C O M M U N I C A T I O N S
Figure 5. Suzuki coupling reaction using Pd nanoparticles.
Palladium is the most important catalyst for carbon-carbon bond
formation, of which Suzuki, Heck, and Stille coupling are examples.
Water-dispersible Pd nanoparticles offer an opportunity here for
green chemistry. The reactivity of aqueous Pd nanoparticless was
investigated using the Suzuki coupling reaction (Figure 5). When
Figure 3. Hydrodynamic radius data of (a) Au, (b) Fe2O3, (c) CdSe/ZnS,
d) phosphine oxide gel in water.
(
4-iodotoluene and phenylboronic acid were reacted in the presence
of 2 mol % water-dispersed Pd nanoparticles, a 97% yield of the
product was obtained. In the second recycle reaction, the yield
decreased to 65%, which is comparable to the reactivity of the
second recycle reaction in organic solvent (71%). A small amount
of black aggregate was also observed, as in organic solvent systems.
We have not investigated the potential biological applications but
expect that PEG-phosphine oxide gel-stabilized nanoparticles could
be used for biomedical imaging of lymph nodes because the
hydrodynamic radii are 15-20 nm.
In conclusion, we have developed a phosphine oxide gel using
bis(dichlorophosphino)ethane and poly(ethylene glycol) that can
be used to transfer various nanoparticles from organic solvents to
water. These aqueous nanoparticles have physical properties and
reactivities comparable to those in organic solvent.
Acknowledgment. This work was supported by the post-
doctoral fellowship program of the Korea Science & Engineering
Foundation, the U.S. National Science Foundation-Materials Re-
search Science and Engineering Center program under grant DMR-
9
0
808941, the U.S. National Institutes of Health grant R33 EB-
0673, and by the Institute for Collaborative Biotechnologies
through grant DAAD19-03-D-0004 from the U.S. Army Research
Office.
Supporting Information Available: Experimental details of syn-
thetic procedure of phosphine oxide gel, ligands exchange. This material
is available free of charge via the Internet at http://pubs.acs.org.
Figure 4. TEM images of Fe2O3 in hexane (a) and water (b); Tl weighting
(
TR ) 100 ms, TE ) 3 ms) (c) and T2 weighting TR ) 1 s, TE ) 41 ms) (d)
in MRI image of Fe2O3 in water; UV spectra of Au NPs (e); absorbance
and photoluminescence spectra of CdSe/ZnS QDs (f).
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