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DOE OSTI2025

Cation Effects on CO 2 Delivery to Cu Electrode in Reactive Capture of CO 2

The direct electrochemical conversion of captured CO 2 , known as reactive capture of CO 2 (RCC), remains a formidable challenge in heterogeneous catalysis. Given that amines are one of the most widely used capture agents for CO 2 , it would be desirable to electrochemically reduce the resultant adducts, such as carbamate, directly in RCC. However, current understanding suggests that the primary species undergoing reduction in RCC with amines is the CO 2 dissociated from the sorbent. Herein, we employ ab initio molecular dynamics (AIMD) with DFT to analyze how the nature of alkali metal cations in the electrolyte affects carbamate at the Cu surface, thereby assessing the possibility of promoting RCC by cation effects. The simulations show that the carbamate’s orientation with respect to the electrode is governed by the optimal distance between the carbamate and the cation, specifically how this distance aligns with the cation’s hydration spheres. Moreover, the slow-growth AIMD results indicate that the CO 2 dissociation barrier correlates with the orientation of carbamate at the interface. When the carbamate resides beyond the cation’s first hydration sphere, it adopts a flat orientation with respect to the surface that promotes the release of CO 2 from the capture agent. In contrast, when the carbamate disrupts the first hydration sphere and exhibits a strong cation−π interaction, it adopts an upright orientation that is less conducive to CO 2 release. These findings reveal a nontrivial cation effect in RCC, suggesting that it should be possible to optimize RCC via the choice of the electrolyte.

ab initio molecular dynamics↗

DOE OSTI2026

Development of an Amine Oxide Polyzwitterion Brush Martini Model with Polarizable Water and Ions

Abstract In order to accurately simulate the fouling process of proteins onto polyzwitterion brushes, models that accurately capture the hydration properties and chain conformations of such brushes must first be established. We developed a Martini coarse-grained (CG) model for amine oxide polyzwitterion (PNOMA) brushes, a promising class of antifouling materials, in polarizable water and ions by fitting to all-atom bond and angle distributions, monomer hydration free energy, monomer–monomer distance potential of mean force (PMF), and monomer–salt radial distribution functions (RDFs). Martini 2.2P was selected for compatibility with the established polarizable water and ion models. For comparison with PNOMA, we also constructed models for conventional sulfobetaine (PSBMA) and phosphorylcholine (PMPC) polyzwitterions and the polycation PMETAC using established nonbonded bead types from the literature and refitting bond and angle potentials. We simulated each polymer brush chemistry for varying grafting density and chain length, validating brush height scaling relations against experimental data. The CG models captured the relative hydration strengths among different polyzwitterion chemistries, and brush heights extrapolated to higher molecular weights are in agreement with experimental ellipsometry data. We find that chain swelling of the superhydrophilic PNOMA brushes lies between that of the traditional polyzwitterions PSBMA/PMPC and the polycation PMETAC. For PNOMA brushes in NaCl solution, simulated brush height decreases with salt concentration due to the selectively strong interactions between amine oxide and sodium ions.

Walker, Christopher C. [Oak Ridge National Laborat↗

DOE OSTI2021

Impact of Controlled Storage Conditions on the Hydrolysis and Surface Morphology of Amorphous-UO 3

The hydration and morphological effects of amorphous (A)-UO 3 following storage under varying temperature and relative humidity have been investigated. This study provides valuable insight into U-oxide speciation following aging, the U-oxide quantitative morphological data set, and, overall, the characterization of nuclear material provenance. A-UO 3 was synthesized via the washed uranyl peroxide synthetic route and aged based on a 3-factor circumscribed central composite design of experiment. Target aging times include 2.57, 7.00, 14.0, 21.0, and 25.4 days, temperatures of 5.51, 15.0, 30.0, 45.0, and 54.5 °C, and relative humidities of 14.2, 30.0, 55.0, 80.0, and 95.8% were examined. Following aging, crystallographic changes were quantified via powder X-ray diffraction and an internal standard Rietveld refinement method was used to confirm the hydration of A-UO 3 to crystalline schoepite phases. The particle morphology from scanning electron microscopy images was quantified using both the Morphological Analysis of MAterials software and machine learning. Results from the machine learning were processed via agglomerative hierarchical clustering analysis to distinguish trends in morphological attributes from the aging study. Significantly hydrated samples were found to have a much larger, plate-like morphology in comparison to the unaged controls. Predictive modeling via a response surface methodology determined that while aging time, temperature, and relative humidity all have a quantifiable effect on A-UO 3 crystallographic and morphological changes, relative humidity has the most significant impact.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Structure–Transport Properties Governing the Interplay in Humidity-Dependent Mixed Ionic and Electronic Conduction of Conjugated Polyelectrolytes

Polymeric mixed ionic-electronic conductors (MIECs) are of broad interest in the field of energy storage and conversion, opto-electronics, and bioelectronics. A class of polymeric MIECs are conjugated polyelectrolytes (CPEs), which possess a p-conjugated backbone imparting electronic transport characteristics along with side chains comprised of a pendant ionic group to allow for ionic transport. Here, our study focuses on the humidity-dependent structure-transport properties of poly[3-(potassium-n-alkanoate) thiophene-2,5-diyl] (P3KnT) CPEs with varied side-chain lengths of n = 4, 5, 6, and 7. UV-Vis spectroscopy along with electronic paramagnetic resonance (EPR) spectroscopy reveal the infiltration of water leads to a hydrated, self-doped state that allows for electronic transport. The resulting humidity-dependent ionic conductivity (σ i ) of the thin films shows a monotonic increase with relative humidity (RH) while electronic conductivity (σ e ) follows a nonmonotonic profile. The values of σ e continue to rise with increasing RH reaching a local maximum after which σ e begins to decrease. P3KnTs with higher n values demonstrate greater resiliency to increasing RH before suffering decrease in σ e . This drop in σ e is attributed to two factors. First, disruption of the locally-ordered π-stacked domains observed through in situ humidity-dependent grazing incidence wide angle X-ray scattering (GIWAXS) experiments can account for some of the decrease in σ e . A second and more dominant factor is attributed to the swelling of the amorphous domains where electronic transport pathways connecting ordered domains are impeded. P3K7T is most resilient to swelling (based on ellipsometry and water uptake measurements) where sufficient hydration allows for high σ i (1.0 × 10 -1 S/cm at 95% RH) while not substantially disrupting σ e (1.7 × 10 -2 S/cm at 85% RH and 8.0 × 10 -3 S/cm at 95% RH). Overall, our study highlights the complexity of balancing electronic and ionic transport in hydrated CPEs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

Substrate-Directed Dimensional and Phase Control of Peptide Assemblies on Two-Dimensional van der Waals Materials

Understanding and controlling biomolecular self-assembly on van der Waals (vdW) materials has the potential to advance hybrid bioelectronic devices by enabling precise tuning of the interface and modulation of the resulting electronic properties of the biomolecule-vdW heterostructure. However, how surface properties of vdW materials direct biomolecule assembly remains poorly understood. To fill this knowledge gap, we investigated the assembly of a peptide known to assemble into two-dimensional (2D) crystalline films on MoS 2 on three representative vdW surfaces: WS 2 , MoS 2 , and highly oriented pyrolytic graphite (HOPG). Using in situ atomic force microscopy (AFM), we find that assembly is substrate-dependent, resulting in multilayers on WS 2 , monolayers on MoS 2 , and multiple coexisting phases on HOPG. WS 2 exhibits a higher negative charge, strong long-range electrostatic interactions, and extensive hydration layering that may promote multilayer stacking. In contrast, MoS 2 has stronger short-range interactions with the peptides but much weaker long-range interactions and hydration structure, which may favor monolayer formation. Molecular dynamics simulations predict a corresponding switch from monolayer to multilayer aggregates of the adsorbed monomers, reflected in their relative mobilities. On hydrophobic HOPG, the peptides bind most strongly and remain as monomers with high surface mobility. The peptide dimers comprising the basic unit of the crystals are more compact on HOPG, which has a smaller lattice constant than WS 2 or MoS 2 , suggesting strain contributes to stabilizing multiple phases. Our results provide mechanistic insights into how surface charge and hydration structure, and the lattice structure of the substrates governs peptide assembly on vdW materials, offering a framework to rationally control the 2D peptide-vdW heterostructures.

Molecular dynamics simulations↗

DOE OSTI2020

Identification and Description of a Silicic Volcaniclastic Layer in Gale Crater, Mars, Using Active Neutron Interrogation

The Dynamic Albedo of Neutrons instrument aboard the Mars Science Laboratory rover, Curiosity, has been used to map a stratigraphically-conformable layer of high-SiO 2 material in Gale crater. Previous work has shown this material contains tridymite, a high-temperature/low-pressure felsic mineral, interpreted to have a volcanic source rock. We describe several characteristics including orientation, extent, hydration, and geochemistry, consistent with a volcaniclastic material conformably deposited within a lacustrine mudstone succession. Relationships with widely dispersed alteration features and orbital detections of hydrated SiO 2 suggest that this high-SiO 2 layer extends at least 17 km laterally. Mineralogical abundances previously reported for this high-SiO 2 material indicated that hydrous species were restricted to the amorphous (non-crystalline) fraction, which is dominated by SiO2. The low mean bulk hydration of this high-SiO 2 layer (1.85 ± 0.13 wt.% water-equivalent hydrogen) is consistent with silicic glass in addition to opal-A and opal- CT. Persistent volcanic glass and tridymite in addition to opal in an ancient sedimentary unit indicates that the conversion to more ordered forms of crystalline SiO 2 has not proceeded to completion and that this material has had only limited exposure to water since it originally erupted, despite having been transported in a uviolacustrine system. Our results, including the conformable nature, large areal extent, and presence of vol- canic glass, indicate that this high-SiO 2 material is derived from the product of evolved magma on Mars. This is the rst identi cation of a silicic volcaniclastic layer on another planet, and has important implications for magma evolution mechanisms on single-plate planets.

58 GEOSCIENCES↗

DOE OSTI2021

Enhanced Visibility of Subduction Slabs by the Formation of Dense Hydrous Phase A

Abstract Phase A (Mg 7 Si 2 O 8 (OH) 6 ) is one of the important dense hydrous magnesium silicates in subducting slab, because it forms after the breakdown of antigorite serpentine and could be the dominant hydrous phase in the upper‐mantle deep slab for the water transportation into deep Earth. In this study, the compressional ( P ) and shear ( S ) wave velocities of phase A were measured at simultaneous pressure and temperature conditions up to 11 GPa and 1073 K. Combined with elastic properties of olivine and pyroxenes, we calculate the hydration effect on the velocities of harzburgite lithology in cold subduction zones throughout the depth ranges where phase A is thermodynamically stable. Our calculations suggest that the hydration increases both P ‐ and S ‐wave velocities of harzburgite; at ∼5 wt% hydration, its seismic detectability is enhanced by 1%–1.5% in velocity contrasts relative to its anhydrous counterpart.

Cai, Nao↗

DOE OSTI2024

A role for subducting clays in the water transportation into the Earth’s lower mantle

Subducting sedimentary layer typically contains water and hydrated clay minerals. The stability of clay minerals under such hydrous subduction environment would therefore constraint the lithology and physical properties of the subducting slab interface. Here we show that pyrophyllite (Al 2 Si 4 O 10 (OH) 2 ), one of the representative clay minerals in the alumina-silica-water (Al 2 O 3 -SiO 2 -H 2 O, ASH) system, breakdowns to contain further hydrated minerals, gibbsite (Al(OH) 3 ) and diaspore (AlO(OH)), when subducts along a water-saturated cold subduction geotherm. Such a hydration breakdown occurs at a depth of ~135 km to uptake water by ~1.8 wt%. Subsequently, dehydration breakdown occurs at ~185 km depth to release back the same amount of water, after which the net crystalline water content is preserved down to ~660 km depth, delivering a net amount of ~5.0 wt% H 2 O in a phase assemblage containing δ-AlOOH and phase Egg (AlSiO 3 (OH)). Our results thus demonstrate the importance of subducting clays to account the delivery of ~22% of water down to the lower mantle.

58 GEOSCIENCES↗

DOE OSTI2024

The hierarchical structure of organic mixed ionic–electronic conductors and its evolution in water

Polymeric organic mixed ionic–electronic conductors underpin several technologies in which their electrochemical properties are desirable. These properties, however, depend on the microstructure that develops in their aqueous operational environment. We investigated the structure of a model organic mixed ionic–electronic conductor across multiple length scales using cryogenic four-dimensional scanning transmission electron microscopy in both its dry and hydrated states. Four-dimensional scanning transmission electron microscopy allows us to identify the prevalent defects in the polymer crystalline regions and to analyse the liquid crystalline nature of the polymer. The orientation maps of the dry and hydrated polymers show that swelling-induced disorder is mostly localized in discrete regions, thereby largely preserving the liquid crystalline order. Therefore, the liquid crystalline mesostructure makes electronic transport robust to electrolyte ingress. Furthermore, this study demonstrates that cryogenic four-dimensional scanning transmission electron microscopy provides multiscale structural insights into complex, hierarchical structures such as polymeric organic mixed ionic–electronic conductors, even in their hydrated operating state.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Structure and thermodynamics of water adsorption in NU-1500-Cr

Abstract Metal-organic frameworks (MOFs) are a class of materials with diverse chemical and structural properties, and have been shown to effectively adsorb various types of guest molecules. The mechanism of water adsorption in NU-1500-Cr, a high-performance atmospheric water harvesting MOF, is investigated using a combination of molecular dynamics simulations and infrared spectroscopy. Calculations of thermodynamic and dynamical properties of water as a function of relative humidity allow for following the adsorption process from the initial hydration stage to complete filling of the MOF pores. Initial hydration begins at the water molecules that saturate the open Cr 3+ sites of the framework, which is then followed by the formation of water chains that extend along the channels connecting the hexagonal pores of the framework. Water present in these channels gradually coalesces and fills the hexagonal pores sequentially after the channels are completely hydrated. The development of hydrogen-bond networks inside the MOF pores as a function of relative humidity is characterized at the molecular level using experimental and computational infrared spectroscopy. A detailed analysis of the OH-stretch vibrational band indicates that the low-frequency tail stems from strongly polarized hydrogen-bonded water molecules, suggesting the presence of some structural disorder in the experimental samples. Strategies for designing efficient water harvesting MOFs are also proposed based on the mechanism of water adsorption in NU-1500-Cr.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Interplay of physically different properties leading to challenges in separating lanthanide cations – an ab initio molecular dynamics and experimental study

Lanthanide elements have well-documented similarities in their chemical behavior, which make the valuable trivalent lanthanide cations (Ln 3+ ) particularly difficult to separate from each other in water. Here, we apply ab initio molecular dynamics simulations to compare the free energies (Δ G ads ) associated with the adsorption of lanthanide cations to silica surfaces at a pH condition where SiO – groups are present. The predicted Δ G ads for lutetium (Lu 3+ ) and europium (Eu 3+ ) are similar within statistical uncertainties; this is in qualitative agreement with our batch adsorption measurements on silica. This finding is remarkable because the two cations exhibit hydration free energies (Δ G hyd ) that differ by >2 eV, different hydration numbers, and different hydrolysis behavior far from silica surfaces. We observe that the similarity in Lu 3+ and Eu 3+ Δ G ads is the result of a delicate cancellation between the difference in Eu 3+ and Lu 3+ hydration (Δ G hyd ), and their difference in binding energies to silica. We propose that disrupting this cancellation at the two end points, either for adsorbed or completely desorbed lanthanides ( e.g. , via nanoconfinment or mixed solvents), will lead to effective Ln 3+ separation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Structural water in amorphous carbonate minerals: ab initio molecular dynamics simulations of X-ray pair distribution experiments

Water is known to play a controlling role in directing mineralization pathways and stabilizing metastable amorphous intermediates in hydrous carbonate mineral MCO 3 ·nH 2 O systems, where M 2+ is a divalent metal cation. Despite this recognition, the nature of the controls on crystallization is poorly understood, largely owing to the difficulty in characterizing the dynamically disordered structures of amorphous intermediates at the atomic scale. Here, we present a series of atomistic models, derived from ab initio molecular dynamics simulation, across a range of experimentally relevant cations (M = Ca, Mg, Sr) and hydration levels (0 ≤ n ≤ 2). Theoretical simulations of the dependence of the X-ray pair distribution function on the hydration level n show good agreement with available experimental data and thus provide further evidence for a lack of significant nanoscale structure in amorphous carbonates. Upon dehydration, the metal coordination number does not change significantly, but the relative extent of water dissociation increases, indicating that a thermodynamic driving force exists for water dissociation to accompany dehydration. Mg strongly favors monodentate conformation of carbonate ligands and shows a marked preference to exchange monodentate carbonate O for water O upon hydration, whereas Ca and Sr exchange mono- and bidentate carbonate ligands with comparable frequency. Finally, water forms an extensive hydrogen bond network among both water and carbonate groups that exhibits frequent proton transfers for all three cations considered suggesting that proton mobility is likely predominantly due to water dissociation and proton transfer reactions rather than molecular water diffusion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Facile synthesis and phase stability of Cu-based Na 2 Cu(SO 4 ) 2 · x H 2 O ( x = 0–2) sulfate minerals as conversion type battery electrodes

Mineral exploration forms a key approach for unveiling functional battery electrode materials. The synthetic preparation of naturally found minerals and their derivatives can aid in designing of new electrodes. Herein, saranchinaite Na 2 Cu(SO 4 ) 2 and its hydrated derivative kröhnkite Na 2 Cu(SO 4 ) 2 ·2H 2 O bisulfate minerals have been prepared using a facile spray drying route for the first time. The phase stability relation during the (de)hydration process was examined synergising in situ X-ray diffraction and thermochemical studies. Kröhnkite forms the thermodynamically stable phase as the hydration of saranchinaite to kröhnkite is highly exothermic (-51.51 ± 0.63 kJ mol -1 ). Structurally, kröhnkite offers a facile 2D pathway for Na+ ion migration resulting in 20 times higher total conductivity than saranchinaite at 60 °C. Both compounds exhibited a conversion redox mechanism for Li-ion storage with the first discharge capacity exceeding 650 mA h g -1 (at 2 mA g -1 vs. Li + /Li) upon discharge up to 0.05 V. Post-mortem analysis revealed that the presence of metallic Cu in the discharged state is responsible for high irreversibility during galvanostatic cycling. This study reaffirms the exploration of Cu-based polyanionic sulfates, which while having limited (de)insertion properties, can be harnessed for conversion-based electrode materials for batteries.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Low hydrogen solubility in clay interlayers limits gas loss in hydrogen geological storage

Gas intercalation into clay interlayers may result in hydrogen loss in the geological storage of hydrogen; a phenomenon that has not been fully understood and quantified. Here we use metadynamics molecular simulations to calculate the free energy landscape of H 2 intercalation into montmorillonite interlayers and the H 2 solubility in the confined water; in comparison with results obtained for CO 2 . Furthermore, the results indicate that H 2 intercalation into hydrated interlayers is thermodynamically unfavorable while CO 2 intercalation can be favorable. H 2 solubility in hydrated clay interlayers is in the same order of magnitude as that in bulk water and therefore no over-solubility effect due to nanoconfinement is observed – in striking contrast with CO 2 . These results indicate that H 2 loss and leakage through hydrated interlayers due to intercalation in a subsurface storage system, if any, is limited.

58 GEOSCIENCES↗

DOE OSTI2025

Cation selectivities in zwitterion grafted nanopores: effect of zwitterion architecture

Selective separation of monovalent cations is a critical challenge in applications such as water purification and lithium recovery from salt brines. Cross-linked zwitterionic amphiphilic copolymer (ZAC-X) membranes have gained attention for their exceptional anion permselectivity, attributed to self-assembled zwitterion-lined nanodomains that interact preferentially with anions according to their hydrated radii r hyd . However, these membranes show minimal selectivity among monovalent cations, despite significant differences in their hydration structures, motivating studies on the underlying mechanisms of cation transport and selectivity in this family of materials. In this study, we conducted molecular dynamics simulations of aqueous salt solutions within zwitterion-functionalized nanopores to elucidate the influence of dipole orientation of the zwitterionic (ZI) ligands on cation diffusivities, partitioning, and permeabilities. To this end, we examined two contrasting ZI ligand architectures: Motif A (surface–cation–anion, S–ZI + –ZI − ) and Motif B (surface–anion–cation, S–ZI − –ZI + ). Our results show that in Motif A, the sulfonate groups of the ZI ligands are localized near the pore center radially, leading to strong electrostatic interactions with small bare cations (Mg 2+ and Li + ). This configuration results in high cation partitioning but low cation diffusion, maintaining solution-diffusion tradeoff typical of functionalized membranes. In contrast, Motif B show that sulfonate groups shift radially toward the mid-region of the pore. This shift, especially for small bare cations, introduces steric constraints that weaken their interactions with the sulfonate groups, thereby enhancing hydration and lowering partitioning, while still maintaining their low self-diffusivity. These findings establish zwitterion dipole orientation as a powerful design lever for tuning cation selectivity in membrane systems and offer molecular-level insights for engineering next-generation ion separation materials.

Morishita, Kazuya [Univ. of Texas, Austin, TX (Uni↗

DOE OSTI2026

Stability Constants of Lanthanide-nitrate Complexes in Aqueous Solutions: A Theoretical Study

Calculating stability constants for lanthanide--nitrate complexes in aqueous solution is challenging due to the complex free-energy landscapes of the participating species. In this work, we compare cluster-continuum solvation and condensed-phase approaches using universal machine learning interatomic potentials (MLIPs) for determining the stability constants of lanthanide--nitrate complexes in aqueous solutions. Within the cluster--continuum solvation framework at the B3LYP level of theory, reactions involving lanthanide coordination numbers of both 8 and 9 are found to be relevant. After an empirical linear free-energy correction, the cluster--continuum results fall on the same order-of-magnitude scale as the experimental stability constants. By contrast, MACE-MP0 MLIP underestimates lanthanide hydration numbers and gives PMF-derived stability constants with large deviations from experiment, whereas MACE-MATPES-R2SCAN improves both hydration structure and the stability-constant scale but still does not quantitatively reproduce the detailed lanthanide trend. Across both approaches, nitrate binding is best viewed as a labile coordination motif rather than a fixed mono- or bidentate structure, with hydration-shell structure influencing which configurations are favored. Overall, the cluster--continuum calculations provide a practical semi-quantitative baseline for the experimental stability-constant scale, while the explicit-solvent MLIP benchmarks show clear progress from MACE-MP0 to MACE-MATPES-r2SCAN but also highlight the need for lanthanide-targeted training, fine-tuning, or improved long-range and polarization treatments to obtain predictive thermodynamics for complex aqueous lanthanide chemistry.

Dinpajooh, Mohammadhasan↗

DOE OSTI2021

Understanding supercooling mechanism in sodium sulfate decahydrate phase-change material

Salt hydrate-based phase-change materials are considered promising for future heat storage applications in residential heating/cooling systems. Smooth phase transition from the liquid to solid phase and vice versa is essential for effective heat exchanger; however, supercooling in salt hydrates delays the onset of liquid–solid phase transition. We investigate the molecular level mechanism of supercooling in sodium sulfate decahydrate (SSD). SSD is a complex salt hydrate whose properties are governed by electrostatic forces that include pure Coulombic interactions as well as hydrogen bonds. Experimentally, we examine the importance of a nucleator in reducing supercooling temperatures. We investigated the effect of various mass concentrations of a borax nucleator on a decrease of supercooling temperatures. Molecular dynamics simulation techniques are used to obtain a basic understanding of supercooling in SSD. We observe that by introducing borax as a nucleator, there is a decrease in the supercooling temperature before nucleation. Our molecular dynamics simulations show that long-range electrostatics between sodium and sulfate ion pairs and that with polar water molecules is responsible for delayed nucleation in SSD that results in supercooling, and also, dynamics of charged molecules slows down. The lack of crystallization leads to amorphous structures in supercooled SSD.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Psilocybin: crystal structure solutions enable phase analysis of prior art and recently patented examples

Psilocybin {systematic name: 3-[2-(dimethylamino)ethyl]-1 H -indol-4-yl dihydrogen phosphate} is a zwitterionic tryptamine natural product found in numerous species of fungi known for their psychoactive properties. Following its structural elucidation and chemical synthesis in 1959, purified synthetic psilocybin has been evaluated in clinical trials and has shown promise in the treatment of various mental health disorders. In a recent process-scale crystallization investigation, three crystalline forms of psilocybin were repeatedly observed: Hydrate A, Polymorph A, and Polymorph B. The crystal structure for Hydrate A was solved previously by single-crystal X-ray diffraction. This article presents new crystal structure solutions for the two anhydrates, Polymorphs A and B, based on Rietveld refinement using laboratory and synchrotron X-ray diffraction data, and density functional theory (DFT) calculations. Utilizing the three solved structures, an investigation was conducted via Rietveld method (RM) based quantitative phase analysis (QPA) to estimate the contribution of the three different forms in powder X-ray diffraction (PXRD) patterns provided by different sources of bulk psilocybin produced between 1963 and 2021. Over the last 57 years, each of these samples quantitatively reflect one or more of the hydrate and anhydrate polymorphs. In addition to quantitatively evaluating the composition of each sample, this article evaluates correlations between the crystal forms present, corresponding process methods, sample age, and storage conditions. Furthermore, revision is recommended on characterizations in recently granted patents that include descriptions of crystalline psilocybin inappropriately reported as a single-phase `isostructural variant.' Rietveld refinement demonstrated that the claimed material was composed of approximately 81% Polymorph A and 19% Polymorph B, both of which have been identified in historical samples. In this article, we show conclusively that all published data can be explained in terms of three well-defined forms of psilocybin and that no additional forms are needed to explain the diffraction patterns.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗