Search

BackgroundCOVID-19 forced healthcare systems to make unprecedented changes in clinical care processes. The authors hypothesized that the COVID-19 pandemic adversely impacted timely access to care, perioperative processes, and clinical outcomes for pediatric patients undergoing primary appendectomy.MethodsA retrospective, international, multicenter study was conducted using matched cohorts within participating centers of the international PEdiatric Anesthesia COVID-19 Collaborative (PEACOC). Patients younger than 18 yr old were matched using age, American Society of Anesthesiologists Physical Status, and sex. The primary outcome was the difference in hospital length of stay of patients undergoing primary appendectomy during a 2-month period early in the COVID-19 pandemic (April to May 2020) compared with prepandemic (April to May 2019). Secondary outcomes included time to appendectomy and the incidence of complicated appendicitis.ResultsA total of 3,351 cases from 28 institutions were available with 1,684 cases in the prepandemic cohort matched to 1,618 in the pandemic cohort. Hospital length of stay was statistically significantly different between the two groups: 29 h (interquartile range: 18 to 79) in the pandemic cohort versus 28 h (interquartile range: 18 to 67) in the prepandemic cohort (adjusted coefficient, 1 [95% CI, 0.39 to 1.61]; P < 0.001), but this difference was small. Eight centers demonstrated a statistically significantly longer hospital length of stay in the pandemic period than in the prepandemic period, while 13 were shorter and 7 did not observe a statistically significant difference. During the pandemic period, there was a greater occurrence of complicated appendicitis, prepandemic 313 (18.6%) versus pandemic 389 (24.1%), an absolute difference of 5.5% (adjusted odds ratio, 1.32 [95% CI, 1.1 to 1.59]; P = 0.003). Preoperative SARS-CoV-2 testing was associated with significantly longer time-to-appendectomy, 720 min (interquartile range: 430 to 1,112) with testing versus 414 min (interquartile range: 231 to 770) without testing, adjusted coefficient, 306 min (95% CI, 241 to 371; P < 0.001), and longer hospital length of stay, 31 h (interquartile range: 20 to 83) with testing versus 24 h (interquartile range: 14 to 68) without testing, adjusted coefficient, 7.0 (95% CI, 2.7 to 11.3; P = 0.002).ConclusionsFor children undergoing appendectomy, the COVID-19 pandemic did not significantly impact hospital length of stay.Editor’s perspective

Many metal-organic frameworks (MOFs) incorporate nodes that are small metal oxide clusters. Some of these MOFs are stable at high temperatures, offering good prospects as catalysts-prospects that focus attention on their defect sites and reactivities-all part of a broader subject: the surface chemistry of metal oxide clusters, illustrated here for MOF nodes and for polyoxocations and polyoxoanions. Ligands on MOF defect sites form during synthesis and are central to the understanding and control of MOF reactivity. Reactions of alcohols are illustrative probes of Zr6O8 node defects in UiO-66, characterized by the interconversions of formate, methoxy, hydroxy, and linker carboxylate ligands and by catalysis of alcohol dehydration reactions. We posit that new reactivities of MOF nodes will emerge from incorporation of a wide range of groups on their surfaces and from targeted substitutions of metals within them.

Conformational changes of the pyrophosphate (Pp)-functionalized uranyl peroxide nanocluster [(UO2)24(O2)24(P2O7)12]48- ({U24Pp12}), dissolved as a Li/Na salt, can be induced by the titration of alkali cations into solution. The most symmetric conformer of the molecule has idealized octahedral (Oh) molecular symmetry. One-dimensional 31P NMR experiments provide direct evidence that both K+ and Rb+ ions trigger an Oh-to-D4h conformational change within {U24Pp12}. Variable-temperature 31P NMR experiments conducted on partially titrated {U24Pp12} systems show an effect on the rates; increased activation enthalpy and entropy for the D4h-to-Oh transition is observed in the presence of Rb+ compared to K+. Two-dimensional, exchange spectroscopy 31P NMR revealed that magnetization transfer links chemically unique Pp bridges that are present in the D4h conformation and that this magnetization transfer occurs via a conformational rearrangement mechanism as the bridges interconvert between two symmetries. The interconversion is triggered by the departure and reentry of K (or Rb) cations out of and into the cavity of the cluster. This rearrangement allows Pp bridges to interconvert without the need to break bonds. Cs ions exhibit unique interactions with {U24Pp12} clusters and cause only minor changes in the solution 31P NMR signatures, suggesting that Oh symmetry is conserved. Single-crystal X-ray diffraction measurements reveal that the mixed Li/Na/Cs salt adopts D2h molecular symmetry, implying that while solvated, this cluster is in equilibrium with a more symmetric form. These results highlight the unusually flexible nature of the actinide-based {U24Pp12} and its sensitivity to countercations in solution.

The boron isotopic composition of tourmaline and hambergite (Be2BO3[OH,F]) from peraluminous (n = 12), peralkaline (n = 1), and peralkaline nepheline syenite (n = 16) pegmatites has been measured by secondary ion mass spectrometry, for which a new hambergite reference material was developed. The focus of this study is on nepheline syenite pegmatites from the Larvik Plutonic Complex (Norway) and one peralkaline pegmatite related to the nearby Eikeren-Skrim Complex (Norway), where we investigate the source of boron as being from magmatic vs. external fluids. Tourmaline-hambergite mineral pairs were also analysed from peraluminous pegmatite localities (Russia, Tajikistan, and Pakistan) to test for systematic B-isotope fractionation between these two minerals. Tourmaline and hambergite from peraluminous granitic pegmatites have light boron ratios (δ11B = −12.9to −1.0‰) associated with S-type granites, whereas peralkaline granitic and nepheline syenite pegmatites have boron ratios (δ11B = −1.7 to 11.8‰), which we interpret is a result of heavy‑boron enrichment from external fluids. Our data show that hambergite tracks isotope variations of its geochemical setting and could therefore be used as a proxy mineral in place of tourmaline when geochemical stability favours hambergite. The results suggest a slight but consistent partitioning of B-isotopes between tourmaline and hambergite, with Δ11B = δ11Btourmaline−δ11Bhambergite in the range of approximately −3‰ to −5‰. Boron is in trigonal coordination with oxygen in both of these mineral phases as verified by NMR. Single crystal XRD analyses of tourmaline and hambergite reveal consistent longer distances of tourmaline relative to hambergite. We attribute the boron isotopic fractionation to the longer bond-lengths in tourmaline compared with hambergite.

The COVID-19 pandemic has inflicted economic pain on the global community as well as physical pain. The pandemic has compounded a series of global problems that preceded the outbreak. These problems include growing nationalism, protectionism, and other forms of anti-globalization. Sharp declines in foreign direct investment (FDI) flows have been recorded, particularly in those developing countries with the greatest need for capital infusions. The short-term effects of the pandemic are already visible with both demand-side and supply-side shocks damaging the global economy. Traditional supply chains have been particularly disrupted. The long-term impact is more difficult to forecast. Whether anti-globalization and declining FDI flows continue over time depends on how national governments, global health agencies, and multinational enterprises ultimately address the underlying economic issues of the pandemic. Keywords: Pandemic, Multinational Enterprises (MNEs), Foreign Direct Investment (FDI), Global Supply Chains (GVCs), Globalization., INTRODUCTION It has been well-established in the scholarly and commercial literature that economic globalization over the past quarter of a century has contributed positively to global growth. An important part [...]

The oxygen-isotope fractionations between brucite and water, portlandite and water, and brucite and portlandite have been calculated over the temperature range of 0 to 450 °C using quantum-chemical methods and several basis sets and functionals. The calculations also employ embedded clusters that are chosen using the Pauling-bond-strength-conserving termination method that maintains a neutral cluster with fractional charges assigned to terminal atoms. These calculations improve upon the previous semiempirical methods for predicting mineral-mineral fractionations. These semiempirical methods fail to accurately predict the relative enrichment and depletion of oxygen isotopes for the brucite-portlandite pair. The quantum calculations presented here also fail to predict at the absolute values for enrichment of oxygen isotopes between minerals and water, and a simple correction must be employed to achieve agreement with experiments if water is in the reaction. No such correction is needed to predict fractionation between minerals. The trends derived from the calculations are robust to changes in basis sets and functionals.

High-pressure NMR has been in existence or 65 years and has evolved to be an essential tool for many disciplines. High-pressure NMR is useful both for determining standard thermodynamic properties and for assigning mechanisms of aqueous ligand-exchange reactions since solvation changes are sensitive to pressure. There have been many different apparatuses to provide and maintain pressure to the chemical systems of interest. Of these different devices, our group has primarily used the clamp-cell probe design, which allows for study of aqueous solute species that are important to geochemistry and at conditions seen in the crust and upper mantle of the Earth.11B and29Si studies are reviewed herein, and directions of future progress in the field are provided.

Aqueous geochemistry could be extended considerably if nuclear-magnetic resonance (NMR) methods could be adapted to study solutions at elevated temperatures and pressures. We therefore designed an NMR probe that can be used to study aqueous solutions at gigapascal pressures. Fluoride solutions were chosen for study because 19F couples to other nuclei in the solutions (31P and 11B) in ways that make peak assignments unequivocal. Correspondingly, NMR spectra of 19F- and 11B were collected on aqueous HBF4-NH4PF6 solutions to pressures up to 2.0 GPa. At pressure, peaks in the 19F spectra were clear and assignable to the BF4−(aq), F−(aq) and BF3OH− (aq) ions, and these aqueous complexes varied in signal intensity with pressure and time, for each solution. Peaks in the 11B spectra at pressure could be assigned to the BF4−(aq) and BF3OH−(aq) species. Additionally, there is a single peak that is assignable to H3BO3o(aq) and B(OH)4−(aq) in rapid-exchange equilibria. These peaks broaden and move with pressure in ways that suggest reversible interconversion of borate and fluoroborate species. The PF6− ion was found to provide a suitable 19F shift and intensity standard for high-pressure spectra because it was chemically inert. The positions and intensities of the doublet peak also remains constant as a function of pressure and pH. Addition of electrolytes considerably distorts the phase diagram of water such that the stability region of the aqueous solution expands to well beyond the 0.8 GPa freezing pressure of pure water; some fluoroborate solutions remain liquid until almost 2.0 GPa.

Niobium is usually considered to be one of the least mobile elements during alteration of rocks in geological processes and is thought to only be mobile at elevated temperatures and/or pressures. Since niobium is assumed to be unaffected by weathering it can be used in geochemical-evolution calculations to estimate the loss of material from the weathering of rocks. There are roughly a hundred niobium-bearing minerals, including those in the pyrochlore group, which comprises the main ores for Nb and Ta. Furthermore, pyrochlores are identified as potential hosts for nuclear waste because of their resistance to weathering. Here we show that niobium can be highly mobile even at near-surface geochemical conditions as a soluble and unreactive polyoxometalate ion. Discovery of the first natural hexaniobate minerals, all formed at near-surface conditions, provides evidence that niobium is being actively leached out of nearby primary minerals and easily transported as polyoxometalate ions. In addition, we show how Nb and Ta can be fractionated during low-temperature processes.

The multi-copper oxidase (MCO) MnxG from marine Bacillus bacteria plays an essential role in geochemical cycling of manganese by oxidizing Mn2+(aq) to form manganese oxide minerals at rates that are three to five orders of magnitude faster than abiotic rates. The MCO MnxG protein is isolated as part of a multi-protein complex, denoted as Mnx, which includes one MnxG unit and a hexamer of MnxE3F3 subunit. During the oxidation of Mn2+(aq) catalyzed by the Mnx protein complex, an enzyme-bound Mn(III) species was trapped recently in the presence of pyrophosphate (PP) and analyzed using parallel-mode electron paramagnetic resonance (EPR) spectroscopy. Herein, we provide a full analysis of this enzyme-bound Mn(III) intermediate via temperature dependence studies and spectral simulations. This Mnx-bound Mn(III) species is characterized by a hyperfine-coupling value of A(55Mn) = 4.2 mT (corresponding to 120 MHz) and a negative zero-field splitting (ZFS) value of D = - 2.0 cm-1. These magnetic properties suggest that the Mnx-bound Mn(III) species could be either six-coordinate with a 5B1g ground state or square-pyramidal five-coordinate with a 5B1 ground state. In addition, as a control, Mn(III)PP is also analyzed by parallel-mode EPR spectroscopy. It exhibits distinctly different magnetic properties with a hyperfine-coupling value of A(55Mn) = 4.8 mT (corresponding to 140 MHz) and a negative ZFS value of D = - 2.5 cm-1. The different ZFS values suggest differences in ligand environment of Mnx-bound Mn(III) and aqueous Mn(III)PP species. These studies provide further insights into the mechanism of biological Mn2+(aq) oxidation.

The kinetics of ligand exchange between the free oxalate ion, C2 O4 2- , and the bis-oxalato NpV complex, [NpO2 (C2 O4 )2 ]3- , in aqueous solution are reported by using 13 C and 17 O NMR spectroscopy methods. Rates of exchange were measured in the pH regime of 6.5-9.0, at which speciation is shown to be suitably simple. Because the neptunium(V) complex is paramagnetic, the rates of ligand exchange were estimated by following the width of the 13 C and 17 O signals assigned to the free oxalate ion in solution and by applying the Swift-Connick method for measuring rates of exchange. A set of experiments were conducted in which pH and total oxalate concentration were varied, and the linear dependence of the rate on these parameters was demonstrated. Variable-temperature NMR spectroscopy was also performed to measure activation parameters of complexation. At pH8.0 there is almost no dependence on temperature, which is interpreted to indicate that hydrolysis is coupled to ligand exchange under these conditions.

The kinetics of ligand exchange between the free oxalate ion, C2 O4 2- , and the bis-oxalato NpV complex, [NpO2 (C2 O4 )2 ]3- , in aqueous solution are reported by using 13 C and 17 O NMR spectroscopy methods. Rates of exchange were measured in the pH regime of 6.5-9.0, at which speciation is shown to be suitably simple. Because the neptunium(V) complex is paramagnetic, the rates of ligand exchange were estimated by following the width of the 13 C and 17 O signals assigned to the free oxalate ion in solution and by applying the Swift-Connick method for measuring rates of exchange. A set of experiments were conducted in which pH and total oxalate concentration were varied, and the linear dependence of the rate on these parameters was demonstrated. Variable-temperature NMR spectroscopy was also performed to measure activation parameters of complexation. At pH8.0 there is almost no dependence on temperature, which is interpreted to indicate that hydrolysis is coupled to ligand exchange under these conditions.

Herein we present the first example of a glycol-coordinated ε-Keggin Al13 chloride (gl-ε-Al13), which is the first chelated version since discovery of Al13 in 1960. The molecular structure consists of [AlO4Al12(OH)12(OC2H4OH)12]Cl7·H2O units with chelating mono-anionic ethylene glycol units replacing one bridging and one terminal oxygen site.

The fractionation factor in the magnesium-isotope fractionation between aqueous solutions of magnesium and brucite changes sign with increasing temperature, as uncovered by recent experiments. To understand this behavior, the Reduced Partition Function Ratios and isotopic fractionation factors (Δ26/24Mgbrucite-Mg(aq)) are calculated using molecular models of aqueous [Mg(OH2)6]2+ and the mineral brucite at increasing levels of density functional theory. The calculations were carried out on the [Mg(OH2)6]2+·12H2O cluster, along with different Pauling-bond-strength-conserving models of the mineral lattice of brucite. Three conclusions were reached: (i) all levels of theory overestimate 〈Mg–O〉 bond distances in the aqua ion complex relative to Tutton's salts; (ii) the calculations predict that brucite at 298.15 K is always enriched in the heavy isotope, in contrast with experimental observations; (iii) the temperature dependencies of Wimpenny et al. (2014) and Li et al. (2014) could only be achieved by fixing the 〈Mg–O〉 bond distances in the [Mg(OH2)6]2+·12H2O cluster to values close to those observed in crystals that trap the hydrated ion.

Herein we present the first example of a glycol-coordinated ε-Keggin Al13 chloride (gl-ε-Al13), which is the first chelated version since discovery of Al13 in 1960. The molecular structure consists of [AlO4Al12(OH)12(OC2H4OH)12]Cl7·H2O units with chelating mono-anionic ethylene glycol units replacing one bridging and one terminal oxygen site.

MnxG, a multicopper oxidase, is an enzyme from the marine Bacillus species, which produces manganese oxide minerals through the aerobic oxidation of dissolved Mn2+ − a key process in global manganese geochemical cycling. When isolated in an active form as a part of the MnxEFG protein complex, the enzymatic activity of MnxG is substantially enhanced by mild oxidative priming. Herein, the mechanism for this effect is probed by using direct current (dc) and Fourier transformed alternating current (ac) voltammetric analysis of the MnxEFG complex and the catalytically inactive MnxEF subunit immobilised on a carbon electrode. Analysis of these ac voltammetric data reveals a significant enhancement in the rate of electron transfer in the Type 2 Cu sites upon oxidative priming of the enzyme, which is attributed to the improved catalytic activity of MnxG in the MnxEFG protein complex.

Geochemists have models to predict solute speciation and mineral equilibria in aqueous solutions up to 1200 °C and 6 GPa. These models are useful to uncover reaction pathways deep in the Earth, though experimental confirmation is extremely difficult. Here we show speciation changes among aqueous silicate complexes to pressures of 1.8 GPa through use of a high-pressure solution-state NMR probe. The radiofrequency circuit uses a microcoil geometry that is coupled with a piston-cylinder pressure cell to generate and maintain these high pressures. The 1.8 GPa pressure corresponds to pressures reached at the lower crust or upper mantle. Although these experiments are limited to ambient temperature, we show that the increased pressure affects complexation and oligomerization reactions by eliminating bulk waters and that the pressure effects are completely reversible.

The conformational dynamics of nanometer-sized actinide ions are exceptionally sensitive to the choice of counter-cations. A new means of following these dynamics in solution is presented that follows 1H NMR signals. The direct bond between hydrogen and phosphorus atoms in the bridging phosphonic groups of the [(UO2)28(O2)20(PHO3)24(H2O)12]32– (U28) cluster allows unparalleled recording of the orientations of these bridges in situ. The µ3-PHO3 bridges are organized into two supersets of conformers (facing inward vs. outward from the cluster), but each of these supersets additionally have four subsets that can be identified based upon orientations of the lone pairs of electrons in the associated oxygen atoms. The ensemble of these subsets changes over days or weeks depending upon bulk solution chemistry, temperature, and pressure. They also reflect cations trapped within the molecule. The 1H NMR spectra at room temperature indicate that the molecular orientation of this enormous ion tunes itself in response to solution composition, which suggests a strategy for selecting host–guest combinations.

The COVID-19 pandemic has inflicted economic pain on the global community as well as physical pain. The pandemic has compounded a series of global problems that preceded the outbreak. These problems include growing nationalism, protectionism, and other forms of anti-globalization. Sharp declines in foreign direct investment (FDI) flows have been recorded, particularly in those developing countries with the greatest need for capital infusions. The short-term effects of the pandemic are already visible with both demand-side and supply-side shocks damaging the global economy. Traditional supply chains have been particularly disrupted. The long-term impact is more difficult to forecast. Whether anti-globalization and declining FDI flows continue over time depends on how national governments, global health agencies, and multinational enterprises ultimately address the underlying economic issues of the pandemic. Keywords: Pandemic, Multinational Enterprises (MNEs), Foreign Direct Investment (FDI), Global Supply Chains (GVCs), Globalization, INTRODUCTION It has been well-established in the scholarly and commercial literature that economic globalization over the past quarter of a century has contributed positively to global growth. An important part [...]

Influence of the conditions for aerobic oxidation of Mn2+(aq) catalysed by the MnxEFG protein complex on the morphology, structure and reactivity of the resulting biogenic manganese oxides (MnOx ) is explored. Physical characterisation of MnOx includes scanning and transmission electron microscopy, and X-ray photoelectron and K-edge Mn, Fe X-ray absorption spectroscopy. This characterisation reveals that the MnOx materials share the structural features of birnessite, yet differ in the degree of structural disorder. Importantly, these biogenic products exhibit strikingly different morphologies that can be easily controlled. Changing the substrate-to-protein ratio produces MnOx either as nm-thin sheets, or rods with diameters below 20 nm, or a combination of the two. Mineralisation in solutions that contain Fe2+(aq) makes solids with significant disorder in the structure, while the presence of Ca2+(aq) facilitates formation of more ordered materials. The (photo)oxidation and (photo)electrocatalytic capacity of the MnOx minerals is examined and correlated with their structural properties.

Recent theoretical advances and molecular-dynamic estimates of the dielectric constant of water have extended the HKF model for aqueous solution chemistry up to 6.0 gigapascals (GPa), which are conditions well beyond the capabilities of conventional NMR spectroscopy (Pan and others, 2013; Sverjensky and others, 2014, see also Wasserman and others, 1995). These developments provide strong motivation to design a simple NMR probe that allows experiments on solutions, at high resolution, to pressures of a few GPa (Pautler and others, 2014; Ochoa and others, 2015, 2016). Here we describe the performance of a compact NMR probe that can reach several GPa pressures. The probe is made by placing a solenoid microcoil inside of a standard piston-cylinder device used in solid-state physics. High pressures are achieved in the sample by applying force to a coaxial piston. Early designs of the probe, although useful, were limited in sample size to 10 to 15 L. Here we describe modifications that allow greatly improved resolution and sensitivity, including 1H-1H NMR correlation spectroscopy, on solutions at 2.8 GPa pressure. Sample sizes can be expanded if, instead of a standard NMR spectrometer that is built around a superconducting magnet, one employs a magnetic-resonance imaging (MRI) system that is built around a permanent magnet. The MRI systems can apply larger magnetic field gradients than conventional spectrometers, and thus have more robust shimming capability, which is needed because of the juxtaposition of different alloys in the pressure cell. More importantly, these systems can have magnetic fields that are oriented perpendicular to the magnet bore, which allows rotation of the coil within the axis of the pressure cell to increase sample volumes and pressure. Sensitivity is improved by replacing the traditional, but reduced-volume, closed sample container mounted in the center of the NMR detection coil with an open NMR coil that dangles freely in solution, thus making the sample solution itself the pressure-transmission fluid. The efficacy of these modifications are demonstrated by measuring 1H NMR spectra for ethyl alcohol and ethyl alcohol/methyl alcohol mixtures at pressures up to 2.8 GPa. Further developments are discussed that will allow geochemists to acquire aqueous solution NMR spectra at higher 3 to 4 GPa pressures.

The bacterial manganese oxidase MnxG of the Mnx protein complex is unique among multicopper oxidases (MCOs) in carrying out a two-electron metal oxidation, converting Mn(II) to MnO2 nanoparticles. The reaction occurs in two stages: Mn(II) → Mn(III) and Mn(III) → MnO2. In a companion study , we show that the electron transfer from Mn(II) to the low-potential type 1 Cu of MnxG requires an activation step, likely forming a hydroxide bridge at a dinuclear Mn(II) site. Here we study the second oxidation step, using pyrophosphate (PP) as a Mn(III) trap. PP chelates Mn(III) produced by the enzyme and subsequently allows it to become a substrate for the second stage of the reaction. EPR spectroscopy confirms the presence of Mn(III) bound to the enzyme. The Mn(III) oxidation step does not involve direct electron transfer to the enzyme from Mn(III), which is shown by kinetic measurements to be excluded from the Mn(II) binding site. Instead, Mn(III) is proposed to disproportionate at an adjacent polynuclear site, thereby allowing indirect oxidation to Mn(IV) and recycling of Mn(II). PP plays a multifaceted role, slowing the reaction by complexing both Mn(II) and Mn(III) in solution, and also inhibiting catalysis, likely through binding at or near the active site. An overall mechanism for Mnx-catalyzed MnO2 production from Mn(II) is presented.

The bacterial protein complex Mnx contains a multicopper oxidase (MCO) MnxG that, unusually, catalyzes the two-electron oxidation of Mn(II) to MnO2 biomineral, via a Mn(III) intermediate. Although Mn(III)/Mn(II) and Mn(IV)/Mn(III) reduction potentials are expected to be high, we find a low reduction potential, 0.38 V (vs Normal Hydrogen Electrode, pH 7.8), for the MnxG type 1 Cu2+, the electron acceptor. Indeed the type 1 Cu2+ is not reduced by Mn(II) in the absence of molecular oxygen, indicating that substrate oxidation requires an activation step. We have investigated the enzyme mechanism via electronic absorption spectroscopy, using chemometric analysis to separate enzyme-catalyzed MnO2 formation from MnO2 nanoparticle aging. The nanoparticle aging time course is characteristic of nucleation and particle growth; rates for these processes followed expected dependencies on Mn(II) concentration and temperature, but exhibited different pH optima. The enzymatic time course is sigmoidal, signaling an activation step, prior to turnover. The Mn(II) concentration and pH dependence of a preceding lag phase indicates weak Mn(II) binding. The activation step is enabled by a pKa > 8.6 deprotonation, which is assigned to Mn(II)-bound H2O; it induces a conformation change (consistent with a high activation energy, 106 kJ/mol) that increases Mn(II) affinity. Mnx activation is proposed to decrease the Mn(III/II) reduction potential below that of type 1 Cu(II/I) by formation of a hydroxide-bridged binuclear complex, Mn(II)(μ-OH)Mn(II), at the substrate site. Turnover is found to depend cooperatively on two Mn(II) and is enabled by a pKa 7.6 double deprotonation. It is proposed that turnover produces a Mn(III)(μ-OH)2Mn(III) intermediate that proceeds to the enzyme product, likely Mn(IV)(μ-O)2Mn(IV) or an oligomer, which subsequently nucleates MnO2 nanoparticles. We conclude that Mnx exploits manganese polynuclear chemistry in order to facilitate an otherwise difficult oxidation reaction, as well as biomineralization. The mechanism of the Mn(III/IV) conversion step is elucidated in an accompanying paper .

Understanding the stability fields and decomposition products of various metal- and actinide-oxide nanoclusters is essential for their development into useful materials for industrial processes. Herein, we explore the spontaneous transformation of the sulfate-centered, phosphate functionalized uranyl peroxide nanocluster {U20P6} to {U24} under aqueous ambient conditions using time-resolved small-angle X-ray scattering, Raman, and 31P NMR spectroscopy. We show that the unusual μ-η1:η2 bridging mode of peroxide between uranyl ions observed in {U20P6} may lead to its rapid breakdown in solution as evidenced by liberation of phosphate groups that were originally present as an integral part of its cage structure. Remarkably, the uranyl peroxide moieties present after degradation of {U20P6} undergo cation-mediated reassembly into the {U24} cluster, demonstrating the propensity of the uranyl peroxide systems to preserve well-defined macro-anions.

Multimeric oxo-hydroxo Al clusters function as models for common mineral structures and reactions. Cluster research, however, is often slowed by a lack of methods to prepare clusters in pure form and in large amounts. Herein, we report a facile synthesis of the little known cluster Al8 (OH)14 (H2 O)18 (SO4 )5 (Al8 ) through a simple dissolution method. We confirm its structure by single-crystal X-ray diffraction and show by 27 Al NMR spectroscopy, electrospray-ionization mass spectrometry, and small- and wide-angle X-ray scattering that it also exists in solution. We speculate that Al8 may form in natural water systems through the dissolution of aluminum-containing minerals in acidic sulfate solutions, such as those that could result from acid rain or mine drainage. Additionally, the dissolution method produces a discrete Al cluster on a scale suitable for studies and applications in materials science.

Large aqueous ions are interesting because they are useful in materials science (for example to generate thin films) but also because they serve as molecular models for the oxide-aqueous mineral interface where spectroscopy is difficult. Here we show that new clusters of the type M[(μ-OH)2 Co(NH3 )4 ]3 (NO3 )6 (M=Al, Ga) can be synthesized using Werner's century-old cluster as a substitutable framework. We substituted Group 13 metals into the hexol Co[(μ-OH)2 Co(NH3 )4 ]36+ ion to make diamagnetic heterometallic ions. The solid-state structure of the hexol-type derivatives were determined by single-crystal XRD and NMR spectroscopy and confirmed that the solid-state structure persists in solution after dissolution into either D2 O or [D6 ]DMSO. Other compositions besides these diamagnetic ions can undoubtedly be made using a similar approach, which considerably expands the number of stable aqueous heteronuclear ions.