Biological Control on Calcite Crystallization by Polysaccharides (original) (raw)
Related papers
Advanced Functional Materials, 2018
Coccolith-associated polysaccharides (CAPs) are thought to be a key part of the biomineralization process in coccolithophores, however their role is not fully understood. We have used two different systems that promote different polymorphs of calcium carbonate to show the effect of CAPs on nucleation and polymorph selection in vitro. Using a combination of time-resolved cryo-transmission electron microscopy (cryoTEM) and scanning electron microscopy (SEM), we examined the mechanisms of calcite nucleation and growth in the presence of the intracrystalline fraction containing CAPs extracted from coccoliths from Gephyrocapsa oceanica and Emiliania huxleyi, two closely related coccolithophore species. The CAPs extracted from G. oceanica were shown to promote calcite nucleation in vitro, even 2 under conditions favouring the kinetic products of calcium carbonate, vaterite and aragonite. This was not the case with CAPs extracted from E. huxleyi, suggesting that the functional role of CAPs in vivo may be different between the two species. Additionally, high-resolution synchrotron powder X-ray diffraction (SXPD) revealed that the polysaccharide is located between grain boundaries of both calcite produced in the presence of the CAPs in vitro and biogenic calcite, rather than within the crystal lattice.
Coccolith biomineralisation studied with atomic force microscopy
Palaeontology, 2004
Biomineralisation can only be understood as an interplay between organic and mineral phases. With this objective, we conducted an investigation of coccoliths using atomic force microscopy (AFM), an ultra-high resolution technique that requires no surface coating and can be used in air or under solution at ambient conditions of temperature and pressure. The detailed morphology, crystal structure, organic scales and organic coating of the coccolith species Coccolithus pelagicus, Helicosphaera carteri and Oolithotus fragilis were investigated. The ®ne structure of coccoliths is very complex, with the calcite either being smooth, dominated by steps or tuberculate; organic cover can be either granular or ®brous. Behaviour of coccolith surfaces during dissolution is in¯uenced both by mineral and organic material and different surface types show variable resistance to dissolution. The organic coating protects element faces against etching. Through atomic resolution AFM, it is possible to establish the crystallographic structure of the distal shields of C. pelagicus and O. fragilis. Though elements of both species are dominated by stable crystal faces, there are important differences between them, with the external edge of elements being parallel to a cleavage direction in C. pelagicus but parallel to the atomic rows in O. fragilis. Thus, there is evidence that the biomineralisation of each species, and also of select areas of coccoliths of the same species, is markedly different.
Acidic Monosaccharides become Incorporated into Calcite Single Crystals**
Chemistry: A European Journal, 2020
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The adsorption of polysaccharides onto mineral surfaces: an acid/base interaction
International Journal of Mineral Processing, 2000
Natural polysaccharides such as starch, dextrin, guar gum, cellulose and their derivatives are promising non-toxic organic depressants. Although generally perceived as non-selective, these polymers have found use in commercial processes or have been tested in laboratories in practically all flotation systems involving every type of minerals. In this communication, the adsorption mechanisms of natural polysaccharides are reviewed, with the objective of promoting the wider applications of the polymers. While it seems generally accepted that natural polysaccharides interact with minerals via surface metal-hydroxylated species, an acidrbase interaction model between the natural polysaccharides and mineral surfaces is proposed to explain many observed adsorption and flotation phenomena. q Q. Liu . 0301-7516r00r$ -see front matter q 2000 Elsevier Science B.V. All rights reserved.
Calcite crystal growth orientation: implications for trace metal uptake into coccoliths
Mineralogical Magazine, 2008
Inorganic calcite precipitation experiments were conducted to determine whether inducing specific orientations of calcite crystal growth can cause the enrichment of cations larger than Ca. Malonic acid (CH 2 (COOH) 2 ), a di-carboxylic acid, was used to poison growth on acute kink sites, promoting growth on obtuse kink sites, causing calcite crystals elongated along their c-axes to form in a mechanism similar to that seen in the growth of E. huxleyi coccoliths. Calcite was precipitated with a range of malonic acid concentrations (0 to 10 À1 M), and 9610 À5 M of either SrCl 2 or MgCl 2 . The results show that calcite crystals precipitated in the presence of large malonic acid concentrations show significant elongation along the c axis, and suggest that increasing malonate concentrations corresponded with increasing D Sr . Experiments with 10 À1 M malonic acid caused elevated D Sr comparable to that predicted
Biophysical Journal, 2000
The mixture of EDTA-soluble proteins found in abalone nacre are known to cause the nucleation and growth of aragonite on calcite seed crystals in supersaturated solutions of calcium carbonate. Past atomic force microscope studies of the interaction of these proteins with calcite crystals did not observe this transition because no information about the crystal polymorph on the surface was obtained. Here we have used the atomic force microscope to directly observe changes in the atomic lattice on a calcite seed crystal after the introduction of abalone shell proteins. The observed changes are consistent with a transition to (001) aragonite growth on a (1014) calcite surface.
Growth modification of seeded calcite using carboxylic acids: Atomistic simulations
Journal of Colloid and Interface Science, 2010
Molecular dynamics simulations were used to investigate possible explanations for experimentally observed differences in the growth modification of calcite particles by two organic additives, polyacrylic acid (PAA) and polyaspartic acid (p-ASP). The more rigid backbone of p-ASP was found to inhibit the formation of stable complexes with counterions in solution, resulting in a higher availability of p-ASP compared to PAA for surface adsorption. Furthermore the presence of nitrogen on the p-ASP backbone yields favorable electrostatic interactions with the surface, resulting in negative adsorption energies, in an upright (brush conformation). This leads to a more rapid binding and longer residence times at calcite surfaces compared to PAA, which adsorbed in a flat (pancake) configuration with positive adsorption energies. The PAA adsorption occurring despite this positive energy difference can be attributed to the disruption of the ordered water layer seen in the simulations and hence a significant entropic contribution to the adsorption free energy. These findings help explain the stronger inhibiting effect on calcite growth observed by p-ASP compared to PAA and can be used as guidelines in the design of additives leading to even more marked growth modifying effects.
Crystal Growth & Design, 2015
We investigate the effect of gelatin, agarose, and silica hydrogel with and without magnesium in the growth medium on calcite single crystal growth and aggregate formation. We characterize the hydrogel and the mineral by cryo-scanning electron microscopy (SEM), high-resolution SEM, and electron backscatter diffraction (EBSD). We image the pristine hydrogel fabric and the fabric of hydrogel incorporated into the mineral. We visualize the hydrogel− mineral interface and investigate the effect of the hydrogels on calcite micro-and mesostructure in the gel/calcite composits. We compare hydrogel fabrics in biomimetic hybrid composites with biopolymer matrices and networks in biological carbonate tissues of bivalves, gastropods, brachiopods, and corraline red algae. In Mg-free environments, silica gel has very little effect on crystal morphology and arrangement; the gel/calcite composite that forms is a single gradient mesocrystal. Agarose and gelatin hydrogels influence mineral organization in gel/calcite aggregates, and these consist of very few subunits separated by hydrogel membranes. With Mg added to the growth medium, large and small angle boundaries highly increase in number: silica gel/calcite aggregates consist of partial spherulites with mesocrystalline subentities; agarose, gelatin gel/calcite aggregates are regular spherulites, and their subentities are single crystals. Thus, calcite crystal organization is influenced by accumulative split growth provoked by incorporation of magnesium.
Molecular dynamics simulation investigation of hexanoic acid adsorption onto calcite (1014) surface
In this paper we report the results of classical molecular dynamics (MD) simulation of hexanoic acid adsorption on calcite (1014) surface plane using Pavese and AMBER force fields for calcite and hexanoic acid, respectively. Pair correlation function, strictly suggests a well-structured adsorption. Density profile indicates the adsorption occurs through double-bonded O atom of the acid head group by direct interaction with Ca atom at calcite surface. Adsorption orientation of H and double-bonded O atoms was found to be as lock and key with respect to calcite surface Ca and O atoms, facilitating an effective adsorption. Adsorption time evolution indicates that O atom adsorption is accompanied by wobbling between two Ca sites. Hence, in spite of H-bonding by acid group, the surface atoms matrix enforces adsorption with some dynamics. Hexanoic acid molecules adopt a well-defined adsorption layer immediate to the surface patterned by the calcite surface structure. The adsorption energy was estimated to be almost 187 times that of octane, a relevant nonpolar fraction of crude oil. These are useful information on the microscopic behavior and adsorption mechanism of crude oil polar fraction in calcite reservoir. The density profile over simulation time steps is proposed as a practical tool to study the dynamics of adsorbed layer in the same way as the most surface spectroscopic method like surface scattering spectroscopy do but in dynamic mode sub-picosecond scale. The intrinsic orientation of double-bonded O and H atoms of the head-group are presented by bivariate maps which helps establishing the key factors of calcite surface activity.