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At least 1,441 records · Page 80
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Energy-resolved mass spectrometry as a tool for identification of lignin depolymerization products

Lignin is the largest source of bio-based aromatic compounds in nature, and its valorization is essential to the sustainability of lignocellulosic biorefining. Characterizing lignin-derived compounds remains challenging due to the heterogeneity of this biopolymer. Tandem mass spectrometry is a promising tool for lignin structural analytics, as fragmentation patterns of model compounds can be extrapolated to identify characteristic moieties in complex samples. This work extends previous resonance excitation type collision-induced dissociation (CID) methods that identified lignin oligomers containing β-Ο-4, β-5, and β-β bonds, to also identify characteristics of 5-5, β-1, and 4-Ο-5 dimers, enabled by quadrupole time-of-flight (QTOF) CID with energy-resolved mass spectrometry (ERMS). Overall, beam type ERMS offers in-depth structural information and could ultimately contribute to tools for high-throughput lignin dimer identification.

09 BIOMASS FUELS↗
DOE OSTI2019

Theoretical and experimental investigation of geometry and stability of small potassium‐iodide KnI(n=2–6) clusters

Small heterogeneous potassium-iodide clusters are investigated by means of ab initio electronic structural methods together with experimental production and detection in mass spectrometry. Experiments were done by using Knudsen cell mass spectrometry (KCMS) modification method, which provided simultaneous generating of all KnI0,+1 (n = 2–6) clusters at once. Clusters with more than two potassium atoms are produced for the first time. The lowest lying isomers of those KnI0,+1 (n = 2–6) clusters were found by using a random-kick procedure. The best description of growth of these clusters is the addition of one potassium atom to a smaller-neighbor cluster. Subsequently, stability of these species was examined. In spite of general trend of decreasing of binding energies, the closed-shell species have slightly larger stability with respect to the open-shell species. Alternation of dissociation energies between closed-shell and open-shell clusters is presented. Experimental setup also allows determination of ionization energies of clusters: the obtained values are in the range of 3.46–3.98 eV, which classify these clusters as “superalkali.” For closed-shell clusters, the theoretical adiabatic ionization energies are close to experimental values, whereas in the case of open-shell clusters, the vertical ionization energies are those that are close to experimental values. © 2019 Wiley Periodicals, Inc.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Photochemistry of cis,trans-[Pt{sup IV}(en)(I){sub 2}(CH{sub 3}COO){sub 2}] complex in aqueous solutions

The photochemistry of aqueous solutions of the cis,trans-[Pt{sup IV}(en)(I){sub 2}(CH{sub 3}COO){sub 2}] complex (1) was studied by stationary photolysis, nanosecond laser flash photolysis and ultrafast kinetic spectroscopy in the time interval from hundreds of femtoseconds to minutes. It is shown that the multistage photolysis, including photochemical reactions of ligand exchange and photoreduction, involves in the fi rst step the formation of the cis-[{sup IV}(en)(I){sub 2}(CH{sub 3}COO){sub 2}] complex with a quantum yield of 0.3 (irradiation at 282 nm). The further ligand exchange and photoreduction reactions occur with much lower quantum yields. The photochemical exchange of the acetate ion occurs in a time interval of ~100 ps with the much slower final step, being probably the acidic dissociation of the product. The key intermediate of the first step of the process was detected in the picosecond time range. Depending on the interpretation of the key intermediate nature, two possible mechanisms of the primary photochemical process are proposed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Efficiency of low-molecular-weight and high-molecular-weight alkoxyamines in the synthesis of polystyrene

The influence of the structure of high-molecular-weight alkoxyamines (obtained in situ from C-phenyl-N-tert-butylnitrone and 2-(benzylideneamino)-2-methyl-1-phenylpropanol-1-N-oxide) and their low-molecular-weight analogs on styrene polymerization in the temperature range 70—110 ° was analyzed. The controlled synthesis of polystyrene in the presence of low-molecular-weight alkoxyamines was revealed to occur most efficiently at 110 °. The use of high-molecular-weight alkoxyamines makes it possible to perform the controlled process under lower-temperature conditions (70—90 °), when the constant polymerization rate and linear increase in the molecular weight with conversion are observed, and the synthesis of polymers with fairly low polydispersity (M{sub w}/M{sub n} ~ 1.26) is also possible. The quantum chemical calculations showed that the energy of the C-ON bond in alkoxyamines is determined by the length of the chains at the nitroxide fragment rather than the structure of the substituents. It is found that the equilibrium dissociation constants of high-molecular-weight alkoxyamines are caused by both the structure of the nitroxide fragment and molecular weights.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Effects of Fluorine on Solidification, Viscosity, Structure, and Heat Transfer of CaO-Al{sub 2}O{sub 3}-Based Mold Fluxes

To mitigate the chemical reaction between mold fluxes and high-Al steel, CaO-Al{sub 2}O{sub 3}-based mold fluxes were proposed to replace the conventional CaO-SiO{sub 2}-based mold fluxes. However, the high viscosity of CaO-Al{sub 2}O{sub 3}-based mold fluxes is harmful to the lubrication to the strand. In this article, the effects of fluorine on solidification, viscosity, structure, and heat transfer of CaO-Al{sub 2}O{sub 3}-based mold fluxes were evaluated. The addition of fluorine increased the break temperature and decreased the heat transfer rate of mold fluxes. It also reduced the flux viscosity at 1673 K (1400 °C) when fluorine content increased from 4.0 to 6.9 mass pct; but a further increase of fluorine to 12.5 mass pct did not notably change the flux viscosity. This phenomenon was correlated to the synergic effects of the dissociation of flux network and the increased potential of nucleation at high temperature with the fluorine addition.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Substance P in Solution: Trans-to-Cis Configurational Changes of Penultimate Prolines Initiate Non-enzymatic Peptide Bond Cleavages

We report ion mobility spectrometry and mass spectrometry studies of the non-enzymatic step-by-step degradation of substance P (subP), an 11-residue neuropeptide, with the sequence Arg{sup 1}-Pro{sup 2}-Lys{sup 3}-Pro{sup 4}-Gln{sup 5}-Gln{sup 6}-Phe{sup 7}-Phe{sup 8}-Gly{sup 9}-Leu{sup 10}-Met{sup 11}-NH{sub 2}, in ethanol. At elevated solution temperatures (55 to 75 °C), several reactions are observed, including a protonation event, i.e., [subP+2H]{sup 2+} + H{sup +} → [subP+3H]{sup 3+}, that appears to be regulated by a configurational change and two sequential bond cleavages (the Pro{sup 2}-Lys{sup 3} peptide bond is cleaved to form the smaller nonapeptide Lys{sup 3}-Met{sup 11}-NH{sub 2} [subP{sub (3–11)}], and subsequently, subP{sub (3–11)} is cleaved at the Pro{sup 4}-Gln{sup 5} peptide bond to yield the heptapeptide Gln{sup 5}-Met{sup 11}-NH{sub 2} [subP{sub (5–11)}]). Each of the product peptides [subP{sub (3–11)} and subP{sub (5–11)}] is accompanied by a complementary diketopiperazine (DKP): cyclo-Arg{sup 1}-Pro{sup 2} (cRP) for the first cleavage, and cyclo-Lys{sup 3}-Pro{sup 4} (cKP) for the second. Insight about the mechanism of degradation is obtained by comparing kinetics calculations of trial model mechanisms with experimental data. The best model of our experimental data indicates that the initial cleavage of subP is regulated by a conformational change, likely a trans→cis isomerization of the Arg{sup 1}-Pro{sup 2} peptide bond. The subP{sub (3–11)} product has a long lifetime (t{sub 1/2} ~ 30 h at 55 °C) and appears to transition through several structural intermediates prior to dissociation, suggesting that subP{sub (3–11)} is initially formed with a Lys{sup 3}-trans-Pro{sup 4} peptide bond configuration and that slow trans→cis isomerization regulates the second bond cleavage event as well. From these data and our model mechanisms, we obtain transition state thermochemistry ranging from ΔH{sup ‡} = 41 to 85 kJ mol{sup −1} and ΔS{sup ‡} = − 43 to – 157 J mol{sup −1} K{sup −1} for each step in the reaction. .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Fundamental Studies on Poly(2-oxazoline) Side Chain Isomers Using Tandem Mass Spectrometry and Ion Mobility-Mass Spectrometry

When polymer mixtures become increasingly complex, the conventional analysis techniques become insufficient for complete characterization. Mass spectrometric techniques can satisfy this increasing demand for detailed sample characterization. Even though isobaric polymers are indistinguishable using simple mass spectrometry (MS) analyses, more advanced techniques such as tandem MS (MS/MS) or ion mobility (IM) can be used. Here, we report proof of concept for characterizing isomeric polymers, namely poly(2-n-propyl-2-oxazoline) (Pn-PrOx) and poly(2-isopropyl-2-oxazoline) (Pi-PrOx), using MS/MS and IM-MS. Pi-PrOx ions lose in intensity at higher accelerating voltages than Pn-PrOx ions during collision-induced dissociation (CID) MS/MS experiments. A Pn/i-PrOx mixture could also be titrated using survival yield calculations of either precursor ions or cation ejection species. IM-MS yielded shape differences in the degree of polymerization (DP) regions showing the structural rearrangements. Combined MS techniques are thus able to identify and deconvolute the molar mass distributions of the two isomers in a mixture. Finally, the MS/MS and IM-MS behaviors are compared for interpretation. .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

UV–Vis Photodissociation Action Spectroscopy on Thermo LTQ-XL ETD and Bruker amaZon Ion Trap Mass Spectrometers: a Practical Guide

We report automated procedures for multiple tandem mass spectra acquisition allowing UV–Vis photodissociation action spectroscopy measurements of ions and radicals. The procedures were developed for two commercial ion trap mass spectrometers and applied to collision-induced and electron–transfer dissociation tandem mass spectrometry modes of ion generation. .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Ligation Kinetics as a Probe for Non-Covalent Electrostatic Bonding and Electron Solvation of Alkali and Alkaline Earth Cations with Ammonia

Mono-ligation kinetics were measured for ammonia reacting with atomic cations in the first two groups of the periodic table (K{sup +}, Rb{sup +}, Cs{sup +} and Ca{sup +}, Sr{sup +}, Ba{sup +}). Also, mono-ligation energies were computed using density functional theory (DFT) in an attempt to assess the role of non-covalent electrostatic interactions in these chemical reactions. The measurements were performed at room temperature in helium bath gas at 0.35 Torr using an inductively coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. Rate coefficients are reported for ammonia addition, the only reaction channel that was observed with all these cations. A systematic decrease in the rate of addition of NH{sub 3} was observed for both group 1 and 2 cations going down the periodic table. The computational studies predict a decrease in the adduct binding energy and an increase in the bond separation going down groups 1 and 2 of the periodic table and provide some insight into the role of the extra selectron in the group 2 radical cations in ligand bonding. A correlation is seen between the efficiency of ligation and the binding energy of the adduct ion and attributed to the lifetime of the intermediate encounter complex against back dissociation which is dependent on its well depth. Higher-order additions of ammonia were also observed. Remarkable differences in the extent and kinetics were seen between the group 1 and 2 cations, and these were attributed to the occurrence of ammonia solvation of the extra s electron in the higher-order adducts of the alkaline earth cations. .

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Co-adsorption of O{sub 2} and C{sub 2}H{sub 4} on a Free Gold Dimer Probed via Infrared Photodissociation Spectroscopy

Infrared multiple photon dissociation (IR-MPD) spectroscopy in conjunction with density functional theory (DFT) calculations has been employed to study the activation of molecular oxygen and ethylene co-adsorbed on a free gold dimer cation Au{sub 2}{sup +}. Both studied complexes, Au{sub 2}O{sub 2}(C{sub 2}H{sub 4}){sup +} and Au{sub 2}O{sub 2}(C{sub 2}H{sub 4}){sub 2}{sup +}, show distinct features of both intact O{sub 2} and ethylene co-adsorbed on the cluster. However, the ethylene C=C double bond is activated, increasing in length by up to 0.07 Å compared with the free molecule, and the red shift of the O–O vibration frequency increases with the number of adsorbed ethylene molecules, indicating a small but increasing activation of the O–O bond. The small O{sub 2} activation and the rather weak interaction between O{sub 2} and C{sub 2}H{sub 4} are also reflected in the calculated electronic structure of the co-adsorption complexes which shows only a small occupation of the empty anti-bonding O{sub 2} 2π{sup *}{sub 2p} orbital as well as the localization of most of the Kohn–Sham orbitals on O{sub 2} and C{sub 2}H{sub 4}, respectively, with only limited mixing between O{sub 2} and C{sub 2}H{sub 4} orbitals. The results are compared with theoretical studies on neutral Au{sub x}O{sub 2}(C{sub 2}H{sub 4}) (x = 3, 5, 7, 9) complexes. .

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Formation of Carbon Dioxide Attached Fragment Ions in the Fragmentation of Deprotonated Tolfenpyrad and Tebufenpyrad

The in-source collision-induced dissociation (CID) and MS/MS mass spectra of deprotonated tolfenpyrad and tebufenpyrad both showed an unusual fragment ion at m/z 187, but its fragmentation pattern and structure could not be explained by logical neutral losses. Accurate mass measurement indicated that the mass difference between this fragment ion and the dominant fragment ion at m/z 143 equaled to a carbon dioxide (CO{sub 2}) molecule. The isolation of the fragment ion m/z 143 in the mass analyzer could spontaneously give rise to the ion m/z 187. The Gibbs free energy of carbon dioxide addition to deprotonated pyrazole ion was significantly negative from the computational results. According to these results, we derived a proposal for the formation and structure of the ion m/z 187, which was an attachment of molecular carbon dioxide to the fragment ion m/z 143 to produce a carboxylate anion. The trace carbon dioxide was speculated to be derived from the residual atmosphere or collision gas in the instrument. This study is valuable for the qualitative and quantitative mass spectrometry analysis of pesticides containing the pyrazole functional group. .

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2021

Determination of affinities of lanthanide-binding proteins using chelator-buffered titrations

The recent discoveries of the first proteins that bind lanthanides as part of their biological function not only are relevant to the emerging field of lanthanide-dependent biology, but also hold promise to revolutionize the technologically critical rare earths industry. Although protocols to assess the thermodynamics of metal–protein interactions are well established for “traditional” metal ions in biology, the characterization of lanthanide-binding proteins presents a challenge to biochemists due to the lanthanides' Lewis acidity, propensity for hydrolysis, and high-affinity complexes with biological ligands. These properties necessitate the preparation of metal stock solutions with very low buffered “free” metal concentrations (e.g., femtomolar to nanomolar) for such determinations. Here in this paper we describe several protocols to overcome these challenges. First, we present standardization methods for the preparation of chelator-buffered solutions of lanthanide ions with easily calculated free metal concentrations. We also describe how these solutions can be used in concert with analytical methods including UV–visible spectrophotometry, circular dichroism spectroscopy, Förster resonance energy transfer (FRET), and sensitized terbium luminescence, in order to accurately determine dissociation constants (K d s) of lanthanide–protein complexes. Finally, we highlight how application of these methods to lanthanide-binding proteins, such as lanmodulin, has yielded insights into selective recognition of lanthanides in biology. We anticipate that these protocols will facilitate discovery and characterization of additional native lanthanide-binding proteins, will motivate the understanding of their biological context, and will prompt their applications in biotechnology.

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

Predicting CaO-(MgO)-Al2O3-SiO2 glass reactivity in alkaline environments from force field molecular dynamics simulations

In this investigation, force field-based molecular dynamics (MD) simulations have been employed to generate detailed structural representations for a range of amorphous quaternary CaO-MgO-Al{sub 2}O{sub 3}-SiO{sub 2} (CMAS) and ternary CaO-Al{sub 2}O{sub 3}-SiO{sub 2} (CAS) glasses. Comparison of the simulation results with select experimental X-ray and neutron total scattering and literature data reveals that the MD-generated structures have captured the key structural features of these CMAS and CAS glasses. Based on the MD-generated structural representations, we have developed two structural descriptors, specifically (i) average metal oxide dissociation energy (AMODE) and (ii) average self-diffusion coefficient (ASDC) of all the atoms at melting. Both structural descriptors are seen to more accurately predict the relative glass reactivity than the commonly used degree of depolymerization parameter, especially for the eight synthetic CAS glasses that span a wide compositional range. Hence these descriptors hold great promise for predicting CMAS and CAS glass reactivity in alkaline environments from compositional information.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Medium-independent hydrogen atom binding isotherms of nickel oxide electrodes

Adsorption and transfer of hydrogen atoms at solid/solution interfaces are fundamental to heterogeneous catalysis for chemical energy transformations and other processes. Reported here are electrochemical and spectroelectrochemical measurements of the thermodynamics of H-atom binding to nickel oxide electrodes, both the average and the distribution of NiO–H bond dissociation free energies (BDFEs). These are perhaps the first measurements of binding isotherms at non-metal electrodes. Remarkably, both the BDFEs and the non-Langmuirian isotherms are the same in water, acetonitrile, and dimethylformamide, and with different buffers and proton activities. Such medium independence of the BDFEs and isotherms has not been previously reported for any binary material. The medium independence supports the common use of computed hydrogen binding energies as intrinsic descriptors of surface reactivity, while the broadened isotherms add a level of complexity to such analyses. Furthermore, this work demonstrates the capability to derive key thermodynamic parameters at chemically reactive solid-liquid interfaces.

13 HYDRO ENERGY↗
DOE OSTI2020

Plasma decay in hydrocarbons and hydrocarbon- and H 2 O-containing mixtures excited by high-voltage nanosecond discharge at elevated gas temperatures

Plasma decay after a high-voltage nanosecond discharge was experimentally and numerically studied in pure hydrocarbons (C 2 H 6 and C 3 H 8 ), and H 2 O:N 2 and C 3 H 8 :O 2 mixtures for pressures in the range 2–4 Torr and gas temperatures from 300 to 600 K. In a stoichiometric C 3 H 8 :O 2 mixture, plasma decay was also studied in a repetitively pulsed discharge for varing numbers of discharge pulses (varying degrees of fuel oxidation). The rate of plasma decay was determined from the temporal evolution of electron density measured using the microwave interferometer. It was observed that gas heating to 600 K leads to a decrease in the rate of plasma decay in all cases. The effect of heating on plasma decay was most profound in the H 2 O:N 2 mixture (after a single discharge pulse) and in the C 3 H 8 :O 2 mixture for high degrees of fuel oxidation. A kinetic scheme was developed to numerically simulate the plasma decay in hydrocarbons and combustible mixtures. Numerical analysis showed that, under the conditions studied, plasma decay was controlled by dissociative electron recombination with simple molecular and cluster ions. Gas heating led to a decrease in the rate of the electron-ion recombination and the rate of conversion of molecular ions to cluster ions. As a result, the gas temperature increase caused a decrease in the fraction of cluster ions for which the recombination coefficients are an order of magnitude higher than the recombination coefficients for molecular ions. The influence of gas heating on the decrease of the amount of cluster ions was more important when the ion composition was dominated by hydrated H 3 O + (H 2 O) k ions. The rates of the formation of these ions are extremely sensitive to any variations in gas temperature. A result, in agreement with our observations, gas heating led to an anomalous decrease in the rates of plasma decay in the H 2 O:N 2 mixture, as well as in the C 3 H 8 :O 2 mixture when H 2 O molecules were produced due to fuel oxidation.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2023

Dedication to James A. Miller

This special memorial issue pays tribute to James (Jim) A. Miller, a giant of combustion science who died in 2021, with a celebration of his enormous influence on the field. We were touched by the responses we received after we sent out the invitations for it. Jim inspired several generations of scientists, who viewed him as a mentor, a father figure, and a friend. Together with Nils Hansen and Peter Glarborg, we have written a detailed account on his life and work. Furthermore, it appeared in this journal shortly after his death; and so here we focus on the scientific areas he had interest in and influence on, and how they relate to the 34 papers in this issue. The topics of these papers span a variety of Jim's interests including nitrogen chemistry, polycyclic aromatic hydrocarbon (PAH) chemistry, oxidation chemistry, energy transfer, prompt dissociations, and codes to facilitate combustion chemistry simulations.

96 KNOWLEDGE MANAGEMENT AND PRESERVATION↗
DOE OSTI2024

Suppressed deprotonation enables a durable buried interface in tin-lead perovskite for all-perovskite tandem solar cells

Low-band-gap tin (Sn)-lead (Pb) perovskites are a critical component in all-perovskite tandem solar cells (APTSCs). Current state-of-the-art Sn-Pb perovskite devices exclusively use poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as the hole-transport layer (HTL) but suffer from undesired buried-interface degradation. Here, we show that the deprotonation of the –SO 3 H group in PSS is the root cause of the interface degradation due to its low acid dissociation constant (pK a ), leading to acidic erosion and iodine volatilization in Sn-Pb perovskites. We identify that HTL featuring the carboxyl (–COOH) group with a higher pK a , such as poly[3-(4-carboxybutyl)thiophene-2,5-diyl] (P3CT), can suppress deprotonation and strengthen the interface, mitigating the buried-interface degradation. Motivated by established P3CT modification, we introduce Pb doping to P3CT to increase its work function and reduce interfacial energy loss. Furthermore, we fabricate APTSCs with a champion efficiency of 27.8% and an operational lifetime of over 1,000 h, with 97% retaining efficiency under maximum power point tracking.

08 HYDROGEN↗
DOE OSTI2022

Evidence for nitrogen binding to surface defects for topological insulator Bi 2 Se 3

Using scanning tunneling spectroscopy and theoretical simulations we have studied the effects of nitrogen gas exposure on the electronic density of states of Bi 2 Se 3 , a well-studied topological insulator. In carefully controlled measurements, Bi 2 Se 3 crystals were initially cleaved in a helium gas environment and then exposed to a 22 SCFH flow of ultra-high purity N 2 gas. We observe a resulting change in the spectral curves, with the exposure effect saturating after approximately 50 min, ultimately bringing the Dirac point about 50 meV closer to the Fermi level. Furthermore, these results are compared to density functional theory calculations, which support a picture of N 2 molecules physisorbing near Se vacancies. Furthermore, ab initio molecular dynamics simulations aided by a Blue Moon ensemble method reveal the dissociative adsorption of N 2 molecules which then bind strongly to Se vacancies at the surface. In this scenario, the binding of the N atom to a Se vacancy site removes the surface defect state created by the vacancy and changes the position of the Fermi energy with respect to the Dirac point.

36 MATERIALS SCIENCE↗