Formation Of Amorphous Calcium Carbonate Research Articles

Effect of Heating/Cooling Rate on the Local Electronic Structure of Amorphous Calcium Carbonate

Here, in the impact of heating/cooling rate was investigated on the formation of amorphous calcium carbonate (calcite) during sol-gel synthesis by probing local electronic structure. The amorphous calcium carbonate was synthesized by annealing precursor at 400oC at different heating/cooling rates i.e., 1.5 and 3oC /min. X-ray diffraction studies revealed amorphous nature at both heating/cooling rates. Fourier transformed infrared spectroscopic measurements characteristics bands in the spectra of both materials. Near edge X-ray absorption fine structure measurements at Ca L-edge, C K-edge and O K-edge were utilized to reveal the associated changes in the local electronic structure during synthesis. Local electronic structure investigation using near edge X-ray absorption fine structure measurements shows onset of moisture absorption on the surface particles when kept in the open environment.

Colloidal pathways of amorphous calcium carbonate formation lead to distinct water environments and conductivity.

CaCO3 is the most abundant biomineral and a major constituent of incrustations arising from water hardness. Polycarboxylates play key roles in controlling mineralization. Herein, we present an analytical and spectroscopic study of polycarboxylate-stabilized amorphous CaCO3 (ACC) and its formation via a dense liquid precursor phase (DLP). Polycarboxylates facilitate pronounced, kinetic bicarbonate entrapment in the DLP. Since bicarbonate is destabilized in the solid state, DLP dehydration towards solid ACC necessitates the formation of locally calcium deficient sites, thereby inhibiting nucleation. Magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy of poly-aspartate-stabilized ACC reveals the presence of two distinct environments. The first contains immobile calcium and carbonate ions and structural water molecules, undergoing restricted, anisotropic motion. In the second environment, water molecules undergo slow, but isotropic motion. Indeed, conductive atomic force microscopy (C-AFM) reveals that ACC conducts electrical current, strongly suggesting that the mobile environment pervades the bulk of ACC, with dissolved hydroxide ions constituting the charge carriers. We propose that the distinct environments arise from colloidally stabilized interfaces of DLP nanodroplets, consistent with the pre-nucleation cluster (PNC) pathway.

The armoured cuticle of the black soldier fly Hermetia illucens

We characterise in detail the larval and pupal cuticle of the black soldier fly Hermetia illucens L. (Diptera: Stratiomyidae), a key insect species in circular economy. In particular, we focus on ultrastructure using scanning and transmission electron microscopy, material characterization and composition (elements and minerals) with confocal laser scanning microscope, energy dispersive X-ray microanalysis, powder X-ray diffraction and mechanical properties with nanoindentation measurements. Calcium carbonate crystallizes on the epicuticle as blocks of calcite in the pupal cuticle. Calcium carbonate granules are stored in two specialised Malpighian tubules. CaCO3 is already present in the cuticle of young larval instars, but it is mainly in the form of amorphous calcium carbonate while the amount of calcite increases during larval development. The presence of calcite leads to cuticle hardening. Larval and pupal cuticles contain large amounts of resilin which guarantee cuticle flexibility.

Magnesium isotope fractionation during natural travertine deposition from Baishuitai, SW China

Travertine samples deposited in Earth's surface environments can be used as an effective archive for paleo-climatic reconstruction. As a common element in carbonates, magnesium (Mg) and its isotopic composition in travertine could provide useful information for evaluating paleo-environment changes. In this study, we investigate the Mg isotope systematics in both endogenic travertines (mainly calcite) and spring/stream waters at Baishuitai, Yunnan, SW China. Our results show a systematic increase in δ26Mg value from −1.37 to −1.26‰ for water samples downstream, but varied δ26Mg values between −4.12 and −3.95‰ (average −4.02‰) for solid carbonates, thus a corresponding fractionation Δ26Mgcalcite-water between −2.76 to −2.59‰ (mean value of −2.69‰). Therefore, the solid carbonates preferentially incorporate light Mg isotopes during travertine formation. More interestingly, the Mg distribution coefficient (KMg/Ca) between travertine and water exhibits two variation trends with the calcite deposition rate (Rp) along the canal, which can be explained by the change of calcite formation mechanism from direct nucleation to precipitation via amorphous calcium carbonate (ACC) intermediate. In the upper-stream, the direct nucleation of calcite results in the rapid incorporation of Mg ions into crystal lattice, while a relatively slow precipitation of calcite downstream would incorporate Mg via ACC formation pathway in a quasi-equilibrium pattern. This is consistent with the grain size distribution and crystal morphology observed under SEM. Our results show the important control of water Mg/Ca ratios on the calcite precipitation during travertine formation, and imply the potential and complexity of using Mg isotopes of travertine deposits to reconstruct paleo-environments.

Effects of amino acids on the multiscale properties of carbonated wollastonite composites

This article presents an insight into the effects of amino acids on the moisture susceptibility, nanomechanical properties, and fracture properties of carbonated wollastonite composites. Paste samples containing various concentrations of amino acids were subjected to a CO2-rich environment. The addition of amino acids resulted in the formation of amorphous calcium carbonate (ACC), vaterite, and aragonite, instead of calcite, in the carbonated composites. Thermogravimetric analysis (TGA), Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and nanoindentation were performed for microstructural analysis. Inductively coupled plasma-optical emission spectrometry (ICP-OES) was performed to determine the leaching of Ca2+ and Si2+ ions from carbonated wollastonite composites. It was observed that the chain lengths of the amino acids have an influence on the formation of crystal phases. For determining fracture properties, the Jenq-Shah model was performed using a notched beam. It was observed that amino acids reduced carbonation reaction and improved fracture properties by 156 %. The formation of metastable CaCO3 enhanced the nanomechanical properties of this carbonated system.

The nano- and meso-scale structure of amorphous calcium carbonate

Understanding the underlying processes of biomineralization is crucial to a range of disciplines allowing us to quantify the effects of climate change on marine organisms, decipher the details of paleoclimate records and advance the development of biomimetic materials. Many biological minerals form via intermediate amorphous phases, which are hard to characterize due to their transient nature and a lack of long-range order. Here, using Monte Carlo simulations constrained by X-ray and neutron scattering data together with model building, we demonstrate a method for determining the structure of these intermediates with a study of amorphous calcium carbonate (ACC) which is a precursor in the bio-formation of crystalline calcium carbonates. We find that ACC consists of highly ordered anhydrous nano-domains of approx. 2 nm that can be described as nanocrystalline. These nano-domains are held together by an interstitial net-like matrix of water molecules which generate, on the mesoscale, a heterogeneous and gel-like structure of ACC. We probed the structural stability and dynamics of our model on the nanosecond timescale by molecular dynamics simulations. These simulations revealed a gel-like and glassy nature of ACC due to the water molecules and carbonate ions in the interstitial matrix featuring pronounced orientational and translational flexibility. This allows for viscous mobility with diffusion constants four to five orders of magnitude lower than those observed in solutions. Small and ultra-small angle neutron scattering indicates a hierarchically-ordered organization of ACC across length scales that allow us, based on our nano-domain model, to build a comprehensive picture of ACC formation by cluster assembly from solution. This contribution provides a new atomic-scale understanding of ACC and provides a framework for the general exploration of biomineralization and biomimetic processes.

Microplastics impact shell and pearl biomineralization of the pearl oyster Pinctada fucata

Microplastics are extremely widespread aquatic pollutants that severely detriment marine life. In this study, the influence of microplastics on biomineralization was investigated. For the first time, multiple forms and types of microplastics were detected and isolated from the shells and pearls of Pinctada fucata. According to the present study, the abundance of microplastics in shells and pearls was estimated at 1.95 ± 1.43 items/g and 0.53 ± 0.37 items/g respectively. Interestingly, microplastics were less abundant in high-quality round pearls. Microplastics may hinder the growth of calcite and aragonite crystals, which are crucial components required for shell formation. During the process of biomineralization microplastics became embedded in shells, suggesting the existence of a novel pathway by which microplastics accumulate in bivalves. After a 96-h exposure to microplastics, the expression level of typical biomineralization-related genes increased, including amorphous calcium carbonate binding protein (ACCBP) gene which experienced a significant increase. ACCBP promotes the formation of amorphous calcium carbonate (ACC), which is the pivotal precursor of shell formation-related biominerals. ACCBP is highly expressed during the developmental stage of juvenile oysters and the shell-damage repair process. The increased expression of ACCBP suggests biomineralization is enhanced as a result of microplastics exposure. These results provide important evidence that microplastics exposure may impact the appearance of biominerals and the expression of biomineralization-related genes, posing a new potential threat to aquatic organisms.

Synthesis and Characterization of Surfactant for Retarding Acid-Rock Reaction Rate in Acid Fracturing.

Acid fracturing is an effective method to develop ultra-low permeability reservoirs. However, the fast reaction rate reduces the effect of the acid fracturing and increases the near-well collapse risk. Therefore, it is necessary to retard the acid–rock reaction rate. In this work, we synthesized an acid-resistant Gemini zwitterionic viscoelastic surfactant (named VES-c), which has good performances such as temperature resistance, salt resistance, and shear resistance. Besides, a low concentration of VES-c increases the viscosity of the acid solution. The CO2 drainage method was used to measure the reaction rate between the dibasic acid and dolomite/broken core. We find that the dibasic acid containing 0.3% VES-c retards the dolomite reaction rate of 3.22 times compared with only dibasic acid. Furthermore, the dibasic acid containing 0.3% VES-c exhibits uniform distribution and is not easy to adhere to the solid surface. The VES-c also is favorable to reduce the formation of amorphous calcium carbonate. Retarding the rate of acid–rock reaction and enhancing the acidification are mainly attributed to VES-c's salt-tolerance, anti-adsorption, and the property of increasing the viscosity of the solution. Hopefully, this kind of surfactant retarding reaction rate is applied to other acid–rock reactions.

In Situ X-ray Absorption Spectroscopy and Droplet-Based Microfluidics: An Analysis of Calcium Carbonate Precipitation.

Droplet-based microfluidic systems are ideally suited for the investigation of nucleation and crystallization processes. To best leverage the features of such platforms (including exquisite time resolution and high-throughput operation), sensitive and in situ detection schemes are needed to extract real-time chemical information about all species of interest. In this regard, the extension of conventional (UV, visible, and infrared) optical detection schemes to the X-ray region of the electromagnetic spectrum is of high current interest, as techniques such as X-ray absorption spectroscopy (XAS) provide for the element-specific investigation of the local chemical environment. Accordingly, herein, we report for the first time the integration of millisecond droplet-based microfluidics with XAS. Such a platform allows for the sensitive acquisition of X-ray absorption data from picoliter-volume droplets moving at high linear velocities. Significantly, the high-temporal resolution of the droplet-based microfluidic platform enables unprecedented access to the early stages of the reaction. Using such an approach, we demonstrate in situ monitoring of calcium carbonate precipitation by extracting XAS spectra at the early time points of the reaction with a dead time as low as 10 ms. We obtain insights into the kinetics of the formation of amorphous calcium carbonate (ACC) as a first species during the crystallization process by monitoring the proportion of calcium ions converted into ACC. Within the confined and homogeneous environment of picoliter-volume droplets, the ACC content reaches 60% over the first 130 ms. More generally, the presented method offers new opportunities for the real-time monitoring of fast chemical and biological processes.

X-ray Total Scattering Study of Phases Formed from Cement Phases Carbonation

Carbonation in cement binders has to be thoroughly understood because it affects phase assemblage, binder microstructure and durability performance of concretes. This is still not the case as the reaction products can be crystalline, nanocrystalline and amorphous. The characterisation of the last two types of components are quite challenging. Here, carbonation reactions have been studied in alite-, belite- and ye’elimite-containing pastes, in controlled conditions (3% CO2 and RH = 65%). Pair distribution function (PDF) jointly with Rietveld and thermal analyses have been applied to prove that ettringite decomposed to yield crystalline aragonite, bassanite and nano-gibbsite without any formation of amorphous calcium carbonate. The particle size of gibbsite under these conditions was found to be larger (~5 nm) than that coming from the direct hydration of ye’elimite with anhydrite (~3 nm). Moreover, the carbonation of mixtures of C-S-H gel and portlandite, from alite and belite hydration, led to the formation of the three crystalline CaCO3 polymorphs (calcite, aragonite and vaterite), amorphous silica gel and amorphous calcium carbonate. In addition to their PDF profiles, the thermal analyses traces are thoroughly analysed and discussed.

Cellular bicarbonate accumulation and vesicular proton transport promote calcification in the sea urchin larva.

The sea urchin embryo develops a calcitic endoskeleton through intracellular formation of amorphous calcium carbonate (ACC). Intracellular precipitation of ACC, requires [Formula: see text] concentrating as well as proton export mechanisms to promote calcification. These processes are of fundamental importance in biological mineralization, but remain largely unexplored. Here, we demonstrate that the calcifying primary mesenchyme cells (PMCs) use Na+/H+-exchange (NHE) mechanisms to control cellular pH homeostasis during maintenance of the skeleton. During skeleton re-calcification, pHi of PMCs is increased accompanied by substantial elevation in intracellular [Formula: see text] mediated by the [Formula: see text] cotransporter Sp_Slc4a10. However, PMCs lower their pHi regulatory capacities associated with a reduction in NHE activity. Live-cell imaging using green fluorescent protein reporter constructs in combination with intravesicular pH measurements demonstrated alkaline and acidic populations of vesicles in PMCs and extensive trafficking of large V-type H+-ATPase (VHA)-rich acidic vesicles in blastocoelar filopodial cells. Pharmacological and gene expression analyses underline a central role of the VHA isoforms Sp_ATP6V0a1, Sp_ATP6V01_1 and Sp_ATPa1-4 for the process of skeleton re-calcification. These results highlight novel pH regulatory strategies in calcifying cells of a marine species with important implications for our understanding of the mineralization process in times of rapid changes in oceanic pH.

Cave bacteria-induced amorphous calcium carbonate formation

Amorphous calcium carbonate (ACC) is a precursor of crystalline calcium carbonates that plays a key role in biomineralization and polymorph evolution. Here, we show that several bacterial strains isolated from a Hungarian cave produce ACC and their extracellular polymeric substance (EPS) shields ACC from crystallization. The findings demonstrate that bacteria-produced ACC forms in water-rich environment at room temperature and is stable for at least half year, which is in contrast to laboratory-produced ACC that needs to be stored in a desiccator and kept below 10 °C for avoiding crystallization. The ACC-shielding EPS consists of lipids, proteins, carbohydrates and nucleic acids. In particular, we identified large amount of long-chain fatty acid components. We suggest that ACC could be enclosed in a micella-like formula within the EPS that inhibits water infiltration. As the bacterial cells lyse, the covering protective layer disintegrates, water penetrates and the unprotected ACC grains crystallize to calcite. Our study indicates that bacteria are capable of producing ACC, and we estimate its quantity in comparison to calcite presumably varies up to 20% depending on the age of the colony. Since diverse bacterial communities colonize the surface of cave sediments in temperate zone, we presume that ACC is common in these caves and its occurrence is directly linked to bacterial activity and influences the geochemical signals recorded in speleothems.

Amorphous calcium carbonate (ACC) in fresco mural paintings

A fresco painting has a calcium carbonate binder produced as result of the carbonation process of a lime paste. The reaction environmental conditions are similar to those of bio-mineral formation where an amorphous calcium carbonate (ACC) phase has been found to be the precursor of other CaCO3 polymorphs following the sequence: hydrated ACC, anhydrous ACC, vaterite, aragonite, and, finally, stable calcite. In order to determine whether ACC is also formed during the fresco drying process, as well as, the final surface calcium carbonate phases present, a series of laboratory mock-ups, replicating as close as possible each of the paint strata and submitted to the same atmospheric conditions have been designed and studied. The results indicate that the continuous supply of water and reagents by the lime and sand mortar promote the ACC formation even at the completion of water evaporation and that the high pH of the medium does not favour the formation of calcium carbonate polymorphs other than calcite. In fact, the results demonstrate that the presence of an ACC layer in the mural painting surface confirms that the original painting technique used was fresco. Finally, the presence of an ACC layer is important for stablishing adequate cleaning (the solubility of hydrated ACC is superior to those of calcite) and conservation protocols (ACC is susceptible to suffer dehydration) for the fresco paintings.

Tailoring Calcite Growth through an Amorphous Precursor in a Hydrogel Environment

The precipitation of calcium carbonate in hydrogel-like environments is used by certain living organisms to build functional mineral–organic composite structures. Here, we investigate a pathway for calcium carbonate mineralization in agarose hydrogels with a wide range of polymer networks. The experimental investigation demonstrates that the formation of amorphous calcium carbonate (ACC) throughout the agarose hydrogels is a diffusion-limited process, and therefore, it is affected by the supersaturation of the solution and by the hydrogel network. In contrast, the inclusion of the polymer into the calcite crystals and their morphology as well as the rate of crystal growth are controlled by the amorphous precursor, and thereby, they are quite unaffected by the initial supersaturation. The nucleation rate of calcite in agarose is sufficiently high to hinder ion diffusion limiting the calcite growth rate, so that a uniform mineralization takes place in the hydrogel, in the absence of concentration gradients....

Gelatinous Siphon Sheath Templates the Starfruit-Shaped Aragonite Aggregate Growth

Biomimetic synthesis of aragonite with various templates in vitro is an important way to understand the biomineralization process and synthesize nacre-like materials. Herein, we used the siphon sheath from the bivalve Lutraria sieboldii as the substrate for the formation of calcium carbonate. We found that the inner layer of the sheath, which is composed of approximately 40% protein and 60% β-chitin, induced the formation of nearly pure aragonite by the transformation of amorphous calcium carbonate (ACC). More surprisingly, unique starfruit-shaped aragonite aggregates were observed on the substrate and were constructed from many adhered, oriented aragonite tablets. We consider that the acid-rich protein from the inner layer of the siphon sheath triggers the formation of ACC, and the swollen β-chitin regulates the transformation of ACC into aragonite by lattice matching and stereochemical recognition. The various surface adhesion energies of the crystal, the change in growth rates on different crystallographic facets, and the hexagonal features of the aragonite tablets led to the formation of starfruit-shaped aragonite aggregates.

New approach to nanolime synthesis at ambient temperature

This study explored the viability of synthesising nanolime at ambient temperature by raising calcium solubility through the formation of complexes with dissolved sugars. Micro-Raman findings confirmed the formation of nanolime particles whilst the percentage of Ca(OH)2 formed, observed to vary with synthesis conditions, was calculated with thermogravimetry. Nanoparticles were synthesised most productively (77%) in a 5% sugary solution at a temperature of 25 °C and a 4 h reaction time. The hexagonal nanoparticles synthesised ranged in size from 200 to 25 nm. Portlandite formation is related to calcium complex formation with less mannitol that sucrose needed to form similar NPs of Ca(OH)2. The sugary media also favoured the formation of amorphous calcium carbonate.

Application of Different Fourier Transform Infrared (FT-IR) Methods in the Characterization of Lime-Based Mortars with Oxblood.

Organic compounds have frequently been added into lime mortars for property modifications, in order to satisfy various functional needs in building techniques. This study applies Fourier transform infrared (FT-IR) spectroscopy in transmission, reflection, and attenuated total reflection (ATR) modes to characterize lime-based mortar specimens containing oxblood, which has been used as additive as a common practice of long history in many parts of the world. The specimens were prepared basing upon a 19th-century Italian historic recipe, with the intention to have a better understanding on the possible characteristics of such mortars. Thermal analysis, color measurement, and static contact angle test were also used. After curing, the specimens show a distinctive dark-red color on the top surface, which is different from the bulk. Color measurements on the surface suggest that this color was formed at an early stage and was able to maintain stable for a relatively long period of time. Both transmission and reflection FT-IR confirm the preferential accumulation of proteins on the top surface, which should have induced their water repellency according to the static contact angle test. In addition, specimens show weaker calcite bands in FT-IR transmission, reflection, as well as ATR spectra; the pattern of ATR spectra after the thermal analysis to 500 °C suggests the formation of amorphous calcium carbonate, which is related to the presence of oxblood.

Secrets of the Sea Urchin Spicule Revealed: Protein Cooperativity Is Responsible for ACC Transformation, Intracrystalline Incorporation, and Guided Mineral Particle Assembly in Biocomposite Material Formation.

The formation of the sea urchin spicule involves the stabilization and transformation of amorphous calcium carbonate (ACC) and assembly of ACC nanoparticle precursors into a mesoscale single crystal of fracture-resistant calcite. This process of particle assembly or attachment is under the control of a family of proteins known as the spicule matrix [Strongylocentrotus purpuratus (SpSM)] proteome. Recently, two members of this proteome, SpSM50 and the glycoprotein SpSM30B/C-G (in recombinant forms), were found to interact together via SpSM30B/C-G oligosaccharide–SpSM50 protein interactions to form hybrid protein hydrogels with unique physical properties. In this study, we investigate the mineralization properties of this hybrid hydrogel alongside the hydrogels formed by SpSM50 and SpSM30B/C-G individually. We find that the SpSM50 + SpSM30B/C-G hybrid hydrogel is synergistic with regard to surface modifications and intracrystalline inclusions of existing calcite crystals, the inhibition of ACC formation, and the kinetic destabilization of ACC to form a crystalline phase. Most importantly, the hybrid hydrogel phase assembles and organizes mineral particles into discrete clusters or domains within in vitro mineralization environments. Thus, the interactions of SpSM50 and SpSM30B/C-G, mediated by carbohydrate–protein binding, reflect the need for protein cooperativity for the ACC-to-crystalline transformation, intracrystalline void formation, and guided mineral particle assembly processes that are instrumental in spicule formation.

Investigation of amorphous calcium carbonate’s formation under high concentration of magnesium: The prenucleation cluster pathway

This paper investigates the formation of amorphous calcium carbonate under high magnesium concentration (Mg/Ca = 6) via several novel methods. While feeding calcium chloride solution into the mixed solution of magnesium chloride and sodium carbonate, a large amount of calcium ions (>0.13 mol/L) stably coexisted with the amorphous calcium carbonate in the solution. The calcium concentration detected by the calcium ion selective electrode was proportional to the calcium concentration added. Surprisingly, the ratio of magnesium to calcium in the amorphous calcium carbonate was just 0.07, and the concentration of calcium continued to increase in the solution after the formation of the amorphous calcium carbonate. We propose that stable prenucleation cluster formed in the solution, which stably coexisted with the amorphous calcium carbonate because of the incorporation of hydrated magnesium ions. The high dehydration free energy barrier of magnesium ions led to its slow dehydration. Also, the hydroxide ion helped to bypass the high dehydration free energy barrier. This research indicates the possible significant role of prenucleation cluster pathway in the calcium carbonate crystallization.

The Initiation and Early Stages of Postmolt Mineralization in the Blue Crab, Callinectes sapidus

Crabs are encased in a rigid exoskeleton or cuticle that is hardened by the both protein crosslinking and calcification. In order to grow, the exoskeleton must be periodically molted. The two outermost layers of the exoskeleton of crabs are deposited prior to the molt, but remain uncalcified until the animal sheds it old exoskeleton. The inhibition of premolt calcification and initiation of postmolt calcification are effected by biochemical changes in the organic matrix. In the two hours after the molt, sugar moieties are enzymatically altered on cuticular glycoproteins by an N-acetylhexosaminidase secreted by the underlying epithelium. These alterations appear to unmask nucleation sites that allow calcification to commence. The initial deposition of mineral is in the form of amorphous calcium carbonate (ACC). As postmolt calcification continues and the principal layer (endocuticle) is deposited and mineralized, the ACC is largely converted to or overgrown by calcite. Prior to the onset of ACC deposition, silicon has been detected in those areas of the exoskeleton that are about to undergo mineralization. As calcification proceeds, silicon is no longer detected. It is hypothesized that silicon is involved in the stabilization of ACC by destabilizing the crystal lattice of calcite before it undergoes the transition to or is overgrown by crystalline calcite.