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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 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↗
DOE OSTI2021

Computational Complexity of Neuromorphic Algorithms

Neuromorphic computing has several characteristics that make it an extremely compelling computing paradigm for post Moore computation. Some of these characteristics include intrinsic parallelism, inherent scalability, collocated processing and memory, and event-driven computation. While these characteristics impart energy efficiency to neuromorphic systems, they do come with their own set of challenges. One of the biggest challenges in neuromorphic computing is to establish the theoretical underpinnings of the computational complexity of neuromorphic algorithms. In this paper, we take the first steps towards defining the space and time complexity of neuromorphic algorithms. Specifically, we describe a model of neuromorphic computation and state the assumptions that govern the computational complexity of neuromorphic algorithms. Next, we present a theoretical framework to define the computational complexity of a neuromorphic algorithm. We explicitly define what space and time complexities mean in the context of neuromorphic algorithms based on our model of neuromorphic computation. Finally, we leverage our approach and define the computational complexities of six neuromorphic algorithms: constant function, successor function, predecessor function, projection function, neuromorphic sorting algorithm and neighborhood subgraph extraction algorithm.

Date, Prasanna↗
DOE OSTI2017

Crystal structure of Mdm12 and combinatorial reconstitution of Mdm12/Mmm1 ERMES complexes for structural studies

Membrane contact sites between organelles serve as molecular hubs for the exchange of metabolites and signals. In yeast, the Endoplasmic Reticulum – Mitochondrion Encounter Structure (ERMES) tethers these two organelles likely to facilitate the non-vesicular exchange of essential phospholipids. Present in Fungi and Amoebas but not in Metazoans, ERMES is composed of five distinct subunits; among those, Mdm12, Mmm1 and Mdm34 each contain an SMP domain functioning as a lipid transfer module. We previously showed that the SMP domains of Mdm12 and Mmm1 form a hetero-tetramer. Here we describe our strategy to diversify the number of Mdm12/Mmm1 complexes suited for structural studies. We use sequence analysis of orthologues combined to protein engineering of disordered regions to guide the design of protein constructs and expand the repertoire of Mdm12/Mmm1 complexes more likely to crystallize. Using this combinatorial approach we report crystals of Mdm12/Mmm1 ERMES complexes currently diffracting to 4.5 Å resolution and a new structure of Mdm12 solved at 4.1 Å resolution. Our structure reveals a monomeric form of Mdm12 with a conformationally dynamic N-terminal β-strand; it differs from a previously reported homodimeric structure where the N-terminal β strands where swapped to promote dimerization. Based on our electron microscopy data, we propose a refined pseudo-atomic model of the Mdm12/Mmm1 complex that agrees with our crystallographic and small-angle X-ray scattering (SAXS) solution data. - Highlights: • We solved a 4.1 Å resolution crystal structure of Mdm12, the soluble subunit of ERMES. • The two Mdm12 apo monomers differ in the conformation of their N-terminal β-strands. • We reconstituted and crystallized two distinct Mdm12/Mmm1 complexes. • SAXS analysis of the complexes agrees with our previous electron microscopy data. • The structure suggests a head-to-tail association in the Mdm12/Mmm1 complex.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Electrochemistry and Spectroelectrochemistry of Luminescent Europium Complexes

Abstract Fast, cost effective, and robust means of detecting and quantifying lanthanides are needed to support more efficient tracking within the nuclear, medicinal, and industrial fields. Furthermore, methods for isolating lanthanide signal from spectroscopic interferents are also needed. Applying spectroelectrochemistry to the detection of these species can meet those needs. However, application of this technique is limited by the low molar absorptivities and quantum yields of the lanthanides. These limitations can be circumvented by complexing the lanthanides with sensitizing ligands that enhance fluorescence, thereby dropping the limits of detection. Complexation will also cause changes in the electrochemical behavior of the lanthanides. To demonstrate this concept, studies were completed using europium as a model lanthanide in complexes with four different sensitizing ligands, which included 2,2′‐bipyridine and related derivatives. Results indicate that all four studied complexes demonstrate quasi‐reversible redox couples and improvements in limits of detection where electrochemical and spectroscopic characteristics showed some dependence on attached ligand. All four complexes studied display the necessary characteristics for spectroelectrochemical analysis, which was successfully and reproducibly applied to all Eu complexes.

Lines, Amanda M.↗
DOE OSTI2018

Mechanistic Understanding of Uranyl Ion Complexation on Montmorillonite Edges: A Combined First-Principles Molecular Dynamics–Surface Complexation Modeling Approach

Systematic first-principles molecular dynamics (FPMD) simulations were carried out to study the structures, free energies, and acidity constants of UO 2 2+ surface complexes on montmorillonite in order to elucidate the surface complexation mechanisms of the uranyl ion (UO 2 2+ ) on clay mineral edges at the atomic scale. Four representative complexing sites were investigated, that is, ≡Al(OH) 2 and ≡AlOHSiO on the (010) surface and ≡AlOHOa and ≡SiOOa on the (110) surface. The results show that uranyl ions form bidentate complexes on these sites. We report all calculated binding free energies for these complexes are very similar. These bidentate complexes can be hydrolyzed, and their corresponding derived p K a values (around 5.0 and 9.0 for p K a1 and p K a2 , respectively) indicate that UO 2 (OH) + and UO 2 (OH) 2 surface groups are the dominant surface species in the environmental pH range. The OH groups of UO 2 (OH) 2 surface complexes can act as complexing sites for subsequent metals. Additional simulations showed that such multinuclear adsorption is feasible and can be important at high pH. Furthermore, FPMD simulation results served as input parameters for an electrostatic thermodynamic surface complexation model (SCM) that adequately reproduced adsorption data from the literature. Overall, this study provides an improved understanding of UO 2 2+ complexation on clay mineral edge surfaces.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Two-center three-electron bonding in ClNH{sub 3} revealed via helium droplet infrared laser Stark spectroscopy: Entrance channel complex along the Cl + NH{sub 3} → ClNH{sub 2} + H reaction

Pyrolytic dissociation of Cl{sub 2} is employed to dope helium droplets with single Cl atoms. Sequential addition of NH{sub 3} to Cl-doped droplets leads to the formation of a complex residing in the entry valley to the substitution reaction Cl + NH{sub 3} → ClNH{sub 2} + H. Infrared Stark spectroscopy in the NH stretching region reveals symmetric and antisymmetric vibrations of a C{sub 3v} symmetric top. Frequency shifts from NH{sub 3} and dipole moment measurements are consistent with a ClNH{sub 3} complex containing a relatively strong two-center three-electron (2c–3e) bond. The nature of the 2c–3e bonding in ClNH{sub 3} is explored computationally and found to be consistent with the complexation-induced blue shifts observed experimentally. Computations of interconversion pathways reveal nearly barrierless routes to the formation of this complex, consistent with the absence in experimental spectra of two other complexes, NH{sub 3}Cl and Cl–HNH{sub 2}, which are predicted in the entry valley to the hydrogen abstraction reaction Cl + NH{sub 3} → HCl + NH{sub 2}.

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

Comparison of the Energy-Transfer Rates in Structural and Spectral Variants of the B800–850 Complex from Purple Bacteria

Photosynthetic light harvesting can occur with a remarkable near-unity quantum efficiency. The B800–850 complex, also known as light-harvesting complex 2 (LH2), is the primary light-harvesting complex in purple bacteria and has been extensively studied as a model system. The bacteriochlorophylls of the B800–850 complex are organized into two concentric rings, known as the B800 and B850 rings. However, depending on the species and growth conditions, the number of constituent subunits, the pigment geometry, and the absorption energies vary. While the dynamics of some B800–850 variants have been exhaustively characterized, others have not been measured. Furthermore, a direct and simultaneous comparison of how both structural and spectral differences between variants affect these dynamics has not been performed. In this work, we utilize ultrafast transient absorption measurements to compare the B800 to B850 energy-transfer rates in the B800–850 complex as a function of the number of subunits, geometry, and absorption energies. The nonameric B800–850 complex from Rhodobacter (Rb.) sphaeroides is 40% faster than the octameric B800–850 complex from Rhodospirillum (Rs.) molischianum, consistent with structure-based predictions. In contrast, the blue-shifted B800–820 complex from Rs. molischianum is only 20% faster than the B800–850 complex from Rs. molischianum despite an increase in the spectral overlap between the rings that would be expected to produce a larger increase in the energy-transfer rate. These measurements support current models that contain dark, higher-lying excitonic states to bridge the energy gap between rings, thereby maintaining similar energy-transfer dynamics. Altogether, these results demonstrate that energy-transfer dynamics in the B800–850 complex are robust to the spectral and structural variations between species used to optimize energy capture and flow in purple bacteria.

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

Influence of Countercation Hydration Enthalpies on the Formation of Molecular Complexes: A Thorium–Nitrate Example

The influence of countercations (A(n+)) in directing the composition of monomeric metalligand (ML) complexes that precipitate from solution are often overlooked despite the wide usage of A(n+) in materials synthesis. Herein, we describe a correlation between the composition of ML complexes and A(+) hydration enthalpies found for two related series of thorium (Th)-nitrate molecular compounds obtained by evaporating acidic aqueous Th-nitrate solutions in the presence of A(+) counterions. Analyses of their chemical composition and solid-state structures demonstrate that A(+) not only affects the overall solid-state packing of the Th-nitrato complexes but also influences the composition of the Th-nitrato monomeric anions themselves. Trends in composition and structure are found to correlate with A(+) hydration enthalpies, such that the A(+) with smaller hydration enthalpies associate with less hydrated and more anionic Th-nitrato complexes. This perspective, broader than the general assumption of size and charge as the dominant influence of A(n+), opens a new avenue for the design and synthesis of targeted metal-ligand complexes.

Jin, Geng Bang↗
DOE OSTI2014

Synchronization in node of complex networks consist of complex chaotic system

A new synchronization method is investigated for node of complex networks consists of complex chaotic system. When complex networks realize synchronization, different component of complex state variable synchronize up to different scaling complex function by a designed complex feedback controller. This paper change synchronization scaling function from real field to complex field for synchronization in node of complex networks with complex chaotic system. Synchronization in constant delay and time-varying coupling delay complex networks are investigated, respectively. Numerical simulations are provided to show the effectiveness of the proposed method.

36 MATERIALS SCIENCE↗
DOE OSTI2016

A new family of metal borohydride guanidinate complexes: Synthesis, structures and hydrogen-storage properties

We report on a new class of complex hydrides: borohydride guanidinate complexes (MBH{sub 4}·nCN{sub 3}H{sub 5}, M=Li, Mg, and Ca). They can be prepared via facile solid-state synthesis routes. Their crystal structures were successfully determined using a combination of X-ray diffraction, first-principles calculations and neutron vibrational spectroscopy. Among these compounds, Mg(BH{sub 4}){sub 2}·6CN{sub 3}H{sub 5} is composed of large complex Mg[CN{sub 3}H{sub 5}]{sub 6}{sup 2+} cations and surrounding BH{sub 4}{sup -} ions, while Ca(BH{sub 4}){sub 2}·2CN{sub 3}H{sub 5} possesses layers of corner-sharing Ca[BH{sub 4}]{sub 4}(CN{sub 3}H{sub 5}){sub 2} octahedra. Our dehydrogenation results show that ≈10 wt% hydrogen can be released from MBH{sub 4}·nCN{sub 3}H{sub 5} (M=Li, Mg, and Ca) at moderate temperatures with minimal ammonia and diborane contamination thanks to the synergistic effect of C-N bonds from guanidine and hydridic H from borohydrides leading to a weakening of the N-H bonds, thus impeding ammonia gas liberation. Further tuning the dehydrogenation with different cation species indicates that Mg(BH{sub 4}){sub 2}·nCN{sub 3}H{sub 5} can exhibit the optimum properties with nearly thermally neutral dehydrogenation and very high purity hydrogen release. - Graphical abstract: A new family of complex hydrides: borohydride guanidinates, was developed with diverse crystal structures and remarkable hydrogen storage properties. - Highlights: • A new family of complex hydrides, borohydride guanidinate complexes, are synthesized. • Their diverse crystal structures are determined using combined characterizations. • These compounds can release ~10 wt% pure H{sub 2} at moderate temperatures. • Dehydrogenation thermodynamics and H{sub 2} purity can be tuned by varying cation species.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Promotion and Tuning of the Electrochemical Reduction of Hetero‐ and Homobimetallic Zinc Complexes**

Abstract Compounds containing multiple metals attract significant interest due to the useful redox and reactivity properties of such species. Here, the electrochemical properties of a family of macrocyclic complexes that feature a zinc(II) center paired with a secondary redox‐inactive metal cation in heterobimetallic (Na + , Ca 2+ , Nd 3+ , Y 3+ ) motifs or homobimetallic (Zn 2+ ) motifs have been investigated. The new complexes were prepared via a divergent strategy, isolated, and structurally characterized with single‐crystal X‐ray diffraction (XRD) analysis. XRD results show that the structures of the complexes are modulated by the identity of the incorporated secondary metal ions. Cyclic voltammetry data reveal that ligand‐centered reduction is promoted in the bimetallic complexes and that the paired metal ions synergistically influence the redox properties of the complexes. Similar to prior work from our group and others, the bimetallic complexes containing stronger Lewis acids undergo more significant reduction potential shifts; contrasting with prior work on complexes containing redox‐active metals, however, the zinc(II) complexes studied here display faster electron transfer (as judged by lower reorganization energies, λ) when incorporating di‐ or tri‐valent Lewis acids in contrast to monovalent (and more weakly acidic) sodium. The quantified trends in these data offer insights that could help distinguish metal‐ versus ligand‐centered reduction of bimetallic complexes.

Kelsey, Shaun R.↗
DOE OSTI2020

Wind Farm Simulation and Layout Optimization in Complex Terrain: Preprint

This work reports on incorporating complex terrain into wind farm simulations for the purpose of layout optimization. Adding complex terrain boundary conditions to NREL's medium fidelity computational fluid dynamics model, WindSE, produces significant separation, flow curvature, and speedup effects that would otherwise be difficult to capture with lower-fidelity models or a flat-terrain assumption. These flow features, in turn, can significantly impact the optimal turbine array layout. We demonstrate the impact of complex terrain on flow in both an idealized and real-world setting, and discuss modifications to the code that enable gradient-based optimization using terrain-aware adjoint gradients. Through several optimization case studies, we show that the layout optimization process takes advantage of speedup effects on terrain high points, and leverages flow curvature effects that modify wake trajectories. This yields substantial power improvements over gridded layouts, and hints at future research directions in simulation and optimization for wake trajectories in complex terrain.

17 WIND ENERGY↗
DOE OSTI2016

Hydrogen-related complexes in Li-diffused ZnO single crystals

Zinc oxide (ZnO) is a wide band gap semiconductor and a potential candidate for next generation white solid state lighting applications. In this work, hydrogen-related complexes in lithium diffused ZnO single crystals were studied. In addition to the well-known Li-OH complex, several other hydrogen defects were observed. When a mixture of Li{sub 2}O and ZnO is used as the dopant source, zinc vacancies are suppressed and the bulk Li concentration is very high (>10{sup 19 }cm{sup −3}). In that case, the predominant hydrogen complex has a vibrational frequency of 3677 cm{sup −1}, attributed to surface O-H species. When Li{sub 2}CO{sub 3} is used, a structured blue luminescence band and O-H mode at 3327 cm{sup −1} are observed at 10 K. These observations, along with positron annihilation measurements, suggest a zinc vacancy–hydrogen complex, with an acceptor level ∼0.3 eV above the valence-band maximum. This relatively shallow acceptor could be beneficial for p-type ZnO.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗