Chemistry Reference
In-Depth Information
oxide nanoparticles to water.
273
In this case, a monomer of the maleic anhy-
dride group was functionalised with PEG by reacting the polymer with amine-
terminated PEG methyl ether, leaving a pendant PEG group and a single
carboxylic acid group for further functionalisation to biological molecules of
interest. The resulting phase-transferred nanoparticles were stable in water
over a wide range of pH, and found to be up to 60 nm in size (the parent
nanoparticles were up to 40 nm in diameter). Further studies on this system
included the use of poly(maleic anhydride-
alt
-1-ODE) to encapsulate a range
of QDs,
274
and it was found that the hydrodynamic diameter could be tuned by
altering the molecular weight of the PEG side chain, with sizes ranging from
24 to 46 nm. Impressively, the quantum yields of the encapsulated QDs were
found to be 34.5
d
n
1
y
4
n
g
|
6
-
54.7% when in water. The particles were also extremely
stable to further harsh reaction conditions, such as sonication at 70
C. The
particles were successfully used in labelling breast cancer cells, with no non-
speci
c binding observed. The toxicity of the particles was explored in human
breast cancer cells, and a relationship between cell death and particle
concentration was found, although the presence of the PEG group was
found to signi
cantly reduce toxicity. Other groups also explored the use of
poly(maleic anhydride-
alt
-1-ODE) to phase-transfer iron oxide nano-
particles.
275
In this case, the particles were slightly larger than the QDs
described above (
ca.
16
-
21 nm) therefore a larger molecular weight polymer
was used (30
50 kDa). Again, individual polymer chains were found to
interact only with a single nanoparticle.
Other functional groups have been added to poly(maleic anhydride-
alt
-1-
ODE) when used with iron oxide, such as the thermoresponsive polymer
poly(
N
-isopropylacrylamide).
276
In this case, the water-soluble particles of
iron oxide capped with the polymer gra
-
.
ed onto the maleic anhydride
backbone showed a large di
erent temperatures,
consistent with the collapse of the polymer chains at lower temperatures. The
particles could easily be isolated with a bar magnet at higher temperatures,
whereas the smaller particle/polymer composites stayed in solution at lower
temperatures.
Work on poly(maleic anhydride-
alt
-1-ODE)
277
was also carried out because
of the commercial discontinuation of the tetradecene-based polymer, but
highlighted a new puri
erence in size at di
cation step based on ultracentrifugation as a key part
of the phase transfer, as the previous use of size exclusion chromatography
did not work to the same degree. The need for a more dilute solution of
nanoparticles and an increased amount of polymer to ensure encapsulation
of a single nanoparticle was also discussed and other factors such as the need
for prolonged sonication were highlighted. The hydrodynamic diameter of
several materials, before and a
er encapsulation, was investigated and as
might be expected, the use of the ODE-based polymer almost doubled the
diameter of the particle, although the use of the tetradecene-based polymer
increased the diameter even more.
The use of a maleic anhydride group to functionalise a polymer back-
bone was extended by Lees
et al.
, producing water-soluble QDs with a
nal
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