40 Search Results

Target of rapamycin (TOR) and sucrose non-fermenting 1–related protein kinase 1 (SnRK1) are conserved regulators of plant growth and metabolism and are often portrayed as functionally antagonistic under nutrient limitation. However, how this relationship operates across different nutrient contexts remains poorly defined. Here, we generated an Arabidopsis dual-reporter line that enables simultaneous monitoring of TOR and SnRK1 activities and profiled their dynamics under carbon and nitrogen perturbations. We found that TOR and SnRK1 activities\r\noverall exhibit a negative relationship during the transition from carbon starvation to carbon abundance; however, their temporal dynamics during that transition do not support a strictly inversemore » correlation. Under dark conditions, TOR activity is gradually repressed, while SnRK1 is initially repressed in the early hours and subsequently activated during extended darkness. During nitrogen starvation, TOR activity is progressively repressed, whereas SnRK1 is activated during early hours and then becomes repressed. In vitro, recombinant SnRK1a1 directly\r\ninhibits the activity of immunoprecipitated TOR (IP-TOR), whereas IP-TOR does not directly affect SnRK1a1 activity. Together, these results support a nutrient dependent model in which TOR and SnRK1 are coordinated primarily by cellular metabolic status.\r\n« less

High-lying Rydberg and autoionizing (AI) states of thorium (Th) have been studied via resonance laser ionization spectroscopy at both TRIUMF Canada’s particle accelerator center and Oak Ridge National Lab (ORNL). Multiple Rydberg series converging to the ionization potential (IP) were observed via different stepwise laser excitation schemes and were assigned to be the 6d²7s (⁴F_3/2) np, nd, and nf series. Analysis of these series enabled the determination of the IP to be 50 868.735(54) cm⁻¹, which improved the precision by two orders of magnitude over the current adopted NIST value of 50 867(2) cm⁻¹. Additionally, four AI Rydberg series weremore » identified and assigned to nf and nd series converging to the 6d²7s ⁴F_5/2 and 6d7s^{2 2}D_3/2 metastable states of Th⁺. In conclusion, the measured energies of the Rydberg and AI Rydberg states are reported, and observed perturbations within the series are discussed.« less

Reaction of 4 equiv. of [Li(TMEDA)]₂[1,2-S₂C₆H₄] with [ThCl₄(DME)₂] or [UCl₄(THF)₃] in THF results in formation of [Li(THF)₂]₄[An(1,2-S₂C₆H₄)₄] (An = Th, 1; An = U, 2), whereas reaction of 4 equiv. of [Li(TMEDA)]₂[1,2-S₂C₆H₄] with UCl₄ in Et₂O results in formation of [Li(TMEDA)]₄[U(1,2-S₂C₆H₄)₄] (3). Complexes 1–3 represent the first reported benzenedithiolate complexes of the actinides. Here, they were characterized by NMR spectroscopy and X-ray crystallography. In the solid state, complexes 1–3 exhibit triangular dodecahedral geometries about their actinide centers. Additionally, their Li⁺ cations are bound by two sulfur atoms of adjacent [1,2-S₂C₆H₄]²⁻ ligands, in addition to two solvent donor atoms. In solution,more » complexes 2 and 3 exhibit spectral data consistent with S₄ symmetry (and non-exchanging Li⁺ sites), whereas complex 1 exhibits spectral properties consistent with labile Li⁺ cations.« less

Rationale: Mass spectrometric measurement of the ²³⁰Th/²³⁴U ratio to calculate the purification age of enriched uranium is typically conducted via a combination of ion counters and faraday detectors, thus requiring an inter-detector calibration scheme. Here, our aim is to understand whether the pursuit of a simplified measurement scheme involving only faraday detectors is feasible. Methods: We investigate the possibility of determining U-Th model ages for two enriched uranium standards (NBL U630 and U850) by direct measurement of the ²³⁰Th/²³⁴U ratio (without chromatographic separation or isotope dilution) on a ThermoFisher Scientific Neoma MC-ICP-MS utilizing both solution and laser ablation (LA)-based samplingmore » techniques and an all-faraday detector configuration. Results: For the solution mode analyses conducted on aliquots containing sub μg/mL total U, we produce composite average ²³⁰Th/²³⁴U model dates of May 19, 1988 (± 351 days), and March 26, 1961 (± 2.5 years) using the directly measured ²³⁰Th/²³⁴U ratios for the NBL U630 and U850 uranium standards, which have certified purification dates of June 6, 1988 (± 190 days), and December 31, 1957 (± 36.5 days), respectively. The ages produced by LA-based sampling of dried residues of the same standards deposited onto cotton TexWipes are less accurate and of poorer precision (June 23, 2004 ± 8.7 years for U630 and December 21, 1965 ± 7.9 years for U850) but still yield meaningful information in regards to the purification date. Conclusions: We believe that further refinement of the all faraday detector measurement approach to include development of a more robust Th/U relative sensitivity factor determination, signal cutoff selection, and data processing protocols will allow for this approach to be confidently applied to enriched uranium materials with unknown purification histories. Potential advantages of the method include the reduced sample handling and infrastructure requirements as well as the ability to simultaneously generate a broad picture of the uranium isotopic composition in tandem with the U-Th age determination.« less

Actinide complexes containing the simplest borohydrides (BH₄)^1- and (MeBH₃)^1- can exhibit remarkably highly volatility, which creates unique hazards and handling challenges, especially when making measurements on solid samples under vacuum. Here we describe efforts to prepare new actinide borohydride complexes with attenuated volatility by adding bulkier benzyl (Bn) and cyclohexyl (Cy) substituents to boron. Reactions of ThCl₄, UI₃(thf)₄, and NdI₃ with the mixed alkali metal salt Li/K(BnBH₃)(thf)_n yielded Th(BnBH₃)₄(thf)₂, U(BnBH₃)₄(thf)₂, and K[Nd(BnBH₃)₄], respectively. Notable amongst these, the reaction with UI₃(thf)₄ proceeds via oxidation of U(III) to U(IV) despite the presence of reducing borohydride ligands. Similarly, reactions of the same metalmore » halides with four equivalents of Li(CyBH₃)(Et₂O)_n yielded Th(CyBH₃)₄, U(CyBH₃)₄(thf)₂, and [Li(Et₂O)₃][Nd(CyBH₃)₄]. Single crystal X-ray diffraction studies of the M(BnBH₃)₄(thf)₂ complexes with M = Th and U confirmed their formulations. Furthermore, the complexes have approximate D_2d point group symmetry and adopt bicapped hexagonal antiprismatic coordination geometries with axial thf ligands and κ³-BnBH₃ ligands bound in the equatorial plane. K[Nd(BnBH₃)₄] and [Li(Et₂O)₃][Nd(CyBH₃)₄], which were prepared for comparison to U(III) complexes that were unsuccessfully targeted, were also structurally characterized to reveal complex anions with tetrahedral arrangements of trihydroborate ligands bound to Nd(III). Crystals obtained for Th(CyBH₃)₄ and U(CyBH₃)₄(thf)₂ were not suitable for XRD studies, but ¹H and ¹¹B NMR spectra were consistent with their formulations. Collectively, these complexes represent rare examples of structurally characterized f-element trihydroborate complexes with carbon substituents other than methyl.« less

Porous metal–organic frameworks (MOFs) have emerged as highly promising adsorbents for capturing radioiodine, a predominant fission product released during nuclear fuel reprocessing. However, systematic investigations into the correlation between MOF structure and iodine uptake capacity remain scarce. Here, we present a novel approach to enhance the iodine adsorption capacity of MOFs by optimizing linker functionalization. Using ligand-functionalized thorium-based MOFs as a structural platform, we demonstrate that ortho-amino-substitution near the node of the dicarboxylate linker significantly increases iodine adsorption capacity compared to meta-amino-substitution, where the amino groups are directed away from the node. Specifically, ortho-substituted Th-UiO-68-3,3”-(NH₂)₂ exhibits higher iodine uptake capacitiesmore » than the meta-substituted Th-UiO-68-2,2”-(NH₂)₂ via both vapor diffusion-based (2.042 vs. 1.087 g/g) and solution-based (0.841 vs. 0.784 g/g) processes. Notably, the I₂ vapor adsorption capacity (2.042 g/g) of Th-UiO-68-3,3”-(NH₂)₂ represents the second highest among all reported Th-MOFs. Pair distribution function (PDF) studies reveal that the superior iodine uptake performance of ortho-functionalized MOFs can be attributed to the reduced steric hindrance of the amino groups compared with the meta-substituted variants. Finally, this research highlights how positional isomerism and its subtle alterations can significantly influence host–guest interactions, extending beyond simple structural considerations.« less

The use of Laser Ion Source for accelerator facilities has the advantage to tune the characteristic of the produced beams by changing the laser parameters using the same primary target. The advantageous and innovative opportunity to manipulate the characteristic of charge state distributions by the use of composed target, may open new possibilities for the ion sources. In this experiment we characterize and study the plasma produced by the laser ablation of coated targets at constant laser parameters. The performed investigation has the double purpose to have a better understanding of penetration depth of laser in composed materials and understandmore » how to tune the charge states by adding coating films. Finally, the obtained results showed that for particular thickness of coating, the low charge states were produced with higher yield than in the case of pure material.« less

Positively charged metal–ammonia complexes are known to host peripheral, diffuse electrons around their molecular skeleton. The resulting neutral species form materials known as expanded or liquid metals. Alkali, alkaline earth, and transition metals have been investigated previously in experimental and theoretical studies of both the gas and condensed phase. This work is the first ab initio exploration of an f-block metal–ammonia complex. The ground and excited states are calculated for Th0–3+ complexes with ammonia, crown ethers, and aza-crown ethers. For Th3+ complexes, the one valence electron Th populates the metal’s 6d or 7f orbitals. For Th0–2+, the additional electrons prefermore » occupation of the outer s- and p-type orbitals of the complex, except Th(NH3)10, which uniquely places all four electrons in outer orbitals of the complex. Although thorium coordinates up to ten ammonia ligands, octa-coordinated complexes are more stable. Crown ether complexes have a similar electronic spectrum to ammonia complexes, but excitations of electrons in the outer orbitals of the complex are higher in energy. Aza-crown ethers disfavor the orbitals perpendicular to the crowns, attributed to the N-H bonds pointing along the plane of the crowns.« less