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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Elucidating the water–anatase TiO 2 (101) interface structure using infrared signatures and molecular dynamics

The structure and dynamics of water on solid surfaces critically affect the chemistry of materials in ambient and aqueous environments. Here, we investigate the hydrogen bonding network of water adsorbed on the majority (101) surface of anatase TiO 2 , a widely used photocatalyst, using polarization- and azimuth-resolved infrared spectroscopy combined with neural network potential molecular dynamics simulations. Our results show that one monolayer of water saturates the undercoordinated titanium (Ti 5c ) sites, forming one-dimensional chains of molecule hydrogen bonded to surface undercoordinated bridging oxygen (O 2c ) atoms. As the coverage increases, water adsorption on O 2c sites leads to significant restructuring of the water monolayer and the formation of a two-dimensional hydrogen bond network characterized by tightly bound pairs of water molecules on adjacent Ti 5c and O 2c sites. This structural motif likely persists at ambient conditions, influencing the reactions occurring there. In conclusion, the results reported here provide critical details of the structure of the water–anatase (101) interface that were previously hypothesized but unconfirmed experimentally.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Subsurface Spectroscopy of Thermal Degradation Inside an Inert Plastic Bonded Explosive (PBX) Simulant Using Feedback-Assisted Wavefront Shaping

We characterize the subsurface thermal degradation of an inert analog of high-explosive molecular crystals (Eu:Y(acac) 3 (DPEPO)) (EYAD) embedded inside of a plastic bonded explosive simulant using feedback-assisted wavefront shaping-based fluorescence and Raman spectroscopies. This technique utilizes wavefront shaping to focus pump light inside a heterogeneous material onto a target particle, which significantly improves its spectroscopic signature. We find that embedding the EYAD crystals in the heterogeneous polymer results in improved thermal stability, relative to bare crystal measurements, with the crystal remaining fluorescent to >612 K inside of the heterogeneous material, while the bare crystal’s fluorescence is fully quenched by 500 K. We hypothesize that this improvement is due to the polymer restricting the effects of EYAD melting, which occurs at 400 K and is the primary mechanism for spectroscopic changes in the temperature range explored.

Anderson, Benjamin R.↗
DOE OSTI2023

Spin–vibronic coherence drives singlet–triplet conversion

Design-specific control over the transitions between excited electronic states with different spin multiplicities is of the utmost importance in molecular and materials chemistry. Previous studies have indicated that the combination of spin-orbit and vibronic effects, collectively termed the spin-vibronic effect, can accelerate quantum-mechanically forbidden transitions at non-adiabatic crossings. However, it has been difficult to identify precise experimental manifestations of the spin-vibronic mechanism. Here we present coherence spectroscopy experiments that reveal the interplay between the spin, electronic and vibrational degrees of freedom that drive efficient singlet-triplet conversion in four structurally related dinuclear Pt(II) metal-metal-to-ligand charge-transfer (MMLCT) complexes. Photoexcitation activates the formation of a Pt-Pt bond, launching a stretching vibrational wavepacket. The molecular-structure-dependent decoherence and recoherence dynamics of this wavepacket resolve the spin-vibronic mechanism. Further, we find that vectorial motion along the Pt-Pt stretching coordinates tunes the singlet and intermediate-state energy gap irreversibly towards the conical intersection and subsequently drives formation of the lowest stable triplet state in a ratcheting fashion. This work demonstrates the viability of using vibronic coherences as probes to clarify the interplay among spin, electronic and nuclear dynamics in spin-conversion processes, and this could inspire new modular designs to tailor the properties of excited states.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

On the Dynamics of the Carbon–Bromine Bond Dissociation in the 1-Bromo-2-Methylnaphthalene Radical Anion

This paper studies the mechanism of electrochemically induced carbon–bromine dissociation in 1-Br-2-methylnaphalene in the reduction regime. In particular, the bond dissociation of the relevant radical anion is disassembled at a molecular level, exploiting quantum mechanical calculations including steady-state, equilibrium and dissociation dynamics via dynamic reaction coordinate (DRC) calculations. DRC is a molecular-dynamic-based calculation relying on an ab initio potential surface. This is to achieve a detailed picture of the dissociation process in an elementary molecular detail. From a thermodynamic point of view, all the reaction paths examined are energetically feasible. The obtained results suggest that the carbon halogen bond dissociates following the first electron uptake follow a stepwise mechanism. Indeed, the formation of the bromide anion and an organic radical occurs. The latter reacts to form a binaphthalene intrinsically chiral dimer. This paper is respectfully dedicated to Professors Anny Jutand and Christian Amatore for their outstanding contribution in the field of electrochemical catalysis and electrosynthesis.

1-bromo-2-methylnaphthalene↗
DOE OSTI2025

Spectroscopic Identification of Carbamate Formation and Synergistic Binding in Amide–CO$^{–}_{2}$ Complexes

Carbamate formation is an elementary step that governs nitrogencentered nucleophilic CO 2 capture across diverse environments, yet a direct, structure-specific understanding has been lacking. Here, we report the first gas-phase characterization of closed-shell carbamate formation by deprotonated amides, using cryogenic ion trap vibrational spectroscopy combined with quantum chemical calculations. Reactions of deprotonated benzamide and isophthalamide anions with CO 2 form carbamate species, with the amide nitrogen serving as the nucleophilic site. Diagnostic, strongly red-shifted antisymmetric CO 2 stretching vibrational bands, supported by a bonding analysis, establish chemisorption with substantial charge transfer. In the multiamide system, an intramolecular N−H···O hydrogen bond provides synergistic stabilization, correlating with larger red shifts and more exothermic binding. These structure-assigned benchmarks provide molecular-level insights into the binding motif, charge redistribution, and hydrogen bond-mediated stabilization of amide carbamates, which aid the characterization of carbamate formation in condensed phase.

Amides↗
DOE OSTI2023

Crystal structure of dihydrofolate reductase from the filarial nematode W. bancrofti in complex with NADPH and folate

Lymphatic filariasis is a debilitating illness with an estimated 50 million cases as of 2018. The majority of cases are caused by the parasitic worm W. bancrofti and additional cases by the worms B. malayi and B. timori. Dihydrofolate reductase (DHFR) is an established target in the treatment of cancer, bacterial, and protozoal infections and may be a potential target for drugs targeting parasitic worm infections, including filariasis. Recent studies have shown that known antifolate compounds, including methotrexate, inhibit the activity of W. bancrofti DHFR (WbDHFR). However, the absence of structural information for filarial DHFRs has limited the study of more in-depth structure-function relationships. We report the structure of WbDHFR complexed with NADPH and folate using X-ray diffraction data measured to 2.47 Å resolution. The structure of WbDHFR reveals the usual DHFR fold and is currently only the second nematode DHFR structure in the Protein Data Bank. The equilibrium dissociation constants for NADPH (90 ± 29 nM) and folate (23 ± 4 nM) were determined by equilibrium titrations. The interactions of known antifolates with WbDHFR were analyzed using molecular docking programs and molecular dynamics simulations. Antifolates with a hydrophobic core and extended linker formed favorable interactions with WbDHFR. These combined data should now facilitate the rational design of filarial DHFR inhibitors, which in turn can be used to determine whether DHFR is a viable drug target for filariasis and whether existing antifolates may be repurposed for its treatment.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Pyridinium Salts of Dehydrated Lanthanide Polychlorides

The reaction of lanthanide (Ln) chloride hydrates ([Ln(H 2 O) n (Cl) 3 ]) with pyridine (py) yielded a set of dehydrated pyridinium (py-H) Ln-polychloride salts. These species were crystallographically characterized as [[py-H-py][py-H] 2 [LnCl 6 ]] (Ln-6; Ln = La, Ce, Pr, Nd, Sm, Eu, Gd) or [[py-H] 2 [LnCl 5 (py)]] ((Ln-5; Ln = Tb, Dy, Ho, Er, Tm, Yb, Lu). The Ln-6 metal centers adopt an octahedral (OC-6) geometry, binding six Cl ligands. The -3 charge is off-set by two py-H moieties and a di-pyridinium (py-H-py) ion. For the Ln-5 species, an OC-6 anion is formed by the Ln cation binding a single py and five Cl ligands. The remaining -2 charge is offset by two py-H + cations that H-bond to the anion. Significant H-bonding occurs between the various cation/anion moieties inducing the molecular stability. The change in structure from the Ln-6 to Ln-5 is believed to be due to the Ln-contraction producing a smaller unit cell, which prevents formation of the py-H-py + cation, leading to the loss of the H-bonding-induced stability. Based on this, it was determined that the Ln-5 structures only exist when the lattice energy is small. While dehydrated polychloride salts can be produced by simply mixing in pyridine, the final structures adopted result from a delicate balance of cation size, Coulombic charge, and stabilizing H-bonding.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Predissociation-based measurements of bond dissociation energies: US 2 , OUS, and USe

The uranium-containing molecules US 2 , OUS, and USe have been investigated using a pulsed laser ablation supersonic beam molecular source with time-of-flight mass spectrometric detection. Spectra have been recorded using the resonant two-photon ionization method over the spectroscopic range from 277 to 238 nm. These species have a myriad of excited electronic states in this spectroscopic region, leading to spectra that are highly congested and appear quasicontinuous. Sharp predissociation thresholds are observed, allowing precise bond dissociation energies to be measured. In the case of the triatomic molecules, it was necessary to use one laser for excitation and a delayed laser for ionization in order to observe a sharp predissociation threshold that allowed a precise bond dissociation energy to be measured. The resulting thermochemical values are D 0 (SU-S) = 4.910 ± 0.003 eV, D 0 (OU-S) = 5.035 ± 0.004 eV, and D 0 (USe) = 4.609 ± 0.009 eV. These results provide the first measurement of D 0 (USe) and reduce the error limits in the previous values of D 0 (SU-S) and D 0 (OU-S) by a factor of more than 70.

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

Ab Initio Molecular Dynamics Insights into Stress Corrosion Cracking and Dissolution of Metal Oxides

Oxide phases such as α-Fe2O3 (hematite) and α-Al2O3 (corundum) are highly insoluble in water; however, subcritical crack growth has been observed in humidity nonetheless. Chemically induced bond breaking at the crack tip appears unlikely due to sterically hindered molecular transport. The molecular mechanics of a crack in corundum with a reactive force field reveal minimal lattice trapping, leading to bond breaking before sufficient space opens for water transport. To address this, we model a pre-built blunt crack with space for H2O molecule adsorption at the tip and show that it reduces fracture toughness by lowering the critical J-integral. Then, we explore stress-enhanced dissolution to understand the mechanism of crack tip blunting in the oxide/water system. Density functional theory combined with metadynamics was employed to describe atomic dissolution from flat hematite and corundum surfaces in pure water. Strain accelerates dissolution, stabilizing intermediate states with broken bonds before full atom detachment, while the free energy profile of unstrained surfaces is almost monotonic. The atomistic calculations provided input for a kinetic model, predicting the shape evolution of a blunt crack tip, which displays three distinct regimes: (i) dissolution primarily away from the tip, (ii) enhanced blunting near but not at the apex, and (iii) sharpening near the apex. The transition between regimes occurs at a low strain, highlighting the critical role of water in the subcritical crack growth of oxide scales, with dissolution as the fundamental microscopic mechanism behind this process.

Chemistry↗
DOE OSTI2025

Supercooling of Alaskan Beetle Larvae as a Winter Survival Strategy

Insects are able to survive subfreezing temperatures by either limiting ice crystal formation in their bodies or through freeze avoidance. Beetle larvae are able to avoid freezing in winter by dehydrating in the fall months and replacing their body water content with high concentrations of glycerol. This enables the body fluid of the insect to supercool, and even vitrify, recovering unharmed when the temperature warms in the spring. Using nondestructive, high‐energy X‐ray synchrotron diffraction experiments, direct insight into how cryopreservation occurs at the atomic level within the beetle larvae has been obtained. The results shed light on the molecular‐level interactions associated with the mechanism responsible for surviving freezing temperatures. The molecular models of severely dehydrated Alaskan beetle larvae, based on glycerol‐water mixtures, yield a total of 4.2 ± 1.2 intermolecular hydrogen bonds per glycerol molecule at 275 K, in good agreement with existing molecular dynamics simulations. Most importantly, they show that if just over half the body fluid content is water, the water clusters are too small to form ice crystals that cause cellular damage.

Benmore, Chris J. [X‐Ray Science Division Advanced↗
DOE OSTI2022

Intramolecular hydrogen bonding analysis

The quasi-atomic orbital (QUAO) bonding analysis is used to study intramolecular hydrogen bonding (IMHB) in salicylic acid and an intermediate that is crucial to the synthesis of aspirin. The bonding analysis rigorously explores IMHB through directly accessing information that is intrinsic to the molecular wave function, thereby bypassing the need for intrinsically biased methods. The variables that affect the strength of IMHB are determined using kinetic bond orders, QUAO populations, and QUAO hybridizations. Important properties include both the interatomic distance between hydrogen and oxygen participating in the IMHB and the hybridization on the oxygen. The bonding analysis further shows that each intramolecular hydrogen bond is a four-electron three-center bond. Here, the bonding analysis is used to understand how aromatic reactivity changes due to the effect of functional groups on the aromatic ring.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Thermodynamic and Kinetic Modulation of Methylammonium Lead Bromide Crystallization Revealed by In Situ Monitoring

Hybrid organic–inorganic perovskite (HOIP) crystals are promising optoelectronic materials, but little is known about either the thermodynamic and kinetic controls on crystal growth or the underlying growth mechanism(s). Herein, we use fluid cell atomic force microscopy (AFM) and solution nuclear magnetic resonance (NMR) spectroscopy to investigate growth of the model HOIP crystal CH 3 NH 3 PbBr 3 (MAPbBr 3 ) and to determine how formic acid (HCOOH) modulates the thermodynamics and kinetics of growth. The results show that growth of MAPbBr 3 in dimethylformamide (DMF) proceeds through the classical pathway by the spreading of atomic crystal steps generated at screw dislocations on the {100} surface. Temperature dependent step velocity measurements demonstrate that with increasing concentration, HCOOH decreases both the solubility of MAPbBr 3 and the kinetic coefficient (b) of step movement. 1 H-NMR measurements indicate that HCOOH increases the lifetime of the methylammonium (MA + ) ions and promotes the association of MAPbBr 3 , thus tuning the solubility of the perovskite. HCOOH also alters the molecular tumbling motion and bulk diffusion of the MA + ions, possibly via H-bonding. Further, our findings establish a direct correlation between the mesoscale crystal growth kinetics and the molecular-scale interactions between organic additives and constituent ions, providing unprecedented insights for developing predictive syntheses of HOIP crystals with defined size, crystal habit and shape, and defect distribution.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Improved Treatment of 1–4 Interactions in Force Fields for Molecular Dynamics Simulations

Traditional force fields commonly use a combination of bonded torsional terms and empirically scaled nonbonded interactions to capture 1-4 energies and forces of atoms separated by three bonds in a molecule. While this approach can yield accurate torsional energy barriers, it often leads to inaccurate forces and erroneous geometries and creates an interdependence between dihedral terms and nonbonded interactions, complicating parametrization and reducing transferability. Here, in this paper, we demonstrate that 1-4 interactions can be accurately modeled using only bonded coupling terms, eliminating the need for arbitrarily scaled nonbonded interactions altogether. Furthermore, by leveraging the automated parametrization capabilities of the Q-Force toolkit, we efficiently determine the necessary coupling terms without the need for manual adjustment. Our approach is first validated on a range of small molecule systems, encompassing both flexible and rigid structures, and shows a significant improvement in force field accuracy, obtaining subkcal/mol mean absolute error for every molecule tested. We further extend the bonded-only model for 1-4 interactions to Amber ff14sb, CHARMM36, and OPLS-AA force fields to reproduce ab initio gas and implicit solvent ϕ,ψ surfaces of alanine dipeptide.

Abdullah, Aalim S. [University of California, Berk↗
DOE OSTI2024

Overdestabilization vs Overstabilization in the Theoretical Analysis of f-Orbital Covalency

The complex nature of the f-orbital electronic structures and their interaction with the chemical environment pose significant computational challenges. Advanced computational techniques that variationally include scalar relativities and spin–orbit coupling directly at the molecular orbital level have been developed to address this complexity. Among these, variational relativistic multiconfigurational multireference methods stand out for their high accuracy and systematic improvement in studies of f-block complexes. Additionally, these advanced methods offer the potential for calibrating low-scaling electronic structure methods such as density functional theory. However, studies on the Cl K-edge X-ray absorption spectra of the [Ce(III)Cl 6 ] 3– and [Ce(IV)Cl 6 ] 2– complexes show that time-dependent density functional theory with approximate exchange–correlation kernels can lead to inaccuracies, resulting in an overstabilization of 4f orbitals and incorrect assessments of covalency. In contrast, approaches utilizing small active space wave function methods may understate the stability of these orbitals. The results herein demonstrate the need for large active space, multireference, and variational relativistic methods in studying f-block complexes.

chemical calculations↗
DOE OSTI2022

Structural basis for the inability of chloramphenicol to inhibit peptide bond formation in the presence of A-site glycine

Ribosome serves as a universal molecular machine capable of synthesis of all the proteins in a cell. Small-molecule inhibitors, such as ribosome-targeting antibiotics, can compromise the catalytic versatility of the ribosome in a context-dependent fashion, preventing transpeptidation only between particular combinations of substrates. Classic peptidyl transferase center inhibitor chloramphenicol (CHL) fails to inhibit transpeptidation reaction when the incoming A site acceptor substrate is glycine, and the molecular basis for this phenomenon is unknown. Here, we present a set of high-resolution X-ray crystal structures that explain why CHL is unable to inhibit peptide bond formation between the incoming glycyl-tRNA and a nascent peptide that otherwise is conducive to the drug action. Our structures reveal that fully accommodated glycine residue can co-exist in the A site with the ribosome-bound CHL. Moreover, binding of CHL to a ribosome complex carrying glycyl-tRNA does not affect the positions of the reacting substrates, leaving the peptide bond formation reaction unperturbed. These data exemplify how small-molecule inhibitors can reshape the A-site amino acid binding pocket rendering it permissive only for specific amino acid residues and rejective for the other substrates extending our detailed understanding of the modes of action of ribosomal antibiotics.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

The Electronic Structure of Zirconium and Hafnium Monochalcogenides

High-level ab initio CCSD(T) and spin–orbit icMRCI+Q calculations were used to predict potential energy curves (PECs) for the lowest-lying states of ZrO, ZrS, HfO, and HfS. The prediction of the ground state is basis set dependent at the icMRCI+Q level for ZrO and ZrS due to the small singlet–triplet splitting between the lowest 1 Σ + and 3 Δ states. CCSD(T) with a spin orbit correction predicted the 1 Σ + ground state in agreement with experiment. New all-electron basis sets were developed for Hf to improve the results over those predicted by use of effective core potentials (ECPs) that subsume the 4f electrons into the definition of the core. The use of the new DK-4f basis sets rather than ECPs became more important for HfO and HfS where there is a lack of a good core–valence separation. icMRCI+Q, CCSD(T), and DFT calculations for the spectroscopic parameters of ZrO, ZrS, HfO, and HfS were benchmarked with available experimental data. Bond dissociation energies (BDEs) of these four systems were calculated at the Feller–Peterson–Dixon (FPD) level to be 762.1 (ZrO), 543.5 (ZrS), 803.8 (HfO), and 575.1 kJ/mol (HfS), in excellent agreement with experiment. The HfS BDE was remeasured using the R3PI method, providing an updated experimental measurement of D 0 (HfS) = 5.978 ± 0.002 eV = 576.8 ± 0.2 kJ/mol. This experimental value, combined with experimental measurements of the ionization energies of Hf and HfS, gives the cationic BDE of D 0 (Hf + -S) = 5.124 ± 0.002 eV = 494.4 ± 0.2 kJ/mol.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Optimization of the Reax force field for the lithium–oxygen system using a high fidelity charge model

Studies using molecular dynamics (MD) have long struggled to simulate the failure modes of materials, predicting unrealistically high ductility and failing to capture brittle fracture. The primary cause of this shortcoming is an inadequate description of bond breaking. While reactive force fields such as ReaxFF show improvements compared to traditional force fields, the charge models used yield unphysical partial charges, especially during dissociation of ionic bonds. This flaw may be remedied by using the atom-condensed Kohn–Sham density functional theory (DFT) approximated to a second order (ACKS2) charge model for determining partial charges. In this work, we present a new ACKS2-enabled Reax force field for fracture simulations of lithium oxide systems, which was obtained by training against an extensive set of DFT, multireference configuration interaction (MRCI), and MRCI+Q reference data using genetic optimization techniques. This new force field significantly improves the bond breaking behavior, but still cannot fully capture the brittle fracture in MD simulations, suggesting more research is needed to improve simulation of brittle fracture.

36 MATERIALS SCIENCE↗