Electron paramagnetic resonance (EPR) investigations of lichens – 1: effects of air pollution

Jezierski, Adam; Bylinska, E; Seaward, M. R. D.

doi:10.1016/s1352-2310(99)00258-7

Cited by 33 publications

(22 citation statements)

References 20 publications

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“…Although these radicals can be obtained efficiently in solutions [5], they have a strong tendency to dimerize upon freezing, hence a limited number of anisotropic data are available. It is noteworthy that anisotropic electron paramagnetic resonance (EPR) signals were detected for the iminoxy radicals gener-ated in the lichens thalli by action of NO 2 on Lasallia pustulata and Umbilicaria lichens [6,7]. The characteristic powder pattern of the EPR spectra has been also found recently for iminoxyls generated by incorporation of the parent oximes into the channels of ZSM-5 zeolite [8,9].…”

Section: Introductionsupporting

confidence: 51%

EPR and density functional studies on 3-pyridylmethaniminoxy radical:1H hyperfine couplings as a structural criterion for iminoxyls derived from pyridinealdoximes

et al. 2000

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Abstract. 3-pyridylmethaniminoxyl has been generated by '-irradiation of the parent oxime in the solid state and by incorporation of 3-pyridinealdoxime into the channels of thermally activated pentasil zeolite ZSM-5. The radical formed by both methods exhibits an electron paramagnetic resonance (EPR) spectrum with a characteristic powder pattern. The assignment of the hyperfine structure of the anisotropic spectra to the couplings with "N and 'H nuclei of Z geometrical isomer of 3-pyridylmethaniminoxy radical has been aided significantly by comparison with the coupling parameters calculated with the density functional theory (DFT). It has been found that 3-and 4-pyridylmethaniminoxyls generated in the oxime matrices, in contrast to the radicals derived from 2-pyridinealdoxime, have a possibility to isomerize. The EPR spectra of y-irradiated 3-and 4-pyridinealdoximes show a distinct temperature dependence of particular isomer contributions which have been correlated with the relative energies of the isomers derived from DFT calculations. Hybrid density functional methods have been also used to determine the structure of transition states for isomerization (via inversion at nitrogen) and rotation (of pyridyl ring) as well as to predict the appropriate energy barriers.

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Section: Introductionsupporting

confidence: 51%

EPR and density functional studies on 3-pyridylmethaniminoxy radical:1H hyperfine couplings as a structural criterion for iminoxyls derived from pyridinealdoximes

et al. 2000

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“…6 These radicals were also identified in lichens thalli collected from atmospherically polluted environments and also generated in laboratory conditions as a result of the nitrogen dioxide action on these composite organisms. 7 Moreover, iminoxyl radicals derived from unsaturated ketoximes are the starting reagents in organic synthesis. Owing to the unpaired electron density -3 -on both the O and N atoms, these iminoxyls were utilized in double-heteroatom-containing cyclizations leading to differently functionalized isoxazolines and cyclic nitrones regarded as important reagents for pharmacology.…”

Section: Introductionmentioning

confidence: 99%

Toward an Understanding of the Ambiguous Electron Paramagnetic Resonance Spectra of the Iminoxy Radical from o-Fluorobenzaldehyde Oxime: Density Functional Theory and ab Initio Studies

Witwicki

Jezierska

2015

J. Phys. Chem. A

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Iminoxy radicals (R1R2C═N—O•) possess an inherent ability to exist as E and Z isomers. Although isotropic hyperfine couplings for the species with R1 = H allow one to distinguish between E and Z, unequivocal assignment of the parameters observed in the EPR spectra of the radicals without the hydrogen atom at the azomethine carbon to the right isomer is not a simple task. The iminoxyl derived from o-fluoroacetophenone oxime (R1 = CH3 and R2 = o-FC6H5) appears to be a case in point. Moreover, for its two isomers the rotation of the o-FC6H5 group brings into existence the syn and anti conformers, depending on the mutual orientation of the F atom and C═N—O• group, making a description of hyperfine couplings to structure even more challenging. To accomplish this, a vast array of theoretical methods (DFT, OO-SCS-MP2, QCISD) was used to calculate the isotropic hyperfine couplings. The comparison between experimental and theoretical values revealed that the E isomer is the dominant radical form, for which a fast interconversion between anti and syn conformers is expected. In addition, the origin of the significant AF increase with solvent polarity was analyzed.

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“…Therefore, since 1991 there has been growing support among the staff for the Western tendencies of Polish defense policy (in 1992 -19 per cent support, 1994 -32 per cent, 1996 -48 per cent, 1997 -62 per cent) 47 and for the integration with NATO (in 1996 -80.4 per cent of respondents approved it, 1997 -83.6 per cent, 1998 -87.7 per cent). 48 Formerly perceived as a threat, NATO has now become the only real guarantor of Poland's security. Two thirds of respondents expressed their satisfaction with Poland's membership in NATO (67 per cent), while only every eighth soldier was dissatisfied (15.5 per cent), and nearly the same percentage had no opinion (16.6 per cent).…”

Section: The Journal Of Slavic Military Studiesmentioning

confidence: 99%

Social changes in the Polish army

Bera

2003

The Journal of Slavic Military Studies

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Electron paramagnetic resonance (EPR) investigations of lichens – 1: effects of air pollution

Cited by 33 publications

References 20 publications

EPR and density functional studies on 3-pyridylmethaniminoxy radical:1H hyperfine couplings as a structural criterion for iminoxyls derived from pyridinealdoximes

EPR and density functional studies on 3-pyridylmethaniminoxy radical:1H hyperfine couplings as a structural criterion for iminoxyls derived from pyridinealdoximes

Toward an Understanding of the Ambiguous Electron Paramagnetic Resonance Spectra of the Iminoxy Radical from o-Fluorobenzaldehyde Oxime: Density Functional Theory and ab Initio Studies

Social changes in the Polish army

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