Search Results (130)

We investigate how grain growth, strain relaxation, and vacancy chemistry shape the near-edge optical response of nanocrystalline Ce${\mathrm{O}}_{2-\delta }$ prepared by a chymosin-assisted Pechini route from nitrate–citrate precursors. Rietveld line-profile analysis shows that phase-pure Ce${\mathrm{O}}_{2-\delta }$ forms after calcination between 400 and 1000 °C. Over this range, the average crystallite size increases from ≈3.4 to ≈57 nm, while the microstrain decreases from 0.79% to 0.05%, with size–strain scaling consistent with interface-controlled grain growth that follows a normal growth law with exponent $m=2$ and activation energy $Q\approx 155$ kJ ${\mathrm{mol}}^{-1}$. Raman spectroscopy tracks the sharpening of the $F_{2g}$ mode and the fading of defect-related bands, X-ray photoelectron spectroscopy reveals a nonmonotonic evolution of the surface ${\mathrm{Ce}}^{3+}$ fraction and separates lattice from adsorbed oxygen species, and electron paramagnetic resonance detects vacancy-bound ${\mathrm{Ce}}^{3+}$ polarons that weaken at high temperature. Diffuse-reflectance UV–Vis spectra show a modest blue shift of the apparent band gap from $E_g\approx 2.78$ to 2.95 eV as crystallites coarsen, while the Urbach energy $E_u$ follows the ${\mathrm{Ce}}^{3+}$ content and sub-gap tailing. The structural, spectroscopic, and optical results together map out a quantitative connection between grain growth, vacancy populations, and near-edge optical properties in ${\mathrm{CeO}}_{2-\delta }$ nanoparticles. Full article

Triarylmethyl radicals (TAMs) have recently emerged as highly effective polarizing agents in dynamic nuclear polarization (DNP) under viscous conditions, enabling substantial hyperpolarization via the solid-effect (SE) DNP mechanism even at room temperature. A comparable, though less pronounced, enhancement was observed for BDPA radicals embedded in phosphocholine-based lipid bilayers. Given the increasing interest in elucidating the structure and dynamics of biopolymers and their high-molecular-weight assemblies—such as cell membranes—this study focuses on the design, synthesis, and characterization of paramagnetic agents tailored for DNP-based structural biology. To this end, we synthesized a series of TAM derivatives functionalized with lipophilic substituents and characterized their magnetic resonance properties, including isotropic hyperfine interaction (HFI) constants on carbon nuclei and electron spin relaxation times (T₁ and T_m) at low temperatures (80 K). Echo-detected EPR spectra and electron spin echo envelope modulations (ESEEM) were recorded for novel TAM incorporated into liposomes composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). These low-temperature measurements revealed that the radicals are localized either at the liposome surface or within the lipid bilayer, ensuring optimal accessibility to water molecules. Crucially, the presence of a single cholesterol moiety provides strong noncovalent anchoring within the hydrophobic core of the bilayer. Guided by these findings, we identify an amphiphilic TAM bearing a single cholesterol group and polar carboxyl functionalities as a highly promising candidate for DNP applications in membrane biology, combining efficient polarization transfer, bilayer integration, and aqueous accessibility. Full article

Solid solutions of the metallocenes ferrocene (Cp₂Fe), nickelocene (Cp₂Ni), and cobaltocene (Cp₂Co) have been prepared by manually grinding the components together, or by co-crystallizing them from solution. In the solid solutions Cp₂Fe/Cp₂Ni and Cp₂Co/Cp₂Ni, the cyclopentadienyl (Cp) protons relax via dipolar electron–proton interactions, which represent the dominant relaxation mechanism. The ¹H T₁ relaxation times of the molecules Cp₂Ni and Cp₂Co, dissolved in CDCl₃, and in the solid solutions, show that the relaxation takes place intramolecularly. The relaxation of the protons is propagated exclusively via the unpaired electrons of the metal centers to which their Cp rings are coordinated, due to the large intermolecular distances that are greater than 3.91 Å. In contrast, the intramolecular distances between the electrons of the metal atoms and the protons of their coordinated Cp rings are merely 2.70 Å. Using these intramolecular distances and the ¹H T₁ relaxation times, the electron relaxation times T_1e have been determined as 17 × 10⁻¹³ s in CDCl₃ solutions and 45 × 10⁻¹³ s in the solid state for Cp₂Ni. The corresponding T_1e times for Cp₂Co are calculated as ca. 5 × 10⁻¹³ s and 20 × 10⁻¹³ s. Grinding Cp₂Fe and Cp₂Ni together leads to two different ¹H T₁ relaxation times for the protons of Cp₂Fe. The longer T₁ relaxation time indicates domains that consist mostly of Cp₂Fe molecules. The short T₁ times show a close contact of Cp₂Fe and Cp₂Ni molecules. An analysis of the short ¹H T₁ times reveals the presence of at least two to three short distances of 3.91 Å between Cp₂Fe and Cp₂Ni molecules. These results support the hypothesis that dry grinding of the metallocenes Cp₂Fe and Cp₂Ni in ratios that were changed in 10% increments from 90%/10% to 30%/70% leads to domains that mostly consist of Cp₂Fe molecules, and additionally to domains that contain a mixture of the components on the molecular level. Full article

Iron(III) (Fe(III)) complexes have recently emerged as safer alternatives to magnetic resonance imaging (MRI) contrast agents (CAs), reigniting interest in biomedical research. Although gadolinium Gd(III)-based contrast agents (CAs) have been widely used in MRI over the past four decades, their use in the current clinical routine is severely constrained due to concerns about high toxicity and environmental impact. Research is now focusing on synthesizing safer contrast agents with alternative paramagnetic ions like Fe(III) or Mn(II). MRI CAs with integrated potent therapeutic moieties may offer synergistic advantages over traditional contrast agents in clinical use. The study explored the use of salinomycin-ferrihydrite composites as possible effective ensembles of imaging and therapeutic units in the same molecule, evaluating their anticancer activity and influence on the signal in MRI. The composites were characterized using Mössbauer spectroscopy and ICP-MS for iron content determination. The in vitro relaxivity measurements in a high-field MR scanner demonstrated the potency of the composites as T₂ enhancers. The antitumor activity of one selected Sal-ferrihydrite composite was tested in three human cancer cell lines: A549 (non-small cell lung cancer); SW480 (colon cancer); and CH1/PA1 (ovarian teratocarcinoma) by the MTT cell viability assay. The new Sal-ferrihydrite composite showed a pronounced cytotoxicity in all three human cancers in line with enhanced signal in MRI, which makes it a promising candidate for future biomedical applications. The superior cytotoxic effect, together with the strong signal enhancement, makes these compounds promising candidates for further detailed investigations as future theranostic agents. Full article

Magnetic resonance techniques are powerful, nondestructive, non-invasive tools with broad applications in radiation dosimetry. Electron paramagnetic resonance (EPR) enables direct quantification of dose-dependent radiation-induced paramagnetic defects, while nuclear magnetic resonance (NMR) reflects the influence of such defects through changes in line width and nuclear spin relaxation. To date, these methods have typically been applied independently. Their combined use to probe radiation damage in the same material offers new opportunities for comprehensive characterization and preferred dosimetry techniques. In this work, we apply both EPR and NMR to investigate radiation damage in lithium carbonate (Li₂CO₃). A detailed EPR analysis of γ-irradiated samples shows that the concentration of paramagnetic defects increases with dose, following two distinct linear regimes: 10–100 Gy and 100–1000 Gy. A gradual decay of the EPR signal was observed over 40 days, even under cold storage. In contrast, ⁷Li NMR spectra and spin–lattice relaxation times in Li₂CO₃ exhibit negligible sensitivity to radiation doses up to 1000 Gy, while ¹H NMR results remain inconclusive. Possible mechanisms underlying these contrasting behaviors are discussed. Full article

Gadolinium-based contrast agents (GBCAs) are the gold standard as MRI probes but are nowadays facing medical limitations and environmental concerns. To address these issues, novel strategies focus on the optimization of Gd(III)-based probes. One promising approach involves incorporating Gd(III) into nanoparticles, particularly coordination polymers, which offer improved relaxivity. In this study, we explore the self-assembly of Gd(III) ions with ascorbate ligand, forming extended coordination polymer architectures. Our investigation focuses on understanding the impact of nanoparticles’ growth and aggregation on their relaxivity properties. Notably, the controlled aggregation process leads to a different distribution of the Gd(III) in the surface and in the bulk of the nanoparticles, mainly responsible for their longitudinal relaxivity. Additionally, the introduction of Eu(III) into the network enables the development of a dual-modal probe with paramagnetic and optical features. Full article

Electron paramagnetic resonance (EPR) spectroscopy is gaining increasing recognition in research on various nanostructures. In the case of iron oxide nanoparticles, EPR measurements offer the possibility of determining the magnetic phase and the exact type (Fe₃O₄, γ-Fe₂O₃, α-Fe₂O₃, or a combination) of the core material. Furthermore, the EPR technique enables the study of relaxation processes, estimation of the effective and surface anisotropy constants, and assessment of the influence of sample aging on the magnetic properties of nanoparticles. The scope of the information obtained can be further expanded by utilizing spin labeling of polymer-coated nanoparticles. By analyzing the signals from the attached nitroxide, one can determine certain properties of the coating and its interactions with the environment (e.g., body fluids, cells, tissues) and also perform imaging of nanoparticles in various media. In some cases, EPR can help monitor the encapsulation of active substances and their release processes. Unfortunately, despite the enormous potential, not all of the possibilities offered by EPR are routinely used in nanoscience. Therefore, the present article aims not only to present the current applications and existing trends but also to indicate directions for future EPR research, constituting a road map. Full article

The pharmaceutical product is a powdered tablets containing bisoprolol fumarate that is used in the treatment of circulatory system diseases. They were examined by X-band (9.3 GHz) electron paramagnetic resonance spectroscopy. The aim of this work was to determine the influence of the physical conditions of storage on the properties and content of free radicals in this pharmaceutical product. The product was subjected to a temperature of 50 °C, UVA radiation, and UVA radiation and then a temperature of 50 °C. The amplitude, integral intensity, linewidth of EPR lines, and g factor, were analyzed. Free radicals were formed in all tested samples; thus, the product containing bisoprolol fumarate should not be stored at a temperature of 50 °C, and it should be protected from UVA radiation, which is in line with the manufacturer’s requirements. The content of free radicals in the examined product was highest after treatment at a temperature of 50 °C. The lowest free radical content characterized the product after the interaction of both UVA radiation and a temperature of 50 °C. EPR lines were not microwave saturated below a power of 70 mW, which indicates fast spin-lattice relaxation processes in the product. It has been demonstrated that free radical formation in the product containing bisoprolol fumarate depends on the type of physical factor. Full article

Electron paramagnetic resonance (EPR) examination of the effect of storage conditions on properties and contents of free radicals formed in the pharmaceutical preparation containing spironolactone, taking into account physical factors such as UVA radiation and the higher temperature, was conducted. The changes in amplitude (A), integral intensity (I) and EPR linewidth (ΔB_pp) of the EPR spectra and free radical contents were determined. It was obtained that free radicals are formed during storage of this preparation under three different treatments: 50 °C, under UVA radiation, and under UVA radiation and a temperature of 50 °C. During storage, the preparation containing spironolactone should be protected from temperatures 50 °C and from UVA radiation. A higher content of free radicals is formed in the tested preparation exposed to both UVA and a temperature of 50 °C, than in the preparation exposed only to UVA or only to a temperature of 50 °C. Similar integral intensities (I) were obtained for the tested preparation exposed to a temperature of 50 °C or exposed to UVA radiation. Fast spin-lattice relaxation processes occur in all tested pharmaceutical preparation samples containing spironolactone. The usefulness of EPR spectral analysis in the study of free radicals formed in pharmaceutical preparations has been confirmed. Full article

Organometallic rare-earth complexes have attracted considerable attention in recent years due to their unique structures and exceptional magnetic properties. In this study, we report the synthesis and magnetic characteristics of a family of monopentamethylcyclopentadienyl-coordinated trinuclear rare-earth hepta-chloride clusters [(Li(THF)(Et₂O))(Cp^*RE)₃(μ-Cl)₄(μ₃-Cl)₂(μ₄-Cl)] (RE₃: RE =Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; Cp* = pentamethylcyclopentadienide). These clusters were synthesized by reacting LiCp* with RECl₃ in a 1:1 molar ratio within a mixed solvent system (THF: Et₂O = 1:9), resulting in high solubility in common organic solvents such as DCM, THF, and Et₂O. Magnetic studies conducted on these paramagnetic clusters reveal the coexistence of ferromagnetic and antiferromagnetic superexchange interactions in Gd₃. Additionally, Dy₃ exhibits both ferromagnetic and antiferromagnetic intramolecular dipolar interactions. Notably, slow magnetic relaxation was observed in Dy₃ below 23 K under a zero DC applied field with an energy barrier of 125(6) cm⁻¹. Full article

Ultra-high magnetic fields and high-sensitivity cryoprobes permit the achievement of a high S/N ratio in ¹³C detection experiments, thus making a ¹³C superWEFT (Super water eliminated Fourier transform) experiment feasible. ¹³C signals that are not visible using ¹H observed heteronuclear experiments, nor with established 2D ¹³C direct detection experiments, become easily observable when a ¹³C relaxation-based filter is used. Within this frame, optimal control pulses (OC pulses) have been, for the first time, applied to paramagnetic systems. Although the duration of OC pulses competes with relaxation, their application to paramagnetic signals has been successfully tested. OC pulses are much more efficient with respect to the phase- and amplitude-modulated ones routinely used at lower fields while providing bandwidth excitation profiles that are sufficient to meet the need to cover up to an 80 ppm spectral region. On the other hand, when paramagnetic relaxation is shorter than the duration of OC pulses, the use of hard, rectangular pulses is, at the present state of the art, the best approach to minimize the loss of signal intensity. Full article

We report two conjugates of gem-diethyl pyrroline nitroxide radicals with D-mannosamine as potential metabolic organic radical contrast agents, mORCAs, circumventing the need for biorthogonal reactions. In-cell EPR spectroscopy, using Jurkat cells and analogous conjugate, based on a pyrrolidine nitroxide radical, shows an efficient incorporation of highly immobilized nitroxides, with a correlation time of τ_cor = 20 ns. In vivo MRI experiments in mice show that the paramagnetic nitroxide radical shortens the T₁ and T₂ relaxation times of protons in water located in the kidney and brain by only up to ~10% after 3 d. Ex vivo EPR spectroscopic analyses indicate that the contrast agents in mouse tissues are primarily localized in the kidney, lung, liver, heart, and blood, which primarily contain immobilized nitroxide radicals with τ_cor = 4–9 ns. The spin concentrations in tissues remain low (1–3 nmol g⁻¹) at 24 h after the third mORCA injection, approximately one to two orders of magnitude lower than those of ORCAFluor and BASP-ORCA (measured at ~24 h post-injection). These low spin concentrations explain the small proton T₁ and T₂ relaxation changes observed in in vivo MRI. Full article

Quantum technologies are currently being explored for various applications, including computing, secure communication, and sensor technology. A critical aspect of achieving high-fidelity spin manipulations in quantum devices is the controlled optical initialization of electron spins. This paper introduces a low-cost programming scheme based on a 32-bit STM32F373 microcontroller, aimed at facilitating high-precision measurements of optically active solid-state spin centers within semiconductor crystals (SiC, hBN, and diamond) utilizing a multi-pulse sequence. The effective shaping of short optical pulses across semiconductor and solid-state lasers, covering the visible to near-infrared range (405–1064 nm), has been validated through photoinduced electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) spectroscopies. The application of pulsed laser irradiation influences the EPR relaxation parameters associated with spin centers, which are crucial for advancements in quantum computing. The presented experimental approach facilitates the investigation of weak electron–nuclear interactions in crystals, a key factor in the development of quantum memory utilizing nuclear qubits. Full article

In this paper, the impact of annealing at different temperatures (973 K, 1073 K, and 1123 K for 1 h) on the magnetic and microstructural properties of MnFePSi-based glass-coated microwires is studied. Annealing significantly influences the magnetic and microstructural properties of Mn–Fe–P–Si glass-coated microwires. XRD analysis reveals that increasing the annealing temperature leads to a notable increase in the Fe₂P phase content, reaching a maximum at 1123 K, while simultaneously reducing the presence of secondary phases observed in the as-prepared sample. The reduction in secondary phases in Mn–Fe–P–Si-based microwires, grain size, and internal stress relaxation have a profound impact on their magnetic behavior. High coercivity values are observed in both the as-prepared and annealed samples. However, annealing at higher temperatures (1073 K and 1123 K) results in a significant reduction in coercivity, decreasing from 1200 Oe for the sample annealed at 973 K to 300 Oe and 150 Oe, respectively. In addition, the sample annealed at 1123 K for 1 h shows a notable paramagnetic behavior for loops measured from 200 K to 300 K. Meanwhile, the other samples show ferromagnetic behavior for all measured temperatures from 5 to 300 K. This study highlights the significant potential for tailoring and modifying various magnetic properties of Mn–Fe–P–Si glass-coated microwires, including metamagnetic phase transitions, magnetic behavior, and the control of magnetic response (hardness/softness). Such tailored properties make Mn–Fe–P–Si glass-coated microwires promising candidates for a wide range of applications. Full article

We study the relaxation dynamics near the critical points of the Yang–Lee edge singularities (YLESs) in the quantum Ising chain in an imaginary longitudinal field with a polarized initial state. We find that scaling behaviors are manifested in the relaxation process after a non-universal transient time. We show that for the paramagnetic Hamiltonian, the magnetization oscillates periodically with the period being inversely proportional to the gap between the lowest energy level; for the ferromagnetic Hamiltonian, the magnetization decays to a saturated value; while for the critical Hamiltonian, the magnetization increases linearly. A scaling theory is developed to describe these scaling properties. In this theory, we show that for a small- and medium-sized system, the scaling behavior is described by the $(0+1)$-dimensional YLES. Full article