Smaller Calcite Lattice Deformation Caused by Occluded Organic Material in Coccoliths than in Mollusk Shell

Abstract

The growth and nucleation of biominerals are directed and affected by associated biological molecules. In this paper, we investigate the influence of occluded biomolecules on biogenic calcite from the coccolithophorid Pleurochrysis carterae and from chalk, a rock composed predominantly of fossil coccoliths. We compare the results with data on chalk from the extensively studied mussel Pinna nobilis that served as a control. Using high resolution synchrotron powder X-ray diffraction combined with in situ heating, the influence of organic compounds on the structure of the inorganic phase was probed. Two heating cycles allow us to differentiate the effects of thermal agitation and organic molecules. Single peak analysis and Rietveld refinement were combined to show significant differences resulting from the occluded biomolecules on the mineral phase in biogenic calcite in the mollusk shell and the coccolithophorids. These differences were reflected in lattice deformation (macrostrain), structure (microstrain), and atomic disorder distributions (δorganic). The influence of the biological macromolecules on the inorganic phase was consistently smaller in the P. carterae compared to P. nobilis. This suggests that the interaction between biomolecules and calcite is not as tight in the coccoliths as in the shell. Although the shape of chalk has been preserved over millions of years, no major influence on the crystal lattice was observed in the chalk samples.

Anisotropic Lattice Distortions in Biogenic Minerals Originated from Strong Atomic Interactions at Organic/Inorganic Interfaces

“…In support of this statement, we mention the measurements in coccoliths, [56] in which lattice distortions are close to zero, as compared with those in mollusk shells. In support of this statement, we mention the measurements in coccoliths, [56] in which lattice distortions are close to zero, as compared with those in mollusk shells.…”

“…[15,55] The maximum value (about 0.25% in Pinna nobilis shell) is fully comparable with that in biogenic aragonite. [56] We will discuss these findings in Section 6. In sea urchin parts, [15] lattice distortions are less pronounced than in mollusk shells.…”

Pyrophosphate-Inhibition of Apatite Formation Studied by In Situ X-Ray Diffraction

“…The final lattice constants do not display any significant dependency on pyrophosphate concentration indicating that only slight macrostrain is inflicted upon the crystals even though very specific interactions take place. This is in contrast to the impact of organic additives on CaCO 3 biominerals [33][34][35][36][37], ZnO [38,39], and apatite [25].…”

Formation and mosaicity of coccolith segment calcite of the marine algae Emiliania huxleyi

“…, Frølich et al. ) but are pushed aside during coccolith maturation. When the coccolith is complete, acidic polysaccharides form an organic sheath that covers the calcite and is located next to the coccolith vesicle membrane (Henriksen et al.…”

“…Thus, like hard tissue formation in extracellular matrices, the start of coccolith formation is also a biopolymer templated process as the first set of calcite crystals nucleate onto an organic template, the base plate. However, distinct from extracellular matrices, biopolymers are not occluded into the calcite of the coccolith (Hoffmann et al 2014b, Frølich et al 2015 but are pushed aside during coccolith maturation. When the coccolith is complete, acidic polysaccharides form an organic sheath that covers the calcite and is located next to the coccolith vesicle membrane (Henriksen et al 2004).…”