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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Effect of Cd on the Nucleation and Transformation of Amorphous Calcium Carbonate
Qualitative measurements observations and field observations measurements indicate mineral coatings are one of the most abundant ways earth materials form, including in sedimentary deposits and certain biominerals. Formation of amorphous carbonates and other metastable intermediates in such these mixed cation systems is poorly understood, however. Using in situ PDF and SAXS, along with ICP-MS and SEM, results from this study 1) determines identify a novel short-range ordered Cd-ACC phase and 2) finds determine amorphous carbonate is stabilized by Cd2+, and 3) support formation of Cd-substituted vaterite, a polymorph of Ca that is not natively formed by Cd CO3. Results are highly dependent on ACC supersaturation, suggesting Cd-induced stability of Cd-ACC are is dependent primarily very sensitive on amorphous phase kinetics rather than thermodynamics to the rate of Cd-ACC nucleation and transformation. Findings provide a quantitative understanding of precursor intermediate phase structure and stability in mixed cation carbonate systems and aggregation that impact and suggest alternate pathways to forming the chemical heterogeneities frequently observed in natural mineral coatings.
Control of Calcium Phosphate Nucleation and Transformation through Interactions of Enamelin and Amelogenin Exhibits the “Goldilocks Effect”
Although amelogenin comprises the vast majority of the matrix that templates calcium phosphate nucleation during enamel formation, other proteins, particularly enamelin, are also known to play an important role in the formation of enamel’s intricate architecture. However, there is little understanding of the interplay between amelogenin and enamelin in controlling processes of mineral nucleation and growth. Here we used an in vitro model to investigate the impact of enamelin co-assembly with amelogenin on calcium phosphate nucleation for a range of enamelin-to-amelogenin ratios. We found that amelogenin alone is a weak promoter of nucleation, but addition of enamelin enhanced nucleation rates in a highly non-linear, non-monotonic manner reaching a sharp maximum at a ratio of 1:50. We provide a phenomenological model to explain this effect that assumes only isolated enamelin proteins can act as sites of enhanced nucleation, while enamelin oligomers cannot. Even when co-assembly is random, the model reproduces the observed behavior, suggesting a simple means to tightly control the timing and extent of nucleation and phase transformation by amelogenin and enamelin.
Novel Strategy To Analyze Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Data of Biomass Pyrolysis Oil for Oligomeric Structure Assignment
Among the most prominent challenges for the analysis of biomass pyrolysis products is the characterization of the abundant oligomer fraction of bio-oil. This fraction is principally made up of pyrolytic lignins and dehydrated, highly modified sugar oligomers, called humins, in liquid phase. An emerging technique for analysis of this oligomer fraction is high-resolution Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS), which allows for accurate determination of C x H y O z formulae for detected oligomers. Additionally, using simple dehydration and fragmentation reaction schemes, similar formulae can be developed from cellulose-, hemicellulose- and lignin-derived oligomers, which are primary depolymerization products. In this paper, FT-ICR MS analysis is coupled with combinatoric dehydration and fragmentation modeling in order to match experimentally detected bio-oil oligomers with hypothetical pathways for their formation during pyrolysis. In this way, we present a novel strategy by which oligomeric structures can be proposed for bio-oils. Using this approach, it becomes possible to advance the understanding of both the molecular structures comprising the bio-oil oligomer fraction and the pathways by which these structures form during biomass pyrolysis reactions.
Vacuum Pyrolysis of Hybrid Poplar Milled Wood Lignin with Fourier Transform-Ion Cyclotron Resonance Mass Spectrometry Analysis of Feedstock and Products for the Elucidation of Reaction Mechanisms
The pyrolysis of lignocellulosic materials is a promising technique to produce fuels and chemicals. It is well known that the most abundant products of lignin pyrolysis are oligomeric molecules, known as pyrolytic lignin (PL). The chemical composition of PL has been extensively studied; however, there is still an important debate whether these oligomers are produced directly from the lignin or from the recombination of monomeric pyrolytic products. Existing theories are unable to describe the effect of vacuum on the distribution of pyrolysis products. Hybrid poplar milled wood lignin (MWL) was initially isolated and thoroughly characterized by Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). Chemical formulas were assigned to each oligomeric compound detected. The MWL was also subjected to vacuum pyrolysis in a modified pyroprobe at 250, 750, and 1000 mbar (absolute pressure), and the resulting liquid products were analyzed by FT-ICR MS. A new strategy to assign structural representations to the oligomeric PL products is proposed, based on the plausible pyrolysis reaction mechanisms of depolymerization/fragmentation applied to original MWL oligomer formulas. Our results support the hypothesis that PL is formed from the removal of moieties from primary lignin pyrolysis products with between three and five aromatic rings. This depolymerization/fragmentation allows the oligomers to reduce their molecular weights to the point where they can be removed from the reaction zone by direct vaporization. Furthermore, this phenomenon highlights the importance of pressure on removal mechanisms and their impact on the molecular weight of the resulting products from lignin pyrolysis.
Insight into the Phase Transformation Pathways of Copper Oxidation: from Oxygen Chemisorption on the Clean Surface to Multi-Layer Bulk Oxide Growth
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Supramolecular Motion Enables Chondrogenic Bioactivity of a Cyclic Peptide Mimetic of Transforming Growth Factor-β1
Transforming growth factor (TGF)-β1 is a multifunctional protein that is essential in many cellular processes that include fibrosis, inflammation, chondrogenesis, and cartilage repair. In particular, cartilage repair is important to avoid physical disability since this tissue does not have the inherent capacity to regenerate beyond full development. We report here on supramolecular coassemblies of two peptide amphiphile molecules, one containing a TGF-β1 mimetic peptide, and another which is one of two constitutional isomers lacking bioactivity. Using human articular chondrocytes, we investigated the bioactivity of the supramolecular copolymers of each isomer displaying either the previously reported linear form of the mimetic peptide or a novel cyclic analogue. Based on fluorescence depolarization and 1 H NMR spin–lattice relaxation times, we found that coassemblies containing the cyclic compound and the most dynamic isomer exhibited the highest intracellular TGF-β1 signaling and gene expression of cartilage extracellular matrix components. Here, we conclude that control of supramolecular motion is emerging as an important factor in the binding of synthetic molecules to receptors that can be tuned through chemical structure.
Pressure-Induced Phase Transformation, Reversible Amorphization, and Anomalous Visible Light Response in Organolead Bromide Perovskite
Abstract not provided
Morphological Transformations in the Magnetite Biomineralizing Protein Mms6 in Iron Solutions: A Small-Angle X-ray Scattering Study
Abstract not provided
Shock-transformation of whitlockite to merrillite and the implications for meteoritic phosphate
Meteorites represent the only samples available for study on Earth of a number of planetary bodies. The minerals within meteorites therefore hold the key to addressing numerous questions about our solar system. Of particular interest is the Ca-phosphate mineral merrillite, the anhydrous end-member of the merrillite-whitlockite solid solution series. For example, the anhydrous nature of merrillite in Martian meteorites has been interpreted as evidence of water-limited late-stage Martian melts. However, recent research on apatite in the same meteorites suggests higher water content in melts. One complication of using meteorites rather than direct samples is the shock compression all meteorites have experienced, which can alter meteorite mineralogy. Here we show whitlockite transformation into merrillite by shock-compression levels relevant to meteorites, including Martian meteorites. The results open the possibility that at least part of meteoritic merrillite may have originally been H + -bearing whitlockite with implications for interpreting meteorites and the need for future sample return.
Sculpting carbon bonds for allotropic transformation through solid-state re-engineering of –sp2 carbon
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High Pressure Phase-Transformation Induced Texture Evolution and Strengthening in Zirconium Metal: Experiment and Modeling
Abstract not provided
Photocatalytic metal–organic frameworks for organic transformations
Metal–organic frameworks (MOFs) have attracted increasing attention for applications in heterogeneous photocatalysis. Here, modifications of metal nodes and organic linkers, as well as encapsulation of active species in the pores of MOFs enable the generation of photoactive materials for catalyzing organic transformations. MOF composites integrating noble metal nanoparticles or traditional photoactive semiconductors can combine the advantages of both materials, and also improve the photocatalytic performance via synergistic effects. In this Highlight, we discuss recent examples of photoactive MOFs and their use as photocatalysts for organic reactions.
Induction time of a polymorphic transformation
When a solution is supersaturated with respect to multiple polymorphs, the polymorph with the lowest nucleation barrier will form first. If this is a metastable polymorph, it will persist until the induction of nuclei of a lower free-energy phase, marking the onset of a polymorphic transformation. Induction of a more stable polymorph can occur under two conditions: a.) during steady-state nucleation, or b.) after complete crystal growth of the metastable phase. Using the theory of competing stochastic processes, we derive the rare probability of forming a higher-barrier, more-stable polymorph during steady-state nucleation, and use this to explain variations in crystallization products between repeat experiments, which may underlie the phenomenon of "Disappearing Polymorphs". We also derive the induction time of a stable phase from a solution equilibrated with a metastable phase, and show that once the stable phase nucleates, bulk metastable crystals will spontaneously ripen onto nanoscale nuclei or seeds of a more stable phase, thermodynamically driving dissolution-reprecipitation processes. Existing strategies to prolong or shorten the lifetimes of transient metastable phases are reviewed and interpreted within the context of polymorphic induction. Finally, the analyses in this work are conducted from classical nucleation and crystal growth theories, suggesting that paradigms shifts to 'non-classical' nucleation theories may not be necessary to rationalize multistage crystallization.
Pressure-induced structural transformations and new polymorphs in BiVO[subscript 4]
Abstract not provided
Phase transformations and indications for acoustic mode softening in Tb-Gd orthophosphate
Abstract not provided
Pressure induced transformation and subsequent amorphization of monoclinic Nb2O5 and its effect on optical properties
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