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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 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Precise transcript targeting by CRISPR-Csm complexes

Robust and precise transcript targeting in mammalian cells remains a difficult challenge using existing approaches due to inefficiency, imprecision and subcellular compartmentalization. Here we show that the clustered regularly interspaced short palindromic repeats (CRISPR)-Csm complex, a multiprotein effector from type III CRISPR immune systems in prokaryotes, provides surgical RNA ablation of both nuclear and cytoplasmic transcripts. As part of the most widely occurring CRISPR adaptive immune pathway, CRISPR-Csm uses a programmable RNA-guided mechanism to find and degrade target RNA molecules without inducing indiscriminate trans-cleavage of cellular RNAs, giving it an important advantage over the CRISPR-Cas13 family of enzymes. Using single-vector delivery of the Streptococcus thermophilus Csm complex, we observe high-efficiency RNA knockdown (90–99%) and minimal off-target effects in human cells, outperforming existing technologies including short hairpin RNA- and Cas13-mediated knockdown. We also find that catalytically inactivated Csm achieves specific and durable RNA binding, a property we harness for live-cell RNA imaging. These results establish the feasibility and efficacy of multiprotein CRISPR-Cas effector complexes as RNA-targeting tools in eukaryotes.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Hierarchical Eutectoid Nano-lamellar Decomposition in an Al 0.3 CoFeNi Complex Concentrated Alloy

This paper reports a novel eutectoid nano-lamellar (FCC + L1 2 )/(BCC + B2) microstructure that has been discovered in a relatively simple Al 0.3 CoFeNi high entropy alloy (HEA) or complex concentrated alloy (CCA). This novel eutectoid nano-lamellar microstructure presumably results from the complex interplay between Al-mediated lattice distortion (due to its larger atomic radius) in a face-centered cubic (FCC) CoFeNi solid solution, and a chemical ordering tendency leading to precipitation of ordered phases such as L1 2 and B2. This eutectoid microstructure is a result of solid-state decomposition of the FCC matrix and therefore distinct from the commonly reported eutectic microstructure in HEAs which results from solidification. This novel nano-lamellar microstructure exhibits a tensile yield strength of 1074 MPa with a reasonable ductility of 8%. The same alloy can be tuned to form a more damage-tolerant FCC + B2 microstructure, retaining high tensile yield stress (~900 MPa) with appreciable tensile ductility (>20%), via annealing at 700 °C. Such tunability of microstructures with dramatically different mechanical properties can be effectively engineered in the same CCA, by exploiting the complex interplay between ordering tendencies and lattice distortion.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Structure of the glucosyltransferase domain of TcdA in complex with RhoA provides insights into substrate recognition

Clostridioides difficile is one of the most common causes of antibiotic-associated diarrhea in developed countries. As key virulence factors of C. difficile, toxin A (TcdA) and toxin B (TcdB) act by glucosylating and inactivating Rho and Ras family small GTPases in host cells, which leads to actin cytoskeleton disruption, cell rounding, and ultimately cell death. Here we present the co-crystal structure of the glucosyltransferase domain (GTD) of TcdA in complex with its substrate human RhoA at 2.60-angstrom resolution. This structure reveals that TcdA GTD grips RhoA mainly through its switch I and switch II regions, which is complemented by interactions involving RhoA’s pre-switch I region. Comprehensive structural comparisons between the TcdA GTD–RhoA complex and the structures of TcdB GTD in complex with Cdc42 and R-Ras reveal both the conserved and divergent features of these two toxins in terms of substrate recognition. Taken together, these findings establish the structural basis for TcdA recognition of small GTPases and advance our understanding of the substrates selectivity of large clostridial toxins.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Intramolecular charge-transfer enhances energy transfer efficiency in carotenoid-reconstituted light-harvesting 1 complex of purple photosynthetic bacteria

In bacterial photosynthesis, the excitation energy transfer (EET) from carotenoids to bacteriochlorophyll a has a significant impact on the overall efficiency of the primary photosynthetic process. This efficiency can be enhanced when the involved carotenoid has intramolecular charge-transfer (ICT) character, as found in light-harvesting systems of marine alga and diatoms. Here, we provide insights into the significance of ICT excited states following the incorporation of a higher plant carotenoid, β-apo-8'-carotenal, into the carotenoidless light-harvesting 1 (LH1) complex of the purple photosynthetic bacterium Rhodospirillum rubrum strain G9+. β-apo-8'-carotenal generates the ICT excited state in the reconstituted LH1 complex, achieving an efficiency of EET of up to 79%, which exceeds that found in the wild-type LH1 complex.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Thiocyanate complexes of the lanthanides, Am and Cm

In this work, the synthesis and single crystal structures of Am( III ) and Cm( III ) thiocyanate complexes are reported along with an isostructural series of lanthanide thiocyanate complexes. Because the complexes are isostructural, a comparative study of the metal–thiocyanate bonds was conducted using Raman spectroscopy indicating very similar and electrostatic metal–ligand interactions.

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

New up-conversion luminescence in molecular cyano-substituted naphthylsalophen lanthanide(iii) complexes

A new naphthylsalophen and its 3:2 ligand-to-lanthanide sandwich-type complexes were isolated. Here, when excited at 380 nm, the complexes display the characteristic metal-centred emission for Nd III , Er III and Yb III . Upon 980 nm excitation, in mixed lanthanide and the Er complexes, Er-centred upconversion emission at 543 and 656 nm is observed, with power densities as low as 2.18 W cm –2 .

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Radiation-Induced Effects on the Extraction Properties of Hexa-n-octylnitrilo-triacetamide (HONTA) Complexes of Americium and Europium

The candidate An(III)/Ln(III) separation ligand hexa-n-octylnitrilo-triacetamide (HONTA) was irradiated under envisioned SELECT (Solvent Extraction from Liquid waste using Extractants of CHON-type for Transmutation) process conditions (n-dodecane/0.1 M HNO 3 ) using a solvent test loop in conjunction with cobalt-60 gamma irradiation. The extent of HONTA radiolysis and complimentary degradation product formation was quantified by HPLC-ESI-MS/MS. Further, the impact of HONTA radiolysis on process performance was evaluated by measuring the change in 243 Am and 154 Eu distribution ratios as a function of absorbed gamma dose. HONTA was found to decay exponentially with increasing dose, affording a dose coefficient of d = (4.48 ± 0.19) × 10 –3 kGy –1 . Multiple degradation products were detected by HPLC-ESI-MS/MS with dioctylamine being the dominant quantifiable species. Both 243 Am and 154 Eu distribution ratios exhibited an induction period of ~70 kGy for extraction (0.1 M HNO 3 ) and back-extraction (4.0 M HNO 3 ) conditions, after which both values decreased with absorbed dose. The decrease in distribution ratios was attributed to a combination of the destruction of HONTA and ingrowth of dioctylamine, which is capable of interfering in metal ion complexation. Furthermore, the loss of HONTA with absorbed gamma dose was predominantly attributed to its reaction with the n-dodecane radical cation (R˙ + ). These R˙ + reaction kinetics were measured for HONTA and its 241 Am and 154 Eu complexes using picosecond pulsed electron radiolysis techniques. All three second-order rate coefficients (k) were essentially diffusion limited in n-dodecane indicating a significant reaction pathway: k(HONTA + R˙ + ) = (7.6 ± 0.8) × 10 9 M –1 s –1 , k(Am(HONTA) 2 + R˙ + ) = (7.1 ± 0.7) × 10 10 M –1 s –1 , and k(Eu(HONTA) 2 + R˙ + ) = (9.5 ± 0.5) × 10 10 M –1 s –1 . HONTA-metal ion complexation afforded an order-of-magnitude increase in rate coefficient. Additional nanosecond time-resolved measurements showed that both direct and indirect HONTA radiolysis yielded the short-lived (< 100 ns) HONTA radical cation and a second long-lived (µs) species identified as the HONTA triplet excited state. The latter was confirmed by a series of oxygen quenching picosecond pulsed electron measurements, affording a quenching rate coefficient of k( 3 [HONTA]* + O 2 ) = 2.2 × 10 8 M –1 s –1 . Overall, both the HONTA radical cation and triplet excited state are important precursors to the suite of measured HONTA degradation products.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

Solvent manipulation of the pre-reduction metal–ligand complex and particle-ligand binding for controlled synthesis of Pd nanoparticles

Understanding how to control the nucleation and growth rates is crucial for designing nanoparticles with specific sizes and shapes. Herein, we show that the nucleation and growth rates are correlated with the thermodynamics of metal–ligand/solvent binding for the pre-reduction complex and the surface of the nanoparticle, respectively. To obtain these correlations, we measured the nucleation and growth rates by in situ small angle X-ray scattering during the synthesis of colloidal Pd nanoparticles in the presence of trioctylphosphine in solvents of varying coordinating ability. The results show that the nucleation rate decreased, while the growth rate increased in the following order, toluene, piperidine, 3,4-lutidine and pyridine, leading to a large increase in the final nanoparticle size (from 1.4 nm in toluene to 5.0 nm in pyridine). Using density functional theory (DFT), complemented by 31 P nuclear magnetic resonance and X-ray absorption spectroscopy, we calculated the reduction Gibbs free energies of the solvent-dependent dominant pre-reduction complex and the solvent-nanoparticle binding energy. The results indicate that lower nucleation rates originate from solvent coordination which stabilizes the pre-reduction complex and increases its reduction free energy. At the same time, DFT calculations suggest that the solvent coordination affects the effective capping of the surface where stronger binding solvents slow the nanoparticle growth by lowering the number of active sites (not already bound by trioctylphosphine). The findings represent a promising advancement towards understanding the microscopic connection between the metal–ligand thermodynamic interactions and the kinetics of nucleation and growth to control the size of colloidal metal nanoparticles.

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

Observing the three-dimensional dynamics of supported metal complexes

Dynamics are intricately linked with activity and selectivity when it comes to catalysis, as noted for instance in the enzymatic principles of induced fit and allostery, and yet the range of motions heterogeneous catalytic sites are able to undergo is poorly understood. Solid-state nuclear magnetic resonance (NMR) spectroscopy is perhaps the only tool capable of probing the rapid conformational dynamics found in heterogeneous catalysts but has historically been restricted by its low sensitivity, limiting the detail with which structures can be resolved. In this work, we apply solid-state NMR and dynamic nuclear polarization, in combination with density functional theory modeling, to reveal the high-resolution structure and motional freedom of a scandium supported complex in three dimensions. The results are contrasted with the study of the analogous homoleptic complex in the crystalline state, highlighting the impacts that surface structure may have on the dynamics of supported complexes.

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

Vibrational characterization of a diiron bridging hydride complex – a model for hydrogen catalysis

A diiron complex containing a bridging hydride and a protonated terminal thiolate of the form [(m,k 2 - bdtH)(m-PPh 2 )(m-H)Fe 2 (CO) 5 ] + has been investigated through 57 Fe nuclear resonance vibrational spectroscopy (NRVS) and interpreted using density functional theory (DFT) calculations. We report the Fe–mH–Fe wagging mode, and indications for Fe–mD stretching vibrations in the D-isotopologue, observed by 57 Fe-NRVS. Our combined approach demonstrates an asymmetric sharing of the hydride between the two iron sites that yields two nondegenerate Fe–mH/D stretching vibrations. The studied complex provides an important model relevant to biological hydrogen catalysis intermediates. The complex mimics proposals for the binuclear metal sites in [FeFe] and [NiFe] hydrogenases. It is also an appealing prototype for the ‘Janus intermediate’ of nitrogenase, which has been proposed to contain two bridging Fe–H–Fe hydrides and two protonated sulfurs at the FeMo-cofactor. The significance of observing indirect effects of the bridging hydride, as well as obstacles in its direct observation, is discussed in the context of biological hydrogen intermediates.

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

Development of sterically hindered siloxide-functionalized polyoxotungstates for the complexation of 5d-metals

In this study, we extend the family of organosilyl-functionalized trivacant Keggin polyoxotungstates, [PW 9 O 34 (RSiOH) 3 ] 3− (R = n Pr, i Pr, t Bu), through the introduction of bulky aryl and aliphatic silanol substituents, namely phenyl, cyclohexyl and biphenyl. This work was performed in order to study the impact of these large functional groups on the accessibility of the well-defined tridentate coordination site. Coordination of hafnium to these type II hybrid polyoxotungstates was conducted in order to study the ability of the bulkier ligand pockets to support larger cations in comparison to those previously reported (e.g. Ti 4+ , V 3+ , V 5+ , Ge 4+ ). Increased steric hindrance around the coordination site from the biphenyl groups resulted in much longer reaction times for the complexation reaction compared to the other functional groups used, but the impact of our design toward stabilizing reactive species proved limited, as all complexes easily undergo hydrolysis of the Hf-O t Bu bond in the presence of water. As a result, electrochemical investigations of the ligands and hafnium complexes reveal that the redox events centered on the polyoxotungstate core can be tuned by varying the substituents on the silyl fragment, and exhibit a cathodic shift after coordination of the redox inactive tetravalent cation.

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

Mechanistic investigation of the aerobic oxidation of 2-pyridylacetate coordinated to a Ru(ii) polypyridyl complex

A new ruthenium polypyridyl complex, [Ru(bpy) 2 (acpy)] + (acpy = 2-pyridylacetate, bpy = 2,2'-bipyridine), was synthesized and fully characterized. Distinct from the previously reported analog, [Ru(bpy) 2 (pic)] + (pic = 2-pyridylcarboxylate), the new complex is unstable under aerobic conditions and undergoes oxidation to yield the corresponding α-keto-2-pyridyl-acetate (acpyoxi) coordinated to the Ru II center. The reaction is one of the few examples of C–H activation at mild conditions using O 2 as the primary oxidant and can provide mechanistic insights with important implications for catalysis. Theoretical and experimental investigations of this aerobic oxidative transformation indicate that it takes place in two steps, first producing the α-hydroxo-2-pyridyl-acetate analog and then the final product. The observed rate constant for the first oxidation was in the order of 10 -2 h -1 . The reaction is hindered in the presence of coordinating solvents indicating the role of the metal center in the process. Theoretical calculations at the M06-L level of theory were performed for multiple reaction pathways in order to gain insights into the most probable mechanism. Our results= indicate that O 2 binding to [Ru(bpy) 2 (acpy)] + is favored by the relative instability of the six-ring chelate formed by the acpy ligand and the resulting Ru III -OO˙- superoxo is stabilized by the carboxylate group in the coordination sphere. C–H activation by this species involves high activation free energies (ΔG ‡ = 41.1 kcal mol -1 ), thus the formation of a diruthenium μ-peroxo intermediate, [(Ru III (bpy) 2 (O-acpy)) 2 O 2 ] 2+ via interaction of a second [Ru(bpy) 2 (acpy)] + was examined as an alternative pathway. The dimer yields two Ru IV =O centers with a low ΔG ‡ of 2.3 kcal mol -1 . The resulting Ru IV =O species can activate C–H bonds in acpy (ΔG ‡ = 23.1 kcal mol -1 ) to produce the coordinated α-hydroxo-2-pyridylacetate. Further oxidation of this intermediate leads to the α-keto-2-pyridyl-acetate product. The findings provide new insights into the mechanism of C–H activation catalyzed by transition-metal complexes using O 2 as the sole oxygen source.

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

Explorations of the nonheme high-valent iron-oxo landscape: crystal structure of a synthetic complex with an [Fe IV 2 (μ-O) 2 ] diamond core relevant to the chemistry of sMMOH

Methanotrophic bacteria utilize methane monooxygenase (MMO) to carry out the first step in metabolizing methane. The soluble enzymes employ a hydroxylase component (sMMOH) with a nonheme diiron active site that activates O 2 and generates a powerful oxidant capable of converting methane to methanol. It is proposed that the diiron(II) center in the reduced enzyme reacts with O 2 to generate a diferric-peroxo intermediate called P that then undergoes O–O cleavage to convert into a diiron(IV) derivative called Q, which carries out methane hydroxylation. Most (but not all) of the spectroscopic data of Q accumulated by various groups to date favor the presence of an Fe IV 2 (μ-O) 2 unit with a diamond core. The Que lab has had a long-term interest in making synthetic analogs of iron enzyme intermediates. To this end, the first crystal structure of a complex with a Fe III Fe IV (μ-O) 2 diamond core was reported in 1999, which exhibited an Fe∙∙∙Fe distance of 2.683(1) Å. Now more than 20 years later, a complex with an Fe IV 2 (μ-O) 2 diamond core has been synthesized in sufficient purity to allow diffraction-quality crystals to be grown. Finally, its crystal structure has been solved, revealing an Fe∙∙∙Fe distance of 2.711(4) Å for comparison with structural data for related complexes with lower iron oxidation states.

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

Elemental chalcogen reactions of a tetravalent uranium imidophosphorane complex: cleavage of dioxygen

Herein we report the first example of a mononuclear uranium complex, [U 4+ (NP(pip) 3 ) 4 ] (1-U), that selectively reduces dioxygen to produce a terminal oxo complex, [U 6+ O(NP(pip) 3 ) 4 ] (2-U; [NP(pip) 3 ] 1- is tris(piperidinyl)imidophosphorane). Reactions between 1-U and the heavier elemental chalcogens, S 8 or Se 0 , result in six-coordinate U(VI) complexes, [U 6+ (κ 2 -E 3 )(NP(pip) 3 ) 4 ] (E = S (3-U) or Se (4-U)).

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2022

Cyclic(alkyl)(amino)carbene ruthenium complexes for Z -stereoselective (asymmetric) olefin metathesis

The first Z-stereoselective catechodithiolate ruthenium complexes containing cyclic(alkyl)(amino)carbene ligands are reported. Isolated in nearly quantitative yields or in situ generated, these catalysts demonstrated remarkable Z selectivity (Z/E ratio up to >98/2) in ring-opening metathesis polymerization (ROMP), ring-opening-cross metathesis (ROCM) and cross-metathesis (CM). Thanks to the efficient chiral HPLC resolution of racemic CAAC-complex precursors, optically pure dithiolated complexes were also synthesized allowing to produce enantioenriched Z-ROCM products in >99/1 Z/E with good levels of enantioselectivity.

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

Synthesis, structure, and electrochemical properties of [LNi(R f )(C 4 F 8 )] - and [LNi(R f ) 3 ] - complexes

The new anionic nickelate complexes [(MeCN)Ni(C 4 F 8 )(CF 3 )] -, [(MeCN)Ni(C 4 F 8 )(C 2 F 5 )] - , [(IMes)Ni(C 4 F 8 )(CF 3 )] - , [(IMes)Ni(CF 3 ) 3 ] - (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), and [(F-NHC)Ni(Rf) 3 ] - (F-NHC = 1,3-bis(2,4-F2Ph), 2,4,6-F 3 Ph- or 3,4,5-F 3 Ph)imidazol-2-ylidene; (R f = CF 3 or C 2 F 5 ) were synthesized and structurally characterized. The electrochemical properties of all new compounds were revealed by cyclic voltammetry studies and compared to the known CF 3 analogue [(MeCN)Ni(CF 3 ) 3 ] -. The IMes-coordinated complexes exhibited initial oxidation events that were well-separated from a second oxidation process in the cyclic voltammograms. The complexes containing F-substituted NHC ligands [(F-NHC)Ni(CF 3 ) 3 ] - are structurally quite similar to the IMes derivative and reveal also two separated oxidation waves in their cyclic voltammograms. The absolute potentials as well as the separation between the two waves vary with the substitution pattern, suggesting that the NHC ligand environment (NHC = N-heterocyclic carbene) is an interesting platform for the development of new redox-triggered reactions that release trifluoromethyl and perfluoroalkyl radicals upon oxidation.

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

Hydrogen bonds and dispersion forces serving as molecular locks for tailored Group 11 bis(amidine) complexes

A flexible polydentate bis(amidine) ligand LH 2 , LH 2 = {CH 2 NH( t Bu)C=N-2-(6-MePy)} 2 , operates as a molecular lock for various coinage metal fragments and forms the dinuclear complexes [LH 2 (MCl) 2 ], M = Cu (1), Au (2), the coordination polymer [{(LH 2 ) 2 (py) 2 (AgCl) 3 }(py) 3 ] n (3), and the dimesityl-digold complex [LH 2 (AuMes) 2 ] (4) by formal insertion of MR fragments (M = Cu, Ag, Au; R = Cl, Mes) into the N–H∙∙∙N hydrogen bonds of LH 2 in yields of 43–95%. Complexes 1, 2, and 4 adopt C 2 -symmetrical structures in the solid state featuring two interconnected 11-membered rings that are locked by two intramolecular N–H∙∙∙R–M hydrogen bonds. QTAIM analyses of the computational geometry-optimized structures 1a, 2a, and 4a reveal 13, 11, and 22 additional bond critical points, respectively, all of which are related to weak intramolecular attractive interactions, predominantly representing dispersion forces, contributing to the conformational stabilization of the C2-symmetrical stereoisomers in the solid state. Variable-temperature 1 H NMR spectroscopy in combination with DFT calculations indicate a dynamic conformational interconversion between two C 2 -symmetrical ground state structures in solution (ΔG ‡ c = 11.1–13.8 kcal mol –1 ), which is accompanied by the formation of an intermediate possessing C i symmetry that retains the hydrogen bonds.

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

Highly stretchable ionically crosslinked acrylate elastomers inspired by polyelectrolyte complexes

Dynamic bonds are a powerful approach to tailor the mechanical properties of elastomers and introduce shape-memory, self-healing, and recyclability. Among the library of dynamic crosslinks, electrostatic interactions among oppositely charged ions have been shown to enable tough and resilient elastomers and hydrogels. In this work, we investigate the mechanical properties of ionically crosslinked ethyl acrylate-based elastomers assembled from oppositely charged copolymers. Using both infrared and Raman spectroscopy, we confirm that ionic interactions are established among polymer chains. We find that the glass transition temperature of the complex is in between the two individual copolymers, while the complex demonstrates higher stiffness and more recovery, indicating that ionic bonds can strengthen and enhance recovery of these elastomers. We compare cycles to increasing strain levels at different strain rates, and hypothesize that at fast strain rates ionic bonds dynamically break and reform while entanglements do not have time to slip, and at slow strain rates ionic interactions are disrupted and these entanglements slip significantly. Further, we show that a higher ionic to neutral monomer ratio can increase the stiffness, but its effect on recovery is minimal. Lastly, taking advantage of the versatility of acrylates, ethyl acrylate is replaced with the more hydrophilic 2-hydroxyethyl acrylate, and the latter is shown to exhibit better recovery and self-healing at a cost of stiffness and strength. The design principles uncovered for these easy-to-manufacture polyelectrolyte complex-inspired bulk materials can be broadly applied to tailor elastomer stiffness, strength, inelastic recovery, and self-healing for various applications.

36 MATERIALS SCIENCE↗