Amino Acid and Oligopeptide Effects on Calcium Carbonate Solutions

Biological
organisms display
sophisticated control of nucleation and crystallization of minerals.
In order to mimic living systems, deciphering the mechanisms by which
organic molecules control the formation of mineral phases from solution
is a key step. We have used computer simulations to investigate the
effects of the amino acids arginine, aspartic acid, and glycine on
species that form in solutions of calcium carbonate (CaCO3) at lower and higher levels of supersaturation. This provides net
positive, negative, and neutral additives. In addition, we have prepared
simulations containing hexapeptides of the amino acids to consider
the effect of additive size on the solution species. We find that
additives have limited impact on the formation of extended, liquid-like
CaCO3 networks in supersaturated solutions. Additives control
the amount of (bi)­carbonate in solution, but more importantly, they
are able to stabilize these networks on the time scales of the simulations.
This is achieved by coordinating the networks and assembled additive
clusters in solutions. The association leads to subtle changes in
the coordination of CaCO3 and reduced mobility of the cations.
We find that the number of solute association sites and the size and
topology of the additives are more important than their net charge.
Our results help to understand why polymer additives are so effective
at stabilizing dense liquid CaCO3 phases.