Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “unprecedented”

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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Unveiling the nanoscale architectures and dynamics of protein assembly with in situ atomic force microscopy

Proteins play a vital role in different biological processes by forming complexes through precise folding with exclusive inter- and intra-molecular interactions. Understanding the structural and regulatory mechanisms underlying protein complex formation provides insights into biophysical processes. Furthermore, the principle of protein assembly gives guidelines for new biomimetic materials with potential applications in medicine, energy, and nanotechnology. Atomic force microscopy (AFM) is a powerful tool for investigating protein assembly and interactions across spatial scales (single molecules to cells) and temporal scales (milliseconds to days). It has significantly contributed to understanding nanoscale architectures, inter- and intra-molecular interactions, and regulatory elements that determine protein structures, assemblies, and functions. This review describes recent advancements in elucidating protein assemblies with in situ AFM. We discuss the structures, diffusions, interactions, and assembly dynamics of proteins captured by conventional and high-speed AFM in near-native environments and recent AFM developments in the multimodal high-resolution imaging, bimodal imaging, live cell imaging, and machine-learning-enhanced data analysis. These approaches show the significance of broadening the horizons of AFM and enable unprecedented explorations of protein assembly for biomaterial design and biomedical research.

36 MATERIALS SCIENCE↗
DOE OSTI2020

A Roadmap for Reaching the Potential of Brain-Derived Computing

Neuromorphic computing is a critical future technology for the computing industry, but it has yet to achieve its promise and has struggled to establish a cohesive research community. A large part of the challenge is that full realization of the potential of brain inspiration requires advances in both device hardware, computing architectures, and algorithms. This simultaneous development across technology scales is unprecedented in the computing field. This article presents a strategy, framed by market and policy pressures, for moving past these current technological and cultural hurdles to realize its full impact across technology. Achieving the full potential of brain-derived algorithms as well as post-complementary metal-oxide-semiconductor (CMOS) scaling neuromorphic hardware requires appropriately balancing the near-term opportunities of deep learning applications with the long-term potential of less understood opportunities in neural computing.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2020

Why Boron Nitride is such a Selective Catalyst for the Oxidative Dehydrogenation of Propane

Abstract Boron‐containing materials, and in particular boron nitride, have recently been identified as highly selective catalysts for the oxidative dehydrogenation of alkanes such as propane. To date, no mechanism exists that can explain both the unprecedented selectivity, the observed surface oxyfunctionalization, and the peculiar kinetic features of this reaction. We combine catalytic activity measurements with quantum chemical calculations to put forward a bold new hypothesis. We argue that the remarkable product distribution can be rationalized by a combination of surface‐mediated formation of radicals over metastable sites, and their sequential propagation in the gas phase. Based on known radical propagation steps, we quantitatively describe the oxygen pressure‐dependent relative formation of the main product propylene and by‐product ethylene. Free radical intermediates most likely differentiate this catalytic system from less selective vanadium‐based catalysts.

Venegas, Juan M.↗
DOE OSTI2020

The Exceptional Diversity of Homoleptic Uranium–Methyl Complexes

Abstract Homoleptic σ‐bonded uranium–alkyl complexes have been a synthetic target since the Manhattan Project. The current study describes the synthesis and characterization of several unprecedented uranium–methyl complexes. Amongst these complexes, the first example of a homoleptic uranium–alkyl dimer, [Li(THF) 4 ] 2 [U 2 (CH 3 ) 10 ], as well as a seven‐coordinate uranium–methyl monomer, {Li(OEt 2 )Li(OEt 2 ) 2 UMe 7 Li} n were both crystallographically identified. The diversity of complexes reported herein provides critical insight into the structural diversity, electronic structure and bonding in uranium–alkyl chemistry.

Sears, Jeffrey D.↗
DOE OSTI2021

Thermal Unequilibrium of PdSn Intermetallic Nanocatalysts: From In Situ Tailored Synthesis to Unexpected Hydrogenation Selectivity

Abstract Effective control on chemoselectivity in the catalytic hydrogenation of C=O over C=C bonds is uncommon with Pd‐based catalysts because of the favored adsorption of C=C bonds on Pd surface. Here we report a unique orthorhombic PdSn intermetallic phase with unprecedented chemoselectivity toward C=O hydrogenation. We observed the formation and metastability of this PdSn phase in situ. During a natural cooling process, the PdSn nanoparticles readily revert to the favored Pd 3 Sn 2 phase. Instead, using a thermal quenching method, we prepared a pure‐phase PdSn nanocatalyst. PdSn shows an >96 % selectivity toward hydrogenating C=O bonds of various α,β‐unsaturated aldehydes, highest in reported Pd‐based catalysts. Further study suggests that efficient quenching prevents the reversion from PdSn‐ to Pd 3 Sn 2 ‐structured surface, the key to the desired catalytic performance. Density functional theory calculations and analysis of reaction kinetics provide an explanation for the observed high selectivity.

Chen, Minda↗
DOE OSTI2021

Site‐Specific Reduction‐Induced Hydrogenation of a Helical Bilayer Nanographene with K and Rb Metals: Electron Multiaddition and Selective Rb + Complexation

Abstract The chemical reduction of π‐conjugated bilayer nanographene 1 (C 138 H 120 ) with K and Rb in the presence of 18‐crown‐6 affords [K + (18‐crown‐6)(THF) 2 ][{K + (18‐crown‐6)} 2 (THF) 0.5 ][C 138 H 122 3− ] ( 2 ) and [Rb + (18‐crown‐6) 2 ][{Rb + (18‐crown‐6)} 2 (C 138 H 122 3− )] ( 3 ). Whereas K + cations are fully solvent‐separated from the trianionic core thus affording a “naked” 1 .3 − anion, Rb + cations are coordinated to the negatively charged layers of 1 .3 − . According to DFT calculations, the localization of the first two electrons in the helicene moiety leads to an unprecedented site‐specific hydrogenation process at the carbon atoms located on the edge of the helicene backbone. This uncommon reduction‐induced site‐specific hydrogenation provokes dramatic changes in the (electronic) structure of 1 as the helicene backbone becomes more compressed and twisted upon chemical reduction, which results in a clear slippage of the bilayers.

Zhou, Zheng↗
DOE OSTI2022

High‐Field NMR, Reactivity, and DFT Modeling Reveal the γ‐Al 2 O 3 Surface Hydroxyl Network**

Abstract Aluminas are strategic materials used in many major industrial processes, either as catalyst supports or as catalysts in their own right. The transition alumina γ‐Al 2 O 3 is a privileged support, whose reactivity can be tuned by thermal activation. This study provides a qualitative and quantitative assessment of the hydroxyl groups present on the surface of γ‐Al 2 O 3 at three different dehydroxylation temperatures. The principal [AlOH] configurations are identified and described in unprecedented detail at the molecular level. The structures were established by combining information from high‐field 1 H and 27 Al solid‐state NMR, IR spectroscopy and DFT calculations, as well as selective reactivity studies. Finally, the relationship between the hydroxyl structures and the molecular‐level structures of the active sites in catalytic alkane metathesis is discussed.

Merle, Nicolas↗
DOE OSTI2022

Fluorinated Rocksalt Cathode with Ultra‐high Active Li Content for Lithium‐ion Batteries

Abstract The key to increasing the energy density of lithium‐ion batteries is to incorporate high contents of extractable Li into the cathode. Unfortunately, this triggers formidable challenges including structural instability and irreversible chemistry under operation. Here, we report a new kind of ultra‐high Li compound: Li 4+ x MoO 5 F x (1≤ x ≤3) for cathode with an unprecedented level of electrochemically active Li (>3 Li + per formula), delivering a reversible capacity up to 438 mAh g −1 . Unlike other reported Li‐rich cathodes, Li 4+ x MoO 5 F x presents distinguished structure stability to immunize against irreversible behaviors. Through spectroscopic and electrochemical techniques, we find an anionic redox‐dominated charge compensation with negligible oxygen release and voltage decay. Our theoretical analysis reveals a “reductive effect” of high‐level fluorination stabilizes the anionic redox by reducing the oxygen ions in pure‐Li conditions, enabling a facile, reversible, and high Li‐portion cycling.

Pei, Yi↗
DOE OSTI2022

Self‐Assembly of Helical Nanofibrous Chiral Covalent Organic Frameworks

Abstract Despite significant progress on the design and synthesis of covalent organic frameworks (COFs), precise control over microstructures of such materials remains challenging. Herein, two chiral COFs with well‐defined one‐handed double‐helical nanofibrous morphologies were constructed via an unprecedented template‐free method, capitalizing on the diastereoselective formation of aminal linkages. Detailed time‐dependent experiments reveal the spontaneous transformation of initial rod‐like aggregates into the double‐helical microstructures. We have further demonstrated that the helical chirality and circular dichroism signal can be facilely inversed by simply adjusting the amount of acetic acid during synthesis. Moreover, by transferring chirality to achiral fluorescent molecular adsorbents, the helical COF nanostructures can effectively induce circularly polarized luminescence with the highest luminescent asymmetric factor ( g lum ) up to ≈0.01.

Tang, Xihao↗
DOE OSTI2023

Ene Reductase Enabled Intramolecular β–C–H Functionalization of Substituted Cyclohexanones for Efficient Synthesis of Bridged Bicyclic Nitrogen Scaffolds

Herein we report that ene reductases (EREDs) can facilitate an unprecedented intramolecular β-C–H functionalization reaction for the synthesis of bridged bicyclic nitrogen heterocycles containing the 6-azabicyclo[3.2.1]octane scaffold. To streamline the synthesis of these privileged motifs, we developed a gram-scale one-pot chemoenzymatic cascade by combining iridium photocatalysis with EREDs, using readily available N-phenylglycines and cyclohexenones that can be obtained from biomass. Further derivatization using enzymatic or chemical methods can convert 6-azabicyclo[3.2.1]octan-3-one into 6-azabicyclo[3.2.1]octan-3α-ols, which can be potentially utilized for the synthesis of azaprophen and its analogues for drug discovery. Furthermore, mechanistic studies revealed the reaction requires oxygen, presumably to produce oxidized flavin, which can selectively dehydrogenate the 3-substituted cyclohexanone derivatives to form the α,β-unsaturated ketone, which subsequently undergoes spontaneous intramolecular aza-Michael addition under basic conditions.

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

Divergent Stabilities of Tetravalent Cerium, Uranium, and Neptunium Imidophosphorane Complexes**

Abstract The study of the redox chemistry of mid‐actinides (U−Pu) has historically relied on cerium as a model, due to the accessibility of trivalent and tetravalent oxidation states for these ions. Recently, dramatic shifts of lanthanide 4+/3+ non‐aqueous redox couples have been established within a homoleptic imidophosphorane ligand framework. Herein we extend the chemistry of the imidophosphorane ligand (NPC=[N=P t Bu(pyrr) 2 ] − ; pyrr=pyrrolidinyl) to tetrahomoleptic NPC complexes of neptunium and cerium ( 1‐M , 2‐M , M=Np, Ce) and present comparative structural, electrochemical, and theoretical studies of these complexes. Large cathodic shifts in the M 4+/3+ (M=Ce, U, Np) couples underpin the stabilization of higher metal oxidation states owing to the strongly donating nature of the NPC ligands, providing access to the U 5+/4+ , U 6+/5+ , and to an unprecedented, well‐behaved Np 5+/4+ redox couple. The differences in the chemical redox properties of the U vs . Ce and Np complexes are rationalized based on their redox potentials, degree of structural rearrangement upon reduction/oxidation, relative molecular orbital energies, and orbital composition analyses employing density functional theory.

Otte, Kaitlyn S.↗
DOE OSTI2023

Tetracopper σ‐Bound μ ‐Acetylide and ‐Diyne Units Stabilized by a Naphthyridine‐based Dinucleating Ligand

Abstract Reactions of a dicopper(I) tert ‐butoxide complex with alkynes possessing boryl or silyl capping groups resulted in formation of unprecedented tetracopper(I) μ ‐acetylide/diyne complexes that were characterized by NMR and UV/Vis spectroscopy, mass spectrometry and single‐crystal X‐ray diffraction. These compounds possess an unusual μ 4 ‐ η 1 : η 1 : η 1 : η 1 coordination mode for the bridging organic fragment, enforced by the rigid and dinucleating nature of the ligand utilized. Thus, the central π system remains unperturbed and accessible for subsequent reactivity and modification. This has been corroborated by addition of a fifth copper atom, giving rise to a pentacopper acetylide complex. This work may provide a new approach by which metal‐metal cooperativity can be exploited in the transformation of acetylide and diyne groups to a variety of substrates, or as a starting point for the controlled synthesis of copper(I) alkyne‐containing clusters.

Ríos, Pablo↗
DOE OSTI2023

Mixed‐Valence Cu I /Cu III Metal–Organic Frameworks with Non‐innocent Ligand for Multielectron Transfer

Abstract We report two novel three‐dimensional copper‐benzoquinoid metal–organic frameworks (MOFs), [Cu 4 L 3 ] n and [Cu 4 L 3 ⋅ Cu(iq) 3 ] n (LH 4 =1,4‐dicyano‐2,3,5,6‐tetrahydroxybenzene, iq=isoquinoline). Spectroscopic techniques and computational studies reveal the unprecedented mixed valency in MOFs, formal Cu(I)/Cu(III). This is the first time that formally Cu(III) species are witnessed in metal–organic extended solids. The coordination between the mixed‐valence metal and redox‐non‐innocent ligand L, which promotes through‐bond charge transfer between Cu metal sites, allows better metal‐ligand orbital overlap of the d‐π conjugation, leading to strong long‐range delocalization and semiconducting behavior. Our findings highlight the significance of the unique mixed valency between formal Cu(I) and highly‐covalent Cu(III), non‐innocent ligand, and pore environments of these bench stable Cu(III)‐containing frameworks on multielectron transfer and electrochemical properties.

Fu, Shang‐Yuan↗
DOE OSTI2024

Steam‐Assisted Selective CO 2 Hydrogenation to Ethanol over Ru−In Catalysts

Abstract Multicomponent catalysts can be designed to synergistically combine reaction intermediates at interfacial active sites, but restructuring makes systematic control and understanding of such dynamics challenging. We here unveil how reducibility and mobility of indium oxide species in Ru‐based catalysts crucially control the direct, selective conversion of CO 2 to ethanol. When uncontrolled, reduced indium oxide species occupy the Ru surface, leading to deactivation. With the addition of steam as a mild oxidant and using porous polymer layers to control In mobility, Ru−In 2 O 3 interface sites are stabilized, and ethanol can be produced with superior overall selectivity (70 %, rest CO). Our work highlights how engineering of bifunctional active ensembles enables cooperativity and synergy at tailored interfaces, which unlocks unprecedented performance in heterogeneous catalysts.

Zhou, Chengshuang↗
DOE OSTI2024

Ion‐Specific Interactions Engender Dynamic and Tailorable Properties in Biomimetic Cationic Polyelectrolytes

Abstract Biomaterials such as spider silk and mussel byssi are fabricated by the dynamic manipulation of intra‐ and intermolecular biopolymer interactions. Organisms modulate solution parameters, such as pH and ion co‐solute concentration, to effect these processes. These biofabrication schemes provide a conceptual framework to develop new dynamic and responsive abiotic soft material systems. Towards these ends, the chemical diversity of readily available ionic compounds offers a broad palette to manipulate the physicochemical properties of polyelectrolytes via ion‐specific interactions. In this study, we show for the first time that the ion‐specific interactions of biomimetic polyelectrolytes engenders a variety of phase separation behaviors, creating dynamic thermal‐ and ion‐responsive soft matter that exhibits a spectrum of physical properties, spanning viscous fluids to viscoelastic and viscoplastic solids. These ion‐dependent characteristics are further rendered general by the merger of lysine and phenylalanine into a single, amphiphilic vinyl monomer. The unprecedented breadth, precision, and dynamicity in the reported ion‐dependent phase behaviors thus introduce a broad array of opportunities for the future development of responsive soft matter; properties that are poised to drive developments in critical areas such as chemical sensing, soft robotics, and additive manufacturing.

Aubrecht, Filip J.↗
DOE OSTI2020

Why Boron Nitride is such a Selective Catalyst for the Oxidative Dehydrogenation of Propane

Boron–containing materials, and in particular boron nitride, have recently been identified as highly selective catalysts for the oxidative dehydrogenation of alkanes such as propane. To date, no mechanism exists that can explain both the unprecedented selectivity, the observed surface oxyfunctionalization, and the peculiar kinetic features of this reaction. Here, we combine catalytic activity measurements with quantum chemical calculations to put forward a bold new hypothesis. We argue that the remarkable product distribution can be rationalized by a combination of surface–mediated formation of radicals over metastable sites, and their sequential propagation in the gas phase. Based on known radical propagation steps, we quantitatively describe the oxygen pressure–dependent relative formation of the main product propylene and by–product ethylene. Free radical intermediates most likely differentiate this catalytic system from less selective vanadium–based catalysts.

03 NATURAL GAS↗
DOE OSTI2020

The Exceptional Diversity of Homoleptic Uranium–Methyl Complexes

Homoleptic σ-bonded uranium–alkyl complexes have been a synthetic target since the Manhattan Project. The current study describes the synthesis and characterization of several unprecedented uranium–methyl complexes. Amongst these complexes, the first example of a homoleptic uranium–alkyl dimer, [Li(THF) 4 ] 2 [U 2 (CH 3 ) 10 ], as well as a seven-coordinate uranium–methyl monomer, {Li(OEt 2 )Li(OEt 2 ) 2 UMe 7 Li} n were both crystallographically identified. We report the diversity of complexes reported herein provides critical insight into the structural diversity, electronic structure and bonding in uranium–alkyl chemistry.

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

Thermal Unequilibrium of PdSn Intermetallic Nanocatalysts: From In Situ Tailored Synthesis to Unexpected Hydrogenation Selectivity

Effective control on chemoselectivity in the catalytic hydrogenation of C=O over C=C bonds is uncommon with Pd-based catalysts because of the favored adsorption of C=C bonds on Pd surface. Here we report a unique orthorhombic PdSn intermetallic phase with unprecedented chemoselectivity toward C=O hydrogenation. We observed the formation and metastability of this PdSn phase in situ. During a natural cooling process, the PdSn nanoparticles readily revert to the favored Pd 3 Sn 2 phase. Instead, using a thermal quenching method, we prepared a pure-phase PdSn nanocatalyst. Furthermore, PdSn shows an >96% selectivity toward hydrogenating C=O bonds of various α,β-unsaturated aldehydes, highest in reported Pd-based catalysts. Further study suggests that efficient quenching prevents the reversion from PdSn- to Pd 3 Sn 2 -structured surface, the key to the desired catalytic performance. Density functional theory calculations and analysis of reaction kinetics provide an explanation for the observed high selectivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗