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Glucuronidation of Methylated Quercetin Derivatives: Chemical and Biochemical Approaches
Botanical supplements derived from grapes are functional in animal model systems for the amelioration of neurological conditions, including cognitive impairment. Rats fed with grape extracts accumulate 3'-O-methyl-quercetin-3-O-β-Dglucuronide (3) in their brains, suggesting 3 as a potential therapeutic agent. To develop methods for the synthesis of 3 and the related 4'-O-methyl-quercetin-7-O-β-D-glucuronide (4), 3-O-methyl-quercetin-3'-O-β-D-glucuronide (5), and 4'-O-methylquercetin-3'-O-β-D-glucuronide (6), which are not found in the brain, we have evaluated both enzymatic semisynthesis and full chemical synthetic approaches. Biocatalysis by mammalian UDP-glucuronosyltransferases generated multiple glucuronidated products from 4'-O-methylquercetin, and is not cost-effective. Chemical synthetic methods, on the other hand, provided good results; 3, 5, and 6 were obtained in six steps at 12, 18, and 30% overall yield, respectively, while 4 was synthesized in five steps at 34% overall yield. Furthermore, a mechanistic study on the unexpected regioselectivity observed in the quercetin glucuronide synthetic steps is also presented.
Bond clusters control rupture force limit in shear loaded histidine-Ni 2+ metal-coordinated proteins
Dynamic noncovalent interactions are pivotal to the structure and function of biological proteins and have been used in bioinspired materials for similar roles. Metal-coordination bonds, in particular, are especially tunable and enable control over static and dynamic properties when incorporated into synthetic materials. Despite growing efforts to engineer metal-coordination bonds to produce strong, tough, and self-healing materials, the systematic characterization of the exact contribution of these bonds towards mechanical strength and the effect of geometric arrangements is missing, limiting the full design potential of these bonds. In this work, we engineer the cooperative rupture of metal-coordination bonds to increase the rupture strength of metal-coordinated peptide dimers. Utilizing all-atom steered molecular dynamics simulations on idealized bidentate histidine-Ni 2+ coordinated peptides, we show that histidine-Ni 2+ bonds can rupture cooperatively in groups of two to three bonds. We find that there is a strength limit, where adding additional coordination bonds does not contribute to the additional increase in the protein rupture strength, likely due to the highly heterogeneous rupture behavior exhibited by the coordination bonds. Further, we show that this coordination bond limit is also found natural metal-coordinated biological proteins. Using these insights, we quantitatively suggest how other proteins can be rationally designed with dynamic noncovalent interactions to exhibit cooperative bond breaking behavior. Altogether, this work provides a quantitative analysis of the cooperativity and intrinsic strength limit for metal-coordination bonds with the aim of advancing clear guiding molecular principles for the mechanical design of metal-coordinated materials.
Selective oxidation of active site aromatic residues in engineered Cu proteins
Engineered metalloproteins that mimic the active sites of natural copper metalloenzymes are used to systematically investigate the influence of aromatic residues within the secondary coordination sphere on reactivity.
Access to Ru(IV)–Ru(V) and Ru(V)–Ru(VI) Redox in Layered Li 7 RuO 6 via Intercalation Reactions
The push to increase the capacity of oxides to store charge as Li-ion battery cathodes has challenged our knowledge of the boundaries of redox chemistry and its relationship to the atomic structure. Layered phases with Ru are now classical models in the quest for refined theories. Current understanding dictates that the highest formal state that can be reached in them is Ru(V), after which activity centered at the oxide anions is triggered. Yet, this picture is challenged by this investigation of the intercalation chemistry of Li 7 RuO 6 . Coupling structural and spectroscopic analysis with computational simulations, we show that Li 7 RuO 6 is capable of highly reversible lithiation to Li 8 RuO 6 through the Ru(V)/Ru(IV) redox couple. Further, Li 7 RuO 6 can also undergo anodic Li deintercalation, showing clear evidence of the reversible formation of Ru(VI) with octahedral coordination, an unusual state that is not accessible in other layered oxides. The results highlight the versatility of the Ru-O bond to undergo distinct redox transitions depending on the specific layered arrangements. They enrich our understanding of redox chemistry in solids while underscoring the need for descriptions of charge compensation that reflect the nuance of covalent interactions.
Indium–Poly(carboxylic acid) Ligand Interactions Modify InP Quantum Dot Nucleation and Growth
Size control through precursor reactivity in InP quantum dot (QD) synthesis has been difficult due to the presence of kinetically persistent InP clusters when using conventional indium carboxylate and tris(trimethylsilyl)phosphine chemistry. However, the advent of indium halide/aminophosphine-based synthesis creates new opportunities to harness precursor design to impact nucleation and growth. Driven to further explore indium coordination as a synthetic handle in InP QD synthesis, we examined the effect of a strongly chelating anion on the nucleation and growth of InP QDs. Increasing the equivalents of metal-chelating aminopoly(carboxylic acid) EDTA ([CH 2 N(CH 2 CO 2 H) 2 ] 2 ) (0–0.75 equiv per indium) is found to decrease the final diameter of InP QDs from 4.5 to 2.3 nm by lowering the initial InP growth rate. This size trend is rationalized by invoking a continuous nucleation model. Control experiments carried out with substoichiometric equivalents of indium do not exhibit a drastic size decrease, pointing to complex effects of EDTA on the indium precursor reactivity. By 1 H NMR spectroscopy, EDTA is identified to form an octahedral complex with indium that is less reactive. Furthermore, this competitive decrease in reactivity and in the effective concentration of indium precursor is proposed to suppress the initial InP growth rates and consequently decrease the final size of the nanocrystals.
Overcoming efficiency and cost barriers for large-area quantum dot photovoltaics through stable ink engineering
The bottom-up construction of electronics from colloidal quantum dots (CQDs) could innovate nanotechnology manufacturing through printing. However, the unstable and expensive semiconductive CQD inks make the scaling up of CQD electronics challenging. Here, in this study, we develop a strategy for engineering the solution chemistry of lead sulfide (PbS) CQD inks prepared from a low-cost direct synthesis method. By creating an iodine-rich environment in weakly coordinating solvents, we convert the iodoplumbates into functional anions, which condense into a robust surface shell. The fully charged electrostatic surface layer prevents aggregation and epitaxial fusion of CQDs, yielding stable inks. By eliminating the fusion-induced inter-band states, we print a compact CQD film with uniformity in three dimensions, flattened energy landscape and improved carrier transport. We achieved a certified efficiency of 13.40% on 0.04 cm 2 cells, with a 300-fold increase in active area, scaling up to a 12.60 cm 2 module with a certified efficiency of 10%.
Safety considerations of lithium-thionyl chloride cells
The use of spirally wound lithium-thionyl chloride (Li-SOCl2) cells is currently limited because of their hazardous behavior. Safety hazards have ranged from mild venting of toxic materials to violent explosions and fires. These incidents may be related to both user- and manufacturer-induced causes. Many explanations have been offered to explain the unsafe behavior of the cells under operating and abuse conditions. Explanations fall into two categories: (1) thermal mechanisms, and (2) chemical mechanisms. However, it is quite difficult to separate the two. Both may be responsible for cell venting or explosion. Some safety problems encountered with these cells also may be due to design deficiencies and ineffective quality control during cell fabrication. A well-coordinated basic and applied research program is needed to develop safe Li-SOCl2 cells. Recommendations include: (1) learnig more about Li-SOL2 cell chemistry; (2) modeling cell and battery behavior; (3) optimizing cell design for safety and performance, (4) implementing quality control procedures; and (5) educating users.
Mobile Observations of Ozone and Aerosols in Alabama: Southeastern US Summer Pollution and Coastal Variability
We present a detailed analysis of measurements of ozone (O 3 ) and aerosols collected using multiple platforms and instruments during a 5-day mini-campaign in Alabama, for improving our understanding of the chemistry and air quality in the Southeastern United States. Our study features the first on-road O 3 lidar profiling on highways and the coordinated airborne observations that captured O 3 and aerosol structures associated with synoptic weather conditions, stratospheric intrusions, wildfire smoke transport, and enhancements in urban areas. The Doppler wind lidar data suggest that the vertical structures and variability of O 3 and aerosols at Dauphin Island, a coastal site in the Gulf of Mexico, were related to both the synoptic flow and local-scale land-sea breeze circulation. The onshore gulf breeze, which typically started in the afternoon, helped to quickly dilute air pollutants near the surface, resulting in large gradients toward inland areas. In contrast, gradients were much smaller on days without a gulf breeze. O 3 and humidity were highly anti-correlated in the lower free troposphere, but weakly anti-correlated in the planetary boundary layer (PBL) suggesting more complicated emissions and sink of O 3 in the PBL. Our on-road and airborne measurement strategies to quantify the vertical and horizontal chemical gradients will be useful for future geostationary satellite validation.
Surface-Activated Corrosion in Tin–Lead Halide Perovskite Solar Cells
Mixed tin–lead halide perovskite solar cells have promising power conversion efficiencies, but long-term stability is still a challenge. Here, we examine the stability of a 60:40 tin–lead perovskite to better understand diminished device performance upon thermal treatment, both in ambient and inert atmosphere. Operando X-ray diffraction shows a stable bulk structure of the perovskite absorber, leading to the hypothesis that surface chemistry dominates the degradation mechanism. X-ray photoelectron spectroscopy reveals two new observations post-thermal annealing that accompany previously reported Sn 4+ evolution: (i) the formation of I 3 – intermediates preceding I 2 loss at the surface and (ii) evidence of under-coordinated tin and lead surface sites (Sn δ<2+ and Pb δ<2+ , respectively) in inert and ambient conditions. These two species indicate an activated corrosion (i.e., both oxidation and reduction) process at the surface as a possible chemical pathway for degradation, which is expected to be accelerated under operando voltage and light biases.
Local Environment of Superoxide Radical Formed on the TiO 2 Surface Produced From Ti(OiPr) 4 Exposed to H 2 O 2
A selective heterogeneous catalyst with the superoxide anion O 2 •– stable at room temperature, generated by treating Ti(OR) 4 (R=iPr, nBu) with H 2 O 2 , was previously reported and used for the oxidation of organic compounds. Furthermore, it was proposed that exceptional stability of the O 2 •– is resulted from its stabilization near Ti +4 cation on the TiO 2 surface with participation of water molecules and/or OH groups. In this article, we performed high-resolution pulsed EPR study on the O 2 •– in this catalyst with the aim to obtain quantitative information about its interactions with the surrounding molecules. Our data has shown that the O 2 •– is involved in weak hyperfine interactions with protons in the nearest environment, which do not exceed a value of 2 MHz. It corresponds to an Os…H distance of ≥ 3 Å that exclude the formation of hydrogen bonds. The analysis of possible structures of O 2 •– adsorption on TiO 2 surface taking into account our results and lack of radical mobility at room temperature previously observed in EPR spectra led us to suggest that the O 2 •– is stabilized in the form of superoxo bridge coordinated with two titanium atoms.
Cobalt-Catalyzed Hydrogenation Reactions Enabled by Ligand-Based Storage of Dihydrogen
The use of supporting ligands that can store either protons or electrons has emerged as a powerful strategy in catalysis. While these strategies are potent individually, natural systems mediate remarkable transformations by combining the storage of both protons and electrons in the secondary coordination sphere. As such, there has been recent interest in using this strategy to enable fundamentally different transformations. Furthermore, outsourcing H-atom or hydrogen storage to ancillary ligands can also enable alternative mechanistic pathways and thereby selectivity. Here, we describe the application of this strategy to facilitate radical reactivity in Co-based hydrogenation catalysis. Metalation of previously reported dihydrazonopyrrole ligands with Co results in paramagnetic complexes, which are best described as having Co(II) oxidation states. These complexes catalytically hydrogenate olefins with low catalyst loadings under mild conditions (1 atm H 2 , 23 °C). Mechanistic, spectroscopic, and computational investigations indicate that this system goes through a radical hydrogen-atom transfer (HAT) type pathway that is distinct from classic organometallic mechanisms and is supported by the ability of the ligand to store H 2 . These results show how ancillary ligands can facilitate efficient catalysis, and furthermore how classic organometallic mechanisms for catalysis can be altered by the secondary coordination sphere.
Identifying the speciation of salt-based actinides in the presence of contaminants [Slides]
Molten salt reactors (MSR) present advantages over light water reactors, such as higher safety and energy efficiency, convenient waste processing, and the ability to use more abundant thorium instead of uranium as the fuel source. However, due to the high temperatures associated with these reactors the reactor container corrosion product can have a high influence on the molten salt system, and they are considered as a part of the fuel salt system. It is essential to have a comprehensive understanding of the chemical reactions that are occurring in the molten salt in the presence of contaminants such as nickel, manganese, chromium chlorides and oxides. Because they can change the local structure of these salts and the local structures of these salts govern the thermophysical properties of the molten salts, which would determine the safety and operational parameters of the reactor. This study is focused on identifying f-element materials speciation resulting from reaction with corrosion/degradation products in a molten salt environment to understand the flow of MSR. In this work, f-element chlorides are mixed with alkali and alkali earth metals and corrosion products such as transition metal chlorides are introduced systematically, inside a glovebox. Then these are heated to around 700 ? and slowly cooled to room temperature. Afterwards, these are analyzed using different characterization techniques such as powder X-ray diffraction, UV-vis and Raman spectroscopy and solid-state NMR. The initial work was conducted with lanthanide chlorides as a surrogate for actinides and the acquired data strongly indicates that in the presence of corrosion products new phase formation/ change in coordination environments occurs. This work has been presented at multiple conference presentations. The proposed work would allow to extend this work to actinides (depleted uranium and thorium) and this would assist to identify the speciation of actinide chloride in the presence of corrosion products. Also, this work would open an opportunity to compare the coordination behavior of lanthanides with the actinides.
Structural chemistry of penta- and hexanitrato thorium($\tiny{IV}$) complexes isolated using N–H donors
In this study, a series of fifteen tetravalent thorium phases were prepared. The compounds were isolated from acidic aqueous nitrate solutions using protonated nitrogen heterocycles of varying hydrogen-bond donation strength. Structural analysis via single crystal X-ray diffraction showed that the structures are built from pentanitrato, [Th(NO 3 ) 5 (H 2 O) 2 ] 1- , and hexanitrato, [Th(NO 3 ) 6 ] 2- , molecular units, with the latter being far more prevalent in the solid state. The vibrational properties of the compounds were examined using Raman and IR spectroscopy; the spectra are dominated by stretches characteristic of nitrate and the organic ions. The relative energetics of nitrate complexation was examined using electronic structure theory. These results confirmed that there are clear thermodynamic sinks for the penta- and hexanitrato structural units that were observed experimentally. Additionally, electrostatic surface potentials (ESPs) were calculated in an effort to better understand the counterion stabilization of the complexes. The ESP surfaces showed that the position of the water and nitrate molecules and the coordination geometry of the metal complex had a clear effect on the polarizability of the two structural motifs. Despite limited speciation of the Th–nitrate structural units, the compounds exhibit rich supramolecular chemistry resulting from hydrogen bonding of the Th complexes with the organic N–H donors and π–π stacking interactions from the protonated N-heterocycles.
Spontaneously supersaturated nucleation strategy for high reproducible and efficient perovskite solar cells
High-quality perovskite films are predominantly prepared by anti-solvent assisted spin-coating method. How- ever, small device size and narrow operation window limit their applications in practical and scalable production. Here, a spontaneously supersaturated nucleation strategy is developed to fabricate high-quality perovskite films without any antisolvents. The rapid precipitation behavior of the precursor solutions could be triggered by the volatilization of methylamine ethanol at the initial film formation stage, forming uniform and compact intermediate phase films. Mirror-like large area (10 cm × 10 cm) methylammonium lead triiodide (MAPbI 3 ) perovskite films with micrometer-sized grains can be achieved by phase transition via annealing. The average power conversion efficiency (PCE) of 19.4% is achieved for 0.1 cm 2 perovskite solar cells (PSCs). The 1 cm 2 device shows a PCE of 17.57% and retains 96.8% after aging for 39 days in the air with a relative humidity of 5–30%. The perovskite module based on the perovskite films prepared by our strategy exhibits a PCE of 13.13%. Here, the perovskite film fabrication method developed in this work shows high reproducibility of the fabrication process due to the spontaneous nucleation process. Meanwhile, it also exhibits significant potential in the application of scalable solution processing deposition techniques toward the commercialization of PSCs.
Basic Energy Sciences Roundtable: Foundational Science to Accelerate Nuclear Energy Innovation
Energy security, availability, and reliability are among the greatest challenges facing the nation and the planet. An abundant potential source of energy resides in the fundamental atomic building blocks of the universe in the form of nuclear fission and fusion reactions. In fact, energy from nuclear fission currently provides the majority of the world’s zero-carbon electricity, and future fusion energy systems offer great promise; carbon-free nuclear energy technologies can be key to the world’s decarbonized energy future. Although contemporary fission systems use well-established technologies to supply safe and efficient baseload power, they could be more fuel efficient and less costly. Moving beyond massive light-water fission reactors to a variety of advanced nuclear systems—which will vary in size and operate in extremes of temperature, corrosivity, and other parameters—will place stringent conditions on materials and chemical systems. New demands will be placed on the coolants and solvents, the materials, and the monitoring tools used in these reactors. Fusion-based nuclear energy will require superior materials to withstand extremely high temperatures, plasma exposure, radiation damage, and implanted gases. The advantages associated with these new fission and fusion technologies will be realized only through continued advancements in the fundamental science underpinning our knowledge of the physics and chemistry of nuclear systems gained via improved experimental and computational methods. In July 2022, the U.S. Department of Energy’s Office of Basic Energy Sciences—in coordination with the Offices of Nuclear Energy, Fusion Energy Sciences, and Advanced Scientific Computing Research—held a virtual roundtable titled “Foundational Science to Accelerate Nuclear Energy Innovation” to discuss the scientific and technical barriers for advanced nuclear energy systems. Five priority research opportunities were identified to address these scientific and technical challenges and to accelerate progress toward the realization of next-generation fusion and fission energy systems. The foundational science gaps inhibiting the advancement of nuclear energy technologies are identified and tackled in five priority research opportunities. These opportunities pave the way to accelerate the development and ultimately the adoption of new nuclear energy systems. They include the fundamental aspects of ion-electron interactions; novel properties of next-generation coolants and solvents; interfacial dynamics, not only in solids, but in other aspects of nuclear reactors; novel operando and in situ monitoring and sensing; and artificial intelligence to accelerate condensed phases discovery. Building on the foundation established by previous Basic Energy Sciences workshops, these opportunities encompass recent advances in fundamental knowledge and focus on the experimental and computational methods needed to resolve major technical challenges for nuclear energy technologies. Through developing fundamental scientific insight as well as pushing the frontiers of modeling complex systems and probing the operation of materials and chemical systems in extreme environments, research motivated by the priorities identified here will further develop the promise, potential, and utilization of nuclear energy for a clean energy future.
Emergent solvation phenomena in non-aqueous electrolytes with multiple anions
As the search for new battery chemistries with higher capacities and more stable supply chains expands, requiring increasingly complex electrolytes with multiple solvents and anions, it is becoming clear that understanding and controlling the working cation solvation structure is key to enabling improved stability and reversibility. In this work, we discover an emergent solvation behavior in multivalent electrolytes containing multiple anions, where bis(trifluoromethane sulfonyl) imide (TFSI⁻) anions that are fully dissociated in isolation form contact ion pairs with Zn 2+ when combined with more strongly coordinating halides. This coordination modifies the electrochemical response, activating additional redox species as the halide association strength weakens (i.e., Cl⁻ > Br⁻ > I⁻) and systematically lowering overpotentials for metal deposition. This work suggests a completely new framework for electrolyte design in which anion chemistry can be used to tune both the bulk speciation and the interfacial solvation structure, enabling profound changes to the electrochemical behavior of the system.