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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Coordination-induced O-H/N-H bond weakening by a redox non-innocent, aluminum-containing radical

Abstract Several renewable energy schemes aim to use the chemical bonds in abundant molecules like water and ammonia as energy reservoirs. Because the O-H and N-H bonds are quite strong (>100 kcal/mol), it is necessary to identify substances that dramatically weaken these bonds to facilitate proton-coupled electron transfer processes required for energy conversion. Usually this is accomplished through coordination-induced bond weakening by redox-active metals. However, coordination-induced bond weakening is difficult with earth’s most abundant metal, aluminum, because of its redox inertness under mild conditions. Here, we report a system that uses aluminum with a redox non-innocent ligand to achieve significant levels of coordination-induced bond weakening of O-H and N-H bonds. The multisite proton-coupled electron transfer manifold described here points to redox non-innocent ligands as a design element to open coordination-induced bond weakening chemistry to more elements in the periodic table.

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

Quantitative U=O bond activation in uranyl complexes via silyl radical transfer

Reductive silylation of the uranyl dication with 1,4-bis(trimethylsilyl)dihydropyrazine, or “Mashima's reagent”, is detailed. The reagent simultaneously delivers silylium ions and electrons to multiple uranyl complexes, i.e. a pyridine dipyrrolide uranyl complex and a common uranyl-containing starting material, UO 2 Cl 2 (OPPh 3 ) 2 . This reaction results in quantitative activation of thermodynamically robust U=O bonds. Furthermore, the reductive functionalization of environmentally persistent actinyl species with Mashima's reagent is seen as a promising solution for nuclear waste remediation.

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

Experimental and computational studies of the kinetics of the reaction of hydrogen peroxide with the amidogen radical

In this work, the pulsed-laser photolysis/laser-induced fluorescence method is used to study the kinetics of the reaction of NH 2 with H 2 O 2 to yield a second-order rate constant of (2.42 ± 0.55) × 10 –14 cm 3 molecule –1 s –1 at 412 K in 10–22 mbar of Ar bath gas. There are no prior measurements for comparison. To check this value and enable reliable extrapolation to other temperatures, we also compute thermal rate constants for this process over the temperature range 298–3000 K via multi-structural canonical variational transition-state theory with small-curvature multidimensional tunneling (MS-CVT/SCT). The CVT/SCT rate constants are derived using a dual-level direct dynamics approach utilizing single-point CCSD(T)-F12b/cc-pVQZ-F12 energies—corrected for core-valence and scalar relativistic effects—and M06-2X/MG3S geometries, gradients, and Hessians—for all stationary and non-stationary points along the reaction path. The multistructural method with torsional anharmonicity, based on a coupled torsional potential, is then employed to calculate correction factors for the rate constants, accounting for the comprehensive effects of torsional anharmonicity on the kinetics of this reaction system. The final MS-CVT/SCT rate constants are found to be in good agreement with our measurements and can be expressed in modified Arrhenius form as 2.13 × 10 –15 (T/298 K) 4.02 exp(–513 K/T) cm 3 molecule –1 s –1 over the temperature range of 298–3000 K.

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

Biocatalytic control of site-selectivity and chain length-selectivity in radical amino acid halogenases

Biocatalytic C–H activation has the potential to merge enzymatic and synthetic strategies for bond formation. Fe II /αKG-dependent halogenases are particularly distinguished for their ability both to control selective C–H activation as well as to direct group transfer of a bound anion along a reaction axis separate from oxygen rebound, enabling the development of new transformations. In this context, we elucidate the basis for the selectivity of enzymes that perform selective halogenation to yield 4-Cl-lysine (BesD), 5-Cl-lysine (HalB), and 4-Cl-ornithine (HalD), allowing us to probe how site-selectivity and chain length selectivity are achieved. We now report the crystal structure of the HalB and HalD, revealing the key role of the substrate-binding lid in positioning the substrate for C 4 vs C 5 chlorination and recognition of lysine vs ornithine. Targeted engineering of the substrate-binding lid further demonstrates that these selectivities can be altered or switched, showcasing the potential to develop halogenases for biocatalytic applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗