Chemistry Reference
In-Depth Information
FIGURE 19.10
A schematic illustration of immobilisation of [Ru(nbd)Cl]
2
complex into apoferritin cage followed by polymerisation of
phenylacetylene catalysed by the ferritin. The polymerisation reaction occurs site-specifically inside of the ferritin cage. (From
Uchida, Kang,
Reichhardt, Harlen, & Douglas, 2010
. Copyright 2010 with permission from Elsevier.)
Besides the interior cavity, the exterior surface of the protein cages can be modified without altering the
interior characteristics. This allows the protein cages to be delivered to a targeted tissue in vivo. The interface
between subunits can also be utilised to create chimeric protein cages. Utilizing such ideas, the ferritin
superfamily (including the Dps proteins) has been exploited for the development of a broad range of materials
with applications from biomedicine to electronics. For example, the two approaches can be combined to
target gadolinium-loaded ferritin to tumour cells for use as a contrast agent, as we describe in more detail in
Chapter 22.
Formation of Magnetite in Magnetotactic Bacteria
Ferrihydrite is not the only mineral form of iron that is found in nature. Magnetite, the Fe
2
þ
/Fe
3
þ
mineral (Fe
3
O
4
),
is found in magnotactic bacteria as well as in bees, birds, and fish, where it is believed to function as a navigational
magnetic sensor. Some bacteria can form pseudo-single crystals of akaganeite (
b
-FeOOH), many millimetres long
in a polysaccharide-template-directed process, and goethite (
a
FeOOH) is found in the radular teeth of limpets
and in some human haemosiderins.
Magnetotactic bacteria are a group of microorganisms which synthesise nano-sized crystals of magnetite
which enable them to use geomagnetic fields for direction sensing. They were discovered by Richard Blakemore
in 1975, and at the time were regarded as a kind of curiosity
the idea that bacteria would swim North or South
according to some kind of internal compass seemed as absurd as asking if there really was a tRNA to incorporate
selenocysteine into proteins (by the way, both turned out subsequently to be correct).
Confronted with the often expensive methods used to synthesise nanomaterials, which involve the use of
hazardous chemicals, there is a growing concern to develop environmental-friendly and sustainable methods for
the synthesis of nanoparticles of different compositions, sizes, shapes, and controlled dispersity, particularly using
a 'green chemistry' approach which interconnects nanotechnology and microbial biotechnology.
Magnetic iron oxide particles, such as magnetite (Fe
3
O
4
)ormaghaemite(
e
-Fe
2
O
3
), are widely used in
medical and diagnostic applications such as magnetic resonance imaging (MRI), cell separation, and drug
delivery. They offer great technological potential since they can be conveniently collected with an external
magnetic field. Magnetotactic bacteria synthesise membrane-enveloped magnetic particles (magnetosomes)
with well-controlled size and morphology, which can be readily dispersed in aqueous solutions, making them
ideal biotechnological materials. They are formed under incredibly mild conditions compared with the usual
synthetic methods, and easily outperform artificial materials. Hence, there has been great interest in the
formation of magnetite and magnetosomes with a view to their exploitation in biomedical applications, which
we review here.
Although magnetotactic bacteria (MTB) have diverse morphologies, they are characterised by the clustering
of the genes required for magnetosome formation (
Komeili, 2007; Matsunaga and Okamura, 2003
)
, which are
g
