scholarly journals EPR Spectroscopy as a Tool to Characterize the Maturity Degree of Humic Acids

Materials ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3410
Author(s):  
Bozena Debska ◽  
Ewa Spychaj-Fabisiak ◽  
Wiesław Szulc ◽  
Renata Gaj ◽  
Magdalena Banach-Szott
Keyword(s):  
Humic Acids ◽  
Epr Spectroscopy ◽  
Plant Material ◽  
Crop Residues ◽  
Triticum Aestivum L ◽  
Epr Spectra ◽  
Thuja Plicata ◽  
Anthropogenic Factors ◽  
Paramagnetic Resonance ◽  
Spin Concentration

The major indicator of soil fertility and productivity are humic acids (HAs) arising from decomposition of organic matter. The structure and properties of HAs depend, among others climate factors, on soil and anthropogenic factors, i.e., methods of soil management. The purpose of the research undertaken in this paper is to study humic acids resulting from the decomposition of crop residues of wheat (Triticum aestivum L.) and plant material of thuja (Thuja plicata D.Don.ex. Lamb) using electron paramagnetic resonance (EPR) spectroscopy. In the present paper, we report EPR studies carried out on two types of HAs extracted from forest soil and incubated samples of plant material (mixture of wheat straw and roots), both without soil and mixed with soil. EPR signals obtained from these samples were subjected to numerical analysis, which showed that the EPR spectra of each sample could be deconvoluted into Lorentzian and Gaussian components. It can be shown that the origin of HAs has a significant impact on the parameters of their EPR spectra. The parameters of EPR spectra of humic acids depend strongly on their origin. The HA samples isolated from forest soils are characterized by higher spin concentration and lower peak-to-peak width of EPR spectra in comparison to those of HAs incubated from plant material.

scholarly journals A tentative approach to the molecular structure of humic acids: the spectral evidence for a derivation of humic acids from plant-borne esters. 1. The electron paramagnetic resonance (EPR) spectra.

1979 ◽  
Vol 27 (1) ◽  
pp. 79-91 ◽  
Author(s):  
G. Minderman
Keyword(s):  
Molecular Structure ◽  
Electron Paramagnetic Resonance ◽  
Humic Acids ◽  
Epr Spectra ◽  
Paramagnetic Resonance ◽  
Spectral Evidence ◽  
Heterogeneous Polymers ◽  
Electron Paramagnetic

It is suggested, from the evidence of EPR spectra, that humic acids are heterogeneous polymers of mixed esters derived from tannins. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Properties of electrochemically generated primary cationradicals of phenyl- and 2-(4-tolyl)-1,3,4,7-tetramethylisoindoles

1980 ◽  
Vol 45 (6) ◽  
pp. 1669-1676 ◽  
Author(s):  
Pavel Kubáček
Keyword(s):  
Electrochemical Oxidation ◽  
Spin Polarization ◽  
High Spin ◽  
Epr Spectroscopy ◽  
Half Life ◽  
Electrochemical Behaviour ◽  
Epr Spectra ◽  
Electrochemical Generation ◽  
Splitting Constant ◽  
Reduced Temperature

The first step of electrochemical oxidation of 2-phenyl- and 2-(4-tolyl)-1,3,4,7-tetramethylisoindoles in anhydrous acetonitrile produces relatively stable cationradicals which have been studied by means of EPR spectroscopy using the method of internal electrochemical generation of radicals under reduced temperature. The same electrochemical behaviour of the both studied derivatives and identical EPR spectra of their cationradicals can be explained within the Huckel MO method. The largest contribution to the magnitude of splitting constant of nitrogen nucleus is due to π-σ-spin polarization of C-N bonds caused by high spin abundance of pz-AO of carbon atoms. Half-life of decomposition of the studied cationradicals is 4 min at -30°C.

scholarly journals EPR Spectra of Sintered Cd1−xCrxTe Powdered Crystals with Various Cr Content

Materials ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3449
Author(s):  
Ireneusz Stefaniuk ◽  
Werner Obermayr ◽  
Volodymyr D. Popovych ◽  
Bogumił Cieniek ◽  
Iwona Rogalska
Keyword(s):  
Curie Temperature ◽  
Room Temperature ◽  
Integral Intensity ◽  
Resonance Field ◽  
Epr Spectra ◽  
Paramagnetic Resonance ◽  
Simple Method ◽  
Paramagnetic Curie Temperature ◽  
Cr Content ◽  
Electron Paramagnetic

In this paper, we show a simple method of producing ferromagnetic materials with a Curie temperature above room temperature. The electron paramagnetic resonance (EPR) spectra of Cd1−xCrxTe (0.002 < x < 0.08) were measured with a dependence on temperature (82 K < T < 381 K). Obtained EPR lines were fitted to a Lorentz-shaped curve. The temperature dependencies of the parameters of the EPR lines, such as the peak-to-peak linewidth (Hpp), the intensity (A), as well as the resonance field (Hr), were studied. Ferromagnetism was noticed in samples at high temperatures (near room temperature). For a sample with a nominal concentration of chrome of x = 0.05, a very strong intrinsic magnetic field is observed. The value of the effective gyromagnetic factor for this sample is ge = 30 at T = 240 K. An increase of chrome concentration above x = 0.05 reduces the ferromagnetic properties considerably. Analysis of the temperature dependencies of the integral intensity of EPR spectra was carried out using the Curie–Weiss law and the paramagnetic Curie temperature was obtained.

The Microscopic Structure Of Shallow Donors In Silicon Carbide

1996 ◽  
Vol 442 ◽  
Author(s):  
J.-M. Spaeth ◽  
S. Greulich-Weber ◽  
M. März ◽  
E. N. Kalabukhova ◽  
S. N. Lukin
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Temperature Dependence ◽  
Double Resonance ◽  
Epr Spectra ◽  
Electron Nuclear Double Resonance ◽  
Paramagnetic Resonance ◽  
Vacancy Pair ◽  
Temperature Spectra ◽  
Electron Paramagnetic

AbstractThe electronic structure of nitrogen donors in 6H-, 4H- and 3C-SiC is investigated by measuring the nitrogen hyperfine (hf) interactions with electron nuclear double resonance (ENDOR) and the temperature dependence of the hf split electron paramagnetic resonance (EPR) spectra. Superhyperfine (shf) interactions with many shells of 13C and 29Si were measured in 6H-SiC. The hf and shf interactions are discussed in the framework of effective mass theory. The temperature dependence is explained with the thermal occupation of the lowest valley-orbit split A1 and E states. It is proposed that the EPR spectra of P donors observed previously in neutron transmuted 6H-SiC at low temperature (<10K) and high temperature (>60K) are all due to substitutional P donors on the two quasi-cubic and hexagonal Si sites, whereby at low temperature the E state is occupied and at high temperature the A1 state. The low temperature spectra are thus thought not to be due to P-vacancy pair defects as proposed previously.

Investigation of Antioxidant Activity of Pomegranate Juices by Means of Electron Paramagnetic Resonance and UV-Vis Spectroscopy

2015 ◽  
Vol 98 (4) ◽  
pp. 866-870 ◽  
Author(s):  
Violetta Kozik ◽  
Krystyna Jarzembek ◽  
Agnieszka Jędrzejowska ◽  
Andrzej Bąk ◽  
Justyna Polak ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Free Radical ◽  
Epr Spectroscopy ◽  
Antioxidant Properties ◽  
Free Radical Scavenger ◽  
Pomegranate Juice ◽  
Radical Scavenger ◽  
Paramagnetic Resonance ◽  
Vis Spectroscopy ◽  
Electron Paramagnetic

Abstract Pomegranate fruit (Punica granatum L.) is a source of numerous phenolic compounds, and it contains flavonoids such as anthocyanins, anthocyanidins, cyanidins, catechins and other complexes of flavonoids, ellagitannins, and hydrolyzed tannins. Pomegranate juice shows antioxidant, antiproliferative, and anti-atherosclerotic properties. The antioxidant capacity (TEAC) of the pomegranate juices was measured using electron paramagnetic resonance (EPR) spectroscopy and 1,1-diphenyl-2-picrylhydrazyl (DPPH•) as a source of free radicals, and the total phenolic (TP) content was measured using UV-Vis spectroscopy. All the examined pomegranate juices exhibited relatively high antioxidant properties. The TEAC values determined by means of EPR spectroscopy using Trolox (TE) as a free radical scavenger were in the range of 463.12 to 1911.91 μmol TE/100 mL juice. The TP content measured by the Folin-Ciocalteu method, using gallic acid (GA) as a free radical scavenger, widely varied in the investigated pomegranate juice samples and ranged from 1673.62 to 5263.87 mg GA/1 L juice. The strongest antioxidant properties were observed with the fresh pomegranate juices obtained from the fruits originating from Israel, Lebanon, and Azerbaijan. Correlation analysis of numerical data obtained by means of EPR spectroscopy (TEAC) and UV-Vis spectroscopy (TP) gave correlation coefficient (r) = 0.90 and determination coefficient (r2) = 0.81 (P &lt;0.05).

Ge-Related Interfacial Defects in Sige Alloy Structures

1995 ◽  
Vol 405 ◽  
Author(s):  
Patricia J. Macfarlane ◽  
M. E. Zvanut ◽  
W. E. Carlos ◽  
M. E. Twigg ◽  
P. E. Thompson
Keyword(s):  
Depth Profile ◽  
Epr Spectra ◽  
Transmission Electron Micrograph ◽  
Dangling Bond ◽  
Electron Micrograph ◽  
Cross Sectional ◽  
Paramagnetic Resonance ◽  
Transmission Electron ◽  
Interfacial Defects ◽  
Electron Paramagnetic

AbstractThis paper reports etching results supporting the identification of the SG1 center as a germanium dangling bond defect at the interface between an oxide and crystalline SiGe. The presence of this defect is significant because, like an analogous center in Si-based systems, it may alter the operation of any microelectronic or micro-optical device which incorporates an interface between SiGe and an overlying oxide. The samples examined are oxygen implanted SiGe layers in which the SG1 center is believed to occur at the interface between oxide precipitates and SiGe. Because of the center's apparent relation to the oxide precipitates distributed through layers of the sample, a depth profile assists in confirming the interfacial nature of the defect. We obtain a depth profile by comparing electron paramagnetic resonance (EPR) spectra of samples etched to decreasing thickness. EPR spectra indicate that the SG1 center decreases with depth in a manner that when correlated to a cross sectional transmission electron micrograph confirms the association with SiO2 and supports its location at the SiGe/SiO2 precipitate interface.

Electron Paramagnetic Resonance of Radicals Formed during Milling

1960 ◽  
Vol 33 (2) ◽  
pp. 462-468 ◽  
Author(s):  
S. E. Bresler ◽  
S. N. Zhurkov ◽  
E. N. Kazbekov ◽  
E. M. Saminskiĭ ◽  
E. E. Tomashevskiĭ
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Gamma Rays ◽  
Epr Spectra ◽  
Mechanical Degradation ◽  
Present Communication ◽  
Surface Layers ◽  
Paramagnetic Resonance ◽  
Mechanical Destruction ◽  
Electron Paramagnetic

Abstract It is well known that during the mechanical degradation of polymers there takes place scission of molecular chains and the formation of macroradicals. It is of considerable interest to study the electron paramagnetic resonance (EPR) spectra of the macroradicals produced by milling, and to compare them with the spectra of the macroradicals formed in the process of polymerization, and also during the irradiation of polymers by gamma rays and neutrons. We may endeavor to compare the amount of macroradicals formed with the extent of mechanical destruction (for instance with the area of the new interface which is formed). In addition, as was found by experience, the macroradicals formed by mechanical scission are good models for the investigation of reactivity since practically all of them are in the newly formed surface layers and are therefore very accessible to various chemical influences. They enter easily into reaction with various agents present in the medium since in this process diffusion from the surface is found in practice not to be a predominating factor. In the present communication we give the first EPR results obtained on mechanically degraded polymers.

scholarly journals Deciphering molecular details of the RAC–ribosome interaction by EPR spectroscopy

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Sandra J. Fries ◽  
Theresa S. Braun ◽  
Christoph Globisch ◽  
Christine Peter ◽  
Malte Drescher ◽  
...  
Keyword(s):  
Protein Folding ◽  
Epr Spectroscopy ◽  
De Novo ◽  
Contact Point ◽  
Ribosomal Subunit ◽  
Paramagnetic Resonance ◽  
40S Ribosomal Subunit ◽  
Site Directed Spin Labeling ◽  
Α Helix ◽  
Chaperone Complex

AbstractThe eukaryotic ribosome-associated complex (RAC) plays a significant role in de novo protein folding. Its unique interaction with the ribosome, comprising contacts to both ribosomal subunits, suggests a RAC-mediated coordination between translation elongation and co-translational protein folding. Here, we apply electron paramagnetic resonance (EPR) spectroscopy combined with site-directed spin labeling (SDSL) to gain deeper insights into a RAC–ribosome contact affecting translational accuracy. We identified a local contact point of RAC to the ribosome. The data provide the first experimental evidence for the existence of a four-helix bundle as well as a long α-helix in full-length RAC, in solution as well as on the ribosome. Additionally, we complemented the structural picture of the region mediating this functionally important contact on the 40S ribosomal subunit. In sum, this study constitutes the first application of SDSL-EPR spectroscopy to elucidate the molecular details of the interaction between the 3.3 MDa translation machinery and a chaperone complex.

scholarly journals Characterizing SPASM/twitch Domain-Containing Radical SAM Enzymes by EPR Spectroscopy

2021 ◽  
Author(s):  
Aidin R. Balo ◽  
Lizhi Tao ◽  
R. David Britt
Keyword(s):  
Epr Spectroscopy ◽  
Continuous Wave ◽  
Spectroscopic Studies ◽  
Paramagnetic Species ◽  
Paramagnetic Resonance ◽  
Iron Sulfur Cluster ◽  
Radical Sam Enzymes ◽  
Iron Sulfur ◽  
Pulse Epr ◽  
Multiple Domains

AbstractOwing to their importance, diversity and abundance of generated paramagnetic species, radical S-adenosylmethionine (rSAM) enzymes have become popular targets for electron paramagnetic resonance (EPR) spectroscopic studies. In contrast to prototypic single-domain and thus single-[4Fe–4S]-containing rSAM enzymes, there is a large subfamily of rSAM enzymes with multiple domains and one or two additional iron–sulfur cluster(s) called the SPASM/twitch domain-containing rSAM enzymes. EPR spectroscopy is a powerful tool that allows for the observation of the iron–sulfur clusters as well as potentially trappable paramagnetic reaction intermediates. Here, we review continuous-wave and pulse EPR spectroscopic studies of SPASM/twitch domain-containing rSAM enzymes. Among these enzymes, we will review in greater depth four well-studied enzymes, BtrN, MoaA, PqqE, and SuiB. Towards establishing a functional consensus of the additional architecture in these enzymes, we describe the commonalities between these enzymes as observed by EPR spectroscopy.

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