Radiation-Induced Defects in Uranyl Trinitrate Solids.

Actinides are inherently radioactive; thus, ionizing radiation is emitted by these elements can have profound effects on its surrounding chemical environment through the formation of free radical species. While previous work has noted that the presence of free radicals in the system impacts the redox state of the actinides, there is little atomistic understanding of how these metal cations interact with free radicals. Herein, we explore the effects of radiation (UV and γ) on three U(VI) trinitrate complexes, M[UO2(NO3)3] (where M = K+, Rb+, Cs+), and their respective nitrate salts in the solid state via electron paramagnetic resonance (EPR) and Raman spectroscopy paired with Density Functional Theory (DFT) methods. We find that the alkali salts form nitrate radicals under UV and γ irradiation, but also note the presence of additional degradation products.  M[UO2(NO3)3] solids also form nitrate radicals and additional DFT calculations indicate the species corresponds to a change from the bidentate bound nitrate anion into a monodentate NO3• radical.  Computational studies also highlight the need to include the second sphere coordination environment around the [UO2(NO3)3]0,1 species to gain agreement between the experimental and predicted EPR signatures.

Synthesis, characterization, and density functional theory investigation of (CH6N3)2[NpO2Cl3] and Rb[NpO2Cl2(H2O)] chain structures.

The actinyl tetrachloro complex [An(V/VI)O2Cl4]2-/3- tends to form discrete molecular units in both solution and solid state materials, but related aquachloro complexes have been observed as both discrete coordination compounds and 1-D chain topologies. Subtle differences in the inner sphere coordination significantly influence the formation of structural topologies in the actinyl chloride system, but the exact reasoning for these variations has not been delineated. In the current study, we present the synthesis, structural characterization, and vibrational analysis of two 1-D neptunyl(V) chain compounds: (CH6N3)2[NpO2Cl3] (Np-Gua) and Rb[NpO2Cl2(H2O)] (Np-Rb). Bonding and non-covalent interactions (NCIs) in the systems were evaluated using periodic Density Functional Theory (DFT) to link these properties to related phases. We observed ∼6.5% and ∼3.9% weakening of NpO bonds in Np-Gua and Np-Rb compared to the reference Cs3[NpO2Cl4]. NCI analysis distinguished specific assembly modes, where Np-Gua was connected via hydrogen bonding (N-H⋯Cleq and N-H⋯Oyl) and Np-Rb contained both cation interactions (Rb+⋯Oyl and Rb+⋯Cleq) and hydrogen bonding (Oeq-H⋯Oyl) networks. Thermodynamically viable formation pathways for both compounds were explored using DFT methodology. The [NpO2Cl4](aq)3- and [NpO2Cl3(H2O)](aq)2- substructures were identified as precursors to Np-Gua and [NpO2Cl3(H2O)](aq)2- and [NpO2Cl2(H2O)2](aq)- were isolated as the primary building units of Np-Rb. Finally, we utilized DFT to analyze the vibrational modes for Np-Gua and Np-Rb, where we found evidence of the NpO bond weakening within the Np(V) chain structures compared to [NpO2Cl4]3-.

Three-Dimensional Noncovalent Interaction Network within [NpO2Cl4]2- Coordination Compounds: Influence on Thermochemical and Vibrational Properties.

Noncovalent interactions (NCIs) can influence the stability and chemical properties of pentavalent and hexavalent actinyl (AnO2+/2+) compounds. In this work, the impact of NCIs (actinyl-hydrogen and actinyl-cation interactions) on the enthalpy of formation (ΔHf) and vibrational features was evaluated using Np(VI) tetrachloro compounds as the model system. We calculated the ΔHf values of these solid-state compounds through density functional theory+ thermodynamics (DFT+ T) and validated the results against experimental ΔHf values obtained through isothermal acid calorimetry. Three structural descriptors were evaluated to develop predictors for ΔHf, finding a strong link between ΔHf and hydrogen bond energy (EHtotal) for neptunyl-hydrogen interactions and total electrostatic attraction energy (Eelectrostatictotal) for neptunyl-cation interactions. Finally, we used Raman spectroscopy together with bond order analysis to probe Np=O bond perturbation due to NCIs. Our results showed a strong correlation between the degree of NCIs by axial oxygen and red-shifting of Np=O symmetrical stretch (ν1) wavenumbers and quantitatively demonstrated that NCIs can weaken the Np=O bond. These properties were then compared to those of related U(VI) and Np(V) phases to evaluate the effects of subtle differences in the NCIs and overall properties. In general, the outcomes of our study demonstrated the role of NCIs in stabilizing actinyl solid materials, which consequently governs their thermochemical behaviors and vibrational signatures.

Synthesis, Characterization, and Density Functional Theory Investigation of the Solid-State [UO2Cl4(H2O)]2- Complex.

A significant number of solid-state [UO2Cl4]2- coordination compounds have been synthesized and structurally characterized. Yet, despite their purposive relative abundance in aqueous solutions, characterization of aquachlorouranium(VI) complexes remain rare. In the current study, a solid-state uranyl aqua chloro complex ((C4H12N2)2[UO2Cl4(H2O)]Cl2) was synthesized using piperazinium as a charge-balancing ligand, and the structure was determined using single-crystal X-ray diffraction. Using periodic density functional theory, the electronic structure of the [UO2Cl4(H2O)]2- complex was compared to [UO2Cl4]2- to uncover the strengthening of the U═O bond in [UO2Cl4(H2O)]2-. Changes in the strength of the U═O bond were validated further with Raman and IR spectroscopy, where uranyl symmetrical (ν1) and asymmetrical (ν3) stretches were blue-shifted compared to the reference [UO2Cl4]2- complex. Furthermore, the formation energy of the solid-state (C4H12N2)2[UO2Cl4(H2O)]Cl2 complex was calculated to be -287.60 ± 1.75 kJ mol-1 using isothermal acid calorimetry. The demonstrated higher stability relative to the related [UO2Cl4]2- complex was related to the relative stoichiometry of the counterions.

Guiding Principles for the Rational Design of Hybrid Materials: Use of DFT Methodology for Evaluating Non-Covalent Interactions in a Uranyl Tetrahalide Model System.

Together with the synthesis and experimental characterization of 14 hybrid materials containing [UO2 X4 ]2- (X=Cl- and Br- ) and organic cations, we report on novel methods for determining correlation trends in their formation enthalpy (ΔHf ) and observed vibrational signatures. ΔHf values were analyzed through isothermal acid calorimetry and a Density Functional Theory+Thermodynamics (DFT+T) approach with results showing good agreement between theory and experiment. Three factors (packing efficiency, cation protonation enthalpy, and hydrogen bonding energy [ E H , norm total ${{E}_{H,{\rm { norm}}}^{{\rm { total}}}}$ ]) were assessed as descriptors for trends in ΔHf . Results demonstrated a strong correlation between E H , norm total ${E_{{\rm{H}},{\rm{norm}}}^{{\rm{total}}} }$ and ΔHf , highlighting the importance of hydrogen bonding networks in determining the relative stability of solid-state hybrid materials. Lastly, we investigate how hydrogen bonding networks affect the vibrational characteristics of uranyl solid-state materials using experimental Raman and IR spectroscopy and theoretical bond orders and find that hydrogen bonding can red-shift U≡O stretching modes. Overall, the tightly integrated experimental and theoretical studies presented here bridge the trends in macroscopic thermodynamic energies and spectroscopic features with molecular-level details of the geometry and electronic structure. This modeling framework forms a basis for exploring 3D hydrogen bonding as a tunable design feature in the pursuit of supramolecular materials by rational design.

Spaceflight associated neuro-ocular syndrome (SANS): an update on potential microgravity-based pathophysiology and mitigation development.

Long-duration spaceflight is associated with neurologic and ophthalmic clinical and imaging findings in astronauts termed spaceflight associated neuro-ocular syndrome (SANS). These microgravity-induced findings have been well documented by the National Aeronautics and Space Administration (NASA) and are clearly a potential risk for future human space exploration. The underlying pathogenesis of SANS is not well understood, although multiple hypotheses have emerged. Terrestrial analogues and potential countermeasures have also been studied to further understand and potentially mitigate SANS. In this manuscript, we review the current understanding of SANS, discuss the prevailing hypotheses for pathogenesis, and describe current developments in terrestrial analogues and potential countermeasures for SANS.

Influencing Bonding Interactions of the Neptunyl (V, VI) Cations with Electron-Donating and -Withdrawing Groups.

Neptunium makes up the largest percentage of minor actinides found in spent nuclear fuel, yet separations of this element have proven difficult due to its rich redox chemistry. Developing new reprocessing techniques should rely on understanding how to control the Np oxidation state and its interactions with different ligands. Designing new ligands for separations requires understanding how to properly tune a system toward a desired trait through functionalization. Emerging technologies for minor actinide separations focus on ligands containing carboxylate or pyridine functional groups, which are desirable due to their high degree of functionalization. Here, we use DFT calculations to study the interactions of carboxylate and polypyridine ligands with the neptunyl cation [Np(V/VI)O2]+/2+. A systematic study is performed by varying the electronic properties of the carboxylate and polypyridine ligands through the inclusion of different electron-withdrawing and electron-donating R groups. We focus on how these groups can affect geometric properties, electronic structure, and bonding characterization as a function of the metal oxidation state and ligand character and discuss how these factors can play a role in neptunium ligand design principles.

Evaluation of Optic Disc Edema in Long-Duration Spaceflight Crewmembers Using Retinal Photography.

BACKGROUND: Long-duration spaceflight crewmembers are at risk for spaceflight-associated neuro-ocular syndrome (SANS). One of the earliest manifestations of SANS is optic disc edema (ODE), which could be missed using the subjective Frisén scale. The primary objective of this study is to determine the inter-rater and intrarater reliability of Frisén grade for SANS-induced ODE among a trained observer cohort. The secondary objective is to propose a standardized evaluation process for SANS-induced ODE across International Space Station Partner Agencies. METHODS: Retrospective, double-blinded diagnostic study. Preflight and postflight fundus photographs were presented to subject matter experts who identified and graded ODE. Pairs of images were also compared side-by-side for disc ranking. Grader concordance was assessed for Frisén grading and disc ranking. RESULTS: Expert graders identified Grade 1 ODE in 17.35% of images from 62 crewmembers (9 female, mean [SD] age, 47.81 [5.19] years). Grades 2 and 3 were identified less than 2% of the time. Concordance in Frisén grades among pairs of graders was 70.99%. Graders identified a difference in preflight and postflight fundus photographs 17.21% of the time when using disc ranking. Pairs of graders had complete concordance in disc ranking 79.79% of the time. Perfect intrarater agreement between Frisén grade and disc ranking occurred 77.7% of the time. CONCLUSIONS: These findings demonstrate intergrader and intragrader variability when using the Frisén scale to identify SANS-induced ODE, which is typically milder in presentation than terrestrial cases of idiopathic intracranial hypertension. It is possible to miss early ODE on fundoscopy alone, making it insufficient as a sole criterion for the diagnosis of SANS. A more sensitive and objective method of surveillance is necessary to monitor international crewmembers for ODE, perhaps using a multimodal approach that includes technology such as optical coherence tomography.

Spaceflight associated neuro-ocular syndrome: proposed pathogenesis, terrestrial analogues, and emerging countermeasures.

Spaceflight associated neuro-ocular syndrome (SANS) refers to a distinct constellation of ocular, neurological and neuroimaging findings observed in astronauts during and following long duration spaceflight. These ocular findings, to include optic disc oedema, posterior globe flattening, chorioretinal folds and hyperopic shifts, were first described by NASA in 2011. SANS is a potential risk to astronaut health and will likely require mitigation prior to planetary travel with prolonged exposures to microgravity. While the exact pathogenesis of SANS is not completely understood, several hypotheses have been proposed to explain this neuro-ocular phenomenon. In this paper, we briefly discuss the current hypotheses and contributing factors underlying SANS pathophysiology as well as analogues used to study SANS on Earth. We also review emerging potential countermeasures for SANS including lower body negative pressure, nutritional supplementation and translaminar pressure gradient modulation. Ongoing investigation within these fields will likely be instrumental in preparing and protecting astronaut vision for future spaceflight missions including deep space exploration.

Incidence and Progression of Chorioretinal Folds During Long-Duration Spaceflight.

Importance: The primary contributing factor for development of chorioretinal folds during spaceflight is unknown. Characterizing fold types that develop and tracking their progression may provide insight into the pathophysiology of spaceflight-associated neuro-ocular syndrome and elucidate the risk of fold progression for future exploration-class missions exceeding 12 months in duration. Objective: To determine the incidence and presentation of chorioretinal folds in long-duration International Space Station crew members and objectively quantify the progression of choroidal folds during spaceflight. Design, Setting, and Participants: In this retrospective cohort study, optical coherence tomography scans of the optic nerve head and macula of crew members completing long-duration spaceflight missions were obtained on Earth prior to spaceflight and during flight. A panel of experts examined the scans for the qualitative presence of chorioretinal folds. Peripapillary total retinal thickness was calculated to identify eyes with optic disc edema, and choroidal folds were quantified based on surface roughness within macular and peripapillary regions of interest. Interventions or Exposures: Spaceflight missions ranging 6 to 12 months. Main Outcomes and Measures: Incidence of peripapillary wrinkles, retinal folds, and choroidal folds; peripapillary total retinal thickness; and Bruch membrane surface roughness. Results: A total of 36 crew members were analyzed (mean [SD] age, 46 [6] years; 7 [19%] female). Chorioretinal folds were observed in 12 of 72 eyes (17%; 6 crew members). In eyes with early signs of disc edema, 10 of 42 (24%) had choroidal folds, 4 of 42 (10%) had inner retinal folds, and 2 of 42 (5%) had peripapillary wrinkles. Choroidal folds were observed in all eyes with retinal folds and peripapillary wrinkles. Macular choroidal folds developed in 7 of 12 eyes (4 of 6 crew members) with folds and progressed with mission duration; these folds extended into the fovea in 6 eyes. Circumpapillary choroidal folds developed predominantly superior, nasal, and inferior to the optic nerve head and increased in prevalence and severity with mission duration. Conclusions and Relevance: Choroidal folds were the most common fold type to develop during spaceflight; this differs from reports in idiopathic intracranial hypertension, suggesting differences in the mechanisms underlying fold formation. Quantitative measures demonstrate the development and progression of choroidal folds during weightlessness, and these metrics may help to assess the efficacy of spaceflight-associated neuro-ocular syndrome countermeasures.

Periodic Density Functional Theory Calculations of Uranyl Tetrachloride Compounds Engaged in Uranyl-Cation and Uranyl-Hydrogen Interactions: Electronic Structure, Vibrational, and Thermodynamic Analyses.

Solid-state uranyl hybrid structures are often formed through unique intermolecular interactions occurring between a molecular uranyl anion and a charge-balancing cation. In this work, solid-state structures of the uranyl tetrachloride anion engaged in uranyl-cation and uranyl-hydrogen interactions were studied using density functional theory (DFT). As most first-principles methods used for systems of this type focus primarily on the molecular structure, we present an extensive benchmarking study to understand the methods needed to accurately model the geometric properties of these systems. From there, the electronic and vibrational structures of the compounds were investigated through projected density of states and phonon analysis and compared to the experiment. Lastly, we present a DFT + thermodynamics approach to calculate the formation enthalpies (ΔHf) of these systems to directly relate to experimental values. Through this methodology, we were able to accurately capture trends observed in experimental results and saw good quantitative agreement in predicted ΔHf compared to the value calculated through referencing each structure to its standard state. Overall, results from this work will be used for future combined experimental and computational studies on both uranyl and neptunyl hybrid structures to delineate how varying intermolecular interaction strengths relates to the overall values of ΔHf.

Investigations of the Cobalt Hexamine Uranyl Carbonate System: Understanding the Influence of Charge and Hydrogen Bonding on the Modification of Vibrational Modes in Uranyl Compounds.

Hydrogen bonding networks within hexavalent uranium materials are complex and may influence the overall physical and chemical properties of the system. This is particularly true if hydrogen bonding takes places between the donor and the oxo group associated with the uranyl cation (UO22+). In the current study, we evaluate the impact of charge-assisted hydrogen bonding on the vibrational modes of the uranyl cation using uranyl tricarbonate [UO2(CO3)3]4- interactions with [Co(NH3)6]3+ as the model system. Herein, we report the synthesis and structural characterization of five novel compounds, [Co(NH3)6]Cl(CO3) (Co_Cl_CO3), [Co(NH3)6]4[UO2(CO3)3]3(H2O)11.67 (Co4U3), [Co(NH3)6]3[UO2(CO3)3]2Cl (H2O)7.5 (Co3U2_Cl), [Co(NH3)6]2[UO2(CO3)3]Cl2 (Co2U_Cl), and [Co(NH3)6]2[UO2(CO3)3]CO3 (Co2U_CO3), which contain differences in the crystalline packing and extended hydrogen bonding networks. We show that these slight changes in the supramolecular assembly and hydrogen bonding networks result in the modification of modes as observed by infrared and Raman spectroscopy. We use density functional theory calculations to assign the vibrational modes and provide an understanding about how uranyl bond perturbation and changes in hydrogen bonding interactions can impact the resulting spectroscopic signals.

Surveillance for jugular venous thrombosis in astronauts.

BACKGROUND: Thrombosis of the left internal jugular vein in an astronaut aboard the International Space Station was recently described, incidentally discovered during a research study of blood flow in neck veins in microgravity. Given this event, and the high incidence of flow abnormalities, the National Aeronautics and Space Administration (NASA) instituted an occupational surveillance program to evaluate astronauts for venous thrombosis. METHODS: Duplex ultrasound of the bilateral internal jugular veins was conducted on all NASA astronauts terrestrially, and at three points during spaceflight. Respiratory maneuvers were performed. Images were analyzed for thrombosis and certain hemodynamic characteristics, including peak velocity and degree of echogenicity. RESULTS: Eleven astronauts were evaluated with matching terrestrial and in-flight ultrasounds. No thrombosis was detected. Compared to terrestrial ultrasound measurements, in-flight peak velocity was reduced and lowest in the left. Six of 11 astronauts had mild-moderate echogenicity in the left internal jugular vein during spaceflight, but none had more than mild echogenicity in the right internal jugular vein. Two astronauts developed retrograde blood flow in the left internal jugular vein. CONCLUSION: Abnormal flow characteristics in microgravity, most prominent in the left internal jugular vein, may signal an increased risk for thrombus formation in some individuals.

Binding of polar and hydrophobic molecules at the LiCoO2 (001)-water interface: force field development and molecular dynamics simulations.

A classical model in the framework of the INTERFACE force field has been developed for treating the LiCoO2 (LCO) (001)/water interface. In comparison to ab initio molecular dynamics (MD) simulations based on density functional theory, MD simulations using the classical model lead to generally reliable descriptions of interfacial properties, such as the density distribution of water molecules. Water molecules in close contact with the LCO surface form a strongly adsorbed layer, which leads to a free energy barrier for the adsorption of polar or charged molecules to the LCO surface. Moreover, due to the strong hydrogen bonding interactions with the LCO surface, the first water layer forms an interface that exhibits hydrophobic characters, leading to favorable adsorption of non-polar molecules to the interface. Therefore, despite its highly polar nature, the LCO (001) surface binds not only polar/charged but also non-polar solutes. As an application, the model is used to analyze the adsorption of reduced nicotinamide adenine dinucleotide (NADH) and its molecular components to the LCO (001) surface in water. The results suggest that recently observed redox activity of NADH at the LCO/water interface was due to the co-operativity between the ribose component, which drives binding to the LCO surface, and the nicotinamide moiety, which undergoes oxidation.

Use of vibrational spectroscopy to identify the formation of neptunyl-neptunyl interactions: a paired density functional theory and Raman spectroscopy study.

Actinyl-Actinyl interactions (AAIs) occur in pentavalent actinide systems, particularly for neptunium (Np), and lead to complex vibrational signals that are challenging to analyze and interpret. Previous studies have focused on neptunyl-neptunyl dimeric species, but trimers and tetramers have been identified as the primary motif for extended topologies observed in solid-state materials. Our hypothesis is that trimeric and tetrameric AAIs lead to the additional signals in the vibrational spectra, but this has yet to be explored systematically. Herein, we investigate three different neptunyl-neptunyl subunits (dimeric, trimeric, tetrameric) and determine the vibrational frequencies of the ONpO stretches using both computational and experimental approaches. Density Functional Theory (DFT) was used to identify distinct vibrational motions related to specific neptunyl oligomers and compared to previous literature precedent from Np(V) in HClO4 and HCl systems. The vibrational behavior of Np(V) in HNO3 was then evaluated via Raman spectroscopy. As the solution evaporated signals were linked to trimeric and tetrameric models. Solid phases produced in the evaporation include (NpO2)2(NO3)2(H2O)5 and newly identified crystalline phase, Na(NpO2)(NO3)2·4H2O (NpNa). The combined computational studies and vibrational analysis provide evidence for unique observable vibrational bands for each polymerized subunit, allowing us to assign spectral features to trimeric and tetrameric models within three different simple anionic systems.

Adsorption of small organic acids and polyphenols on hematite surfaces: Density Functional Theory + thermodynamics analysis.

HYPOTHESIS: The interactions of organic molecules with mineral surfaces are influenced by several factors such as adsorbate speciation, surface atomic and electronic structure, and environmental conditions. When coupled with thermodynamic techniques, energetics from atomistic modeling can provide a molecular-level picture of which factors determine reactivity. This is paramount for evaluating the chemical processes which control the fate of these species in the environment. EXPERIMENTS: Inner-sphere adsorption of oxalate and pyrocatechol on (001), (110), and (012) α-Fe2O3 surfaces was modeled using Density Functional Theory (DFT). Unique bidentate binding modes were sampled along each facet to study how different adsorbate and surface factors govern site preference. Adsorption energetics were then calculated using a DFT + thermodynamics approach which combines DFT energies with tabulated data and Nernst-based corrective terms to incorporate different experimental parameters. FINDINGS: Instead of a universal trend, each facet displays a unique factor that dominates site preference based on either strain (001), functional groups (110), or topography (012). Adsorption energies predict favorable inner-sphere adsorption for both molecules but opposite energetic trends with varying pH. Additionally, vibrational analysis was conducted for each system and compared to experimental IR data. The work presented here provides an effective, computational methodology to study numerous adsorption processes occurring at the surface-aqueous interface.

Opposite response of blood vessels in the retina to 6° head-down tilt and long-duration microgravity.

The Spaceflight Associated Neuro-ocular Syndrome (SANS), associated with the headward fluid shifts incurred in microgravity during long-duration missions, remains a high-priority health and performance risk for human space exploration. To help characterize the pathophysiology of SANS, NASA's VESsel GENeration Analysis (VESGEN) software was used to map and quantify vascular adaptations in the retina before and after 70 days of bed rest at 6-degree Head-Down Tilt (HDT), a well-studied microgravity analog. Results were compared to the retinal vascular response of astronauts following 6-month missions to the International Space Station (ISS). By mixed effects modeling, the trends of vascular response were opposite. Vascular density decreased significantly in the 16 retinas of eight astronauts and in contrast, increased slightly in the ten retinas of five subjects after HDT (although with limited significance). The one astronaut retina diagnosed with SANS displayed the greatest vascular loss. Results suggest that microgravity is a major variable in the retinal mediation of fluid shifts that is not reproduced in this HDT bed rest model.

Density functional theory and thermodynamics analysis of MAl12 Keggin substitution reactions: Insights into ion incorporation and experimental confirmation.

Polyaluminum cations, such as the MAl12 Keggin, undergo atomic substitutions at the heteroatom site (M), where nanoclusters with M = Al3+, Ga3+, and Ge4+ have been experimentally studied. The identity of the heteroatom M has been shown to influence the structural and electronic properties of the nanocluster and the kinetics of ligand exchange reactions. To date, only three ε-analogs have been identified, and there is a need for a predictive model to guide experiment to the discovery of new MAl12 species. Here, we present a density functional theory (DFT) and thermodynamics approach to predicting favorable heteroatom substitution reactions, alongside structural analyses on hypothetical ε-MAl12 nanocluster models. We delineate trends in energetics and geometry based on heteroatom cation properties, finding that Al3+-O bond lengths are related to heteroatom cation size, charge, and speciation. Our analyses also enable us to identify potentially isolable new ε-MAl12 species, such as FeAl12 7+. Based upon these results, we evaluated the Al3+/Zn2+/Cr3+ system and determined that substitution of Cr3+ is unfavorable in the heteroatom site but is preferred for Zn2+, in agreement with the experimental structures. Complimentary experimental studies resulted in the isolation of Cr3+-substituted δ-Keggin species where Cr3+ substitution occurs only in the octahedral positions. The isolated structures Na[AlO4Al9.6Cr2.4(OH)24(H2O)12](2,6-NDS)4(H2O)22 (δ-CrnAl13-n-1) and Na[AlO4Al9.5Cr2.5(OH)24(H2O)12](2,7-NDS)4(H2O)18.5 (δ-CrnAl13-n-2) are the first pieces of evidence of mixed Al3+/Cr3+ Keggin-type nanoclusters that prefer substitution at the octahedral sites. The δ-CrnAl13-n-2 structure also exhibits a unique placement of the bound Na+ cation, which may indicate that Cr3+ substitution can alter the surface reactivity of Keggin-type species.

Formation of Nanoscale [Ge4 O16 Al48 (OH)108 (H2 O)24 ]20+ from Condensation of ϵ-GeAl12 8+ Keggin Polycations*.

Keggin-type polyaluminum cations belong to a unique class of compounds with their large positive charge, hydroxo bridges, and divergent isomerization/oligomerization. Previous reports indicated that oligomerization of this species can only occur through one isomer (δ), but herein we report the isolation of largest Keggin-type cluster that occurs through self-condensation of four ϵ-isomers ϵ-GeAl12 8+ to form [Ge4 O16 Al48 (OH)108 (H2 O)24 ]20+ cluster (Ge4 Al48 ). The cluster was crystallized and structurally characterized by single-crystal X-ray diffraction (SCXRD) and the elemental composition was confirmed by ICP-MS and SEM-EDS. Additional dynamic light scattering experiments confirms the presence of the Ge4 Al48 in thermally aged solutions. DFT calculations reveal that a single atom Ge substitution in tetrahedral site of ϵ-isomer is the key for the formation of Ge4 Al48 because it activates deprotonation at key surface sites that control the self-condensation process.

Decreased Vascular Patterning in the Retinas of Astronaut Crew Members as New Measure of Ocular Damage in Spaceflight-Associated Neuro-ocular Syndrome.

Purpose: Ocular structural and functional changes, collectively termed spaceflight-associated neuro-ocular syndrome (SANS), have been described in astronauts undergoing long-duration missions in the microgravity environment of the International Space Station. We tested the hypothesis that retinal vascular remodeling, particularly by smaller vessels, mediates the chronic headward fluid shifts associated with SANS. Methods: As a retrospective study, arterial and venous patterns extracted from 30° infrared Heidelberg Spectralis retinal images of eight crew members acquired before and after six-month missions were analyzed with NASA's recently released VESsel GENeration Analysis (VESGEN) software. Output parameters included the fractal dimension and overall vessel length density that was further classified into large and small vascular branching generations. Vascular results were compared with SANS-associated clinical ocular measures. Results: Significant postflight decreases in Df, Lv, and in smaller but not larger vessels were quantified in 11 of 16 retinas for arteries and veins (P value for Df, Lv, and smaller vessels in all 16 retinas were ≤0.033). The greatest vascular decreases occurred in the only retina displaying clinical evidence of SANS by choroidal folds and optic disc edema. In the remaining 15 retinas, decreases in vascular density from Df and Lv ranged from minimal to high by a custom Subclinical Vascular Pathology Index. Conclusions: Together with VESGEN, the Subclinical Vascular Pathology Index may represent a new, useful SANS biomarker for advancing the understanding of SANS etiology and developing successful countermeasures for long duration space exploration in microgravity, although further research is required to better characterize retinal microvascular adaptations.