High Amino Acid Lattice Loading at Nonambient Conditions Causes Changes in Structure and Expansion Coefficient of Calcite

Abstract

Biogenic crystals produced by organisms have been known for several decades to exhibit intracrystalline organic macromolecules. Here, using a reductionist approach, we tackle the question of whether the incorporation of single amino acids is driven by kinetics or by thermodynamics. We show that when calcite is grown in the presence of amino acids under nonambient conditions, extremely high loading levels of up to 6.12 mol % of aspartic acid (Asp) are achieved. This incorporation leads to marked changes in the host calcite crystal’s structure and expansion coefficient. The latter is as much as twice as high as that of pure calcite. This is the first example showing that an organic molecule incorporated into an inorganic host can strongly affect the expansion coefficient. Most importantly, we show that the incorporation of amino acids in calcite is controlled by their thermodynamic solubility in calcite rather than kinetically and that hybrid amino acid-calcite crystals can indeed be considered a solid solution.

Acidic monosaccharides become incorporated into calcite single crystals

“…Interestingly, calcite-GlcA crystals exhibited the elongated scalenohedral-like morphology (Figure 1c) resembling that observed for calcite crystals containing high amounts of incorporated amino acids, in particular aspartic acid. [23] As also seen in Figure 1, calcite-GalA crystals reached a size of about 1 mm, whereas calcite-GlcA crystals were about 100 µm in size. These first observations indirectly indicated that MSs probably become incorporated into the lattice of calcite crystals.…”

“…Previous reports on biogenic and synthetic calcite crystals containing organic inclusions have clearly verified the concept of a direct correlation between the magnitude of induced lattice distortions and the amount of incorporated organics. [21][22][23] We may therefore conclude that also in the present case, the MS concentrations within crystals displaying larger lattice distortions clearly exceed 1 wt%.…”

“…Our recent study of the growth of calcite crystals in the presence of amino acids and under hydrothermal (HT) conditions indicated that both high temperature and high pressure promote the incorporation of amino acids and lead to significantly higher levels of incorporation than those achieved under ambient conditions. [23] We, therefore, attempted to further increase the (Figure 2c, f), similar to that observed in the case of aspartic incorporation [23] via the HT method. We employed synchrotron high-resolution powder X-ray diffraction (HRPXRD) to precisely determine the lattice parameters of crystals grown in the presence of GlcA or GalA via both VD and HT methods.…”

“…However, as observed by the magnitude of the diffraction peak shifts, the level of incorporation is higher in the case of the HT than of the VD method of synthesis, a phenomenon we have already reported in the case of aspartic acid incorporation. [23] Moreover, while (104) and (006) diffraction peaks demonstrate a shift towards lower 2θ upon incorporation of MSs via the VD and HT methods (Figure 3a,b and Figure S3, S4), in the case of calcite crystals grown via the HT method solely, the (110) diffraction peak shifts in the opposite direction and towards higher 2θ angles (Figure 2c,d). These findings imply that whereas the calcite lattice expands in all crystallographic directions when incorporation occurs under ambient conditions (i.e.…”

“…[15] Many of these protein mixtures have been tested in vitro for their ability to inhibit the precipitation of CaCO3 [16] or to modify the size and morphology of calcite crystals. [17] More surprisingly, proteins, [18][19][20] or their most elementary building blocks, amino acids, [21][22][23][24] were found to induce anisotropic lattice distortions in their calcitic, aragonitic or vateritic crystalline hosts. Several synthetic assays also showed that other molecules can get incorporated into calcite such as gels, [25,26] diblock copolymer particles [27] and many more.…”