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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Reactions of the ˙NO 3 radical with nuclear extraction ligands in alkane solution

Here, the reactivity of the nitrate radical (NO 3 ˙) with organophosphorus and amidic actinide and lanthanide complexing agents of interest to nuclear solvent extraction applications was measured, resulting in the first-ever reported bimolecular rate constants for this radicals’ reactions in dodecane solution. The order of reactivity for neutral organophosphorus compounds showed faster rate constants with increasing electron density on the phosphoryl phosphorus atom, indicating an increasing facility for electron abstraction reactions occurring in addition to H-atom abstraction from the ligand alkane chains. The only acidic organophosphorus compound investigated, HEH[EHP], showed low reactivity with the NO 3 ˙ radical, attributed to its dimerization in this non-polar solvent. Amide ligand reaction rates were faster than for organophosphorus molecules, suggesting more facile H-atom abstraction from carbonyl activated methylene and amyl groups. While all rate constants were slower than the diffusion-limited rate they were still rapid enough to result in significant oxidation of solvent extraction ligands in dodecane solution.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2021

QuaSiMo: A composable library to program hybrid workflows for quantum simulation

Abstract A composable design scheme is presented for the development of hybrid quantum/classical algorithms and workflows for applications of quantum simulation. The proposed object‐oriented approach is based on constructing an expressive set of common data structures and methods that enables programming of a broad variety of complex hybrid quantum simulation applications. The abstract core of the scheme is distilled from the analysis of the current quantum simulation algorithms. Subsequently, it allows synthesis of new hybrid algorithms and workflows via the extension, specialisation, and dynamic customisation of the abstract core classes defined by the proposed design. The design scheme is implemented using the hardware‐agnostic programming language QCOR into the QuaSiMo library. To validate the implementation, the authors test and show its utility on commercial quantum processors from IBM and Rigetti, running some prototypical quantum simulations.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

Post-transition state dynamics and product energy partitioning following thermal excitation of the F∙∙∙HCH 2 CN transition state: Disagreement with experiment

Born-Oppenheimer direct dynamics simulations were performed to study atomistic details of the F + CH 3 CN → HF + CH 2 CN H-atom abstraction reaction. The simulation trajectories were calculated with a combined M06-2X/MP2 algorithm utilizing the 6-311++G** basis set. In accord with experiment and assuming the accuracy of transition state theory (TST), the trajectories were initiated at the F-HCH 2 CN abstraction TS with a 300 K Boltzmann distribution of energy and directed towards products. Recrossing of the TS was negligible, confirming the accuracy of TST for the simulation. HF formation was rapid, occurring within 0.014 ps of the trajectory initiation. The intrinsic reaction coordinate (IRC) for reaction involves rotation of HF about CH 2 CN and then trapping in the CH 2 CN-HF post-reaction potential energy well of ~10 kcal/mol with respect to the HF + CH 2 CN products. In contrast to this IRC, five different trajectory types were observed, with the majority involving direct dissociation and only 11% approximately following the IRC. The HF vibrational and rotational quantum numbers, n and J, were calculated when HF was initially formed and they increase as potential energy is released in forming the HF + CH 2 CN products. The population of the HF product vibrational states is only in qualitative agreement with experiment, with the simulations showing depressed and enhanced populations of the n = 1 and 2 states as compared to experiment. From the simulations and with an anharmonic zero-point energy constraint, the percentage partitioning of the product energy to relative translation, HF rotation, HF vibration, CH 2 CN rotation and CH 2 CN vibration is 5, 11, 60, 7, and 16%, respectively. In contrast the experimental energy partitioning percentages to HF rotation and vibration are 6 and 41%. Comparisons are made between the current simulation and those for other F + H-atom abstraction reactions. The simulation product energy partitioning and HF vibrational population for F + CH 3 CN → HF + CH 2 CN are similar to those for these other reactions. Finally, a detailed discussion is given of possible origins of the difference between the simulation and experimental energy partitioning dynamics for the F + CH 3 CN → HF + CH 2 CN reaction. The F + CH 3 CN reaction also forms the CH 3 C(F)N intermediate, in which the F-atom adds to the C≡N bond. However, this intermediate and the F---CH 3 CN and CH 3 CN-F van der Waals complexes are not expected to affect the F + CH 3 CN → HF + CH 2 CN product energy partitioning.

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

High-level theoretical characterization of the vinoxy radical ( • CH 2 CHO) + O 2 reaction

Numerous processes in atmospheric and combustion chemistry produce the vinoxy radical ( • CH 2 CHO). To understand the fate of this radical and to provide reliable energies needed for kinetic modeling of such processes, we have examined its reaction with O 2 using highly reliable theoretical methods. Utilizing the focal point approach, the energetics of this reaction and subsequent reactions were obtained using coupled-cluster theory with single, double, and perturbative triple excitations [CCSD(T)] extrapolated to the complete basis set limit. These extrapolated energies were appended with several corrections including a treatment of full triples and connected quadruple excitations, i.e., CCSDT(Q). In addition, this study models the initial vinoxy radical + O 2 reaction for the first time with multireference methods. We predict a barrier for this reaction of approximately 0.4 kcal mol –1 . This result agrees with experimental findings but is in disagreement with previous theoretical studies. The vinoxy radical + O 2 reaction produces a 2-oxoethylperoxy radical which can undergo a number of unimolecular reactions. Abstraction of a β-hydrogen (a 1,4-hydrogen shift) and dissociation back to reactants are predicted to be competitive to each other due to their similar barriers of 21.2 and 22.3 kcal mol –1 , respectively. The minimum-energy β-hydrogen abstraction pathway produces a hydroperoxy radical (QOOH) that eventually decomposes to formaldehyde, CO, and • OH. Two other unimolecular reactions of the peroxy radical are α-hydrogen abstraction (38.7 kcal mol –1 barrier) and HO 2 • elimination (43.5 kcal mol –1 barrier). Furthermore, these pathways lead to glyoxal + • OH and ketene + HO 2 • formation, respectively, but they are expected to be uncompetitive due to their high barriers.

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

New reactions of diazene and related species for modelling combustion of amine fuels

Potential energy surfaces for reactions involving N 2 H 2 isomers of diazene (diimide) have been explored using density functional theory, with energies based on coupled-cluster theory. A focus is on processes that create or consume these species, and isomerisation between the E (trans) and Z (cis) forms of HNNH. Furthermore, these include isomerisation and dissociation pathways for HNNH, addition of H atoms to form N 2 H 3 , abstraction by H atoms yielding short-lived NNH, and abstraction reactions of H with N 2 H 3 . Transition state and capture theories are applied for high-pressure-limiting behaviour, while low-pressure and falloff regions are characterised via the methods of Troe and coworkers. Rate constants and thermochemistry are provided to improve models of diamine chemistry, relevant to the combustion of NH 3 especially at high concentrations, high pressures or under reducing conditions. Results indicate that amine radical recombination mainly yields the E HNNH isomer, while H-abstraction from N 2 H 3 results in E HNNH and H 2 NN. However, at elevated temperature E → Z isomerisation becomes competitive, and Z HNNH, being more reactive, acts to enhance the diazene consumption rate.

10 SYNTHETIC FUELS↗
DOE OSTI2013

UNVEILING THE NATURE OF UNIDENTIFIED GAMMA-RAY SOURCES. II. RADIO, INFRARED, AND OPTICAL COUNTERPARTS OF THE GAMMA-RAY BLAZAR CANDIDATES

A significant fraction ({approx}30%) of the high-energy gamma-ray sources listed in the second Fermi Large Area Telescope catalog (2FGL) are still of unknown origin, being not yet associated with counterparts at low energies. We recently developed a new association method to identify if there is a {gamma}-ray blazar candidate within the positional uncertainty region of a generic 2FGL source. This method is entirely based on the discovery that blazars have distinct infrared colors with respect to other extragalactic sources found, thanks to the Wide-field Infrared Survey Explorer (WISE) all-sky observations. Several improvements have also been performed to increase the efficiency of our method in recognizing {gamma}-ray blazar candidates. In this paper we applied our method to two different samples, the first constituted by unidentified {gamma}-ray sources (UGSs), and the second by active galaxies of uncertain type, both listed in the 2FGL. We present a catalog of IR counterparts for {approx}20% of the UGSs investigated. Then, we also compare our results for the associated sources with those present in the literature. In addition, we illustrate the extensive archival research carried out to identify the radio, infrared, optical, and X-ray counterparts of the WISE-selected, {gamma}-ray blazar candidates. Finally, we discuss the future developments of our method based on ground-based follow-up observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Kinetics and selectivity of methane oxidation on an IrO 2 (110) film

Undercoordinated, bridging O-atoms (O br ) are highly active as H-acceptors in alkane dehydrogenation on IrO 2 (110) surfaces but transform to HO br groups that are inactive toward hydrocarbons. The low C–H activity and high stability of the HO br groups cause the kinetics and product selectivity during CH 4 oxidation on IrO 2 (110) to depend sensitively on the availability of O br atoms prior to the onset of product desorption. From temperature programmed reaction spectroscopy (TPRS) and kinetic simulations, we identified two O br -coverage regimes that distinguish the kinetics and product formation during CH 4 oxidation on IrO 2 (110). Under excess O br conditions, when the initial O br coverage is greater than that needed to oxidize all the CH 4 to CO 2 and HO br groups, complete CH 4 oxidation is dominant and produces CO 2 in a single TPRS peak between 450 and 500 K. However, under O br -limited conditions, nearly all the initial O br atoms are deactivated by conversion to HO br or abstracted after only a fraction of the initially adsorbed CH 4 oxidizes to CO 2 and CO below 500 K. Thereafter, some of the excess CH x groups abstract H and desorb as CH 4 above ~500 K while the remainder oxidize to CO 2 and CO at a rate that is controlled by the rate at which Obr atoms are regenerated from HObr during the formation of CH 4 and H 2 O products. We also show that chemisorbed O-atoms ('on-top O') on IrO 2 (110) enhance CO 2 production below 500 K by efficiently abstracting H from Obr atoms and thereby increasing the coverage of O br atoms available to completely oxidize CH x groups at low temperature. Furthermore, our results provide new insights for understanding factors which govern the kinetics and selectivity during CH 4 oxidation on IrO 2 (110) surfaces.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

1‐Formyl‐7‐hydroxy‐6,7‐dihydro‐5 H ‐pyrrolizine (9‐CHO‐DHP) ‐ A Biologically Proximate Pyrrolic Metabolite of Carcinogenic Pyrrolizidine Alkaloids

Pyrrolizidine alkaloids (PAs) are phytochemical constituents of more than 6000 plant species worldwide; approximately half of the PAs are hepatotoxic, genotoxic, and carcinogenic. Because of their wide exposure and carcinogenicity, the International Programme on Chemical Safety (IPCS) concluded that PAs are a threat to human health and safety. We recently determined that the metabolic activation pathway of PA‐induced liver tumor initiation is mediated by a set of four (±)‐6,7‐dihydro‐7‐hydroxy‐1‐hydroxymethyl‐5H‐pyrrolizine (DHP)‐derived DNA adducts, and proposed that these DHP‐DNA adducts are potential biomarkers of PA exposure and liver tumor initiation. To validate the generality of this metabolic activation pathway and DHP‐DNA adducts as biomarkers, it is important to identify the spectrum of reactive metabolites associated with this metabolic activation pathway. Segall et al. ( Drug Metab. Disposit. , 12, 68–71, 1984) reported that 1‐formyl‐7‐hydroxy‐6,7‐dihydro‐5 H ‐pyrrolizine (9‐CHO‐DHP) is a metabolite formed from the mouse liver microsomal metabolism of senecionine. In this present study, we examined the metabolism of six hepatocarcinogenic PAs (riddelliine, senecionine, monocrotaline, senkirkine, intermedine, and heliotrine) and one non‐carcinogenic PA (platphylline) by human, rat, and mouse liver microsomes. 9‐CHO‐DHP was found as a common metabolite from the metabolism of the six hepatotoxic PAs, but not from platphylline. Incubation of 9‐CHO‐DHP in HepG2 cells and A549 cells resulted in the formation of the same set of DHP‐DNA adducts, as assessed by both LC/MS SRM mode and selected ion monitoring analyses through comparison to synthetic standards. In the incubation medium of HepG2 cells, both DHP and 7‐cysteine‐DHP were identified. These metabolites have previously shown to be capable of binding to cellular DNA to produce DHP‐DNA adducts. Thus, when incubated with HepG2 cells, 9‐CHO‐DHP was metabolized to the reactive metabolites DHP and 7‐cysteine‐DHP, metabolites associated with the DHP‐DNA adduct formation. These results indicate that 9‐CHO‐DHP is a DNA proximate metabolite of hepatotoxic PAs and further support the generality of this metabolic activation pathway mediated by the formation of these DHP‐DNA adducts. [This abstract is not an official U.S. Food and Drug Administration (FDA) guidance or policy statement. No offcial support or endorsement by the U.S. FDA is intended or should be inferred. The authors declare no competing financial interest.] Support or Funding Information This research was supported in part by appointment (X.H.) to the Postgraduate Research Program at the NCTR administered by the Oak Ridge Institute for Science and Education through an interagency agreement between the U.S. Department of Energy and the FDA. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

Xia, Qingsu↗
DOE OSTI2018

Organophosphate Hydrolase (OPH) Designed as a Functional Monomer

Organophosphate hydrolase (OPH) mutants haveshown potential use as a medical countermeasure against a range of differentorganophosphorus compounds (OPs). OPH is typicallyexpressed in bacteria as a homodimer. Two separate monomers (~37kDa each) self‐assemble throughnon‐covalent bonding at the enzyme face close to the putative active site, andenzyme activity is dependent upon dimer formation. OPH homodimers do notsecrete expediently from mammalian cells and are often misfolded. This causespotential problems when trying to express the protein from a heterologous plasmidor viral delivery system. To enhance secretion of OPH from mammalian cells, wesought to increase protein solubility without catastrophic detriment toactivity and without addition of fusion proteins. To this end, we designed OPH tobe expressed as a functional monomer by joining two OPH subunits with a poly‐glycinelinker and expressing it as a single polypeptide in bacteria to evaluateactivity. We created the single polypeptide OPH with a tether 10 or 35 aminoacids in length between the two halves, and named them T10 and T35, respectively. Western blot analysis and paraoxon hydrolysis assays revealedthat T10 was being produced and there was a 71% loss in specific activity comparedto an untethered homodimer positive control. This was a surprise as we expectedT10 to have no enzymatic activity since the tether was too short to allowproper dimer formation. The T35 functional monomer (~76 kDa) was produced showing 29% loss of specific activity. Both T10 and T35 OPH showed high molecular weight aggregate formation greater than 250 kDa in dynamic light scattering and native polyacrylamide gels. Construction of a functional OPH monomer with activity against OPs is instrumental in designing secretable OPHs for adeno‐associatedviral expression. It may also prove useful in the development of chimeric OPHs for maintaining control over the composition of each OPH half, allowing blended activities against a combination of organophosphorus substrates. This is the first attempt known for producing OPH as a functional monomer. Support or Funding Information The views expressed in this abstract are those of the author(s) and do not reflect the official policy of the Department of Army, Department of Defense, or the U.S. Government. This research was supported by the Defense Threat Reduction Agency – Joint Science and Technology Office, Medical S&T Division. This research was supported in part by an appointment to the Postgraduate Research Participation Program at the U.S. Army Medical Research Institute of Chemical Defense administered by the Oak Ridge Institute for Science and Education through an interagency agreement between the U.S. Department of Energy and USAMRMC. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

Baker, Cetara↗
DOE OSTI2018

Evaluating the Pharmacodynamics and Protective Efficacy of Catalytic Bioscavenger following Subcutaneous Administration in Guinea Pigs

Previous studies determined the guinea pig was a viableanimal model for evaluating subcutaneous ( s.c. )injection as an alternative route of administration of catalytic Bioscavengers:enzymes designed to render nerve agents non‐toxic in systemic circulation following exposure. Recent studies have focused on evaluating the pharmacodynamics (PD) and protective efficacy (PE) of the lead bioscavenger candidate, organophosphorus hydrolase (OPH) variant, YT, as both unmodified and modified (PEGylated) versions of the enzyme. A comparative study was conducted with YT and three progressively sized PEG‐YT variants (934, 935, and 936) following a single bolus s.c. dose (5 mg/kg). Bioavailability increased linearly with molecular size such that the largest sized PEG‐YT variant, 936, afforded the highest bioavailability, thus promoting 936 to subsequent PD and PEstudies. Dose dependence on bioavailability was also examined via three cohorts of guinea pigs receiving doses (5, 15, 20 mg/kg) of either YT or 936 in which a linear dose response was also found. Guinea pigs receiving either YT or 936 (5 mg/kg) via intramuscular (i.m. )or s.c. routes had superimposable PD profiles regardless of route, suggesting an identical absorption pathway for the drugs. Protective efficacy was also evaluated by exposing the animals to 2xLD 50 of sarin (GB) 7 dayspost‐enzyme administration; only the animals receiving 936 ( i.m. and s.c. ) survived 24 hours post‐exposure. Periodic s.c. dosing strategies were also evaluated with 936 in which three injections were administered either 2 or 24 hours apart for a total dose of 15 mg/kg followed by a protective efficacy assessment 8 days post‐administration. Overall these data support the use of s.c . injection as a practical route of administration for catalytic bioscavenger with PE Gylation, synergistically enhancing both bioavailability and extending drug half‐life in circulation. Support or Funding Information The views expressed in this abstract are those of the author(s) and do not reflect the official policy of the Department of Army, Department of Defense, or the U.S. Government. The experimental protocol was approved by the Animal Care and Use Committee at the United States Army Medical Research Institute of ChemicalDefense and all procedures were conducted in accordance with the principlesstated in the Guide for the Care and Use of Laboratory Animals and the AnimalWelfare Act of 1966 (P.L. 89–544), as amended. This work was supported by the Defense Threat Reduction Agency‐Joint Science and Technology Office, MedicalS&T Division. *Thisresearch was supported in part by an appointment to the Postgraduate ResearchParticipation Program at the U.S. Army Medical Research Institute of ChemicalDefense administered by the Oak Ridge Institute for Science and Educationthrough an interagency agreement between the U.S. Department of Energy and USAMRMC. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

Dao, Thuy↗
DOE OSTI2019

Optimization of an in Vitro CYP450 Induction Assay Using Cryopreserved Cell Lines

Cytochrome P450 (CYP450) enzymes are responsible for the majority for Phase I metabolism. Induction occurs when a drug increases the rate of CYP450 enzyme production. As a result, the rates of metabolism of subsequent drugs increase, posing concerns for dosing and safety. To further expand the USAMRICD Absorption, Distribution, Metabolism, Excretion, and Toxicity Center of Excellence (ADMET CoE) profiling capabilities, a CYP450 induction assay is being developed using alternative cell lines to primary human hepatocytes to measure changes in gene expression of CYP1A2 and CYP3A4 isoenzymes. Primary human hepatocytes are the gold standard for evaluating P450 induction in vitro ; however, they have inherent limitations such as high costs, fastidious nature, and significant lot‐to‐lot variability. Induction assessments using cryopreserved hepatocytes and two immortalized cell lines, HepaRG and HepatoCells, are being conducted to determine a more robust, cost‐effective alternative model. Each cell line was exposed to the standard inducers rifampicin and omeprazole to assess CYP3A4 and CYP1A2 activity, respectively. Following a 72‐hour incubation period, RNA from the cell cultures was extracted and purified. Fold changes of gene expression were measured using real‐time quantitative PCR (RT‐qPCR). Hepatocytes displayed an average fold change of 92.7 for CYP3A4 and 49.6 for CYP1A2, whereas HepaRG displayed changes of 28.6 and 179.5, respectively. Average values for CYP3A4 and CYP1A2 for HepatoCells were 58.7 and 43.9. Based on the data, HepatoCells most closely mimicked cryopreserved hepatocytes in comparison to HepaRG cells. Additional data on assay parameters and technique optimization will be presented. Support or Funding Information Opinion disclaimer: The views expressed in this abstract are those of the authors and do not reflect the official policy of the Department of the Army, Department of Defense, or the U.S. Government. This project was generously supported in part by an appointment to the Postgraduate Research Participation Program at the U.S. Army Medical Research Institute of Chemical Defense administered by the Oak Ridge Institute for Science and Education through an interagency agreement between the U.S. Department of Energy and U.S. Army Medical Research and Materiel Command. Support is also provided by the Defense Threat Reduction Agency – Joint Science and Technology Office, Medical S&T Division. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

Lim, Tae Young↗