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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Ligand and Linkage Isomers of Bis(ethylthiocarbamato) Copper Complexes with Cyclic C 6 H 8 Backbone Substituents: Synthesis, Characterization, and Antiproliferation Activity

Abstract A series of isomeric bis(alkylthiocarbamate) copper complexes have been synthesized, characterized, and evaluated for antiproliferation activity. The complexes were derived from ligand isomers with 3‐methylpentyl (H 2 L 2 ) and cyclohexyl (H 2 L 3 ) backbone substituents, which each yield a pair of linkage isomers. The thermodynamic products CuL 2a/3a have two imino N and two S donors resulting in three five‐member chelate rings (555 isomers). The kinetic isomers CuL 2b/3b have one imino and one hydrazino N donor and two S donors resulting in four‐, six‐, and five‐member rings (465 isomers). The 555 isomers have more accessible Cu II/I potentials (E 1/2 =−811/−768 mV vs. ferrocenium/ferrocene) and lower energy charge transfer bands than their 465 counterparts (E 1/2 =−923/‐854 mV). Antiproliferation activities were evaluated against the lung adenocarcinoma cell line (A549) and nonmalignant lung fibroblast cell line (IMR‐90) using the MTT assay. CuL 2a was potent ( A549 EC 50 =0.080 μM) and selective ( IMR‐90 EC 50 / A549 EC 50 =25) for A549. Its linkage isomer CuL 2b had equivalent A549 activity, but lower selectivity ( IMR‐90 EC 50 / A549 EC 50 =12.5). The isomers CuL 3a and CuL 3b were less potent with A549 EC 50 values of 1.9 and 0.19 M and less selective with IMR‐90 EC 50 / A549 EC 50 ratios of 2.3 and 2.65, respectively. There was no correlation between reduction potential and A549 antiproliferation activity/selectivity.

Chemistry↗
DOE OSTI2021

Surface vs Homogeneous Organo-Hafnium Catalyst Ion-Pairing and Ligand Effects on Ethylene Homo- and Copolymerizations

Heterogeneous catalysts have long dominated polyethylene and polypropylene production, but understanding their catalysis is challenged by uncertainties in active site structures and percentages. Surface-bound organometallic catalysts are an emerging strategy to combine successful homogeneous catalysts having well-understood structures, relatively high percentages of active sites, and exceptional control of selectivity, with the attractions of surface catalysts, to transition promising homogeneous systems to large-scale heterogeneous ones. Nevertheless, surface-bound olefin polymerization catalysts typically produce ultrahigh M w ’s but with low activity and comonomer selectivity. Here, we report the systematic synthesis and characterization of a series of pyridylamido–Hf complexes and their corresponding surface catalysts chemisorbed on sulfated alumina (AlS) and zirconia (ZrS). Comparative ethylene homo- and 1-octene copolymerizations reveal similar activity and 1-octene selectivity trends in the homogeneous and heterogeneous systems. For the surface pyridylamido–Hf catalyst series, large variations in activity (up to 10×) and 1-octene incorporation (up to 28×) are achieved by ligand and support manipulation. Interestingly, while the homogeneous catalysts exhibit positive comonomer effects in ethylene/1-octene copolymerization, the surface catalysts behave oppositely. Extended X-ray absorption fine structure (EXAFS) reveals significantly elongated Hf···O bond distances vs typical Hf–O covalent bonds (2.06 vs 1.97 Å). Furthermore, density functional theory (DFT) analysis of the heterolytic ion pair separation enthalpies, olefin insertion energetics, and NBO/Bader charges also suggest electrostatic Hf cation–anionic support binding and catalytic patterns, which are modulated by the ion-pairing energetics and ligand architecture.

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

Critical differences in 3D atomic structure of individual ligand-protected nanocrystals in solution

Precise three-dimensional (3D) atomic structure determination of individual nanocrystals is a prerequisite for understanding and predicting their physical properties. Nanocrystals from the same synthesis batch display what are often presumed to be small but possibly important differences in size, lattice distortions, and defects, which can only be understood by structural characterization with high spatial 3D resolution. We solved the structures of individual colloidal platinum nanocrystals by developing atomic-resolution 3D liquid-cell electron microscopy to reveal critical intrinsic heterogeneity of ligand-protected platinum nanocrystals in solution, including structural degeneracies, lattice parameter deviations, internal defects, and strain. These differences in structure lead to substantial contributions to free energies, consequential enough that they must be considered in any discussion of fundamental nanocrystal properties or applications.

Kim, Byung Hyo↗
DOE OSTI2020

Manganese Catalysts with Tetradentate N-donor Pyridine-Appended Bipiperidine Ligands for Olefin Epoxidation Reactions: Ligand Electronic Effect and Mechanism

In this work, we described an electron-rich manganese mesoPYBP catalyst, Mn-SR-mesoPYBP(ClO4)2, by introducing electron-donating substituents on the mesoPYBP ligand. We optimized the catalytic performance in olefin epoxidation with H2O2 in the presence of acetic acid. The electron paramagnetic resonance (EPR) and cyclic voltammetry (CV) studies supported that an electronic effect could stabilize the high-valent intermediates in the catalytic cycles of the catalyst, which largely improved the catalytic performance and the reactivity of olefin epoxidation.

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

Theoretical Evaluation of Metal–Ligand Bonding in Neptunium Compounds in Relation to 237 Np Mössbauer Spectroscopy

The 237 Np Mössbauer isomer shift and quadrupole splitting (QS) are powerful probes for the metal–ligand bonding of neptunium, a 5f-element of vital importance in the nuclear fuel cycle. A large set of Np compounds with different oxidation states (III) to (VII) is studied to investigate, by first-principles calculations, isomer shifts and the QS trends in relation to the Np oxidation state. Natural Bond Orbital analysis reveals that in addition to donation bonding to the 5f shell, participation of the 6d and 7s neptunium shells in covalent (donation) bonding substantially impacts the isomer shifts. The isomer shift cannot be interpreted solely by the 5f shell electron count. The isomer shift for Np(II) compounds is estimated to be in the range of 31–34 mm/s, less positive than for Np(III) compounds. For the QS, density functional calculations fail to reproduce the quadrupole splitting for some Np(VI) ionic solids. A multiconfigurational wave function approach reproduces the observed QS trends. The calculations give a semiquantitative interpretation of the trends for Np oxidation states (V) to (VII). Furthermore, the contrasting QS for standard and “reverse” neptunyl(VI), at the opposite extremes of the observed QS scale, arises predominantly from the different crystal environments.

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

Solvent manipulation of the pre-reduction metal–ligand complex and particle-ligand binding for controlled synthesis of Pd nanoparticles

Understanding how to control the nucleation and growth rates is crucial for designing nanoparticles with specific sizes and shapes. Herein, we show that the nucleation and growth rates are correlated with the thermodynamics of metal–ligand/solvent binding for the pre-reduction complex and the surface of the nanoparticle, respectively. To obtain these correlations, we measured the nucleation and growth rates by in situ small angle X-ray scattering during the synthesis of colloidal Pd nanoparticles in the presence of trioctylphosphine in solvents of varying coordinating ability. The results show that the nucleation rate decreased, while the growth rate increased in the following order, toluene, piperidine, 3,4-lutidine and pyridine, leading to a large increase in the final nanoparticle size (from 1.4 nm in toluene to 5.0 nm in pyridine). Using density functional theory (DFT), complemented by 31 P nuclear magnetic resonance and X-ray absorption spectroscopy, we calculated the reduction Gibbs free energies of the solvent-dependent dominant pre-reduction complex and the solvent-nanoparticle binding energy. The results indicate that lower nucleation rates originate from solvent coordination which stabilizes the pre-reduction complex and increases its reduction free energy. At the same time, DFT calculations suggest that the solvent coordination affects the effective capping of the surface where stronger binding solvents slow the nanoparticle growth by lowering the number of active sites (not already bound by trioctylphosphine). The findings represent a promising advancement towards understanding the microscopic connection between the metal–ligand thermodynamic interactions and the kinetics of nucleation and growth to control the size of colloidal metal nanoparticles.

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

Trinuclear and Tetranuclear Ruthenium Carbonyl Nitrosyls: Oxidation of a Carbonyl Ligand by an Adjacent Nitrosyl Ligand

Trinuclear and tetranuclear ruthenium carbonyls of the types Ru3(CO)n(NO)2, Ru3(N)(CO)n(NO), Ru3(N)2(CO)n, Ru3(N)(CO)n(NCO), Ru3(CO)n(NCO)(NO), Ru4(N)(CO)n(NO), Ru4(N)(CO)n(NCO), and Ru4(N)2(CO)n related to species observed experimentally in the chemistry of Ru3(CO)10(µ-NO)2 have been investigated using density functional theory. In all cases, the experimentally observed structures have been found to be low-energy structures. The low-energy trinuclear structures typically have a central strongly bent Ru–Ru–Ru chain with terminal CO groups and bridging nitrosyl, isocyanate, and/or nitride ligands across the end of the chain. The low-energy tetranuclear structures typically have a central Ru4N unit with terminal CO groups and a non-bonded pair of ruthenium atoms bridged by a nitrosyl or isocyanate group.

Biochemistry & Molecular Biology↗