Screening the Incorporation of Amino Acids into an Inorganic Crystalline Host: the Case of Calcite

Abstract

Organisms have the ability to produce structures with superior characteristics as in the course of biomineralization. One of the most intriguing characteristics of biominerals is the existence of intracrystalline macromolecules.Despite several studies over the last two decades and efforts to mimic the incoporation of macromolecules synthetically, a fundamental understanding of the mechanism of incorporation is as yet lacking. For example, which of the common 20 amino acids are really responsible for the interaction with the mineral phase? Here a reductionist approach, based on high-resolution synchrotron powder diffraction and analytical chemistry, is utilized to screen all of these amino acids in terms of their incorporation into calcite. We showed that the important factors are amino-acid charge, size, rigidity and the relative pKa of the carboxyl and amino functional groups. It is also demonstrated that cysteine, surprisingly, interacts very strongly with the mineral phase and therefore, like acidic amino acids, becomes richly incorporated. The insights gained from this study shed new light on the incorporation of organic molecules into an inorganic host in general, and in particular on the biomineralization process.

Hybrid Gold Single Crystals Incorporating Amino Acids

“…After annealing, all samples exhibited diffraction peak narrowing (see Figure ) owing to the increase in coherence length and decrease in microstrain fluctuations. This was in contrast to our observations for biogenic crystals and for amino acid incorporation into synthetic calcite . The difference can probably be explained by the much higher diffusion rates of gold than of carbonates at these lower temperatures, allowing for an increase in crystallite size lowering the defect concentration in gold.…”

Additives Control the Stability of Amorphous Calcium Carbonate via Two Different Mechanisms: Surface Adsorption versus Bulk Incorporation

“…The c ‐lattice parameter showed an expansion for ACC B ‐3% as compared to ACC‐0% as evidenced by a shift of the 006 peak to larger d‐spacing (Δ d / d = 7.9 × 10 −4 ), while the a ‐ and b ‐lattice parameters showed shrinkage evidenced by a shift to lower d‐spacing for the 012 peak (Δ d / d = −8.4 × 10 −4 ), the 104 peak (Δ d / d = −2.2 × 10 −4 ), and the 110 peak (Δ d / d = −1.3 × 10 −3 ). These observations are similar to those reported for biogenic calcite crystals [ 22c ] and synthetic calcite incorporating amino acids. [ 22a ] The broadening of the diffraction peaks is typically ascribed to the decrease of the size of coherently scattering crystalline blocks and / or the increase of the microstrain fluctuations, [ 22c ] due to the smaller particle size of ACC and the degradation of intra‐crystalline organic macromolecules upon mild annealing treatments.…”

“…These observations are similar to those reported for biogenic calcite crystals [ 22c ] and synthetic calcite incorporating amino acids. [ 22a ] The broadening of the diffraction peaks is typically ascribed to the decrease of the size of coherently scattering crystalline blocks and / or the increase of the microstrain fluctuations, [ 22c ] due to the smaller particle size of ACC and the degradation of intra‐crystalline organic macromolecules upon mild annealing treatments. These results, together with the AAA and XPS data, confirm that pAsp molecules were mostly incorporated in the bulk of ACC B ‐ x % nanoparticles, whereas for ACC S ‐ x % samples they were present mainly at the surface of the nanoparticles.…”

Rapid Screening of Calcium Carbonate Precipitation in the Presence of Amino Acids: Kinetics, Structure, and Composition

“…The quantities of Val incorporated were very low, reaching a maximum of 0.09 mol %, and no trends were recorded with respect to occlusion and the solution conditions. That the amino acids with acidic side-chains occlude most efficiently is in good agreement with previous studies, and the data provide further confirmation that Asp incorporates significantly more readily than Glu …”