Amorphous Precursor Phase Research Articles

ACP-Mediated Phase Transformation for Collagen Mineralization: A New Understanding of the Mechanism.

Despite significant efforts utilizing advanced technologies, the contentious debate surrounding the intricate mechanism underlying collagen fibril mineralization, particularly with regard to amorphous precursor infiltration and phase transformation, persists. This work proposes an amorphous calcium phosphate (ACP)-mediated pathway for collagen fibril mineralization and utilizing stochastic optical reconstruction microscopy technology, and has experimentally confirmed for the first time that the ACP nanoparticles can infiltrate inside collagen fibrils. Subsequently, the ACP-mediated phase transformation occurs within collagen fibrils to form HAP crystallites, and significantly enhances the mechanical properties of the mineralized collagen fibrils compared to those achieved by the calcium phosphate ion (CPI)-mediated mineralization and resembles the natural counterpart. Furthermore, demineralized dentin can be effectively remineralized through ACP-mediated mineralization, leading to complete restoration of its mechanical properties. This work provides a new paradigm of collagen mineralization via particle-mediated phase transformation, deepens the understanding of the mechanism behind the mineralization of collagen fibrils, and offers a new strategy for hard tissue repair.

Evidence for liquid-liquid phase separation during the early stages of Mg-struvite formation.

The precipitation of struvite, a magnesium ammonium phosphate hexahydrate (MgNH4PO4 · 6H2O) mineral, from wastewater is a promising method for recovering phosphorous. While this process is commonly used in engineered environments, our understanding of the underlying mechanisms responsible for the formation of struvite crystals remains limited. Specifically, indirect evidence suggests the involvement of an amorphous precursor and the occurrence of multi-step processes in struvite formation, which would indicate non-classical paths of nucleation and crystallization. In this study, we use synchrotron-based in situ x-ray scattering complemented by cryogenic transmission electron microscopy to obtain new insights from the earliest stages of struvite formation. The holistic scattering data captured the structure of an entire assembly in a time-resolved manner. The structural features comprise the aqueous medium, the growing struvite crystals, and any potential heterogeneities or complex entities. By analysing the scattering data, we found that the onset of crystallization causes a perturbation in the structure of the surrounding aqueous medium. This perturbation is characterized by the occurrence and evolution of Ornstein-Zernike fluctuations on a scale of about 1nm, suggesting a non-classical nature of the system. We interpret this phenomenon as a liquid-liquid phase separation, which gives rise to the formation of the amorphous precursor phase preceding actual crystal growth of struvite. Our microscopy results confirm that the formation of Mg-struvite includes a short-lived amorphous phase, lasting >10s.

Room temperature magnetron sputtering and laser annealing of ultrathin amorphous sulfur-rich MoSx films

Room temperature magnetron sputtering of an ultra-thin transition-metal dichalcogenide amorphous precursor and subsequent laser annealing-induced phase transformations were investigated for the synthesis of polycrystalline 2H-MoS2 semiconducting thin films. Radio frequency magnetron sputtering of a MoS3.6 target was used to produce amorphous precursors with S to Mo ratios greater than 2:1 on thermally annealed SiO2 substrates, glass, indium tin oxide coated glass, and amorphous boron-oxy-nitride. The influence of working pressure on the MoS2 and MoS3 interatomic bonding arrangements in amorphous MoSx films was explored with x-ray photoelectron spectroscopy. A 248 nm pulsed laser was used for annealing 1 cm2 sized areas of the amorphous precursor in an ambient atmosphere at fluences of 100–450 mJ for 1, 5, and 10 pulses to form a crystalline 2H-MoS2 phase. The role of laser fluence and substrate choice on phase transformation from the amorphous precursor to the 2H phase, as well as the competition between oxidation, elemental sulfur segregation, and ablation is discussed. Hall effect measurements confirmed p-type behavior of the produced semiconducting films and established mobility and charge carrier density characteristics of the laser-annealed films. The feasibility of scalable processing by combining sputtering from sulfur-rich targets and laser annealing for production of p-type 2H-MoS2 ultrathin films on various substrates is presented.

Nucleation and Crystallization of Ferrous Phosphate Hydrate via an Amorphous Intermediate.

The fundamental processes of nucleation and crystallization are widely observed in systems relevant to material synthesis and biomineralization; yet most often, their mechanism remains unclear. In this study, we unravel the discrete stages of nucleation and crystallization of Fe3(PO4)2·8H2O (vivianite). We experimentally monitored the formation and transformation from ions to solid products by employing correlated, time-resolved in situ and ex situ approaches. We show that vivianite crystallization occurs in distinct stages via a transient amorphous precursor phase. The metastable amorphous ferrous phosphate (AFEP) intermediate could be isolated and stabilized. We resolved the differences in bonding environments, structure, and symmetric changes of the Fe site during the transformation of AFEP to crystalline vivianite through synchrotron X-ray absorption spectroscopy at the Fe K-edge. This intermediate AFEP phase has a lower water content and less distorted local symmetry, compared to the crystalline end product vivianite. Our combined results indicate that a nonclassical, hydration-induced nucleation and transformation driven by the incorporation and rearrangement of water molecules and ions (Fe2+ and PO43-) within the AFEP is the dominating mechanism of vivianite formation at moderately high to low vivianite supersaturations (saturation index ≤ 10.19). We offer fundamental insights into the aqueous, amorphous-to-crystalline transformations in the Fe2+-PO4 system and highlight the different attributes of the AFEP, compared to its crystalline counterpart.

The Use of Microfluidic Platforms with Raman Spectroscopy for Investigating the Co-Precipitation of Metals and Radionuclides in Carbonates

In the context of long-term safety assessments of deep geological repositories for radio-active wastes, a rigorous understanding of the retention of radionuclides such as 226Ra due to co-precipitation with carbonate and sulphate minerals is important for a realistic prediction of radionuclide migration behaviour in the repository near and far field. The co-precipitation of 226Ra in sulphate minerals, in particular barite, has been studied experimentally and numerically in detail throughout the last decade to establish the thermodynamic properties and mixing behaviour of its solid solutions over a wide range of temperatures. However, so far, few studies have been dedicated to the incorporation of 226Ra into carbonates, and little is known about the mixing behaviour of 226Ra and calcium carbonate phases such as calcite, aragonite, or vaterite. The aim of the work presented here was to develop and explore innovative microfluidic experiments in combination with in situ Raman spectroscopy that can be used to investigate co-precipitation processes of radionuclides in carbonate minerals, using stable Ba as a chemical analogue for 226Ra in the first step, due to their similar ionic radii. Different microfluidic set-ups were developed to address co-precipitation in bulk solution as well as in confinement or under diffusive flow regimes. It could be shown by XRD and SEM-EDX analyses that high amounts of Ba can be incorporated into the lattice of calcite when formed via an amorphous precursor phase, suggesting that the formation of calcium carbonates can contribute to the retention of 226Ra in the repository environment, which will be verified in future studies using the presented microfluidic platforms.

Size Control of Iron Oxide Nanoparticles Synthesized by Thermal Decomposition Methods

The controlled synthesis of superparamagnetic iron oxide nanoparticles is crucial for a variety of biomedical applications. Among different synthesis routes, thermal precursor decomposition methods are the most versatile, yielding monodisperse nanoparticles on the multigram scale. Recent in situ kinetic studies of the nucleation and growth processes during thermal decomposition routes revealed nonclassical nucleation and growth paths involving amorphous precursor phases and aggregative growth steps. With the knowledge of this kinetic mechanism, we systematically examined a range of different iron oxide heat-up synthesis routes to understand and conclude which methods allow good and reproducible size control over a range of relevant nanoparticle diameters. Using transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) for the characterization of the nanoparticle size distribution, we find that a set of solvents (1-octadecene, trioctylamine, docosane) provides access to a temperature range between 300 and 370 °C, allowing us to synthesize monodisperse nanoparticles in a size range of 6–24 nm on a large scale. We confirm that a thermal pretreatment of the iron oxide precursor is essential to achieve reproducible size control. We find that each solvent provides access to a certain temperature range, within which the variation of temperature, heating rate, or precursor concentration allows us to reproducibly control the nanoparticle size.

The role of amorphous ZIF in ZIF-8 crystallization kinetics and morphology

Understanding the composition and structure of amorphous precursor phases is fundamental for elucidating two-step crystallization mechanisms and designing shape- and size-controlled nanomaterials. However, that understanding is largely lacking for metal–organic framework compounds despite their growing significance as functional materials. Here, we report the crystallization of zeolite imidazolate frameworks-8 (ZIF-8, Zn(C4H5N2)2) via an amorphous ZIF (am-ZIF) solid precursor phase with a rough stoichiometric composition of Zn(C4H5N2)1.78(C4H6N2)0.17(CH3COO)0.22. The formation of am-ZIF is attributed to the incomplete deprotonation of 2-Methylimidazole (HmIm) and the involvement of the hydrogen bond between CH3COO– and –HN, which can further transform into the dense Dia(Zn) structure with a diamondoid crystal topology in pure water. Taking am-ZIF as a precursor, the tunable dissolution and recrystallization kinetics of am-ZIF into ZIF-8, due to the addition of EtOH and CTAB, allows the selective fabrication of dodecahedral, cubic, and hollow ZIF-8. Overall, an in-depth understanding of the differences in composition and structure of am-ZIF from ZIF-8 and the resulting crystallization kinetics suggests a novel approach to designing metal–organic frameworks with controlled crystal morphology.

Sub-micrometric spatial distribution of amorphous and crystalline carbonates in biogenic crystals using coherent Raman microscopy

In living organisms, calcium carbonate biomineralization combines complex bio-controlled physical and chemical processes to produce crystalline hierarchical hard tissues (usually calcite or aragonite) typically from an amorphous precursor phase. Understanding the nature of the successive transient amorphous phases potentially involved in the amorphous-to-crystalline transition requires characterization tools, which are able to provide a spatial and spectroscopic analysis of the biomineral structure. In this work, we present a highly sensitive coherent Raman microscopy approach, which allows one to image molecular bond concentrations in post mortem shells and living animals, by exploiting the vibrational signature of the different carbonates compounds. To this end, we target the ν1 calcium carbonate vibration mode and produce spatially and spectroscopically resolved images of the shell border of a mollusk shell, the Pinctada margaritifera pearl oyster. A novel approach is further presented to efficiently compare the amount of amorphous carbonate with respect to its crystalline counterpart. Finally, the whole microscopy method is used to image in vivo the shell border and demonstrate the feasibility and the reproducibility of the technique. These findings open chemical imaging perspectives for the study of biogenic and bio-inspired crystals.

Local Heating Transforms Amorphous Calcium Carbonate to Single Crystals with Defined Morphologies

AbstractThe use of amorphous calcium carbonate (ACC) as a precursor phase affords organisms with outstanding control over the formation of calcite and aragonite biominerals. Essential to this strategy is that the ACC is maintained within confined volumes in the absence of bulk water. This ensures that the ACC undergoes a pseudomorphic transformation and that the organism can independently control nucleation and growth. However, comparable control has proven hard to achieve in synthetic systems. Here, a straightforward method is demonstrated for controlling the crystallization of ACC thin films in which nucleation is first triggered using a heated probe, and then growth is sustained by incubating the film at a lower temperature. By independently controlling nucleation and growth, sub‐millimeter calcite single crystals can be generated when and where it is desired, morphologies ranging from discs to squares to serpentine strips can be created, and arrays of crystals formed. The mechanism and energetics of crystallization of the ACC are studied using in situ transmission electron microscopy and continuity between the ACC and calcite at the growth front is demonstrated. It is envisaged that this method can be applied to the formation of large single crystals of alternative functional materials that form via amorphous precursor phases.

Faster Crystallization during Coral Skeleton Formation Correlates with Resilience to Ocean Acidification.

The mature skeletons of hard corals, termed stony or scleractinian corals, are made of aragonite (CaCO3). During their formation, particles attaching to the skeleton’s growing surface are calcium carbonate, transiently amorphous. Here we show that amorphous particles are observed frequently and reproducibly just outside the skeleton, where a calicoblastic cell layer envelops and deposits the forming skeleton. The observation of particles in these locations, therefore, is consistent with nucleation and growth of particles in intracellular vesicles. The observed extraskeletal particles range in size between 0.2 and 1.0 μm and contain more of the amorphous precursor phases than the skeleton surface or bulk, where they gradually crystallize to aragonite. This observation was repeated in three diverse genera of corals, Acropora sp., Stylophora pistillata—differently sensitive to ocean acidification (OA)—and Turbinaria peltata, demonstrating that intracellular particles are a major source of material during the additive manufacturing of coral skeletons. Thus, particles are formed away from seawater, in a presumed intracellular calcifying fluid (ICF) in closed vesicles and not, as previously assumed, in the extracellular calcifying fluid (ECF), which, unlike ICF, is partly open to seawater. After particle attachment, the growing skeleton surface remains exposed to ECF, and, remarkably, its crystallization rate varies significantly across genera. The skeleton surface layers containing amorphous pixels vary in thickness across genera: ∼2.1 μm in Acropora, 1.1 μm in Stylophora, and 0.9 μm in Turbinaria. Thus, the slow-crystallizing Acropora skeleton surface remains amorphous and soluble longer, including overnight, when the pH in the ECF drops. Increased skeleton surface solubility is consistent with Acropora’s vulnerability to OA, whereas the Stylophora skeleton surface layer crystallizes faster, consistent with Stylophora’s resilience to OA. Turbinaria, whose response to OA has not yet been tested, is expected to be even more resilient than Stylophora, based on the present data.

Coarse-Grained Model for the Hydrothermal Synthesis of Zeolites

Zeolites are the most used solid catalysts in the chemical industry. The hydrothermal synthesis of these porous aluminosilicate crystals is a multistep process that involves the polymerization of silica from solution to form amorphous aggregates, their crystallization, growth by oriented attachment, and eventually dehydration by heating. The molecular pathways by which zeolites are formed from the precursor solution are not yet fully understood. Molecular simulations can play an important role in elucidating these microscopic processes but are limited by the lack of models able to represent both the polymerization of silica and its crystallization with feasible computational costs. Here, we present a simple, computationally efficient coarse-grained model for the hydrothermal synthesis of zeolites from aqueous solutions. Our TS + W model has three components: silica, a structure-directing agent, and water, each represented by a single particle with short-range interactions. The model quantitatively reproduces the experimental evolution of silica species during the polymerization from solution, yielding amorphous nanoparticles with shape, composition, and silica speciation in agreement with the amorphous precursors of zeolites in experiments. Importantly, the TS + W model spontaneously nucleates and grows zeolites from the amorphous precursor phase and reproduces the temperature required for their dehydration. Our simulations indicate that the preferential formation of zeolites at the amorphous–water interface does not arise from an ability of that surface to heterogeneously nucleate the zeolite. The simplicity and computational efficiency of the TS + W model make it ideal to investigate the interplay between polymerization and crystallization in zeolite synthesis.

New insights in the mechanisms of the reaction 3.65 Å phase = clinoenstatite + water down to nanoscales

Abstract. The reaction of 3.65 Å phase <=> clinoenstatite + water was investigated in five experiments at 10 GPa, 470–600 ∘C, using a rotating multi-anvil press. Under these P/T conditions, clinoenstatite exists in its high-pressure modification, which, however, is not quenchable to ambient conditions but transforms back to low-pressure clinoenstatite. The quenched run products were characterized by electron microprobe analyses (EMPA), powder X-ray diffraction (XRD), Raman spectroscopy and by high-resolution transmission electron microscopy (HRTEM) on focused ion beam (FIB)-cut foils. We bracketed the reaction in the T range 470 to 510 ∘C (at 10 GPa). The hydration of clinoenstatite to the 3.65 Å phase at 470 ∘C was very sluggish and incomplete even after 96 h. Clinoenstatites range in size from less than 1 to up to 50 µm. Usually clinoenstatite has a very small grain size and shows many cracks. In sub-micron-sized broken clinoenstatite, an amorphous phase (0.91Mg:1.04Si, with about 20 wt % H2O) was observed, which further transformed with increasing reaction time into the 3.65 Å phase (1Mg:1Si, with 34 wt % H2O). Thus, the sub-micron-sized fractured clinoenstatite transformed via an amorphous water-bearing precursor phase to the 3.65 Å phase. The dehydration to clinoenstatite was faster but still incomplete after 72 h at 600 ∘C. From the backscattered electron images of the recovered sample of the dehydration experiment, it is obvious that there is a high porosity due to dehydration of the 3.65 Å phase. Again, the grain size of clinoenstatite ranges from less than 1 up to 50 µm. There are still some clinoenstatite crystals from the starting material present, which can clearly be distinguished from newly formed sub-micron-sized clinoenstatite. Additionally, we observe a water-rich crystalline phase, which does not represent the 3.65 Å phase. Its Raman spectra show the double peaks around 700 and 1000 cm−1 characteristic for enstatite and strong water bands at 3700 and 3680 cm−1. The Mg:Si ratio of 0.90:1.04 was determined by EMPA, totalling to 81 wt %, in accordance with its high water content. Diffraction patterns from high-resolution images (fast Fourier transform – FFT) are in agreement with an orthoenstatite crystal structure (Pbca). The surprising observation of this study is that, in both directions of the investigated simple reaction, additional metastable phases occur which are amorphous in the hydration and crystalline in the dehydration reaction. Both additional phases are water rich and slightly deviate in composition from the stable products 3.65 Å phase and clinoenstatite, respectively. Thus, as a general remark, conventional investigations on reaction progress should be complemented by nanoscale investigations of the experimental products because these might reveal unpredicted findings relevant for the understanding of mantle processes. The extreme reduction in grain size observed in the dehydration experiments due to the formation of nanocrystalline clinoenstatite rather than the slowly released fluids might cause mechanical instabilities in the Earth's mantle and, finally, induce earthquakes.

Exploiting Confinement to Study the Crystallization Pathway of Calcium Sulfate

AbstractCharacterizing the pathways by which crystals form remains a significant challenge, particularly when multiple pathways operate simultaneously. Here, an imaging‐based strategy is introduced that exploits confinement effects to track the evolution of a population of crystals in 3D and to characterize crystallization pathways. Focusing on calcium sulfate formation in aqueous solution at room temperature, precipitation is carried out within nanoporous media, which ensures that the crystals are fixed in position and develop slowly. The evolution of their size, shape, and polymorph can then be tracked in situ using synchrotron X‐ray computed tomography and diffraction computed tomography without isolating and potentially altering the crystals. The study shows that bassanite (CaSO4 0.5H2O) forms via an amorphous precursor phase and that it exhibits long‐term stability in these nanoscale pores. Further, the thermodynamically stable phase gypsum (CaSO4 2H2O) can precipitate by different pathways according to the local physical environment. Insight into crystallization in nanoconfinement is also gained, and the crystals are seen to grow throughout the nanoporous network without causing structural damage. This work therefore offers a novel strategy for studying crystallization pathways and demonstrates the significant impact of confinement on calcium sulfate precipitation, which is relevant to its formation in many real‐world environments.

Boron isotope fractionation during the formation of amorphous calcium carbonates and their transformation to Mg-calcite and aragonite

The non-classical crystallization pathway of carbonate minerals proceeds through the initial formation of an amorphous precursor phase and commonly takes place during biomineralization. Although the isotopic composition of marine calcifiers is often used to reconstruct paleo-environmental conditions, the impact of the crystallization pathway followed by these organisms on the isotope composition of their skeletons has rarely been quantified. This study presents the first examination of B partitioning and isotope fractionation during CaCO3 formation via an amorphous calcium carbonate phase, which provides new insights into the incorporation of B into marine calcite and aragonite that form via this route. Boron concentrations and isotope compositions of the fluids and the formed solids were characterized during the course of experiments that lasted two years and were performed at 25 °C under controlled pH conditions. The results suggest that during Mg-ACC formation, B distribution coefficients are 1.5–4 orders of magnitude higher than those reported earlier in the literature for calcite and aragonite. Additionally, B isotope fractionation during Mg-ACC formation is strongly affected by the continuous exchange of solutes between the nanoporous solid phase and the bulk fluid. The isotope composition of the transient amorphous phase is not inherited in the crystalline carbonate mineral phase that ultimately forms, because crystallization proceeds via a continuous dissolution/re-precipitation process and/or chemical/isotope exchange between the solid surface and the fluid. Interestingly, the isotope fractionation between the fluid and the final crystalline products is different from those achieved in earlier studies where mineral growth proceeded via the standard mechanism of ion-by-ion addition of solutes to advancing steps. The B isotope fractionations measured in this study are in good agreement with results of equilibrium first principle calculations for calcite and aragonite (Balan et al., 2018) except in the case of calcite formed at pH = 8.9, suggesting that changes in aqueous speciation (i.e. increase of NaB(OH)4° and CO32− concentrations) may be responsible for slight changes of the calcite BO4 environment and isotope composition. It is expected that this study will help to better decipher the mechanisms controlling B isotope fractionation during the non-classical growth of calcium carbonates involving the formation of transient amorphous precursors.

Recombinant major ampullate spidroin-particles as biotemplates for manganese carbonate mineralization

Mineral deposition in biological systems is often templated by organic matrices including proteins directing the nucleation and growth of bioceramics by interacting with early stage species of the mineralization process or coordinating specific facets of the forming crystal. Structurally, charged surface patches are a characteristic motif of biomineralization-associated proteins, which are able to accumulate and bind ions from the surrounding media and, therefore, initiate, promote or inhibit mineralization. Controlled protein engineering enables the manipulation and control of bioinspired in vitro precipitation systems, and thus not only opens prospects for the design of environmentally benign synthetic strategies towards hierarchically structured functional materials, but also enhances the understanding of fundamental interaction mechanisms in biomineralization processes. Here, two recombinant variants of the spider silk protein ADF4 were engineered with oppositely charged peptide tags. Both were processed into micrometer-sized particles and investigated for their influence on manganese carbonate mineralization. Micro- and nano-structured manganese carbonate represents an attractive material for diverse applications including catalysis and wastewater treatment. While both types of spider silk particles were incorporated into the mineral structure, the positively tagged proteins appeared to interact more strongly with the formed manganese carbonate crystals than their negatively charged counterparts. Combination of the spider silk particles and poly(acrylic acid) (PAA), a water-soluble structure-directing agent associated with the stabilization of amorphous precursor phases in carbonates, resulted in the formation of film-like non-equilibrium structures of MnCO3 entrapping the spider silk particles. With the aim to gain mechanistic insights and to elucidate the interaction between the different components involved in the mineralization process, we studied the interplay between PAA, positively or negatively tagged spider silk particles, and Mn(II) ions by time-resolved dynamic light scattering. The here used set-up affords the possibility to identify control strategies for the template-mediated mineralization of manganese carbonate.

Structure of the amorphous titania precursor phase of N-doped photocatalysts.

Amorphous titania samples prepared by ammonia solution neutralization of titanyl sulphate have been characterized by chemical and thermal analyses, and with reciprocal-space and real-space fitting of wide-angle synchrotron X-ray scattering data. A model that fits both the chemical and structural data comprises small segments of lepidocrocite-type layer that are offset by corner-sharing as in the monoclinic titanic acids H2TinO2n+1·mH2O. The amorphous phase composition that best fits the combined chemical and scattering data is [(NH4)3H21Ti20O52]·14H2O, where the formula within the brackets is the cluster composition and the H2O outside the brackets is physically adsorbed. The NH4+ cations are an integral part of the clusters and are bonded to layer anions at the corners of the offset layers, as occurs in the alkali metal stepped-layer titanates. The stepped-layer model is shown to give a consistent mechanism for the reaction of aqueous ammonia with solid hydrated titanyl sulphate, in which the amorphous product retains the exact size and shape of the reacting titanyl sulphate crystals.

Cemp1-p3 Peptide Promotes the Transformation of Octacalcium Phosphate into Hydroxyapatite Crystals

Dental cementum contains unique molecules that regulate the mineralization process in vitro and in vivo, such as cementum protein 1 (CEMP1). This protein possesses amino acid sequence motifs like the human recombinant CEMP1 with biological activity. This novel cementum protein 1-derived peptide (CEMP1-p3, from the CEMP1’s N-terminal domain: (QPLPKGCAAVKAEVGIPAPH), consists of 20 amino acids. Hydroxyapatite (HA) crystals could be obtained through the combination of the amorphous precursor phase and macromolecules such as proteins and peptides. We used a simple method to synthesize peptide/hydroxyapatite nanocomposites using OCP and CEMP1-p3. The characterization of the crystals through scanning electron microscopy (SEM), powder X-ray diffraction (XRD), high--resolution transmission electron microscopy (HRTEM), and Raman spectroscopy revealed that CEMP1-p3 transformed OCP into hydroxyapatite (HA) under constant ionic strength and in a buffered solution. CEMP1-p3 binds and highly adsorbs to OCP and is a potent growth stimulator of OCP crystals. CEMP1-p3 fosters the transformation of OCP into HA crystals with crystalline planes (300) and (004) that correspond to the cell of hexagonal HA. Octacalcium phosphate crystals treated with CEMP1-p3 grown in simulated physiological buffer acquired hexagonal arrangement corresponding to HA. These findings provide new insights into the potential application of CEMP1-p3 on possible biomimetic approaches to generate materials for the repair and regeneration of mineralized tissues, or restorative materials in the orthopedic field.

Oligo(l-glutamic acids) in Calcium Phosphate Precipitation: Chain Length Effect.

The understanding of calcium phosphate precipitation is of major interest in different fields of science, including medicine, biomaterials, and physical chemistry. The presence of additive biomacromolecules has been known to influence various stages of the precipitation process from nucleation to crystal growth. In the current work, well-defined sequences of short, negatively charged peptides, oligo(l-glutamic acids), were utilized as a model, inspired by contiguous sequences of acidic amino acids in natural biomineralization proteins. The precipitate morphology and phases, the element time profile in solution and in the precipitates, as well as the kinetics during the precipitation process were analyzed to explain the effect of these short peptides on calcium phosphate precipitation. The results show that peptides can delay the phase transformation of an amorphous precursor phase to hydroxyapatite and that there is an optimal chain length for this effect at a given concentration of peptide. This study is the first part of a two-part series and is followed by a subsequent work to reveal the mechanism by which these short peptides influence the calcium phosphate precipitation.

Direct Observation of Amorphous Precursor Phases in the Nucleation of Protein-Metal-Organic Frameworks.

Protein-metal-organic frameworks (p-MOFs) are a prototypical example of how synthetic biological hybrid systems can be used to develop next-generation materials. Controlling p-MOF formation enables the design of hybrid materials with enhanced biological activity and high stability. However, such control is yet to be fully realized due to an insufficient understanding of the governing nucleation and growth mechanisms in p-MOF systems. The structural evolution of p-MOFs was probed by cryo-transmission electron microscopy, revealing nonclassical pathways via dissolution-recrystallization of highly hydrated amorphous particles and solid-state transformation of a protein-rich amorphous phase. On the basis of these data, we propose a general description of p-MOF crystallization which is best characterized by particle aggregation and colloidal theory for future synthetic strategies.

Growth Kinetics of Cobalt Carbonate Nanoparticles Revealed by Liquid-Phase Scanning Transmission Electron Microscopy

Amorphous precursor phases have been observed in many crystallization processes in aqueous solution, yet their growth kinetics are not fully understood because of their often transient and unstable nature. In this work, we try to close this knowledge gap by employing liquid-phase scanning transmission electron microscopy (LPSTEM) to study the growth kinetics using amorphous cobalt carbonate (CoCO3) as a model system. Using simultaneous acquisition of bright-field and annular dark-field LPSTEM images, we observe that the volume of the amorphous CoCO3 nanoparticles grows linearly with time. By quantifying and extrapolating electron beam effects to zero dose, the growth rate at native solution conditions is obtained. From the observed linear volume growth and the observation of 10 nm-sized nanoparticles by cryotransmission electron microscopy (cryoTEM), we conclude that growth of amorphous CoCO3 nanoparticles proceeds through assembly of the 10 nm primary particles. Our observations not only provide unique insights into the nanoscale growth kinetics of an amorphous phase in aqueous solution that may open the way to improved synthesis protocols of the Co catalyst for Fischer–Tropsch synthesis.