Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “WASHING”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Highly Graphitic Mesoporous Fe,N-Doped Carbon Materials for Oxygen Reduction Electrochemical Catalysts

The synthesis, characterization, and electrocatalytic properties of mesoporous carbon materials doped with nitrogen atoms and iron are reported and compared for the catalyzed reduction of oxygen gas at fuel cell cathodes. Mixtures of common and inexpensive organic precursors, melamine, and formaldehyde were pyrolyzed in the presence of transition-metal salts (e.g., nitrates) within a mesoporous silica template to yield mesoporous carbon materials with greater extents of graphitization than those of others prepared from small-molecule precursors. In particular, Fe,N-doped carbon materials possessed high surface areas (~800 m 2 /g) and high electrical conductivities (~19 S/cm), which make them attractive for electrocatalyst applications. The surface compositions of the mesoporous Fe,N-doped carbon materials were postsynthetically modified by acid washing and followed by high-temperature thermal treatments, which were shown by X-ray photoelectron spectroscopy to favor the formation of graphitic and pyridinic nitrogen moieties. Such surface-modified materials exhibited high electrocatalytic oxygen reduction activities under alkaline conditions, as established by their high onset and half-wave potentials (1.04 and 0.87 V, respectively vs reversible hydrogen electrode) and low Tafel slope (53 mV/decade). These values are superior to many similar transition-metal- and N-doped carbon materials and compare favorably with commercially available precious-metal catalysts, e.g., 20 wt % Pt supported on activated carbon. As a result, the analyses indicate that inexpensive mesoporous Fe,N-doped carbon materials are promising alternatives to precious metal-containing catalysts for electrochemical reduction of oxygen in polymer electrolyte fuel cells.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Steam-Stable Basic Immobilized Amine Sorbent Pellets for CO 2 Capture Under Practical Conditions

Pelletization of basic immobilized amine sorbent (BIAS) particles is required to improve their mechanical strength and facilitate their practical CO 2 capture application under fixed or dynamic reactor conditions. Herein, we utilized two methods to prepare amine-functionalized BIAS pellets. Method (ii-a) involved combining latex polychloroprene (PC)/polyamine solutions with fly ash (FA)/BIAS powder to form sorbent pellets. Alternatively, method (ii-b) entailed shaping and drying wet pastes of binder solution plus FA/SiO 2 powder into pellet supports. These supports were then functionalized with leach-resistant polyethylenimine MW = 800 (PEI 800 )/N-N-diglycidyl-4-glycidyloxyaniline (tri-epoxide cross-linker, E3) or ethylenamine E100/E3 mixtures. All pellets were screened for CO 2 capture by thermogravimetric analysis (dry 14% CO 2 /N 2 , 55–75 °C), H 2 O stability by accelerated water washing, and mechanical strength by crush and ball-mill attrition testing. The mechanism of superior method (ii-b) pellet formation was uncovered by N 2 physisorption measurements, diffuse reflectance infrared Fourier transform spectroscopy, and scanning electron microscopy. Extended fixed bed testing of optimum E3/PEI 800 -0.13/1 pellets under practical conditions revealed complete CO 2 capture stability of 1.5 mmol CO 2 /g after 48 h of continuous steam exposure (7.2% H 2 O/He, 105 °C) and minimal 14.6% loss in capacity after 75 hours of combined CO 2 capture cycling and steam treating (48 h). This slight oxidative degradation could be alleviated by incorporating a K 2 CO 3 antioxidant into the pellet formulation. Overall, the robust physiochemical properties of the polyamine/cross-linker method (ii-b) pellets confirm their suitability for pilot-scale testing.

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

2D in-Plane Ordered MXene Nanosheets Derived from (Mo 2/3 Er 1/3 ) 2 AlC Rare-Earth i-MAX for Energy Storage Applications

MXenes have become one of the most versatile families of two-dimensional (2D) materials due to their high conductivity, hydrophilicity, and remarkable electrochemical performance. This has stimulated intense efforts to design and synthesize MXenes, including structurally unique in-plane ordered 2D MXenes called i-MXenes. Here, we have synthesized the quaternary rare earth (RE)-based i-MAX phase (Mo 2/3 Er 1/3 ) 2 AlC using an arc melting method, and the corresponding 2D i-MXene was then obtained through a LiF/HCl soft etching process. Literature studies have shown that Al and the RE element are etched out during the etching process, leading to the formation of pure vacancy-ordered Mo1.33C 2D i-MXene. However, our investigation reveals that upon exposure to a fluorine solution, the i-MAX phase forms RE fluoride impurities, which are challenging to remove through HCl−DI water washing and persist in the final product, resulting in impure Mo 1.33 C@Er i-MXene. These results were confirmed by various characterizations such as X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and scanning transmission electron microscopy. Although the Mo 1.33 C@Er electrode showed a 24-fold increase in specific capacitance compared to its parent i-MAX phase, it still exhibited a high charge-transfer resistance arising from the insulating nature of RE fluoride byproducts, which adversely influence the overall capacitance behavior of the synthesized 2D Mo 1.33 C@Er i-MXenes. This study contributes to identifying pathways for the preparation of pure 2D i-MXenes from RE-based i-MAX phases and developing improved synthesis methods. With additional process optimization, the 2D i-MXene holds a strong potential for electrochemical energy storage applications. Additionally, the electronic structures of Mo 1.33 C were theoretically studied using first-principles density functional theory calculations, which revealed that pristine Mo 1.33 C is metallic, and this metallic nature is preserved even with −O, −F, and mixed functionalization.

chemical structure↗
DOE OSTI2021

Deactivation by Potassium Accumulation on a Pt/TiO 2 Bifunctional Catalyst for Biomass Catalytic Fast Pyrolysis

Biomass-derived feedstocks bring significant challenges to the longevity of the catalysts used for their conversion, and alkali metals, for example, K, in the feedstock have been widely ascribed as one of the important factors causing catalyst deactivation. To address this challenge, it is critical to understand the mechanism of catalyst deactivation caused by K accumulation to guide the improvement of catalysts and processes and the development of catalyst regeneration strategies. In this work, we report a deep understanding of the impact of K on a bifunctional Pt/TiO 2 catalyst, which is an efficient catalyst for the ex situ catalytic fast pyrolysis of biomass. We simulated the K-poisoning of Pt/TiO 2 catalysts by purposely loading different amounts of K (100-6000 ppm by weight) on the catalysts. A series of characterization approaches, including scanning transmission electron microscopy, Fourier transform infrared spectroscopy, and chemical titration, were combined with a kinetic assessment of multiple probe reactions to elucidate the mechanism of Pt/TiO 2 deactivation by K accumulation. At low K loadings (<800 ppm), K preferentially poisons the strong Lewis acid sites, leading to significantly reduced activity for acid-catalyzed alcohol dehydration. However, acetone condensation is less sensitive to the poisoning of strong Lewis acid sites. Reactions that occur on Pt sites or at the metal-support interface, including alkene hydrogenation, m-cresol hydrodeoxygenation (HDO), and CO oxidation, were not impacted. At high K loadings (>800 ppm), K starts to accumulate on the Pt-TiO 2 interfacial area, poisoning the interfacial active sites for HDO and CO oxidation reactions. We further found that the poisoning of the Pt/TiO 2 catalyst by K is reversible, and water washing can successfully remove the accumulated K and recover the activities for both alcohol dehydration and m-cresol HDO reactions.

09 BIOMASS FUELS↗
DOE OSTI2015

Trace Levels of Copper in Carbon Materials Show Significant Electrochemical CO 2 Reduction Activity

Carbon materials are frequently used as supports for electrocatalysts because they are conductive and have high surface area. However, recent studies have shown that these materials can contain significant levels of metallic impurities that can dramatically alter their electrochemical properties. Here, the electrocatalytic activity of pure graphite (PG), graphene oxide (GO), and carbon nanotubes (CNT) dispersed on glassy carbon (GC) are investigated for the electrochemical CO 2 reduction reaction (CO 2 RR) in aqueous solution. It was observed that GO and CNT dispersed on GC all exhibit significant electrochemical activity that can be ascribed to impurities of Ni, Fe, Mn, and Cu. The level of Cu in GO can be particularly high and is the cause for the appearance of methane in the products produced over this material when it is used for the CO 2 RR. Washing these supports in ultrapure nitric acid is effective in removing the metal impurities and results in a reduction in the electrochemical activity of these forms of carbon. In particular, for GO, nearly all of the catalytically relevant metals can be removed. Electrochemical deposition of Cu on GO and PG supported on GC, and on GC itself, increased both the electrochemical activity of these materials and the production of methane via the CO 2 RR. Particularly high rates of methane formation per unit of Cu mass were obtained for Cu electrodeposited on GO and PG supported on GC. We suggest that this high activity may be due to the preferential deposition of Cu onto defects present in the graphene sheets comprising these materials.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Insight into the Ligand-Mediated Synthesis of Colloidal CsPbBr 3 Perovskite Nanocrystals: The Role of Organic Acid, Base, and Cesium Precursors

While convenient solution-based procedures have been realized for the synthesis of colloidal perovskite nanocrystals, the impact of surfactant ligands on the shape, size, and surface properties still remains poorly understood, which calls for a more detailed structure-morphology study. Here in this paper we have systematically varied the hydrocarbon chain composition of carboxylic acids and amines to investigate the surface chemistry and the independent impact of acid and amine on the size and shape of perovskite nanocrystals. Solution phase studies on purified nanocrystal samples by (1)H NMR and IR spectroscopies have confirmed the presence of both carboxylate and alkylammonium ligands on surfaces, with the alkylammonium ligand being much more mobile and susceptible to detachment from the nanocrystal surfaces during polar solvent washes. Moreover, the chain length variation of carboxylic acids and amines, ranging from 18 carbons down to two carbons, has shown independent correlation to the size and shape of nanocrystals in addition to the temperature effect. We have additionally demonstrated that employing a more soluble cesium acetate precursor in place of the universally used Cs 2 CO 3 results in enhanced processability without sacrificing optical properties, thus offering a more versatile recipe for perovskite nanocrystal synthesis that allows the use of organic acids and amines bearing chains shorter than eight carbon atoms. Overall our studies have shed light on the influence of ligand chemistry on crystal growth and stabilization of the nanocrystals, which opens the door to functionalizable perovskite nanocrsytals through surface ligand manipulation.

colloidal nanocrystal↗
DOE OSTI2018

Gate-Controlled Metal–Insulator Transition in TiS 3 Nanowire Field-Effect Transistors

We explore the electrical characteristics of TiS 3 nanowire field-effect transistor (FETs), over the wide temperature range from 3 to 350 K. These nanomaterials have a quasi-one-dimensional (1D) crystal structure and exhibit a gate-controlled metal–insulator transition (MIT) in their transfer curves. Their room-temperature mobility is ~20–30 cm 2 /(V s), 2 orders of magnitude smaller than predicted previously, a result that we explain quantitatively in terms of the influence of polar-optical phonon scattering in these materials. In the insulating state (<~220 K), the transfer curves exhibit unusual mesoscopic fluctuations and a current suppression near zero bias that is common to charge-density wave (CDW) systems. The fluctuations have a nonmonotonic temperature dependence and wash out at a temperature close to that of the bulk MIT, suggesting they may be a feature of quantum interference in the CDW state. Overall, our results demonstrate that quasi-1D TiS 3 nanostructures represent a viable candidate for FET realization and that their functionality is influenced by complex phenomena.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Impact of Controlled Storage Conditions on the Hydrolysis and Surface Morphology of Amorphous-UO 3

The hydration and morphological effects of amorphous (A)-UO 3 following storage under varying temperature and relative humidity have been investigated. This study provides valuable insight into U-oxide speciation following aging, the U-oxide quantitative morphological data set, and, overall, the characterization of nuclear material provenance. A-UO 3 was synthesized via the washed uranyl peroxide synthetic route and aged based on a 3-factor circumscribed central composite design of experiment. Target aging times include 2.57, 7.00, 14.0, 21.0, and 25.4 days, temperatures of 5.51, 15.0, 30.0, 45.0, and 54.5 °C, and relative humidities of 14.2, 30.0, 55.0, 80.0, and 95.8% were examined. Following aging, crystallographic changes were quantified via powder X-ray diffraction and an internal standard Rietveld refinement method was used to confirm the hydration of A-UO 3 to crystalline schoepite phases. The particle morphology from scanning electron microscopy images was quantified using both the Morphological Analysis of MAterials software and machine learning. Results from the machine learning were processed via agglomerative hierarchical clustering analysis to distinguish trends in morphological attributes from the aging study. Significantly hydrated samples were found to have a much larger, plate-like morphology in comparison to the unaged controls. Predictive modeling via a response surface methodology determined that while aging time, temperature, and relative humidity all have a quantifiable effect on A-UO 3 crystallographic and morphological changes, relative humidity has the most significant impact.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Effect of Diel Cycling Temperature, Relative Humidity, and Synthetic Route on the Surface Morphology and Hydrolysis of α -U 3 O 8

The speciation and morphological changes of α-U 3 O 8 following aging under diel cycling temperature and relative humidity (RH) have been examined. This work advances the knowledge of U-oxide hydration as a result of synthetic route and environmental conditions, ultimately giving novel insight into nuclear material provenance. α-U 3 O 8 was synthesized via the washed uranyl peroxide (UO 4 ) and ammonium uranyl carbonate (AUC) synthetic routes to produce unaged starting materials with different morphologies. α-U 3 O 8 from UO 4 is comprised of subrounded particles, while α-U 3 O 8 from AUC contains blocky, porous particles approximately an order of magnitude larger than particles from UO 4 . For aging, a humidity chamber was programmed for continuous daily cycles of 12 “high” hours of 45 °C and 90% RH, and 12 “low” hours of 25 °C and 20% RH. Samples were analyzed at varying intervals of 14, 24, 36, 43, and 54 days. At each aging interval, crystallographic changes were measured via powder X-ray diffraction coupled with whole pattern fitting for quantitative analysis. Morphologic effects were studied via scanning electron microscopy and 12-way classification via machine learning. While all samples were found to have distinguishing morphologic characteristics (93.2% classification accuracy), α-U 3 O 8 from UO 4 had more apparent change with increasing aging time. Nonetheless, α-U 3 O 8 from AUC was found to hydrate more quickly than α-U 3 O 8 from UO 4 , which can likely be attributed to its larger surface area and porous starting material morphology.

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

Rapid Evaluation of Amine-Functionalized Solvents for Biomass Deconstruction Using High-Throughput Screening and One-Pot Enzymatic Saccharification

Efficient and sustainable pretreatment of lignocellulosic biomass is critical for biofuel and biochemical production, yet its optimization is often hindered by slow, labor-intensive experimental methods. Here, we report the first demonstration of a custom-built, miniaturized, high-throughput screening platform integrated with one-pot enzymatic saccharification, enabling parallel evaluation of solvent type, feedstock, and temperature with minimal material use and high reproducibility. As a proof-of-concept, the HTX platform was used to screen five amine-functionalized solvents, including isopropanolamine, butylamine, N-methylbutylamine, ethanolamine, and ethanolamine acetate across three bioenergy crops (sorghum, poplar, and switchgrass) and pretreatment temperatures ranging from 80 to 140 °C. Vacuum drying successfully removed more than 99% of the solvents from the pretreated biomass, eliminating the need for water washing prior to saccharification. Isopropanolamine and N-methylbutylamine yielded the highest glucose (70–80%) and xylose (58–67%) release, with trends reflecting feedstock recalcitrance. The produced hydrolysates supported robust growth of an engineered strain of the yeast Rhodosporidium toruloides, confirming biocompatibility. This high-throughput platform provides a scalable, feedstock-agnostic framework for rapid pretreatment screening, accelerating solvent–feedstock pairing and process optimization. Its ability to integrate pretreatment, solvent removal, saccharification, and microbial conversion in a miniaturized format offers significant advantages for cost-competitive biorefinery development.

Biomass↗
DOE OSTI2026

Nitrogenated Graphene Quantum Dot-Derived Copper Single-Atom Catalyst for Oxygen Reduction Reaction

Despite the promise of fuel cells as sustainable energy conversion technologies, their widespread adoption is hindered by the high cost of platinum group metal (PGM) catalysts, particularly for catalyzing the oxygen reduction reaction (ORR) at the cathode. Here, we report copper-based single-atom catalysts (Cu-SACs) as cost-effective non-PGM alternatives for ORR. The catalysts were synthesized via simple pyrolysis of pyrene-derived amine-terminated graphene quantum dots (GQDs) in the presence of nitrogen and metal precursors. The abundant nitrogen functionality in GQDs effectively stabilized isolated Cu atoms during their conversion to porous carbon. A subsequent acid-washing step yielded a high density of atomically dispersed Cu active sites. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and high-resolution scanning transmission electron microscopy (HR-STEM) confirmed the effective incorporation of isolated Cu atoms into the carbon matrix through copper–nitrogen (Cu-N) coordination. Electrochemical measurements revealed excellent ORR activity with a dominant four-electron pathway. This synthetic strategy provides a practical route to developing economically viable, non-precious metal catalysts.

catalysts↗
DOE OSTI2018

SAPO-34/5A Zeolite Bead Catalysts for Furan Production from Xylose and Glucose

SAPO-34 zeolite crystals were grown on zeolite 5A beads, characterized, and then utilized to produce furfural from xylose and 5-hydroxymethylfurfural (HMF) from glucose. The SAPO-34/5A bead catalysts resulted in moderate furfural and HMF yields of 45% from xylose and 20% from glucose (463 K; 3 h) and were easier to recover than the SAPO-34 powder catalyst. At 463 K, the SAPO-34/5A beads were more selective than 0.02 M sulfuric acid for producing HMF and, unlike the sulfuric acid system, no levulinic acid was formed. The SAPO-34/5A bead catalysts had no significant loss in activity after three rounds of recycle when water washed or heated overnight between reactions; however, the heat-treated beads did show signs of thermal stress after the second reuse. The SAPO-34/5A bead catalysts show promise for dehydration reactions to produce furfural and HMF from xylose and glucose, respectively, and adapting the catalyst and the support bead could lead to even higher selectivities and yields.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Characterization of Products from Fast Micropyrolysis of Municipal Solid Waste Biomass

Biomass feedstock costs remain one of the largest impediments to biofuel production economics. Municipal solid waste (MSW) represents an attractive feedstock with year-round availability, an established collection infrastructure paid for by waste generators, low cost and the potential to be blended with higher cost feedstocks to reduce overall feedstock costs. Paper waste, yard waste and construction and demolition waste (C&D) were examined for their applicability in the pyrolysis conversion pathway. Paper waste consisted of non-recyclable paper such as mixed low grade paper, food and beverage packaging, kitchen paper wastes and coated paper; yard waste consisted of grass clippings and C&D wastes consisted of engineered wood products obtained from a construction waste landfill. We tested the waste materials for thermochemical conversion potential using a bench scale fast micro-pyrolysis process. Bio-oil yields were the highest for the C&D materials and lowest for the paper waste. The C&D wastes had the highest level of lignin derived compounds (phenolic and cyclics) while the paper waste had higher levels of carbohydrate derived compounds (aldehydes, organic acids, ketones, alcohols and sugar derived). But, the paper material had higher amounts of lignin derived compounds than expected based upon lignin content that is likely due to the presence of polyphenolic resins used in paper processing. The paper and yard wastes had significantly higher levels of ash content than the C&D wastes (14-15% versus 0.5-1.3%), which further correlated to higher levels of alkali and alkaline earth metals, which are known to reduce pyrolysis bio-oil yields. There appeared to be an inverse correlation of both calcium and potassium content with the amount of chromatographic product peaks, indicative of cracking reactions occurring during product formation. Furthermore the effect of acid washing was evaluated for grass clipping and waste paper and the bio-oil yield was increased from 58% to 73% and 67% to 73%, respectively.

09 BIOMASS FUELS↗
DOE OSTI2013

Synthesis of One-Dimensional SiC Nanostructures from a Glassy Buckypaper

A simple and scalable synthetic strategy was developed for the fabrication of one-dimensional SiC nanostructures - nanorods and nanowires. Thin sheets of single-walled carbon nanotubes (SWNTs) were prepared by vacuum filtration and were washed repeatedly with sodium silicate (Na₂SiO₃) solution. The resulting “glassy buckypaper” was heated at 1300 - 1500 °C under Ar/H₂ to allow a solid state reaction between C and Si precursors to form a variety of SiC nanostructures. The morphology and crystal structures of SiC nanorods and nanowires were characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), energy dispersive xray spectroscopy (EDX), electron diffraction (ED) and x-ray diffraction (XRD) techniques. Furthermore, electrical conductance measurements were performed on SiC nanorods, demonstrating their potential applications in high-temperature sensors and control systems.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2011

Immobilization of 99-Technetium (VII) by Fe(II)-Goethite and Limited Reoxidation

During the nuclear waste vitrification process volatilized {sup 99}Tc will be trapped by melter off-gas scrubbers and then washed out into caustic solutions, and plans are currently being contemplated for the disposal of such secondary waste. Solutions containing pertechnetate [{sup 99}Tc(VII)O{sub 4}{sup -}] were mixed with precipitating goethite and dissolved Fe(II) to determine if an iron (oxy)hydroxide-based waste form can reduce Tc(VII) and isolate Tc(IV) from oxygen. The results of these experiments demonstrate that Fe(II) with goethite efficiently catalyzes the reduction of technetium in deionized water and complex solutions that mimic the chemical composition of caustic waste scrubber media. Identification of the phases, goethite + magnetite, was performed using XRD, SEM and TEM methods. Analyses of the Tc-bearing solid products by XAFS indicate that all of the Tc(VII) was reduced to Tc(IV) and that the latter is incorporated into goethite or magnetite as octahedral Tc(IV). Batch dissolution experiments, conducted under ambient oxidizing conditions for more than 180 days, demonstrated a very limited release of Tc to solution (2-7 {micro}g Tc/g solid). Incorporation of Tc(IV) into the goethite lattice thus provides significant advantages for limiting reoxidation and curtailing release of Tc disposed in nuclear waste repositories.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2014

Coupled Mercury–Cell Sorption, Reduction, and Oxidation on Methylmercury Production by Geobacter sulfurreducens PCA

G. sulfurreducens PCA cells have been shown to reduce, sorb, and methylate Hg(II) species, but it is unclear whether this organism can oxidize and methylate dissolved elemental Hg(0) as shown for Desulfovibrio desulfuricans ND132. Using Hg(II) and Hg(0) separately as Hg sources in washed cell assays in phosphate buffered saline (pH 7.4), in this paper we report how cell-mediated Hg reduction and oxidation compete or synergize with sorption, thus affecting the production of toxic methylmercury by PCA cells. Methylation is found to be positively correlated to Hg sorption (r = 0.73) but negatively correlated to Hg reduction (r = -0.62). These reactions depend on the Hg and cell concentrations or the ratio of Hg to cellular thiols (-SH). Oxidation and methylation of Hg(0) are favored at relatively low Hg to cell–SH molar ratios (e.g., <1). Increasing Hg to cell ratios from 0.25 × 10 –19 to 25 × 10 –19 moles-Hg/cell (equivalent to Hg/cell–SH of 0.71 to 71) shifts the major reaction from oxidation to reduction. In the absence of five outer membrane c-type cytochromes, mutant ΔomcBESTZ also shows decreases in Hg reduction and increases in methylation. However, the presence of competing thiol-binding ions such as Zn 2+ leads to increased Hg reduction and decreased methylation. Finally, these results suggest that the coupled cell-Hg sorption and redox transformations are important in controlling the rates of Hg uptake and methylation by G. sulfurreducens PCA in anoxic environments.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

A Solvatochromic Near Infrared Fluorophore Sensitive to the Full Amyloid Beta Aggregation Pathway

Alzheimer's disease has long been associated with the aggregation of amyloid beta peptides (Aβ42) into macroscale plaques, although specific neurodegenerative agents have not been definitively identified. Much evidence has pointed to the soluble nanoscale oligomers that form early in the Aβ42 aggregation pathway, but there is little understanding of these structures, their mechanisms of formation, or how they grow into plaques. Here, we show that a solvatochromic fluorophore with near-infrared (NIR) emission can track synthetic Aβ42 aggregation through environment-sensitive spectral shifts from the earliest time points through plaque formation. This azide-functionalized phosphine oxide azetidine rhodol (Phazr-N3) shows large polarity-dependent changes in fluorescence emission, with maxima shifting from 630 nm in toluene to 703 nm in aqueous buffer, and a maximum quantum yield of 62%. Upon induction of Aβ42 aggregation, we observe immediate solvatochromic changes in Phazr-N3 fluorescence, with multiple apparent phases over 12 h, and which culminate before the onset of any major fluorescence changes of conformation-specific aggregation fluorophore thioflavin T. Solution anisotropy measurements show a low micromolar affinity of Phazr-N3 for disordered, free Aβ42 in solution, and real-time measurements are consistent with rapid liquid-liquid phase separation and slow dehydration of the growing aggregate. Spectral imaging of synthetic plaques stained in the presence of live cells and lipid-binding protein albumin shows over 4000-fold Phazr-N3 fluorescence intensity above background under no-wash conditions, and over 100-fold intensity above coplated microglial cells or a large excess of albumin. This use of a solvatochromic probe with structure-independent binding to free Aβ42 offers real-time, minimally invasive insight into the full Aβ42 aggregation pathway.

Wang, Zeming↗