Search Results (82)

Gadolinium-doped hydroxyapatite nanoparticles (HapGd NPs) have emerged as promising multifunctional platforms for biomedical applications due to their unique combination of biocompatibility, structural tunability, and magnetic responsiveness. In this work, HapGd nanoparticles were synthesized using a microwave-assisted method and subsequently functionalized with curcumin and folic acid to enhance therapeutic efficiency and selective targeting. The synthesized nanostructures were characterized using various techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), vibrating sample magnetometry (VSM), and relaxometry. Structural analyses revealed successful incorporation of Gd³⁺ ions into the Hap lattice, resulting in reduced unit cell volume and slight lattice distortion, while preserving the apatite crystalline framework. Surface functionalization with curcumin and folic acid was confirmed through spectroscopic characterization, demonstrating effective molecular attachment. Nuclear Magnetic Resonance (NMR) relaxation measurements indicated that Gd doping endowed paramagnetic behavior suitable for contrast enhancement in magnetic resonance imaging (MRI). Relaxometry studies revealed a strong linear correlation between 1/T₁ and the Gd³⁺ concentration, especially in the functionalized samples, with performance comparable to the commercial contrast agent Omniscan™. The developed HapGd-based nanoplatform exhibits integrated diagnostic and therapeutic potential, providing a foundation for future research in biomedical applications. Full article

Chromium complexes with triamidoamine derivatives bearing bulky substituents at the terminal positions of the ligands, tris(2-(3-pentylamino)ethyl)amine (H₃L^Pen) and tris(2-dicyclohexylmethylaminoethyl)amine (H₃L^Cy), are prepared: [{Cr(L^Pen)}₂(μ-N₂)] (1), [{CrK(L^Pen)(μ-N₂)(Et₂O)}₂] (2), [CrCl(L^Pen)] (3), [Cr(L^Cy)] (4), [CrK(L^Cy)(μ-N₂)(18-crown-6)(THF)] (5(THF)), and [CrCl(L^Cy)] (6). The preparation of these complexes is confirmed by X-ray diffraction analysis. Complexes 1, 2, and 5(THF) have coordinated dinitrogen molecules, with N–N bond lengths of 1.185(3), 1.174(9), and 1.162(3) Å, respectively. These lengths are significantly elongated compared to that of a free dinitrogen molecule (1.10 Å), indicating that the N₂ ligands are activated. The ν(¹⁴N–¹⁴N) values of 1, 2, and 5(THF) are 1715 cm⁻¹ for 1 (Raman, in solution), 1787, 1743 cm⁻¹ for 2 (IR, in solid), and 1824 cm⁻¹ for 5(THF) (IR, in solid), respectively. These values are markedly smaller than free nitrogen (2331 cm⁻¹), confirming that the dinitrogen is interacting with the metal ions and is activated. The structures of 2 and 5(THF) in solution are also studied by ¹H NMR and solution IR spectroscopies. ¹H NMR spectra of these complexes reveal that the peaks of 2 and 5(THF) are observed in the diamagnetic region, whereas those for the other complexes (1, 3, 4, and 6) exhibit paramagnetic shifts. The reactions of these complexes with K[C₁₀H₈] and HOTf under N₂ in THF yield hydrazine and a small amount of ammonia; however, they are not catalytic. The ¹H NMR and IR spectra of the products obtained by reacting 1 or 3 with reductant K in THF under N₂ atmosphere indicate that 2 is formed based on spectral agreement. Similarly, upon examining for 4 or 6, it is confirmed that a species similar to 5(THF) is generated. Full article

Solid-state spin centers are at the forefront of developing advanced quantum technologies, engaging in applications of sensing, communication and computing. A semiconductor host matrix compatible with existing silicon technology provides a robust platform for holding spin defects and an opportunity for external manipulation. In this article, negatively charged nitrogen-vacancy (NV) centers in the hexagonal hh position in a 6H polytype silicon carbide crystal was studied using high-frequency (94 GHz) electron paramagnetic (EPR) and electron nuclear double resonances (ENDOR) spectroscopy. Experimentally determined values of hyperfine and quadrupole interactions of ¹⁴N were compared with the values obtained for the centers in NV_k2k1 positions. The distribution of spin density of the defect within a supercell of the SiC crystal lattice was calculated using the density functional theory approach. The theoretical estimation of electron-nuclear interaction constants turned out to be in close agreement with the experimental values, which allows us to refine the microscopic model of a point defect. The temperature dependence of the spin Hamiltonian values (δA/δT ≅ 180 Hz/K) was studied with the possibility of observing the ¹⁴N NMR signal at room temperature. The fundamental knowledge gained about interactions’ parameters’ behavior lays the foundation for the creation of promising quantum platforms. Full article

Background: Transition metal complexes incorporating fluorinated counter anions represent a significant class of compounds with broad applications in industry, pharmaceuticals, and biomedicine. These fluorinated anions are known to enhance the solubility, stability, and reactivity of the complexes, thereby expanding their functional utility in various chemical and biological contexts. Methods: A set of metal(II) complexes of the general formula [MPy₆][B(C₆F₅)₄]₂ where (Py = pyridine, M = Mn (1), Fe (2), Co (3), Ni (4), Cu (5), Zn (6)) have been synthesized by direct reaction of metal halides and pyridine in the presence of Ag[B(C₆F₅)₄]. The complexes were characterized using different techniques to assure their purity, such as elemental analysis (EA), electron paramagnetic resonance (EPR) spectroscopy, thermogravimetric analysis (TGA), ultraviolet–visible (UV–Vis) spectroscopy, ¹¹B-NMR, ¹H-NMR, and FT-IR spectroscopy. The antimicrobial and antifungal properties against different types of bacteria and fungi were studied for all prepared complexes. Results: The synthesized complexes exhibited broad-spectrum antimicrobial activity, demonstrating variable efficacy compared to the reference antibiotic, oxytetracycline (positive control). Notably, complex 6 displayed exceptional antibacterial activity against Streptococcus pyogenes, with a minimum inhibitory concentration (MIC) of 4 µg/mL, outperforming the control (MIC = 8 µg/mL). Complexes 1, 2, and 4 showed promising activity against Shigella flexneri, Klebsiella pneumoniae, and Streptococcus pyogenes, each with MIC values of 8 µg/mL. Conversely, the lowest activity (MIC = 512 µg/mL) was observed for complexes 3, 5, and 6 against Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae, respectively. Regarding antifungal properties, complexes 5 and 6 demonstrated the highest activity against Candida albicans, with MIC values of 8 µg/mL, equivalent to that of the positive control, fluconazole. Density functional theory (DFT) calculations confirmed an overall octahedral coordination geometry for all complexes, with tetragonal distortions identified in complexes 3, 4, and 5. Full article

Partial reduction of transition metal oxides via defect engineering is a promising strategy to enhance their electronic and photocatalytic properties. In this study, we systematically explored the mechanochemical reduction of Nb₂O₅ using LiBH₄ and NaBH₄ as reducing agents. Electron paramagnetic resonance (EPR) spectroscopy confirmed a successful partial reduction of the oxide, as seen by the presence of unpaired electrons. Interestingly, larger hydride concentrations did not necessarily enable a higher degree of reduction as large amounts of boron hydrides acted as a buffer material and thus hindered the effective transfer of mechanical energy. Powder X-ray diffraction (PXRD) and ⁷Li solid-state NMR spectroscopy indicated the intercalation of Li⁺ into the Nb₂O₅ lattice. Raman spectroscopy further revealed the increased structural disorder, while optical measurements showed a decreased band gap compared with pristine Nb₂O₅. The partially reduced samples showed significantly enhanced photocatalytic performance for methylene blue degradation relative to the unmodified oxides. Full article

Nitroxides are stable organic free radicals with a wide range of applications. They have found applications in chemistry, biochemistry, biophysics, molecular biology, and biomedicine as EPR/NMR imaging techniques. As spin labels and probes, they are used in electron paramagnetic resonance (EPR) spectroscopy in the study of proteins, lipids, nucleic acids, and enzymes, as well as for measuring oxygen concentration in cells and cellular organelles, as well as tissues and intracellular pH. Their unique redox properties have allowed them to be used as exogenous antioxidants. In this review, we have discussed the chemical properties of nitroxides and their antioxidant properties. Furthermore, we have considered their use as radioprotectors and protective agents in ischemia/reperfusion in vivo and in vitro. We also presented other applications of nitroxides in protecting cells and tissues from oxidative stress and in protein studies and discussed their use in EPR/MRI. Full article

Humic acids (HAs) possess diverse functionalities, endowing them with multiple applications as bioactive compounds in agriculture. Alkaline extraction is key to obtaining HAs from their source material. The presence of oxygen during extraction can lead to oxidative changes in the humic structure. The extent of HA transformation depending on their origin remains poorly understood, and the effect of alkaline extraction on the HA biological activities is yet to be estimated. Here, we compare the physicochemical properties of HAs extracted from fresh organic material, compost, in air (HA-O₂) and under nitrogen (HA-N₂). We also assess the antioxidant properties of HAs-O₂ and HAs-N₂ from compost (HAC), Retisol (HAR), and Chernozem (HACh) and relate them to the HA biological activities. Changes in the HAC properties were analyzed using the following techniques: elemental composition, ultraviolet–visible and infrared spectroscopy, ¹³C nuclear magnetic resonance (¹³C-NMR), electron paramagnetic resonance (EPR), gel filtration using Sephadex G-75 gel, and potentiometric titration. The HA antioxidant properties were explored using the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) assay (antiradical activity) and phosphomolybdenum assay (total antioxidant capacity). The HA biological activity was estimated by priming radish and wheat seeds (0.5 g L⁻¹ HAs, 25 °C, 5 h for radish and 14 h for wheat), followed by germination tests. Alkaline extraction of HAC in air vs. nitrogen resulted in a 1.2-fold increase in the O/C ratio and optical density at E₄₆₅, oxidation of aliphatic fragments, a 2-fold increase in the contents of functional groups, and a 1.2-fold increase in the number of paramagnetic centers. All HA-O₂ preparations have demonstrated an enhanced antiradical activity (1.3–1.6 times) and total antioxidant capacity (1.1–1.3 times) compared to HA-N₂. The Vigor Index of seeds primed with HA-O₂ was 1.1-to-1.8-fold higher than those treated with HA-N₂, depending on the HA origin. We demonstrate that alkaline treatment in air benefits the antiradical and biological activities of HAs, making such preparations more attractive for use as natural antioxidants and priming agents. This opens up new perspectives for using O₂-modified HAs as innovative plant stimulants in agriculture. Full article

We have synthesized novel cobalt(II) and nickel(II) pincer ligand complexes containing novel tridentate ligand precursors that coordinate via oxygen, nitrogen, and oxygen donor atoms. The novel tridentate ONO ligands, which are neutral, incorporate a carbonyl-substituted imidazole functionality and contain R groups of ethyl, isopropyl, or tert-butyl. The ligand precursors were thoroughly characterized using NMR spectroscopy, ESI-MS, and IR spectroscopy. The metal complexes were thoroughly characterized using single crystal X-ray diffraction, elemental analysis, ESI-MS, and cyclic voltammetry. The nickel(II) and cobalt(II) complexes with ethyl, isopropyl, and t-butyl wingtip groups had a pseudo-octahedral geometry about the metal center. The nickel(II) complex with R = isopropyl had a monoclinic lattice with C121 space group (a = 21.7639(8); b = 11.0649(5); c = 10.9225(4); alpha = 90.0 degrees; beta = 90.609(3) degrees; gamma = 90.0 degrees). The cobalt(II) complex with R = ethyl had a monoclinic lattice with P2₁/n space group (a = 17.7907(7); b = 21.5278(6); c = 21.8597(7); alpha = 90.0 degrees; beta = 95.063(3) degrees; gamma = 90.0 degrees). The cobalt(II) complexes were paramagnetic with μ_eff = 1.59 BM (R = ethyl) and 6.67 BM (R = t-butyl). The nickel(II) complex was paramagnetic with μ_eff = 2.59 BM. The ligand precursors and metal complexes are redox-active. Full article

The synthesis of two polycyclic aromatic hydrocarbon (PAH) monoradicals, terbenzoolympicenyl radical (BOR1) and tetrabenzoolympicenyl radical (BOR2), is reported. One-electron oxidation of both BOR1 and BOR2 yielded stable cationic species BOR1+ and BOR2+, whose structures were unambiguously characterized using 2D nuclear magnetic resonance (NMR) spectroscopy. The physical properties of BOR1 and BOR2 were investigated by means of electron paramagnetic resonance (EPR), UV-vis-NIR, cyclic voltammetry (CV), and density functional theory (DFT) calculations. BOR1+ and BOR2+ exhibited intense near-infrared (NIR) absorption, which may be of potential use in the biological fields. Full article

Grafting of paramagnetic transition and rare earth metal ions onto the surface of detonation nanodiamonds (DNDs) was successfully implemented in the recent decade and opened new opportunities in the biomedical application of these compounds, particularly as novel contrast agents for magnetic resonance imaging. The grafting was studied mainly using EPR, NMR, and magnetic measurements. Such a highly surface-sensitive, quantitative, chemical analytic technique as X-ray photoelectron spectroscopy (XPS) was very rarely used. In this paper, we report the XPS study of grafting transition and rare-earth metal ions (Cu²⁺, Co²⁺, Mn²⁺, and Gd³⁺) onto the surface of DNDs. Binding energies for metal, carbon, oxygen, and nitrogen atoms were determined and attributed to the corresponding ion states and atomic groups. Comparing XPS and EPR findings, we showed that the developed synthesis route resulted in almost complete grafting of manganese and gadolinium atoms in the form of paramagnetic ions Mn²⁺ and Gd³⁺ to the diamond surface, while only 30% of the copper atoms on the surface are in the paramagnetic state Cu²⁺, and the rest 70% are in the non-magnetic Cu⁺ state. It was not possible to draw a similar conclusion regarding Co²⁺ ions due to the lack of data on the amount of these paramagnetic ions on the DND surface. Full article

The spectral characteristics of cyclosporin C (CsC) with the addition of Dy³⁺ ions in acetonitrile (CD₃CN) and CsC with Dy³⁺ incorporated into dodecylphosphocholine (DPC) micelle in deuterated water were investigated by high-resolution NMR spectroscopy. The study was focused on the interaction between Dy³⁺ ions and CsC molecules in different environments. Using a combination of one-dimensional and two-dimensional NMR techniques, we obtained information on the spatial features of the peptide molecule and the interaction between CsC and the metal ion. The non-uniform effect of the metal ion on different NMR signals of CsC was observed. The paramagnetic attenuation parameter was calculated for the amide, alpha, and beta protons of CsC upon the addition of Dy³⁺. The metal ion was found to interact with the polar part of the DPC micelle, and the ion also has a significant effect on the NMR signals of amino acid residues from Sar₃ to d-Ala₈. This pattern is reproduced in both environments studied here and also agrees with earlier investigations of the CsA–Dy³⁺ complex. Full article

Gossypol and its derivatives arouse interest due to their broad spectrum of biological activities. Despite its wide potential application, there is no reported example of gossypol derivatives bearing stable radical functional groups. The first gossypol nitroxide hybrid compound was prepared here via formation of a Schiff base. By this approach, synthesis of a gossypol nitroxide conjugate was performed by condensation of gossypol with a 4-amino-TEMPO (4-amino-2,2,6,6-tetramethylpiperidin-1-oxyl) free radical, which afforded the target product in high yield. Its structure was proven by a combination of NMR and EPR spectroscopy, infrared spectroscopy, mass spectrometry, and high-resolution mass spectrometry. In addition, the structure of the gossypol nitroxide was determined by single-crystal X-ray diffraction measurements. In crystals, the paramagnetic Schiff base exists in an enamine–enamine tautomeric form. The tautomer is strongly stabilized by the intra- and intermolecular hydrogen bonds promoted by the resonance of π-electrons in the aromatic system. NMR analyses of the gossypol derivative proved that in solutions, the enamine–enamine tautomeric form prevailed. The gossypol nitroxide at micromolar concentrations suppressed the growth of tumor cells; however, compared to gossypol, the cytotoxicity of the obtained conjugate was substantially lower. Full article

Folic acid (FA) is an essential vitamin involved in crucial metabolic processes, while copper(II) ions play significant roles in various biological functions. This study aims to investigate the interaction between FA and Cu²⁺ using ¹H and ¹³C NMR spectroscopy under different pH levels and concentrations. The research employed detailed NMR analysis to explore how Cu²⁺ binds to FA, focusing on changes in chemical shifts, diffusion coefficients, and copper-induced paramagnetic effects. The key findings reveal that Cu²⁺ predominantly coordinates with the pteridine ring (PTE) of FA, with minimal involvement from the glutamic acid (Glu) moiety. The interaction is strongly concentration-dependent: at lower FA concentrations, Cu²⁺ binds effectively to the PTE ring, while at higher concentrations, intermolecular interactions among FA molecules hinder copper binding. The study also observed pronounced paramagnetic effects on the PTE and p-aminobenzoic acid protons, with negligible effects on Glu signals. These results provide new insights into the structural characteristics of FA-Cu²⁺ complexes, contributing to a better understanding of their biochemical interactions and implications for folate metabolism. Full article

A paramagnetic A₃B-type Mn(III)-porphyrin was synthesized and characterized by physical–chemical methods (UV-Vis, FT-IR, ¹H-NMR spectroscopy). The obtained compound was tested as a sensitive material for the spectrophotometric and potentiometric detection of iodine species. Using UV-Vis spectroscopy, the triiodide anions could be detected with high precision in the concentration interval of 1.02 × 10⁻⁵ to 2.3 × 10⁻⁵ M, with an LOD of 9.44 × 10⁻⁶ M. The PVC-based electrode using DOP as a plasticizer showed a sensitivity toward iodide in a wide concentration range of 1.0 × 10⁻⁵ to 1.0 × 10⁻¹ M, with an LOD of 8.0 × 10⁻⁶ M. Both methods are simple, low-cost, and efficient for the detection of iodine species in synthetic samples and pharmaceuticals. Full article

The metallocenes ferrocene (Cp₂Fe, 1), nickelocene (Cp₂Ni, 2), and cobaltocene (Cp₂Co, 3) crystallize in the same space group (P2₁/a) and they have the same shape and similar size. Therefore, they form solid solutions with random distribution of the different molecules when crystallized from solution. Alternatively, the solid metallocenes can be ground together manually, and the solid solutions form at any molar ratio within minutes. The metallocenes 2 and 3 are paramagnetic. Solid solutions of 1/3 and 2/3 have been studied by paramagnetic solution and solid-state NMR spectroscopy. The effect of the paramagnetic species on the other components in the solid solutions has been investigated. The impact on the chemical shifts is limited. However, the halfwidths and the signal shapes, as defined by the rotational sideband intensities, change with increasing amounts of paramagnetic components. The ¹H T₁ relaxation times are shortened for diamagnetic protons in the presence of paramagnetic metallocenes in the solid solutions. It has been demonstrated that all metallocenes mix at the molecular level within the polycrystalline samples. The EPR spectra of the solid solutions are dominated by the most intensive signal of any paramagnetic metallocene in the solid samples. Full article