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

The Water–Amorphous Calcium Carbonate Interface and Its Interactions with Amino Acids

Amorphous calcium carbonate is often the first phase to precipitate during the mineralisation of calcium carbonate, before the formation of one of the crystalline polymorphs. In vivo, this phase is believed to be essential for the manufacture of minerals displaying non-equilibrium morphologies. The precipitation of this, usually transient, phase and its subsequent transformation into one of the crystalline polymorphs can be controlled by organic molecules. Here, we present a series of Molecular Dynamics simulations that explore the amorphous calcium carbonate – water interface, the attachment of amino acids onto both hydrous and anhydrous amorphous calcium carbonate and their effect on the surface. The results show that surface ions have a different coordination number distribution from bulk ions and can diffuse up to two orders of magnitude faster than their bulk counterparts, suggesting that crystallisation is much more likely to occur in this region. All the amino acids investigated bind to the amorphous calcium carbonate surfaces. However, acidic amino acids have a clear preference for the surface of amorphous CaCO3.H2O. The favoured mode of interaction of the amino acids is through amine and/or guanidine moieties. The important ramifications of the results for our understanding of protein-mineral interactions are discussed

Simulation of Calcium Phosphate Pre-Nucleation Clusters in Aqueous Solution: Association Beyond Ion Pairing

© 2019 American Chemical Society. Classical molecular dynamics simulations and free energy methods have been used to obtain a better understanding of the molecular processes occurring prior to the first nucleation event for calcium phosphate biominerals. The association constants for the formation of negatively charged complexes containing calcium and phosphate ions in aqueous solution have been computed, and these results suggest that the previously proposed calcium phosphate building unit, [Ca(HPO4)3]4-, should only be present in small amounts under normal experimental conditions. However, the presence of an activation barrier for the removal of an HPO42- ion from this complex indicates that this species could be kinetically trapped. Aggregation pathways involving CaHPO4, [Ca(HPO4)2]2-, and [Ca(HPO4)3]4- complexes have been explored with the finding that dimerization is favorable up to a Ca/HPO4 ratio of 1:2

Simulation of calcium phosphate species in aqueous solution: force field derivation

A new force field has been derived for the aqueous calcium phosphate system that aims to reproduce the key thermodynamic properties of the system, including free energies of hydration of the ions and the solubility of the solid mineral phases. Interactions of three phosphate anions (PO43-, HPO42-, and H2PO4-) with water were calibrated through comparison with the results obtained from ab initio molecular dynamics using both GGA and hybrid density functional theory with dispersion corrections. In the solid state, the force field has been evaluated by benchmarking against experiment and other existing models and is shown to reproduce the structural and mechanical properties well, despite the primary focus being on thermodynamics. To validate the force field, the thermodynamics of ion pairing for calcium phosphate species in water has been computed and shown to be in excellent agreement with experimental data

Interaction of stable aggregates drives the precipitation of calcium phosphate in supersaturated solutions

Calcium phosphate is the main mineral phase within our bodies, but despite many studies there is not yet a consensus on how it nucleates. We have used molecular dynamics simulations to investigate the interactions of ions in solution and the stability of nanoparticles. At high concentrations, we show that calcium and hydrogen phosphate ions associate to form negatively charged clusters that grow further through a combination of ion attachment and particle–particle interactions. Additional analysis of a cluster of 16 ions at experimental concentrations showed that this is (meta)stable in solution and actually densifies during the simulation. Free energy calculations probing the stability of the nanoparticles further demonstrated that they occupy a free energy minimum lower than the free ions or ion pairs in solution suggesting that calcium phosphate nucleation and growth may occur through the aggregation of small negatively charged clusters

Promoting environmental justice in contaminated areas by combining environmental public health and community theatre practices

Communities affected by contaminated sites are often overburdened by environmental and social fragilities living a depression in their potentialities and destabilisation in health and quality of life. The paradigm of Environmental Justice and the framework of community capacity (com- munity capacities) are at stake in promoting environmental public health in communities affected by contaminated sites. Three community changes foreseeing the following objectives appear as priorities: centralisation in decisions regarding the use of their territories; an active (i.e. partic- ipated) role in decision-making processes; a view of a possible future without contamination. These transitions require the activation of technical, scientific, and cultural domains. While environmental public health research, especially if implemented through a community partici- pative approach, has a central role in promoting the community capacity of ‘knowledge’, per- forming arts have great potential for empowering the other capacities. Different collective theatrical approaches are reviewed and analysed in the cultural domain, identifying those of community theatre as the practices with the greatest participative and transformative impact. A community-based approach for promoting environmental justice in contaminated sites requires the development of interventions integrating technical-scientific with cultural domains

Self-assembly of glycerol monooleate with the antimicrobial peptide LL-37: a molecular dynamics study

Over the past decade, the rapid increase in the incidence of antibiotic-resistant bacteria has promoted research towards alternative therapeutics such as antimicrobial peptides (AMPs), but their biodegradability limits their application. Encapsulation into nanocarriers based on the self-assembly of surfactant-like lipids is emerging as a promising strategy for the improvement of AMPs' stability and their protection against degradation when in biological media. An in-depth understanding of the interactions between the structure-forming lipids and AMPs is required for the design of nanocarriers. This in silico study, demonstrates the self-assembly of the amphiphilic lipid glycerol monooleate (GMO) with the antimicrobial peptide LL-37 into nanocarriers on the molecular scale. Molecular dynamics (MD) simulations show the formation of direct micelles, with either one or two interacting LL-37, and vesicles in this two- component system in agreement with experimental results from small-angle X- ray scattering studies. The hydrophobic contacts between LL-37 and GMOs in water appear responsible for the formation of these nanoparticles. The results also suggest that the enhanced antimicrobial efficiency of LL-37 in these nanocarriers that was previously observed experimentally can be explained by the availability of its side chains with charged amino acids, an increase of the electrostatic interaction and a decrease of the peptide's conformational entropy upon interacting with GMO. The results of this study contribute to the fundamental understanding of lipid–AMP interactions and may guide the comprehensive design of lipid-based self-assembled nanocarriers for antimicrobial peptides