Ab initio and metadynamics studies on the role of essential functional groups in biomineralization of calcium carbonate and environmental situations

A Simplified Model for Shear Behavior of Mortar Using Biomimetic Carbonate Precipitation

As a common molecule in biomineralization, L-aspartic acid (L-Asp) has been proven to be able to induce in vitro CaCO3 precipitation, but its application in sand reinforcement has never been studied. In this study, L-Asp was employed in sand reinforcement for the first time through the newly developed biomimetic carbonate precipitation (BCP) technique. Specimens with different number of BCP spray cycles were prepared, and a series of direct shear tests were conducted to investigate the impact of spray number on shear strength, critical displacement, and residual strength. Then a simplified power model for shear stress-displacement behavior was established and calibrated with the measured data. The results show that BCP can significantly improve the shear strength of sand. As the number of spray cycles increases, both the shear strength and residual strength increase, while the critical displacement decreases. Such variations can be described with two sigmoid models and a linear model, respectively. The simplified power model performs well in most cases, especially at higher spray numbers. This study is expected to provide a practical model for the shear behavior of BCP-treated mortar.

Biopolymer recovery from waste activated sludge toward self-healing mortar crack

Activated sludge (AS) offers great potential for resource recovery considering its high organic and nutrient content. However, low recovery efficiency and high costs are directing the focus toward the high-valuable resource recovery. This study extracted 71.5 ± 5.9 mg/g VSS of alginate-like exopolysaccharides from AS (ALE/AS) and applied it to mortar as a novel biopolymer agent for crack self-healing. With a mortar crack of 120 μm, addition of 0.5 wt% ALE/AS yielded a high crack closure ratio of 86.5 % within 28 days. In comparison to commercial healing agents, marginal flexural strength reduction with ALE/AS addition (17.9 % vs 30.2-50.5 %) was demonstrated. The abundance of COO^- group in GG blocks of ALE/AS resulted in a higher cross-link capacity with Ca²⁺, while the reduction of hydrophilic residues (e.g., COO^- and OH) after complexation engendered a lower swelling capacity, which facilitated self-healing and flexural strength maintenance. Molecular dynamics (MD) revealed that lower Ca²⁺ diffusivity, arising from the stronger electrostatic interactions between the COO^- groups and Ca²⁺, resulted in a high Ca²⁺ concentration around the cracks, leading to CaCO₃ deposition and healed cracks. The outcomes of this study provided light on ALE-based mortar crack healing and presented a possibility for multi-level AS resource recovery.

Simulating the binding of key organic functional groups to aqueous calcium carbonate species

The interaction of organic molecules with mineral systems is relevant to a wide variety of scientific problems both in the environment and minerals processing. In this study, the coordination of small organics that contain the two most relevant functional groups for biomineralisation of calcium carbonate, namely carboxylate and ammonium, with the corresponding mineral ions are examined in aqueous solution. Specifically, two force fields have been examined based on rigid-ion or polarisable models, with the latter being within the AMOEBA formalism. Here the parameters for the rigid-ion model are determined to target the accurate reproduction of the hydration structure and solvation thermodynamics, while both force fields are designed to be compatible with the corresponding recently published models for aqueous calcium carbonate. The application of these force fields to ion pairing in aqueous solution is studied in order to quantitatively determine the extent of association.

Bio-inspired mineral fluorescent hydrogels cross-linked by amorphous rare earth carbonates

The bio-inspired mineral plastic hydrogel based on calcium carbonate and polyacrylic acid has been recently investigated as a promising sustainable material. Here we report that rare earth carbonates can act as cross-linkers to fabricate analogous hydrogels and provide remarkable optical properties.

Amino Acid and Oligopeptide Effects on Calcium Carbonate Solutions

Biological organisms display sophisticated control of nucleation and crystallization of minerals. In order to mimic living systems, deciphering the mechanisms by which organic molecules control the formation of mineral phases from solution is a key step. We have used computer simulations to investigate the effects of the amino acids arginine, aspartic acid, and glycine on species that form in solutions of calcium carbonate (CaCO₃) at lower and higher levels of supersaturation. This provides net positive, negative, and neutral additives. In addition, we have prepared simulations containing hexapeptides of the amino acids to consider the effect of additive size on the solution species. We find that additives have limited impact on the formation of extended, liquid-like CaCO₃ networks in supersaturated solutions. Additives control the amount of (bi)carbonate in solution, but more importantly, they are able to stabilize these networks on the time scales of the simulations. This is achieved by coordinating the networks and assembled additive clusters in solutions. The association leads to subtle changes in the coordination of CaCO₃ and reduced mobility of the cations. We find that the number of solute association sites and the size and topology of the additives are more important than their net charge. Our results help to understand why polymer additives are so effective at stabilizing dense liquid CaCO₃ phases.

Molecular dynamics simulation of protein-mediated biomineralization of amorphous calcium carbonate

The protein-mediated biomineralization of calcium carbonate (CaCO₃) in living organisms is primarily governed by critical interactions between the charged amino acids of the protein, solvent, calcium (Ca²⁺) and carbonate (CO₃²⁻) ions. The present article investigates the molecular mechanism of lysozyme-mediated nucleation of amorphous calcium carbonate (ACC) using molecular dynamics and metadynamics simulations. The results reveal that, by acting as nucleation sites, the positively charged side chains of surface-exposed arginine residues form hydrogen bonds with carbonates and promote aggregation of ions around them leading to the formation and growth of ACC on the protein surface. The newly formed ACC patches were found to be less hydrated due to ion aggregation-induced expulsion of water from the nucleation sites. Despite favorable electrostatic interactions of the negatively charged side chains of aspartate and glutamate with calcium ions, these residues contribute minimally to the growth of ACC on protein surface. The activation barrier for the growth of partially hydrated ACC patches on lysozymes was determined from the free energy profiles obtained from metadynamics simulations.

The protein-mediated biomineralization of calcium carbonate (CaCO₃) in living organisms is primarily governed by critical interactions between the charged amino acids of the protein, solvent, calcium (Ca²⁺) and carbonate (CO₃²⁻) ions.

Diatom-inspired skeletonisation of insulin - Mechanistic insights into crystallisation and extracellular bioactivity

In this paper, we encage insulin within calcium carbonate by means of a biomineralisation process. We find that both dogbone and crossbone morphologies develop during the crystallisation process. The crystals break down into small nanocrystals after prolonged immersion in phosphate buffer solution, which adhere extracellularly to mammalian cells without causing any observable damage or early cell-death. The mechanisms behind calcium carbonate encaging of single insulin monomers are detailed. This communication elucidates a novel, diatom-inspired approach to the mineral skeletonisation of insulin.