Electron Paramagnetic Resonance Spectroscopy Measurements Research Articles

Electron Paramagnetic Resonance (EPR) Spectroscopy to Measure Oxidative Stress (OS) in Ulcerative Colitis Mouse

Background: Inflammatory bowel disease (IBD) refers to a group of chronic, complex, relapsing and remitting inflammatory disorders that affect the gastrointestinal (GI) tract. Crohn’s disease (CD) and ulcerative colitis (UC) are the two commonly diagnosed forms of IBD that affect over 3 million Americans, or 1.3% of the US population. In CD, patchy inflammation penetrating through multiple epithelial layers is present in any part of the GI tract, whereas UC is characterized by uniform inflammation restricted to the colon and rectum. Studies have shown increased oxidative stress (OS) as one of the major mechanisms involved in the pathogenesis of UC. Increased OS has thus far been measured using Biochemical assay-kits. In recent studies, electron paramagnetic resonance (EPR) spectroscopy has been extensively used to quantitatively characterize OS level in various tissues. Hypothesis: We hypothesize that EPR technique could be used to characterize OS in epithelia of colon. Aim: We aimed to develop EPR spectroscopy technique to quantify the level of OS in epithelia of normal and UC mouse colon. Methods: Normal mice (C57BL/6 male; 6 – 7 weeks old; Charles River, Wilmington, MA) were given regular water, while acute UC mice were given 5% Dextran-Sulfate-Sodium (DSS) water ad libitum for 7-days. EPR spectroscopy measurements were performed using the redox sensitive hydroxylamine spin probe, 1-hydroxy-3-carboxymethyl-2,2,5,5-tetramethyl-pyrrolidine (CMH; EPR silent). CMH is oxidized by reactive species/oxidants to 3-carboxymethyl-2,2,5,5- tetramethyl-pyrrolidinyloxy radical (CM•; EPR active). We used EPR detected CM• level as a quantitative marker of OS level. OS levels were measured both in serum and distal colon collected from euthanized mice. OS levels were presented as arbitrary units of EPR intensity. Results: OS levels were increased by 41% in serum from UC mice (normal vs UC: 33.6 ± 2.2 vs 47.0 ± 2.0 units; p < 0.011). OS levels were also significantly (60%) increased in UC mice colon compared to normal colon (normal vs UC: 3.5 ± 0.1 vs 5.6 ± 0.7 EPR units; p < 0.02). OS levels were approximately 9-fold higher in serum compared to colon in both normal and UC mice (normal: 3.5 ± 0.1 vs 33.6 ± 2.2; UC: 5.6 ± 0.7 vs 47.0 ± 2.0 EPR signals). Conclusions: We conclude that: 1) EPR spectroscopy technique could successfully be used for the precise measurement of OS levels in serum and colon; 2) OS levels were significantly increased in both serum and colon of UC mice; and 3) increased tissue oxidants were continuously released into the blood. Speculation: Increased serum oxidants may eventually affect other tissues in the body. This study was supported by the West Virginia Clinical and Translational Science Institute (WVCTSI) pilot grant (JTK), and Transition Grant Support, Offce of Research and Graduate Education, WVU Health Sciences Center (VMR). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

LaCoO3/SBA-15 as a high surface area catalyst to activate peroxymonosulfate for degrading atrazine in water

An efficient perovskite-based heterogeneous catalyst is highly desired to activate peroxymonosulfate (PMS) for removing organic pollutants in water. A high surface area PMS-activator was fabricated by loading LaCoO3 on SBA-15 to degrade atrazine (ATR) in water. The LaCoO3/SBA-15 depicted better textural properties and higher catalytic activity than LaCoO3. In 6.0 min, atrazine (ATZ) degradation in the selected LaCoO3/SBA-15/PMS system, LaCoO3, adsorption by LaCoO3/SBA-15, sole PMS processes reached approximately 100%, 55.15%, 12.80%, and 16.65 % respectively. Furthermore, 0.04 mg L−1 Co was leached from LaCoO3/SBA-15 during PMS activation by LaCoO3/SBA-15. The LaCoO3/SBA-15 showed stable catalytic activity after reuse. The use of radical scavengers and electron paramagnetic resonance spectroscopy (EPR) demonstrated that ROS such as 1O2, O2•−, •OH, and SO4•− were generated by PMS activated by LaCoO3/SBA-15 owing to redox reactions [Co2+/Co3+, and O2−/O2]. EPR, XPS, ATR-FTIR, EIS, LSV, and chronoamperometric measurements were used to explain the catalytic mechanism for PMS activation. Excellent atrazine degradation was due to high surface area, porous nature, diffusion-friendly structure, and ROS. Our investigation proposes that perovskites with different A and B metals and modified perovskites can be loaded on high surface area materials to activate PMS into ROS.

Radiological injuries under low energy x-rays in mice depending on dose and protocol: comparative characterization of lesion severity and impact of the in vivo bone response on retrospective dose estimations

Objective. To improve our knowledge about the biological effects of over exposures involving low-energy x-rays, we developed and characterized a preclinical mouse model allowing to mimic different lesion severity degrees induced by 80 kV x-ray depending on the dose and protocol (single or repeated exposure). Approach. Mice were locally exposed (paw) to 80 kV x-rays in a single (15, 30 or 45 Gy in K air) or repeated exposition (2 × 15 or 3 × 15 Gy in K air) to assess different degrees of lesion severity. Six post-irradiation euthanasia time points (0, 7, 14, 21, 42, and 84 days) were determined to follow up the evolution of lesions based on the lesion score, weighing and cutaneous blood perfusion. The bone dose was estimated at the different time points by electron paramagnetic resonance (EPR) spectroscopy. Main results. The monitoring of the lesion severity allows to classify the exposure protocols according to their severity. EPR spectroscopy measurements allow to determine the bone dose on the day of irradiation which is 7 times higher than the initial dose for single protocols. However, the initial signal measured at the end of the repeated exposure was 27% lower than the signal measured for a single dose. The study of the kinetics of EPR signal showed a decrease of the EPR signal which is dependent on the exposure protocol but not on dose highlighting the impact of bone physiology on the bone dose estimation. Significance: the preclinical model developed allows to assess the impact of the dose and protocol on the lesion severity induced by low-energy x-ray. For the first time, the dynamics of free radicals have been quantified in an in vivo model, highlighting that the doses actually administered can be underestimated if samples are taken weeks or even months after exposure.

Influences of Metal Electrodes on Stability of Non‐Fullerene Acceptor‐Based Organic Photovoltaics

AbstractUnderstanding chemical degradation at the interface between different layers in an organic photovoltaic device (OPV) is crucial to improving the long‐term stability of OPVs. Herein, molecular‐level insights are provided into the impact of different metal top electrodes on the interfacial morphology and stability of photoactive layers in PM6:Y6 bulk‐heterojunction (BHJ) OPVs. OPVs with an aluminum (Al) top electrode exhibit inferior stability compared to silver (Ag) electrode devices upon thermal annealing, whereby thermal stress induces the diffusion of both Al and Ag atoms to the PM6:Y6 BHJ layer. The diffused Al atoms cause surface recombination at the interface between the photoactive layer and an interlayer. Specifically, X‐ray photoelectron spectroscopy suggests the different local chemical environments of PM6 and Y6 moieties in PM6:Y6/Al‐contact devices. These results are corroborated by solid‐state nuclear magnetic resonance and electron paramagnetic resonance spectroscopy measurements, indicating the formation of ionic and organo‐metallic‐like species at the sub‐layers of the PM6:Y6 BHJ morphology, which are estimated to be less than 5 wt% of the PM6:Y6/Al blend. By comparison, the Ag atoms do not adversely affect PM6:Y6 BHJ morphology and the associated device physics. The investigation of reactive electrode‐BHJ interfaces by multiscale characterization techniques and device physics is expected to provide guidance to future interfacial engineering strategies to develop stable and efficient OPVs.

Stabilized and Controlled Release of Radicals within Copper Formate-Based Nanozymes for Biosensing.

Fenton-like radical processes are widely utilized to explain catalytic mechanisms of peroxidase-like nanozymes, which exhibit remarkable catalytic activity, cost-effectiveness, and stability. However, there is still a need for a comprehensive understanding of the formation, stabilization, and transformation of such radicals. Herein, a copper formate-based nanozyme (Cuf-TMB) was fabricated via a pre-catalytic strategy under ambient conditions. The as-prepared nanozyme shows comparable catalytic activity (Km, 1.02 × 10-5 mM-1; Kcat, 3.09 × 10-2 s-1) and kinetics to those of natural peroxidase toward H2O2 decomposition. This is attributed to the feasible oxidation by *OH species via the *O intermediate, as indicated by density functional theory calculations. The key ·OH radicals were detected to be stable for over 52 days and can be released in a controlled manner during the catalytic process via in situ electron spin-resonance spectroscopy measurements. Based on the understanding, an ultrasensitive biosensing platform was constructed for the sensitive monitoring of biochemical indicators in clinic settings.

Magnetic Behavior of Trigonal (Bi-)pyramidal 3d8 Mononuclear Nanomagnets: The Case of [Ni(MDABCO)2Cl3]ClO4.

This paper attempts to shed light on the origin of the magnetic behavior specific to trigonal bi- and pyramidal 3d8 mono- and polynuclear nanomagnets. The focus lies on entirely unraveling the system's intrinsic microscopic mechanisms and fundamental quantum mechanical relations governing the underlying electron dynamics. To this end, we develop a self-consistent approach to characterize, in great detail, all electron correlations and the ensuing fine structure of the energy spectra of a broad class of 3d8 systems. The mathematical framework is based on the multiconfigurational self-consistent field method and is devised to account for prospective quantum mechanical constraints that may confine the electron orbital dynamics while preserving the properties of all measurable quantities. We successfully characterize the experimentally observed magnetic anisotropy properties of a slightly distorted trigonal bipyramidal Ni2+ coordination complex, demonstrating that such compounds do not exhibit intrinsic huge zero-field splitting and inherent giant magnetic anisotropy. We reproduce qualitatively and quantitatively the behavior of the low-field magnetic susceptibility, magnetization, low-, and high-field electron paramagnetic resonance spectroscopy measurements and provide an in-depth analysis of the obtained results.

Catalytic behavior of nitrous acid for acetaminophen transformation during the freezing process

This study demonstrates the transformation of acetaminophen by reactive nitrous acid in a frozen solution and its abnormal stoichiometry. The chemical reaction between acetaminophen and nitrous acid (AAP/NO2− system) was negligible in the aqueous solution; however, the reaction rapidly progressed if the solution started to freeze. The ultrahigh performance liquid chromatography–electrospray ionization tandem mass spectrometry measurements showed that polymerized acetaminophen and nitrated acetaminophen were formed in the proceeding reaction. Electron paramagnetic resonance spectroscopy measurements showed that nitrous acid oxidized acetaminophen via a one-electron transfer reaction producing acetaminophen-derived radical species, which is the cause of acetaminophen polymerization. We demonstrated that a relatively smaller dose of nitrite than acetaminophen caused significant acetaminophen degradation in the frozen AAP/NO2− system and revealed that the dissolved oxygen content notably affected acetaminophen degradation. We showed that the reaction occurs in a natural Arctic lake matrix (nitrite and acetaminophen spiked). Considering that the freezing phenomenon is common in the natural environment, our research provides a possible scenario for the freezing chemistry of nitrite and pharmaceuticals in environmental chemistry.

Monitoring the Local Structure and Magnetic Properties of the Dinuclear Cu2-Paddle Wheel Nodes in the Mesoporous Metal–Organic Framework, DUT-49(Cu), upon Adsorption-Induced Breathing Transitions

DUT-49(Cu) is a well-studied representative of flexible mesoporous frameworks, in particular, famous for long-lived overloaded metastable states in the presence of a variety of gases at defined temperatures, leading to “negative gas adsorption” transitions. Important mechanistic insights into these transitions in DUT-49 were obtained via in situ powder X-ray diffraction (PXRD) studies conducted in parallel to gas physisorption. However, for strongly X-ray absorbing probe molecules, such as xenon, such studies are not feasible, even if synchrotron radiation is used. Here we employ in situ electron paramagnetic resonance spectroscopy (EPR), PXRD, and adsorption isotherm measurements to explore the phase transformations in DUT-49(Cu) in the presence of xenon and compare its properties with the corresponding adsorption/desorption behavior of ethylene for this material. The antiferromagnetically coupled CuII–CuII dimers in the paddle-wheel (PW) units of this pillared layer MOF serve as local magnetic probes in the in situ EPR measurement. These experiments allowed us to monitor the op ↔ cp phase transformations during the xenon physisorption through the structural changes at the PW units encoded in the zero-field splitting parameters of the S = 1 state of the CuII dimers. The EPR data indicates an expansion of the unit cell for the cp phase in the presence of xenon. This novel EPR-derived insight into the phase transformation phenomena of the xenon-loaded DUT-49(Cu) could be validated by combined in situ EPR, PRXD, and adsorption isotherm measurements for ethylene adsorption over the same MOF material in a comparable temperature range.

Influence of the Structure on Magnetic Properties of Calcium-Phosphate Systems Doped with Iron and Vanadium Ions.

The aim of this study was to prepare and characterize the glasses made of x(Fe2O3∙V2O5)∙(100 - x)[P2O5∙CaO] with x ranging of 0-50%. The contribution of Fe2O3 and V2O5 amount on the structure of P2O5·CaO matrix was investigated. The vitreous materials were characterized by XRD (X-ray diffraction analysis), EPR (Electron Paramagnetic Resonance) spectroscopy, and magnetic susceptibility measurements. A hyperfine structure typical for isolated V4+ ions was noticed to all spectra containing low amount of V2O5. The XRD spectra show the amorphous nature of samples, apart x = 50%. An overlap of the EPR spectrum of a broad line without the hyperfine structure characteristic of clustered ions was observed with increasing V2O5 content. The results of magnetic susceptibility measurements explain the antiferromagnetic or ferromagnetic interactions expressed between the iron and vanadium ions in the investigated glass.

A Highly Stable Organic Luminescent Diradical.

It is very challenging to obtain stable room-temperature luminescent open-shell singlet diradicals. Herein we report the first stable Müller's hydrocarbon TTM-PhTTM with luminescent properties. Variable-temperature electron paramagnetic resonance spectroscopy measurements and theoretical calculations show that TTM-PhTTM has an open-shell singlet ground state with a diradical character of 90 %. Because of a small singlet-triplet energy gap, the open-shell singlet ground state can be thermally excited to a triplet state. TTM-PhTTM shows room-temperature deep-red emission in various solutions. Unusually high stability of TTM-PhTTM was also observed owing to effective steric hindrance and spin delocalization. Our results are beneficial to the rational design and discovery of more stable luminescent diradical materials.

A Highly Stable Organic Luminescent Diradical

AbstractIt is very challenging to obtain stable room‐temperature luminescent open‐shell singlet diradicals. Herein we report the first stable Müller's hydrocarbon TTM‐PhTTM with luminescent properties. Variable‐temperature electron paramagnetic resonance spectroscopy measurements and theoretical calculations show that TTM‐PhTTM has an open‐shell singlet ground state with a diradical character of 90 %. Because of a small singlet‐triplet energy gap, the open‐shell singlet ground state can be thermally excited to a triplet state. TTM‐PhTTM shows room‐temperature deep‐red emission in various solutions. Unusually high stability of TTM‐PhTTM was also observed owing to effective steric hindrance and spin delocalization. Our results are beneficial to the rational design and discovery of more stable luminescent diradical materials.

3D Variable Range Hopping Electrical Conduction of a Carbon from Polyaniline Vapor

Carbon with a metallic reflection was prepared from polyaniline (PANI) vapor deposited on the inner quartz wall of a furnace. Electron probe microanalyzer analysis proved that the resultant contained carbon, oxygen, nitrogen, and sulfur atoms. A Dysonian line shape with paramagnetic properties was observed for the resulting carbon from PANI in the electron spin-resonance spectroscopy measurement. The resistance vs. temperature curve of the carbon indicated semiconductor-insulator properties in a low-temperature range. Electrical conduction in the carbon was carried out with 3D variable range hopping.

Cooperative effects of zinc interstitials and oxygen vacancies on violet-blue photoluminescence of ZnO nanoparticles: UV radiation induced enhanced latent fingerprint detection

Understanding the mechanisms of the violet-blue (VB) photoluminescence (PL) emissions is very important for possible applications of ZnO nanoparticles (NPs) in optoelectronics and forensic. Origin of the VB PL emissions of ZnO NPs of sizes of 27–54 nm synthesized in water using chemical co-precipitation method at a temperature of ∼100 oC for heating duration of 1–3 h, respectively, has been established here. For both below band gap excitation (BBE) and above band gap excitation (ABE), narrow ultraviolet and broad visible PL emissions including VB emissions have been observed. For BBE, VB emission is due to the direct transition of electrons from Zni/ex-Zni to valence band edge. The weak VB emission in case of ABE, usually ignored in earlier studies, has been studied here very carefully and systematically. The two predominant defect states and their cooperative effects are clearly found to be responsible for VB emissions. The Zni and Vo defect centers have been confirmed from the Raman and electron paramagnetic resonance spectroscopic measurements. As an important forensic applications, detection of latent finger prints (taken on different substances) using as-synthesized ZnO NPs through PL emissions has been demonstrated by illuminating using ultraviolet light even after 40 days.

Enhancement of Mechanophore Activation by Electrostatic Interaction

Abstract Mechanophores, which change their chemical structure in response to mechanical stimuli, are widely used to develop mechanoresponsive materials, and their reactivity is greatly affected by the surrounding environment. Here, we focus on the effect of electrostatic interactions on the activation of mechanophores. A series of radical-type mechanophores with ionic functional groups, as well as mixed systems of these radical-type mechanophores with dicarboxylic acid groups and divalent ions were prepared, and their mechano-responsiveness in the bulk was investigated via ball-milling and subsequent electron paramagnetic resonance spectroscopy measurements. The results revealed that the mechano-responsiveness is governed by the introduction of electrostatic interactions into the mechanophores.

Visible Light-Induced Catalyst-Free Activation of Peroxydisulfate: Pollutant-Dependent Production of Reactive Species.

Activation of peroxydisulfate (PDS, S2O82-) via various catalysts to degrade pollutants in water has been extensively investigated. However, catalyst-free activation of PDS by visible light has been largely ignored. This paper reports effective visible light activation of PDS without any additional catalyst, leading to the degradation of a wide range of organic compounds of high environmental and human health concerns. Importantly, the formation of reactive species is distinctively different in the PDS visible light system with and without pollutants [e.g., atrazine (ATZ)]. In addition to SO4•- generated via S2O82- dissociation under visible light irradiation, O2•- and 1O2 are also produced in both systems. However, in the absence of ATZ, H2O2 and O2•- are key intermediates and precursors for 1O2, whereas in the presence of ATZ, a different pathway was followed to produce O2•- and 1O2. Both radical and nonradical processes contribute to the degradation of ATZ in the PDS visible light system. The active role of 1O2 in the degradation of ATZ besides SO4•- is manifested by the enhanced degradation of contaminants and electron paramagnetic resonance spectroscopy measurements in D2O.

Central nervous system and systemic oxidative stress interplay with inflammation in a bile duct ligation rat model of type C hepatic encephalopathy

The role and coexistence of oxidative stress (OS) and inflammation in type C hepatic encephalopathy (C HE) is a subject of intense debate. Under normal conditions the physiological levels of intracellular reactive oxygen species are controlled by the counteracting antioxidant response to maintain redox homeostasis. Our previous in-vivo1H-MRS studies revealed the longitudinal impairment of the antioxidant system (ascorbate) in a bile-duct ligation (BDL) rat model of type C HE.Therefore, the aim of this work was to examine the course of central nervous system (CNS) OS and systemic OS, as well as to check for their co-existence with inflammation in the BDL rat model of type C HE. To this end, we implemented a multidisciplinary approach, including ex-vivo and in-vitro electron paramagnetic resonance spectroscopy (EPR) spin-trapping, which was combined with UV–Vis spectroscopy, and histological assessments. We hypothesized that OS and inflammation act synergistically in the pathophysiology of type C HE.Our findings point to an increased CNS- and systemic-OS and inflammation over the course of type C HE progression. In particular, an increase in the CNS OS was observed as early as 2-weeks post-BDL, while the systemic OS became significant at week 6 post-BDL. The CNS EPR measurements were further validated by a substantial accumulation of 8-Oxo-2′-deoxyguanosine (Oxo-8-dG), a marker of oxidative DNA/RNA modifications on immunohistochemistry (IHC). Using IHC, we also detected increased synthesis of antioxidants, glutathione peroxidase 1 (GPX-1) and superoxide dismutases (i.e.Cu/ZnSOD (SOD1) and MnSOD (SOD2)), along with proinflammatory cytokine interleukin-6 (IL-6) in the brains of BDL rats. The presence of systemic inflammation was observed already at 2-weeks post-surgery. Thus, these results suggest that CNS OS is an early event in type C HE rat model, which seems to precede systemic OS. Finally, our results suggest that the increase in CNS OS is due to enhanced formation of intra- and extra-cellular ROS rather than due to reduced antioxidant capacity, and that OS in parallel with inflammation plays a significant role in type C HE.

Structural and magnetic studies of cobalt substituted magnetite ferrofluids

In this work, hydrocarbon based ferrofluids of cobalt substituted magnetite (Fe3O4) having the composition CoxFe3-xO4 (0.0≤x≤ 0.3 in steps of 0.1) were prepared using co-precipitation method, with oleic acid as the surfactant. The structural, microstructural and magnetic studies were carried out using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscope (FESEM), Vibrating sample magnetometer (VSM) and Electron spin resonance spectroscopy (ESR). It is aimed to investigate the role of incorporation of high anisotropy cobalt on the structural and magnetic properties of the basic system. The X-ray diffraction pattern and Rietveld refinement confirm the inverse spinel structure of magnetite with space group Fd-3 m. Residual lattice strain was estimated using Williamson-Hall plot. FESEM depicts the presence of spherical nanoparticles with average size 15 nm to 16 nm. Saturation magnetization values recorded using VSM was found to decrease with Co2+ substitution with negligible remanence and coercivity confirming the superparamagnetic behaviour of the ferrofluids. The peak-to-peak line width (ΔHpp), g-factor and the resonant magnetic field (Hr) were calculated from ESR measurement. The spin resonance characteristics reveal an increase in the ΔHpp and g-value and a decrease in Hr with increase of Co2+ content. Spin-lattice and spin–spin relaxation time were calculated and analysed to interpret the relaxation mechanism taking place in the ferrofluids. Based on the results of these characterizations and their analysis the investigated ferrofluids may find suitability as potential materials for hyperthermia application and radar absorbing materials respectively.

Single-Crystal-to-Single-Crystal Cluster Transformation in a Microporous Molybdoarsenate(V)-Metalorganic Framework.

The hybrid compound [Cu(cyclam)(H2O)2]0.5[{Cu(cyclam)}1.5{B-H2As2Mo6O26(H2O)}]·9H2O (1) (cyclam = 1,4,8,11-tetraazacyclotetradecane) was synthesized in aqueous solution by reacting the {Cu(cyclam)}2+ complex with a mixture of heptamolybdate and an arsenate(V) source. Crystal packing of 1 exhibits a supramolecular open-framework built of discrete covalent molybdoarsenate/metalorganic units and additional [Cu(cyclam)(H2O)2]2+ cations, the stacking of which generates squarelike channels parallel to the z axis with an approximate cross section of 10 × 11 Å2 where all the hydration water molecules are hosted. Thermal evacuation of solvent molecules yields a new anhydrous crystalline phase, but compound 1 does not preserve its single-crystalline nature upon heating. However, when crystals are dehydrated under vacuum, they undergo a structural transformation that proceeds via a single-crystal-to-single-crystal pathway, leading to the anhydrous phase [{Cu(cyclam)}2(A-H2As2Mo6O26)] (2). Total dehydration results in important modifications within the inorganic cluster skeleton which reveals an unprecedented solid-state B to A isomerization of the polyoxoanion. This transition also involves changes in the CuII bonding scheme that lead to covalent cluster/metalorganic layers by retaining the open-framework nature of 1. Compound 2 adsorbs ambient moisture upon air exposure, but it does not revert back to 1, and the hydrated phase [{Cu(cyclam)}2(A-H2As2Mo6O26)]·6H2O (2h) is obtained instead. Structural variations between 1 and 2 are reflected in electron paramagnetic resonance spectroscopy measurements, and the permanent microporosity of 2 provides interesting functionalities to the system such as the selective adsorption of gaseous CO2 over N2.

Activation of peroxymonosulfate by bicarbonate and acceleration of the reaction by freezing

This study demonstrates the positive effects of dissolved bicarbonate and carbonate anions on peroxymonosulfate (PMS) induced oxidation and the remarkable acceleration of the reaction by freezing. More than 90% of the initial 4-chlorophenol (4-CP) decomposed in the frozen case, whereas only less than 20% of the 4-CP was removed in the aqueous case in the same time period. This accelerated reaction is attributed to the freeze-concentration of the dissolved substrates (i.e., PMS, bicarbonate, and pollutants) in the quasi-liquid layer at the ice grain boundaries between ice crystals. The reaction between bicarbonate and PMS was found to be unique because none of the effects were observed in the phosphate and hydroxide cooperated system with freezing, although the base activation of PMS could participate under basic conditions (pH > 9). Based on electron paramagnetic resonance spectroscopy measurements and comparison with the photo-excited Rose Bengal system as a reference system for singlet oxygen (1O2) generation, 1O2 was found to have a minor effect on the oxidation of 4-CP in the frozen bicarbonate-PMS system. While, direct electron transfer from the target organic substrate to the PMS was suggested as a major mechanism of 4-CP oxidation, because the selected target organic substrates were decomposed with different tendencies, and the consumption of PMS was accelerated by the presence of an electron donating compound. The results show the potential applicability of the freezing phenomenon, which occurs naturally in the mid-latitude and polar area, to help a decomposition of water dissolved organic pollutants by the imitation of the natural purification process.

Impact of solar radiation on chemical structure and micromechanical properties of cellulose-based humidity-sensing material Cottonid

Renewable and environmentally responsive materials are an energy- and resource-efficient approach in terms of civil engineering applications, e.g. as so-called smart building skins. To evaluate the influence of different environmental stimuli, like humidity or solar radiation, on the long-term actuation behavior and mechanical robustness of these materials, it is necessary to precisely characterize the magnitude and range of stimuli that trigger reactions and the resulting kinetics of a material, respectively, with suitable testing equipment and techniques. The overall aim is to correlate actuation potential and mechanical properties with process- or application-oriented parameters in terms of demand-oriented stimuli-responsive element production. In this study, the impact of solar radiation as environmental trigger on the cellulose-based humidity-sensing material Cottonid, which is a promising candidate for adaptive and autonomously moving elements, was investigated. For simulating solar radiation in the lab, specimens were exposed to short-wavelength blue light as well as a standardized artificial solar irradiation (CIE Solar ID65) in long-term aging experiments. Photodegradation behavior was analyzed by Fourier-transform infrared as well as electron paramagnetic resonance spectroscopy measurements to assess changes in Cottonid’s chemical composition. Subsequently, changes in micromechanical properties on the respective specimens’ surface were investigated with roughness measurements and ultra-micro-hardness tests to characterize variations in stiffness distribution in comparison to the initial condition. Also, thermal effects during long-term aging were considered and contrasted to pure radiative effects. In addition, to investigate the influence of process-related parameters on Cottonid’s humidity-driven deformation behavior, actuation tests were performed in an alternating climate chamber using a customized specimen holder, instrumented with digital image correlation (DIC). DIC was used for precise actuation strain measurements to comparatively evaluate different influences on the material’s sorption behavior. The infrared absorbance spectra of different aging states of irradiated Cottonid indicate oxidative stress on the surface compared to unaged samples. These findings differ under pure thermal loads. EPR spectra could corroborate these findings as radicals were detected, which were attributed to oxidation processes. Instrumented actuation experiments revealed the influence of processing-related parameters on the sorption behavior of the tested and structurally optimized Cottonid variant. Experimental data supports the definition of an optimal process window for stimuli-responsive element production. Based on these results, tailor-made functional materials shall be generated in the future where stimuli-responsiveness can be adjusted through the manufacturing process.