Kinetic Stabilization of Growing Gold Clusters by Passivation with Thiolates

Abstract

Small gold clusters (<1 nm), protected by monolayers of glutathione, N-(2-mercaptopropionyl)glycine, or mercaptosuccinic acid, were prepared by reducing the corresponding Au(I)-thiolate polymers and were fractionated by size using polyacrylamide gel electrophoresis (PAGE). Mass analysis of the fractionated clusters revealed that their core sizes varied with the molecular structures of the thiolates. This finding indicates that the reduction of the Au(I)-thiolate polymers yields small clusters whose growth is kinetically hindered by passivation with thiolates. Optical spectra of the clusters with identical compositions exhibited different profiles depending on the thiolate molecular structures. This observation implies that deformation of the underlying gold cores is induced by interligand interactions.

The Effect of Ligand Denticity in Size‐Selective Synthesis of Calix[n]arene‐Stabilized Gold Nanoparticles: A Multitechnique Approach

“…[32] We can take the relative abundance of Au(a) together with S/Au ratios as an indirect measure of the nuclearity of the nanoparticles, thus allowing for a distinction to be made between s, m, and l. In fact, the experimental S/Au and Au(b)/Au(a) ratios are inversely pro- www.chemeurj.org portional to the size of the nanoparticles. This trend is consistent with the observation that the smaller the core size of the NPs, the larger the percentage of surface Au atoms bound to S. In addition to that, we could tentatively infer the nuclearity of the NPs by comparing the present results with the expected values in the notable cases of previously reported Au 11 , Au 13 On the basis of the data in Table 2 on the S/Au and Au(b)/Au(a) ratios, the nuclearities of 2 s and 3 s are both likely assigned to Au 11 or Au 13 (which can be hardly distinguished by XPS only), whereas 2 m NPs belong to highernuclearity species. As regards to 2 l, the S/Au and Au(b)/ Au(a) ratios are too small to find a correspondence with the above range of Au nuclearity, thus hinting at a larger range of nanoparticle diameters.…”

“…During elution, the desired (2 s) nanoparticles were visible as a dark brown band. Organic fraction: 64 %; 13 Nanoparticles stabilized with the tridentate calix [6]arene ligand 3 Cx 6 S 3 /Au (3 s): Complex 3 (1.57 g; 1 mmol corresponding to S/Au 3:1) was used as the gold passivating agent. The solid residue obtained after the centrifugation cycle required a further purification step to eliminate the large excess amount of free 3 that was contaminating the nanoparticles.…”

“…A chromatographic separation was accomplished using a 9:1 mixture of CH 2 Cl 2 /CH 3 OH as eluent. Organic fraction: 77 %; 13 …”

“…[12] Tsukuda et al later proposed that the isolated nanoparticles correspond to kinetically trapped intermediates of the growing gold core. [13] Nevertheless, the effect of the ligand "denticity" on the growth of the nanoparticles cores has not been systematically investigated yet. A perusal of the literature data only offers evidence that multidentate thiolate ligands can promote the preparation of more stable AuNPs, [14] but it could be also envisioned that multidentate ligands may also exert a relevant kinetic effect on the growth of the gold core.…”

On the structure of the Au18(SR)14 cluster

“…[1][2][3][4] Gold clusters covered by glutathione, Au n (SG) m , and other related ligands had been synthesized and size-separated by Tsukuda's group. 5,6 High mass resolution and accurate mass calibration in their electrospray ion mass spectrometry (ESI-MS) data allowed the exact determination of the cluster chemical composition. 5,6 The nine smallest compounds were assigned to cluster sizes with n : m ratio: 10 : 10, 15 : 13, 18 : 14, 22 : 16, 22 : 17, 25 : 18, 29 : 20, 33 : 22, and 39 : 24, respectively.…”