Nucleation of One Polymorph by Another Lian Yu, School of Pharmacy and Dept of Chemistry, University of Wisconsin - Madison 50 µm
R05
Contrary to common view, crystallization in polymorphic systems is not necessarily defined by the initial nucleation. Fast-nucleating polymorph may grow slowly (Y04 in the example to the left), allowing fast-growing polymorph (R05) to nucleate on it and dominate the product.
Y04
enantiomorph AR or AS
S
N
liquid of R or S
O O
TZF liquid of R and S (racemic)
se ed in g
We elucidated how crossnucleation is controlled by thermodynamic and kinetic factors and how it can aid the discovery of new polymorphs. In the example to the right, crossnucleation is used to nucleate the rarest of the three outcomes of crystallizing a racemic liquid – the solid solution of enantiomers.
B
B
A
A
R
S racemic compound RCI
solid solution SS-0.5
RA/SB
RA/SB
SA/RB
SA/RB
