We investigated the kinetics of conversion of hemin to
β-hematin
in aqueous-acetate medium in the absence and in the presence of two
concentrations of chloroquine by using 11 reported kinetic equations.
The two best kinetic equations are the combination of order 1 and
Avrami and the combination of second order and logistic equations,
based on the statistical parameter variance and overall errors. The
best fitted equations are composed of two terms from which we model
the formation of β-hematin as the result of two processes: the
availability of reactive precursors and the formation of nucleation
and growth sites. The crystals exhibit needle-like morphologies about
760-nm-long and 140-nm-wide. However, the increment of chloroquine
favors the formation of crystal twinning with nonhomogenous distribution,
crystals with lower sizes of similar heights and widths, and crystals
symmetrically tapered at the ends of the needles. The lattice volumes,
obtained from Rietveld analysis of powder X-ray diffraction patterns,
were not regularly affected by chloroquine. The main IR absorption
bands did not appreciably change in positions nor in intensities with
varying chloroquine concentration. However, important changes were
observed in the 2000–4000 cm–1 region. We
used density functional theory calculations to understand these changes.