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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.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Impacts of climate change on estuarine stratification and implications for hypoxia within a shallow subtropical system

Vertical density stratification often plays an important role in the formation and expansion of coastal hypoxic zones through its effect on near-bed circulation and vertical oxygen flux. However, the impact of future climate change on estuarine circulation is widely unknown. Here, we developed and calibrated a three-dimensional hydrodynamic model for Pensacola Bay, a shallow subtropical estuary in the northeastern Gulf of Mexico. Model simulations based on years 2013–2017 were applied to examine changes in salinity, temperature, and density under future climate scenarios, including increased radiative forcing (IR) and temperature (T), increased freshwater discharge (D), sea level rise (SLR), and wind intensification (W). Simulations showed that the impacts of climate change on modeled state variables varied over time with external forcing conditions. The model demonstrated the potential for sea level rise and increased freshwater discharge to episodically increase vertical density gradients in the Bay. However, increased wind forcing destabilized vertical gradients, at times reducing the spatial extent and duration of stable stratification. For time periods with low freshwater discharge, moderate increases in wind speed (10%) can destabilize density gradients strengthened by increased discharge (10%) and sea level rise (0.48 m). In contrast, destruction of strong density gradients that form near the mid-Bay channel following flood events requires stronger wind forcing. Furthermore, these results highlight the importance of considering natural variability in freshwater and wind forcing, as well as local phenomena that are generally unresolved by global climate models.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Efficacy of “HLE”—a multidrug efflux-pump inhibitor—as a disinfectant against surface bacteria

Highlights: • HLE disinfectant had effective antimicrobial and anti-biofilm activity. • HLE disinfectant destabilized biofilm structures eradicating them. • Sub-inhibitory concentrations of HLE inhibited multidrug efflux pumps. • Disinfection based on HLE may avoid spreading multi-drug resistant bacteria. We evaluated the efficacy of a new disinfectant product, HLE, to inhibit multiple species of planktonic and biofilm bacterial cultures. The HLE disinfectant comprised of EDTA, lactic acid and hydrogen peroxide, and our data indicated that the disinfectant had effective antimicrobial and anti-biofilm activity even at low concentrations (0.15% to 0.4% HLE, v/v). Furthermore, the HLE disinfectant destabilized biofilm structures eradicated them due to the synergistic effect of EDTA and both antimicrobials (lactic acid and hydrogen peroxide), as revealed by confocal laser scanning microscopy. Additionally, sub-inhibitory concentrations of HLE disinfectant, with EDTA as an efflux pump inhibitor, inhibited the expression of multidrug EfrAB, NorE and MexCD efflux pumps in both planktonic and biofilm cultures. This could provide an alternative way to disinfect surfaces to avoid spreading multi-drug resistant strains in the food chain and the environment by decreasing efflux pump expression and consequently reducing the antibiotic selective pressure caused by systemic antibiotics and disinfectant use.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Thermal and solubility effects on fault leakage during geologic carbon storage

Geologic carbon storage (GCS) is a promising method for reducing anthropogenic CO 2 emissions to the atmosphere. To safely deploy GCS in the field, it is necessary to assess risks and the effect of uncertainty on safe storage. The effect of uncertainty can be quantified using batches of simulations, but the high computational costs of high-resolution simulations necessitate use of reduced-order models (ROMs). Previous work involves ROMs for quantifying the risk of different potential leakage paths from storage reservoirs to shallow formations. However, previous studies on development of fault-leakage ROMs have limited numbers of uncertain parameters and do not explicitly examine impacts of CO 2 solubility and thermal stresses on fault reactivation, which can generate high-permeability pathways and compromise CO 2 storage. Here, we analyze an ensemble of simulations considering CO 2 leakage from a storage reservoir to a shallow aquifer through a fault while varying a number of uncertain parameters related to thermo-hydro-mechanical properties and CO 2 injection. We show the effects of solubility on: free-phase CO 2 -leakage rates, brine-leakage rates, and poroelastic fault destabilization. We find that CO 2 solubility is more important for estimating free-phase CO 2 -leakage rates compared to brine-leakage rates or poroelastic fault destabilization. We also find that thermal stresses and overpressures have different spatial distributions within the fault, indicating that the spatial variability of overpressures due to variation in flow parameters does not necessarily make the spatial variability of thermal stresses negligible. We suggest the use of the CO 2 phase-change path as a variable in future fault-leakage ROMs.

03 NATURAL GAS↗
DOE OSTI2020

Kinetics of low-temperature methane activation on IrO 2 (1 1 0): Role of local surface hydroxide species

The ability of the IrO 2 (1 1 0) surface to promote CH 4 activation at low temperatures (~150 K) suggests possibilities for developing IrO 2 -based catalysts to selectively convert light alkanes to high-value chemicals. In this study, we present experimental results and microkinetic simulations, based on density functional theory (DFT) calculations, of temperature programmed reaction spectra (TPRS) obtained for CH 4 σ-complexes adsorbed on IrO 2 (1 1 0), and focus on clarifying how surface OH groups modify the branching between CH 4 desorption, activation and subsequent reactions during TPRS. Our DFT results predict that surface OH groups strongly destabilize CH 4 σ-complexes on IrO 2 (1 1 0) in addition to deactivating surface O-atoms that are needed to achieve CH 4 activation at low temperature. We demonstrate that a microkinetic model that incorporates the influence of surface OH groups on the CH 4 binding and reactivity reproduces experimental TPRS results which show that adsorbed CH 4 σ-complexes preferentially dissociate at low CH 4 coverage, but that an increasing fraction of the adsorbed CH 4 desorbs at low temperature (~120 K) with increasing initial CH 4 or H coverage. The simulations reveal that low-temperature CH4 desorption during TPRS arises primarily from CH 4 σ-complexes that are kinetically-trapped between adjacent surface OH groups, and are thus destabilized and unable to access reactive O-atoms. In addition, when the effect of adjacent OH groups is incorporated we find that the PBE-D3 functional incorporating dispersion provides CH 4 binding energies that agree more closely with that obtained from the TPRS experiments. Overall, our results demonstrate that the local effect of adjacent OH groups must be incorporated into any microkinetic models to properly capture the selectivity between extensive and partial oxidation in alkane conversion on IrO 2 (1 1 0) under reaction conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

The impact of chemical doping on the magnetic state of the Sr{sub 2}YRuO{sub 6} double perovskite

The impact of chemical doping of the type Sr{sub 2−x}A{sub x}YRuO{sub 6} (A=Ca, Ba) on the low temperature magnetic properties of Sr{sub 2}YRuO{sub 6}, probed using variable temperature magnetic susceptibility, neutron diffraction and heat capacity measurements, are described. Specific-heat measurements of un-doped Sr{sub 2}YRuO{sub 6} reveal two features at ∼26 and ∼30 K. Neutron scattering measurements at these temperatures are consistent with a change from a 2D ordered state to the 3D type 1 AFM state. Magnetic and structural studies of a number of doped oxides are described that highlight the unique low temperature behavior of Sr{sub 2}YRuO{sub 6} and demonstrate that doping destabilizes the intermediate 2D ordered state. - Graphical abstract: Neutron diffraction measurements of the ordered double perovskite Sr{sub 2}YRuO{sub 6}reveal a with a change from a 2D ordered state to the 3D type 1 AFM state upon cooling. The impact of chemical doping Sr{sub 2−x}A{sub x}YRuO{sub 6} (A=Ca, Ba) on the low temperature magnetic properties have also been investigated and these highlight the unique low temperature behavior of Sr{sub 2}YRuO{sub 6} with doping destabilizing the intermediate 2D ordered state. - Highlights: • Crystal and Magnetic Structure of Sr{sub 2}YRuO{sub 3} was studied using Neutron Diffraction. • Effect of doping on the magnetic ground state established. • Origin of two low temperature transitions discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Thermal stability and phase transformation in fully indium oxide (InO{sub 1.5}) stabilized zirconia

Indium oxide (InO{sub 1.5}) stabilized zirconia (InSZ) is an attractive material as electrolyte, or electrode, in solid oxide fuel cells (SOFCs), and as corrosion resistant top coat in thermal barrier coatings. However, little is known about the phase stability of cubic InSZ at temperatures that simulate the conditions in an operating SOFC or turbine. This article provides an investigation of the phase stability and phase transformations in cubic InSZ after heat treatments at 800, 1000, and 1200 °C for periods up to 2000 h. The results revealed that cubic InSZ is not stable during annealing at 1000 and 1200 °C, owing to a fast destabilization of the initial cubic phase to tetragonal, and eventually to monoclinic (c → t → m). The c → t → m transition in InSZ is intimately associated with the indium volatilization. On the other hand, cubic InSZ remained stable for 2000 h at 800 °C, although the partial formation of the tetragonal phase was observed along with a 0.25% contraction in the unit cell volume of the cubic phase, caused by short-range ordering. These results demonstrate that technological applications of cubic InSZ are restricted to temperatures at which the volatilization of the InO{sub 1.5} stabilizer does not occur. - Highlights: •Phase stability of fully InO{sub 1.5} stabilized zirconia (cubic InSZ) was evaluated. •Cubic InSZ is instable at temperatures ≥ 1000 °C, owing to the cubic-to-tetragonal-to-monoclinic destabilization. •Cubic InSZ undergoes the cubic-to-tetragonal transformation at ~ 800 °C. •Owing to the low phase stability, applications of cubic InSZ in TBCs or SOFCs are restricted.

36 MATERIALS SCIENCE↗
DOE OSTI2021

An effective human uracil-DNA glycosylase inhibitor targets the open pre-catalytic active site conformation

Human uracil DNA-glycosylase (UDG) is the prototypic and first identified DNA glycosylase with a vital role in removing deaminated cytosine and incorporated uracil and 5-fluorouracil (5-FU) from DNA. UDG depletion sensitizes cells to high APOBEC3B deaminase and to pemetrexed (PEM) and floxuridine (5-FdU), which are toxic to tumor cells through incorporation of uracil and 5-FU into DNA. To identify small-molecule UDG inhibitors for pre-clinical evaluation, we optimized biochemical screening of a selected diversity collection of >3,000 small-molecules. We found aurintricarboxylic acid (ATA) as an inhibitor of purified UDG at an initial calculated IC 50 < 100 nM. Subsequent enzymatic assays confirmed effective ATA inhibition but with an IC50 of 700 nM and showed direct binding to the human UDG with a K D of <700 nM. ATA displays preferential, dose-dependent binding to purified human UDG compared to human 8-oxoguanine DNA glycosylase. ATA did not bind uracil-containing DNA at these concentrations. Yet, combined crystal structure and in silico docking results unveil ATA interactions with the DNA binding channel and uracil-binding pocket in an open, destabilized UDG conformation. Biologically relevant ATA inhibition of UDG was measured in cell lysates from human DLD1 colon cancer cells and in MCF-7 breast cancer cells using a host cell reactivation assay. Collective findings provide proof-of-principle for development of an ATA-based chemotype and “door stopper” strategy targeting inhibitor binding to a destabilized, open pre-catalytic glycosylase conformation that prevents active site closing for functional DNA binding and nucleotide flipping needed to excise altered bases in DNA.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Priming mechanisms providing plants and microbes access to mineral-associated organic matter

Mineral-associated organic matter (MAOM) is considered a stable reservoir for soil nutrients that influences long-term soil carbon (C) and nitrogen (N) dynamics. However, recent experimental and theoretical evidence shows that root exudates may mobilize MAOM, thereby providing plants and microbes access to a large and N-rich pool. Given the mechanisms underlying MAOM C and N mobilization remain largely untested, we examined direct and indirect pathways by which root exudates destabilize this nutrient pool in laboratory mesocosms. We simulated root exudation with 13 C-labeled oxalic acid to test whether root exudates are directly capable of mobilizing MAOM from mineral surfaces; and with 13 C-labeled glucose to test whether indirect stimulation of microbial and extracellular enzyme activity leads to MAOM decomposition. We also tested the potential for oxalic acid and glucose to mobilize MAOM in an additional subset of sterilized soils to clarify the potential for non-microbial pathways of MAOM destabilization. Over the course of the 12-day MAOM incubation with and without simulated exudates, we measured C cycling (CO 2 respiration rates, 13 C–CO 2 efflux), N cycling (inorganic N pools, gross N mineralization) and related microbial processes (enzyme activities and microbial community composition via phospholipid fatty acid analysis). Both of the simulated root exudates enhanced MAOM-C mineralization, with cumulative respiration increasing 35–89% relative to the water-only control. Likewise, glucose additions enhanced the production of an exo-cellulase and a chitinase by up to 130% and 39%, respectively, while oxalic acid enhanced oxidative enzyme activities up to 91% greater than control rates. We observed a positive association between glucose-induced shifts in enzyme activities, MAOM-C mineralization, and gross ammonification. Oxalic acid additions were associated with initial increases in fungal relative abundance and in sterile soils appeared to stimulate the release of metals and dissolved organic nitrogen into exchangeable pools. Our results indicate that common root exudates, like glucose and oxalic acid, can significantly increase the turnover and potential release of C and N from MAOM through indirect (e.g., enzyme induction) and direct (e.g., mobilization of metal oxides) mechanisms.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Cytoskeletal organization in microtentacles

Microtentacles are thin, flexible cell protrusions that have recently been described and whose presence enhances efficient attachment of circulating cells. They are found on circulating tumor cells and can be induced on a wide range of breast cancer cell lines, where they are promoted by factors that either stabilize microtubules or destabilize the actin cytoskeleton. Evidence suggests that they are relevant to the metastatic spread of cancer, so understanding their structure and formation may lead to useful therapies. Microtentacles are formed by microtubules and contain vimentin intermediate filaments, but beyond this, there is little information about their ultrastructure. We have used electron microscopy of high pressure frozen sections and tomography of cryo-prepared intact cells, along with super resolution fluorescence microscopy, to provide the first ultrastructural insights into microtubule and intermediate filament arrangement within microtentacles. By scanning electron microscopy it was seen that microtentacles form within minutes of addition of drugs that stabilize microtubules and destabilize actin filaments. Mature microtentacles were found to be well below one micrometer in diameter, tapering gradually to below 100 nm at the distal ends. They also contained frequent branches and bulges suggestive of heterogeneous internal structure. Super resolution fluorescence microscopy and examination of sectioned samples showed that the microtubules and intermediate filaments can occupy different areas within the microtentacles, rather than interacting intimately as had been expected. Cryo-electron tomography of thin regions of microtentacles revealed densely packed microtubules and absence of intermediate filaments. The number of microtubules ranged from several dozen in some areas to just a few in the thinnest regions, with none of the regular arrangement found in axonemes. Improved understanding of the mechanism of microtentacle formation, as well as the resultant structure, will be valuable in developing therapies against metastasis, if the hypothesized role of microtentacles in metastasis is confirmed. This work provides a significant step in this direction. - Highlights: • Microtentacles can form within minutes of the addition of inducing drugs. Microtentacle diameters are in the range of a tenth of a micrometer. • Microtubules are clearly resolved in microtentacles by cryo-electron tomography. • There is little microtubule-intermediate filament interaction in drug-induced microtentacles.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Design of Diverse Asymmetric Pockets in De Novo Homo-oligomeric Proteins

A challenge for design of protein–small-molecule recognition is that incorporation of cavities with size, shape, and composition suitable for specific recognition can considerably destabilize protein monomers. This challenge can be overcome through binding pockets formed at homo-oligomeric interfaces between folded monomers. Interfaces surrounding the central homo-oligomer symmetry axes necessarily have the same symmetry and so may not be well suited to binding asymmetric molecules. To enable general recognition of arbitrary asymmetric substrates and small molecules, we developed an approach to designing asymmetric interfaces at off-axis sites on homo-oligomers, analogous to those found in native homo-oligomeric proteins such as glutamine synthetase. We symmetrically dock curved helical repeat proteins such that they form pockets at the asymmetric interface of the oligomer with sizes ranging from several angstroms, appropriate for binding a single ion, to up to more than 20 Å across. Of the 133 proteins tested, 84 had soluble expression in E. coli, 47 had correct oligomeric states in solution, 35 had small-angle X-ray scattering (SAXS) data largely consistent with design models, and 8 had negative-stain electron microscopy (nsEM) 2D class averages showing the structures coming together as designed. Both an X-ray crystal structure and a cryogenic electron microscopy (cryoEM) structure are close to the computational design models. The nature of these proteins as homo-oligomers allows them to be readily built into higher-order structures such as nanocages, and the asymmetric pockets of these structures open rich possibilities for small-molecule binder design free from the constraints associated with monomer destabilization.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

H-cluster Intermediates and Catalytic Properties of Clostridium pasteurianum [FeFe]-Hydrogenase III

[FeFe]-Hydrogenases are structurally diverse enzymes that catalyze reversible H2 activation at a catalytic cofactor or H-cluster. The H-cluster is a [4Fe-4S] cubane linked by a cysteine thiolate to a diiron subsite containing unique CO, CN-, and dithiomethylamine ligands. The established H-cluster resting state of [4Fe-4S]2+-[FeII-FeI], or Hox, functions in H2 binding and oxidation, or by proton-coupled reduction initiates H2 evolution. In contrast, in Clostridium pasteurianum [FeFe]-hydrogenase III (CpIII) the resting state of the H-cluster is fully oxidized, [4Fe-4S]2+-[FeII-FeII], or Hox+1. To begin to understand if Hox+1 has a role in the mechanism of CpIII, we determined the spectroscopic and redox properties of CpIII H-cluster states under catalytic conditions. CpIII poised in Hox+1 and either equilibrated under 1 atm of H2 or reduced with sodium dithionite, resulted in a mixture of reduced states including Hox (Em8 = -407 mV), Htrans-like [4Fe-4S]+-[FeII-FeII] (Em8 = -418 mV), Hred [4Fe-4S]+-[FeII-FeI], and HredH+ [4Fe-4S]2+-[FeI-FeI] (Em8 = -455-480 mV). Under H2 the population of the Htrans-like state was >20-fold higher than Hox, implicating a role in CpIII catalysis. Unlike other enzymes, there was no spectral evidence of fully reduced states, such as HsredH+ ([4Fe-4S]+-[FeI-FeI]) or Hhyd ([4Fe-4S]+-[FeII-FeII]-H-). Thus, while the H-cluster states of CpIII encompass most of the catalytic intermediates, it is either unable to form HsredH+ and Hhyd, or these states are highly destabilized in CpIII. Thus, these results demonstrate that catalytic intermediates of reduced CpIII differ from the typical intermediates of other catalytic [FeFe]-hydrogenases and may explain the catalytic preference for H2 production.

08 HYDROGEN↗
DOE OSTI2017

Compression-Induced Crystallization in Sucrose-Polyvinylpyrrolidone Amorphous Solid Dispersions

Tablets of amorphous sucrose and sucrose-polyvinylpyrrolidone (PVP) amorphous solid dispersions were compressed at 25, 75, or 150 MPa at dwell times ranging from 5 to 900 s. Compression-induced physical destabilization was evident from differential scanning calorimetry. Crystallization kinetics was monitored using a laboratory source X-ray diffractometer, while crystallization was detected using highly sensitive synchrotron radiation. At the highest compression pressure, sucrose crystallization was evident immediately after compression. However, the addition of PVP, even at a low concentration of 1% w/w, inhibited crystallization. Furthermore, nucleation itself was completely prevented at higher PVP concentrations (≥15% w/w) under a compression pressure of practical interest (150 MPa with 5 s dwell time). However, an increase in dwell time (e.g., to 60 s) facilitated nucleation, and there was an increase in nucleation density as a function of dwell time. Both polymer content and sample history were pivotal factors limiting compression-induced crystallization in plasticized amorphous systems. Furthermore, plasticization was found to amplify compression-induced destabilization. PVP, in a concentration dependent manner, attenuated this effect.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Quantifying the Impact of Magnesium on the Stability and Water Binding Energy of Hydrated Calcium Carbonates by ab initio Thermodynamics

Determining conditions that drive carbonate formation is important for establishing paleoindicators for mineral deposition, understanding the carbon cycle and biomineralization, and designing industrial applications such as scale inhibition, manufacturing of cement and concrete, and environmental remediation. Mg and incorporated water have been observed to play critical roles in nonclassical crystallization pathways of calcium carbonate, the dominant carbonate found in nature, through promoting formation of low energy metastable intermediates such as monohydrocalcite (CaCO3H2O), ikaite (CaCO36H2O), and amorphous calcium carbonate (CaCO3H2O). The impact of Mg on the thermodynamics and water binding ability of these hydrated intermediates is challenging to measure and is not understood at the molecular level. In this work density-functional theory and ab initio thermodynamics are used to quantify the impact of Mg on structure, thermodynamics and water binding energies of the crystalline hydrated Ca carbonates as a function of temperature in aqueous and ultra-high vacuum conditions, as well as CO2-rich environments relevant to carbon sequestration. For monohydrocalcite, Mg incorporation is found to destabilize the structure despite a dramatic increase in the water-binding energy, thus confirming that Mg promotes monohydrocalcite formation kinetically rather than thermodynamically. For ikaite, however, Mg promotes its formation both kinetically and thermodynamically, expanding the stability region for ikaite in cold water. For portlandite Ca(OH)2, Mg significantly destabilizes the structure which cannot shift atomic positions to accommodate the smaller cation, unlike the positional flexibility afforded by water molecules and carbonate groups in monohydrocalcite and ikaite. Mg does result in a decreased lattice volume for ikaite and monohydrocalcite, but only a very small amount and hence cannot be used to quantify the amount of Mg incorporation in natural samples.

calcite, ikaite, monohydrocalcite, magnesium, carb↗
DOE OSTI2017

Equilibrium denaturation and preferential interactions of an RNA tetraloop with urea

Urea is an important organic cosolute with implications in maintaining osmotic stress in cells and differentially stabilizing ensembles of folded biomolecules. We report an equilibrium study of urea-induced denaturation of a hyperstable RNA tetraloop through unbiased replica exchange molecular dynamics. We find that, in addition to destabilizing the folded state, urea smooths the RNA free energy landscape by destabilizing specific configurations, and forming favorable interactions with RNA nucleobases. A linear concentration-dependence of the free energy (m-value) is observed, in agreement with the results of other RNA hairpins and proteins. Additionally, analysis of the hydrogen-bonding and stacking interactions within RNA primarily show temperature-dependence, while interactions between RNA and urea primarily show concentration-dependence. Lastly, our findings provide valuable insight into the effects of urea on RNA folding and describe the thermodynamics of a basic RNA hairpin as a function of solution chemistry.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Electrolyte-Assisted Hydrogen Storage Reactions

Use of electrolytes, in the form of LiBH 4 /KBH 4 and LiI/KI/CsI eutectics, is shown to significantly improve (by more than a factor of 10) both the dehydrogenation and full rehydrogenation of the MgH 2 /Sn destabilized hydride system and the hydrogenation of MgB 2 to Mg(BH 4 ) 2 . The improvement revealed that interparticle transport of atoms heavier than hydrogen can be an important rate-limiting step during hydrogen cycling in hydrogen storage materials consisting of multiple phases in powder form. Electrolytes enable solubilizing heavy ions into a liquid environment and thereby facilitate the reaction over full surface areas of interacting particles. In conclusion, the examples presented suggest that use of electrolytes in the form of eutectics, ionic liquids, or solvents containing dissolved salts may be generally applicable for increasing reaction rates in complex and destabilized hydride materials.

08 HYDROGEN↗
DOE OSTI2023

Amphiphilic Co-Solvents Modulate the Structure of Membrane Domains

Biofuels are an increasing part of the sustainable energy picture. This makes it a societal and economic imperative to optimize biofuel production. Mitigating the toxic effects of amphiphilic co-solvents is one way to improve the efficiency of biofuel production. Amphiphiles partition into cellular membranes, leading to membrane thinning, destabilization, loss of membrane potential, and, ultimately, cell death. However, this picture of solvent toxicity misses the disruptive impact of co-solvents on lateral membrane organization, which is increasingly recognized as critical for membrane protein sorting and oligomerization. The alteration or disruption of membrane domains has deleterious effects on cellular processes. Here, in this work, we pursue the hypothesis that membrane lateral organization is disrupted by the presence of co-solvents at concentrations lower than those which lead to full membrane destabilization. The disruption occurs due to an increasing interfacial tension between the co-existing phases, resulting in conformational changes to minimize the interfacial length-to-area ratio. This represents an unrecognized mode of solvent-induced stress and a new target for interventions to improve fermentation yields.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Atomic Layer-by-Layer Deposition of Platinum on Palladium Octahedra for Enhanced Catalysts toward the Oxygen Reduction Reaction

We systematically evaluated two different approaches to the syntheses of Pd@PtnL (n = 2–5) core–shell octahedra. We initially prepared the core–shell octahedra using a polyol-based route by titrating a Pt(IV) precursor into the growth solution containing Pd octahedral seeds at 200 °C through the use of a syringe pump. The number of Pt atomic layers could be precisely controlled from two to five by increasing the volume of the precursor solution while fixing the amount of seeds. We then demonstrated the synthesis of Pd@Pt nL octahedra using a water-based route at 95 °C through the one-shot injection of a Pt(II) precursor. Due to the large difference in reaction temperature, the Pd@Pt nL octahedra obtained via the water-based route showed sharper corners than their counterparts obtained through the polyol-based route. When compared to a commercial Pt/C catalyst based upon 3.2 nm Pt particles, the Pd@Pt nL octahedra prepared using both methods showed similar remarkable enhancement in terms of activity (both specific and mass) and durability toward the oxygen reduction reaction. These calculations based upon periodic, self-consistent density functional theory suggested that the enhancement in specific activity for the Pd@Pt nL octahedra could be attributed to the destabilization of OH on their Pt nL */Pd(111) surface relative to the {111} and {100} facets exposed on the surface of Pt/C. Finally. the destabilization of OH facilitates its hydrogenation, which was found to be the rate-limiting step of the oxygen reduction reaction on all these surfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

How Asymmetries Between Arctic and Antarctic Climate Sensitivity Are Modified by the Ocean

Abstract We investigate how the ocean response to CO 2 forcing affects hemispheric asymmetries in polar climate sensitivity. Intermodel comparison of Phase 5 of the Coupled Model Intercomparison Project CO 2 quadrupling experiments shows that even in models where hemispheric ocean heat uptake differences are small, Arctic warming still exceeds Antarctic warming. The polar climate impact of this evolving ocean response to CO 2 forcing is then isolated using slab ocean experiments in a state‐of‐the‐art climate model. Overall, feedbacks over the Southern Hemisphere more effectively dissipate top‐of‐atmosphere anomalies than those over the Northern Hemisphere. Furthermore, a poleward shift in ocean heat convergence in both hemispheres amplifies destabilizing ice albedo and lapse rate feedbacks over the Arctic much more so than over the Antarctic. These results suggest that the Arctic is intrinsically more sensitive to both CO 2 and oceanic forcings than the Antarctic and that ocean‐driven climate sensitivity asymmetry arises from feedback destabilization over the Arctic rather than feedback stabilization over the Antarctic.

54 ENVIRONMENTAL SCIENCES↗