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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Catalytic Oxidation of Alcohol via Nickel Phosphine Complexes with Pendant Amines

Nickel complexes were prepared with diphosphine ligands that contain pendant amines, and these complexes catalytically oxidize primary and secondary alcohols to their respective aldehydes and ketones. Kinetic and mechanistic studies of these prospective electrocatalysts were performed to understand what influences the catalytic activity. For the oxidation of diphenylmethanol, the catalytic rates were determined to be dependent on the concentration of both the catalyst and the alcohol. The catalytic rates were found to be independent of the concentration of base and oxidant. The incorporation of pendant amines to the phosphine ligand results in substantial increases in the rate of alcohol oxidation with more electron-donating substituents on the pendant amine exhibiting the fastest rates. We thank Dr. John C. Linehan, Dr. Elliott B. Hulley, Dr. Jonathan M. Darmon, and Dr. Elizabeth L. Tyson for helpful discussions. Research by CJW, PD, DLM, and AMA was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Research by MLH was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2018

Influence of a Heterocyclic Nitrogen-Donor Group on the Coordination of Trivalent Actinides and Lanthanides by Aminopolycarboxylate Complexants

Here, the novel metal chelator – N -2-pyridylmethyl-diethylenetriamine- N,N',N'',N'' -tetraacetic acid, DTTA-PyM – was designed to replace a single O-donor acetate group of the well-known aminopolycarboxylate complexant diethylenetriamine- N,N,N',N'',N'' -pentaacetic acid (DTPA) with an N-donor 2-pyridylmethyl. Potentiometric, spectroscopic, computational, and radioisotope distribution methods show distinct differences for the 4f and 5f coordination environments and enhanced actinide binding due to the nitrogen bearing heterocyclic moiety. The Am 3+ , Cm 3+ , Ln 3+ complexation studies for DTTA-PyM reveal an enhanced preference, relative to DTPA, for trivalent actinide binding. Fluorescence studies indicate no changes to the octadentate coordination of trivalent curium, while evidence of heptadentate complexation of trivalent europium is found in mixtures containing EuHL (aq) complexes at the same aqueous acidity. The denticity change observed for Eu 3+ suggests that complex protonation occurs on the pyridyl nitrogen. Formation of the CmHL(aq) complex is likely due to the protonation of an available carboxylate group since the carbonyl oxygen can maintain octadentate coordination through a rotation. The observed suppressed protonation of the pyridyl nitrogen in the Cm complexes may be attributed to stronger trivalent actinide binding by DTTA-PyM. Density functional theory calculations indicate that added stabilization of the actinide complexes with DTTA-PyM may originate from p back-bonding interactions between singly occupied 5 f orbitals of Am 3+ and the pyridyl nitrogen. The differences between the stability of trivalent actinide chelates (Am 3+ , Cm 3+ ) and trivalent lanthanide chelates (La 3+ -Lu 3+ ) are observed in liquid-liquid extraction systems, yielding unprecedented 4 f /5 f differentiation when using DTTA-PyM as an aqueous holdback reagent. In addition, the enhanced N -donor softness of the new DTTA-PyM chelator was perturbed by adding a fluorine onto the pyridine group. The comparative characterization of N -(3-fluoro-2-pyridylmethyl)-diethylenetriamine- N,N',N'',N'' -tetraacetic acid, DTTA-3-F-PyM, showed subdued 4 f /5 f differentiation due to the presence of this electron-withdrawing group.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

CO{sub 2} binding in the (quinoline-CO{sub 2}){sup −} anionic complex

We have studied the (quinoline-CO{sub 2}){sup −} anionic complex by a combination of mass spectrometry, anion photoelectron spectroscopy, and density functional theory calculations. The (quinoline-CO{sub 2}){sup −} anionic complex has much in common with previously studied (N-heterocycle-CO{sub 2}){sup −} anionic complexes both in terms of geometric structure and covalent bonding character. Unlike the previously studied N-heterocycles, however, quinoline has a positive electron affinity, and this provided a pathway for determining the binding energy of CO{sub 2} in the (quinoline-CO{sub 2}){sup −} anionic complex. From the theoretical calculations, we found CO{sub 2} to be bound within the (quinoline-CO{sub 2}){sup −} anionic complex by 0.6 eV. We also showed that the excess electron is delocalized over the entire molecular framework. It is likely that the CO{sub 2} binding energies and excess electron delocalization profiles of the previously studied (N-heterocycle-CO{sub 2}){sup −} anionic complexes are quite similar to that of the (quinoline-CO{sub 2}){sup −} anionic complex. This class of complexes may have a role to play in CO{sub 2} activation and/or sequestration.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Rhodium Bis(quinolinyl)benzene Complexes for Methane Activation and Functionalization

A series of rhodium (III) bis(quinolinyl)benzene (bisq x ) complexes was researched as candidates for the homogeneous partial oxidation of methane. Density functional theory (DFT) (M06 with Poisson continuum solvation) was used to investigate a variety of (bisq x ) ligand candidates involving different functional groups to determine the impact on RhIII(bisq x ) catalyzed methane functionalization. The free energy activation barriers for methane C–H activation and Rh–methyl functionalization at 298 K and 498 K were determined. DFT studies predict that the best candidate for catalytic methane functionalization is Rh III coordinated to unsubstituted bis(quinolinyl)benzene (bisq). Support is also found for the prediction that the η 2 -benzene coordination mode of (bisq x ) ligands on Rh encourages methyl group functionalization by serving as an effective leaving group for S N 2 and S R 2 attack.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Photoelectron spectroscopy of hexachloroplatinate-nucleobase complexes: Nucleobase excited state decay observed via delayed electron emission

We report low-temperature photoelectron spectra of isolated gas-phase complexes of the hexachloroplatinate dianion bound to the nucleobases uracil, thymine, cytosine, and adenine. The spectra display well-resolved, distinct peaks that are consistent with complexes where the hexachloroplatinate dianion is largely intact. Adiabatic electron detachment energies for the hexachloroplatinate-nucleobase complexes are measured as 2.26-2.36 eV. The magnitudes of the repulsive Coulomb barriers (RCBs) of the complexes are all ∼1.7 eV, values that are lower than the RCB of the uncomplexed PtCl{sub 6}{sup 2−} dianion as a result of charge solvation by the nucleobases. In addition to the resolved spectral features, broad featureless bands indicative of delayed electron detachment are observed in the 193 nm photoelectron spectra of the four clusters. The 266 nm spectra of the PtCl{sub 6}{sup 2−} ⋅ thymine and PtCl{sub 6}{sup 2−} ⋅ adenine complexes also display very prominent delayed electron emission bands. These results mirror recent results on the related Pt(CN){sub 4}{sup 2−} ⋅ nucleobase complexes [A. Sen et al., J. Phys. Chem. B 119, 11626 (2015)]. The observation of delayed electron emission bands in the PtCl{sub 6}{sup 2−} ⋅ nucleobase spectra obtained in this work, as for the previously studied Pt(CN){sub 4}{sup 2−} ⋅ nucleobase complexes, is attributed to one-photon excitation of nucleobase-centred excited states that can effectively couple to the electron detachment continuum, producing strong electron detachment. Moreover, the selective, strong excitation of the delayed emission bands in the 266 nm spectra is linked to fundamental differences in the individual nucleobase photophysics at this excitation energy. This strongly supports our previous suggestion that the dianion within these clusters can be viewed as a “dynamic tag” which has the propensity to emit electrons when the attached nucleobase decays over a time scale long enough to allow autodetachment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Surface-Induced Dissociation of Protein Complexes in a Hybrid Fourier Transform Ion Cyclotron Resonance Mass Spectrometer

Mass spectrometry continues to develop as a valuable tool in the analysis of proteins and protein complexes. In protein complex mass spectrometry studies, surface-induced dissociation (SID) has been successfully applied in quadrupole time-of-flight (Q-TOF) instruments. SID provides structural information on non-covalent protein complexes that is complementary to other techniques. However, the mass resolution of Q-TOF instruments can limit the information that can be obtained for protein complexes by SID. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) provides ultrahigh resolution and ultrahigh mass accuracy measurements. In this study, an SID device was designed and successfully installed in a hybrid FT-ICR instrument in place of the standard gas collision cell. The SID-FT-ICR platform has been tested with several protein complex systems (homooligomers, a heterooligomer, and a protein-ligand complex, ranging from 53 kDa to 85 kDa), and the results are consistent with data previously acquired on Q-TOF platforms, matching predictions from known protein interface information. SID fragments with the same m/z but different charge states are well-resolved based on distinct spacing between adjacent isotope peaks, and the addition of metal cations and ligands can also be isotopically resolved with the ultrahigh mass resolution available in FT-ICR.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2016

Nickel Bis-Diphosphine Complexes: Controlling the Binding and Heterolysis of H2

Two new Ni(II) complexes, the homoleptic [Ni-(8PCy2NH)2]2+ complex (8PCy 2NH = 3,7-cyclohexyl-1-amino-3,7-diphosphacyclooctane) containing two pendant amines on adjacent ligands, and the heteroleptic [Ni(8PCy2NH)(dppe)]2+ complex (dppe = bis-(diphenylphosphino)ethane) containing only a single pendant amine, have been synthesized, and their electrochemical properties are reported. The [Ni(8PCy2NH)(dppe)]2+ complex is capable of heterolytically cleaving hydrogen, allowing for the first observation of an endoprotonated nickel hydride related to the [Ni(PR2NR'2)2]2+ family of complexes. The [Ni(8PCy2NH)(dppe)]2+ complex did not exhibit electrocatalytic H2 oxidation activity; however, [Ni(8PCy2NH)2]2+ is an active electrocatalyst for H2 oxidation with a maximum turnover frequency (kobs) of 18 s-1 under 1 atm H2 at Ecat/2 = -0.71 V versus the ferrocenium/ferrocene (Cp2Fe+/0) couple. In addition to an analysis of the effect of the number of pendant amines on the rates of electrocatalytic H2 oxidation of compounds related to the [Ni(PR 2NR'2)2]2+ family, the effect of the secondary pendant amine on intermolecular deprotonation is discussed.

Stolley, Ryan M.↗
DOE OSTI2017

The primed SNARE–complexin–synaptotagmin complex for neuronal exocytosis

Synaptotagmin, complexin, and neuronal SNARE (soluble N -ethylmaleimide sensitive factor attachment protein receptor) proteins mediate evoked synchronous neurotransmitter release, but the molecular mechanisms mediating the cooperation between these molecules remain unclear. Here we determine crystal structures of the primed pre-fusion SNARE–complexin–synaptotagmin-1 complex. These structures reveal an unexpected tripartite interface between synaptotagmin-1 and both the SNARE complex and complexin. Simultaneously, a second synaptotagmin-1 molecule interacts with the other side of the SNARE complex via the previously identified primary interface. Mutations that disrupt either interface in solution also severely impair evoked synchronous release in neurons, suggesting that both interfaces are essential for the primed pre-fusion state. Ca 2+ binding to the synaptotagmin-1 molecules unlocks the complex, allows full zippering of the SNARE complex, and triggers membrane fusion. In conclusion, the tripartite SNARE–complexin–synaptotagmin-1 complex at a synaptic vesicle docking site has to be unlocked for triggered fusion to start, explaining the cooperation between complexin and synaptotagmin-1 in synchronizing evoked release on the sub-millisecond timescale.

59 BASIC BIOLOGICAL SCIENCES↗