Article,
Polymorph Switching in the Calcium Carbonate System by Well-Defined Alginate Oligomers
Cryst. Growth Des., 11 (2): 520--529 (February 2011)
DOI: 10.1021/cg101337g
Abstract
Functional biominerals formed in living organisms require high control
of inorganic phase crystal polymorphs, morphology, size, and orientation.
Such control is often governed by both soluble and insoluble functional
molecules, where the soluble ones usually are highly negatively charged
proteins and polymers. Here, the effect of alginate and well-defined
alginate oligomers on calcium carbonate crystallization is explored,
by seeded and unseeded experiments, to separate the effects of the
additive on the crystal growth process from the effect on nucleation.
The experiments were done at well-defined activity-based levels of
supersaturation, controlled pH and temperature. In the seeded experiments,
crystal growth of calcite, aragonite, and vaterite were studied separately,
and the observations were used to explain a switch in polymorphism
when alginate oligomers were present during the crystallization process.
Unseeded experiments showed that low concentrations of G-blocks (oligomers
of alpha-L-guluronic acid) switched the precipitation product from
aragonite and vaterite to calcite, at conditions that would normally
precipitate only aragonite or vaterite. This effect was explained
by growth inhibition of aragonite and vaterite, as shown by seeded
experiments in the presence of G-blocks. The growth rate of calcite
was not affected to the same extent, apart from the stabilization
of faces other than 104, which are usually expressed in additive
free systems. These observations may be used to design composite
materials at ambient conditions, inspired by the strategies nature
applies to control biomineral formation.
Tags
- acid;
- aragonite;
- biomimetic
- crystal-growth;
- crystallization;
- mechanism;
- mineralization;
- morphology;
- transformation
- vaterite;
- water;
