Probing the Structure and Charge State of Glutathione-Capped Au₂₅(SG)₁₈ Clusters by NMR and Mass Spectrometry

Abstract

Despite the recent crystallographic determination of the crystal structure of Au(25)(SCH(2)CH(2)Ph)(18) clusters, the question--whether all thiolate-capped, 25-atom gold clusters adopt the same structure, regardless of the types of thiols (e.g., long-chain alkylthiols, aromatic thiols, or other functionalized ones)--still remains unanswered. To crystallize long-chain or bulky ligand (e.g., glutathione)-capped Au(25)(SR)(18) clusters has proven to be difficult due to the major amorphousness caused by such ligands; therefore, one needs to seek other strategies to probe the structural information of such gold clusters. Herein, we report a strategy to probe the Au(25) core structure and surface thiolate ligand distribution by means of NMR in combination with mass spectrometry. We use glutathione-capped Au(25)(SG)(18) clusters as an example to demonstrate the utility of this strategy. One-dimensional (1D) and two-dimensional (2D) correlation NMR spectroscopic investigation of Au(25)(SG)(18) reveals fine spectral features that explicitly indicate two types of surface binding modes of thiolates, which is consistent with the ligand distribution in the Au(25)(SCH(2)CH(2)Ph)(18) cluster. Laser desorption ionization (LDI) mass spectrometry analysis shows that Au(25)(SG)(18) exhibits an identical ionization and core fragmentation pattern with phenylethylthiolate-capped Au(25) clusters. The charge state of the native Au(25)(SG)(18) clusters was determined to be -1 by comparing their optical spectrum with those of [Au(25)(SCH(2)CH(2)Ph)(18)](q) of different charge states (q = -1, 0). Taken together, our results led to the conclusion that glutathione-capped Au(25)(SG)(18) clusters indeed adopt the same structure as that of Au(25)(SCH(2)CH(2)Ph)(18). This conclusion is also valid for other types of thiolate-capped Au(25) clusters, including hexyl- and dodecylthiolates. Interestingly, the chiral optical responses (e.g., circular dichroism (CD) signals in the visible wavelength region) from the Au(25)(SG)(18) clusters seem to be imparted by the chiral glutathione ligands because no similar CD signals were observed in Au(25)(SCH(2)CH(2)Ph)(18).

Protein stabilized Au nanoclusters: spectral properties and photostability

“…Currently, considerable research efforts are directed towards investigation of Au NCs synthesis [4][5][6][7][8][9][10], structure [7,11,12], optical properties [4,[13][14][15][16], photostability [17][18][19][20][21] and possible applications for material sensing [5,[22][23][24] as fluorescence [25,26] and dual-modality imaging contrast agents [27,28]. However, colloidal stability, photostability, dependence of optical properties on temperature, interaction of BSA-Au NCs with biomolecules are still poorly investigated.…”

Thiolate‐Protected Aun Nanoclusters as Catalysts for Selective Oxidation and Hydrogenation Processes

“…This work is largely built upon our recent success in preparing atomically monodisperse, robust gold-thiolate nanoclusters. [12][13][14][15] Such ultrasmall nanoparticles are composed of a well-defined metal core with a precisely controlled, specific number of gold atoms, formulated as Au n (SR) m , where, n and m represent the respective number of gold atoms and thiolate ligands. In this work, we explore them as homogeneous or supported catalysts for selective oxidation and hydrogenation processes, respectively.…”

“…[ [12][13][14][15] Electrospray ionization mass spectrometry (ESI-MS) shows true monodispersity of Au 25 and Au 38 nanoclusters, see Figure 1A and 1B, respectively. The Au 144 (SR) 60 nanoclusters (1.6 nm in diameter) were prepared by a modified version of a literature method.…”

Isolation and structural characterization of magic silver clusters protected by 4-(tert-butyl)benzyl mercaptan

“…For Au:SR clusters, it is known that 40 the C-S bond of the protecting thiolates is selectively and completely dissociated by laser irradiation. [21][22][23][24] Since similar laserinduced dissociation was also reported for Ag:SR clusters, 13(b)(c) this decrease in mass can be ascribed to desorption of the arylgroup of SBB due to C-S bond dissociation. A decrease in the 45 mass of 18 kDa corresponds to dissociation of ~120 BBS aryl groups.…”