Search Results (38)

The objective of this study was to introduce Diplorhynchus condylocarpon as a potential latex source. In addition, the physicochemical properties of the polymer as a trap for NO₂ were investigated. Advanced spectroscopic methods, such as FTIR-ATR, EPR, and ¹H and ¹³C NMR, were used in addition to traditional elemental analysis to evaluate the properties of the latex. Analysis of latex from the Diplorhynchus condylocarpon tree revealed the presence of rubber. In addition to rubber, analyses revealed the presence of other aromatic and aliphatic compounds in the latex sample. The presence of semiquinone radicals indicates the presence of antioxidant phenolic structures in Diplorhynchus condylocarpon. The reaction of latex with NO₂ resulted in the formation of a stable nitroxyl radical, as proven by the characteristic EPR parameters. Full article

To obtain data on the effects of ozonolysis on the structural and dynamic parameters of ultrafine fibers based on the binary compositions of poly-(3-hydroxybutyrate) (PHB) and polyvinylpyrrolidone (PVP) with varying ratios of polymer components ranging from 0/100 to 100/0 mass%, produced by electrospinning, a study was conducted. The morphology and structural–dynamic characteristics of the ultrafine fibers were examined. Comprehensive research was carried out, combining thermophysical measurements (DSC), dynamic measurements using an electron paramagnetic resonance (EPR) technique, scanning electron microscopy, and infrared spectroscopy. The influence of the mixture’s composition and ozonolysis on the degree of crystallinity of PHB and the molecular mobility of the TEMPO radical (tetramethylpiperidine-1-oxyl) in the amorphous regions of the PHB/PVP fiber material was demonstrated. The low-temperature maximum on the DSC thermograms provided information about the fraction of hydrogen bonds in the mixed compositions, allowing for the enthalpy of thermal destruction of these bonds in both the original and oxidized samples to be determined. The study showed significant changes in the degree of crystallinity of PHB, the enthalpy of hydrogen bond destruction, molecular mobility, moisture absorption of the compositions, and the activation energy of rotational diffusion in the amorphous regions of the PHB/PVP mixed compositions. It was established that within the 50/50% PHB/PVP ratio, an inversion transition occurs from the dispersion material to the dispersion medium. Ozonolysis induces a sharp change in the material’s structure. The conducted research provided the first opportunity to assess the impact of ozonolysis on the structural and dynamic characteristics of PHB/PVP ultrafine fibers at a molecular level. These materials may serve as a therapeutic system for controlled drug delivery. Full article

Wine is a rich source of biologically active compounds, particularly polyphenols, which exhibit antioxidant and antiradical properties. The objective of this study was to optimize the vinification procedures of Polish wines from the hybrid white grape cv. ‘Johanniter’ and red grape cv. ‘Regent’, grown in the temperate climate of central Europe, by applying different skin maceration times: 4, 8, 12, 16, and 20 days. The wines were compared for their basic oenological characteristics and polyphenolic (UHPLC–MS) content as well as their antioxidant (FRAP test) and antiradical (DPPH test, ORAC-fl and EPR spectroscopy) capacities. Both wines demonstrated a substantial increase in their total phenolic content and antioxidant and antiradical capacities after a 4-day maceration; further treatment did not lead to considerable enrichment in bioactive compounds. Scavenging activities against nitroxyl radicals and DPPH were divergent for the tested wines and depended on the analytical method applied, which indicated distinct molecular mechanisms. In turn, the activity of peroxyl radical scavengers, antioxidant capacity, and the total content of phenolics were higher in all the red wine samples. The antioxidant and antiradical properties of the examined wines were comparable or even exceeded those determined for most wines produced in regions with a rich winemaking tradition. Full article

The antioxidant/prooxidant effects of dinitrosyl iron complexes (DNICs), physiological donors of nitric oxide (NO^•), are studied in reaction systems modeling processes with cytochrome c occurring in mitochondria under oxidative stress and leading to apoptosis. Using luminol-dependent chemiluminescence, DNICs with glutathione and phosphate ligands were shown to decrease the level of prooxidants in a reaction system containing ferricytochrome c and cumene hydroperoxide. Electron paramagnetic resonance (EPR) spectroscopy revealed that glutathione DNICs (DNICs-GS) intercepted the free radicals formed during the interaction between cytochrome c and tert-butyl hydroperoxide. DNICs-GS were also shown to prevent the formation of oligomeric forms of cytochrome c, which were induced by organic hydroperoxides. Reduced glutathione was less effective as an antioxidant than DNICs-GS or could even occasionally exhibit the prooxidant properties. Ferricytochrome c also catalyzed the formation of DNICs-GS with nitroxyl anion (NO⁻) taking part. Full article

Phenylene-based bis-oxamate polydentate ligands offer a unique opportunity for creating a large variety of coordination compounds, in which paramagnetic metal ions are strongly magnetically coupled. The employment of imino nitroxyl (IN) radicals as supplementary ligands confers numerous benefits, including the strong ferromagnetic interaction between Ni and IN. Furthermore, the chelating IN can act as a capping ligand, thereby impeding the formation of coordination polymers. In this study, we present the molecular and crystal structure and experimental and theoretical magnetic behavior of an exceptional neutral trinuclear complex [Ni(L³⁻)₂(IN)₃]∙5CH₃OH (1) (L is N,N′-1,3-phenylenebis-oxamic acid; IN is [4,4,5,5-tetramethyl-2-(6-methylpyridin-2-yl)-4,5-dihydro-1H-imidazol-1-yl]oxidanyl radical) with a cyclic triangular arrangement. Moreover, in this compound three Ni²⁺ ions are linked by the two bis-oxamate ligands playing a rare tritopic function due to an unprecedented triple deprotonation of the related meta-phenylene-bis(oxamic acid). The main evidence of such a deprotonation of the ligand is the neutrality of the cluster, since there are no anions or cations compensating for its charge in the crystals of the compound. Despite the presence of six possible magnetic couplings in the trinuclear cluster 1, its behavior was reproduced with a high degree of accuracy using a three-J model and ZFS, under the assumption that the three different Ni-IN interactions are equal to each other, whereas only two equivalent-in-value Ni-Ni interactions were taken into account, with the third one being equated to zero. Our study indicates the presence of two opposite-in-nature types of magnetic interactions within the triangular core. DFT and CASSCF/NEVPT2 calculations were completed to support the experimental magnetic data simulation. 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

In this paper, we investigate the magnetic exchange interaction and magnetization dynamics of two new members of the [LnRad(NO₃)₃] family, where Rad is a tripodal nitroxide, and Ln is Er(III) or Yb(III), having the prolate type electron density. Single OK crystal and powder X-ray diffraction studies showed that these complexes are isostructural with their previously investigated Y, Gd, Dy, Tm, Tb, Eu, and Lu congeners. A magnetometric investigation, supported by ab initio calculations, showed the presence of antiferromagnetic coupling between the lanthanide ion and the radical in both compounds with estimated J values of ≈7 and ≈20 cm⁻¹ for Er and Yb, respectively (+J S_eff∙ S formalism). Full article

A binuclear cobalt–radical complex formed by the reaction of Co(hfac)₂·2H₂O (hfac = hexafluoroacetylacetonate) with the 2,2-bis(1-oxyl-3-oxide-4,4,5,5-tetramethylimidazolinyl) biradical (BR) has been synthesized. The complex {(hfac)Co^II(BN)Co^II(hfac)} crystallizes in the triclinic space group P$\overline{1}$ :  C₃₄H₂₈Co₂F₂₄N₄O₁₂, a = 11.1513(5) Å, b = 12.8362(7) Å, c = 18.2903(8) Å, α = 103.061(1)°, β = 100.898(2)°, γ = 102.250(1)°, Z = 2. The compound consists of two non-equivalent pseudo-octahedral Co^II ions, each bearing two hfac ancillary ligands bridged by the tetradentate bis-nitroxide (BN). The temperature dependence of the magnetic susceptibility indicates a strong antiferromagnetic exchange between each of the Co²⁺ ions and the nitroxyl biradical, as well as between the spins within the bridging ligand, forming a spin-frustrated system. Micro-squid investigations, performed on a single crystal of {(hfac)Co^II(BN)Co^II(hfac)}, reveal a peculiarity of the M(H) graph at temperatures below 0.4 K displaying a step that is a result of ground and first excited levels mixing by the applied magnetic field due to a small energy gap between them, as inferred from ab initio calculation. The latter was also carried out for two models of mononuclear Co²⁺ complexes in order to obtain a set of initial parameters for fitting the experimental magnetic curves using the Phi program. Moreover, direct CAS(12,10)/def2-TZVP calculations of the magnetic dependences χT(T) and M(H) were performed, which satisfactorily reproduced the experimental ones. Full article

Acenes, as a class of polycyclic aromatic hydrocarbons, attract considerable attention due to their remarkable nonlinear optical and magnetic properties. The aim of this work was the elucidation of the capability of radical-substituted acene derivatives to undergo spin-state-switching rearrangements. For this purpose, a series of acene-based (anthracene, pentacene, heptacene) molecules bearing fluorenyl and tert-butyl-nitroxyl radicals were investigated through comprehensive quantum chemical modeling of their electronic structures, isomerization and magnetic properties. A possible mechanism of the transformation of the closed-shell folded isomer into the biradical twisted structure of the bis-fluorenyl anthracene has been ascertained by applying the procedure of searching for the Minimum Energy Crossing Point. The conditions favoring the occurrence of spin-state-switching in such classes of polycyclic aromatic hydrocarbon derivatives have been formulated. By varying the size of an acene core and the type of radical substituent, the compounds capable of changing their magnetic properties have been revealed. Considering the unique features of radical-bearing acene-based derivatives, the proposed molecules can be used as functional materials in photonics and electronics. Full article

Nitroxides are stable radicals consisting of a nitroxyl group, >N-O^•, which carries an unpaired electron. This group is responsible for the paramagnetic and antioxidant properties of these compounds. A recent study evaluated the effects of pyrrolidine and pyrroline derivatives of nitroxides on the antioxidant system of human red blood cells (RBCs). It showed that nitroxides caused an increase in the activity of superoxide dismutase (SOD) and the level of methemoglobin (MetHb) in cells (in pyrroline derivatives) but had no effect on the activity of catalase and lactate dehydrogenase. Nitroxides also reduced the concentration of ascorbic acid (AA) in cells but did not cause any oxidation of proteins or lipids. Interestingly, nitroxides initiated an increase in thiols in the plasma membranes and hemolysate. However, the study also revealed that nitroxides may have pro-oxidant properties. The drop in the AA concentration and the increase in the MetHb level and in SOD activity may indicate the pro-oxidant properties of nitroxides in red blood cells. Full article

The influence of bovine serum albumin (BSA) on collapsing poly(N-isopropylacrylamide) (PNIPAM) chains was studied with turbidimetry and spin probe and spin label electron paramagnetic resonance spectroscopy. An increased ratio of collapsed chains in aqueous solutions in the narrow temperature region near the LCST appeared in the presence of 2.5–10 wt% BSA. The spin probe EPR data indicate that the inner cavities of the BSA dimers are probably responsive to the capture of small hydrophobic or amphiphilic molecules, such as TEMPO nitroxyl radical. The observed features of the structure and dynamics of inhomogeneities of aqueous PNIPAM-BSA solutions, including their mutual influence on the behavior of the polymer and protein below the LCST, should be considered when developing and investigating PNIPAM-based drug delivery systems. Full article

In cancer diagnostics, magnetic resonance imaging (MRI) uses contrast agents to enhance the distinction between the target tissue and background. Several promising approaches have been developed to increase MRI sensitivity, one of which is Overhauser dynamic nuclear polarization (ODNP)-enhanced MRI (OMRI). In this study, a macromolecular construct based on human serum albumin and nitroxyl radicals (HSA-NIT) was developed using a new synthesis method that significantly increased the modification to 21 nitroxide residues per protein. This was confirmed by electron paramagnetic resonance (EPR) spectroscopy and matrix-assisted laser desorption/ionization time-of-flight (MALDI ToF) mass spectrometry. Gel electrophoresis and circular dichroism showed no significant changes in the structure of HSA-NITs, and no oligomers were formed during modification. The cytotoxicity of HSA-NITs was comparable to that of native albumin. HSA-NITs were evaluated as potential “metal-free” organic radical relaxation-based contrast agents for ¹H-MRI and as hyperpolarizing contrast agents for OMRI. Relaxivities (longitudinal and transversal relaxation rates r₁ and r₂) for HSA-NITs were measured at different magnetic field strengths (1.88, 3, 7, and 14 T). Phantoms were used to demonstrate the potential use of HSA-NIT as a T₁- and T₂-weighted relaxation-based contrast agent at 3 T and 14 T. The efficacy of ¹H Overhauser dynamic nuclear polarization (ODNP) in liquids at an ultralow magnetic field (ULF, B₀ = 92 ± 0.8 μT) was investigated for HSA-NIT conjugates. The HSA-NITs themselves did not show ODNP enhancement; however, under the proteolysis conditions simulating cancer tissue, HSA-NIT conjugates were cleaved into lower-molecular-weight (MW) protein fragments that activate ODNP capabilities, resulting in a maximum achievable enhancement |E_max| of 40–50 and a radiofrequency power required to achieve half of E_max, P_1/2, of 21–27 W. The HSA-NIT with a higher degree of modification released increased the number of spin probes upon biodegradation, which significantly enhanced the Overhauser effect. Thus, HSA-NITs may represent a new class of MRI relaxation-based contrast agents as well as novel cleavable conjugates for use as hyperpolarizing contrast agents (HCAs) in OMRI. Full article

Nitroxyl radicals, characterized by unique redox properties, have been investigated for their potential influence on the photovoltaic conversion properties of dye-sensitized solar cells (DSSCs). In this study, we investigated the influence of nitroxyl radicals as donor sites in DSSCs. We observed that the redox activity of nitroxyl radicals significantly enhanced the photovoltaic conversion efficiency of DSSCs; this finding can offer new insights into the application of these radicals in solar energy conversion. Furthermore, we found that increasing the proportion of nitroxyl radicals improved the DSSC performance. Through a combination of experimental and analytical approaches, we elucidated the mechanism underlying this enhancement and highlighted the potential for more efficient DSSCs using nitroxyl radicals as key components. These findings provide new avenues for developing advanced DSSCs with improved performances and sustainability. Full article

Dinitrosyl iron complexes (DNICs) are important physiological derivatives of nitric oxide. These complexes have a wide range of biological activities, with antioxidant and antiradical ones being of particular interest and importance. We studied the interaction between DNICs associated with the dipeptide L-carnosine or serum albumin and prooxidants under conditions mimicking oxidative stress. The ligands of these DNICs were histidine residues of carnosine or His39 and Cys34 in bovine serum albumin. Carnosine-bound DNICs reduced the level of piperazine free radicals in the reaction system containing tert-butyl hydroperoxide (t-BOOH), bivalent iron ions, a nitroxyl anion donor (Angeli’s salt), and HEPES buffer. The ability of carnosine DNICs to intercept organic free radicals produced from t-BOOH decay could lead to this effect. In addition, carnosine DNICs reacted with the superoxide anion radical (O₂^•−) formed in the xanthine/xanthine oxidase enzymatic system. They also reduced the oxoferryl form of the heme group formed in the reaction of myoglobin with t-BOOH. DNICs associated with serum albumin were found to be rapidly destroyed in a model system containing metmyoglobin and t-BOOH. At the same time, these protein DNICs inhibited the t-BOOH-induced oxidative degradation of coenzymes Q₉ and Q₁₀ in rat myocardial homogenate. The possible mechanisms of the antioxidant and antiradical action of the DNICs studied and their role in the metabolism of reactive oxygen and nitrogen species are discussed. Full article

Redox flow batteries (RFBs) have attracted significant attention as a promising electrochemical energy storage technology, offering various advantages such as grid-scale electricity production with variable intermittent electricity delivery, enhanced safety compared to metal-ion batteries, decoupled energy and power density, and simplified manufacturing processes. For this review, we exclusively focus on organic, non-aqueous redox flow batteries. Specifically, we address the most recent progress and the major challenges related to the design and synthesis of robust redox-active organic compounds. An extensive examination of the synthesis and characterization of a wide spectrum of redox-active molecules, focusing particularly on derivatives of posolytes such as quinone, nitroxyl radicals, dialkoxybenzenes, and phenothiazine and negolytes such as viologen and pyridiniums, is provided. We explore the incorporation of various functional groups as documented in the references, aiming to enhance the chemical and electrochemical stability, as well as the solubility, of both the neutral and radical states of redox-active molecules. Additionally, we offer a comprehensive assessment of the cell-cycling performance exhibited by these redox-active molecules. Full article