Protonated o-semiquinone radical as a mimetic of the humic acids native radicals: A DFT approach to the molecular structure and EPR properties

Witwicki, Maciej; Jezierska, Julia

doi:10.1016/j.gca.2012.03.010

Cited by 15 publications

(15 citation statements)

References 44 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In addition, the effect of g parameter reduction (determined by EPR studies) of semiquinone radicals naturally occurring in HAs of increasing aromaticity (Knüpling at al. [95]) was confirmed and explained theoretically by Witwicki and Jezierska [96] on the basis of quantum mechanical calculations of g parameters for model semiquinone radicals.…”

Section: Electron Paramagnetic Resonance Of Hasmentioning

confidence: 58%

Influence of Drainage on Peat Organic Matter: Implications for Development, Stability, and Transformation

et al. 2020

View full text Add to dashboard Cite

The agricultural use of peatlands, the stabilization of the substrate for building or road construction or for increasing the capacity of soil to support heavy machinery for industrial activities (peat and petroleum extraction), harvesting to provide peat for energy, and the growing media and initiation of chemical processes must be preceded by drainage. As a consequence of drainage, peat underwent an irreversible conversion into moorsh (secondary transformation of the peat). The object of the study was to investigate comparatively the organic matter composition and molecular structure of humic acids (HAs) in the raised bog, fen, and peat-moorsh soils developed in various compositions of botanical cover, peat-forming species, and oxic and anoxic conditions as a result of the oscillation of ground water during drainage as well as to evaluate the vulnerability of soil organic matter (SOM) to decomposition. Drainage was shown to be the principal factor causing the various chemical compositions and physicochemical properties of HAs. Large and significant differences in chemical composition of peat and the properties of HAs were found to be related to the degree of decomposition. The HAs from drained peatlands were less chemically mature. In contrast, the HAs from fen and raised bog were found to be more mature than that of the corresponding drained peatlands. The above findings showed the distinguishable structure of HAs within the soil profile created by the plant residue biodegradation and formed in both oxic and anoxic conditions. The analytical methods of thermal analysis together with the optical densities and paramagnetic behaviour are suitable and effective tools for studying structure–property relationships characterizing the origin and formation process of HAs in various environmental conditions.

show abstract

Section: Electron Paramagnetic Resonance Of Hasmentioning

confidence: 58%

Influence of Drainage on Peat Organic Matter: Implications for Development, Stability, and Transformation

et al. 2020

View full text Add to dashboard Cite

show abstract

“…Agreement between the experimental and theoretical g x , g y and g z values was supposed to indicate which of the models well represented the real systems, reflecting their molecular and electronic structure. This approach was proven effective (Witwicki et al, 2009a;Witwicki and Jezierska, 2012).…”

Section: Introductionmentioning

confidence: 98%

Understanding natural semiquinone radicals – Multifrequency EPR and relativistic DFT studies of the structure of Hg(II) complexes

2015

Self Cite

View full text Add to dashboard Cite

Multifrequency EPR spectroscopy and DFT calculations were used to investigate Hg(II) complexes with semiquinone radical ligands formed in a direct reaction between the metal ions and tannic acid (a polyphenol closely related to tannins). Because of the intricate structure of tannic acid a vast array of substituted phenolic compounds were tested to find a structural model mimicking its ability to react with Hg(II) ions. The components of the g matrix (the g tensor) determined from the high field (208 GHz) EPR spectra of the Hg(II) complexes with the radical ligands derived from tannic acid and from the model compounds were analogous, indicating a similar coordination mode in all the studied Hg(II) complexes. Since catechol (1,2-dihydroxybenzene) was the simplest compound undergoing the reaction with Hg(II) it was selected for DFT studies which were aimed at providing an insight into the structural properties of the investigated complexes. Various coordination numbers and different conformations and protonation states of the ligands were included in the theoretical analyses. g Matrices were computed for all the DFT optimized geometries. A good agreement between the theoretical and experimental values was observed only for the model with the Hg(II) ion tetracoordinated by two ligands, one of the ligands being monoprotonated with the unpaired electron mainly localized on it.

show abstract

“…Among them are electronic (UV/Vis), vibrational (infrared and Raman), nuclear magnetic resonance (NMR), and electron paramagnetic resonance (EPR) spectroscopy. The latter—also called electron spin resonance (ESR) spectroscopy—has proved to be indispensable in studies of radical species, which attract the attention of researchers due to their important roles in physics, chemistry, biochemistry, environmental, and material science …”

Section: Introductionmentioning

confidence: 99%

“…However, modern computational techniques can predict spectral data with an accuracy sufficient for a meaningful comparison with their experimental counterparts, and thus in such difficult situations they can support or verify the conclusions of experiments or link spectral features to the structural properties . Computational methods have proven especially successful in the interpretation of EPR data acquired experimentally for a broad representation of radicals based on the first‐row elements . However, to date, significantly less attention has been paid to the applications of theoretical methods to the properties of radicals with an unpaired electron significantly located on the heavier atoms, even though such systems draw the significant attention of researchers .…”

Section: Introductionmentioning

confidence: 99%

Density functional theory and ab initio studies on hyperfine coupling constants of phosphinyl radicals

Witwicki

2018

Int J of Quantum Chemistry

Self Cite

View full text Add to dashboard Cite

The 31P hyperfine coupling constants for various phosphinyl radicals were calculated using density functional theory (DFT) as well as the ab initio orbital‐optimized spin‐component‐scaled MP2 (OO‐SCS‐MP2) and coupled cluster methods (with relaxed and unrelaxed density). However before that, electron correlation in phosphinyl radicals was investigated by means of the fractional occupation number weighted electron density (FOD). The isotropic hyperfine coupling constants for phosphinyl radicals posed a considerable challenge to DFT; among other issues, the well‐known functional B3LYP substantially underperformed, but TPSS0 provided highly accurate results. Two tested double hybrid functionals, namely B2PLYP and mPW2PLYP, and OO‐SCS‐MP2 were found to be reasonably accurate. The unbalanced description of spin polarization in the valance region was identified as the root of the problems of DFT methods with correct prediction of the isotropic hyperfine coupling constants. In calculations at the coupled cluster level, relaxed and unrelaxed density matrices were tested and both were proved to provide highly satisfactory results for phosphinyl radicals. This was confirmed for a set of small paramagnetic species.

show abstract

Protonated o-semiquinone radical as a mimetic of the humic acids native radicals: A DFT approach to the molecular structure and EPR properties

Cited by 15 publications

References 44 publications

Influence of Drainage on Peat Organic Matter: Implications for Development, Stability, and Transformation

Influence of Drainage on Peat Organic Matter: Implications for Development, Stability, and Transformation

Understanding natural semiquinone radicals – Multifrequency EPR and relativistic DFT studies of the structure of Hg(II) complexes

Density functional theory and ab initio studies on hyperfine coupling constants of phosphinyl radicals

Contact Info

Product

Resources

About