C O M M U N I C A T I O N S
prevent their spontaneous aggregation and/or surface poisoning by
the resulting carboxylates. This high level of stability has never
yet been reported for any type of polymer-stabilized Au NCs.
After the reaction, the clusters were successfully separated by
decantation at a temperature higher than the clouding point such
as 60 °C. This simple procedure allows almost quantitative recovery
of the cluster. When reused, they showed catalytic activity that was
very similar to that of the virgin counterpart. Furthermore, the
catalytic activity was maintained at least until the sixth use, with
the oxidation of benzyl alcohol occurring almost quantitatively
(>99%) in each run (Table 1). In contrast, Au NCs using PVP
Figure 2. Temperature dependence of transmittance for aqueous solutions
could not be reused because of their negative aggregation during
the catalytic reaction.7
,8
(1.0 wt %) of star poly(EOEOVE) and Au NCs supported by star poly-
(EOEOVE), monitored with a UV-vis spectrometer at 500 nm.
In conclusion, we have developed a simple preparation for stable
and durable Au nanoclusters of less than 4 nm using thermosensitive
vinyl ether star polymers obtained by living cationic polymerization.
The resulting clusters effectively catalyzed the aerobic oxidation
of alcohols such as benzyl alcohol. The clusters were easily
separated from the reaction mixture by utilizing their thermosen-
sitive nature, allowing for repeated reuse.
Table 1. Reusability and Versatility of Au NCs
Acknowledgment. This study was partly sponsored by the Shiga
Prefecture, JST, Osaka University (Global COE), CREST program
by JST, IMS (the Joint Studies Program, 2005-2007), and MEXT.
Supporting Information Available: Experimental procedures, UV
diagrams, and TEM images after the oxidation reaction. This material
is available free of charge via the Internet at http://pubs.acs.org.
a,b
[
Substrate]0 ) 16.7 mM, [Au] ) 0.33 mM, [KOH] ) 50 mM, at 27
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7
of EOEOVE and isobutyl vinyl ether or PVP, which did undergo
aggregation during the reaction. In these star-polymer-stabilized
Au NCs, gold clusters are likely to exist in hydrophobic layers (the
core region of a star polymer). Such isolation of Au NCs would
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J. AM. CHEM. SOC.
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