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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

The Influence of Water on the Alkyl Region Structure in Variable Chain Length Imidazolium-Based Ionic Liquid/Water Mixtures

In this work, solutions of room temperature ionic liquids (RTILs) and water were studied by observing the reorientational dynamics of the fluorescent probe perylene. Perylene is solvated in the alkyl regions of the RTILs. Its D 2h symmetry made it possible to extract dynamical information on both in-plane and out-of-plane reorientation from time resolved fluorescence anisotropy measurements. Perylene reorientation reports on its interactions with the alkyl chains. The RTILs were a series of 1-alkyl-3-methylimidazolium tetrafluoroborates (C n mimBF 4 , where n is the number of carbons in the alkyl chain), and the effects on perylene’s dynamics were observed when varying the alkyl chain length of the cation (n = 4, 6, 8, and 10; butyl, hexyl, octyl, decyl) and varying the water content from pure RTIL to roughly three water molecules per RTIL ion pair. Time correlated single photon counting was used to measure the fluorescence anisotropy decays to determine the orientational dynamics. The friction coefficients for both the in-plane and out-of-plane reorientation were determined to eliminate the influence of changes in viscosity caused by both the addition of water and the different alkyl chain lengths. The friction coefficients provided information on the interactions of the perylene with it alkyl environment and how these interactions changed with chain length and water content. As chain length increased, the addition of water had less of an effect on the local alkyl environment surrounding the perylene. The friction coefficients generally increased with higher water contents; the inplane orientational motion was hindered significantly more than the out-of-plane motion. The restructuring of the alkyl regions is likely a consequence of a rearrangement of the ionic imidazolium head groups to accommodate partial solvation by water, which results in a change in the arrangement of the alkyl chains. At very high water content, BmimBF4 broke this general trend, with both in-plane and out-of-plane rotational friction decreasing above a water content of one water per ion pair. This decrease indicates a major reorganization of the overall liquid structure in high water content mixtures. In contrast to BmimBF 4 , the longer chain length RTILs are not infinitely miscible with water, and do not show evidence of a major reorganization before reaching saturation and phase-separating. The results suggest that phase separation in longer chain length BF 4 RTILs is a consequence of their inability to undergo the reorganization of the alkyl regions necessary to accommodate high water concentrations.

14 SOLAR ENERGY↗
DOE OSTI2023

Cobalt‐Catalyzed Electroreductive Alkylation of Unactivated Alkyl Chlorides with Conjugated Olefins

Abstract Reactions of unactivated alkyl chlorides under mild and sustainable conditions are rare compared to those of alkyl bromides or iodides. As a result, synthetic methods capable of modifying the vast chemical space of chloroalkane reagents, wastes, and materials are limited. We report the cobalt‐catalyzed reductive addition of unactivated alkyl chlorides to conjugated alkenes. Co‐catalyzed activation of alkyl chlorides is performed under electroreductive conditions, and the resulting reactions constitute formal alkyl‐alkyl bond formation. In addition to developing an operationally simple methodology, detailed mechanistic studies provide insights into the elementary steps of a proposed catalytic cycle. In particular, we propose a switch in the mechanism of C−Cl bond activation from nucleophilic substitution to halogen atom abstraction, which is critical for efficiently generating alkyl radicals. These mechanistic insights were leveraged in designing ligands that enable couplings of primary, secondary, and tertiary alkyl chlorides.

Al Zubaydi, Samir↗
DOE OSTI2023

Cobalt‐Catalyzed Electroreductive Alkylation of Unactivated Alkyl Chlorides with Conjugated Olefins

Abstract Reactions of unactivated alkyl chlorides under mild and sustainable conditions are rare compared to those of alkyl bromides or iodides. As a result, synthetic methods capable of modifying the vast chemical space of chloroalkane reagents, wastes, and materials are limited. We report the cobalt‐catalyzed reductive addition of unactivated alkyl chlorides to conjugated alkenes. Co‐catalyzed activation of alkyl chlorides is performed under electroreductive conditions, and the resulting reactions constitute formal alkyl‐alkyl bond formation. In addition to developing an operationally simple methodology, detailed mechanistic studies provide insights into the elementary steps of a proposed catalytic cycle. In particular, we propose a switch in the mechanism of C−Cl bond activation from nucleophilic substitution to halogen atom abstraction, which is critical for efficiently generating alkyl radicals. These mechanistic insights were leveraged in designing ligands that enable couplings of primary, secondary, and tertiary alkyl chlorides.

Al Zubaydi, Samir↗
DOE OSTI2016

Conformation-specific spectroscopy of alkyl benzyl radicals: Effects of a radical center on the CH stretch infrared spectrum of an alkyl chain

An important initial step in the combustion of gasoline and diesel fuels is the abstraction of hydrogen from alkylbenzenes to form resonance-stabilized alkyl benzyl radicals. This work uses, for the first time, double resonance spectroscopy methods to explore the conformation-specific vibronic and infrared spectroscopy of the α-ethylbenzyl (αEtBz) and α-propylbenzyl (αPrBz) radicals. Local mode Hamiltonian modeling enables assignment of the alkyl CH stretch IR spectra, accounting for Fermi resonance that complicates aliphatic alkyl CH stretch IR spectroscopy. The ground state conformational preferences of the ethyl and propyl chains are changed from those in the alkylbenzenes themselves, with global minima occurring for an in-plane orientation of the alkyl chain (trans) about its first dihedral angle (Φ f123 , numbers are alkyl C atoms. C 1 is CH radical site). This in-plane structure is the only observed conformer for the α-EtBz radical, while two conformers, tt and tg' share this orientation at the first dihedral, but differ in the second (Φ 1234 ) for the αPrBz radical. The in-plane orientation lowers the local site frequencies of the CH 2 group stretches immediately adjacent to the benzylic radical site by about 50 cm -1 relative to those in pure alkyl chains or alkylbenzenes. This effect of the radical site is localized on the first CH 2 group, with little effect on subsequent members of the alkyl chain. In the D 1 excited electronic state, an out-of-plane orientation is preferred for the alkyl chains, leading to torsional mode Franck-Condon activity in the D 0 -D 1 spectra that is both conformer-specific and diagnostic of the conformational change.

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

Hybrid-Lipid Bilayers Induce n -Alkyl-Chain Order in Reversed-Phase Chromatographic Surfaces, Impacting their Shape Selectivity for Aromatic Hydrocarbon Partitioning

Shape selectivity is important in reversed-phase liquid chromatographic separations, where stationary phases are capable of separating geometric isomers, thereby resolving solutes based on their three-dimensional structure or shape rather than other chemical differences. Numerous chromatographic studies have been carried out using n-alkyl-chain-modified columns to understand how molecular shape affects retention. For polycyclic aromatic hydrocarbons (PAHs), it was found that planar compounds were selectively retained over non-planar structures of comparable molecular weight on surfaces with longer n-alkyl chains, higher chain-density, or at lower temperatures, where selectivity likely arises with greater ordering of the n-alkyl chains. A limitation of these studies, however, is the small range of chain ordering that can be achieved and lack of a direct measure of the n-alkyl-chain order of the stationary phases. In this work, we employ a C 18 stationary phase modified with a monolayer of phospholipid as a means of significantly varying the n-alkyl chain order. These hybrid-supported lipid bilayers, which have previously been employed as membrane-like stationary phases for measuring lipophilicity, provide a unique approach to control n-alkyl chain ordering by varying the acyl chain length and degree of unsaturation of the phospholipid modifier. The degree of alkyl-chain order of the resulting modified surfaces is determined from the ratio of trans- versus gauche-conformers, measured in situ within individual porous particles by confocal Raman microscopy. This methodology was also used to assess the affinity of these surfaces for planar versus non-planar PAH molecules. The retention selectivity for the planar versus non-planar compounds, thus determined, was found to vary significantly and systematically with the degree of order of the acyl/alkyl chains in the hybrid-supported lipid bilayers. Furthermore, the investigation also demonstrates the utility of confocal Raman microscopy for interrogating the impact of solute partitioning on stationary-phase structure within porous chromatographic particles.

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

Preparation and reactivity of macrocyclic rhodium(III) alkyl complexes

We found that the macrocyclic rhodium(II) complexes LRh(H 2 O) 2+ (L = L 1 = cyclam and L 2 = meso-Me-6-cyclam) react with alkyl hydroperoxides RC(CH 3 ) 2 OOH to generate the corresponding rhodium(III) alkyls L(H 2 O)RhR 2+ (R = CH 3 , C 2 H 5 , PhCH 2 ). Methyl and benzyl complexes can also be prepared by bimolecular group transfer from alkyl cobaloximes (dmgH) 2 (H 2 O) CoR and (dmgBF 2 ) 2 (H 2 O) CoR (R = CH 3 , PhCH 2 ) to LRh(H 2 O) 2+ . Moreover, the new complexes were characterized by solution NMR and by crystal structure analysis. They exhibit great stability in aqueous solution at room temperature, but undergo efficient Rh-C bond cleavage upon photolysis.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Poly(alkyl methacrylate) Brush-Grafted Silica Nanoparticles as Oil Lubricant Additives: Effects of Alkyl Pendant Groups on Oil Dispersibility, Stability, and Lubrication Property

This paper reports on the synthesis of a series of poly(alkyl methacrylate) brush-grafted, 23 nm silica nanoparticles (hairy NPs) and the study of the effect of alkyl pendant length on their use as oil lubricant additives for friction and wear reduction. The hairy NPs were prepared by surface-initiated reversible addition–fragmentation chain transfer polymerization from trithiocarbonate chain transfer agent (CTA)-functionalized silica NPs in the presence of a free CTA. We found that hairy NPs with sufficiently long alkyl pendant groups (containing >8 carbon atoms, such as 12, 13, 16, and 18 in this study) could be readily dispersed in poly(alphaolefin) (PAO), forming clear, homogeneous dispersions, and exhibited excellent stability at low and high temperatures as revealed by visual inspection and dynamic light scattering studies. Whereas poly(n-hexyl methacrylate) hairy NPs cannot be dispersed in PAO under ambient conditions or at 80 °C, interestingly, poly(2-ethylhexyl methacrylate) hairy NPs can be dispersed in PAO at 80 °C but not at room temperature, with a reversible clear-to-cloudy transition observed upon cooling. High-contact-stress ball-on-flat reciprocating sliding tribological tests at 100 °C showed significant reductions in both the coefficient of friction (up to 38%) and wear volume (up to 90% for iron flat) for transparent, homogeneous dispersions of hairy NPs in PAO at a concentration of 1.0 wt % compared with neat PAO. Finally, the formation of a load-bearing tribofilm at the rubbing interface was confirmed using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Mechanisms and Reactivity of Tl(III) Main-Group-Metal–Alkyl Functionalization in Water

Metal-mediated C–H activation reactions generate metal–alkyl intermediates that can be converted into carbon–oxygen bonds through functionalization reactions. Although the mechanisms and reactivity of C–H activation reactions have been well studied for transition-metal complexes, much less is known about functionalization reactions, especially for main-group-metal–alkyl complexes. Here we report density functional theory calculations on the reaction thermodynamics and kinetic pathways for main-group, p-block-metal Tl III –methyl functionalization reactions in water using a combination of continuum and explicit/continuum solvent models. Particularly, we examined the oxygen functionalization of (OAc)Tl III (CH 3 ) 2 and (OAc) 2 Tl III (CH 3 ) in water where in both cases functionalization gives methyl acetate and methanol. Our calculations suggest that (OAc)Tl III (CH 3 ) 2 is thermodynamically and kinetically stable against bond homolysis, heterolysis, protonolysis, and all reductive functionalization pathways. Functionalization is only possible after methyl anion group transfer to Tl III (OAc) 3 to give (OAc) 2 Tl III (CH 3 ). Our calculations indicate that this monomethyl structure is functionalized by acetate dissociation to give a Tl monocation and then a one-step nucleophilic functionalization where water and acetate have competitive transition states.

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

Suppression of alkylating agent induced cell transformation and gastric ulceration by low-dose alkylating agent pretreatment

Highlights: •Low-dose MNNG pretreatment suppresses high-dose MNNG induced in vitro transformation. •Gastric ulcers induced by high-dose MNNG decreased after low-dose MNNG pretreatment. •Efficacy of low-dose MNNG related to resistance of mutation and oxidative stress. -- Abstract: Exposure to mild stress by chemicals and radiation causes DNA damage and leads to acquired stress resistance. Although the linear no-threshold (LNT) model of safety assessment assumes risk from any dose, evidence from radiological research demonstrates a conflicting hormetic phenomenon known as the hormesis effect. However, the mechanisms underlying radiation hormesis have not yet been clarified, and little is known about the effects of low doses of chemical carcinogens. We analyzed the efficacy of pretreatment with low doses of the alkylating agent N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) on the subsequent induction of cell transformation and gastric ulceration by high-dose MNNG. We used an in vitro Balb/3T3 A31-1-1 cell transformation test and monitored the formation of gastric ulcers in 5-week-old male ICR mice that were administered MNNG in drinking water. The treatment concentrations of MNNG were determined by the cell survival rate and past reports. For low-dose in vitro and in vivo experiments, MNNG was used at 0.028 μM, and 2.8 μg/mL, respectively. The frequency of cell transformation induced by 10 μm MNNG was decreased by low-dose MNNG pretreatment to levels similar to that of spontaneous transformation. In addition, reactive oxygen species (ROS) and mutation frequencies induced by 10 μm MNNG were decreased by low-dose MNNG pretreatment. Importantly, low-dose MNNG pretreatment had no effect on cell proliferation. In vivo studies showed that the number of gastric ulcers induced by 1 mg/mL MNNG decreased after low-dose MNNG pretreatment. These data indicate that low-dose pretreatment with carcinogens may play a beneficial role in the prevention of chemical toxicity under specified conditions.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Redox Behavior of 2,3-Diamino-1,4-naphthoquinone and its N-Alkylated Derivatives

Electrochemical reduction and oxidation potentials and standard heterogeneous electron transfer rate constants are reported for 2,3-diamino-1,4-naphthoquinone and two of its N-alkylated derivatives in acetonitrile. For two of the compounds, spectroelectrochemistry was used to obtain the absorption spectra of the radical cation and the radical anion. The compounds can be viewed as captodative biradicaloids and as such are of interest for photophysical studies of singlet fission.

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

110th Anniversary : Properties of Imidazolium-Based Ionic Liquids Bearing Both Benzylic and n -Alkyl Substituents

Reports of imidazoliumionic liquids (ILs) with at least one benzylic substituent bound to the imidazolium cation are far less common than the ubiquitous 1-alkyl-3-methylimidazolium ILs ([C n mim][X]). Furthermore, there is significant motivation to determine structure–property relationships for imidazolium-based ILs with at least one benzylic substituent. Not only are these ILs just as straightforward to synthesize as [C n mim][X] ILs, but ILs with benzylic substituents are also representative segments of poly(ILs) and ionenes where imidazolium cations with benzylic groups are commonly found. This report focuses on the effects of benzyl and methylbenzyl substituents on the density and viscosity of a series of imidazolium cations paired with bis[(trifluoromethyl)sulfonyl]imide (more commonly known as bistriflimide) ([Tf 2 N] – ) anions. Furthermore, the solubility of CO 2 in 1-benzyl-3-methylimidazolium bistriflimide [Bnmim][Tf 2 N] (CAS: 433337-24-7) was measured at 303.15, 318.15, 333.15, and 348.15 K at pressures in the range of 1–9 bar.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗