Tiopronin Gold Nanoparticle Precursor Forms Aurophilic Ring Tetramer

Abstract

In the two step synthesis of thiolate-monolayer protected clusters (MPCs), the first step of the reaction is a mild reduction of gold(III) by thiols that generates gold(I) thiolate complexes as intermediates. Using tiopronin (Tio) as the thiol reductant, the characterization of the intermediate Au4Tio4 complex was accomplished with various analytical and structural techniques. Nuclear magnetic resonance (NMR), elemental analysis, thermogravimetric analysis (TGA), and matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) were all consistent with a cyclic gold(I)-thiol tetramer structure, and final structural analysis was gathered through the use of powder diffraction and pair distribution functions (PDF). Crystallographic data has proved challenging for almost all previous gold(I)-thiolate complexes. Herein, a novel characterization technique when combined with standard analytical assessment to elucidate structure without crystallographic data proved invaluable to the study of these complexes. This in conjunction with other analytical techniques, in particular mass spectrometry, can elucidate a structure when crystallographic data is unavailable. In addition, luminescent properties provided evidence of aurophilicity within the molecule. The concept of aurophilicity has been introduced to describe a select group of gold-thiolate structures, which possess unique characteristics, mainly red photoluminescence and a distinct Au-Au intramolecular distance indicating a weak metal-metal bond as also evidenced by the structural model of the tetramer. Significant features of both the tetrameric and aurophilic properties of the intermediate gold(I) tiopronin complex are retained after borohydride reduction to form the MPC, including gold(I) tiopronin partial rings as capping motifs, or “staples”, and weak red photoluminescence that extends into the Near Infrared region.

Incremental Binding Energies of Gold(I) and Silver(I) Thiolate Clusters

“…The values we calculated for E inc and E av shown in Table 1 are in agreement with H€ akkinen, Gr€ onbeck, and co-workers. 6,8 Our cyclic clusters are also in agreement with experimentally known gold structures found by Bau, 2 Simpson et al, 9 LeBlanc et al, 10 In comparison, the PBE monomer fragmentation energies of the dimers are 1.17 eV for the cis configuration and 1.18 eV for the trans configuration. At the TPSS/TZP level of theory, these fragmentation energies are predicted to be 1.11 and 1.13 eV, respectively.…”

Direct Gold Plating Selectively on UV Modified Polymer Film Using Tiopronin-Gold

“…Characterization of TPN-Au.-The broadened NMR spectrum and absorption at 340 nm in the UV-vis spectrum were appropriate for the polymeric TPN-Au that Simpson et al 20 characterized as a cyclic tetramer shown in Figure 1. Formation of the TPN-Au tetramer was confirmed by observation of the deprotonated molecular ion in the MALDI mass negative ion spectrum and molecular ion with 1-4 potassium atoms in the positive ion spectrum.…”

“…The particle diameter was consistent with gold nano-cluster formation by collapse of the tetramer ring. 20 By indirect observation, the 20-40 nm Au particles from the suspension could also selectively adhere to the modified COP surface sufficiently, allowing catalyst adsorption and adhesive electroless gold plating. Irradiation of PEN film also resulted in formation of a 30-40 nm deep oxygen rich modified layer.…”

“…Preparation of TPN-Au and the electroless plating bath.-The TPN-Au (structure shown in Figure 1) was synthesized by a procedure based on the method reported by Brust et al 19,20 A tetrachloroauric acid solution, prepared by dissolving gold (20.0 g, 102 mmol) in aqua regia (75 ml hydrochloric acid and 25 ml nitric acid), was added to a 2 L aqueous solution of TPN (54.9 g, 337 mmol) and acetic acid (30.0 g, 500 mmol). Reduction of the Au(III) to Au(I) was accompanied by a color change from dark orange-red to clear and precipitation of TPN-Au.…”

Biomolecule-Coated Metal Nanoparticles on Titanium

“…The greater number of Au−S interactions in the 20AuMPG system is afforded by the smaller size and less bulky MPG ligand, resulting in a higher cumulative Au−S surface interaction area. 29 When comparing the size of the particles imaged by SEM, it is determined that the size of the 20AuBSA nanoparticles is 9.6 ± 2.3 nm ( Figure 1A,B), while the 20AuMPG nanoparticles are 4.7 ± 2.0 nm in size ( Figure 1C,D). The distribution statistics are based on thousands of particles from multiple SEM images of the same samples.…”