Paramagnetic Properties Research Articles

Gd-doped diamond synthesized using Gd@C82 under high pressure and high temperature

Our work studied the structural changes of Gd@C82 under high pressure and successfully synthesized Gd-doped diamond which has the paramagnetic properties using Gd@C82 precursors under high pressure and high temperature.

Triplet states in the reaction center of Photosystem II.

In oxygenic photosynthesis sunlight is harvested and funneled as excitation energy into the reaction center (RC) of Photosystem II (PSII), the site of primary charge separation that initiates the photosynthetic electron transfer chain. The chlorophyll ChlD1 pigment of the RC is the primary electron donor, forming a charge-separated radical pair with the vicinal pheophytin PheoD1 (ChlD1+PheoD1-). To avert charge recombination, the electron is further transferred to plastoquinone QA, whereas the hole relaxes to a central pair of chlorophylls (PD1PD2), subsequently driving water oxidation. Spin-triplet states can form within the RC when forward electron transfer is inhibited or back reactions are favored. This can lead to formation of singlet dioxygen, with potential deleterious effects. Here we investigate the nature and properties of triplet states within the PSII RC using a multiscale quantum-mechanics/molecular-mechanics (QM/MM) approach. The low-energy spectrum of excited singlet and triplet states, of both local and charge-transfer nature, is compared using range-separated time-dependent density functional theory (TD-DFT). We further compute electron paramagnetic resonance properties (zero-field splitting parameters and hyperfine coupling constants) of relaxed triplet states and compare them with available experimental data. Moreover, the electrostatic modulation of excited state energetics and redox properties of RC pigments by the semiquinone QA- is described. The results provide a detailed electronic-level understanding of triplet states within the PSII RC and form a refined basis for discussing primary and secondary electron transfer, charge recombination pathways, and possible photoprotection mechanisms in PSII.

Synthesis and Characterization of Nd2O3 Nanoparticles Using Urea As Precipitation Agent

Nanoparticles (NPs) of neodymium oxide were prepared by homogeneous co-precipitation method using neodymium nitrate and urea as precursors. X-ray diffraction (XRD) patterns have been refined by the Rietveld method and the Fourier-transform infrared spectroscopy (FT-IR) showed that the sample had a bandgap of about 4.59 eV. On the other hand, the photoluminescence (PL) spectrum indicated that the sample had a low concentration of singly ionized oxygen vacancies. The paramagnetic property of the NPs has been also tested by vibrating-sample magnetometer (VSM) measurements.

Biosynthesis of novel NiFe12O19-X (X = ZnO and TiO2) magnetic nanophotocatalyst toward the degradation pharmaceutical ceftriaxone sodium from aqueous solution under sunlight irradiation and antibacterial activity

Since antibiotics are used in various sciences, the occurrence of antibiotics in the water environments has drawn significant concerns in recent years. In this study, novel NiFe 12 O 19 coupled ZnO and TiO 2 (NiFe 12 O 19 -X; X = ZnO and TiO 2 ) were synthesized via a green route, and their photocatalytic properties were assessed. Crataegus microphylla fruit extract was used as a natural capping agent to obtain regular and homogeneous products. The as-synthesized nanocomposites were characterized by various analyzes, including TEM, EDS, DRS, FT-IR, XRD, FESEM, and VSM. The analysis confirmed that the biosynthesized nanocomposites had spherical and oval-like morphologies, with a crystallite size of about 50–70 nm, narrow bandgap, and super paramagnetic properties. Band-gap calculated using UV-DRS (2.95 eV and 3.03 eV) shows that NiFe 12 O 19 –ZnO and NiFe 12 O19–TiO 2 are good candidate for photocatalytic degradation. Ceftriaxone sodium (CFX) as the model contaminant was tested to assess the photocatalytic performance of the biosynthesized magnetic nanocomposite under UV and sunlight irradiations. The effect of critical parameters including nanocatalyst dose (0.08, 0.2, 0.4, and 0.6 g/L), pH (5, 7, and 10), CFX initial concentration (10, 25, 50, and 100 mg/L), and light source (UV and sunlight) were studied to achieve the optimum degradation of ceftriaxone sodium. Under optimum conditions, the biosynthesized NiFe 12 O 19 –ZnO and NiFe 12 O 19 –TiO 2 photocatalyst revealed excellent performance in the degradation of the CFX compound with an evaluated efficiency of 98.47% and 95.45% under UV irradiation, respectively. Also, the percentage of antibiotic degradation for these materials was 79.15% and 76.62%, respectively, under sunlight irradiation. Furthermore, the antibacterial characteristic features of the prepared nanocomposite against gram-positive and gram-negative bacteria were satisfactory. After careful examination of the results and diagrams, the suggested NiFe 12 O 19 -X (X = ZnO and TiO 2 ) nanocomposites might be applied in a water treatment plant to eliminate the danger of pharmaceutical waste in the aqueous medium.

Recyclable ferroferric oxide@titanium dioxide@molybdenum disulfide with enhanced enzyme-like activity under visible light for effectively inhibiting the growth of drug-resistant bacteria in sewage.

With the development of social industry and the increase in domestic sewage discharge, pathogenic bacterial contamination in water has become a serious health and environmental problem. It is important to design sewage treatment reagents with effective pathogenic bacterial removal and recyclability. In this work, we developed a nanocomposite, Fe3O4@TiO2@MoS2, with once-for-all effects of photocatalytic, magnetic, and peroxidase-like activities for solving the above-mentioned problems. The loading of MoS2 may cause the band gap of Fe3O4@TiO2 to decrease from 3.11 eV to 2.85 eV, demonstrating increased photocatalytic activity under visible light, based on the synergistic impact of Fe3O4@TiO2 and MoS2. In return, the peroxidase-like activity of Fe3O4@TiO2@MoS2 was significantly higher than that of Fe3O4 and MoS2 alone, resulting in the generation of more hydroxyl radicals (˙OH) for combating the drug-resistant broad-spectrum β-lactamase-producing Escherichia coli and methicillin-resistant Staphylococcus aureus. The antibacterial mechanism study showed that Fe3O4@TiO2@MoS2 could effectively inhibit bacterial growth by destroying the bacterial biofilm and genome via the peroxidase-like activity as well as photocatalytic activity. In addition, Fe3O4@TiO2@MoS2 has excellent paramagnetic properties, which can achieve magnetic recovery after wastewater treatment. Even after three times of recycling, its antibacterial effect can remain above 98.8%.

NMR exchange dynamics studies of metal-capped cyclodextrins reveal multiple populations of host-guest complexes in solution.

Metal-capped molecular hosts are unique in supramolecular chemistry, benefitting from the inner cavity's hydrophobic nature and the metal center's electrochemical properties. It is shown here that the paramagnetic properties of the metals in lanthanide-capped cyclodextrins (Ln-α-CDs and Ln-β-CDs) are a convenient NMR indicator for different populations of host-guest complexes in a given solution. The paramagnetic guest exchange saturation transfer (paraGEST) method was used to study the exchange dynamics in systems composed of Ln-α-CDs or Ln-β-CDs with fluorinated guests, revealing multiple co-existing populations of host-guest complexes exclusively in solutions containing Ln-β-CDs. The enhanced spectral resolution of paraGEST, achieved by a strong pseudo contact shift induction, revealed that different molecular guests can adopt multiple orientations within Ln-β-CDs' cavities and, in contrast, only a single orientation inside Ln-α-CDs. Thus, paraGEST, which can significantly improve NMR detectability and spectral resolution of host-guest systems that experience fast exchange dynamics, is a convenient tool for studying supramolecular systems of metal-capped molecular hosts.

Enhanced in vitro inhibition of MCF-7 and magnetic properties of cobalt incorporated calcium phosphate (HAp and β-TCP) nanoparticles

The Co2+ (0.1 M) incorporated hydroxyapatite (HAp) and beta tricalcium phosphate (β-TCP) nanoparticles were synthesized by the microwave assisted technique and sintering of HAp respectively. The samples were thermally treated at temperatures ranging from 200 to 1000°C. The partial substitutions of Co2+ at the Ca2+ site of HAp were confirmed from the slight shift (∼0.2°) in the (002) and (211) XRD peaks. The morphology of the nanoparticles was transformed from nanospheres to twinned particles on thermal treatment. In addition, the particle size of Co-600 was increased (from ∼50 nm to ∼100 nm) due to the recrystallization process. Further, the thermal treatment enhanced the crystallinity (41.15 to 90.16%), retentivity (Mr) and coercivity (Hc) of the nanoparticles. The cobalt incorporated HAp and β-TCP possessed paramagnetic property. The excellent bioactivity of β-TCP has been confirmed by the mineralization in simulated body fluid (SBF). Compared to HAp, β-TCP possessed better compatibility towards C2C12 cells on cobalt incorporation as evidenced by the in vitro cell viability. Moreover, both HAp and β-TCP have significantly inhibited the growth of MCF-7 on increasing the interaction time (72 h). Hence, the inhibition characteristics of Co2+ incorporated calcium phosphate (CaP) towards MCF-7 (without affecting the normal cells) demonstrate its competency as a potential material for cancer therapy over the already existing nanoparticles.

Layer‐by‐layer preparation of electromagnetic NH2‐SiO2/polypyrrole/Ni nanocomposites, characterization and their electrochemical properties

AbstractCombinations of organic conducting polymers and inorganic electromagnetic materials have drawn much attention in various fields like energy storage materials, biosensors, biomedical applications, catalysis and removal of heavy metals from water. In this investigation an attempt is made to decorate polypyrrole (PPy), a semiconducting electroactive polymer, with Ni nanoparticles on a functional silica (SiO2) support. First, amine‐functionalized mesoporous NH2‐SiO2 seed particles are prepared by the sol–gel method using hexamethylenediamine as a surface‐functionalizing agent and cetyltrimethylammonium bromide as a template. Second, NH2‐SiO2/PPy composite particles are prepared via in situ seeded chemical oxidative polymerization of pyrrole. The surface of the NH2‐SiO2/PPy composite particles is finally immobilized/doped with Ni nanoparticles via in situ chemical reduction of Ni(II) salt. The surface morphology, structure modification, size distribution and magnetic properties of the prepared NH2‐SiO2/PPy/Ni nanocomposite particles are confirmed using various spectroscopic techniques, electron microscopy, Brunauer–Emmett–Teller measurements, X‐ray diffraction and vibrating sample magnetometry. The NH2‐SiO2/PPy/Ni nanocomposite particles possess good paramagnetic properties. A comparative study of electrochemical properties revealed improvement in specific capacitance of NH2‐SiO2/PPy composite compared to PPy but further decoration with Ni nanoparticles under alkaline condition reduces the capacitance value. © 2022 Society of Industrial Chemistry.

Adsorptive removal of aflatoxin B1 from contaminated peanut oil via magnetic porous biochar from soybean dreg

The contamination of mycotoxin in edible oil has always been a major threat to human health. In this study, magnetic soybean dreg-based biochar SDB-6-K-9@Fe3O4 was prepared via co-precipitation and used to remove aflatoxin B1 (AFB1) from contaminated oil. The adsorbent characterization results revealed that the Fe3O4 was successfully loaded to the SDB-6-K-9. The 0.45SDB-6-K-9@Fe3O4 had paramagnetic properties with a saturation magnetization of 45.15 emu/g, which could be quickly separated from the peanut oil using an external magnet. The maximum adsorption capacity of peanut oil contaminated with 200 ng/mL AFB1 by 50 mg 0.45SDB-6-K-9@Fe3O4 for 2 h reached 0.1354 mg/g, while the removal process minimally affected the quality of the oil. The adsorption behavior results followed a pseudo-second-order kinetic and fitted well with the Freundlich model. The excellent adsorption removal efficiency and facile magnetic separation of the adsorbents provide a simple and efficient method for removing contaminants from the oil.

Synthesis, Structural and Magnetic Properties of Cobalt-Doped GaN Nanowires on Si by Atmospheric Pressure Chemical Vapor Deposition.

GaN nanowires (NWs) grown on silicon via atmospheric pressure chemical vapor deposition were doped with Cobalt (Co) by ion implantation, with a high dose concentration of 4 × 1016 cm-2, corresponding to an average atomic percentage of ~3.85%, and annealed after the implantation. Co-doped GaN showed optimum structural properties when annealed at 700 °C for 6 min in NH3 ambience. From scanning electron microscopy, X-ray diffraction, high resolution transmission electron microscope, and energy dispersive X-ray spectroscopy measurements and analyses, the single crystalline nature of Co-GaN NWs was identified. Slight expansion in the lattice constant of Co-GaN NWs due to the implantation-induced stress effect was observed, which was recovered by thermal annealing. Co-GaN NWs exhibited ferromagnetism as per the superconducting quantum interference device (SQUID) measurement. Hysteretic curves with Hc (coercivity) of 502.5 Oe at 5 K and 201.3 Oe at 300 K were obtained. Applied with a magnetic field of 100 Oe, the transition point between paramagnetic property and ferromagnetic property was determined at 332 K. Interesting structural and conducive magnetic properties show the potential of Co-doped GaN nanowires for the next optoelectronic, electronic, spintronic, sensing, optical, and related applications.

Effect of Infill Density of the Printed PET-G Structures Containing Iron Oxides on Magnetic Properties

This work aims to characterize printing structures with various infill densities composed of a thermoplastic material containing magnetic particles composed of mainly Iron(III) oxides with regard to their possible processing with the additive technology of Fused Filament Fabrication. A polyethylene terephthalate glycol (PET-G) structural thermoplastic with the addition of Iron(III)) oxides has been selected, and correct processing temperatures have been determined using thermal analysis. The paramagnetic properties of printed products consisting of different filling densities have been tested. Relative permeability has been identified to be strongly dependent on the printed internal structures of tested products. The samples composed of the densest structure have shown relative permeability higher by 18% with respect to the sample printed with the least dense structure. Finite Element Modelling (FEM) simulations have been applied to determine magnetic field distributions and, moreover, to calculate the holding forces of all printed samples. The performed simulations confirmed that produced composites might be utilized as magnetic switches and sensors or as more advanced components for homogenizing electric motors’ magnetic fields. Moreover, magnetic properties might be tuned according to the specific needs printing structure with the suitable density.

Dioxygen and reactive oxygen species’ paramagnetic properties are important factors in dermatology

Dioxygen (the O2 molecule) is an important component of all tissues including skin. Even small fluctuations of O2 amount (dioxygen concentration changes in the tissue microenvironment) can strongly affect the signaling functions of cells through the reactive oxygen species (ROSs) activity and hence - the whole cellular metabolism, the cell proliferation, and differentiation, etc [1,2].

Paramagnetic Semiconducting Se–Mn Clusters: A Mn3Se4-Stabilized Selenide Radical Intermediate and Its Aggregated Derivatives

The transition metal-stabilized heavy main group radicals are extremely scarce due to their highly reactive natures, making them difficult to be isolated and identified. We report here a rare class of the Se radical-containing manganese carbonyl anionic cluster, [(μ-Se)(μ3-Se2)2Mn3(CO)9]•2- (1), which was successfully obtained from the one-pot reaction of Se powder and Mn2(CO)10 in concentrated KOH/MeOH/MeCN solutions at 90 °C. Dianion 1 and its dimeric cluster, [(μ4-Se2){(μ3-Se2)2Mn3(CO)9}2]4- [(1)2], could undergo the reversible Se-Se bond breakage or reformation by the thermal cracking of (1)2 or self-dimerization of 1, showing the μ-Se•- radical character of 1. Complex 1 could react with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) to form the Se radical-captured complex [(μ-Se(TEMPO)) (μ3-Se2)2Mn3(CO)9]2- (1-TEMPO) or could react with alkylene bromides (CH2)nBr2 (n = 1, 2) to give the Mn4-based oxidative coupling products, [(μ4-Se2)(μ-Se2LSe)2Mn4(CO)12]2- (L = CH2, 2-CH2; Se, 2-Se). In addition, dianion 1 and its aggregated derivatives (1)2, 1-TEMPO, 2-CH2, and 2-Se exhibited unusual paramagnetic properties with the spin-state switching from S = 1 (Mn) + 1/2 (Se) to S = 1 (Mn), in which their magnetic centers were proved to be mixed-valent Mn atoms and the μ-Se•- radical, as evidenced by Evans method, superconducting quantum interference device, X-ray photoelectron spectra, electron paramagnetic resonance, and density functional theory calculations. Importantly, these clusters showed semiconducting behaviors with low and tunable energy gaps (1.50-2.01 eV) and varied electrical conductivities (2.52 × 10-8-4.58 × 10-9 S/cm), where efficient electron transports mainly arose from C-H(phenyl)···O(carbonyl) interactions within the solid-state frameworks.

Magnetic multi-walled carbon nanotubes as an efficient sorbent for pirimicarb removal from aqueous solutions in continuous (FBAC) and batch formats: thermodynamic, kinetic, isotherm study, optimization and modeling by RSM-ANN

In this study magnetic carbon nanotubes (CNT) were synthesized and used for the removal of pirimicarb insecticide. For characterization of CNT/Fe3O4 nanocomposite, various analyses such as FT-IR, XRD, VSM, SEM, EDX, Map, and TEM were used. The results of this analysis showed that the CNT/Fe3O4 nanocomposite was well-synthesized and had great paramagnetic properties (with Ms = 38.12 emu/g) and effective functional groups. The removal of pirimicarb process by this nanocomposite was performed in fixed bed adsorption column (FBAC) and batch format. In batch format, the effects of pH, contact time, composite dosage, and concentration of pirimicarb were studied using surface response method-central composite design (RSM-CCD) and artificial neural network (ANN). The results of response surface methodology demonstrated that the maximum efficiency of adsorption is 94.62 % while pH, contact time, composite dosage, and concentration of pirimicarb are 6.72, 47.56 min, 1.07 g/L and 43.91 ppm, respectively. Also, RSM-CCD modeling was more capable of expressing the adsorption process than artificial neural network modeling due to higher correlation coefficient and lower error. The equilibrium and kinetic studies showed that the process follows the sips model and pseudo-second-order model respectively and is physically desirable. Also, the mechanism of adsorption was best fitted in double-exponential model and is consisted of both inter and intra-particle diffusion. Thermodynamic studies suggested that pirimicarb adsorption onto CNT/Fe3O4 was a spontaneous and exothermic process. In addition, the results of FBAC showed that the breakthrough time was reduced from 365 min to 9 min by increasing temperature (25 °C, 35 °C and 45 °C) and exhaustion time was diminished by increasing in temperature.

Impedance-based Rapid Diagnostic Tool for Single Malaria Parasite Detection.

This paper presents a custom, low-cost electronic system specifically designed for rapid and quantitative detection of the malaria parasite in a blood sample. The system exploits the paramagnetic properties of malaria-infected red blood cells (iRBCs) for their magnetophoretic capture on the surface of a silicon chip. A lattice of nickel magnetic micro-concentrators embedded in a silicon substrate concentrates the iRBCs above coplanar gold microelectrodes separated by 3 μm for their detection through an impedance measurement. The sensor is designed for a differential operation to remove the large contribution given by the blood sample. The electronic readout automatically balances the sensor before each experiment and reaches a resolution of 15 ppm in the impedance measurement at 1 MHz allowing a limit of detection of 40 parasite/μl with a capture time of 10 minutes. For better reliability of the results, four sensors are acquired during the same experiment. We demonstrate that the realized platform can also detect a single infected cell in real experimental conditions, measuring human blood infected by Plasmodium falciparum malaria specie.

High-Field (3.4 T) Electron Paramagnetic Resonance, 1H Electron-Nuclear Double Resonance, ESEEM, HYSCORE, and Relaxation Studies of Asphaltene Solubility Fractions of Bitumen for Structural Characterization of Intrinsic Carbon-Centered Radicals

Petroleum asphaltenes are considered the most irritating components of various oil systems, complicating the extraction, transportation, and processing of hydrocarbons. Despite the fact that the paramagnetic properties of asphaltenes and their aggregates have been studied since the 1950s, there is still no clear understanding of the structure of stable paramagnetic centers in petroleum systems. The paper considers the possibilities of various electron paramagnetic resonance (EPR) techniques to study petroleum asphaltenes and their solubility fractions using a carbon-centered stable free radical (FR) as an intrinsic probe. The dilution of asphaltenes with deuterated toluene made it possible to refine the change in the structure at the initial stage of asphaltene disaggregation. From the measurements of samples of bitumen, a planar circumcoronene-like model of FR structure and FR-centered asphaltenes is proposed. The results show that EPR-based approaches can serve as sensitive numerical tools to follow asphaltenes' structure and their disaggregation.

Luminescence, Paramagnetic, and Electrochemical Properties of Copper Oxides-Decorated TiO2/Graphene Oxide Nanocomposites

The properties of newly synthesized Cu2O/CuO-decorated TiO2/graphene oxide (GO) nanocomposites (NC) were analyzed aiming to obtain insight into their photocatalytic behavior and their various applications, including water remediation, self-cleaning surfaces, antibacterial materials, and electrochemical sensors. The physico-chemical methods of research were photoluminescence (PL), electron paramagnetic resonance (EPR) spectroscopy, cyclic voltammetry (CV), and differential pulse voltammetry (DPV). The solid samples evidenced an EPR signal that can be attributed to the oxygen-vacancy defects and copper ions in correlation with PL results. Free radicals generated before and after UV-Vis irradiation of powders and aqueous dispersions of Cu2O/CuO-decorated TiO2/GO nanocomposites were studied by EPR spectroscopy using two spin traps, DMPO (5,5-dimethyl-1-pyrroline-N-oxide) and CPH (1-hydroxy-3-carboxy-2,2,5,5-tetramethylpyrrolidine), to highlight the formation of hydroxyl and superoxide reactive oxygen species, respectively. The electrochemical characterization of the NC modified carbon-paste electrodes (CPE) was carried out by CV and DPV. As such, modified carbon-paste electrodes were prepared by mixing carbon paste with copper oxides-decorated TiO2/GO nanocomposites. We have shown that GO reduces the recombination process in TiO2 by immediate electron transfer from excited TiO2 to GO sheets. The results suggest that differences in the PL, respectively, EPR data and electrochemical behavior, are due to the different copper oxides and GO content, presenting new perspectives of materials functionalization.

Preparation of novel magnetic porous biochar and its adsorption mechanism on cerium in rare earth wastewater

A novel and efficient process for the removal of Ce(IV) from aqueous solutions was sought, and a new magnetic porous biochar (PBC/ZF) was synthesized by loading ZnFe2O4 (ZF) onto porous biochar (PBC) using a one-step hydrothermal method. The SEM observation of the external features showed that the cubic spinel structured ZnFe2O4 (ZF) particles were loaded onto the porous biochar (PBC) surface. This resulted in a composite with superb paramagnetic properties as well as higher adsorption properties. In addition, the microstructure was characterized by FTIR, which demonstrated that the target material was supplied with a large amount of carboxyl groups (-COOH) by citric acid during the synthesis process. The BET showed that the target material had a higher specific surface area than ZnFe2O4 with PBC, confirming the successful preparation of the target material after activation of the biomass using ZnCl2 immersion as well. The effect of different factors on the adsorption effect was investigated experimentally. The results showed that PBC/ZF had a good adsorption effect on Ce(IV) with a short adsorption equilibrium time and a maximum adsorption capacity of 228.9 mg/g at room temperature with lower acidity (pH = 2.5). The adsorption kinetics and isotherm analysis showed that the Ce(IV) adsorption process fitted well with the quasi-secondary kinetic model and Langmuir model. It indicates that the process is a single molecular layer adsorption process. It was demonstrated that PBC/ZF also has high removal rate for high concentration Ce(IV) solution, and it is easy for solid-liquid separation under the action of applied magnetic field after adsorption. It provides a new treatment method and theoretical support for the adsorption treatment technology of Ce (IV) wastewater.

Collective Effects in Ionic Liquid [emim][Tf2N] and Ionic Paramagnetic Nitrate Solutions without Long-Range Structuring.

Mesoscopic shear elasticity has been revealed in ordinary liquids both experimentally by reinforcing the liquid/surface interfacial energy and theoretically by nonextensive models. The elastic effects are here examined in the frame of small molecules with strong electrostatic interactions such as room temperature ionic liquids [emim][Tf2N] and nitrate solutions exhibiting paramagnetic properties. We first show that these charged fluids also exhibit a nonzero low-frequency shear elasticity at the submillimeter scale, highlighting their resistance to shear stress. A neutron scattering study completes the dynamic mechanical analysis of the paramagnetic nitrate solution, evidencing that the magnetic properties do not induce the formation of a structure in the solution. We conclude that the elastic correlations contained in liquids usually considered as viscous away from any phase transition contribute in an effective way to collective effects under external stress whether mechanical or magnetic fields.

Characterization of Humic Substances from Taiga and Tundra Soils by EPR Spectroscopy

Paramagnetic activity is a fundamental property of humic substances (HSs). The agricultural use of soils does not only affect the qualitative and quantitative compositions of HSs, but also the content of free radicals (FRs) in their structure. Changes in the composition of incoming plant residues and hydrothermal conditions have an effect on soil humification rates and the paramagnetic properties of humic (HAs) and fulvic acids (FAs). Data on the influence of various factors on the content of FRs in HAs and FAs are not enough. Therefore, the purpose of this study was to examine the influence of the degree of hydromorphism and agricultural use on the paramagnetic properties of HA and FA samples obtained from taiga and tundra soils. Studies have shown that the increased hydromorphism in taiga soils leads to the growing concentration of FRs in the HA molecular structure. HAs in virgin tundra soils exhibit a lower content of unpaired electrons when shifting from automorphic soils to hydromorphic ones. Going from the south to the north, the paramagnetic activity of both HAs and FAs tends to decrease due to the overall reduction of the number of polyconjugated systems in the tundra soil HSs. The comparative analysis of the paramagnetic properties in HAs and FAs of virgin and arable soils revealed that their agricultural use reduces the FR concentration in the structure of HSs, in other words it leads to the accumulation of biothermodynamically stable and more humified compounds in the arable horizons. This contributes to the stabilization of SOM in arable soils.