Electron Paramagnetic Spectroscopy Research Articles

The role of surface hydroxyls on the radiolysis of gibbsite and boehmite nanoplatelets

Understanding mechanistic pathways to radiolytic hydrogen generation by metal oxyhydroxide nanomaterials is challenging because of the difficulties of distinguishing key locations of OH bond scission, from structural interiors to hydroxylated surfaces to physi-sorbed water molecules. Here we exploited the interface-selectivity of vibrational sum frequency generation (VSFG) to isolate surface versus bulk hydroxyl groups for gibbsite and boehmite nanoplatelets before and after 60Co irradiation at dose levels of approximately 7.0 and 29.6 Mrad. While high-resolution microscopy revealed no effect on particle bulk and surface structures, VSFG results clearly indicated up to 83% and 94% radiation-induced surface OH bond scission for gibbsite and boehmite, respectively, a substantially higher proportion than observed for interior OH groups by IR and Raman spectroscopy. Electron paramagnetic spectroscopy revealed that the major radiolysis products bound in the mineral structures are trapped electrons, O, O2− and possibly F-centers in gibbsite, and H, O and O3− in boehmite, which persist on the time frame of several months. The entrapped radiolysis products appear to be highly stable, enduring re-hydration of particle surfaces, and likely reflect a permanent adjustment in the thermodynamic stabilities of these nanomaterials.

(Invited) The Relationship of Morphology and Catalytic Activity: A Case Study of Iron Corrole Incorporated in High Surface Area Carbon Supports

In the past several years we have been thoroughly studying the performance of molecular catalysts for oxygen reduction based on metallo-corrole. We studied the effect of the metal center, substituents in their meso and beta positions and ORR mechanism at a wide pH range. The most influential factor was found to be the metal center while the effect of electro-negative substituents seems to diminish once these molecular catalysts were incorporated in porous carbon supports. Moreover, the overall activity and reaction selectivity has increased dramatically after this incorporation, and was found to be dependent on the carbon support. Specifically, metallo-corroles have shown to have unique catalytic properties for oxygen reduction when adsorbed on a high surface area carbon: BP2000. The nature of the interaction between carbon surfaces and metallo-corroles was identified in this work. The results suggests that the catalytic activity lays not in a bond between the carbon surface and the corrole molecule, but rather in the arrangement of corrole molecules within the porous structure of the carbon surface. This hypothesis was studied here using Electron Paramagnetic Resonance (EPR), X-ray diffraction (XRD), UV-VIS spectroscopy, elemental analysis, N2 adsorption and several electrochemical methods. BP2000 carbon was compared to four other carbons with different properties (oxygen surface groups, surface area, porous structure and crystallinity). All of these show that the Fe-corrole that was incorporated in BP2000 tends to adsorb in pores of 20-25 nm in diameter, which allow synergistic effects to take place, and enhance the electrocatalysis of oxygen reduction reaction.

Effects of a mitochondria targeted antioxidant on skeletal muscle mitochondrial function with cigarette smoke exposure and Chronic Obstructive Pulmonary Disease

Reactive oxygen species (ROS) are important signaling molecules in cells. However, the exaggerated free radical production accompanying mitochondrial dysfunction with Chronic Obstructive Pulmonary Disease (COPD) has been suggested to play a crucial role in the development of metabolic abnormalities in these patients. Consequently, selective inhibition of mitochondrial ROS could be a potential therapeutic strategy to restore mitochondrial function and subsequently attenuate exercise‐induced metabolic disturbance during exercise in COPD patients. The goal of this study was therefore to determine the effects of a mitochondria targeted antioxidant, MitoQ, on free radical levels, mitochondrial function, and skeletal muscle metabolism in six patients with moderate to very‐severe COPD and a smoking mouse model (C57/Bl6 exposed to cigarette smoke for 8 months) using electron paramagnetic spectroscopy (EPR), 31P/1H magnetic resonance spectroscopy (1H/31P MRS), high‐resolution respirometry in permeabilized skeletal muscle fiber. 4 weeks of MitoQ supplementation (MQ) decreased blood free radical levels measured by EPR (control, CTL: 4.3 ± 3.3 a.u.; MQ: 1.8 ± 1.7 a.u.; P<0.05). Nevertheless, the exercise‐induced changes in intracellular O2 partial pressure, high‐energy phosphate, and pH measured by 1H/31P MRS in the plantar flexor muscles of patients with COPD were not significantly altered with MitoQ. Also, the peak rate of oxidative ATP synthesis measured by 31P‐MRS was lower with MitoQ (CTL: 19 ± 6 mM.min−1; MQ: 14 ± 4 mM.min−1, P<0.05), suggesting an impaired mitochondrial function in vivo. This finding was further supported by the lower muscle respiratory capacity measured in permeabilized skeletal muscle fibers incubated with MitoQ (−43%, P<0.05) from a smoking mouse model. Specifically, complex I (−42%) and free‐fatty acid (−51%) linked respiration were significantly decreased with MitoQ (P<0.05). Together, these findings suggest that decreasing ROS levels using a mitochondria targeted antioxidant may, in fact, be detrimental to oxidative phosphorylation capacity in the skeletal muscle of COPD patients.Support or Funding InformationThis work was funded in part by grants from the Flight Attendant Medical Research Institute (FAMRI), NIH National Heart, Lung, and Blood Institute (HL125756)

Caveolin‐1 frame‐shift mutation induce changes in cellular morphology and function

Caveolins, Cav1–3, are oligomeric proteins critical for the formation of membrane caveolae that regulates cell physiology. A frameshift mutation (Cav1F160X) in Cav1 (Cav1M) was described in a patient with a progeria‐like phenotype, which presents nuclear morphology alterations. We hypothesize that Cav1M presents dominant negative function that perturb cellular physiology, particularly nuclear morphology, mitochondrial function, exocytic behavior a plasma membrane structure. Transmission electron microscopy (TEM) of patient‐derived dermal fibroblasts (PCav1M) showed abnormal nuclear shape, increased rough endoplasmic reticulum, abnormal mitochondrial size/shape, increased number of autophagosomes and reduce number of membrane caveolae. Patient‐derive serum shown an increase in exosomes and extracellular vesicles, compared with the unaffected family members. PCav1M fibroblasts showed 4‐fold increase in exosome secretion; PCav1M present also increased exosome secretion compared with Hutchinson‐Gilford progeria patient dermal fibroblasts. Nanotracking and TEM analysis revealed a significant reduction in nanoparticle size in PCav1M‐derived exosomes. Human dermal fibroblasts (HDF) treated to express Cav1M or exogenously exposed to exosomes from PCav1M fibroblasts showed altered nuclear morphology, exosome secretion profile, proteomics, and miRNA analysis. Cellular membrane structure analysis by means of membrane fractions and electron paramagnetic spectroscopy shows an altered localization of proteins commonly found in caveolae fractions and increased membrane fluidity. Our results indicate that mutations in the C‐terminus of Cav1 lead to significant membrane alterations regulating exosome secretion and other cellular morpho‐functional features. Our findings identify a novel role of caveolin in linking plasma and nuclear membrane dynamics that have potential implications for cellular communication, impacting physiology and pathophysiology.Support or Funding InformationNational Institutes of Health (HL091071, AG052722) and Veterans Administration (BX001963).

Unique electrochemical system for in situ SO4[rad]− generation and pollutants degradation

Sulfate-based electrochemical advanced oxidation is of rising importance for pollutant removal, however, adscititious sulfate has adverse effects on water salinity. A novel electrochemical system which could exploit the existed SO42− for in situ generation of SO4− was successfully constructed with boron doped diamond (BDD) anode and hierarchical 1D Co3O4 nanowire array cathode. The in situ electrochemical electron paramagnetic spectroscopy and titration were used to study the positive correlation between the increase of sulfate radicals (SRs) and the efficient activation of peroxydisulfate (PDS) by hierarchical 1D Co3O4 nanowire array cathode. Electrochemical impedance and X-ray photoelectron spectroscopy revealed that the efficient activation of PDS by the Co3O4 cathode was derived from the excellent electron transport capability of the 1D nanostructure, and the electric field accelerates the reduction of Co(III). The novel hierarchical 1D Co3O4 nanowire array cathode can completely degrade dibutyl phthalate in 45% less time with 38% less energy compared to a traditional graphite cathode without the requirement of extra chemicals. The possible mechanism of anodic PDS accumulation and cathodic SRs generation was firstly revealed, and this advanced electrochemical oxidation system provides a good reference for the in situ sustainable remediation in sulfate-containing water.

The relationship of morphology and catalytic activity: A case study of iron corrole incorporated in high surface area carbon supports

Metallo-corroles have shown to have unique catalytic properties for oxygen reduction when adsorbed on a high surface area carbon such as BP2000. The nature of the interaction between carbon surfaces and metallo-corroles has yet to be identified. This work suggests that the catalytic activity lays not in a bond between the carbon surface and the corrole molecule, but rather in the arrangement of corrole molecules within the porous structure of the carbon surface. This hypothesis was studied here using Electron Paramagnetic Resonance (EPR), X-ray diffraction (XRD), UV-VIS spectroscopy, elemental analysis, N2 adsorption and several electrochemical methods. BP2000 carbon was compared to four other carbons with different properties (oxygen surface groups, surface area, porous structure and crystallinity). All of these show that the Fe-corrole that was incorporated in BP2000 tends to adsorb in pores of 20–25 nm in diameter, which allow synergistic effects to take place, and enhance the electrocatalysis of oxygen reduction reaction.

Photocatalytic Hydrogen Production by Boron Modified TiO2/Carbon Nitride Heterojunctions

AbstractBoron‐doped anatase TiO2 particles were effectively coupled with carbon nitride (CN) forming nanocomposites. The materials were fully characterized by DR‐UV‐Vis, N2 adsorption‐desorption isotherms, XRD, Raman, FTIR, TGA, XPS, TEM, electron energy loss spectroscopy, photoluminescence, and electron paramagnetic spectroscopy (EPR) spectroscopy. The developed heterojunctions were applied as photocatalysts for hydrogen (H2) evolution by the photoreforming process of ethanol under solar irradiation, using minimal amount of Pt nanoparticles (0.1 wt. %) as co‐catalyst. The effects of boron addition and CN content were evaluated and optimized nanocomposite presented 85 % increase in H2 evolution compared with the pure anatase TiO2 catalyst. The observed higher H2 evolution rates were ascribed to improvements in charge formation and separation efficiency due to the B‐dopant and the presence of CN.

Effect of Fe3+ ion doping on photocatalytic ability of nanozirconia ceramic to degrade 2, 4, 6- trichlorophenol

Pure and a series of Fe3+ doped zirconia nanopowders were synthesized combining colloidal chemistry and solvothermal method from organometallic precursors in order to correlate doping and properties of zirconia matrix. After annealing of washed nanopowders at 600 °C, detailed characterization was performed using X-ray diffraction, UV/Vis absorption and luminescence, infrared and electron paramagnetic spectroscopy, transmission electron microscopy and BET measurements. Zirconia samples had mixed monoclinic and tetragonal crystalline phase; increasing Fe3+ ions concentration was followed by increasing of tetragonal phase share. In the sample with highest Fe3+ concentration, hematite can be detected. Also, UV/Vis spectrophotometry showed that Fe3+ doping lowers effective band gap of zirconia matrix from 4.5 eV (bulk value) to 2.1 eV for doped/nanocomposite samples. EPR measurements proved presence of dopant and showed that isolated Fe3+ ions in zirconia matrix exist in both crystalline phases; monoclinic and tetragonal (g ~ 4.8 and g ~ 4.27–4.2, respectively) surroundings. Zirconia samples were also successfully used as photocatalysts for photocatalytic degradation of 2, 4, 6, trichlorophenol.

Spin‐Polarized Electronic Transport through Ferromagnet/Organic–Inorganic Hybrid Perovskite Spinterfaces at Room Temperature

AbstractOrganic–inorganic hybrid perovskites (OIHPs) have been explosively investigated mainly due to their potential applications in optoelectronics. Despite the electronic charge transport, phenomena regarding the spin‐polarized electronic transport in OIHPs‐based spintronic devices and the role of ferromagnet/OIHP spinterfaces remain unclear. In this work, the spin injection, accumulation, transport, and detection at room temperature for a vertical perovskite spin valve (PeSV) consisting of Ni/CH3NH3PbI3−xClx/Ni is reported. An in‐plane anisotropic magnetoresistance (AMR) and a PeSV related magnetoresistance (MR) show remarkable magnetic switching behaviors due to the formation of Ni/CH3NH3PbI3−xClx spinterfaces, and the ferromagnetic coupling between two spin quantization axes of the spinterfaces. With assists of capacitance–frequency (C − − f) measurements under magnetic fields, the spin accumulation that occurs at the Ni/CH3NH3PbI3−xClx interface can be detected at the spin parallel (↑↑) and antiparallel (↑↓) configurations. Owing to a strong orbital interaction at the Ni/CH3NH3PbI3−xClx hybrid interface, the spin‐sensitive electron paramagnetic spectroscopy (EPR) reveals significant change of the magnetic moment (µ). It is believed that the solution processed CH3NH3PbI3−xClx and the formation of the Ni/CH3NH3PbI3−xClx spinterface may hold an exceptionally important role for future hybrid optospintronic applications.

Mononuclear vs. binuclear carboxylates of copper(II) with 2,2′‐bipyridine: Synthesis, characterization, structural description, and properties

AbstractTwo new copper(II) carboxylate complexes with 2,2′‐bipyridine and para‐nitrophenyl acetate (complex 1) and phenyl acetate (complex 2) have been synthesized; isolated in quantitative yield; and characterized using fourier‐transform infrared spectroscopy (FT‐IR), electron paramagnetic resonance, absorption spectroscopy, electrochemistry, and powder and single crystal X‐ray diffraction (XRD) techniques. Being mononuclear, the geometry around copper in complex 1 is a Jahn–Teller distorted octahedral, while complex 2 is binuclear with slightly distorted square pyramidal geometry around both copper ions. Powder XRD indicated several peaks in spectra of both complexes, which coincided with their theoretical spectra. FT‐IR results of the carboxylate stretching frequency were in accordance with the single crystal structure data. Electron paramagnetic resonance spectra of complexes 1 and 2 yielded g┴ values of 2.06161 and 2.24623 and 1.94959, respectively, indicating a localized electron in b1 (d x2–y2‐orbital). Ultra‐violet (UV)–visible spectroscopy and electrochemistry helped in characterization, as well as in deoxyribonucleic acid (DNA)‐binding ability of the complexes, yielding DNA‐binding constant values = 1.351 × 104 and 1.361 × 104 and 1.820 × 104 and 2.426 × 104 M−1, respectively, for complexes 1 and 2. The complexes demonstrate good biological potential.

Copper (II) complexes of 3,5‐di‐tert‐butyl‐2‐hydroxybenzoylhydrazones of 2‐formylpyridine and 2‐acetylpyridine, with tautomeric azine‐scaffold‐based architecture: Synthesis, crystal structures, the effect of counteranions on complexation, and their anti‐microbial and anti‐tuberculosis evaluation

A series of air‐ and moisture‐stable copper (II) complexes of 3,5‐di‐tert‐butyl‐2‐hydroxy‐N′‐(pyridin‐2‐ylmethylene)benzohydrazide (L1H) and 3,5‐di‐tert‐butyl‐2‐hydroxy‐N′‐(1‐(pyridin‐2‐yl)ethylidene)benzohydrazide (L2H) were synthesized. The two newly designed hydrazone Schiff base ligands with the tautomeric azine‐scaffold involving N, N and O ligating architecture were derived from the condensation of 3,5‐di‐tert‐butyl‐2‐hydroxybenzoylhydrazide with 2‐formylpyridine and 2‐acetylpyridine, respectively. The resultant ligands and their copper complexes were characterized using various spectro‐analytical techniques, like infrared (IR), 1H‐NMR, 13C‐NMR, electron paramagnetic resonance, electronic spectroscopy, thermogravimetric analysis and conductance measurements. The interesting inter‐convertible E/Z geometrical isomeric forms of the ligand L1H was established by NMR and IR spectra. In addition, the molecular structures of L2H, C3 and C4 were unambiguously established using the single‐crystal X‐ray diffraction technique. The dichlorido‐bridged dinuclear square pyramidal complexes, with the [Cu2(μ‐Cl)2L2] type of core units, were resulted for the complexes C1 and C3, whereas z‐in compressed mononuclear 1:2 (M:L) octahedral complex geometries resulted for C2, C4 and the rest of the complexes even when various copper (II) precursor salts with different counteranions were used. The ligands and their complexes were investigated for the anti‐microbial activities against gram‐positive and gram‐negative bacteria. The ligand L2H and its complexes C3 and C4 exhibited better anti‐tuberculosis activity than the controls.

Oxidation Pathways Involving a Sulfide-Endcapped Donor-Acceptor-Donor π-Conjugated Molecule and Antimony(V) Chloride.

The oxidation pathways and products of a discrete, sulfide-endcapped donor-acceptor-donor (D/A/D) molecule, namely, propylenedioxythiophene-benzothiadiazole-propylenedioxythiophene, are investigated. The electrochemical and chemical oxidations proceed by two distinct routes. Specifically, electrochemical oxidation undergoes a sequential two-step, one-electron (1e-) oxidation route with a 117 mV difference between consecutive half-wave potentials. In contrast, chemical oxidation by antimony(V) chloride (SbCl5) causes the generation of four different oxidized species: (a) the 1e- oxidation state, (b) a decomposition product, (c) the 2e- oxidation state, and (d) a chloride adduct of the 2e- oxidation state. The decomposition product is generated by the reaction of the 1e- oxidation state with residual water, resulting in nucleophilic aromatic substitution at the sulfide group terminal positions. This reaction leads to the formation of a 2e-oxidized, oxygen atom (ketone)terminated decomposed molecule. The chloride adduct is determined to be produced by electrophilic chloronium ion (2e-) oxidation by the SbCl4+ complex, which is a product of SbCl5 ligand disproportionation. The formation of the 2e-oxidizedchlorine adduct shows to be linearly dependent on the molarity of SbCl5 in dichloromethane, giving new insight into the concentrationdependent reactivity of SbCl5 as a 2e- oxidant. The electronic, optical, and magnetic properties and geometric structures of the 1e-and 2e-oxidizedhexachloroantimonate salts are fully characterized by a combination of electrochemistry, X-ray crystallography, UV-vis-NIR, electron paramagnetic resonance, NMR spectroscopies, and density functional theory calculations. The aim of this study is to provide a thorough understanding of the redox pathways of a D/A/D π-conjugated organic molecule for potential application in organic electrochromic devices.

Biocompatible FeOOH-Carbon quantum dots nanocomposites for gaseous NOx removal under visible light: Improved charge separation and High selectivity

Development of biocompatible photocatalysts with improved charge separation and high selectivity is essential for effective removal of air pollutants. Iron-containing catalysts have attracted extensive attention due to their low-toxicity and high natural abundance. Here, carbon quantum dots (CQDs) modified FeOOH nanocomposites fabricated using a facile hydrothermal route showed enhanced NO removal efficiency (22%) compared to pure FeOOH. Moreover, generation of toxic NO2 intermediates was significantly inhibited using the nanocomposites, demonstrating high selectivity for final nitrate formation. Photo-electrochemical results showed that both charge separation and transfer efficiency were significantly improved by CQDs addition, and the lifetime of photo-generated carriers was increased eventually. Density functional theory calculations further elucidated that the suppressed recombination of photo-induced electron-hole pairs was due to enhanced electron migration from the FeOOH to CQDs. A NO degradation mechanism was proposed based on detection of the reactive oxygen species using electron paramagnetic spectroscopy. In addition, the nanocomposite showed good biocompatibility and low cytotoxity, ensuring minimal environmental impact for potential application in large-scale.

Properties and structure of a low-potential, penta-heme cytochrome c552 from a thermophilic purple sulfur photosynthetic bacterium Thermochromatium tepidum.

The thermophilic purple sulfur bacterium Thermochromatium tepidum possesses four main water-soluble redox proteins involved in the electron transfer behavior. Crystal structures have been reported for three of them: a high potential iron-sulfur protein, cytochrome c', and one of two low-potential cytochrome c552 (which is a flavocytochrome c) have been determined. In this study, we purified another low-potential cytochrome c552 (LPC), determined its N-terminal amino acid sequence and the whole gene sequence, characterized it with absorption and electron paramagnetic spectroscopy, and solved its high-resolution crystal structure. This novel cytochrome was found to contain five c-type hemes. The overall fold of LPC consists of two distinct domains, one is the five heme-containing domain and the other one is an Ig-like domain. This provides a representative example for the structures of multiheme cytochromes containing an odd number of hemes, although the structures of multiheme cytochromes with an even number of hemes are frequently seen in the PDB database. Comparison of the sequence and structure of LPC with other proteins in the databases revealed several characteristic features which may be important for its functioning. Based on the results obtained, we discuss the possible intracellular function of this LPC in Tch. tepidum.

Understanding the Effects of Sulfate/Bisulfate Ions on Electrolytes for Vanadium/Sulfuric Acid Redox Flow Batteries

Redox flow batteries are a promising utility scale energy storage technology, recognized for the safe storage of surplus energy harnessed by wind and solar. Of particular promise is the all vanadium redox flow battery (VRFB) which relies on two redox couples of VO2 + (V5+)/VO2+(V4+) on the cathodic side and V3+/V2+ on the anodic side. Significant efforts in recent years have focused on the optimization of operating conditions of VRFBs required for widespread commercialization. However many of these endeavors rely on incomplete or inappropriate data applied to specific systems, (e.g. wrong diffusion coefficients under specific conditions) which is necessary for a more complete and robust model. One such phenomena inherent to the operation of a VRFB is proton and vanadium ion crossover.1–4 Proton transport is a requirement for the electrochemical reactions and to maintain charge balance. However, in practice vanadium ions also transport across the membrane causing parasitic and other unknown effects. For example, it is difficult to monitor changes to proton concentration (e.g. pH) as chemical treatment (titration) is clouded by the precipitation of VO(OH)2, and pH measurements under operational conditions are impossible or impractical. This presentation will report our fundamental measurements of VRFB electrolytes by first investigating concentration effects of SO4 2-/HSO4 - to gain insight on the discharged (VO2+) electrolyte and the chemical equilibrium with a goal of being able to identify proton concentration. This understanding will allow for the determination of proton concentrations of the charged electrolytes and shed light on vanadium crossover which has occurred during charging. Those data will be compared to our experimental electron paramagnetic spectroscopy EPR vanadium crossover data. J. S. Lawton, A. M. Jones, Z. Tang, M. Lindsey, and T. Zawodzinski, J. Electrochem. Soc. , 164, A2987–A2991 (2017) http://jes.ecsdl.org/content/164/13/A2987.abstract.J. S. Lawton et al., J. Electrochem. Soc., 163, A5229–A5235 (2016).R. A. Elgammal, Z. Tang, C.-N. Sun, J. Lawton, and T. A. Zawodzinski, Electrochim. Acta, 237, 1–11 (2017) http://linkinghub.elsevier.com/retrieve/pii/S0013468617306138.R. M. Darling, a. Z. Weber, M. C. Tucker, and M. L. Perry, J. Electrochem. Soc., 163, A5014–A5022 (2015) http://jes.ecsdl.org/cgi/doi/10.1149/2.0031601jes.

Investigating the Conformational Dynamics and Membrane Interaction Near the Catalytic Serine of Exou Upon Interaction with Diubiquitin and Membranes by EPR Spectroscopy

Pseudomonas aeruginosa (P. aeruginosa) is a Gram negative, opportunistic pathogen that is a rising health concern as an ESKAPE pathogen resistant to multiple antimicrobial agents. P. aeruginosa manipulates the host response by translocating effector proteins into the host cell via a type III secretion system (T3SS). P. aeruginosa's most cytotoxic T3SS effector, ExoU, is a potent patatin-like phospholipase with a catalytic serine-aspartate dyad that destroys host cell membranes once activated by non-covalent interaction with ubiquitin. Two crystal structures of ExoU in complex with its chaperone SpcU have been reported, however the activated conformational state of ExoU in the presence of ubiquitin remains unknown. Consequently, ExoU's mechanism of action remains poorly understood. This study focuses on elucidating the conformational dynamics, membrane interaction, and structure of sites near the catalytic serine upon interaction with a ubiquitin cofactor and membrane substrate. Site-directed spin labeling (SDSL) in conjunction with electron paramagnetic (EPR) spectroscopy was used to examine the motional dynamics of sites near the catalytic serine upon interaction with diubiquitin (diUb) and membranes. Membrane penetration of the same sites upon interaction with diUb and membranes was investigated using power saturation EPR spectroscopy in the presence of various paramagnetic relaxation agents. Changes in spin label motion and membrane penetration were observed for sites near the catalytic serine in the presence of diUb and membranes combined, but not in the presence of either diUb or membranes alone, suggesting that a synergistic interaction with both ubiquitin and membranes is necessary to form an active catalytic site. Supported by NIH grant GM114234.

In Vivo Molecular Electron Paramagnetic Resonance-Based Spectroscopy and Imaging of Tumor Microenvironment and Redox Using Functional Paramagnetic Probes.

A key role of the tumor microenvironment (TME) in cancer progression, treatment resistance, and as a target for therapeutic intervention is increasingly appreciated. Among important physiological components of the TME are tissue hypoxia, acidosis, high reducing capacity, elevated concentrations of intracellular glutathione (GSH), and interstitial inorganic phosphate (Pi). Noninvasive in vivo pO2, pH, GSH, Pi, and redox assessment provide unique insights into biological processes in the TME, and may serve as a tool for preclinical screening of anticancer drugs and optimizing TME-targeted therapeutic strategies. Recent Advances: A reasonable radiofrequency penetration depth in living tissues and progress in development of functional paramagnetic probes make low-field electron paramagnetic resonance (EPR)-based spectroscopy and imaging the most appropriate approaches for noninvasive assessment of the TME parameters. Here we overview the current status of EPR approaches used in combination with functional paramagnetic probes that provide quantitative information on chemical TME and redox (pO2, pH, redox status, Pi, and GSH). In particular, an application of a recently developed dual-function pH and redox nitroxide probe and multifunctional trityl probe provides unsurpassed opportunity for in vivo concurrent measurements of several TME parameters in preclinical studies. The measurements of several parameters using a single probe allow for their correlation analyses independent of probe distribution and time of measurements. The recent progress in clinical EPR instrumentation and development of biocompatible paramagnetic probes for in vivo multifunctional TME profiling eventually will make possible translation of these EPR techniques into clinical settings to improve prediction power of early diagnostics for the malignant transition and for future rational design of TME-targeted anticancer therapeutics. Antioxid. Redox Signal. 28, 1365-1377.

Chloride-enhanced oxidation of organic contaminants by Cu(II)-catalyzed Fenton-like reaction at neutral pH

The Cu(II)-catalyzed Fenton-like reaction was found to be significantly accelerated in the presence of chloride ion (i.e., the Cu(II)/H2O2/Cl− system), enhancing the oxidative degradation of organic contaminants at neutral pH. The degradation of carbamazepine (a select target contaminant) by the Cu(II)/H2O2 system using 1μM Cu(II) and 10mM H2O2 was accelerated by 28-fold in the presence of 10,000mg/L Cl− at pH 7. The observed rate of carbamazepine degradation generally increased with increasing doses of Cu(II), H2O2, and Cl−, and exhibited an optimal value at around pH 7.5. Various other organic contaminants such as propranolol, phenol, acetaminophen, 4-chlorophenol, benzoic acid, and caffeine were also effectively degraded by the Cu(II)/H2O2/Cl− system. Experiments using oxidant probe compounds and electron paramagnetic spectroscopy suggested that cupryl (Cu(III)) species are the major reactive oxidants responsible for the degradation of these organic contaminants. The enhanced kinetics was further confirmed in natural seawater.

Activation Thermodynamics and H/D Kinetic Isotope Effect of the Hox to HredH+ Transition in [FeFe] Hydrogenase.

Molecular complexes between CdSe nanocrystals and Clostridium acetobutylicum [FeFe] hydrogenase I (CaI) enabled light-driven control of electron transfer for spectroscopic detection of redox intermediates during catalytic proton reduction. Here we address the route of electron transfer from CdSe→CaI and activation thermodynamics of the initial step of proton reduction in CaI. The electron paramagnetic spectroscopy of illuminated CdSe:CaI showed how the CaI accessory FeS cluster chain (F-clusters) functions in electron transfer with CdSe. The Hox→HredH+ reduction step measured by Fourier-transform infrared spectroscopy showed an enthalpy of activation of 19 kJ mol-1 and a ∼2.5-fold kinetic isotope effect. Overall, these results support electron injection from CdSe into CaI involving F-clusters, and that the Hox→HredH+ step of catalytic proton reduction in CaI proceeds by a proton-dependent process.

Apple pectin-derived oligosaccharides produce carbon dioxide radical anion in Fenton reaction and prevent growth of Escherichia coli and Staphylococcus aureus

Pectin is the main soluble fiber in apples or citruses. It may be fermented by gut microbiota to metabolites showing local intestinal and systemic effects. A wide range of beneficial effects of dietary pectin includes impacts on the redox milieu and microbiota profile. We prepared pectin-derived oligosaccharides (apple (APDO) and citrus) and polygalacturonic acid-derived oligosaccharides, using alkaline hydrolysis by hydrogen peroxide, and analyzed them by Fourier Transform Infrared spectrometry. Furthermore, we analyzed the effects of pectin-derived oligosaccharides on hydroxyl radical (HO)-generating Fenton reaction using electron paramagnetic resonance spin-trapping spectroscopy, and the effects on the growth of Escherichia coli and Staphylococcus aureus in the presence of dietary-relevant HO-generating system (iron+ascorbate). The oligosaccharides react with HO radical to produce carbon dioxide radical anion (CO2−). A comparative analysis showed that APDO has the most prominent bacteriostatic effect. This might be at least partially related to the higher capacity of APDO to produce CO2−, which specifically targets proteins and appears to have a longer lifetime and larger diffusion radius in biological systems compared to HO.