Asymmetric Transformation of Monolayer-Protected Gold Nanoclusters via Chiral Phase Transfer
Asymmetric Transformation of Monolayer-Protected Gold Nanoclusters via Chiral Phase Transfer
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DOI：
10.1021/jp803858r
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发表时间：
2008-10-01
影响因子：
3.7
通讯作者：
Kimura, Keisaku
中科院分区：
文献类型：
--
作者：
Yao, Hiroshi;Fukui, Toshiyuki;Kimura, Keisaku
外消旋青霉胺保护的金纳米团簇的相转移是通过用手性麻黄正离子疏水阴离子纳米团簇表面(即手性相转移)，使光学不活跃的金纳米团簇发生不对称变换或对称性破缺来实现的：相转移纳米团簇在金属基电子过渡区表现出明显的光学活性。麻黄正离子含有R，S绝对构型的手性取代基，因此也可以通过对映体(S)或(R)-青霉胺保护的金纳米团簇与手性阳离子的相转移而生成“纳米团簇非对映异构体”。在相转移时，金纳米团簇的吸收光谱几乎不变，而它们的圆二向色性(CD)信号在金属基电子跃迁区域显示出显著的变化。根据不对称转变的金纳米团簇的光学/手性响应以及模型量子化学计算，诱导的光学活性很可能是由于表面立体结构带来的配位体不对称场。
Phase transfer of aqueous racemic penicillamine-protected gold nanoclusters into chloroform is achieved by hydrophobizing the anionic nanocluster surface with a chiral ephedrinium cation (that is, chiral phase transfer), yielding asymmetric transformation or symmetry breaking of the optically inactive gold nanoclusters: The phase-transferred nanoclusters display appreciable optical activity in the metal-based electronic transition region. The ephedrinium cation contains chiral substituents with R,S absolute configuration, so that "nanocluster diastereomers" also can be produced via the phase transfer of enantiopure (S)- or (R)-penicillamine-protected gold nanoclusters with the chiral cations. Upon phase transfer, absorption spectra of the gold nanoclusters are almost invariant, whereas their circular dichroism (CD) signals exhibit a significant change in the metal-based electronic transition region. On the basis of the optical/chiroptical responses of the asymmetrically transformed gold nanoclusters as well as model quantum chemical calculations, the induced optical activity is most likely due to the ligand dissymmetric field brought about by the surface stereostructures.