posted on 2020-04-01, 16:33authored byRobert Stepić, Lara Jurković, Ksenia Klementyeva, Marko Ukrainczyk, Matija Gredičak, David M. Smith, Damir Kralj, Ana-Sunčana Smith
In many living organisms,
biomolecules interact favorably with
various surfaces of calcium carbonate. In this work, we considered
the interactions of aspartate (Asp) derivatives, as models of complex
biomolecules, with calcite. Using kinetic growth experiments, we investigated
the inhibition of calcite growth by Asp, Asp2, and Asp3.This entailed the determination of a step-pinning growth
regime as well as the evaluation of the adsorption constants and binding
free energies for the three species to calcite crystals. These latter
values are compared to free energy profiles obtained from fully atomistic
molecular dynamics simulations. When a flat (104) calcite surface
is used in the models, the measured trend of binding energies is poorly
reproduced. However, a more realistic model comprised of a surface
with an island containing edges and corners yields binding energies
that compare very well with experiments. Surprisingly, we find that
most binding modes involve the positively charged ammonium group.
Moreover, while attachment of the negatively charged carboxylate groups
is also frequently observed, it is always balanced by the aqueous
solvation of an equal or greater number of carboxylates. These effects
are observed on all calcite features including edges and corners,
the latter being associated with dominant affinities to Asp derivatives.
As these features are also precisely the active sites for crystal
growth, the experimental and theoretical results point strongly to
a growth inhibition mechanism, whereby these sites become blocked,
preventing further attachment of dissolved ions and halting further
growth.