Chiral Monolayer-Protected Bimetallic Au鈥揂g Nanoclusters: Alloying Effect on Their Electronic Structure and Chiroptical Activity

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• 作者：Ryota Kobayashi ; Yoshiyuki Nonoguchi ; Akito Sasaki ; Hiroshi Yao
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：July 17, 2014
• 年：2014
• 卷：118
• 期：28
• 页码：15506-15515
• 全文大小：526K
• ISSN：1932-7455

文摘

Chiral glutathione (GSH)-protected bimetallic Au鈥揂g nanoclusters (AuAg(SG)) are synthesized by the reduction of mixtures of Au and Ag salts at the feed mole ratio of Au/Ag = 3/1 in the presence of GSH and isolated by gel electrophoretic separation, yielding a family of magic-numbered bimetallic Au鈥揂g nanoclusters. The PAGE pattern similarity between Au(SG) and AuAg(SG) as well as the analyses based on small-angle X-ray scattering and X-ray photoelectron spectroscopy (XPS) allow comparisons of their chemical compositions for each family of nanoclusters, and the fractioned nanocluster compounds (three samples) are identified as Au_12.2Ag_2.8(SG)₁₃, Au_14.4Ag_3.6(SG)₁₄, and Au_17.6Ag_7.4(SG)₁₈. The XPS study also suggests that (i) incorporation of Ag heteroatoms into smaller-sized Au nanoclusters is less favorable and (ii) Ag heteroatoms preferentially occupy sites on the cluster鈥檚 core (including the core-surface and center) rather than the peripheral semiring shell. Optical spectroscopy shows that the electronic structures of Au nanoclusters are significantly modulated by incorporation of Ag atoms. Interestingly, the bimetallic Au鈥揂g nanocluster compounds exhibit weaker circular dichroism (CD) responses than those of the corresponding Au counterparts. Such a decrease in chiroptical responses can be explained in terms of the increased geometrical isomers that are formed by statistical distribution of Ag heteroatoms in the nanocluster because an increased number of possible configurations is expected to give the average in the CD response with positive and negative bands of different optical isomers.