Characterization of Structure in Biogenic Amorphous Calcium Carbonate: Pair Distribution Function and Nuclear Magnetic Resonance Studies of Lobster Gastrolith

Abstract

Total X-ray scattering and pair distribution function analysis are combined with nuclear magnetic resonance spectroscopy to identify key differences in structural properties between biogenic and synthetic samples of amorphous calcium carbonate (ACC). Biogenic samples studied are gastroliths taken from the American lobster and are composed of hydrated ACC containing minor impurities. X-ray pair distribution functions reveal that the short- and medium-range structure found in synthetic ACC also occurs in gastrolith ACC, notably with atomic pair correlations extending up to ∼10 Å. The 13C NMR spectra of gastrolith ACC show a distribution of carbonate environments as seen in synthetic hydrated ACC. However, 1H NMR spectroscopy reveals that a mobile H2O component and hydroxyl groups found in synthetic hydrated ACC are absent in the gastrolith ACC. This difference may arise from differences in local conditions of ACC formation. The 31P NMR results indicate that inorganic phosphate is the principal form of the minor phosphorus. Gastrolith that was allowed to age shows the presence of calcite and vaterite, as well as residual ACC. 31P NMR also reveals trace amounts of monetite (CaHPO4) in aged samples, raising the possibility that fresh gastrolith ACC may contain a minor component of amorphous calcium phosphate. The findings suggest that important differences in the hydrous components between synthetic and biogenic hydrated ACC influence stability of the amorphous phase and its transformation to crystalline forms, thereby extending the foundation for advanced materials applications in engineered systems.

Using simulation to understand the structure and properties of hydrated amorphous calcium carbonate

“…Water within these micropores should be significantly more mobile than water within an ionic glass, and so gives an average diffusion coefficient that is much larger than for water in the non-microporous ACC systems. This is reminiscent of the experimental results obtained by Michel et al 22 and Reeder et al 25 using proton NMR to analyse synthetic ACC. In that work half of the water molecules were largely immobile and were labelled as structural while the rest were capable of restricted motion.…”

“…Proton solid-state nuclear magnetic resonance showed that two different types of water are present within the structure. One is largely immobile and labelled as structural, but the other showed an increased mobility 22,25,26 . The location of this water appears, again, to be dependent on the sample origin.…”

High-resolution structural and elemental analyses of calcium storage structures synthesized by the noble crayfish Astacus astacus

“…The presence and distribution of P were recently determined in Cherax quadricarinatus gastroliths in organic molecules as well as in the mineral phase as ACP (Luquet et al, 2016;Reeder et al, 2013). Phosphorylated proteins have been characterized and hypothesized as playing a role in Cherax gastrolith ACC stabilization Glazer and Sagi, 2012;Glazer et al, 2010;Shechter et al, 2008b).…”

“…Akiva-Tal et al, 2011;Bentov et al, 2010;Habraken et al, 2015;Luquet et al, 2016;Reeder et al, 2013;Reid et al, 2012;Sato et al, 2011). Nevertheless, it is well known that if the main mineral used by invertebrates for hardening their skeleton is calcium carbonate, numerous other minerals are also found, notably phosphate and silica-based minerals Knoll, 2003;Lowenstam, 1972;Lowenstam and Weiner, 1989;Murdock and Donohue, 2011;Simkiss and Wilbur, 1989).…”

Indications that Amorphous Calcium Carbonates Occur in Pathological Mineralisation—A Urinary Stone from a Guinea Pig

“…They serve as a calcium reservoir regularly needed upon molting, as the carapace cannot grow with the animal. Gastroliths are mostly constituted of amorphous calcium carbonate (ACC) [19], due to its higher solubility and better bioavailability as compared to crystalline calcium carbonates. One example of pathologically formed calcium carbonate is the urinary stones of guinea pigs.…”