Chemistry Reference
In-Depth Information
quick selective desorption of the thiolate layers from the cluster surface. The
surviving Au cores underwent then a much slower energy minimization process
via structural rearrangement and were finally stabilized in the cuboctahedral struc-
ture and protected by triphenylphosphine in hexane environment. Interestingly, the
authors found that accompanied with the change of atomic structure, the character
of the electronic structure transits from semiconductor to metal-like, indicating the
strong structure-property relationship.
3.6 Au
15
Nanoclusters
Recently, Pradeep and coworkers [
65
,
66
] demonstrated a high-yield synthesis of
Au
15
nanoclusters anchored to cyclodextrin (CD) cavities via the core etching of
larger clusters. In a typical synthesis, Au nanoparticles protected by -SG ligands
were first synthesized. The synthesized Au nanoparticles were dissolved in water
containing excess amount of GSH and cyclodextrin and then heated at 70
C for
48 h. Finally, brown powders with intense red emission in the solid state were
obtained after centrifugation and freeze-dry treatment. Here, the excess GSH was
used as etchant and cyclodextrin acted as host cavities which trapped the
as-synthesized Au clusters and protected them from further core reduction
[
67
]. Well-defined optical absorption spectrum in aqueous solution with absorption
peaks at 318, 458, and 580 nm, which resembles the molecule-like absorption of
Au
15
SG
13
reported previously [
68
]. The characteristic UV-Vis spectrum together
with ESI-MS confirms that the formed species are Au
15
nanoclusters.
1
HNMRof
the as-prepared Au nanoclusters showed the presence of both -SG protection and
CD in the cluster products.
3.7 Au
18
Nanoclusters
Gold nanoclusters capped by glutathione and other similar ligands have been
synthesized and size-separated by Tsukuda's group [
68
,
69
]. In the work, a series
of fractions were separated from the original clusters by polyacrylamide gel
electrophoresis (PAGE), and the chemical compositions of the nine smallest
compositions were assigned to Au
10
(SG)
10
,Au
15
(SG)
14
,Au
18
(SG)
14
,Au
22
(SG)
16
,
Au
22
(SG)
17
,Au
25
(SG)
1
8, Au
29
(SG)
20
,Au
33
(SG)
22
, and Au
39
(SG)
24
, respectively,
by ESI-MS with high mass resolution and accurate mass calibration. Interestingly,
the most abundant compound with enhanced stability was found to be the
Au
18
(SG)
14
nanoclusters, although it also has been shown that the Au
25
(SG)
18
nanoclusters exhibited the highest stability against core etching [
70
]. Recently,
Dass and coworkers [
71
] synthesized a mixture of thiolated gold nanoclusters with
the most abundant cluster component of Au
18
(SR)
14
. In their synthesis, the usually
needed tetraoctylammonium bromide surfactant was eliminated by dissolving the
