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At least 1,297 records · Page 72

Harnessing Particle Size‐Control and DNA‐Oligo Functionalization in ZIF‐76 for Biological Applications

Abstract Advanced therapeutics require novel nanocarriers to ensure their functionality is preserved during transit. Zeolitic imidazolate frameworks (ZIFs) have emerged as promising materials in this field owing to their combined biocompatibility, high porosity, and tunable chemistry. While a diverse family of ZIFs has been reported, few have been explored beyond the prototypical ZIF‐8. Herein, the size‐controlled synthesis of three distinct ZIF‐76 analogs is demonstrated, overcoming the unique synthetic challenges intrinsic to the lta topology and complex crystallization kinetics associated with the mixed linker approach. This assesses the materials’ platform effectiveness for intracellular delivery first by exploring the structural and colloidal stability in biologically relevant media. To circumvent particle aggregation, fluorescently labeled DNA oligonucleotides are post‐synthetically attached to the ZIF surface. This modification significantly improves the colloidal stability in media and facilitates particle internalization tracking. Finally, the particle‐cell interactions are assessed, revealing rapid cell membrane association with macrophages, but not lung epithelial cells, and ZIF accumulation within macrophages which increased over time. Importantly, this study outlines a generalized approach toward expanding the available library of ZIFs for biological applications, enabling the potential for targeted therapeutic delivery for intracellular infections treatment.

Deneff, Jacob I.↗

Nickel hydroxide–nickel carbonate competitive growth on carbonate surfaces

The thermodynamic and kinetic factors controlling the competitive heterogeneous nucleation and growth of ubiquitous metal carbonate and hydroxide phases are poorly understood. In this work, calcite (CaCO 3 ) and magnesite (MgCO 3 ) powders were reacted with NiCl 2 (0–600 μM) for 7 days at 22 °C and 5 °C. The reacted powders were analyzed with X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, and energy-dispersive X-ray spectroscopy to characterize the Ni surface precipitates formed. Evidence from these techniques pointed to the formation of mixed Ni carbonate-Ni hydroxide amorphous surface precipitates. On calcite, XPS detected primarily Ni(OH) 2 despite the initial solutions being more supersaturated with respect to gaspéite (NiCO 3 ) than to theophrastite (Ni(OH) 2 ) by a factor of 17–18. In contrast, NiCO 3 was the dominant component detected by XPS on magnesite in the same conditions. Decreasing the temperature had the effect of increasing the proportion of NiCO 3 to the detriment of Ni(OH) 2 . The experimental observations were consistent with low lattice/cation size mismatch favoring NiCO 3 nucleation and temperature most influencing Ni(OH) 2 nucleation. Comparison to previous work on Co-reacted powders indicated the differences in lattice/cation size mismatch and/or water exchange rate impacted the composition of the surface precipitates more than the relative thermodynamic stabilities of the competing minerals. This work explored the heterogeneous growth regime of Ni carbonate and hydroxide phases on carbonate surfaces and shed light on the factors that control the competition between surface precipitates when mineral surfaces are in contact with aqueous solutions supersaturated with respect to multiple mineral phases. In conclusion, these results contribute to geochemists’ efforts toward interpreting data from geochemical systems with elevated Ni concentrations, improving Ni environmental remediation and recovery strategies, and predicting the fate and transport of Ni in geochemical systems.

Heterogeneous nucleation↗

A 7.5-Year Dataset of SSM/I-Derived Surface Turbulent Fluxes Over Global Oceans

The surface turbulent fluxes of momentum, latent heat, and sensible heat over global oceans are essential to weather, climate and ocean problems. Wind stress is the major forcing for driving the oceanic circulation, while Evaporation is a key component of hydrological cycle and surface heat budget. We have produced a 7.5-year (July 1987-December 1994) dataset of daily, individual monthly-mean and climatological (1988-94) monthly-mean surface turbulent fluxes over the global oceans from measurements of the Special Sensor Microwave/Imager (SSM/I) on board the US Defense Meteorological Satellite Program F8, F10, and F11 satellites. It has a spatial resolution of 2.0x2.5 latitude-longitude. Daily turbulent fluxes are derived from daily data of SSM/I surface winds and specific humidity, National Centers for Environmental Prediction (NCEP) sea surface temperatures, and European Centre for Medium-Range Weather Forecasts (ECMWF) air-sea temperature differences, using a stability-dependent bulk scheme. The retrieved instantaneous surface air humidity (with a 25-km resolution) IS found to be generally accurate as compared to the collocated radiosonde observations over global oceans. The surface wind speed and specific humidity (latent heat flux) derived from the F10 SSM/I are found to be -encrally smaller (larger) than those retrieved from the F11 SSM/I. The F11 SSM/I appears to have slightly better retrieval accuracy for surface wind speed and humidity as compared to the F10 SSM/I. This difference may be due to the orbital drift of the F10 satellite. The daily wind stresses and latent heat fluxes retrieved from F10 and F11 SSM/Is show useful accuracy as verified against the research quality in si -neasurerrients (IMET buoy, RV Moana Wave, and RV Wecoma) in the western Pacific warm pool during the TOGA COARE Intensive observing period (November 1992-February 1993). The 1988-94 seasonal-mean turbulent fluxes and input variables derived from FS and F11 SSM/Is show reasonable patterns related to seasonal variations of atmospheric general circulation. This dataset of SSM/I-derived turbulent fluxes is useful for climate studies, forcing of ocean models, and validation of coupled ocean-atmosphere global models and can be accessed through the NASA/GSFC Distributed Active Archive Center.

Chou, Shu-Hsien↗

A Multiyear Dataset of SSM/I-Derived Global Ocean Surface Turbulent Fluxes

The surface turbulent fluxes of momentum, latent heat, and sensible heat over global oceans are essential to weather, climate and ocean problems. Evaporation is a key component of the hydrological cycle and the surface heat budget, while the wind stress is the major forcing for driving the oceanic circulation. The global air-sea fluxes of momentum, latent and sensible heat, radiation, and freshwater (precipitation-evaporation) are the forcing for driving oceanic circulation and, hence, are essential for understanding the general circulation of global oceans. The global air-sea fluxes are required for driving ocean models and validating coupled ocean-atmosphere global models. We have produced a 7.5-year (July 1987-December 1994) dataset of daily surface turbulent fluxes over the global oceans from the Special Sensor microwave/Imager (SSM/I) data. Daily turbulent fluxes were derived from daily data of SSM/I surface winds and specific humidity, National Centers for Environmental Prediction (NCEP) sea surface temperatures, and European Centre for Medium-Range Weather Forecasts (ECMWF) air-sea temperature differences, using a stability-dependent bulk scheme. The retrieved instantaneous surface air humidity (with a 25-km resolution) validated well with that of the collocated radiosonde observations over the global oceans. Furthermore, the retrieved daily wind stresses and latent heat fluxes were found to agree well with that of the in situ measurements (IMET buoy, RV Moana Wave, and RV Wecoma) in the western Pacific warm pool during the TOGA COARE intensive observing period (November 1992-February 1993). The global distributions of 1988-94 seasonal-mean turbulent fluxes will be presented. In addition, the global distributions of 1990-93 annual-means turbulent fluxes and input variables will be compared with those of UWM/COADS covering the same period. The latter is based on the COADS (comprehensive ocean-atmosphere data set) and is recognized to be one of the best climatological analyses of fluxes derived from ship observations.

Chou, Shu-Hsien↗

Effects of Subsurface Sampling & Processing on Martian Simulant Containing Varying Quantities of Water

The presence of water-ice in the Martian subsurface is a subject of much debate and excited speculation. Recent results from the gammaray spectrometer (GRS) on board NASA's Mars Odyssey spacecraft indicate the presence of large amounts of hydrogen in regions of predicted ice stability. The combination of chemistry, low gravitational field (3.71 m/s(exp 2)) and a surface pressure of about 6.36 mbar at the mean radius, place limits on the stability of H2O on the surface, however, results from the GRS indicate that the hydrogen rich phase may be present at a depth as shallow as one meter in some locations on Mars. The potential for water on Mars leads directly to the speculation that life may once have existed there, since liquid water is the unifying factor for environments known to support life on Earth. Lubricant-free drilling has been considered as a means of obtaining water-rich subsurface samples on Mars, and two recent white papers sponsored by the Mars Program have attempted to identify the problems associated with this goal. The two major issues identified were: the engineering challenges of drilling into a water-soil mixture where phase changes may occur; and the potential to compromise the integrity of in-situ scientific analysis due to contamination, volatilization, and mineralogical or chemical changes as a result of processing. This study is a first attempt to simulate lubricantfree drilling into JSC Mars-1 simulant containing up to 50% water by weight. The goal is to address the following: 1) Does sample processing cause reactions or changes in mineralogy which will compromise the interpretation of scientific measurements conducted on the surface? 2) Does the presence of water-ice in the sample complicate (1)? 3) Do lubricant-free drilling and processing leave trace contaminants which may compromise our understanding of sample composition? 4) How does the torque/power required for drilling change as a function of water content and does this lead to unexpected thermal effects?

Menard, J.↗

Designing a Decontamination Solution for the Low-Earth-Orbit, Cryogenic SPHEREx Mission

To address the scientific goals of NASA’s astrophysics division, the JPL and Caltech’s SPHEREx mission conducts the first near-infrared all-sky spectral survey in low-earth-orbit using a passively-cooled, cryogenic telescope. Several unique water contamination issues arise due to the combination of cryogenic operation temperatures and the limited temperature control authority of passive cooling. Because water molecules have adsorption bands within the wavelengths of interest for SPHEREx’s survey, it is imperative that water contamination be controlled and minimized. In this work, a model is developed for the SPHEREx mission to predict the transport and accumulation of outgassed water onto sensitive payload components. The model utilizes the time dependent thermal profiles of the individual payload components, initial water content, and spacecraft geometry to calculate the time dependent water diffusion, transport, and adsorption. This model is subsequently used to predict water contamination risks and design decontamination solutions for each risk. Two major water contamination risks were predicted, water accumulation during cooldown and on cryogenic surfaces during the mission. The first risk occurs during the cooldown of the payload to cryogenic temperatures, predicting water accumulation on optical surfaces in excess of the allowable levels. To mitigate this accumulation, the temperature of the optical surfaces is controlled during cooldown through a combination of heaters and spacecraft pointing. The second risk is that over the course of the mission, is unavoidable water accumulation onto the payload thermal system’s cryogenic surfaces, possibly jeopardizing thermal performance and temperature stability, both of which are required for science success. To decontaminate any water that had collected onto cryogenic thermal system surfaces, a decontamination maneuver was designed. In this decontamination maneuver, cryogenic surfaces of the thermal system are warmed to a temperature where water will desorb by spacecraft pointing while still meeting all avoidance constraints, and thereby avoiding undue risk to the observatory hardware. Through application of the developed analytical model and inclusion of the decontamination maneuver in the mission design, SPHEREx can confidently demonstrate that it is able to decontaminate, at the start of and during the mission as needed to meet its end of life science performance requirements.

Soares, Carolos E.↗

Liquified SO 2 induced solid/cathode electrolyte interphase for lithium ion batteries

Formation of robust solid/cathode electrolyte interphases (S/CEI) is vital for long-term stability and high-performance operation of lithium-ion batteries (LIBs), particularly under high voltage regimes. However, engineering electrochemically stable S/CEIs that effectively suppress interfacial side reactions remains a key challenge. Herein, we introduce a liquefied sulfur dioxide (SO 2 )– ionic liquid complex as a fluorine-free multifunctional electrolyte additive for the first time that significantly improves the formation of sulfate/sulfite-rich S/CEI layers at both graphite and NMC811 interfaces. The unique SO 2 -N coordination with a 1,2,4-triazolide-based ionic liquid enables homogeneous SO 2 dissolution, resulting in controlled SO 2 decomposition during the initial electrochemical cycle. This decomposition yields sulfur-rich interphase species that stabilize the electrolyte-electrode interface, reduce impedance growth, and lessen electrolyte decomposition. Electrochemical tests show significantly improved cycle life, reduced polarization, and increased Coulombic efficiency for both anodes and cathodes. XPS confirms the presence of SO 2 -derived surface species that contribute to interfacial stability. In conclusion, this approach highlights a new direction for interphase engineering using liquefied gas additives and opens pathways for sulfur-based S/CEI chemistry in advanced battery systems.

Graphite↗

Stabilizing the heavily-doped and metallic phase of MoS 2 monolayers with surface functionalization

Monolayer molybdenum disulfide (MoS 2 ) is one of the most studied two-dimensional (2D) transition metal dichalcogenides that is being investigated for various optoelectronic properties, such as catalysis, sensors, photovoltaics, and batteries. One such property that makes this material attractive is the ease in which 2D MoS 2 can be converted between the semiconducting (2H) and metallic/semi-metallic (1T/1T') phases or heavily n-type doped 2H phase with ion intercalation, strain, or excess negative charge. Using n-butyl lithium (BuLi) immersion treatments, we achieve 2H MoS 2 monolayers that are heavily n-type doped with shorter immersion times (10–120 mins) or conversion to the 1T/1T' phase with longer immersion times (6–24 h); however, these doped/converted monolayers are not stable and promptly revert back to the initial 2H phase upon exposure to air. To overcome this issue and maintain the modification of the monolayer MoS 2 upon air exposure, we use BuLi treatments plus surface functionalization p-(CH 3 CH 2 ) 2 NPh-MoS 2 (Et 2 N-MoS 2 )—to maintain heavily n-type doped 2H phase or the 1T/1T' phase, which is preserved for over two weeks when on indium tin oxide or sapphire substrates. We also determine that the low sheet resistance and metallic-like properties correlate with the BuLi immersion times. These modified MoS 2 materials are characterized with confocal Raman/photoluminescence, absorption, x-ray photoelectron spectroscopy as well as scanning Kelvin probe microscopy, scanning electrochemical microscopy, and four-point probe sheet resistance measurements to quantify the differences in the monolayer optoelectronic properties. We will demonstrate chemical methodologies to control the modified monolayer MoS 2 that likely extend to other 2D transition metal dichalcogenides, which will greatly expand the uses for these nanomaterials.

2D TMDC↗

Insights into the Stability of Zeolitic Imidazolate Frameworks in Humid Acidic Environments from First-Principles Calculations

Understanding the degradation mechanisms of zeolitic imidazolate frameworks (ZIFs) is crucial to improve their chemical stability and realize their potential industrial applications. In this work, we conduct a comprehensive study utilizing dispersion-corrected density functional theory calculations to investigate the chemical stability of bulk ZIFs and their external surfaces under conditions of acid-gas exposure. We examine the influence of steric factors such as topology and ligand functionalization on the relative chemical stability of prototypical ZIFs (ZIF-2 and ZIF-8), including their hypothetical polymorphs. We find that defect formation is more thermodynamically and kinetically favorable at ZIF external surfaces versus the bulk, and that both topology and ligand functionalization impact defect formation. In addition, we provide a detailed mechanism for the reaction of ZIFs with sulfurous and sulfuric acids, of which the latter serves as a catalyst in potential degradation reactions of ZIFs. We also provide information about the adsorption strength of a range of acid gases to defective ZIF structures, which can inform potential strategies to regenerate ZIFs and/or achieve defect engineering in these materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Reaction pathways for HCN on transition metal surfaces

In this work, the adsorption and decomposition of HCN on the Pd(111) and Ru(001) surfaces have been studied with reflection absorption infrared spectroscopy and density functional theory calculations. The results are compared to earlier studies of HCN adsorption on the Pt(111) and Cu(100) surfaces. In all cases the initial adsorption at low temperatures gives rise to a ν (C–H) stretch peak at ~3300 cm –1 , which is very close to the gas phase value indicating that the triple CN bond is retained for the adsorbed molecule. When the Pd(111) surface is heated to room temperature, the HCN is converted to the aminocarbyne species, CNH 2 , which was also observed on the Pt(111) surface. DFT calculations confirm the high stability of CNH 2 on Pd(111), and suggest a bi-molecular mechanism for its formation. When HCN on Cu(100) is heated, it desorbs without reaction. In contrast, no stable intermediates are detected on Ru(001) as the surface is heated, indicating that HCN decomposes completely to atomic species.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Ice in the Martian regolith

A number of possible morphologic indicators of ground ice on Mars are discussed, with emphasis on rampart craters and terrain softening. Geologic evidence indicates that the Martian surface has been substantially modified by the action of liquid water, and that much of that water still resides beneath the surface as ground ice. Calculations of the thermodynamic stability of ground ice on Mars suggest that it can exist very close to the surface at high latitudes, but can persist only at substantial depths near the equator. A variety of observed Martian landforms can be attributed to creep of the Martian regolith abetted by deformation of ground ice. Global mapping of creep features also supports the idea that ice is present in near-surface materials at latitudes higher than +/- 30 deg, and suggests that ice is largely absent from such materials at lower latitudes.

Squyres, S. W.↗

Tiperon

A control surface for an air vehicle (e.g., an aircraft, rocket, or missile) is useful for flight control at both subsonic and supersonic speeds. The control surface defines the outboardmost tip of a flight structure (e.g., a wing, tail or other stabilizer) of the air vehicle. Hence, the control surface is referred to as a `tiperon`. The tiperon has an approximately L-shaped configuration, and can be rotated relative to a fixed portion of the flight structure about a control axis. The respective surface areas of the tiperon sections forward and aft of the control axis are proportioned to place the subsonic center of pressure aft of the control axis to enhance aircraft control, and preferably also forward of the centroid of tiperon surface area. Also, the control surface sections forward and aft of the control axis are preferably mass-balanced, or at least nearly so, to enhance aircraft control at supersonic speeds. Either of the tiperon sections forward and aft of the control axis can be tapered to reduce the dependence of the moment exerted by air flow about the control axis, upon the tiperon's angle-of-attack. The tiperon also has enough surface area to control the air vehicle, even at low airspeeds. The invention is also directed to air vehicles incorporating one or more such control surfaces.

Lewis, Carl E.↗

Li-rich Li[Li1/6Fe1/6Ni1/6Mn1/2]O2 (LFNMO) Cathodes: Atomic Scale Insight on the Mechanisms of Cycling Decay and of the Improvement due to Cobalt Phosphate Surface Modification

Lithium-rich Li[Li1/6Fe1/6Ni1/6Mn1/2]O2(0.4Li2MnO3-0.6LiFe1/3Ni1/3Mn1/3O2, LFNMO) is a new member of the xLi2MnO3·(1-x)LiMO2 family of high capacity - high voltage LIB cathodes. Unfortunately, it suffers from the severe degradation during cycling both in terms of reversible capacity and operating voltage. We are the first to document the corresponding degradation occurring in LFNMO at an atomic scale using aberration- corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) , as well as tracing the elemental crossover to the Li metal anode using XPS. We also demonstrate that a phosphate coating significantly boosts LFNMO cycling stability and rate capability. Due to cycling, the unmodified LFNMO undergoes extensive elemental dissolution (especially Mn) and O loss, forming Kirkendall-type voids. The associated structural degradation is from the as-synthesized R-3m layered structure to a disordered rock-salt phase. Prior to cycling, the phosphate coating shares the crystallography of the parent material. During cycling, a 2-3 nm thick disordered Co-based rock-salt structure is formed on the Mod-LFNMO surface, while the bulk material retains R-3m crystallography. Electrochemical impedance spectroscopy (EIS) analysis highlights how the phosphide treatment stabilizes the charge transfer resistance (RCT), the CEI resistance (RCEI), and the lithium ion diffusion coefficient (DLi). XPS analysis demonstrates that the coating also reduces the amount of cross-over Mn, Fe and especially Ni deposited on the Li metal anode, which is expected to lead to a more stable SEI layer during cycling. These combined cathode - anode findings significantly advance the microstructural design principles for next generation Li-rich cathode materials and coatings.

: high voltage cathode, Li - and Mn - rich cathode↗

Ligand-Dependent Energetics for Dehydrogenation: Implications in Li-Ion Battery Electrolyte Stability and Selective Oxidation Catalysis of Hydrogen-Containing Molecules

The hydrogen adsorption energetics on the surface of inorganic compounds can be used to predict electrolyte stability in Li-ion batteries and catalytic activity for selective oxidation of small molecules such as H 2 and CH 4 . Using first-principles density functional theory (DFT), the hydrogen adsorption was found to be unfavorable on high-band-gap insulators, which could be attributed to a lower energy level associated with adsorbed hydrogen relative to the bottom of the conduction band. In contrast, the hydrogen adsorption was shown to be the most favorable on metallic and semiconducting compounds, which results from an electron transfer from adsorbed hydrogen to the Fermi level or the bottom of the conduction band. Of significance, computed hydrogen adsorption energetics on insulating, semiconducting, and metallic oxides; phosphates; fluorides; and sulfides were decreased by lowering the ligand p band center, while the energy penalty for ligand vacancy formation was increased, indicative of decreased surface reducibility. A statistical regression analysis, where 16 structural and electronic parameters such as metal–ligand distance, electronegativity difference, Bader charges, bulk and surface metal and ligand band centers, band gap, ligand band width, and work function were examined, further showed that the surface ligand p band center is the most accurate single descriptor that governs the hydrogen adsorption tendency, and additional considerations of the band gap and average metal–ligand distance further reconcile the differences among compounds with different ligands/structures, whose ligand bands are different in shape and width. We discuss the implications of these findings for passivating coatings and design of catalysts and the need for novel theoretical methods to accurately estimate these quantities from first principles. Furthermore, these results establish a universal design principle for future high-throughput studies aiming to design electrode surfaces to minimize electrolyte oxidation by dehydrogenation in Li-ion batteries and enhance the H–H and C–H activation for selective oxidation catalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Evaluation of platinum resistance thermometers

An evaluation procedure for the characterization of industrial platinum resistance thermometers (PRTs) for use in the temperature range -120 to 160 C was investigated. This evaluation procedure consisted of calibration, thermal stability and hysteresis testing of four surface measuring PRTs. Five different calibration schemes were investigated for these sensors. The IPTS-68 formulation produced the most accurate result, yielding average sensor systematic error of 0.02 C and random error of 0.1 C. The sensors were checked for thermal stability by successive and thermal cycling between room temperature, 160 C, and boiling point of nitrogen. All the PRTs suffered from instability and hysteresis. The applicability of the self-heating technique as an in situ method for checking the calibration of PRTs located inside wind tunnels was investigated.

Daryabeigi, Kamran↗

From bulk to surface: Structure and dynamics of amorphous alumina from deep potential molecular dynamics

Understanding the atomic-scale structure and dynamics of amorphous oxide surfaces is essential for interpreting their chemical reactivity, mechanical stability, and interfacial behavior, yet direct experimental characterization remains challenging. We employ Deep Potential (DP) molecular dynamics to generate large-scale, ab initio -quality models of amorphous Al 2 O 3 bulk glasses and melt-quenched free surfaces, enabling a quantitative analysis of both structure and relaxation dynamics with statistical confidence inaccessible to direct ab initio simulation. The trained DP model reproduces experimental liquid and glass structure, captures the cooling-rate dependence of the bulk glass transition, and corrects systematic biases in the polyhedral populations predicted by widely used classical force fields. At the free surface, mass density recovers to bulk values over ~10 Å, while local coordination requires a slightly wider subsurface region to fully converge. The outermost layer is oxygen-enriched, exhibits altered polyhedral connectivity with contracted Al–O bonds, and hosts a broad population of under-coordinated motifs (notably AlO 3 and OAl 2 ) whose abundances are governed by glass stability. These under-coordinated surface motifs exhibit distinct vibrational signatures and occur as locally paired Lewis acid and Brønsted base sites consistent with bond-valence compensation, yet remain spatially dispersed rather than aggregating into extended clusters. Despite this pronounced structural heterogeneity, surface relaxation and the glass-transition temperature remain comparable to their bulk counterparts, suggesting that the disordered surface is kinetically stable once formed. Together, these results establish a molecular-level picture of amorphous alumina surfaces and demonstrate the capability of machine-learned potentials to resolve structure–property relationships in disordered oxide interfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗