Negishi Yuichi, Nobusada Katsuyuki, Tsukuda Tatsuya
Research Center for Molecular-Scale Nanoscience and Department of Theoretical Studies, Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan.
J Am Chem Soc. 2005 Apr 13;127(14):5261-70. doi: 10.1021/ja042218h.
Small gold clusters (approximately 1 nm) protected by molecules of a tripeptide, glutathione (GSH), were prepared by reductive decomposition of Au(I)-SG polymers at a low temperature and separated into a number of fractions by polyacrylamide gel electrophoresis (PAGE). Chemical compositions of the fractionated clusters determined previously by electrospray ionization (ESI) mass spectrometry (Negishi, Y. et al. J.Am. Chem. Soc. 2004, 126, 6518) were reassessed by taking advantage of freshly prepared samples, higher mass resolution, and more accurate mass calibration; the nine smallest components are reassigned to Au10(SG)10, Au15(SG)13, Au18(SG)14, Au22(SG)16, Au22(SG)17, Au25(SG)18, Au29(SG)20, Au33(SG)22, and Au39(SG)24. These assignments were further confirmed by measuring the mass spectra of the isolated Au:S(h-G) clusters, where h-GSH is a homoglutathione. It is proposed that a series of the isolated Au:SG clusters corresponds to kinetically trapped intermediates of the growing Au cores. The relative abundance of the isolated clusters was correlated well with the thermodynamic stabilities against unimolecular decomposition. The electronic structures of the isolated Au:SG clusters were probed by X-ray photoelectron spectroscopy (XPS) and optical spectroscopy. The Au(4f) XPS spectra illustrate substantial electron donation from the gold cores to the GS ligands in the Au:SG clusters. The optical absorption and photoluminescence spectra indicate that the electronic structures of the Au:SG clusters are well quantized; embryos of the sp band of the bulk gold evolve remarkably depending on the number of the gold atoms and GS ligands. The comparison of these spectral data with those of sodium Au(I) thiomalate and 1.8 nm Au:SG nanocrystals (NCs) reveals that the subnanometer-sized Au clusters thiolated constitute a distinct class of binary system which lies between the Au(I)-thiolate complexes and thiolate-protected Au NCs.
通过在低温下对Au(I)-SG聚合物进行还原分解，制备了由三肽谷胱甘肽（GSH）分子保护的小金簇（约1纳米），并通过聚丙烯酰胺凝胶电泳（PAGE）将其分离成多个组分。利用新制备的样品、更高的质量分辨率和更精确的质量校准，对先前通过电喷雾电离（ESI）质谱法测定的分级簇的化学成分（Negishi, Y.等人，《美国化学会志》，2004年，126卷，6518页）进行了重新评估；九个最小的组分被重新指定为Au10(SG)10、Au15(SG)13、Au18(SG)14、Au22(SG)16、Au22(SG)17、Au25(SG)18、Au29(SG)20、Au33(SG)22和Au39(SG)24。通过测量分离出的Au:S(h-G)簇的质谱进一步证实了这些归属，其中h-GSH是同型谷胱甘肽。有人提出，一系列分离出的Au:SG簇对应于生长中的金核的动力学捕获中间体。分离出的簇的相对丰度与抗单分子分解的热力学稳定性密切相关。通过X射线光电子能谱（XPS）和光谱学探测了分离出的Au:SG簇的电子结构。Au(4f) XPS光谱表明，在Au:SG簇中，金核向GS配体有大量的电子给予。光吸收和光致发光光谱表明，Au:SG簇的电子结构得到了很好的量子化；块状金的sp带的胚胎根据金原子和GS配体的数量有显著的演化。将这些光谱数据与硫代苹果酸金（I）钠和1.8纳米Au:SG纳米晶体（NCs）的光谱数据进行比较，结果表明，硫醇化的亚纳米级金簇构成了一类独特的二元体系，它介于硫醇金（I）配合物和硫醇保护的金纳米晶体之间。
