A Quasi-Time-Resolved CryoTEM Study of the Nucleation of CaCO3under Langmuir Monolayers
- 28 February 2008
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 130 (12), 4034-4040
- https://doi.org/10.1021/ja710416h
Abstract
Calcium carbonate biomineralization uses complex assemblies of macromolecules that control the nucleation, growth, and positioning of the mineral with great detail. To investigate the mechanisms involved in these processes, for many years Langmuir monolayers have been used as model systems. Here, we descibe the use of cryogenic transmission electron microscopy in combination with selected area electron diffraction as a quasi-time-resolved technique to study the very early stages of this process. In this way, we assess the evolution of morphology, polymorphic type, and crystallographic orientation of the calcium carbonate formed. For this, we used a self-assembled Langmuir monolayer of a valine-based bisureido surfactant (1) spread on a CaCl2-containing subphase and deposited on a holey carbon TEM grid. In a controlled environment, the grid is exposed to an atmosphere containing NH3 and CO2 (the (NH4)2CO3 diffusion method) for precisely determined periods of time (reaction times 30−1800 s) before it was plunged into melting ethane. This procedure allows us to observe amorphous calcium carbonate (ACC) particles growing from a few tens of nanometers to hundreds of nanometers and then crystallizing to form [00.1] oriented vaterite. The vaterite in turn transforms to yield [10.0] oriented calcite. We also performed the reaction in the absence of monolayer or in the presence of a nondirective monolayer of surfactant containing an oligo(ethylene oxide) 2 head group. Both experiments also showed the formation of a transient amorphous phase followed by a direct conversion into randomly oriented calcite crystals. These results imply the specific though temporary stabilization of the (00.1) vaterite by the monolayer. However, experiments performed at higher CaCl2 concentrations show the direct conversion of ACC into [10.0] oriented calcite. Moreover, prolonged exposure to the electron beam shows that this transformation can take place as a topotactic process. The formation of the (100) calcite as final product under different conditions shows that the surfactant is very effective in directing the formation of this crystal plane. In addition, we present evidence that more than one type of ACC is involved in the processes described.Keywords
This publication has 47 references indexed in Scilit:
- Structural adaptability in an organic template for CaCO3 mineralizationCrystEngComm, 2007
- Asprich mollusk shell protein: in vitro experiments aimed at elucidating function in CaCO3 crystallizationCrystEngComm, 2007
- When is template directed mineralization really template directed?CrystEngComm, 2003
- Polymer-Controlled Growth Rate of an Amorphous Mineral Film Nucleated at a Fatty Acid MonolayerLangmuir, 2002
- Aligned Growth of Calcite Crystals on a Self-Assembled MonolayerAdvanced Materials, 2002
- Oriented crystallization of calcite single crystals grown underneath monolayers of tetracarboxyresorc[4]arenesCrystEngComm, 2002
- Templated Crystallisation of Calcium and Strontium Carbonates on Centred Rectangular Self-Assembled Monolayer SubstratesChemistry – A European Journal, 1998
- Porphyrin Amphiphiles as Templates for the Nucleation of Calcium CarbonateJournal of the American Chemical Society, 1997
- Controlled crystallization of CaCO3 under stearic acid monolayersNature, 1988
- Cryo-electron microscopy of vitrified specimensQuarterly Reviews of Biophysics, 1988