Reply to 'Experimental measurement of assembly indices are required to determine the threshold for life'.

We clarify misunderstandings of Walker et al. (Walker 2024 21, 20240367 (doi:10.1098/rsif.

In Situ Uranium Extraction through the Synthesis of the Uranyl Peroxide Studtite Using a Nonthermal Plasma.

Extraction of uranium from water is an essential step in leach (ISL) mining and environmental decontamination. This is often done by precipitating uranium in solution as the uranyl peroxide studtite, [(UO)(O)(HO)](HO), by adding hydrogen peroxide, which is energy-intensive to produce and hazardous to transport. Here, we present a method for synthesizing studtite, by generating reactive oxygen species in solution using a nonthermal plasma.

Activation of uranyl peroxides by ionizing radiation prior to uranyl carbonate formation.

The solid form of the uranyl peroxide cage (UPC) cluster LiU (Li[(UO)(O)]) was irradiated by 5 MeV He ions to achieve doses up to 42 MGy. An intermediate compound formed that reacts with atmospheric CO to form uranyl carbonates. The role of water in the UPC to uranyl carbonate transformation was studied by flowing either dry or hydrated Ar over samples during He irradiation, and by storing samples in dry and humid environments before and after irradiation.

Formation of Uranyl Peroxide Compounds via Dissolution of Studtite, [(UO)(O)(HO)](HO), in Ionic Liquids.

Four uranyl peroxide compounds with novel structures were formed following the dissolution of studtite, [(UO)(O)(HO)](HO), in imidazolium-based ionic liquids. The compounds were characterized using single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), Raman and infrared (IR) spectroscopy, and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS). The ionic liquids used in the experiments were 1-ethyl-3-methylimidazolium (EMIm) diethyl phosphate, EMIm ethyl sulfate, and EMIm acetate.

A Two-Step Intermolecular Interaction Of Molecular Macroions With Multivalent Counterions.

Macroion-counterion interaction is essential for regulating the solution behaviors of hydrophilic macroions, as simple models for polyelectrolytes. Here, we explore the interaction between uranyl peroxide molecular cluster LiK(OH)[UO(O)OH] (U) and multivalent counterions. Different from interaction with monovalent counterions that shows a simple one-step process, isothermal titration calorimetry, combined with light/X-ray scattering measurements and electron microscopy, confirm a two-step process for their interaction with multivalent counterions: an ion-pairing between U and the counterion with partial breakage of hydration shells followed by strong U-U attraction, leading to the formation of large nanosheets with severe breakage and reconstruction of hydration shells.

Radiological Analyses of Ra and U in Surface Water and Sediments from the Jackpile Member of the Morrison Formation, Pueblo of Laguna, New Mexico.

Surface water and sediments from the Jackpile mine, St. Anthony mine, Rio Paguate, Rio Moquino, and Mesita Dam areas near Pueblo of Laguna, New Mexico, were analyzed for Ra and U using gamma (γ) spectroscopy and inductively coupled plasma mass spectroscopy, respectively. Activity ratios for Ra/U for solid samples range from 0.

Coacervate Formation in Dilute Aqueous Solutions of Inorganic Molecular Clusters with Simple Divalent Countercations.

We report a complex coacervate formed by a 2.5 nm-diameter, rigid uranyl peroxide molecular cluster (LiK(OH))[UO(O)OH], U) and SrCl salt in dilute aqueous solutions, including its location in the phase diagram, composition, rheological features, and critical conditions for phase transitions. In this coacervate, the Sr cations are a major building component, and the coacervate phase covers a substantial region of the phase diagram.

Actinide Sulfate Structures from Caustic Solvents.

Four unique actinide sulfates were synthesized using solvothermal techniques with strong acids. The first plutonium(III) sulfate structure, Pu(HSO), was synthesized and is isostructural with analogous lanthanide-based frameworks. A similar synthesis approach yielded crystals of NpNa(HSO)(SO), which has a comparable framework to the Pu(III) compound, but the neptunium metal is tetravalent and sodium is incorporated into the structure, as confirmed by chemical analysis.

Critical Conditions Regulating the Gelation in Macroionic Cluster Solutions.

The critical gelation conditions observed in dilute aqueous solutions of multiple nanoscale uranyl peroxide molecular clusters are reported, in the presence of multivalent cations. This gelation is dominantly driven by counterion-mediated attraction. The gelation areas in the corresponding phase diagrams all appear in similar locations, with a characteristic triangle shape outlining three critical boundary conditions, corresponding to the critical cluster concentration, cation/cluster ratio, and the degree of counterion association with increasing cluster concentration.

A New Molybdenum Blue Structure Type: How Uranium Expands this Family of Polyoxometalates.

The assembly of molybdenum polyoxometalates (POMs) has afforded large discrete nanoclusters with varied degrees of reduction such as the ~20 % reduced molybdenum blues. While many heterometals have been incorporated into these clusters to afford new properties, uranium has yet to be reported. Here we report the first uranium containing molybdenum blue clusters and the unique properties exhibited by this incorporation.

Molecular assembly indices of mineral heteropolyanions: some abiotic molecules are as complex as large biomolecules.

Molecular assembly indices, which measure the number of unique sequential steps theoretically required to construct a three-dimensional molecule from its constituent atomic bonds, have been proposed as potential biosignatures. A central hypothesis of assembly theory is that any molecule with an assembly index ≥15 found in significant local concentrations represents an unambiguous sign of life. We show that abiotic molecule-like heteropolyanions, which assemble in aqueous solution as precursors to some mineral crystals, range in molecular assembly indices from 2 for HCO or Si(OH) groups to as large as 21 for the most complex known molecule-like subunits in the rare minerals ewingite and ilmajokite.

Pu(VI) Oxalate Crystal Structure and Evidence of Photoreduction to Pu(IV) Oxalate.

We report the first crystal structure of a Pu(VI)-oxalate compound. This compound, [PuO(CO)(HO)]·2(HO) (), crystallizes in space group 2/ with = 5.5993(3) Å, = 16.

Removal of Aqueous Uranyl and Arsenate Mixtures after Reaction with Limestone, PO, and Ca.

The co-occurrence of uranyl and arsenate in contaminated water caused by natural processes and mining is a concern for impacted communities, including in Native American lands in the U.S. Southwest.

Insight into the Structural Ambiguity of Actinide(IV) Oxalate Sheet Structures: A Case for Alternate Coordination Geometries.

Invited for the cover of this issue is the group of Amy Hixon at the University of Notre Dame. The image depicts the newly identified structure of a Pu oxalate sheet compared to the historically assumed structure. Read the full text of the article at 10.

Kinetics of Na- and K- uranyl arsenate dissolution.

We integrated aqueous chemistry analyses with geochemical modeling to determine the kinetics of the dissolution of Na and K uranyl arsenate solids (UAs) at acidic pH. Improving our understanding of how UAs dissolve is essential to predict transport of U and As, such as in acid mine drainage. At pH 2, NaH(UO)(AsO)(HO) (NaUAs) and KH(UO)(AsO)(HO) (KUAs) both dissolve with a rate constant of 3.

Insight into the Structural Ambiguity of Actinide(IV) Oxalate Sheet Structures: A Case for Alternate Coordination Geometries.

Plutonium(IV) oxalate hexahydrate (Pu(C O )  ⋅ 6 H O; PuOx) is an important intermediate in the recovery of plutonium from used nuclear fuel. Its formation by precipitation is well studied, yet its crystal structure remains unknown. Instead, the crystal structure of PuOx is assumed to be isostructural with neptunium(IV) oxalate hexahydrate (Np(C O )  ⋅ 6 H O; NpOx) and uranium(IV) oxalate hexahydrate (U(C O )  ⋅ 6 H O; UOx) despite the high degree of unresolved disorder that exists when determining water positions in the crystal structures of the latter two compounds.

Predicting new mineral occurrences and planetary analog environments via mineral association analysis.

The locations of minerals and mineral-forming environments, despite being of great scientific importance and economic interest, are often difficult to predict due to the complex nature of natural systems. In this work, we embrace the complexity and inherent "messiness" of our planet's intertwined geological, chemical, and biological systems by employing machine learning to characterize patterns embedded in the multidimensionality of mineral occurrence and associations. These patterns are a product of, and therefore offer insight into, the Earth's dynamic evolutionary history.

Electrospray Ionization Tandem Mass Spectrometry With Collision Induced Dissociation of Uranyl Peroxide Nanoclusters Containing Various Uranyl Bridging Ligands.

Electrospray ionization tandem mass spectrometry with collision-induced dissociation (ESI-MS/MS) was utilized to study the gas phase fragmentation of uranyl peroxide nanoclusters with hydroxo, peroxo, oxalate, and pyrophosphate bridging ligands. These nanoclusters fragment into uranium monomers and dimers with mass-to-charge (m/z) ratios in the 280-380 region. The gas phase fragmentation of each cluster studied yields a distinct UO anion attributed to the cleavage of a uranyl ion bound to 2 peroxide groups, along with other anions that can be attributed to the initial composition of the nanoclusters.

Electrochemistry of Uranyl Peroxide Solutions during Electrospray Ionization.

The ionization of uranyl triperoxide monomer, [(UO)(O)] (UT), and uranyl peroxide cage cluster, [(UO)(O)(OH)] (U), was studied with electrospray ionization mass spectrometry (ESI-MS). Experiments including tandem mass spectrometry with collision-induced dissociation (MS/CID/MS), use of natural water and DO as solvent, and use of N and SF as nebulizer gases, provide insight into the mechanisms of ionization. The U nanocluster under MS/CID/MS with collision energies ranging from 0 to 25 eV produced the monomeric units UO ( = 3-8) and UOH ( = 4-8, = 1, 2).

Solubility and Thermodynamic Investigation of Meta-Autunite Group Uranyl Arsenate Solids with Monovalent Cations Na and K.

We investigated the aqueous solubility and thermodynamic properties of two meta-autunite group uranyl arsenate solids (UAs). The measured solubility products (log ) obtained in dissolution and precipitation experiments at equilibrium pH 2 and 3 for NaUAs and KUAs ranged from -23.50 to -22.

Ozone-Facilitated Formation of Uranyl Peroxide in Humid Conditions.

Metaschoepite, [(UO)O(OH)](HO), maintained in a high relative humidity (RH) environment with air initially transformed into an intermediate phase that subsequently was replaced by the peroxide phase studtite, [(UO)(O)(HO)](HO), over the course of 42 days, as observed using Raman and infrared spectroscopy and powder X-ray diffraction. Addition of atmospheric ozone vastly increased the rate and extent of the transformation to studtite but only in a high-RH atmosphere. Owing to its strong affinity for peroxide, uranyl reacted with hydrogen peroxide as it formed and precipitated stable studtite.

One of Nature's Puzzles Is Assembled: Analog of the Earth's Most Complex Mineral, Ewingite, Synthesized in a Laboratory.

Through the combination of low-temperature hydrothermal synthesis and room-temperature evaporation, a synthetic phase similar in composition and crystal structure to the Earth's most complex mineral, ewingite, was obtained. The crystal structures of both natural and synthetic compounds are based on supertetrahedral uranyl-carbonate nanoclusters that are arranged according to the cubic body-centered lattice principle. The structure and composition of the uranyl carbonate nanocluster were refined using the data on synthetic material.

Targeting Diverse Bridging Motifs within Actinide Borosulfates and Establishing an Unconventional Structural Hierarchy.

The first actinide borosulfates, (UO)[B(SO)(SOOH)] (TSUBOS-1) and (UO)[BO(SO)(SOOH)] (TSUBOB-1), were synthesized solvothermally in oleum using UO. The classical borosulfate crystal structure of TSUBOS-1 is partially consistent with an established conventional hierarchy. Uranyl pentagonal bipyramids limit the anionic network linkages and isolate sulfate tetrahedra within the anionic network.