Pollution with microplastic particles is a major environmental challenge of our time. However, little is known about the ecological hazards degraded polymer particles pose. To answer this, a qualification and quantification of the functional groups created by photooxidation of the polymer is necessary. A versatile tool to study this is the bulk method NMR spectroscopy. However, the low sensitivity of this technique makes it difficult to identify and correctly quantify defects in small concentrations. The sensitivity of NMR spectroscopy can be improved via dynamic nuclear polarisation which uses persistent radicals added to the sample. In this work, we investigate four methods to apply these radicals to weathered microplastic samples and discuss the benefits and drawbacks of each method. Our findings show that dissolving the microplastic particles in a solution of AsymPol in trichloroethylene and evaporating the solvent, to create a film yields the best sample for DNP enhanced NMR spectroscopy, as no disturbing solvent peaks remain in the spectrum and the measurement time can by decreased by a factor 35 compared to conventional solid state NMR spectroscopy. With this enhanced sensitivity we were able to measure and identify all defects of a microplastic sample weathered for 3200 h in less than a minute. Furthermore, for the first time, defects are observed in a microplastic sample weathered for only 400 h. This application of DNP enhanced NMR spectroscopy will allow for rapid screening of weathered microplastic particles enabling defect quantification at low concentrations.

This work explores the combination of Microwave Cavity Perturbation (MCP) with the concept of Iso-Potential Operando Spectroscopy (IPOS) to develop IPO-MCP for measuring conductivity changes in a catalyst within a catalytic fixed-bed reactor (FBR). As proof-of-concept, spatially resolved dielectric properties, species, and temperature profiles were recorded during the reverse water-gas shift (rWGS) reaction on a commercial copper-zinc-alumina (CZA) catalyst. These results reveal a linear electronic structure-activity relationship along the catalyst packing demonstrating that hydrogen significantly enhances the Q-value compared to carbon dioxide in line with previous investigations. This research motivates further application of IPO-MCP to other catalytic systems with distinct conductivity changes.

HMGB1, a nuclear DNA-binding protein, can be secreted by activated immune cells or passively released from damaged cells. In such cases, HMGB1 functions as an alarmin that activates the immune system. Excessive inflammation may lead to pathogenesis, whereas this response can be dampened by polyanion binding, which impedes further receptor recognition. Moreover, HMGB1 is known to form liquid droplets in the cellular environment─a phase separation directly linked to its proper function. While the A-Box domain is believed to be primarily responsible for heparin binding due to its conserved binding site, the association and phase separation behavior of HMGB1 may be mediated by the B-box domain, owing to its extended hydrophobic regions. In this study, we first demonstrated that the B-box protein forms 30 nm large self-associates while maintaining its structure. Next, using molecularly sensitive EPR spectroscopy, we showed that the presence of these protein associates significantly enhances interactions with heparin. Notably, the local conformational changes induced by heparin are similar in both individual protein chains and their self-associated forms. To explain this effect, AlphaFold modeling was employed, revealing that the formation of protein multimers induces charge redistribution, resulting in an extended positively charged region that enhances electrostatic attraction to negatively charged polyanions such as heparin.

Temperature-dependent in situ continuous wave (cw) electron spin resonance (ESR) measurements are used for investigating changes in magnetization upon reduction and reoxidation in La-deficient La x Fe0.7Mn0.3O3 (x < 1) samples to advance the understanding of structural and chemical changes in these materials where A-site deficiency was shown to affect catalytic performance. For these defect-rich mixed perovskites with ferromagnetic ordering, the magnetic properties as characterized by in situ cw ESR spectroscopy are sensitive probes for structural changes in these materials. To this end, the ESR spectra observed in a redox cycle in H2- and O2-containing atmospheres not only show structural changes that were not observed by XRD but also provide evidence for heterogeneity in the magnetic phases, which notably depends on the La deficiency of the samples. This not only demonstrates the potential of such investigations for obtaining information complementary to other methods but also emphasizes the sensitivity of magnetic properties as probed by ESR to elucidate structural and chemical changes in such complex perovskite materials. While the XRD results lack indication for the presence of structural heterogeneity, STEM measurements provide evidence for a compositional heterogeneity between the grains but not for the presence of an additional magnetic phase, as observed by ESR for one of the samples. Importantly, the different magnetic phases exhibit distinct responses to reducing and (re)oxidizing atmospheres indicating for the sample with a lower La deficiency a facilitated reaction under reducing conditions at low temperatures but an overall higher structural stability. Both effects are expected to affect the reactivity in the redox reactions. Thus, these results provide new and complementary insights that can enhance the understanding of the effect of A-site deficiency in perovskite materials in redox reactions considered to be important for the catalytic activity of these systems.

In this study, Al-doped ZnO (AZO) is investigated by combining in situ and operando continuous wave (cw) electron spin resonance (ESR) measurements with other methods, including microwave cavity perturbation technique (MCPT), magnetization, TGA, 27Al-NMR, transmission electron microscopy, and XRD measurements. As Al-doped ZnO (AZO) is the support of Cu/ZnO:Al (CZA), an industrially used catalyst for methanol synthesis, studying the evolution of defects and changes in electronic structure under conditions used for reductive activation of the CZA catalyst or typical conditions for the r-WGS reaction is of interest to gain further insight into the complex interplay between the different components in the CZA catalyst. Next to paramagnetic defect sites, a ferromagnetic phase was observed forming upon activation in reducing atmospheres, which is modified, but not destroyed in (re)oxidizing conditions. The results prove the oxidizing effect of CO2 on the paramagnetic defects as well as the ferromagnetic phase of an activated AZO. Comparison with prior results on CZA provides insight into the effect of Cu on AZO and enhances the understanding of the synergistic effects in the catalyst.

HMGB1, a nuclear DNA-binding protein, can be secreted by activated immune cells or passively released from damaged cells. In such cases, HMGB1 functions as an alarmin that activates the immune system. Excessive inflammation may lead to pathogenesis, whereas this response can be dampened by polyanion binding, which impedes further receptor recognition. Moreover, HMGB1 is known to form liquid droplets in the cellular environment—a phase separation directly linked to its proper function. While the A-Box domain is believed to be primarily responsible for heparin binding due to its conserved binding site, the association and phase separation behavior of HMGB1 may be mediated by the B-box domain, owing to its extended hydrophobic regions. In this study, we first demonstrated that the B-box protein forms 30-nm large self-associates while maintaining its structure. Next, using molecularly sensitive EPR spectroscopy, we showed that the presence of these protein associations significantly enhances interactions with heparin. Notably, the local conformational changes induced by heparin are similar in both individual protein chains and their self-associated forms. To explain this effect, AlphaFold modeling was employed, revealing that the formation of protein multimers induces charge redistribution, resulting in an extended positively charged region that enhances electrostatic attraction to negatively charged polyanions, such as heparin. ### Competing Interest Statement The authors have declared no competing interest.

The industrially important Cu/ZnO:Al (CZA) catalyst is known as a dynamic system adapting to reaction conditions, which renders the application of in situ and operando methods key to establish structure function correlations. Herein, a CZA catalyst close to the industrially used compostion was studied using noninvasive and bulk-sensitive in situ/operando microwave cavity perturbation technique and electron paramagnetic resonance spectroscopy during activation and reverse water gas shift reaction. The transient changes of catalytic activity track with the transients of the dielectric properties providing evidence for the importance of bulk properties for catalytic activity. Furthermore, convincing support for the redox reaction mechanism is obtained, and it is shown that H2 and CO2 uptake is not competing kinetically with each other. In addition, the reservoir of H2 and CO2 transiently present in the catalyst during catalysis is determined by the chemical potential of the respective reactant, which is directly coupled to the catalytic activity of the system. The findings fit the model of a Schottky barrier at the Cu/ZnO:Al interface, altered by the gas phase composition which in turn alters the catalytic properties of the system.

The thermal unfolding of lysozyme in aqueous solution has been analyzed by (nano) differential scanning fluorimetry (nanoDSF) and differential scanning calorimetry (DSC). In addition, dynamic light scattering (DLS) acquired in parallel to the DSF measurements, was used to confirm that the change in hydrodynamic radius upon unfolding is rather small (RH,f =1.75 nm in the folded state; and RH,u=1.91 nm in the unfolded state). NanoDSF measurements were evaluated to characterize the folding/unfolding transition within the classical two-state folding model. The temperature of unfolding (Tm) is found to be the most robust quantity. The unfolding enthalpy Δ H u ${{\rm \Delta }{H}_{u}}$ and the change of specific heat were also obtained and errors in the range of 5-10 % and 30-50 % were determined, respectively. A comparison of thermodynamic parameters from nanoDSF and DSC measurements provides evidence for an increasing unfolding enthalpy Δ H u ${{\rm \Delta }{H}_{u}}$ with protein concentration. A comparison with data from literature suggests that a weak association in the folded state can lead to the observed change of the unfolding enthalpy. For Δcp significantly higher values is deduced from the analysis of temperature dependent nanoDSF measurements (10 kJ/(K mol)) as compare to DSC (3-5 kJ/(K mol)).

Despite the common expectation that conjugated organic molecules on metals adsorb in a flat-lying layer, several recent studies have found coverage-dependent transitions to upright-standing phases, which exhibit notably different physical properties. In this work, we argue that from an energetic perspective, thermodynamically stable upright-standing phases may be more common than hitherto thought. However, for kinetic reasons, this phase may often not be observed experimentally. Using first-principles kinetic Monte Carlo simulations, we find that the structure with lower molecular density is (almost) always formed first, reminiscent of Ostwald's rule of stages. The phase transitions to the upright-standing phase are likely to be kinetically hindered under the conditions typically used in surface science. The simulation results are experimentally confirmed for the adsorption of tetracyanoethylene on Cu(111) using infrared and X-ray photoemission spectroscopy. Investigating both the role of the growth conditions and the energetics of the interface, we find that the time for the phase transition is determined mostly by the deposition rate and, thus, is mostly independent of the nature of the molecule.

Partial methanol oxidation proceeds with high selectivity to methyl formate (MeFo) on nanoporous gold (npAu) catalysts. As low-coordinated sites on npAu were suggested to affect the selectivity, we experimentally investigated their role in the isothermal selectivity for flat Au(111) and stepped Au(332) model surfaces using a molecular beam approach under well-defined conditions. Direct comparison shows that steps enhance desired MeFo formation and lower undesired overoxidation. DFT calculations reveal differences in oxygen distribution that enhance the barriers to overoxidation at steps. Thus, these results provide an atomic-level understanding of factors controlling the complex reaction network on gold catalysts, such as npAu.

Graphene-supported Co clusters were investigated by high-resolution XPS, TPD and IRRAS using CO as a probe molecule. CO adsorption was observed at edge, on-top and bridge/hollow sites on the as-prepared clusters. Temperature-programmed XPS showed CO dissociation at T > 300 K. The CO desorption temperatures were determined by TPD measurements to be 260, 320 and 400 K for CObridge/hollow, COedge and COtop, respectively. The CO dissociation products were used to investigate the adsorption of CO on carbon and oxygen precovered Co clusters. Site blocking by these adatoms was found resulting in the absence of COedge (XPS and TPD) and a decrease of the CO adsorption capacity (XPS, TPD and IRRAS). Additionally, no CO dissociation was found on the precovered clusters concluding a blocking of the catalytically active sites which are the edge sites of the clusters.

To elucidate the role of low-coordinated sites in the partial methanol oxidation to methyl formate (MeFo), the isothermal reactivity of flat Au(111) and stepped Au(332) in pulsed molecular beam experiments was compared for a broad range of reaction conditions. Low-coordinated step sites were found to enhance MeFo selectivity, especially at low coverage conditions, as found at higher temperatures. The analysis of the transient kinetics provides evidence for the essential role of Au x O y phases for MeFo formation and the complex interplay of different oxygen species for the observed selectivity. Ab initio molecular dynamic simulations yielded microscopic insights in the formation of Au x O y phases on flat and stepped gold surfaces emphasizing the role of low-coordinated sites in their formation. Moreover, associated surface restructuring provides atomic-scale insights which align with the experimentally observed transient kinetics in MeFo formation.

Nanoporous gold (npAu) was tested as a catalyst for oxidations of various benzylic sp(3)-carbon positions in 9H-fluorene derivatives and similar hydrocarbons using tertbutyl hydroperoxide (TBHP) as an oxidant. The silver content in the npAu catalyst had a major influence on the overall conversion: Lower silver amounts (0.53 mol%) led to higher conversions, whereas higher amounts of silver increasingly resulted in the disproportionation of TBHP as a competing reaction. Because residual silver from the bulk alloy was oxidized by TBHP and leached into the solution during the reaction, the Ag content diminished over time. Therefore, the recycling of the catalyst had a positive effect on the conversion after each use. Using electron paramagnetic resonance (EPR) spectroscopy, the formation of radicals from TBHP by npAu was evidenced indicating a radical-based reaction mechanism which was further elucidated by NMR spectroscopic and GC-MS (trace) product analysis. Subsequent oxidations of benzylic sp(3)-carbon positions gave good to excellent conversions and chemoselectivities featuring npAu as a suitable catalyst for such reactions.

Nanoporous gold (NPG) is characterized by a bicontinuous network of nanometer-sized metallic struts and interconnected pores formed spontaneously by oxidative dissolution of the less noble element from gold alloys. The resulting material exhibits decent catalytic activity for low-temperature, aerobic total as well as partial oxidation reactions, the oxidative coupling of methanol to methyl formate being the prototypical example. This review not only provides a critical discussion of ways to tune the morphology and composition of this material and its implication for catalysis and electrocatalysis, but will also exemplarily review the current mechanistic understanding of the partial oxidation of methanol using information from quantum chemical studies, model studies on single-crystal surfaces, gas phase catalysis, aerobic liquid phase oxidation, and electrocatalysis. In this respect, a particular focus will be on mechanistic aspects not well understood, yet. Apart from the mechanistic aspects of catalysis, best practice examples with respect to material preparation and characterization will be discussed. These can improve the reproducibility of the materials property such as the catalytic activity and selectivity as well as the scope of reactions being identified as the main challenges for a broader application of NPG in target-oriented organic synthesis.

The adsorption of organic electron acceptors on metal surfaces is a powerful way to change the effective work function of the substrate through the formation of charge-transfer-induced dipoles. The work function of the interfaces is hence controlled by the redistribution of charges upon adsorption of the organic layer, which depends not only on the electron affinity of the organic material but also on the adsorption geometry. As shown in this work, the latter dependence controls the work function also in the case of adsorbate layers exhibiting a mixture of various adsorption geometries. Based on a combined experimental (core-level and infrared spectroscopy) and theoretical (density functional theory) study for tetracyanoethylene (TCNE) on Cu(111), we find that TCNE adsorbs in at least three different orientations, depending on TCNE coverage. At low coverage, flat lying TCNE dominates, as it possesses the highest adsorption energy. At a higher coverage, additionally, two different standing orientations are found. This is accompanied by a large increase in the work function of almost 3 eV at full monolayer coverage. Our results suggest that the large increase in work function is mainly due to the surface dipole of the free CN groups of the standing molecules and less dependent on the charge-transfer dipole of the differently oriented and charged molecules. This, in turn, opens new opportunities to control the work function of interfaces, e.g., by synthetic modification of the adsorbates, which may allow one to alter the adsorption geometries of the molecules as well as their contributions to the interface dipoles and, hence, the work function.

Particle attachment and neck formation inside TiO2 nanoparticle networks determine materials performance in sensing, photo-electrochemistry, and catalysis. Nanoparticle necks can feature point defects with potential impact on the separation and recombination of photogenerated charges. Here, we investigated with electron paramagnetic resonance a point defect that traps electrons and predominantly forms in aggregated TiO2 nanoparticle systems. The associated paramagnetic center resonates in the g factor range between g = 2.0018 and 2.0028. Structure characterization and electron paramagnetic resonance data suggest that during materials processing, the paramagnetic electron center accumulates in the region of nanoparticle necks, where O2 adsorption and condensation can occur at cryogenic temperatures. Complementary density functional theory calculations reveal that residual carbon atoms, which potentially originate from synthesis, can substitute oxygen ions in the anionic sublattice, where they trap one or two electrons that mainly localize at the carbon. Their emergence upon particle neck formation is explained by the synthesis- and/or processing-induced particle attachment and aggregation facilitating carbon atom incorporation into the lattice. This study represents a substantial advance in linking dopants, point defects, and their spectroscopic fingerprints to microstructural features of oxide nanomaterials.

Paramagnetic defects of thin CaO(001) films grown on Mo(001) are characterized using electron paramagnetic resonance (EPR) spectroscopy under ultrahigh vacuum conditions. A variety of paramagnetic centers located in the volume of the films are identified whose speciation as well as relative abundance was found to depend on the growth rate of the films. Pristine films prepared at a lower growth rate exhibited a larger number and a different speciation of paramagnetic defects than films grown at a higher rate. Annealing of the films to 1030 K, which improves their long-range order, results in quenching of most of the paramagnetic species observed for the pristine film; however, films prepared at a lower growth rate exhibit new paramagnetic signals upon annealing, which are absent in films prepared at a higher growth rate. The signals can be assigned to paramagnetic Mo ions previously shown to diffuse into these films. These results indicate that the amount and speciation of the transition metal ions depend on the preparation conditions which in turn can also affect the surface chemistry of these systems.

Since the first studies reporting on its surprising catalytic properties, nanoporous gold (npAu) has emerged as a novel and ever since intensively investigated type of Au based catalyst. To judge its genuine catalytic potential and to be able to optimize its use in applications, it is mandatory, however, to quantify the influence of mass transport in the porous structure on the observed catalytic rates, i.e., to study the interplay between diffusion and reaction. To this end, we used pulsed field gradient (PFG) NMR for the first time to directly determine the diffusivities of reaction gases in a nanoporous metal - in this case for CO and CO2 as species involved in low temperature CO oxidation efficiently catalyzed by npAu. By comparing the diffusion coefficients within the 20 nm pores of the material with the values in the bulk gas phase, the tortuosity of npAu's pore system was assessable as the central geometrical parameter describing the extent to which diffusive transport in the pore system is slowed down. This knowledge allowed us in the following to disentangle the contributions of mass transport and the kinetics of the sur-face reaction (microkinetics). In particular, we were able to determine the rate constant and turnover fre-quency for low-temperature CO oxidation without previous ambiguities arising from potential transport limitations and to compare the results with other reported values. Based on the results, it was further-more possible to predict optimized dimensions of the catalyst, resulting in minimized or even suppressed diffusion limitations. These predictions could be successfully verified, using np-Au platelets with lateral dimensions in the range of a few hundred microns. In this way, the catalytic conversion could be ramped up by 50 % and an activity level advanced which reflected the microkinetic potential of np-Au.(c) 2022 Published by Elsevier Inc.

In this study, first-row transition metal-doped calcium oxide materials (Mn, Ni, Cr, Co., and Zn) were synthesized, characterized, and tested for the OCM reaction. Doped carbonate precursors were prepared by a co-precipitation method. The synthesis parameters were optimized to yield materials with a pure calcite phase, which was verified by XRD. EPR measurements on the doped CaO materials indicate a successful substitution of Ca2+ with transition metal ions in the CaO lattice. The materials were tested for their performance in the OCM reaction, where a beneficial effect towards selectivity and activity effect could be observed for Mn, Ni, and Zn-doped samples, where the selectivity of Co- and Cr-doped CaO was strongly reduced. The optimum doping concentration could be identified in the range of 0.04-0.10 atom%, showing the strongest decrease in the apparent activation energy, as well as the maximum increase in selectivity.