of the trip-quartet/trip-doublet composite states and their selective quenching via a charge transfer state.