Chemistry Reference
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hydrodynamic diameter similar to that of a surface-exchanged species.
278
In this study, poly(styrene-
co
-maleic anhydride) (PSMA) was adding to
a chloroform solution of QDs, and then the polymer converted to an
amphiphilic species
in situ
by addition of either ethanolamine or a poly-
ether amine (essentially an amine-terminated PEG) as ring-opening agents,
leaving pendant carboxylic acid groups and either an alcohol-terminated
short chain or, in the case of the polyether amine, a PEG group. Following
this, the particles could simply be transferred to water. Small QDs phase-
transferred using ethanolamine as a ring-opening agent showed a reduc-
tion in emission quantum yields, whereas larger particles actually
displayed a signi
d
n
1
y
4
n
g
|
6
cant increase in emission. The QDs passivated with the
polyether amine/PSMA displayed exceptional stability across a wide range
of pHs, whereas
the ethanolamine/PSMA particles appeared stable
primarily at pH 5
7. The ethanolamine-functionalised particles were,
however, extremely small; the hydrodynamic diameter of CdSe/ZnS parti-
cles (displaying an emission peak at 551 nm) exhibited a diameter of 14.8
nm when phase-transferred using a PEGylated DHLA as described earlier.
Phase transfer of the same material with PSMA/ethanolamine resulted in
a diameter of 13.4 nm, which is unusually small. However, phase transfer
using the more stable polyether amine resulted in a diameter of 17.8 nm,
and ethanolamine-functionalised poly(maleic anhydride-
alt
-1-ODE) resul-
ted in notably larger particles of 24.5 nm. This highlights that PSMA
functionalised with the shorter chain can in fact rival phase-transferred
material produced by surfactant exchange. The exchanged material does,
however, maintain the PEG pendant group, so one must choose between
size and surface functionality. Particles with the polyether amine group
were also found to exhibit reduced non-speci
-
.
c binding in cell labelling,
again attributable to the PEG group.
The use of a poly(maleic anhydride) backbone was extended by slightly
varying the structure of the materials by reacting a fraction of the anhydride
rings (75%) on poly(isobutylene-
alt
-maleic acid) with DDA to form the hydro-
phobic intercalating arms of the polymer, rather than relying on the polymer
already having
a hydrophobic
pendant
side
chain attached to
the backbone.
279
This le
25% of the maleic acid groups available for further
conjugation, which was carried out to PEG, proteins, biotin, dyes and sugars.
Importantly, the hydrophobic side chains and other groups could be added to
the polymer backbone before the polymer was wrapped around a nanoparticle.
An interesting and unusual use of QDs within a micelle is the prepara-
tion of a QD
inorganic chelate composite with extreme sensitivity to nitric
oxide, and important biological free radicals. This composite is unusual as
it does not directly involve a surface modi
-
cation as TOPO-capped QDs are
phase-transferred into a cetyltrimethylammonium cationic micelle, which
was electrostatically linked with tris(
N
-(dithiocarboxy)sarcosine)iron(
III
).
A
uorescence was found to have
quenched due to overlapping electronic spectra of the ligand with the QD
emission. Addition of a NO-donating compound resulted in restoration of
er synthesis of the composite, QD
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