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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Advancing ionomer design to boost interfacial and thin-film proton conductivity via styrene-calix[4]arene-based ionomers

Sub-micrometer-thick ion-conducting polymer (ionomer) layers often suffer from poor ionic conductivity at the substrate/catalyst interface. The weak proton conductivity makes the electrochemical reaction at the cathode of proton-exchange-membrane fuel cells sluggish. To address this, here we report on a class of polystyrene-based ionomers having sub-nanometer-sized, sulfonated macrocyclic calix[4]arene-based pendants (PS-calix). In films with thickness comparable to that of ionomer-based binder layers, the conductivity of PS-calix film (~41 mS/cm) is ~13 times higher than that of the current state-of-the-art ionomer, Nafion. We observe a similar improvement in proton conductivity when PS-calix interfaces with Pt nanoparticles, demonstrating the potential of PS-calix in catalyst ink. Leveraging a favorable interfacial chemical composition, PS-calix enhances proton conduction at the film-substrate interface, a shortcoming of Nafion. Moreover, the water in PS-calix films diffuses faster than bulk water and the water confined in Nafion films, suggesting an important role played by sub-nanometer-sized calix[4]arene cavities in creating unique water/ion transport pathways.

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

Supramolecular Arene‐Perfluoroarene Assembly Enhances Photoiniferter Polymerization Kinetics

Ultra-high-molecular-weight (UHMW, >106 Da) polymers have unique thermomechanical properties due to their large number of physical entanglements. Producing UHMW styrenic polymers is challenging because of their prohibitively slow homopolymerization kinetics. In this report, we show that alternating photoiniferter copolymerization between methoxy-functionalized styrenic monomers and pentafluorostyrene can circumvent this limitation under conditions where arene–perfluoroarene (AP) interactions contribute to favorable monomer association and accelerate copolymerization. Increasing methoxy substitution on the styrene arene ring leads to pronounced rate enhancements that correlate with electronic complementarity between the styrenic comonomers. Density functional theory calculations reveal increasingly favorable AP interaction energies across the series, consistent with monomer association contributing to faster propagation. The result is up to 2000% enhancement in propagation rate in copolymerizations compared to styrene homopolymerization. Despite these rate enhancements, the resulting materials retain broadly similar glass-transition temperatures and network-like thermomechanical behavior, with only modest softening across the series. Here, we then leverage the approach to produce UHMW trialkoxystyrene copolymers bearing sterically encumbered pendants, which are ultrasoft (Young's modulus of 8 kPa) and highly extensible (560%). These results establish that designed supramolecular association between styrenics is a powerful tool for controlling reactivity in radical polymerization and generating otherwise difficult-to-obtain materials.

Marquez, Joshua D. [University of Florida, Gainesv↗
DOE OSTI2023

Induction and Stabilization of Columnar Mesophases in Fluorinated Polycyclic Aromatic Hydrocarbons by Arene‐Perfluoroarene Interactions

Abstract The straightforward synthesis of several Fluorinated Polycyclic Aromatic Hydrocarbons by the efficient, transition‐metal‐free, arene fluorine nucleophilic substitution reaction is described, and the full investigation of their liquid crystalline and optical properties reported. The key precursors for this study, i. e. 2,2’‐dilithio‐4,4′,5,5′‐tetraalkoxy‐1,1’‐biphenyl derivatives, were obtained in two steps from the highly selective Scholl oxidative homo‐coupling of 3,4‐dialkoxy‐1‐bromobenzene, followed by quantitative double‐lithiation. In situ room temperature nucleophilic annulation with either perfluorobenzene or perfluoronaphthalene leads to 1,2,3,4‐tetrafluoro‐6,7,10,11‐tetraalkxoytriphenylenes and 9,10,11,12,13,14‐hexafluoro‐2,3,6,7‐tetraalkoxybenzo[f]tetraphenes, respectively, in good yields. Exploiting the same strategy, subsequent double annulations resulted in the formation of 9,18‐difluoro‐2,3,6,7,11,12,15,16‐octa(alkoxy)tribenzo[f,k,m]tetraphenes and 9,10,19,20‐tetrafluoro‐2,3,6,7,12,13,16,17‐octakis(hexyloxy)tetrabenzo[a,c,j,l]tetracenes, respectively. Despite the presence of only four alkoxy chains, the polar “Janus” mesogens display a columnar hexagonal mesophase over broad temperature ranges, with higher mesophase stability than the archetypical 2,3,6,7,10,11‐hexa(alkoxy)triphenylenes and their hydrogenated counterparts. The improvement or induction of mesomorphism is attributed to efficient antiparallel face‐to‐face π‐stacking driven by the establishment of non‐covalent perfluoroarene‐arene intermolecular interactions. The larger lipophilic discotic π‐extended compounds also exhibit columnar mesomorphism, over similar temperature ranges and stability than their hydrogenated homologs. Finally, these fluorinated molecules form stringy gels in various solvents, and show interesting solvatochromic emission properties in solution as well as strong emission in thin films and gels.

Chemistry↗
DOE OSTI2021

Allosteric binding properties of a 1,3-alternate thiacalix[4]arene-based receptor having phenylthiourea and 2-pyridylmethyl moieties on opposite faces

The synthesis of three new heteroditopic receptors (5a–c) which are based on thiacalix[4]arenes in the 1,3-alternate conformation is reported herein. These new receptors each have two thiourea moieties linking phenyl groups, two of which are substituted with electron-withdrawing groups at their para-positions, and at the opposite side of the thiacalix[4]arene cavity, with two 2-pyridylmethyl groups. One example (5a) was also characterized by X-ray crystallography. A limited 1 H-NMR and UV-vis anion complexation study was conducted. DFT computational determinations indicated that 5c, which has strongly electron-withdrawing NO 2 groups, had the most effective recognition ability towards the selected anions. The binding of Ag + at the 2-pyridyl moieties, and the binding of the anions at the two thiourea NH groups of the p-substituted phenylthioureido moieties, respectively, was also investigated. The appearance of a positive allosteric effect with receptor 5b was also found using 1 H-NMR titration experiments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

A bis-calix[4]arene-supported [Cu II 16 ] cage

Reaction of 2,2'-bis-p- t Bu-calix[4]arene (H 8 L) with Cu(NO 3 ) 2 ·3H 2 O and N-methyldiethanolamine (Me-deaH 2 ) in a basic dmf/MeOH mixture affords [Cu II 16 (L) 2 (Me-dea) 4 (μ 4 -NO 3 ) 2 (μ-OH) 4 (dmf) 3.5 (MeOH) 0.5 (H 2 O) 2 ](H 6 L)·16dmf·4H 2 O (4), following slow evaporation of the mother liquor. The central core of the metallic skeleton describes a tetracapped square prism, [Cu 12 ], in which the four capping metal ions are the CuII ions housed in the calix[4]arene polyphenolic pockets. The [Cu II 8 ] square prism is held together “internally” by a combination of hydroxide and nitrate anions, with the N-methyldiethanolamine co-ligands forming dimeric [Cu II 2 ] units which edge-cap above and below the upper and lower square faces of the prism. Charge balance is maintained through the presence of one doubly deprotonated H 6 L 2- ligand per [Cu 16 ] cluster. Magnetic susceptibility measurements reveal the predominance of strong antiferromagnetic exchange interactions and an S = 1 ground state, while EPR is consistent with a large zero-field splitting.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

A novel inclusion complex of oxybenzone with C -methylresorcin[4]arene deters skin permeation

Oxybenzone (OXB), a very widely used sunscreen ingredient has the potential to block both UVA and UVB but can penetrate through skin. Studies have revealed its presence in the blood and urine of most humans, which may lead to long-term health effects. As the confined cavities of macrocycles can alter the physical and chemical properties of encapsulated guests, in this study, we investigated the formation of host–guest complexes between C-methylresorcin[4]arene and OXB. Combined experimental (NMR spectroscopy, UV/vis absorption, and fluorescence spectroscopy) and theoretical investigation confirmed the formation of a weak host–guest complex that had a 1 : 1 stoichiometry. Furthermore, skin permeation testing revealed that complexation by C-methylresorcin[4]arene significantly reduced the skin permeation of OXB which can potentially limit the harmful effects of this organic sunscreen.

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

Intermolecular C–H silylations of arenes and heteroarenes with mono-, bis-, and tris(trimethylsiloxy)hydrosilanes: control of silane redistribution under operationally diverse approaches

Operationally diverse C–H silylations of (hetero) arenes with a broad silane scope are reported. The control of silane redistribution improves overall catalytic efficiency, affording the various arylsiloxysilanes useful for polysiloxane materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Regioselective Arene C−H Alkylation Enabled by Organic Photoredox Catalysis

Abstract Expanding the toolbox of C−H functionalization reactions applicable to the late‐stage modification of complex molecules is of interest in medicinal chemistry, wherein the preparation of structural variants of known pharmacophores is a key strategy for drug development. One manifold for the functionalization of aromatic molecules utilizes diazo compounds and a transition‐metal catalyst to generate a metallocarbene species, which is capable of direct insertion into an aromatic C−H bond. However, these high‐energy intermediates can often require directing groups or a large excess of substrate to achieve efficient and selective reactivity. Herein, we report that arene cation radicals generated by organic photoredox catalysis engage in formal C−H functionalization reactions with diazoacetate derivatives, furnishing sp 2 –sp 3 coupled products with moderate‐to‐good regioselectivity. In contrast to previous methods utilizing metallocarbene intermediates, this transformation does not proceed via a carbene intermediate, nor does it require the presence of a transition‐metal catalyst.

Holmberg‐Douglas, Natalie↗
DOE OSTI2025

Ligand‐Directed Actinide Oxo‐Bond Manipulation in Actinyl Thiacalix[4]arene Complexes

Abstract Understanding the chemistry of the inert actinide oxo bond in actinyl ions AnO 2 2+ is important for controlling actinide behavior in the environment, during separations, and in nuclear waste (An=U, Np, Pu). The thioether calixarene TC4A (4‐ tert ‐butyltetrathiacalix[4]arene) binds equatorially to the actinyl cation forming a conical pocket that differentiates the two trans‐ oxo groups. The ‘ate’ complexes, [A] 2 [UO 2 (TC4A)] (A=[Li(DME) 2 ], HNEt 3 ) and [HNEt 3 ] 2 [AnO 2 (TC4A)] (An=U, Np, Pu), enable selective oxo chemistry. Silylation of the U VI oxo groups by bis(trimethylsilyl)pyrazine occurs first at only the unencapsulated exo oxo and only one silylation is needed to enable migration of the endo oxo out of the cone, whereupon a second silylation affords the stable U IV cis‐ bis(siloxide) [A] 2 [U(OSiMe 3 ) 2 (TC4A)]. Calculations confirm that only one silylation event is needed to initiate oxo rearrangement, and that the putative cis dioxo isomer of [UO 2 (TC4A)] 2− would be stable if it could be accessed synthetically, at only 23 kcal.mol −1 in energy above the classical trans dioxo. Calculations for the transuranic cis [AnO 2 (TC4A)] 2− (An=Np, Pu) are at higher energies, 30–35 kcal.mol −1 , retaining the U complexes as the more obvious target for a cis ‐dioxo actinyl ion. The aryloxide (OAr) groups of the macrocycle are essential in stabilizing this as‐yet unseen uranyl geometry as further bonding in the TC4A U‐O Ar groups stabilizes the U=O ‘yl’ bonds, explaining the stability of the putative cis [UO 2 (TC4A)] 2− in this ligand framework.

Pyrch, Mikaela M. [College of Chemistry University↗
DOE OSTI2020

Regioselective Arene C−H Alkylation Enabled by Organic Photoredox Catalysis

Abstract Expanding the toolbox of C−H functionalization reactions applicable to the late‐stage modification of complex molecules is of interest in medicinal chemistry, wherein the preparation of structural variants of known pharmacophores is a key strategy for drug development. One manifold for the functionalization of aromatic molecules utilizes diazo compounds and a transition‐metal catalyst to generate a metallocarbene species, which is capable of direct insertion into an aromatic C−H bond. However, these high‐energy intermediates can often require directing groups or a large excess of substrate to achieve efficient and selective reactivity. Herein, we report that arene cation radicals generated by organic photoredox catalysis engage in formal C−H functionalization reactions with diazoacetate derivatives, furnishing sp 2 –sp 3 coupled products with moderate‐to‐good regioselectivity. In contrast to previous methods utilizing metallocarbene intermediates, this transformation does not proceed via a carbene intermediate, nor does it require the presence of a transition‐metal catalyst.

Holmberg‐Douglas, Natalie↗
DOE OSTI2025

Ligand‐Directed Actinide Oxo‐Bond Manipulation in Actinyl Thiacalix[4]arene Complexes

Understanding the chemistry of the inert actinide oxo bond in actinyl ions AnO2 2+ is important for controlling actinide behavior in the environment, during separations, and in nuclear waste (An=U, Np, Pu). The thioether calixarene TC4A (4-tert-butyltetrathiacalix[4]arene) binds equatorially to the actinyl cation forming a conical pocket that differentiates the two trans-oxo groups. The 'ate' complexes, [A]2[UO2(TC4A)] (A=[Li(DME)2], HNEt3) and [HNEt3]2[AnO2(TC4A)] (An=U, Np, Pu), enable selective oxo chemistry. Silylation of the UVI oxo groups by bis(trimethylsilyl)pyrazine occurs first at only the unencapsulated exo oxo and only one silylation is needed to enable migration of the endo oxo out of the cone, whereupon a second silylation affords the stable UIV cis-bis(siloxide) [A]2[U(OSiMe3)2(TC4A)]. Calculations confirm that only one silylation event is needed to initiate oxo rearrangement, and that the putative cis dioxo isomer of [UO2(TC4A)]2- would be stable if it could be accessed synthetically, at only 23 kcal.mol-1 in energy above the classical trans dioxo. Calculations for the transuranic cis[AnO2(TC4A)]2- (An=Np, Pu) are at higher energies, 30-35 kcal.mol-1, retaining the U complexes as the more obvious target for a cis-dioxo actinyl ion. The aryloxide (OAr) groups of the macrocycle are essential in stabilizing this as-yet unseen uranyl geometry as further bonding in the TC4A U-OAr groups stabilizes the U=O 'yl' bonds, explaining the stability of the putative cis[UO2(TC4A)]2- in this ligand framework.

Pyrch, Mikaela M↗
DOE OSTI2025

Impact of Ligands on the Ion–Ion Selectivity of Ligand-Appended-Pillar[ n ]arene Channels

Ligand-appended pillar[5]arene (LAP) channels are emerging as a promising platform for ion-selective membranes. In this study, we investigated the ion selectivities of three LAP channels functionalized with distinct ligands: diglycolamine, carbamoylmethyl phosphine oxide, and propionamide phosphonic acid. These ligands were chosen based on their demonstrated affinities for lanthanides in solvent extraction studies. We examined the selectivity of each channel toward a series of monovalent, divalent, and trivalent ions: Li + , Na + , K + , Mg 2+ , Ca 2+ , La 3+ , Eu 3+ , and Yb 3+ . To quantify ion-channel interactions and the energetics of translocation, we computed the potential of mean force (PMF) profiles for each ion. These PMFs were subsequently recast into permeability coefficients, enabling a direct evaluation of ion permselectivity. Our results reveal distinct selectivity patterns governed by the chemical nature of the appended ligands. The diglycolamine-functionalized channel exhibits strong interactions with monovalent ions, leading to replication of the Li + bulk hydration shell within the channel. This promotes preferential transport Li + ions while effectively excluding divalent and trivalent species. In contrast, the carbamoylmethyl phosphine oxide-functionalized channel displays a reduced selectivity between monovalent ions while similarly exhibiting an effective rejection of divalent and trivalent ions. This arises from steric hindrance around channel-lining oxygens imposed by the ligand's bulky phenyl groups which limits heavy ion coordination and promotes retention of hydration shells effectively increasing effective ion size. The propionamide phosphonic acid-functionalized channel exhibits a different trend, favoring ions with lower hydration free energies, with K + ions showing enhanced permeation. These findings highlight the critical role of ligand-ion interactions in modulating ion selectivity within LAP channels. In particular, the strong coordination exhibited by diglycolamine and propionamide phosphonic acid ligands significantly influences the ion transport energetics and selectivity profiles.

hydration↗
DOE OSTI2022

Pathway toward Optical Cycling and Laser Cooling of Functionalized Arenes

Rapid and repeated photon cycling has enabled precision metrology and the development of quantum information systems using atoms and simple molecules. Extending optical cycling to structurally complex molecules would provide new capabilities in these areas, as well as in ultracold chemistry. Increased molecular complexity, however, makes realizing closed optical transitions more difficult. Building on already established strong optical cycling of diatomic, linear triatomic, and symmetric top molecules, recent work has pointed the way to cycling of larger molecules, including phenoxides. The paradigm for these systems is an optical cycling center bonded to a molecular ligand. Theory has suggested that cycling may be extended to even larger ligands, like naphthalene, pyrene, and coronene. For this paper, we study optical excitation and fluorescent vibrational branching of CaO-[illus. chemical structure], SrO-[illus. chemical structure], and CaO-[illus. chemical structure] and find only weak decay to excited vibrational states, indicating a promising path to full quantum control and laser cooling of large arene-based molecules.

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

Immobilization of “Capping Arene” Cobalt(II) Complexes on Ordered Mesoporous Carbon for Electrocatalytic Water Oxidation

We report the synthesis, characterization, and electrocatalytic water oxidation activity of two cobalt complexes, (6-FP)Co(NO 3 ) 2 (1) (6-FP = 8,8'-(1,2-phenylene)diquinoline) and (5-FP)Co(NO 3 ) 2 (2) (5-FP = 1,2-bis(N-7-azaindolyl)benzene), containing "capping arene" bidentate ligands with nitrogen atom donors. The cobalt complexes 1 and 2 were supported on ordered mesoporous carbon (OMC) by π-π stacking, resulting in heterogenized cobalt materials 6-FP-Co-OMC-1 and 5-FP-Co-OMC-2, respectively, and studied for electrocatalytic water oxidation. We find that 6-FP-Co-OMC-1 exhibits an overpotential of 355 mV for a current density of 10 mA cm -2 and a turnover frequency (TOF) of ~0.53 s -1 at an overpotential of 400 mV at pH 14. 6-FP-Co-OMC-1 exhibits activity that is ~1.6 times that of 5-FP-Co-OMC-2, which gives a TOF of 0.32 s -1 at 400 mV overpotential. The structural stability of the single-atom Co site was demonstrated for 6-FP-Co-OMC-1 using X-ray absorption spectroscopy for the molecular complex supported on OMC, but slow degradation in catalyst activity can be attributed to eventual formation of Co oxide clusters. DFT computations of electrocatalytic water oxidation using the molecular complexes as models provide a description of the catalytic mechanism. These studies reveal that the mechanism for O-O bond formation involves an intermediate Co IV oxo complex that undergoes an intramolecular reductive O-O coupling to form a Co II -OOH species. Further, the calculations predict that the molecular 6-FP-Co structure is more active for electrocatalytic water oxidation than 5-FP-Co, which is consistent with experimental studies of 6-FP-Co-OMC-1 and 5-FP-Co-OMC-2, highlighting the possibility that the ligand structure influences the catalytic activity of the supported molecular catalysts.

25 ENERGY STORAGE↗
DOE OSTI2020

Magneto-structural studies of an unusual [Mn III Mn II Gd III (OR) 4 ] 4– partial cubane from 2,2'-bis- p- t Bu-calix[4]arene

Reaction of 2,2'-bis- p - t Bu-calix[4]arene (H 8 L) with MnCl 2 ·4H 2 O, GdCl 3 ·6H 2 O and 2,6-pyridinedimethanol (H 2 pdm) affords [Mn III Mn II Gd III (H 3 L)(pdmH)(pdm)(MeOH) 2 (dmf)]·3MeCN·dmf ( 3 ·3MeCN·dmf) upon vapour diffusion of MeCN into the basic dmf/MeOH mother liquor. 3 crystallises in the tetragonal space group P 4 1 2 1 2 with the asymmetric unit comprising the entire cluster. The highly unusual core contains a triangular arrangement of Mn III Mn II Gd III ions housed within a [Mn III Mn II Gd III (OR) 4 ] 4– partial cubane. Magnetic susceptibility and magnetisation data reveal best fit parameters J Mn(II)–Mn(III) = +0.415 cm –1 , J Mn(III)–Gd(III) = +0.221 cm –1 , J Mn(II)–Gd(III) = –0.258 cm –1 and D Mn(III) = –4.139 cm –1 . Theoretically derived magnetic exchange interactions, anisotropy parameters, and magneto-structural correlations for 3 are in excellent agreement with the experimental data.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Facile synthetic routes to bridge-functionalised calix[4]arenes

Ring-opening of furans at the equatorial methylene bridge positions of a calix[4]arene gives access to a range of new molecules (in good yield) that have widespread potential impact in supramolecular chemistry amongst other areas.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗