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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Efficient derivatization of methylphosphonic and aminoethylsulfonic acids related to nerve agents simultaneously in soils using trimethyloxonium tetrafluoroborate for their enhanced, qualitative detection and identification by EI-GC–MS and GC–FPD

Trimethyloxonium tetrafluoroborate (TMO·BF 4 ) has been used here in the simultaneous derivatization of phosphonic and 2-aminoethylsulfonic acids related to nerve agents in different soils for their enhanced detection and identification by electron ionization gas chromatography-mass spectrometry (EI-GC–MS). The panel of acids consisted of five Schedule 2 phosphonic acids (methyl methylphosphonic acid, ethyl methylphosphonic acid, isopropyl methylphosphonic acid, pinacolyl methylphosphonic acid and cyclohexyl methylphosphonic acid) along with two sulfonic acids, N,N-diethyl-2-aminoethylsulfonic acid and N,N-diisopropyl-2-aminoethylsulfonic acid. The acids were converted to their corresponding methyl esters at ambient temperature when present at a 10 μg g -1 concentration in three separate soils: Virginia type A soil, Ottawa sand and Nebraska EPA soil. The concentration of the acids reflects values typically encountered during proficiency tests (PTs) administered annually by the Organisation for the Prohibition of Chemical Weapons (OPCW). Derivatization times to yield detectable signals for the methyl ester products for all the acids was found to vary among all three soil samples, however, it was found that generally the most optimal time across all the matrices involved was 3 h after the addition of TMO·BF 4 . Concomitantly, the analysis of the samples was complemented using GC coupled to flame photometric detection (GC–FPD). The inclusion of GC–FPD in the analysis yielded stronger signals for all seven methylated analytes making their detection after merely 3 h possible relative to the ones initially obtained with EI-GC–MS. Regarding the three soils employed in our study, a greater methylating efficiency was found in the Virginia type A soil and Ottawa sand yielding results that were significantly larger in magnitude to those found during the same time points for the Nebraska EPA soil sample. Prolonged reaction times (up to 72 h) were explored to find the time for the highest yield of methyl ester production were found instead to be deleterious to the process showcasing the importance of the fast yielding nature of the process specifically in situations where time-sensitive analysis is crucial (e.g. OPCW-PT).

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

Ab Initio Reaction Kinetics of CH 3 O$\dot{C}$(=O) and $\dot{C}$H 2 OC(=O)H Radicals

The dissociation and isomerization kinetics of the methyl ester combustion intermediates methoxycarbonyl radical (CH3O$\dot{C}$(=O)) and (formyloxy)methyl radical ($\dot{C}$H2OC(=O)H) are investigated theoretically using high-level ab initio methods and Rice–Ramsperger–Kassel–Marcus (RRKM)/master equation (ME) theory. Geometries obtained at the hybrid density functional theory (DFT) and coupled cluster singles and doubles with perturbative triples correction (CCSD(T)) levels of theory are found to be similar. We employ high-level ab initio wave function methods to refine the potential energy surface: CCSD(T), multireference singles and doubles configuration interaction (MRSDCI) with the Davidson–Silver (DS) correction, and multireference averaged coupled-pair functional (MRACPF2) theory. MRSDCI+DS and MRACPF2 capture the multiconfigurational character of transition states (TSs) and predict lower barrier heights than CCSD(T). The temperature- and pressure-dependent rate coefficients are computed using RRKM/ME theory in the temperature range 300–2500 K and a pressure range of 0.01 atm to the high-pressure limit, which are then fitted to modified Arrhenius expressions. Dissociation of CH3O$\dot{C}$(=O) to $\dot{C}$H3 and CO2 is predicted to be much faster than dissociating to CH3$\dot{O}$ and CO, consistent with its greater exothermicity. Isomerization between CH3O$\dot{C}$(=O) and $\dot{C}$H2OC(=O)H is predicted to be the slowest among the studied reactions and rarely happens even at high temperature and high pressure, suggesting the decomposition pathways of the two radicals are not strongly coupled. The predicted rate coefficients and branching fractions at finite pressures differ significantly from the corresponding high-pressure-limit results, especially at relatively high temperatures. Finally, because it is one of the most important CH3$\dot{O}$ removal mechanisms under atmospheric conditions, the reaction kinetics of CH3$\dot{O}$ + CO was also studied along the PES of CH3O$\dot{C}$(=O); the resulting kinetics predictions are in remarkable agreement with experiments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1994

Permeability of membranes to amino acids and modified amino acids: mechanisms involved in translocation

The amino acid permeability of membranes is of interest because they are one of the key solutes involved in cell function. Membrane permeability coefficients (P) for amino acid classes, including neutral, polar, hydrophobic, and charged species, have been measured and compared using a variety of techniques. Decreasing lipid chain length increased permeability slightly (5-fold), while variations in pH had only minor effects on the permeability coefficients of the amino acids tested in liposomes. Increasing the membrane surface charge increased the permeability of amino acids of the opposite charge, while increasing the cholesterol content decreased membrane permeability. The permeability coefficients for most amino acids tested were surprisingly similar to those previously measured for monovalent cations such as sodium and potassium (approximately 10(-12)-10(-13) cm s-1). This observation suggests that the permeation rates for the neutral, polar and charged amino acids are controlled by bilayer fluctuations and transient defects, rather than partition coefficients and Born energy barriers. Hydrophobic amino acids were 10(2) more permeable than the hydrophilic forms, reflecting their increased partition coefficient values. External pH had dramatic effects on the permeation rates for the modified amino acid lysine methyl ester in response to transmembrane pH gradients. It was established that lysine methyl ester and other modified short peptides permeate rapidly (P = 10(-2) cm s-1) as neutral (deprotonated) molecules. It was also shown that charge distributions dramatically alter permeation rates for modified di-peptides. These results may relate to the movement of peptides through membranes during protein translocation and to the origin of cellular membrane transport on the early Earth.

Review↗
DOE OSTI2014

Reconciling macro- with nano- carrier mobility measurements in organic photovoltaic blends

Conductive atomic force microscopy (CAFM) is a valuable tool for electrical characterization of organic photovoltaics. However, the quantitative interpretation of the data is complicated by an apparent disagreement between the carrier mobilities calculated by CAFM and those determined by macroscopic measurements, with no apparent physical explanation for the discrepancy. In the present work, the space charge limited current model (specifically Mott-Gurney law) and its assumptions are assessed, and a physical model reconciling this discrepancy is proposed. Its applicability on the tip-sample system used in CAFM measurements is discussed, by accounting for the high electric fields arising around the tip of the CAFM probe and affecting carrier mobility. Charge carrier mobility is calculated from current-voltage curves obtained from conductive atomic force microscopy spectroscopy scans done on Poly(3-hexylthiophene-2,5-diyl): 95% PC{sub 70}BM ([6,6]-Phenyl-C71-butyric acid methyl ester)/5% PC{sub 60}BM ([6,6]-Phenyl-C61-butyric acid methyl ester) samples for different concentration ratios of donor and acceptor. We show that charge carrier mobilities obtained with this model are in satisfactory agreement with macroscopic measurements available in literature.

36 MATERIALS SCIENCE↗
DOE OSTI2014

C{sub 60}-dyad aggregates: Self-organized structures in aqueous solutions

Extensive full-atomistic molecular dynamics simulations are performed to study the self-organization of C{sub 60}-fullerene dyad molecules in water, namely phenyl-C{sub 61}-butyric acid methyl ester and fulleropyrrolidines, which have two elements of ordering, the hydrophobic fullerene cage and the hydrophilic/ionic group. While pristine fullerene or phenyl-C{sub 61}-butyric acid methyl ester forms spherical droplets in order to minimize the surface tension, the amphiphilic nature of charged solute molecules leads to the formation of supramolecular assemblies having cylindrical shape driven by charge repulsion between the ionic groups located on the surface of the aggregates. We show that formation of non-spherical micelles is the geometrical consequence if the fullerene derivatives are considered as surfactants where the ionized groups are only hydrophilic unit. The agglomeration behavior of fullerenes is evaluated by determining sizes of the clusters, solvent accessible surface areas, and shape parameters. By changing the size of the counterions from chloride over iodide to perchlorate we find a thickening of the cylinder-like structures which can be explained by stronger condensation of larger ions and thus partial screening of the charge repulsion on the cluster surface. The reason for the size dependence of counterion condensation is the formation of a stronger hydration shell in case of small ions which in turn are repelled from the fullerene aggregates. Simulations are also in good agreement with the experimentally observed morphologies of decorated C{sub 60}-nanoparticles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Ligand‐Mediated Quantum Yield Enhancement in 1‐D Silver Organothiolate Metal–Organic Chalcogenolates

X-ray free electron laser (XFEL) microcrystallography and synchrotron single-crystal crystallography are used to evaluate the role of organic substituent position on the optoelectronic properties of metal–organic chalcogenolates (MOChas). MOChas are crystalline 1D and 2D semiconducting hybrid materials that have varying optoelectronic properties depending on composition, topology, and structure. While MOChas have attracted much interest, small crystal sizes impede routine crystal structure determination. A series of constitutional isomers where the aryl thiol is functionalized by either methoxy or methyl ester are solved by small molecule serial femtosecond X-ray crystallography (smSFX) and single crystal rotational crystallography. While all the methoxy examples have a low quantum yield (0-1%), the methyl ester in the ortho position yields a high quantum yield of 22%. Here, the proximity of the oxygen atoms to the silver inorganic core correlates to a considerable enhancement of quantum yield. Four crystal structures are solved at a resolution range of 0.8–1.0 Å revealing a collapse of the 2D topology for functional groups in the 2- and 3- positions, resulting in needle-like crystals. Further analysis using density functional theory (DFT) and many-body perturbation theory (MBPT) enables the exploration of complex excitonic phenomena within easily prepared material systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Microlens array induced light absorption enhancement in polymer solar cells

Over the last decade, polymer solar cells (PSCs) have attracted a lot of attention and highest power conversion efficiencies (PCE) are now close to 10%. Here we employ an optical structure – the microlens array (MLA) – to increase light absorption inside the active layer, and PCE of PSCs increased even for optimized devices. Normal incident light rays are refracted at the MLA and travel longer optical paths inside the active layers. Two PSC systems – poly(3-hexylthiophene-2,5-diyl):(6,6)-phenyl C61 butyric acid methyl ester (P3HT:PCBM) and poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl]:(6,6)-phenyl C71 butyric acid methyl ester (PCDTBT:PC70BM) – were investigated. In the P3HT:PCBM system, MLA increased the absorption, absolute external quantum efficiency, and the PCE of an optimized device by [similar]4.3%. In the PCDTBT:PC70BM system, MLA increased the absorption, absolute external quantum efficiency, and PCE by more than 10%. In addition, simulations incorporating optical parameters of all structural layers were performed and they support the enhancement of absorption in the active layer with the assistance of MLA. Our results show that utilizing MLA is an effective strategy to further increase light absorption in PSCs, in which optical losses account for [similar]40% of total losses. MLA also does not pose materials processing challenges to the active layers since it is on the other side of the transparent substrate.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Biosynthesis of polycyclopropanated high energy biofuels

Cyclopropane-functionalized hydrocarbons are excellent fuels due their high energy density. However, the organic synthesis of these molecules is challenging and harmful to the environment. In this work we produced polycyclopropanated fatty acids in bacteria. These molecules can be easily converted into renewable fuels for high energy applications such as shipping, long-haul transport, aviation, and rocketry. We explored the chemical diversity encoded in the genome of thousands of bacteria to identify and repurpose naturally occurring cyclopropanated molecules. We identified a set of candidate iterative polyketide synthases (iPKSs) predicted to produce polycyclopropanated fatty acids (POP-FAs), expressed these PKSs in Streptomyces coelicolor and produced the POP-FAs. We determined the structure of the molecules and increased their production 22-fold. Polycyclopropanated fatty acid methyl esters (POP-FAMEs) were obtained by methyl esterifying the POP-FAs. Finally, we calculated that our POP fuel candidates can have energy densities of more than 50 MJ/L. Our research shows that POP-FAMEs and other polyketide derived POPs have the energetic properties for energy-demanding applications for which sustainable alternatives are scarce.

09 BIOMASS FUELS↗
DOE OSTI2019

Methylation protocol for the retrospective detection of isopropyl-, pinacolyl- and cyclohexylmethylphosphonic acids, indicative markers for the nerve agents sarin, soman and cyclosarin, at low levels in soils using EI-GC–MS

A practical and efficient protocol for the derivatization and detection by GC-EI-MS of isopropyl-, pinacolyl- and cyclohexylmethylphosphonic acids, key diagnostic degradation products of the nerve agents sarin, soman and cyclosarin respectively, in six different types of soil matrices is presented here. The method involves the in situ conversion of the phosphonic acids to their respective methyl esters using trimethyloxonium tetrafluoroborate when present in the soils at low levels (10 μg g -1 ) without any prior extractions or soil preparation. The soils employed in our study were Nebraska EPA soil, Georgia soil, silt, Virginia type A soil, regular sand and Ottawa sand and were chosen for their vast differences in composition and physical features. Appealing attributes of the protocol include its rapidity (t < 30 min), mildness (ambient temperature), and practicality that includes the production of the phosphonic methyl esters that can be easily detected by GC-EI–MS and corroborated with the instrument&#x27;s internal NIST spectral library or the Organisation for the Prohibition of Chemical Weapons (OPCW) central analytical database (OCAD v.21_2019). The overall efficacy of the protocol was then tested on a soil sample featured in the 44th OPCW PT that our laboratory participated in. After preparing the soil so as to give pinacolyl methylphosphonic acid at a 5 μg g -1 concentration, the acid was successfully methylated and detected by GC-EI-MS. The protocol's performance mirrors that of the universally employed diazomethane protocol but accomplishes this without any of the explosive hazards and time consuming reagent preparation commonly associated with it.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Optimization of microwave-enhanced methanolysis of algal biomass to biodiesel under temperature controlled conditions

The effect of a "controlled temperature" approach was investigated in the microwave-enhanced simultaneous extraction and transesterification of dry algae. Experimental runs were designed using a response surface methodology (RSM). The process parameters such as dry algae to methanol ratio, reaction time, and catalyst concentrations were optimized to evaluate their effects on the fatty acid methyl ester (FAME) yield under the "controlled temperature" conditions. Thermal energy associated with the microwave transesterification process was calculated at various temperature levels using the optimized process parameters. Algal biomass characterization and algal biodiesel analysis were carried out using various analytical instruments such as FTIR, TEM, GC-MS and confocal laser scanning microscopy. Thermogravimetric analysis under both nitrogen and oxygen environments was performed to examine the thermal and oxidative stability of the algal fatty acid methyl esters.

09 BIOMASS FUELS↗
DOE OSTI2015

Structure–activity relationships of imidazole-derived 2-[N-carbamoylmethyl-alkylamino]acetic acids, dual binders of human insulin-degrading enzyme

Insulin degrading enzyme (IDE) is a zinc metalloprotease that degrades small amyloid peptides such as amyloid-â and insulin. So far the dearth of IDE-specific pharmacological inhibitors impacts the understanding of its role in the physiopathology of Alzheimer's disease, amyloid-â clearance, and its validation as a potential therapeutic target. Hit 1 was previously discovered by high-throughput screening. Here we describe the structure-activity study, that required the synthesis of 48 analogues. We found that while the carboxylic acid, the imidazole and the tertiary amine were critical for activity, the methyl ester was successfully optimized to an amide or a 1,2,4-oxadiazole. Along with improving their activity, compounds were optimized for solubility, lipophilicity and stability in plasma and microsomes. The docking or co-crystallization of some compounds at the exosite or the catalytic site of IDE provided the structural basis for IDE inhibition. The pharmacokinetic properties of best compounds 44 and 46 were measured in vivo . As a result, 44 (BDM43079) and its methyl ester precursor 48 (BDM43124) are useful chemical probes for the exploration of IDE's role.

Charton, Julie↗
NASA NTRS1999

A large blood pressure-raising effect of nitric oxide synthase inhibition in humans

In experimental animals, systemic administration of nitric oxide synthase (NOS) inhibitors causes large increases in blood pressure that are in part sympathetically mediated. The aim of this study was to determine the extent to which these conclusions can be extrapolated to humans. In healthy normotensive humans, we measured blood pressure in response to two NOS inhibitors, NG-monomethyl-L-arginine (L-NMMA) and NG-nitro-L-arginine methyl ester (L-NAME), the latter of which recently became available for use in humans. The major new findings are 3-fold. First, L-NAME produced robust increases in blood pressure that were more than 2 times larger than those previously reported in humans with L-NMMA and approximated those seen in experimental animals. L-NAME (4 mg/kg) raised mean arterial pressure by 24+/-2 mm Hg (n=27, P<0.001), whereas in subjects who received both inhibitors, a 12-fold higher dose of L-NMMA (50 mg/kg) raised mean arterial pressure by 15+/-2 mm Hg (n=4, P<0.05 vs L-NAME). Second, the L-NAME-induced increases in blood pressure were caused specifically by NOS inhibition because they were reversed by L-arginine (200 mg/kg, n=12) but not D-arginine (200 mg/kg, n=6) and because NG-nitro-D-arginine methyl ester (4 mg/kg, n=5) had no effect on blood pressure. Third, in humans, there is an important sympathetic component to the blood pressure-raising effect of NOS inhibition. alpha-Adrenergic blockade with phentolamine (0.2 mg/kg, n=9) attenuated the L-NAME-induced increase in blood pressure by 40% (P<0.05). From these data, we conclude that pharmacological inhibition of NOS causes large increases in blood pressure that are in part sympathetically mediated in humans as well as experimental animals.

Non-NASA Center↗
DOE OSTI2016

Density functional study of the electronic structure of dye-functionalized fullerenes and their model donor-acceptor complexes containing P3HT

We study the electronic structure of C{sub 60} fullerenes functionalized with a thiophene-diketo-pyrrolopyrrole-thiophene based chromophore using density functional theory combined with large polarized basis sets. As the attached chromophore has electron donor character, the functionalization of the fullerene leads to a donor-acceptor (DA) system. We examine in detail the effect of the linker and the addition site on the electronic structure of the functionalized fullerenes. We further study the electronic structure of these DA complexes with a focus on the charge transfer excitations. Finally, we examine the interface of the functionalized fullerenes with the widely used poly(3-hexylthiophene-2,5-diyl) (P3HT) donor. Our results show that all functionalized fullerenes with an exception of the C{sub 60}-pyrrolidine [6,6], where the pyrrolidine is attached at a [6,6] site, have larger electron affinities relative to the pristine C{sub 60} fullerene. We also estimate the quasi-particle gap, lowest charge transfer excitation energy, and the exciton binding energies of the functionalized fullerene-P3MT model systems. Results show that the exciton binding energies in these model complexes are slightly smaller compared to a similarly prepared phenyl-C{sub 61}-butyric acid methyl ester (PCBM)-P3MT complex.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1972

Capillary gas chromatography with two new moderately high temperature phases.

Gas chromatography test results are presented for two new moderately high-temperature phases of Dexsil 400-GC with free hydroxyl end groups (uncapped) and with end groups covered by trimethyl silyl groups (capped). The two Dexsil 400-GC phases were tested for their ability to resolve N-TFA-DL-(+)-2-butyl esters and n-butyl esters, as well as fatty acid methyl esters and hydrocarbon standards. Generally the more polar uncapped phase was superior to the capped phase in all separation comparisons, except for the hydrocarbons.

Pollock, G. E.↗
DOE OSTI2015

Scaling relation for high-temperature biodiesel surrogate ignition delay times

High-temperature Arrhenius ignition delay time correlations are useful for revealing the underlying parameter dependencies of combustion models, for simplifying and optimizing combustion mechanisms for use in engine simulations, for scaling experimental data to new conditions for comparison purposes, and for guiding in experimental design. Here, we have developed a scaling relationship for Fatty Acid Methyl Ester (FAME) ignition time data taken at high temperatures in 4%O 2 /Ar mixtures behind reflected shocks using an aerosol shock tube: τ ign [ms] = 2.24 x 10 -6 [ms] (P [atm]) -.41 ($\phi$) 0.30 (C n ) -.61 x exp $$ \left(\frac{37.1 [kcal/mol]}{\hat{R}_u [kcal / mol K] T [K]}\right) $$ In addition, we have combined our ignition delay time data for methyl decanoate, methyl palmitate, methyl oleate, and methyl linoleate with other experimental results in the literature in order to derive fuel-specific oxygen-mole-fraction scaling parameters for these surrogates. In conclusion, in this article, we discuss the significance of the parameter values, compare our correlation to others found in the literature for different classes of fuels, and contrast the above expression’s performance with correlations obtained using leading FAME kinetic models in 4%O 2 /Ar mixtures.

09 BIOMASS FUELS↗
DOE OSTI2017

Total Fatty Acid Content Determination of Whole Microalgal Biomass Using In Situ Transesterification

The aliphatic chains of fatty acids are the most prominent and potentially the highest value precursor constituents of algal biomass, and thus accurately quantifying the algal biomass total fatty acid content is a prerequisite for comparing algal strains, growth conditions, and processes. Direct, acid-catalyzed transesterification of whole microalgal biomass is a simple, effective, and widely used method to determine the fatty acid content in whole algal biomass. Such a direct transesterification procedure typically covers the following steps: first, solubilizing the lipids in the biomass matrix and then liberating the fatty acids to make these available for catalytic upgrading to fatty acid methyl esters (FAMEs), subsequent extraction into hexane, and then quantification by gas chromatography. The method we describe here requires less than 10 mg of biomass per sample and is considered high-throughput and highly accurate.

09 BIOMASS FUELS↗
DOE OSTI2018

Production of High Performance Lubricants from Cellulosic Sugar

Certain classes of fatty acids are valuable raw materials that can used to produce bio-based lubricants; however, their broader use has been limited by the high cost and limited availability. The project described in this report was focused on producing a fatty acid methyl ester (FAME) of a specific chain length from cellulosic sugars. Development of a biological pathway and engineered organisms for production of low-cost FAME from cellulosic sugar is a novel and potentially disruptive technology that is supportive of BETO’s mission to displace all fractions of a barrel of crude oil. The project was organized around four tasks that focus on A) production pathway engineering, B) host strain engineering, C) assembly of production pathway in host strain, and D) fermentation process development. Pathway engineering focused on discovery and improvement of two key pathway enzymes, namely 3-keto acetyl CoA synthase (KAS) and wax ester synthase (WES). Both enzymes were improved using a variety of enzyme engineering and mutagenesis approaches, and assembled into a host strain with relevant additional pathway genes and genome modifications. Assembled strains were evaluated in 2-L benchtop fermenters using a commercially produced cellulosic hydrolysate to supply carbon source for FAME production. These evaluations demonstrated that performance targets and final milestones were met or exceeded for sugar uptake rate, product titer, product specificity, and production rate.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1978

Synthesis of perfluoroalkylene aromatic diamines

Analogues of methylene dianilines were synthesized, in which the methylene group between the two aromatic nuclei was replaced by various perfluoroalkylene linkage. The hydrolytic thermal, and thermal oxidative stabilities of PMR Polyimides derived from these diamines were determined. Three types of PMR Polyimide discs were fabricated from the dimethyl ester of 3,3', 4,4'-benzophenonetetracarboxylic acid, the methyl ester of 5-norbornene-2,3-dicarboxylic acid, and one of the following three diamines: methyl dianiline, 1,3-bis(4-aminophenyl)hexafluoropropane, and 2,2-bis(4-aminophenyl)hexafluoropropane. The polyimide based on 2,2-bis(4-aminophenyl)hexafluoropropane exhibited the best hydrolytic, thermal, and thermal oxidative stability as determined by moisture uptake and thermogravimetric analysis.

Paciorek, K. L.↗