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At least 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Up-regulating TIPE2 alleviates inflammatory pain by suppressing microglial activation-mediated inflammatory response via inhibiting Rac1/NF-κB pathway

TNF-α-inducible protein 8-like 2 (TIPE2) is a recently discovered regulator of inflammation that can maintain immune homeostasis, exerting a significant role in the development of inflammation-related diseases. Here, we aimed to explore the role and potential regulatory mechanism of TIPE2 in the progression of inflammatory pain. In the present study, a mouse BV2 microglia cell activation-mediated inflammatory model was developed with LPS induction, and a mouse inflammatory pain model was established with complete Freund's adjuvant (CFA) injection. In vitro, the TIPE2 expression was decreased in LPS-induced BV2 cells. Overexpression of TIPE2 mitigated LPS-medicated microglial activation via decreasing nitric oxide (NO) generation and the expression of microglia marker IBA-1. Notably, increasing TIPE2 expression alleviated microglial activation-triggered expression levels and releases of proinflammatory factors such as TNF-α, IL-1β, and IL-6. Mechanism analysis verified that overexpression of TIPE2 blunted Rac1-mediated activation of NF-κB pathway following LPS stimulation. More importantly, CFA injection reduced the expression of TIPE2 in a mouse inflammatory pain model and overexpression of TIPE2 alleviated CFA-mediated pain hypersensitivity and inflammatory response, and inactivated microglia cell in vivo. Furthermore, overexpression of TIPE2 decreased Rac1 expression and suppressed the activation of NF-κB pathway in spinal cord after CFA injection. In summary, the present study revealed that overexpression of TIPE2 mitigated inflammatory pain through suppressing microglial activation-induced inflammation by inactivating Rac1/NF-κB pathway. The study provides a novel theoretical foundation for the therapy of inflammatory pain.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Interleukin-35 inhibits lipopolysaccharide-induced endothelial cell activation by downregulating inflammation and apoptosis

Inflammation is an essential factor contributing to sepsis-induced endothelial cell (EC) activation. Interleukin-35 (IL-35) is an anti-inflammatory/immunosuppressive cytokine that exerts protective effects on many inflammatory diseases. In this study, we investigated the effects of IL-35 on lipopolysaccharide (LPS)-induced EC activation and the potential underlying mechanism. Human umbilical vein endothelial cells (HUVECs) were incubated with LPS (1 μg/ml) for 24 h and then cocultured with different concentrations (0, 1, 10, or 100 ng/ml) of recombinant human IL-35 (rhIL-35) for 12 h. Flow cytometry analysis revealed that IL-35 inhibited LPS-induced HUVEC apoptosis in a dose-dependent manner. RT-qPCR and Western blot analyses showed significantly higher mRNA and protein levels of the adhesion molecules intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) and the inflammatory factors IL-6 and IL-8 in the LPS group than in the control group. These changes were alleviated by IL-35 treatment, suggesting that IL-35 protects ECs by downregulating inflammation. Furthermore, IL-35 induced signal transducer and activator of transcription 1 (STAT1) and STAT4 activation and promoted their interaction. Blocking STAT1 or STAT4 expression by fludarabine (STAT1 inhibitor) treatment or siRNA-STAT4-interfering fragment transfection inhibited the protective effect of IL-35 on ECs. Moreover, we observed a similar protective effect of IL-35 treatment on ECs in a mouse sepsis model induced by intraperitoneal LPS injection. This study indicated that IL-35 exerts anti-inflammatory and antiapoptotic effects on LPS-induced EC activation by activating the STAT1 and STAT4 signaling pathways.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Atomic-Scale Structural Mapping of Active Sites in Monolayer PGM-Free Catalysts by Low-Voltage 4D-STEM

Two-dimensional (2D) materials have attracted a large amount of attention in both basic and applied fields, and scanning transmission electron microscopy (STEM) is often uniquely well-suited for characterizing the atomic-scale structure of these materials [1-4]. As a result, STEM is poised to significantly impact progress on platinum group metal (PGM)-free catalysts, which are currently under intense development to enable low-cost, commercially viable hydrogen fuel cells [5]. While recent advancements have resulted in fuel cell performance comparable to Pt catalysts by some measures [6], cell durability remains a significant challenge, limiting practical applications [7]. Catalytically active sites in PGM-free materials are proposed to be FeN4 complexes embedded in a graphene lattice (Fig. 1b) within layered or other larger materials, but this is still under debate largely due to the range of potential actives sites predicted by computational methods and lack of methods for directly validating these models [5]. Fundamental insights into the atomic structure and resulting degradation pathways of proposed active sites are therefore needed to fully understand and control cell performance and durability [6].2D materials typically make ideal samples for STEM, but those within PGM-free catalysts present additional challenges since these materials are often defect-rich, with a high density of edges, dopant atoms, etc., which significantly increase susceptibility to beam damage at standard operating voltages. This makes analysis of potential FeN4 active sites particularly challenging, since a large proportion of Fe exists at edge sites where beam-induced atomic displacements can prohibit high-resolution structural characterization [6]. Conventional dark-field imaging compounds this problem by producing less signal for a given dose and being less sensitive to light elements than dose-efficient phase contrast imaging techniques such as those enabled by four-dimensional (4D)-STEM [8-10] (Fig. 1a). Consequently, active site structural analysis is often left to methods such as low-resolution imaging combined with quantum chemical calculations [6], which hinders accurate determination of reaction and degradation mechanisms.Here, we demonstrate direct atomic-scale structural mapping of FeN4 sites by performing low-voltage 4D-STEM on a model PGM-free catalyst system with many exposed monolayer regions. To accomplish this, we pair a 30 keV aberration-corrected probe with a fast pixelated detector that has optimal performance at low beam voltages [11]. This enables us to simultaneously image light and heavy elements with high signal-to-noise by center-of-mass analysis (Fig. 1c) while minimizing beam-induced atomic displacements at sensitive sites. The monolayer nature of these materials additionally allows for experimental validation by direct comparison with multislice simulations [12] of model structures (Fig. 1d-e). This work demonstrates how low-voltage 4D-STEM will provide new insights into the atomic-scale structure and degradation mechanisms of active sites in PGM-free catalysts, facilitating the development of low-cost hydrogen fuel cells and other energy conversion technologies in the future [13].

Zachman, Michael↗
DOE OSTI2024

Activity-Based Protein Profiling to Probe Relationships between Cytochrome P450 Enzymes and Early-Age Metabolism of Two Polycyclic Aromatic Hydrocarbons (PAHs): Phenanthrene and Retene

A growing body of literature has linked early life exposures to polycyclic aromatic hydrocarbons (PAH) with adverse neurodevelopmental effects. Once in the body, metabolism serves as a powerful mediator of PAH toxicity by bioactivating and detoxifying PAH metabolites. Since enzyme expression and activity varies considerably throughout human development, we evaluated infant metabolism of PAHs as a potential contributing factor to PAH susceptibility. Here, we measured and compared rates of phenanthrene and retene (two primary PAH constituents of woodsmoke) metabolism in human hepatic microsomes from individuals ≤21 months of age to a pooled sample (n = 200) consisting primarily of adults. We used activity-based protein profiling (ABPP) to characterize cytochrome P450 enzymes (CYPs) in the same hepatic microsome samples. Once incubated in microsomes, phenanthrene demonstrated rapid depletion. Best fit models for phenanthrene metabolism demonstrated either 1 or 2 phases, depending on the sample, indicating that multiple enzymes could metabolize phenanthrene. We observed no statistically significant differences in phenanthrene metabolism as a function of age, although samples from the youngest individuals had the slowest phenanthrene metabolism rates. We observed slower rates of retene metabolism compared to phenanthrene also in multiple phases. Rates of retene metabolism increased in an age-dependent manner until adult (pooled) levels were achieved at ~12 mo. ABPP identified 28 unique CYPs among all samples, and we observed lower amounts of active CYPs in individuals ≤21 months of age compared to the pooled sample. Phenanthrene metabolism correlated to CYPs 1A1, 1A2, 2C8, 4A22, 3A4, and 3A43 and activities and retene metabolism correlated to CYPs 1A1, 1A2, and 2C8 activities measured by ABPP and vendor-supplied substrate marker activities. These results will aid efforts to determine human health risk and susceptibility to PAHs exposures during early life.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Synthesis, Characterization, and Biological Activity of Hybrid Thiosemicarbazone–Alkylthiocarbamate Metal Complexes

A series of hybrid ligands (H 2 L 1 –H 2 L 3 ) derived from 4-methyl-3-thiosemicarbazide and hydrazinecarbothioic acid O-alkyl esters were synthesized and characterized by NMR. The ligands were chelated with copper (4–6), nickel (7–9), and zinc (10–12) and characterized by spectroscopy, electrochemistry, and single crystal X-ray crystallography. The chelated metals displayed substantial anodic shifts in the Cu II/I reduction potential of ~160 mV relative to their bis(thiosemicarbazone) analogues. The metal chelates 4–12 were evaluated for potential anticancer activity by MTT assays, and selected results were confirmed by clonogenic and trypan blue assays. The copper derivatives 4 and 6 were found to have potent and cancer-selective antiproliferative effects, with GI 50 values less than 100 nM in A549 lung adenocarcinoma cells compared with at least 20-fold less activity in IMR90 nonmalignant lung fibroblasts. In comparison, the nickel complexes were much less active and had little cancer-selectivity. Varying by ligand, the zinc complexes were less potent or had comparable activity compared to that of the corresponding copper complex. UV–visible spectroscopy indicated that zinc complex 10 was transmetalated in the presence of equimolar copper, whereas nickel complex 7 was not. Copper complexes 4 and 6 were also assessed in the NCI60 screen and were found to have cytotoxic activity against most solid tumor cell lines. In MTT assays, 4 and 6 were substantially more active against A549 cancer cells than Cu(ATSM) and were more cancer-selective (for A549 compared to IMR-90) than Cu(GTSM). Finally, our results suggest that hybrid thiosemicarbazone–alkylthiocarbamate copper complexes have potential for development as new anticancer agents.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Methane Activation on Metal-Doped (111) and (100) Ceria Surfaces with Charge-Compensating Oxygen Vacancies

Reducing the temperature for methane activation is an important objective that would benefit many technological applications. In this work we explore the possibility to achieve this goal using single atom catalysts (SACs) on ceria surfaces. In particular, we focus on Ag SACs, which have recently been suggested to be promising catalysts for both the oxidation of molecular hydrogen and CH 4 activation. The rate limiting step of methane activation on ceria is the breaking of the first C-H bond. Using first principles calculations, we investigate this reaction on CeO 2 (111) and (100) surfaces, which are both frequently exposed on ceria nanoparticles. For undoped ceria, our results show that the dissociation of CH 4 to CH 3 + H has a lower barrier on the (001) surface than on the (111) one. On both surfaces, the presence of Ag enhances the binding of CH 4 to the surface and reduces the activation energy for its dissociation. Interestingly, the formation of methanol via the Mars-van Krevelen mechanism has a slightly lower energy barrier than the dissociation of CH 4 to CH 3 + H on Ag-doped CeO 2 (111), suggesting that methanol is a likely product of methane activation on this surface. Here, a novel aspect of our work relative to previous studies on CH 4 activation over transition metal doped ceria is that we mainly focus on stable surface structures where each Ag dopant substituting a Ce atom forms a complex with a surface oxygen vacancy (VO). Our results show that these Ag-VO complexes play a critical role and accounting for their presence is essential for a proper description of the surface reactivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Identification of Active Sites of Pure and Nitrogen-Doped Carbon Materials for Oxygen Reduction Reaction Using Constant-Potential Calculations

Nitrogen-doped carbon materials are promising metal-free catalysts for the electrochemical oxygen reduction reaction (ORR). A better theoretical understanding on the nature of the active site(s) would help further optimization of their ORR activity. Although quantum mechanical calculations have been widely employed to elucidate the active sites over various catalysts, these calculations are typically done assuming constantcharge conditions rather than the experimentally relevant constant-potential conditions. In this study, we employ the double-reference method to simulate the energetics of the ORR over pure and N-doped carbon materials under constant-potential conditions. We demonstrate that constant-potential calculations enable more accurate theoretical predictions, comparing well with existing experiments. Our key findings are (1) the zigzag edge of pure graphite is highly active for ORR, (2) the pyridinic N-doped armchair edge is highly active for ORR in alkaline media but not in acid, and (3) graphitic N can donate electrons to pyridinic N to enhance the ORR activity. Furthermore, these fundamental insights provide guidelines for the design of better carbonbased ORR catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Unraveling Fundamental Activity–Stability Relationships in Rutile Oxides

The oxygen evolution reaction (OER) is a key anodic half-cell reaction that accompanies several critical electrochemical reduction reactions of interest to a variety of applications. Despite steady advances in understanding and qualitatively predicting OER activity and selectivity trends, a comprehensive description or prediction of material aqueous (in)stability and degradation mechanisms remains elusive, even though these processes critically influence device lifetime and economic feasibility. In this work, we investigate the interplay, or lack thereof, between OER activity and material aqueous stability across rutile oxides, with a particular focus on iridium oxide (IrO 2 ). By applying a Born–Haber cycle, we calculate the thermodynamic driving force for metal dissolution as a function of the applied bias and electrolyte conditions. We apply interpretable machine learning techniques, including principal component analysis and symbolic regression, to analyze trends across rutile oxides and find that key thermodynamic descriptors for OER activity and surface stability are only very weakly correlated. Instead, the local atomic environment─especially electronic structure signatures for interactions between the active site and its neighbors─plays a more important role in predicting material stability. Leveraging these insights, we investigate the impact of doping IrO 2 with a range of transition metals and show that the stability of Ir active sites can be tuned largely independently of its predicted OER activity. These insights lay the foundation for material design to improve stability with respect to corrosion, with the ultimate aim to enhance long-term stability without sacrificing catalytic performance in the OER.

evolution reactions↗
DOE OSTI2025

Temperature Evolution of the Activation Barriers Leads to Meyer−Neldel Rules for Structural Relaxation and Transport in Polymers

Understanding activation barriers controlling structural relaxation in glass-forming liquids, molecular transport, and ionic conductivity in amorphous polymers is a grand challenge of fundamental scientific and materials engineering interest across disciplines. Over decades, intriguing but puzzling empirical correlations between the elementary time scale of activated barrier crossing and the apparent Arrhenius activation energy, the so-called Meyer−Neldel (MN) rules, have been discovered in diverse liquids and glasses. Here, in this study, we formulate and successfully apply a new experimental analysis and an explicitly dynamical theoretical framework which provides an understanding of the origin, validity, and failure of such correlations, that bridge and unify the three fields of structural relaxation, molecular transport, and ionic conductivity in liquids and quenched glasses. Distinct quasi-universal laws are predicted in equilibrated liquids and nonequilibrium glasses, consistent with experiments. Our analysis reveals that even if the relaxation appears Arrhenius over a limited temperature range, the physical activation barrier is generally temperature-dependent in polymeric systems even below glass transition temperature. In addition, we show that the approximate validity of classical MN rules hinges on a linear temperature dependence of this barrier and the temperature range probed in experiments. Our findings are relevant for controlling the activation barrier in functional soft polymeric materials relevant to molecular separations, barrier coatings, and charge transport, and also provide new constraints on the theoretical understanding of the mechanism underlying slow activated dynamics in glass-forming condensed matter.

Meyer-Neldel rules↗
DOE OSTI2020

Cationic α-Diimine Nickel and Palladium Complexes Incorporating Phenanthrene Substituents: Highly Active Ethylene Polymerization Catalysts and Mechanistic Studies of syn/anti Isomerization

α-Diimine palladium complexes incorporating phenanthryl- and 6,7-dimethylphenanthrylimino groups have been synthesized and characterized. The (diimine)PdMeCl complexes prepared from 2,3-butanedione and acenaphthenequinone bearing the unsubstituted phenanthrylimino groups, 12a and 14a, respectively, exist as a mixture syn and anti isomers in a ca. 1:1 ratio. Separation and X-ray diffraction analysis of 14a-syn and 14a-anti isomers confirms the syn/anti assignments. The barrier to interconversion of 14a-syn and 14a-anti via ligand rotation, ΔG ‡ , was found to be 25.5 kcal/mol. The corresponding (diimine)PdMeCl complex prepared from acenaphthenequinone and incorporating the 6,7-dimethylphenanthrylimino group exists solely as the anti isomer, 14b, due to steric crowding which destabilizes the syn isomer. Analogous (diimine)NiBr2 complexes were prepared from 2,3-butanedione incorporating the phenanthrylimino group, 16a, and the 6,7-dimethylphenanthrylimino group, 16b. Nickel-catalyzed polymerizations of ethylene were carried out by activation of the dibromide complexes 16a and 16b using various aluminum alkyl activators. Complex 16a yields a bimodal distribution polymer, the low molecular weight fraction originating from the syn isomer and the high molecular weight fraction arising from the anti isomer. Polymerizations carried out by 16b yield only high molecular weight polymers with monomodal distributions due to the existence of a single isomer (anti) as the active catalyst. All polymers are linear or nearly so. All catalysts are highly active but catalysts derived from 16b are somewhat more active than 16a and exhibit turnover frequencies general over 10 6 and up to 5 × 10 6 per hour (40 °C, 27.2 atm ethylene, 15 min). Here, active palladium ethylene oligomerization catalysts were generated by conversion of the neutral methyl chloride complexes 14a and 14b to the cationic nitrile complexes 15a and 15b via halide abstraction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Activation of Low-Valent, Multiply M–M Bonded Group VI Dimers toward Catalytic Olefin Metathesis via Surface Organometallic Chemistry

Olefin metathesis is a broadly employed reaction with applications that range from fine chemicals to materials and petrochemicals. The design and investigation of olefin metathesis catalysts have been ongoing for over half a century, with advancements made in terms of activity, stability, and selectivity. Immobilization of organometallic complexes onto solid supports such as silica or alumina is a promising strategy for catalyst heterogenization, often resulting in increased activity and stability. Consequently, a broad range of early transition metal catalysts bearing alkyl, oxide/alkoxide, and amide ligands have been grafted onto silica and their reactivities investigated. In this paper, we report a series of silica-supported tungsten and molybdenum dimers (X 3 M≡MX 3, where M = W and Mo; X = neopentyl, tert-butoxide, and dimethyl amide) and their reactivities toward catalytic olefin metathesis. Dynamic nuclear polarization (DNP)-enhanced solid-state nuclear magnetic resonance (SSNMR), diffuse reflectance infrared Fourier transform (DRIFT), UV resonance Raman, and X-ray absorption (XAS) spectroscopies suggest that upon heterogenization the dimers bind to the surface in a monopodal fashion, with the M≡M triple bond remaining intact. These structural assignments were further corroborated by density functional theory (DFT) calculations. While the homogeneous dimer counterparts are inert, the supported low-valent alkyl W and Mo dimers become active for the disproportionative self-metathesis of propylene to ethylene and butenes and 4-nonene to 4-octene and 5-decene under mild conditions. The lack of activity observed for the free and supported tert-butoxide and dimethyl amide dimers likely suggests that the neopentyl groups are necessary for the formation of a putative alkylidene active species. The difference in reactivity between the free and supported dimers could be explained either by the lowering of the activation barrier of the complex through the electronic effects of the surface or by site isolation of catalytically relevant reactive intermediates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Dislocation-Activated Low Platinum-Loaded PtCu Nanoparticles Welded onto the Substrate for Practical Acidic Hydrogen Generation

Although transition metal (M) alloying with platinum (Pt) is a promising approach to reduce the Pt dosage required in the hydrogen evolution reaction (HER), the catalytic activity and durability of PtM alloy are often unsatisfactory for acidic HER, especially at high currents, due to a reduced number of highly active sites (Pt) at the atomic level and challenges in stabilizing them to prevent detachment and aggregation. Herein, we report a robust functional structure integrated electrode (D-PtCu/CF) with abundant edge dislocations and very low platinum content (0.1 mg cm -2 ) to achieve high activity and stability in acidic HER within a proton exchange membrane water electrolysis cell (PEMWE). D-PtCu/CF exhibits high Pt mass activity (10.28 A mg Pt -1 ) and excellent operational stability (negligible decay after 200 h). X-ray absorption spectroscopy and in situ electrochemical experiments reveal that the lattice distortion caused by edge dislocations in PtCu mainly affects Pt atoms by compressing strain, reducing their ability to adsorb H. At the same time, Cu atoms are subjected to tensile strain, enhancing the bonding between Cu and H. Therefore, edge dislocations not only improve the intrinsic catalytic activity of Pt atoms but also increase the number of active sites (Cu) available for hydrogen adsorption, which synergistically accelerates the kinetics of the HER reaction. Finally, the PEMWE employing the D-PtCu/CF catalytic electrode can operate stably for 100 h at an industrial-level current density of 500 mA cm -2 with 1.63 V.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2022

Effect of Support on Oxygen Reduction Reaction Activity of Supported Iron Porphyrins

In this work, we report the oxygen reduction reaction (ORR) activity in acid of an Fe porphyrin on different supports. While the activity is high (E 1/2 = 0.34 V vs RHE with n = 3.8) when the Fe porphyrin is adsorbed on XC72 (a graphitic carbon), this activity is much lower when the porphyrin is adsorbed on either MoS 2 (E 1/2 = -0.15 V vs RHE with n = 2.2) or g-C 3 N 4 (E 1/2 = -0.24 V vs RHE with n = 3.1). Electron paramagnetic resonance (EPR), X-ray absorption fine structure (XAFS), and magnetometry measurements show the electronic structure around the Fe center is the same for all three supports. Only the Fe porphyrin supported on XC72 exhibits a pH dependence in its ORR activity. This observation, coupled with the increased hydrophilicity of XC72 relative to the other supports, suggests that the support-electrolyte interaction controls the ORR activity. Modification of MoS 2 to increase its hydrophilicity results in a more active ORR catalyst.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Engineering Active Surface Oxygen Sites of Cubic Perovskite Cobalt Oxides toward Catalytic Oxidation Reactions

Unraveling the role of surface oxygen sites in transition metal oxides during catalytic reactions has always been the focus of environmental and energy chemistry research. For this work, active surface oxygen sites of cubic perovskite cobalt oxide were engineered to comprehend their crucial role and catalytic mechanism at the molecular level. By removing those inert Sr/La–O termination layers, active oxygen sites were exposed on the Co terminated surface of Sr 0.6 La 0.4 CoO 3–δ that furnished the dominant catalytic process of CO oxidation via the Mars–van Krevelen (MvK) mechanism. The fabrication of five-coordinate cobalt ions and the enhanced covalency of Co–O bonds not only optimize the surface electronic structure of Co 3d–O 2p, but also supply active surface oxygen sites, which effectively oxidizes CO to CO 2 with a significantly improved oxidation performance and stability as evidenced by soft/hard XAS, XPS, and O 2 -TPD. Furthermore, online isotopic 18 O 2 mass spectrometry, in situ DRIFTS, and theoretical simulation demonstrate that the activity of surface oxygen sites enhances the kinetics of the MvK reaction, while unsaturated coordination sites from five-coordinate cobalt ions primarily contribute to the activated oxygen molecules and the stable catalytic cycle. The results reported here provide a deep insight into the comprehension of the relationships among active oxygen sites, surface electronic structure, and the reaction mechanism of transition metal oxides necessary for catalytic oxidation reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Using Domain Insertion to Create Sulfite Reductases That Present Chemical-Dependent Activities

Domain insertion can be used to create oxidoreductases whose activities are dependent upon analyte binding. To date, most domain insertion studies have targeted relatively small oxidoreductases of known structure, so it remains unclear how to apply this protein engineering approach to large hetero-oligomeric proteins that require dynamic conformational changes for catalysis. To address this question, we studied the effects of peptide and domain insertions on the activity of NADPH-dependent sulfite reductase (SiR) from Escherichia coli, a dodecameric oxidoreductase containing four hemoprotein and eight flavoprotein subunits. SiR mutational tolerance was first evaluated using systematic octapeptide insertion and a cellular selection, which identified regions across the hemoprotein structure that retain parent-like activity following insertion. When a ligand-binding domain was inserted at backbone locations tolerant to peptide insertion, including sites proximal and distal from the intersubunit interfaces, ∼90% retained catalytic activity, and >50% presented activity that is regulated by an endocrine disruptor. With one domain insertion variant, the conditional production of sulfide could be monitored electrochemically from cells using a bioelectrochemical reactor. These results show how systematic peptide insertion can be used to inform domain insertion in a large heterooligomeric protein complex, and they illustrate how SiR can be engineered to convert chemical information in the environment into a redox-active metabolite that diffuses across the cell membrane.

bacteria↗
DOE OSTI2024

Dynamic Behavior of Pt Multimetallic Alloys for Active and Stable Propane Dehydrogenation Catalysts

Improving the use of platinum in propane dehydrogenation catalysts is a crucial aspect to increasing the efficiency and sustainability of propylene production. A known and practiced strategy involves incorporating more abundant metals in supported platinum catalysts, increasing its activity and stability while decreasing the overall loading. Here, using colloidal techniques to control the size and composition of the active phase, we show that Pt/Cu alloy nanoparticles supported on alumina (Pt/Cu/Al 2 O 3 ) displayed elevated rates for propane dehydrogenation at low temperature compared to a monometallic Pt/Al 2 O 3 catalyst. We demonstrate that the enhanced catalytic activity is correlated with a higher surface Cu content and formation of a Pt-rich core and Cu-rich shell that isolates Pt sites and increases their intrinsic activity. However, rates declined on stream because of dynamic metal diffusion processes that led to a more uniform alloy structure. This transformation was only partially inhibited by adding excess hydrogen to the feed stream. Instead, cobalt was introduced to provide trimetallic Pt/Cu/Co catalysts with stabilized surface structure and stable activity and higher rates than the original Pt/Cu system. In conclusion, the structure–activity relationship insights in this work offer improved knowledge of propane dehydrogenation catalyst development featuring reduced Pt loadings and notable thermal stability for propylene production.

Alloys↗
DOE OSTI2025

Optimizing CO 2 -Loaded Aqueous Amine Solutions for Higher Electrocatalytic CO 2 Reduction Activity

The activity of aqueous-based carbon dioxide reduction (CO 2 R) reactions is often limited by the solubility of CO 2 . The addition of amines can increase the total dissolved carbon in water through the formation of bicarbonate and carbamate species, which has been used to a great effect to capture CO 2 from dilute streams. Here, in this study, we explore the effect of 12 primary and secondary amines of varying Brønsted basicity, steric profile, and hydrogen-bonding capabilities on the aqueous CO 2 R to CO activity of a molecular Ni(cyclam)Cl 2 catalyst with a Hg electrode. Addition of some of the amines results in greater activity and selectivity for CO production compared to equivalent aqueous solutions without added amines. Under optimal conditions (0.4 M 3-amino-propionitrile), there is an over sevenfold increase in partial current density and greater selectivity for CO compared to equivalent conditions with no amine. Interestingly, the increase in activity did not correlate to any single property across the 12 amines. To elucidate the effect of the amine additives on catalysis, we used vapor–liquid equilibrium modeling (VLE), 13 C NMR spectroscopy, and computational analysis to determine the carbon speciation of the solutions. These results indicate that for amines without ethylalcohol functionalities, CO 2 R activity correlates with carbamate concentration, which is in turn governed by amine basicity and steric effects. However, this correlation does not persist for amines with ethylalcohol functionalities, which can form more stable carbamates through intramolecular-hydrogen bonding. These studies demonstrate that amine additives can enhance aqueous CO 2 R activity and selectivity and describe amine properties that lead to these higher performance metrics.

Amines↗
DOE OSTI2026

Correlating Protein Dynamics and Catalytic Activity of a Model Hydrogenase Using Paramagnetic and Biological Nuclear Magnetic Resonance Spectroscopy

Rational catalyst design remains a significant challenge, with electronic structure, steric, and electrostatic effects known to contribute to activity. Recently, dynamics has been recognized as another factor that impacts catalysis, though identifying and predicting these effects has remained out of reach. Nickel-substituted rubredoxin (NiRd), a protein-based mimic of a hydrogenase enzyme, serves as a model catalytic system in which dynamics can be systematically investigated with respect to activity. While over 30 secondary-sphere mutants of NiRd have been shown to be catalytically active, no significant correlation was observed between the rates and catalytic overpotential or electronic structure, prompting questions about the protein-derived factors that modulate activity. Here, in this work, NMR spectroscopy was used to investigate the roles of substrate accessibility, protein dynamics, and protein stability in controlling catalysis. Significant paramagnetic effects from the nickel center (S = 1) isolate the methylene proton resonances of the metal-coordinating cysteine residues. The sensitivity of resonance positions and linewidths to local environment offers an opportunity to study dynamical molecular changes around the metal center with high resolution. Machine learning algorithms were employed to identify correlations between the catalytic activity and the paramagnetic NMR spectra. These analyses revealed spectroscopic features of specific cysteine protons that report on catalytic overpotential and increased turnover rates, which are further supported by the results obtained using high-field NMR techniques. Collectively, these studies indicate the potential for multifrequency NMR techniques to resolve key contributors to catalytic activity and highlight the importance of local and outer-sphere dynamics.

Protein Engineering↗