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Results for “coordination complex”

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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Cobalt-polypyrrole-carbon black (Co-PPY-CB) Electrocatalysts for the Oxygen Reduction Reaction (ORR) in Fuel Cells: Composition and Kinetic Activity

Electrocatalysts consisting of polypyrrole (PPY) and Co deposited on carbon black (CB) at several compositions were prepared and tested for the oxygen reduction reaction (ORR) in a HClO4 buffer (pH = 1) using a rotating ring-disk electrode (RRDE). It was determined that the most favorable catalyst composition (prior to calcination) had a CB:PPY weight ratio of 2 and a pyrrole:Co (i.e., PY:Co) molar ratio of 4. This catalyst had an onset potential of 0.785 V (vs. RHE) and a mass activity of ca. 1 A/g{sub cata} at the fuel cell relevant voltage of 0.65 V. Furthermore, it was found that the number of electrons exchanged during the ORR with the catalyst was ca. 3.5 and resulted in 28% yield of H{sub 2}O{sub 2} at 0.65 V, which hints to an indirect 4e{sup -} reduction of O{sub 2} to H{sub 2}O, with H{sub 2}O{sub 2} as an intermdiate. From energy dispersive spectroscopy (EDS) and extended X-ray absorption fine structure (EXAFS) analysis, it is proposed that a PY:Co ratio of 4 favors the formation, prior to calcination, in the catalyst precursor of Co-N complexes in which Co is coordinated to 3 or 4 N atoms, resulting in strong Co-N interactions that limit the formation upon calcination of low ORR activity Co nanoparticles. These Co-N complexes give rise upon calcination to CoN{sub x-2} sites in which the coordination of Co could favor the adsorption on them of O{sub 2}, which would make those sites particularly active and selective. At the same mass acitivity of 1 A/g{sub cata}, the voltage yielded by the catalyst was 200 mV lower than that for a state-of-the-art Pt (10 wt.%) catalyst, whoch H{sub 2}O{sub 2} output at 0.85 V was 39% and involves the exchange of 3.2 e{sup -}, overall making our material an attractive substitute to noble metal ORR electrocatalysts.

04 OIL SHALES AND TAR SANDS↗
DOE OSTI2019

A Graph Theory Method for Identification of a Minimum Breakpoint Set for Directional Relay Coordination

The energy grid becomes more complex with increasing penetration of renewable resources, distributed energy storage, distributed generators, and more diverse loads such as electric vehicle charging stations. The presence of distributed energy resources (DERs) requires directional protection due to the added potential for energy to flow in both directions down the line. Additionally, contingency requirements for critical loads within a microgrid may result in looped or meshed systems. Computation speeds of iterative methods required to coordinate loops are improved by starting with a minimum breakpoint set (MBPS) of relays. A breakpoint set (BPS) is a set of breakers such that, when opened, breaks all loops in a mesh grid creating a radial system. A MBPS is a BPS that consists of the minimum possible number of relays required to accomplish this goal. In this paper, a method is proposed in which a minimum spanning tree is computed to indirectly break all loops in the system, and a set difference is used to identify the MBPS. The proposed method is found to minimize the cardinality of the BPS to achieve a MBPS.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2016

Tungsten Biscorroles: New Chiral Sandwich Compounds

Abstract The oxidative metalation method, involving the interaction of free‐base meso ‐triarylcorroles and W(CO) 6 in refluxing decalin, led to a set of three tungsten(VI) biscorroles, the first homoleptic sandwich compounds involving corroles. Single‐crystal X‐ray structures of two of the complexes revealed square‐antiprismatic coordination and strongly domed corroles with long W−N distances of 2.15–2.22 Å and a substantial displacement of ∼1.17 Å of the metal relative to the mean N 4 planes of the ligands. The structures correspond to approximate C 2 symmetry and are thus chiral. DFT calculations strongly indicate that the enantiomers are configurationally stable and hence amenable to chiral resolution. Their other notable properties include a strongly blueshifted Soret band at (357±2) nm, a relatively intense π→W(d ) near‐IR feature at (781±3) nm, and a low electrochemical HOMO–LUMO gap of approximately 1.3 V. The results obtained herein suggest that metallobiscorroles may emerge as a new class of inherently chiral chromophores with novel optical and electrochemical properties.

Alemayehu, Abraham B.↗
DOE OSTI2013

NHERF-1 regulation of EGF and neurotensin signalling in HT-29 epithelial cells

Highlights: ► NHERF-1 expression was abundant throughout HT-29 cells consistent with a cancerous phenotype. ► Knockdown of NHERF-1 lead to a significant reduction in cell proliferation. ► EGF and neurotensin-mediated proliferation was inhibited by knockdown of NHERF-1. ► Neurotensin-mediated Ca{sup 2+} response was abolished by knockdown of NHERF-1. -- Abstract: Neurotensin receptors (NT-R) and the epidermal growth factor receptors (EGF-R) are commonly overexpressed in many epithelial origin tumours. In addition to their role as mitogenic mediators through specific cell signalling, recent studies indicate that the activity/expression of scaffold proteins responsible for the assembly and coordination of the signalling complexes may also have central roles in epithelial transformation. In particular, the “epithelial” PSD-95/Dlg/Zo-1 (PDZ) scaffold/adapter protein, Na{sup +}/H{sup +} exchanger regulatory factor isoform one (NHERF-1), has been identified as a potential regulator of cellular transformation. NHERF-1 is a known regulator of EGF-R function and plays numerous roles in G-protein-coupled receptor signalling. Because of the synergistic signalling between these two potent mitogens, we investigated a potential role for NHERF-1 in the molecular mechanism linking the aberrant proliferative phenotype initiated by some G-Protein-coupled receptor activators in the colon adenocarcinoma HT-29 cell line. Knockdown (80%) of endogenous NHERF-1 leads to significant reduction in proliferation rate; an effect that could not be recovered by exogenous application of either NT or EGF. Inhibition of the EGF-R with AG1487 also inhibited proliferation and this effect could not be recovered with NT. Knockdown of NHERF-1 significantly altered the expression of the EGF-R, and almost completely abolished the NT-mediated increases in intracellular free Ca{sup 2+}. Knockdown of NHERF-1 also attenuated UTP-mediated purinergic Ca{sup 2+} signalling. Taken together, these data suggest that NHERF-1 plays a more central role in cell proliferation by modulating Gq-mediated signalling pathways.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Structural Basis of Lysosomal Phospholipase A 2 Inhibition by Zn 2+

Lysosomal phospholipase A 2 (LPLA 2 /PLA2G15) is a key enzyme involved in lipid homeostasis and is characterized by both phospholipase A2 and transacylase activity and by an acidic pH optimum. Divalent cations such as Ca 2+ and Mg 2+ have previously been shown to have little effect on the activity of LPLA 2 , but the discovery of a novel crystal form of LPLA 2 with Zn 2+ bound in the active site suggested a role for this divalent cation in regulating enzyme activity. In this complex, the cation directly coordinates the serine and histidine of the α/β-hydrolase triad and stabilizes a closed conformation. This closed conformation is characterized by an inward shift of the lid loop, which extends over the active site and effectively blocks access to one of its lipid acyl chain binding tracks. Therefore, we hypothesized that Zn 2+ would inhibit LPLA 2 activity at a neutral but not acidic pH because histidine would be positively charged at lower pH. Indeed, Zn 2+ was found to inhibit the esterase activity of LPLA 2 in a noncompetitive manner exclusively at a neutral pH (between 6.5 and 8.0). Because lysosomes are reservoirs of Zn 2+ in cells, the pH optimum of LPLA 2 might allow it to catalyze acyl transfer unimpeded within the organelle. Here, we conjecture that Zn 2+ inhibition of LPLA 2 at higher pH maintains a lower activity of the esterase in environments where its activity is not typically required.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

Lanthanide(III) di- and tetra-nuclear complexes supported by a chelating tripodal tris(amidate) ligand

Syntheses, structural, and spectroscopic characterization of multinuclear tris(amidate) lanthanide complexes is described. Addition of K 3 [N(o-PhNC(O) t Bu) 3 ] to LnX 3 (LnX 3 = LaBr 3 , CeI 3 , and NdCl 3 ) in N,N-dimethylformamide (DMF) results in the generation of dinuclear complexes, [Ln(N(o-PhNC(O) t Bu) 3 )(DMF)] 2 (μ-DMF) (Ln = La (1), Ce (2), Nd(3)), in good yields. Syntheses of tetranuclear complexes, [Ln(N(o-PhNC(O) t Bu) 3 )] 4 (Ln = Ce (4), Nd(5)), resulted from protonolysis of Ln[N(SiMe 3 ) 2 ] 3 (Ln = Ce, Nd) with N(o-PhNCH(O) t Bu) 3 . As a result, in the solid-state, complexes 1–5 exhibit coordination modes of the tripodal tris(amidate) ligand that are unique to the 4f elements and have not been previously observed in transition metal systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Surface-Initiated Atom Transfer Radical Polymerization Using Hydrogel Reactors

Atom transfer radical polymerization (ATRP) is a controlled radical polymerization method that enables the synthesis of tailored polymeric materials with low dispersity, highlighting its immense potential for green fabrication of advanced materials. However, its broader implementation is limited by challenges in product isolation, maintaining catalyst activity, and mitigating atmospheric sensitivity arising from oxygen-sensitive metal catalysts. Here, gelatin hydrogels (GHs) are introduced as a soft “reactor” matrix for interfacial ATRP, operating with minimal metal-catalyst loading while exhibiting possibly an organoreductive behavior. This strategy leverages activator regeneration via electron transfer through a ligand–metal charge-transfer (LMCT) mechanism to reduce oxidized metal catalysts within the GH network. Polymerization is evaluated by growing polymer brushes at an active interface formed between GHs swollen in monomer solution and an initiating surface, and sequential growth experiments confirmed that GH-mediated ATRP preserves living character. Under UV illumination, LMCT is activated, producing polymers both at the desired interface and within the GH bulk. UV–Vis spectroscopy revealed active reduction of Cu(II) to Cu(I) along with concentration-dependent complex formation, indicating dynamic coordination chemistry within the hydrogel. The redox-active arginine- and glutamic acid-rich gelatin backbone coordinates and reduces the metal center, enabling ATRP at ppm-level catalyst concentrations. While polymerization proceeds in GH-Cu(II) reactors, adding external mobile ligands to the GH results in longer polymer brushes. Here, the results reported here are exploratory. More experiments are needed to characterize polymer brush growth in GHs and compare it to conventional surface-initiated polymerization in solution.

Absorption↗
DOE OSTI2021

Liquid-induced topological transformations of cellular microstructures

The fundamental topology of cellular structures—the location, number and connectivity of nodes and compartments—can profoundly affect their acoustic, electrical5, chemical, mechanical and optical properties, as well as heat, fluid and particle transport. Approaches that harness swelling, electromagnetic actuation and mechanical instabilities in cellular materials have enabled a variety of interesting wall deformations and compartment shape alterations, but the resulting structures generally preserve the defining connectivity features of the initial topology. Achieving topological transformation presents a distinct challenge for existing strategies: it requires complex reorganization, repacking, and coordinated bending, stretching and folding, particularly around each node, where elastic resistance is highest owing to connectivity. Here we introduce a two-tiered dynamic strategy that achieves systematic reversible transformations of the fundamental topology of cellular microstructures, which can be applied to a wide range of materials and geometries. Our approach requires only exposing the structure to a selected liquid that is able to first infiltrate and plasticize the material at the molecular scale, and then, upon evaporation, form a network of localized capillary forces at the architectural scale that ‘zip’ the edges of the softened lattice into a new topological structure, which subsequently restiffens and remains kinetically trapped. Reversibility is induced by applying a mixture of liquids that act separately at the molecular and architectural scales (thus offering modular temporal control over the softening–evaporation–stiffening sequence) to restore the original topology or provide access to intermediate modes. Guided by a generalized theoretical model that connects cellular geometries, material stiffness and capillary forces, we demonstrate programmed reversible topological transformations of various lattice geometries and responsive materials that undergo fast global or localized deformations. In conclusion, we then harness dynamic topologies to develop active surfaces with information encryption, selective particle trapping and bubble release, as well as tunable mechanical, chemical and acoustic properties.

42 ENGINEERING↗
DOE OSTI2016

Mechanistic investigation of the Zn/Pd/C catalyzed cleavage and hydrodeoxygenation of lignin

While current biorefinery processes use lignin only for its heat value, the conversion of lignin to high value chemicals is an area of increasing interest. In this article we present a detailed mechanistic study of the hydrodeoxygenation (HDO) of lignin by using a synergistic Pd/C and Zn II catalyst through use of both lignin model compounds and lignocellulosic biomass. Spectroscopic data coupled with the study of lignin model compounds suggest that Zn II activates and facilitates removal of the hydroxyl group at the Cγ position of the β-O-4 ether linkage. Activation is proposed to occur through formation of a six-membered ring complex of Zn II coordinated to the oxygen atoms at Cα and Cγ of the lignin model compound guaiacylglycerol-β-guaiacyl.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Rare Earth Arylsilazido Compounds with Inequivalent Secondary Interactions

Here, a new bulky silazido ligand, –N(SiHMe 2 )Dipp (Dipp = C 6 H 3 -2,6- i Pr 2 ) supports planar, three-coordinate homoleptic rare earth complexes Ln{N(SiHMe 2 )Dipp} 3 (Ln = Sc, Y, Lu) that each contain three secondary Ln←HSi interactions and one agostic CH bond. Y{N(SiHMe 2 )Dipp} 3 and acetophenone react via hydrosilylation, rather than by insertion into the Y–N bond or enolate formation.

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

Ligand substituents modulate excited-state lifetime and energy-transfer reactivity in Cu( I ) photosensitizers supported by salicylaldimine and isocyanide ligands

The design of earth-abundant molecular photosensitizers with desirable photophysical properties and good excited-state reactivity is critical for sustainable photochemical applications. Herein, we report a new family of three-coordinate heteroleptic Cu(I) complexes supported by monoanionic salicylaldimine (N^O) chelating ligands and aryl isocyanides. By systematically tuning the steric bulk on each ligand, we establish clear structure–property relationships that govern the excited-state lifetimes and photocatalytic performance metrics of these complexes. Increasing steric congestion on the salicylaldimine ligand, which contributes to the HOMO, results in faster nonradiative decay and shortens excited-state lifetimes. In contrast, introducing steric bulk on the isocyanide ligand, where the LUMO is primarily localized, suppresses nonradiative decay, most likely by inhibiting excited-state geometric relaxation, thereby extending the lifetime up to 375 ns. These photophysical trends correlate directly with performance in triplet–triplet energy transfer (TTET) photocatalysis, where longer-lived complexes enable faster E/Z isomerization of trans-stilbene. This work demonstrates that remote steric modulation of ligand frameworks offers a simple yet powerful strategy for tuning the excited-state dynamics and catalytic properties of this new class of Cu(I) photosensitizers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Persistent topological features of dynamical systems

Inspired by an early work of Muldoon et al., Physica D 65, 1–16 (1993), we present a general method for constructing simplicial complex from observed time series of dynamical systems based on the delay coordinate reconstruction procedure. The obtained simplicial complex preserves all pertinent topological features of the reconstructed phase space, and it may be analyzed from topological, combinatorial, and algebraic aspects. In focus of this study is the computation of homology of the invariant set of some well known dynamical systems that display chaotic behavior. Persistent homology of simplicial complex and its relationship with the embedding dimensions are examined by studying the lifetime of topological features and topological noise. The consistency of topological properties for different dynamic regimes and embedding dimensions is examined. The obtained results shed new light on the topological properties of the reconstructed phase space and open up new possibilities for application of advanced topological methods. The method presented here may be used as a generic method for constructing simplicial complex from a scalar time series that has a number of advantages compared to the mapping of the same time series to a complex network.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Color center in β -Ga 2 O 3 emitting at the telecom range

Transition metal (TM) ions incorporated into a host from a wide bandgap semiconductor are recognized as a promising system for quantum technologies with enormous potential. In this work, we report on a TM color center in β-Ga 2 O 3 with physical properties attractive for quantum information applications. The center is found to emit at 1.316 μm and exhibits weak coupling to phonons, with optically addressable higher-lying excited states, beneficial for single-photon emission within the telecom range (O-band). Using magneto-photoluminescence (PL) complemented by time-resolved PL measurements, we identify the monitored emission to be internal 1 E→ 3 A 2 spin-forbidden transitions of a 3d 8 TM ion with a spin-triplet ground state—a possible candidate for a spin qubit. We tentatively attribute this color center to a complex involving a sixfold coordinated Cu 3+ ion.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Source term method for binary neutron stars initial data

The initial condition problem for a binary neutron star system requires a Poisson equation solver for the velocity potential with a Neumann-like boundary condition on the surface of the star. Difficulties that arise in this boundary value problem are: (a) the boundary is not known a priori, but constitutes part of the solution of the problem; (b) various terms become singular at the boundary. In this work, we present a new method to solve the fluid Poisson equation for irrotational/spinning binary neutron stars. The advantage of the new method is that it does not require complex fluid surface fitted coordinates and it can be implemented in a Cartesian grid, which is a standard choice in numerical relativity calculations. This is accomplished by employing the source term method proposed by Towers, where the boundary condition is treated as a jump condition and is incorporated as additional source terms in the Poisson equation, which is then solved iteratively. The issue of singular terms caused by vanishing density on the surface is resolved with an additional separation that shifts the computation boundary to the interior of the star. We present two-dimensional tests to show the convergence of the source term method, and we further apply this solver to a realistic three-dimensional binary neutron star problem. By comparing our solution with the one coming from the initial data solver cocal, we demonstrate agreement to approximately 1%. We report our method can be used in other problems with non-smooth solutions like in magnetized neutron stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

A family of α/β hydrolases removes phytol from chlorophyll metabolites for tocopherol biosynthesis in Arabidopsis

Tocopherol synthesis requires phytyl diphosphate derived from phytol esterified to chlorophyll metabolites. The >600-member Arabidopsis thaliana α/β hydrolase (ABH) gene family contains 4 members that can release phytol from chlorophyll metabolites in vitro; however, only pheophytinase (PPH) affects tocopherol synthesis when mutated, reducing seed tocopherols by 5%. We report the biochemical analysis of 2 previously uncharacterized ABHs, chlorophyll dephytylase 2 (CLD2) and CLD3, and their respective mutants singly and in combinations with pph and cld1 alleles. While all CLDs localized to the thylakoid and could hydrolyze phytol from chlorophylls and Pheophytin a in vitro, CLD3 had the highest in vitro activity and the largest effect on tocopherol synthesis in vivo. The 3 CLDs acted cooperatively to provide phytol for 31% of tocopherols synthesized in light-grown leaf tissue. Dark-induced leaf senescence assays showed PPH is required for 18% of the tocopherols synthesized. Though the cld123 triple mutant had no impact on dark-induced tocopherol content, cld123 in the pph background reduced tocopherol levels by an additional 18%. In seeds, pph and cld123 each reduced tocopherol content by 5% and by 15% in the cld123pph quadruple mutant. VTE7 ( ViTamin E7 ) is an envelope-localized ABH that specifically affects chlorophyll biosynthetic intermediates in vivo and is required for 55% of seed tocopherol synthesis. The introduction of cld123pph into the vte7 background further reduced seed tocopherol levels to 23% of that of the wild type. Our findings demonstrate that phytol provision for tocopherol biosynthesis and homeostasis is a complex process involving the coordinated spatiotemporal expression of multiple ABH family members.

arabidopsis↗