Precise Separation of Thiolate-Protected Alloy Clusters Based on High Resolution
Separation with Chromatography
Y. Niihori1, Y. Negishi1
1
Graduate School of Chemical Science and Technology/Tokyo University of Science, Japan
[email protected]
[Introduction] Thiolate-protected gold clusters have attracted a great deal of attention as new
functionalized nano-materials. It will be able to change their chemical/physical properties by
changing their size, surrounding ligands, or by doping with hetero-metal atoms in the core.
However, in many cases, the synthesis of cluster in solution system results in a mixture with
various distribution of composition. To control their chemical composition, precise separation
technique is required. High-Performance Liquid Chromatography (HPLC) is one of the best
way to separate these cluster-mixture [1-3]. Herein we report on precise separation by the
number of hetero-atoms in alloy-clusters protected by hydrophobic ligands (Aun−xAgx(SR)m)
by using reversed-phase chromatography (RPC).
[Result and Discussion] The mixture of alloy-clusters with different number of hetero Ag
atoms (Au38−nAgn(SR)24) were synthesized in metal exchange reaction [4]. Figure 1(a) shows
a chromatogram of Au38−nAgn(SR)24 cluster. Several peaks were collected and chemical
compositions were characterized by mass spectrometry. Figure 1(b) shows mass spectra of
each fractions (I - III). The peak attributed to Au36 Ag2 (SR)24 , Au 37 Ag(SR)24 , Au 38 (SR)24
were observed in each fractions with high purity. This suggest that precise separation
of alloy cluster was succeeded for the first time. Chromatographic separation also
revealed the polarity depended on the number of the hetero Ag atoms. In general,
component with high polar has faster retention time when the reversed -phase column
was used. Chromatogram suggests that doping more Ag atom can make their polarity
higher. Figure 1(c) shows absorption feature of each Ag doped Au 38 (SR)24 cluster. It
has revealed that doping Ag atom can slightly change their electronic structure. Our
method could be also applied another sized alloy-clusters (Au25−nAgn(SR)18 cluster). In
this way, characterization of precise alloy-cluster has been succeeded for the first time.
Figure 1: (a) Chromatogram of the mixture of alloy-clusters with different number of Ag
atoms (Au38−nAgn(SR)24). (b) Mass spectra of each fractions. (c) UV-Vis-NIR absorption
spectra of each fractions.
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