  Dehydration of water from surface Mg2+ is most likely the rate-limiting step
in the dolomite growth at low temperature. Here, we investigate the role of
polysaccharide in this step using classical molecular dynamics (MD)
calculations. Free energy (potential of mean force, PMF) calculations have been
performed for water molecules leaving the first two hydration layers above the
dolomite (104) surface under the following three conditions: without catalyst,
with monosaccharide (mannose) and with oligosaccharide (three units of
mannose). MD simulations reveal that there is no obvious effect of
monosaccharide in lowering the dehydration barrier for surface Mg2+. However,
we found that there are metastable configurations of oligosaccharide, which can
decrease the dehydration barrier of surface Mg2+ by about 0.7-1.1 kcal/mol. In
these configurations, the molecule lies relatively flat on the surface and
forms a bridge shape. The hydrophobic space near the surface created by the
non-polar -CH groups of the oligosaccharide in the bridge conformation is the
reason for the observed reduction of dehydration barrier.
