Adsorption of Aspartate Derivatives to Calcite Surfaces in Aqueous Environment

Abstract

In many living organisms, biomolecules interact favorably with various surfaces of calcium carbonate. In this work, we have considered the interactions of aspartate (Asp) derivatives, as models of complex biomolecules, with calcite. Using kinetic growth experiments, we have investigated the inhibition of calcite growth by Asp, Asp2 and Asp3.This entailed the determination of a step-pinning growth regime as well as the evaluation of the adsorption constants and binding free energies for the three species to calcite crystals. These latter values are compared to free energy profiles obtained from fully atomistic molecular dynamics simulations. When using a flat (104) calcite surface in the models, the measured trend of binding energies is poorly reproduced. However, a more realistic model comprised of a surface with an island containing edges and corners, yields binding energies that compare very well with experiments. Surprisingly, we find that most binding modes involve the positively charged, ammonium group. Moreover, while attachment of the negatively charged carboxylate groups is also frequently observed, it is always balanced by the aqueous solvation of an equal or greater number of carboxylates. These effects are observed on all calcite features including edges and corners, the latter being associated with dominant affinities to Asp derivatives. As these features are also precisely the active sites for crystal growth, the experimental and theoretical results point strongly to a growth inhibition mechanism whereby these sites become blocked, preventing further attachment of dissolved ions and halting further growth. File list (2) download file view on ChemRxiv ASP-230919-Manuscript.pdf (773.33 KiB) download file view on ChemRxiv ASP-230919-SI.pdf (1.78 MiB)

Calcium carbonate: controlled synthesis, surface functionalization, and nanostructured materials

“…31 Since acidic macromolecules are traditionally considered to be critical to CaCO 3 biomineralization, many different classes of charged small organic compounds or polyelectrolytes, such as polysaccharides, polypeptides, or proteins and different experimental strategies and conditions have been systematically applied to discern the roles they play in the biomineralization of CaCO 3 . [165][166][167] Amino acids with different surface charges, polarity, and side chains can regulate the nucleation, growth, and crystal structure of CaCO 3 (Fig. 6).…”

Comparison of the Effect of the Amino Acids on Spontaneous Formation and Transformation of Calcium Phosphates

“…AAs can either decrease the solution supersaturation through the complexation of calcium or phosphate ions or they can interact with the solid phase by non-specific adsorption at surfaces or at growing sites [20][21][22][23][24][25], which both intuitively lead to inhibition [18]. It should be noted that the AAs affinity towards the solid phases, which appear in biomineralization, is influenced by the overall charge and the charge of specific AAs segments, their ability to form chemical bonds, and their stereochemical or geometrical properties [18,20,21,31,[50][51][52]. In addition to the complexity in the mechanism of action, the reason for contradictory results also lies in the fact that the employed experimental conditions (reactant concentration, temperature, mode of mixing) and experimental setup (seeded growth, constant composition, spontaneous precipitation) vary considerably between different studies.…”

Role of Hydrodynamics, Li+ Addition and Transformation Kinetics on the Formation of Plate-Like {001} Calcite Crystals

“…Calcium carbonate precipitation was initiated by mixing equal volumes (200 cm 3 ) of solutions containing LiCl and CaCl 2 with NaHCO 3 solution, all freshly prepared. Deionized water (conductivity < 0.055 µS cm −1 ) and analytical grade chemicals LiCl (Fluka, Buchs, Switzerland), CaCl 2 • 2 H 2 O (Acros organics, Geel, Belgium) and NaHCO 3 (Sigma Aldrich, St. Louis, MS, USA) were used for the preparation of the solutions.…”

“…The kinetics of the vaterite dissolution were conducted in magnetically stirred systems, undersaturated with respect to vaterite and prepared by mixing bicarbonate and calcium solutions: V = 400 cm 3 , c i (NaHCO 3 ) = c i (CaCl 2 ) = 0.058 mol dm −3 , c(HCl) = c(NaCl)= 0.042 mol dm −3 and (0.0 < c(LiCl) < 0.3 mol dm −3 ). The vaterite crystals used in these experiments were obtained from the US model system, and isolated after 10 min of sonication and dried at 100 • C for one hour.…”

“…Calcium carbonate crystals, particularly those of calcite, are interesting model systems for studying the interfacial interactions on crystal planes, namely, for any detailed analysis of crystal growth kinetics and mechanisms, or investigation of basic molecular interactions that may happen at the solid-liquid interfaces. To perform this investigation, crystal seed material uniform in size and with well exposed crystallographic planes is necessary [1][2][3][4][5][6]. Calcite crystals of different morphologies may be precipitated from aqueous solutions at different technological or environmental conditions or during the biomineralization processes.…”