# Distinct Physical Properties of β-Hematin in Two Synthetic Media: Compelling Evidence

## TL;DR

This study shows that the physical properties of β-hematin crystals vary depending on the synthetic medium used, which is crucial for malaria research and drug development.

## Contribution

The paper provides compelling evidence that synthesis media significantly influence the physicochemical properties of β-hematin.

## Key findings

- β-hematin synthesized in aqueous-acetate has needle-like particles with larger lattice parameters and paramagnetic properties.
- β-hematin in aqueous-oily medium has smaller particles, superparamagnetic behavior, and different surface composition.
- Mössbauer spectra reveal distinct spin relaxation times and iron oxidation states depending on the synthesis medium.

## Abstract

It is now widely accepted that detailed knowledge of
the physicochemical
characteristics of the β-hematin crystals, i.e., the synthetic
versions of the natural hemozoin crystals, is important for understanding
their formation, the design of antimalarial medicines, and malarial
diagnosis. We report that the overall physical properties exhibited
by β-hematins greatly depend on the synthetic media. Here, we
synthesize β-hematin from hemin in aqueous-acetate and in aqueous-oily
media and characterize their properties by several techniques. Infrared
spectra clearly demonstrate the formation of β-hematin in both
media. The β-hematin crystals prepared in aqueous-acetate are
composed by needle-like particles with average lengths around 760–770
nm; their lattice parameters and unit cell volumes are larger than
those reported in the literature. They are paramagnetic at 300 K and
antiferromagnetic at very low temperatures. Their Mössbauer
spectra at 298 K, 77 K, and 10 K are consistent with the presence
of high-spin Fe (III) and are less asymmetric as a result of the occurrence
of fast spin–spin relaxation time, and their surface composition
is complex, showing the presence of a multiplicity of iron oxidation
and spin states (although with a majority of high-spin Fe3+ ions). In comparison, the β-hematin crystals prepared in aqueous-oily
medium have significantly smaller lengths (ca. 560 nm) and slightly
larger unit cell volume in comparison to the previous sample. The
magnetic measurements show that they are affected by superparamagnetism
and paramagnetism at 298 K and the coexistence of weakly ferromagnetic
or possibly ferrimagnetic and paramagnetic phases at 80 K. Their Mössbauer
spectra at 298 K, 77 K, and 10 K, also consistent with the presence
of high-spin Fe (III), show longer spin–spin relaxation times,
and their surface composition is also complex containing less surface
OH– groups and higher amounts of Fe (II) ions in
low- and high-spin states. The observed differences are discussed
in relation to the specific formation conditions present in the synthesis
medium. The results reported here are of outmost importance for understanding
how the physicochemical properties of β-hematins depend on the
synthesis conditions.