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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Stabilizing Ru-Formyl CO 2 Reduction Intermediates by Formation of Lewis Acid–Base Adducts: A Combined 2DIR and NMR Study

This work demonstrates how the stability of a Ru(II) formyl complex (cis-[Ru(bpy) 2 (CO)(CHO)][PF 6 ]), which is known to decarbonylate to form the metal hydride complex, is greatly enhanced by the addition of a Lewis acidic cation (Li + or Mg 2+ ). Multinuclear NMR is used to measure equilibrium constants of adduct formation, and then ultrafast 2DIR spectroscopy is applied to determine how the electronic structure and local molecular dynamics change upon complexation of the formyl ligand with the Lewis acid. We attribute the stabilization of the complex to the formation of a carbene-like structure where the bond strength between the Ru and the formyl group increases. The change in electronic structure is evidenced by steady-state NMR spectroscopy and DFT calculations. 2DIR measurements further confirm both the complexation of the formyl ligand with the Lewis acid and the change in electronic structure, where changes in vibrational frequency, relaxation kinetics, and a slowdown in the time scale of rotation about the metal-formyl bond are observed in the presence of Lewis acids.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Molecular Design of Al(II) Intermediates for Small Molecule Activation

Promoting societally important small molecule activation processes with earth-abundant metals is foundational for a sustainable chemistry future. In this context, mapping new reaction pathways that would enable abundant main-group elements to mimic the behaviors of d- and f-block elements is facilitated by exploring unusual oxidation states. The most abundant metal on earth, aluminum, has been well studied in the Lewis acidic +III and Lewis basic +I oxidation states but rarely in the potentially biphilic +II oxidation state until recently, when a renaissance of Al(II) chemistry emerged from a range of research groups. In this Perspective, we review the chemistry of mononuclear Al radicals, including both Al-centered radicals (i.e., Al(II) compounds) and redox non-innocent systems (i.e., formally Al(II) species that are physically Al(III) with ligand-centered radicals), with an emphasis on small molecule reactivity. We also provide a meta-analysis of the Al(II) literature to summarize how different design strategies (e.g., redox non-innocence, strained coordination geometries) have been shown to impart biphilic character to Al radicals and tune their behavior, thus allowing Al radicals to mimic the chemistry of certain d- and f-block metal ions such as Ti(III) and Sm(II). We expect these molecular design concepts to inform future Al(II) studies as the chemistry of this unusual oxidation state of Al continues to grow.

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

Trafficking of a nitrogenase FeMo-cofactor assembly intermediate

The maturation of the unique FeMo-cofactor of molybdenum nitrogenase is a multistep process requiring the sequential action of a series of maturase complexes. As a final step, the NifEN complex forms FeMo-cofactor from the precursor NifB-co, also called L-cluster, through replacement of an apical iron ion by molybdenum and the attachment of an organic homocitrate ligand. NifB-co is delivered by a small cofactor chaperone, NifX, and initially bound near the surface of the maturase NifEN. Here, we report high-resolution cryo-electron microscopy structures of NifEN in complex with NifX, showing NifB-co binding to NifEN in full detail, capturing both interacting partners in the act of cluster transfer. In a dynamic transfer complex, the large metal cluster is coordinated by single residues from both NifEN and NifX. In silico studies concur with these structures but suggest a third, internal conversion site where cluster maturation likely takes place.

metalloproteins↗
DOE OSTI2024

Infrared spectroscopy of the syn -methyl-substituted Criegee intermediate: A combined experimental and theoretical study

An IR–vacuum ultraviolet (VUV) ion-dip spectroscopy method is utilized to examine the IR spectrum of acetaldehyde oxide (CH3CHOO) in the overtone CH stretch (2νCH) spectral region. IR activation creates a depletion of the ground state population that reduces the VUV photoionization signal on the parent mass channel. IR activation of the more stable and populated syn-CH3CHOO conformer results in rapid unimolecular decay to OH + vinoxy products and makes the most significant contribution to the observed spectrum. The resultant IR–VUV ion-dip spectrum of CH3CHOO is similar to that obtained previously for syn-CH3CHOO using IR action spectroscopy with UV laser-induced fluorescence detection of OH products. The prominent IR features at 5984 and 6081 cm−1 are also observed using UV + VUV photoionization of OH products. Complementary theoretical calculations utilizing a general implementation of second-order vibrational perturbation theory provide new insights on the vibrational transitions that give rise to the experimental spectrum in the overtone CH stretch region. The introduction of physically motivated small shifts of the harmonic frequencies yields remarkably improved agreement between experiment and theory in the overtone CH stretch region. The prominent features are assigned as highly mixed states with contributions from two quanta of CH stretch and/or a combination of CH stretch with an overtone in mode 4. The generality of this approach is demonstrated by applying it to three different levels of electronic structure theory/basis sets, all of which provide spectra that are virtually indistinguishable despite showing large deviations prior to introducing the shifts to the harmonic frequencies.

Chemistry↗
DOE OSTI2024

Infrared signature of the hydroperoxyalkyl intermediate (·QOOH) in cyclohexane oxidation: An isomer-resolved spectroscopic study

Infrared (IR) action spectroscopy is utilized to characterize carbon-centered hydroperoxy-cyclohexyl radicals (·QOOH) transiently formed in cyclohexane oxidation. The oxidation pathway leads to three nearly degenerate ·QOOH isomers, β-, γ-, and δ-QOOH, which are generated in the laboratory by H-atom abstraction from the corresponding ring sites of the cyclohexyl hydroperoxide (CHHP) precursor. The IR spectral features of jet-cooled and stabilized ·QOOH radicals are observed from 3590 to 7010 cm −1 (∼10–20 kcal mol −1 ) at energies in the vicinity of the transition state (TS) barrier leading to OH radicals that are detected by ultraviolet laser-induced fluorescence. The experimental approach affords selective detection of β-QOOH, arising from its significantly lower TS barrier to OH products compared to γ and δ isomers, which results in rapid unimolecular decay and near unity branching to OH products. The observed IR spectrum of β-QOOH includes fundamental and overtone OH stretch transitions, overtone CH stretch transitions, and combination bands involving OH or CH stretch with lower frequency modes. The assignment of β-QOOH spectral features is guided by anharmonic frequencies and intensities computed using second-order vibrational perturbation theory. The overtone OH stretch (2ν OH ) of β-QOOH is shifted only a few wavenumbers from that observed for the CHHP precursor, yet they are readily distinguished by their prompt vs slow dissociation rates to OH products.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Multistep catalytic abiotic CO2 conversion to sugars through C1 intermediates

Carbon dioxide (CO2) to multicarbon (Cn) upgrading for commodity chemicals, fuel production, or artificial food synthesis using renewable energy input is a golden target for researchers in sustainable carbon emission reduction. Here, we explore and analyze a flexible modular roadmap for the task, utilizing sequential electro-, photo-, and organocatalysis to develop a strategy for CO2 conversion using the key and elusive formaldehyde precursor of interest for sugar generation. We study the electrochemical carbon dioxide reduction reaction to methanol in a flow cell and its discontinuous photooxidation to formaldehyde (PMOR) with excellent selectivity. Utilizing a highly active N-heterocyclic carbene catalyst enables tunable generation of C4-C6 aldoses without undesirable byproducts, with carbon conversion yield reaching 60 to 80% for desired pentose, tetrose, and triose product mixtures and over 20% for hexose. This approach presents a roadmap for CO2 valorization, aiming to bridge carbon waste streams with sustainable sugar synthesis and opening broad avenues for green chemical production.

CO2 valorization↗
DOE OSTI2025

The role of intermediate ΔΔ states in nucleon–nucleon scattering in the large-Nc and unitary limits, and ΔΔ and ΩΩ scattering

We explore potential explanations for why using large-Nc (Nc is the number of colors) scaling to determine the relative size of few-nucleon low-energy operators agrees with experiment even when dynamical Δ’s are not explicitly included. Given that the large-Nc analysis is predicated on the nucleons and Δ’s being degenerate, this is a curious result. We show that for purely S-wave interactions the relationships dictated by large-Nc scaling are unaffected whether the Δ is included or not. In the case of higher partial waves that do not mix with S-waves, the impact of the Δ is perturbative, which makes the agreement with naive (Δ-less) large-Nc ordering unsurprising. For higher partial waves that mix with S-waves, the nucleon and Δ would need to decouple to get agreement with naive large-Nc ordering. We find all NN, ΔN, and ΔΔ low energy coefficients for leading-order baryon–baryon scattering in Δ-full pionless effective field theory in terms of the two independent parameters dictated by the SU(2F) spin-flavor symmetry that arises in the Nc → ∞ limit. Because of recent lattice quantum chromodynamics results and experimental interest, we extend our analysis to the three-flavor case to study ΩΩ scattering. We show that in the unitary limit (where scattering lengths become infinite) one of the two SU(2F) parameters is driven to zero, resulting in enhanced symmetries, which agree with those found in spin-1/2 entanglement studies.

Richardson, Thomas R↗
DOE OSTI2025

Evidence for large baryonic feedback at low and intermediate redshifts from kinematic Sunyaev-Zel’dovich observations with ACT and DESI photometric galaxies

Recent advances in cosmological observations have provided an unprecedented opportunity to investigate the distribution of baryons relative to the underlying matter. In this work, we show that the gas is more extended than the dark matter, and the amount of baryonic feedback at $z \lesssim 1$ disfavors low-feedback models such as that of state-of-the-art hydrodynamical simulation IllustrisTNG compared with high-feedback models such as that of the original Illustris simulation. This has important implications for bridging the gap between theory and observations and understanding galaxy formation and evolution. Furthermore, a better grasp of the baryon-dark matter link is critical to future cosmological analyses, which are currently impeded by our limited knowledge of baryonic feedback. Here, we measure the kinematic Sunyaev-Zel'dovich (kSZ) effect from the Atacama Cosmology Telescope (ACT), stacked on the luminous red galaxy (LRG) sample of the Dark Energy Spectroscopic Instrument (DESI) imaging survey. This is the first analysis to use photometric redshifts for reconstructing galaxy velocities. Due to the large number of galaxies comprising the DESI imaging survey, this is the highest signal-to-noise stacked kSZ measurement to date: we detect the signal at 13$σ$, finding strong evidence that the gas is more spread out than the dark matter, as well as a preference for larger feedback compared to some commonly used state-of-the-art hydrodynamical simulations. Here, our work opens up the possibility of recalibrating large hydrodynamical simulations using the kSZ effect. In addition, our findings highlight the importance of properly accounting for baryonic feedback with future surveys such as LSST through direct probes such as the kSZ, and shed light on long-standing enigmas in astrophysics, such as the “missing baryon” problem.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Pressure dependence of intermediate-range order and elastic properties of glassy Baltic amber

Amber is a unique example of a fragile glass that has been extensively aged below its glass transition temperature, thus reaching a state that is not accessible under normal experimental conditions. In this paper, we studied the medium-range order of Baltic amber by x-ray diffraction (XRD) at high pressures. The pressure dependences of the low-angle XRD intensity between 0 and 5 Å -1 were measured from 0 to 7.3 GPa by the energy-dispersive XRD. The first diffraction peak at 1.1 Å -1 and ambient pressure has a doublet structure consisting of the first sharp diffraction peak (FSDP) at 1.05 Å -1 and the second feature at 1.40 Å -1 . The peak position and the width of the FSDP increase as the pressure increases, while the intensity of the FSDP decreases. Below P 0 = 2.4 GPa, the rapid increase of the FSDP peak position was observed, while above P 0 , the gradual increase was observed. Below P 0 , voids and holes in a relatively low-density state are suppressed, whereas above P 0 , the suppression becomes mild. Such a change suggests the crossover from the low- to high-density state at P 0 . There is a close correlation between the pressure dependence of XRD and previously reported sound velocity results. The correlation between the mean-square fluctuation of the shear modulus on the nanometer scale and fragility in amber and other glass formers is also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2025

State of the Art in Thermal Catalytic Upgrading of Biomass and Biomass-Derived Intermediates

Biomass-derived energy sources represent a promising domestic route for fuel and chemical production, taking advantage of largely underutilized biological and waste resources. Heterogeneous catalysis plays a key role in these biomass conversion processes, as reflected by all American Society for Testing and Materials–approved pathways for producing sustainable aviation fuel proceeding through a catalytic step. This concise review seeks to establish the state of the art in thermal catalytic process development for various biomass-derived feedstocks and the current enabling capabilities that aid this development. Research needs are identified and described throughout the article, as further advancements in heterogeneous catalysis are required to improve the affordability and realize the full potential of biomass-derived products.

09 BIOMASS FUELS↗