Electron Spin Resonance Studies Research Articles

A Water-Soluble Wavy Coordination Polymer of Cu(II) as a Turn-On Luminescent Probe for Histidine and Histidine-Rich Proteins/Peptides.

Histidine plays an essential role in most biological systems. Changes in the homeostasis of histidine and histidine-rich proteins are connected to several diseases. Herein, we report a water-soluble Cu(II) coordination polymer, labeled CuCP, for the fluorimetric detection of histidine and histidine-rich proteins and peptides. Single-crystal structure determination of CuCP revealed a two-dimensional wavy network structure in which a carboxylate group connects the individual Cu(II) dimer unit in a syn-anti conformation. The weakly luminescent and water-soluble CuCP shows turn-on blue emission in the presence of histidine and histidine-rich peptides and proteins. The polymer can also stain histidine-rich proteins via gel electrophoresis. The limits of quantifications for histidine, glycine-histidine, serine-histidine, human serum albumin (HSA), bovine serum albumin, pepsin, trypsin, and lysozyme were found to be 300, 160, 600, 300, 600, 800, 120, and 290 nM, respectively. Utilizing the fluorescence turn-on property of CuCP, we measured HSA quantitatively in the urine samples. We also validated the present urinary HSA measurement assay with existing analytical techniques. Job's plot, 1H NMR, high-resolution mass spectrometry (HRMS), electron paramagnetic resonance (EPR), fluorescence, and UV-vis studies confirmed the ligand displacement from CuCP in the presence of histidine.

Stabilization of a Photoradiated Naphthalene Diimide-Based Organic Radical Anion Inside a Peptide-Based Gel Matrix with an Improvement of Optoelectronic Properties.

An amino acid-conjugated naphthalene diimide (NDI)-based highly red fluorescent radical anion has been found in a water medium under the photoradiated condition. This molecule has failed to form the radical anion in the monomeric state; however, the J aggregation in the aqueous medium has ensured the formation of radical anion in the ambient condition after the irradiation of both sunlight and UV light exposure. Electron paramagnetic resonance (EPR) studies clearly suggest the formation of radical anions. Herein, the stability of the radical anion in the aqueous medium is only a few minutes as a small amount of shaking is enough to quench the radical anion in the solution state. Furthermore, the incorporation of this molecule into a peptide-based hydrogel matrix and the consequent photoirradiation have not only helped to develop radical anion in the gel matrix but also increased the enormous stability of the radical anion inside the hydrogel matrix even for 30 days. It is envisaged that the formation of the radical anion within the gel matrix prevents the free movement of the NDI molecules and restricts the diffusion of molecular oxygen in the system, which leads to the stability of the radical anions in the gel. Moreover, the stability of the radical anion within the gel has helped to enhance the conductivity of the hybrid gel to a great extent. Interestingly, the radical anion-containing hybrid hydrogel has shown a potential photoswitching property.

Manganese- and Platinum-Driven Oxidative and Nitrosative Stress in Oxaliplatin-Associated CIPN with Special Reference to Ca4Mn(DPDP)5, MnDPDP and DPDP.

Platinum-containing chemotherapeutic drugs are efficacious in many forms of cancer but are dose-restricted by serious side effects, of which peripheral neuropathy induced by oxidative-nitrosative-stress-mediated chain reactions is most disturbing. Recently, hope has been raised regarding the catalytic antioxidants mangafodipir (MnDPDP) and calmangafodipir [Ca4Mn(DPDP)5; PledOx®], which by mimicking mitochondrial manganese superoxide dismutase (MnSOD) may be expected to overcome oxaliplatin-associated chemotherapy-induced peripheral neuropathy (CIPN). Unfortunately, two recent phase III studies (POLAR A and M trials) applying Ca4Mn(DPDP)5 in colorectal cancer (CRC) patients receiving multiple cycles of FOLFOX6 (5-FU + oxaliplatin) failed to demonstrate efficacy. Instead of an anticipated 50% reduction in the incidence of CIPN in patients co-treated with Ca4Mn(DPDP)5, a statistically significant increase of about 50% was seen. The current article deals with confusing differences between early and positive findings with MnDPDP in comparison to the recent findings with Ca4Mn(DPDP)5. The POLAR failure may also reveal important mechanisms behind oxaliplatin-associated CIPN itself. Thus, exacerbated neurotoxicity in patients receiving Ca4Mn(DPDP)5 may be explained by redox interactions between Pt2+ and Mn2+ and subtle oxidative-nitrosative chain reactions. In peripheral sensory nerves, Pt2+ presumably leads to oxidation of the Mn2+ from Ca4Mn(DPDP)5 as well as from Mn2+ in MnSOD and other endogenous sources. Thereafter, Mn3+ may be oxidized by peroxynitrite (ONOO-) into Mn4+, which drives site-specific nitration of tyrosine (Tyr) 34 in the MnSOD enzyme. Conformational changes of MnSOD then lead to the closure of the superoxide (O2•-) access channel. A similar metal-driven nitration of Tyr74 in cytochrome c will cause an irreversible disruption of electron transport. Altogether, these events may uncover important steps in the mechanism behind Pt2+-associated CIPN. There is little doubt that the efficacy of MnDPDP and its therapeutic improved counterpart Ca4Mn(DPDP)5 mainly depends on their MnSOD-mimetic activity when it comes to their potential use as rescue medicines during, e.g., acute myocardial infarction. However, pharmacokinetic considerations suggest that the efficacy of MnDPDP on Pt2+-associated neurotoxicity depends on another action of this drug. Electron paramagnetic resonance (EPR) studies have demonstrated that Pt2+ outcompetes Mn2+ and endogenous Zn2+ in binding to fodipir (DPDP), hence suggesting that the previously reported protective efficacy of MnDPDP against CIPN is a result of chelation and elimination of Pt2+ by DPDP, which in turn suggests that Mn2+ is unnecessary for efficacy when it comes to oxaliplatin-associated CIPN.

On the Microstructure and Dynamics of Membranes Formed by Lipid as From Stenotrophomonas maltophilia, a Member of Gut Microbiome: An EPR Study

AbstractLipid As are the main components of the external leaflet of the outer membrane of Gram-negative bacteria. Their molecular structure has evolved to allow the bacteria survival in specific environments. In the present work, we investigate how and to what extent lipid membranes that include in their composition lipid A molecules of a bacterium of the gut microbiota, Stenotrophomonas maltophilia, differ from those formed by the lipid A of the common Gram-negative bacterium Salmonella enterica, which is not specific to the gut and is here used as a reference. Electron Paramagnetic Resonance (EPR) spectroscopy, using spin-labelled lipids as molecular probes, allows the segmental order of the acyl chain and the polarity across the bilayer to be analyzed in detail. Both considered lipid As cause a stiffening of the outermost segments of the acyl chains. This effect increases with increasing the lipid A content and is stronger for the lipid A extracted from Stenotrophomonas maltophilia than for that extracted from Salmonella enterica. At the same time, the local polarity of the bilayer region just below the interface increases. As the inner core of the bilayer is considered, it is found that the lipid A from Salmonella enterica causes a local disorder and a significant reduction of the local polarity, an effect not found for the lipid A from Stenotrophomonas maltophilia. These results are interpreted in terms of the different lengths and distributions of the acyl tails in the two lipid As. It can be concluded that the symmetrically distributed short tails of the lipid A from Stenotrophomonas maltophilia favors a regular packing within the bilayer.

Electron paramagnetic resonance as a tool to determine the sodium charge storage mechanism of hard carbon

Hard carbon is a promising negative electrode material for rechargeable sodium-ion batteries due to the ready availability of their precursors and high reversible charge storage. The reaction mechanisms that drive the sodiation properties in hard carbons and subsequent electrochemical performance are strictly linked to the characteristic slope and plateau regions observed in the voltage profile of these materials. This work shows that electron paramagnetic resonance (EPR) spectroscopy is a powerful and fast diagnostic tool to predict the extent of the charge stored in the slope and plateau regions during galvanostatic tests in hard carbon materials. EPR lineshape simulation and temperature-dependent measurements help to separate the nature of the spins in mechanochemically modified hard carbon materials synthesised at different temperatures. This proves relationships between structure modification and electrochemical signatures in the galvanostatic curves to obtain information on their sodium storage mechanism. Furthermore, through ex situ EPR studies we study the evolution of these EPR signals at different states of charge to further elucidate the storage mechanisms in these carbons. Finally, we discuss the interrelationship between EPR spectroscopy data of the hard carbon samples studied and their corresponding charging storage mechanism.

Efficient activation of periodate using MnFe2O4/BC composite for removal of organic contaminants: Performance and mechanism

The periodate (PI)-based advanced oxidation process (AOP) is an economical and energy-saving method for remediating water by degrading pollutants. An efficient system for PI activation was developed by loading manganese ferrite spinel (MnFe2O4) on biochar (BC) through a facile method, affording a metal-oxide MnFe2O4/BC composite catalyst. The developed system demonstrated significant effectiveness in eliminating various organic pollutants, particularly achieving high removal (5.26 and 2.83 times that of biochar and MnFe2O4, respectively) and mineralization (49.7 %) of the model pollutant tetracycline hydrochloride (TC) within 30 min. The system exhibited outstanding catalytic performance under various environmental conditions (pH, inorganic salts, humic acid, and real water bodies), as evidenced by quenching experiments and electron paramagnetic resonance (EPR) studies, proving that superoxide radicals (O2•-) are the main reactive species for TC degradation in the reaction system, in addition to singlet oxygen (1O2), iodyl radicals (IO3•) and hydroxyl radicals (•OH). Potential pathways for TC degradation in this system were revealed based on density functional theory (DFT) and the ecological toxicity of the intermediates was analyzed through quantitative structure–activity relationship (QSAR) assessment. Analysis of the magnetic hysteresis and cycling stability demonstrated that the composites were stable and could be recycled by applying a magnetic field. This work opens a new pathway for designing efficient PI activators for the selective oxidation of organic pollutants and highlights the potential application of this system in practical wastewater treatment.

Oxygen vacancy enhanced photocatalytic activity of Cu2O/TiO2 heterojunction

In this study, a method was developed to create oxygen vacancies in Cu2O/TiO2 heterojunctions. By varying the amounts of ethylenediaminetetraacetic acid (EDTA), sodium citrate, and copper acetate, Cu2O/TiO2 with different Cu ratios were synthesized. Tests on CO2 photocatalytic reduction revealed that Cu2O/TiO2's performance is influenced by Cu content. The ideal Cu mass fraction in Cu2O/TiO2, determined by inductively coupled plasma (ICP), is between 0.075% and 0.55%, with the highest CO yield being 10.22μmol g-1 h-1, significantly surpassing pure TiO2. High-resolution transmission electron microscopy and electron paramagnetic resonance studies showed optimal oxygen vacancy in the most effective heterojunction. Density functional theory (DFT) calculations indicated a 0.088 eV lower energy barrier for ∗CO2 to ∗COOH conversion in Cu2O/TiO2 with oxygen vacancy compared to TiO2, suggesting that oxygen vacancies enhance photocatalytic activity.

Investigating oxidant-catalyst interactions in the persulfate system: Implications for efficient removal of phenolics and antibiotics

Persulfate (PS) activation by carbon catalyst holds both scientific and practical significance to curb the toxicity effects of organic pollutants in the natural water environment. Here, we investigated a relatively unfamiliar characteristics (i.e., oxidant-catalyst interaction) that influence the removal efficiency in PS activated system, utilizing N-doped mesoporous carbon hollow spheres (N-MCHS; size ∼385 nm) as a catalyst. The selection of this catalyst was motivated by its desired physicochemical characteristics such as high dispersibility, uniformly distributed pores and high specific surface area (1109 m2 g−1) for catalytic application. The removal performance was studied by degrading bisphenol A at very low PS (0.25 mM) and catalyst (10.0 mg L−1) concentrations. Through this study, we established a correlation between the surface charge of N-MCHS and PS interaction on the catalytic performance. Further, electron spin resonance (ESR) and radical scavenger studies were carryout out to prove the nonradical oxidation process. Electrochemical studies provided a strong evidence for PS complexation and electron transfer during oxidative removal of bisphenol A. Additional studies with different phenolics and antibiotics demonstrated that N-doping significantly accelerates the degradation rate and enhances the removal efficiency. The results of present study unveil the potential use of PS+N-MCHS in the degradation of different organic contaminants at low catalyst dosages.

Electron paramagnetic resonance study of the paramagnetic centers in gamma-irradiated 4-Nitrobenzaldehyde single crystal

4-Nitrobenzaldehyde (C7H5NO3) (4NB) single crystals were obtained by slow evaporation technique. Single crystals were made paramagnetic by irradiation with a 60Co-gamma rays. Electron Paramagnetic Resonance (EPR) Spectroscopy method was used to detect the radiation damage center formed in the single crystals. As a result of temperature scanning of EPR spectra at different temperatures between 120 and 470 K, it was found to be independent of temperature. That's why the EPR study was done only at 300 K. The radiation effect caused the formation of the 4NB anion radical in the 4NB single crystal. All the protons in the structure created hyperfine structure splittings. The principal values of the hyperfine structure constants resulting from the interaction of the unpaired electron with protons, the principal values of the g-tensor and their direction cosines were calculated.

Calcination temperature dependence of tri-magnetic nanoferrite Ni0.33Cu0.33Zn0.33Fe2O4: Structural, morphological, and magnetic properties

The calcination temperature plays a pivotal role in determining the physical and magnetic properties of ferrite nanoparticles, influencing their performance and applicability in various applications. In this study, Ni0.33Cu0.33Zn0.33Fe2O4 nano ferrites were produced using the coprecipitation method and subsequently calcined at different temperatures, specifically 500 °C, 550 °C, 600 °C, 650 °C, and 700 °C. The X-ray diffraction analysis confirmed the presence of cubic spinel ferrite phase (Fd-3m) and revealed an increase in crystallite size from 12.84 to 20.19 nm as the calcination temperature increased from 500 °C to 700 °C. X-ray photoelectron spectroscopy analysis provided insights into chemical oxidation states. Scanning electron microscopy and transmission electron microscopy images revealed that at higher calcination temperatures, nanoparticles tend to aggregate. This aggregation is associated with an observable rise in particle size, increasing from 18.16 to 29.11 nm for nanoparticles calcined at 500 °C and 700 °C, respectively. Energy-dispersive X-ray confirmed pure elemental compositions. Fourier transform infrared spectroscopy identified red and blue shifts in wavenumbers corresponding to tetrahedral and octahedral group complexes, respectively. Nanoparticles calcined at 700 °C exhibited the highest saturation magnetization (62.642 emu/g) and coercivity (75.27 G), as revealed from the vibrating sample magnetometry analysis. Upon increasing the calcination temperature from 500 °C to 700 °C, the ferromagnetic contribution was improved from 24.26% to 98.64% along with a reduction in superparamagnetic contribution from 75.74% to 1.34%, respectively. The electron paramagnetic resonance (EPR) study showed an increase in the values of g and ΔHpp with the rise in calcination temperature. This observation suggests an enhancement in dipole–dipole interactions. Furthermore, a linear relationship was discovered between the g factor and crystallite size, inducting the formation of single domain. Finally, altering the calcination temperature adjusted the physical and magnetic properties of Ni0.33Cu0.33Zn0.33Fe2O4 nanoparticles. This adjustment indicates their potential for versatile applications, particularly in hyperthermia treatment and as T2 contrast agents in magnetic resonance imaging.

ZnAl2O4:Er3+ Upconversion Nanophosphor for SPECT Imaging and Luminescence Modulation via Defect Engineering.

This work reports an "all-in-one" theranostic upconversion luminescence (UCL) system having potential for both diagnostic and therapeutic applications. Despite considerable efforts in designing upconversion nanoparticles (UCNPs) for multimodal imaging and tumor therapy, there are few reports investigating dual modality SPECT/optical imaging for theranostics. Especially, research focusing on in vivo biodistribution studies of intrinsically radiolabeled UCNPs after intravenous injection is of utmost importance for the potential clinical translation of such formulations. Here, we utilized the gamma emission from 169Er and 171Er radionuclides for the demonstration of radiolabeled ZnAl2O4:171/169Er3+ as a potent agent for dual-modality SPECT/optical imaging. No uptake of radio nanoformulation was detected in the skeleton after 4 h of administration, which evidenced the robust integrity of ZnAl2O4:169/171Er3+. Combining the therapeutics using the emission of β- particulates from 169Er and 171Er will be promising for the radio-theranostic application of the synthesized ZnAl2O4:169/171Er3+ nanoformulation. Cell toxicity studies of ZnAl2O4:1%Er3+ nanoparticles were examined by an MTT assay in B16F10 mouse melanoma cell lines, which demonstrated good biocompatibility. In addition, we explored the mechanism of UCL modulation via defect engineering by Bi3+ codoping in the ZnAl2O4:Er3+ upconversion nanophosphor. The UCL color tuning was successfully achieved from the red to the green region as a function of Bi3+ codoping concentrations. Further, we tried to establish a correlation of UCL tuning with the intrinsic oxygen and cation vacancy defects as a function of Bi3+ codoping concentrations with the help of electron paramagnetic resonance (EPR) and positron annihilation lifetime spectroscopy (PALS) studies. This study contributes to building a bridge between nature of defects and UC luminescence that is crucial for the design of advanced UCNPs for theranostics.

Carbon Dioxide Electroreduction and Formic Acid Oxidation by Formal Nickel(I) Complexes of Di-isopropylphenyl Bis-iminoacenaphthene.

Processing CO2 into value-added chemicals and fuels stands as one of the most crucial tasks in addressing the global challenge of the greenhouse effect. In this study, we focused on the complex (dpp-bian)NiBr2 (where dpp-bian is di-isopropylphenyl bis-iminoacenaphthene) as a precatalyst for the electrochemical reduction of CO2 into CH4 as the sole product. Cyclic voltammetry results indicate that the realization of a catalytically effective pattern requires the three-electron reduction of (dpp-bian)NiBr2. The chemically reduced complexes [K(THF)6]+[(dpp-bian)Ni(COD)]- and [K(THF)6]+[(dpp-bian)2Ni]- were synthesized and structurally characterized. Analyzing the data from the electron paramagnetic resonance study of the complexes in solutions, along with quantum-chemical calculations, reveals that the spin density is predominantly localized at their metal centers. The superposition of trajectory maps of the electron density gradient vector field and the electrostatic force density field per electron, as well as the atomic charges, discloses that, within the first coordination sphere, the interatomic charge transfer occurs from the metal atom to the ligand atoms and that the complex anions can thus be formally described by the general formulae (dpp-bian)2-Ni+(COD) and (dpp-bian)2 -Ni+. It was also shown that the reduced nickel complexes can be oxidized by formic acid; resulting from this reaction, the two-electron and two-proton addition product dpp-bian-2H is formed.

EPR studies of ferredoxin in spinach and cyanobacterial thylakoids related to photosystem I-driven NADP+ reduction.

Photosynthetic light-dependent reactions occur in thylakoid membranes where embedded proteins capture light energy and convert it to chemical energy in the form of ATP and NADPH for use in carbon fixation. One of these integral membrane proteins is Photosystem I (PSI). PSI catalyzes light-driven transmembrane electron transfer from plastocyanin (Pc) to oxidized ferredoxin (Fd). Electrons from reduced Fd are used by the enzyme ferredoxin-NADP+ reductase (FNR) for the reduction of NADP+ to NADPH. Fd and Pc are both small soluble proteins whereas the larger FNR enzyme is associated with the membrane. To investigate electron shuttling between these diffusible and embedded proteins, thylakoid photoreduction of NADP+ was studied. As isolated, both spinach and cyanobacterial thylakoids generate NADPH upon illumination without extraneous addition of Fd. These findings indicate that isolated thylakoids either (i) retain a "pool" of Fd which diffuses between PSI and membrane bound FNR or (ii) that a fraction of PSI is associated with Fd, with the membrane environment facilitating PSI-Fd-FNR interactions which enable multiple turnovers of the complex with a single Fd. To explore the functional association of Fd with PSI in thylakoids, electron paramagnetic resonance (EPR) spectroscopic methodologies were developed to distinguish the signals for the reduced Fe-S clusters of PSI and Fd. Temperature-dependent EPR studies show that the EPR signals of the terminal [4Fe-4S] cluster of PSI can be distinguished from the [2Fe-2S] cluster of Fd at > 30K. At 50K, the cw X-band EPR spectra of cyanobacterial and spinach thylakoids reduced with dithionite exhibit EPR signals of a [2Fe-2S] cluster with g-values gx = 2.05, gy = 1.96, and gz = 1.89, confirming that Fd is present in thylakoid preparations capable of NADP+ photoreduction. Quantitation of the EPR signals of P700+ and dithionite reduced Fd reveal that Fd is present at a ratio of ~ 1 Fd per PSI monomer in both spinach and cyanobacterial thylakoids. Light-driven electron transfer from PSI to Fd in thylakoids confirms Fd is functionally associated (< 0.4 Fd/PSI) with the acceptor end of PSI in isolated cyanobacterial thylakoids. These EPR experiments provide a benchmark for future spectroscopic characterization of Fd interactions involved in multistep relay of electrons following PSI charge separation in the context of photosynthetic thylakoid microenvironments.

Li3V2(PO4)3 Cathode Material: Synthesis Method, High Lithium Diffusion Coefficient and Magnetic Inhomogeneity.

Li3V2(PO4)3 cathodes for Li-ion batteries (LIBs) were synthesized using a hydrothermal method with the subsequent annealing in an argon atmosphere to achieve optimal properties. The X-ray diffraction analysis confirmed the material's single-phase nature, while the scanning electron microscopy revealed a granular structure, indicating a uniform particle size distribution, beneficial for electrochemical performance. Magnetometry and electron spin resonance studies were conducted to investigate the magnetic properties, confirming the presence of the relatively low concentration and highly uniform distribution of tetravalent vanadium ions (V4+), which indicated low lithium deficiency values in the original structure and a high degree of magnetic homogeneity in the sample, an essential factor for consistent electrochemical behavior. For this pure phase Li3V2(PO4)3 sample, devoid of any impurities such as carbon or salts, extensive electrochemical property testing was performed. These tests resulted in the experimental discovery of a remarkably high lithium diffusion coefficient D = 1.07 × 10-10 cm2/s, indicating excellent ionic conductivity, and demonstrated impressive stability of the material with sustained performance over 1000 charge-discharge cycles. Additionally, relithiated Li3V2(PO4)3 (after multiple electrochemical cycling) samples were investigated using scanning electron microscopy, magnetometry and electron spin resonance methods to determine the extent of degradation. The combination of high lithium diffusion coefficients, a low degradation rate and remarkable cycling stability positions this Li3V2(PO4)3 material as a promising candidate for advanced energy storage applications.

Comparative EPR Studies on the Influence of Genistein on Free Radicals in Non-Irradiated and UV-Irradiated MCF7, T47D and MDA-MB-231 Breast Cancer Cells.

The antioxidant activity and the association of genistein with carcinogenesis are widely documented. Few studies directly measure the number of free radicals generated in cells, either during the action of factors stimulating their formation, e.g., ultraviolet (UV), or after exposure to antioxidants. The most suitable method for analysing free radicals is electron paramagnetic resonance (EPR) spectroscopy. The EPR method detects a paramagnetic centre with a single electron. Antioxidants neutralize free radicals, therefore, EPR analysis of antioxidant efficacy is as valuable and important as studying the paramagnetic centres of radicals. The aim of the study was to determine the influence of genistein on free radicals basal level and after UV exposure in breast cancer cell lines MCF7, T47D and MDA-MB-231 cell lines. The impact of genistein on cell viability was investigated at concentrations of 0.37 μM, 3.7 μM, 37 μM and 370 μM. Genistein at a concentration of 370 μM revealed a cytotoxic effect on the cells of all three tested breast cancer lines. Genistein at a concentration of 0.37 μM showed no significant effect on the cell viability of all tested breast cancer lines. Therefore, cell proliferation and antioxidant properties were examined using genistein at a concentration of 0.37 μM and 37 μM. X-band (9.3 GHz) EPR spectra of three different types of breast cancer cells (ER-positive, PR-positive and HER-2 negative: MCF7 and T47D and triple-negative MDA-MB-231) were compared. UV irradiation was used as a factor to generate free radicals in cells. The effect of free radical interactions with the antioxidant genistein was tested for non-UV-irradiated (corresponding to the basal level of free radicals in cells) and UV-irradiated cells. The levels of free radicals in the non-irradiated cells studied increased in the following order in breast cancer cells: T47D < MDA-MB-231 < MCF7 and UV-irradiated breast cancer cells: MDA-MB-231 < MCF7 < T47D. UV-irradiation altered free radical levels in all control and genistein-cultured cells tested. UV irradiation caused a slight decrease in the amount of free radicals in MCF7 cells. A strong decrease in the amount of free radicals was observed in UV-irradiated MDA-MB-231 breast cancer cells. The amount of free radicals in T47D cancer cells increased after UV irradiation. Genistein decreased the amount of free radicals in non-irradiated and UV-irradiated MCF7 cells, and only a weak effect of genistein concentrations was reported. Genistein greatly decreased the amount of free radicals in UV-irradiated T47D cancer cells cultured with genistein at a concentration of 3.7 μM. The effect of genistein was negligible in the other samples. Genistein at a concentration of 3.7 μM decreased the amount of free radicals in non-irradiated MDA-MB-231 cancer cells, but genistein at a concentration of 37 μM did not change the amount of free radicals in these cells. An increase in the amount of free radicals in UV-irradiated MDA-MB-231 cancer cells was observed with increasing genistein concentration. The antioxidant efficacy of genistein as a potential plant-derived agent supporting the treatment of various cancers may be determined by differences in signalling pathways that are characteristic of breast cancer cell line subtypes and differences in activation of oxidative stress response pathways.

Effect of grain boundary segregation and oxygen vacancy annihilation on aging resistance of cobalt oxide-doped 3Y-TZP ceramics for biomedical applications

Abstract This study aims to investigate the diffusion stabilization process of nano-Co2O3 during the non-precursor transformation of 3Y-TZP. 3Y-TZP was set as the control group, and the experimental groups were 0.1–0.3 mol% nano-Co2O3-doped 3Y-TZP. The samples were prepared by the ball milling process, isostatic cool pressing, and sintering. All samples were hydrothermally treated at 134°C and 2 bar for different time periods. The resistance to low-temperature degradation of nano-Co2O3-doped 3Y-TZP was analyzed by X-ray diffraction. The microstructure of zirconia ceramic samples was determined by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and electron paramagnetic resonance studies. The addition of nano-Co2O3 into 3Y-TZP resulted in higher hydrothermal aging resistance than 3Y-TZP. The addition of 0.2 mol% nano-Co2O3 dopants resulted in the highest hydrothermal aging resistance among nano-Co2O3-doped 3Y-TZP ceramics. The grain sizes of 3Y-0.2Co are smaller than those in the control group. With the increase of cobaltous oxide doping contents, the segregation of Co3+ ions at the crystal boundary increased. The content of oxygen vacancies on the surface of the sample increased with the increase of the Co2O3 doping content. The oxygen vacancy concentrations of 3Y-0.2Co increased obviously after aging. 3Y-0.1Co, 3Y-0.3Co, and the control showed decreased oxygen vacancy concentrations after aging. Trivalent element doping of 3Y-TZP effectively improved the aging resistance of 3Y-TZP. The addition of 0.2 mol% nano-Co2O3 resulted in the highest hydrothermal aging resistance. Improved aging resistance is attributed to the nano-Co2O3 doping resulting in the 3Y-TZP grain size inhibition, grain boundary segregation of cobalt ions, and oxygen vacancy maintenance. This work is expected to provide an effective reference for the development and application of budget dental materials by regulating grain boundary engineering.

Measuring conformational equilibria in allosteric proteins with time-resolved tmFRET

Proteins are the workhorses of biology, orchestrating a myriad of cellular functions through intricate conformational changes. Protein allostery, the phenomenon where binding of ligands or environmental changes induce conformational rearrangements in the protein, is fundamental to these processes. We have previously shown that transition metal Förster resonance energy transfer (tmFRET) can be used to interrogate the conformational rearrangements associated with protein allostery and have recently introduced novel FRET acceptors utilizing metal-bipyridyl derivatives to measure long (>20 Å) intramolecular distances in proteins. Here, we combine our tmFRET system with fluorescence lifetime measurements to measure the distances, conformational heterogeneity, and energetics of maltose-binding protein, a model allosteric protein. Time-resolved tmFRET captures near-instantaneous snapshots of distance distributions, offering insights into protein dynamics. We show that time-resolved tmFRET can accurately determine distance distributions and conformational heterogeneity of proteins. Our results demonstrate the sensitivity of time-resolved tmFRET in detecting subtle conformational or energetic changes in protein conformations, which are crucial for understanding allostery. In addition, we extend the use of metal-bipyridyl compounds, showing that Cu(phen)2+ can serve as a spin label for pulse dipolar electron paramagnetic resonance (EPR) spectroscopy, a method that also reveals distance distributions and conformational heterogeneity. The EPR studies both establish Cu(phen)2+ as a useful spin label for pulse dipolar EPR and validate our time-resolved tmFRET measurements. Our approach offers a versatile tool for deciphering conformational landscapes and understanding the regulatory mechanisms governing biological processes.

Effects of intramolecular hydrogen bonding on nuclear magnetic resonance, electron paramagnetic resonance and molecular docking studies: Mexiletine molecule.

In this study, the molecular structure of the mexiletine molecule was investigated. Since the Mexiletine molecule is a drug active ingredient, its molecular structure and spectroscopic properties are important. The effects of intramolecular hydrogen bonding on Nuclear Magnetic Resonance Parameters (NMR), Electron Paramagnetic Resonance (EPR) parameters and molecular docking studies were examined in the mexiletine molecule. The effects of intramolecular hydrogen bonding on EPR parameters and molecular docking studies are the most important steps for this study. Conformational space scanning required for molecular structure calculations was carried out with the Molecular Mechanic Force Field method. DFT method with 6-311 + + G(d,p) basis set level was used to obtain the most stable structure among the conformations. NMR parameters (1H and 13C chemical shift values) were also performed using the same basis set as the DFT method. The radicals created to calculate the Electron Paramagnetic Resonance parameters were modeled using the DFT/B3LYP/6-311 + + G(d,p) method basis set level. Molecular Docking studies were carried out with the Autodock vina program.

Structure and Function of Canine SP-C Mimic Proteins in Synthetic Surfactant Lipid Dispersions.

Lung surfactant is a mixture of lipids and proteins and is essential for air breathing in mammals. The hydrophobic surfactant proteins B and C (SP-B and SP-C) assist in reducing surface tension in the lung alveoli by organizing the surfactant lipids. SP-B deficiency is life-threatening, and a lack of SP-C can lead to progressive interstitial lung disease. B-YL (41 amino acids) is a highly surface-active, sulfur-free peptide mimic of SP-B (79 amino acids) in which the four cysteine residues are replaced by tyrosine. Mammalian SP-C (35 amino acids) contains two cysteine-linked palmitoyl groups at positions 5 and 6 in the N-terminal region that override the β-sheet propensities of the native sequence. Canine SP-C (34 amino acids) is exceptional because it has only one palmitoylated cysteine residue at position 4 and a phenylalanine at position 5. We developed canine SP-C constructs in which the palmitoylated cysteine residue at position 4 is replaced by phenylalanine (SP-Cff) or serine (SP-Csf) and a glutamic acid-lysine ion-lock was placed at sequence positions 20-24 of the hydrophobic helical domain to enhance its alpha helical propensity. AI modeling, molecular dynamics, circular dichroism spectroscopy, Fourier Transform InfraRed spectroscopy, and electron spin resonance studies showed that the secondary structure of canine SP-Cff ion-lock peptide was like that of native SP-C, suggesting that substitution of phenylalanine for cysteine has no apparent effect on the secondary structure of the peptide. Captive bubble surfactometry demonstrated higher surface activity for canine SP-Cff ion-lock peptide in combination with B-YL in surfactant lipids than with canine SP-Csf ion-lock peptide. These studies demonstrate the potential of canine SP-Cff ion-lock peptide to enhance the functionality of the SP-B peptide mimic B-YL in synthetic surfactant lipids.

Tridentate NacNac Tames T-Shaped Nickel(I) Radical.

The reaction of a nickel(II) chloride complex containing a tridentate β-diketiminato ligand with a picolyl group [2,6-iPr2 -C6 H3 NC(Me)CHC(Me)NH(CH2 py)]Ni(II)Cl (1)] with KSi(SiMe3 )3 conveniently afforded a nickel(I) radical with a T-shaped geometry (2). The compound's metalloradical nature was confirmed through electron paramagnetic resonance (EPR) studies and its reaction with TEMPO, resulting in the formation of a highly unusual three-membered nickeloxaziridine complex (3). When reacted with disulfide and diselenide, the S-S and Se-Se bonds were cleaved, and a coupled product was formed through carbon atom of the pyridine-imine group. The nickel(I) radical activates dihydrogen at room temperature and atmospheric pressure to give the monomeric nickel hydride.