Bimetallic silver-gold clusters by matrix-assisted laser desorption/ionization

Abstract

Pure gold clusters (Au n ϩ ) were produced up to the cluster size of n ϭ 100 by matrix-assisted laser desorption/ionization (MALDI). The mass spectrum of the resulting clusters showed alteration in the ion intensity at odd-even clusters size. On the other hand, intensity drops at cluster size predicted by the jellium model theory was also observed. Positively and negatively charged bimetallic silver-gold clusters were produced under MALDI conditions from the mixture of HAuCl 4 /silver trifluoroacetate and the 2-(4-hydroxyphenylazo)benzoic acid (HABA) matrix. A linear correlation was found between the intensity ratio of Au n Ag m ϩ to Au nϩ1 Ag mϪ1 ϩ cluster ions and the molar ratio of the gold to silver salt. It was observed that the composition and the distribution of the clusters can be varied with the molar ratio of the silver and gold salts. It was also found that the resulting cluster sizes obey the lognormal distribution. The variation of the atom types building up the cluster and/or the composition, as well as the size of the cluster offers various possibilities to engineer their properties for specific technological and scientific demands. However, to achieve these specific goals much information on the physical and chemical properties of the clusters as the function of their composition and size should be gained. Mass spectrometric methods provide a unique experimental tool for the investigation of the electronic and geometric properties of small-size metal clusters [6].In the past decades several methods were explored to induce gas-phase generation of metal clusters, and most of these techniques were based on the evaporation of metals by heating [7,8], or using laser ablation [9 -11] and ion-bombardment [12][13][14][15]. The production and investigation of binary silver-gold [2,16,17] and those of the pure silver [12][13][14]18] and gold clusters [12,13] has been reported by several research groups. However, in contrast to the information available on the pure silver and gold clusters, only very limited experimental [16,17] and theoretical studies [19] on the properties of small size silver-gold clusters have been reported. Recently, the generation of silver-cluster ions in matrix-assisted laser desorption/ionization (MALDI) [20,21] was reported using silver salts and various matrixes [22][23][24]. In a previous paper [24] we have shown that both positively and negatively charged silver clusters up to the size of 200 can be effectively produced from silver ions under MALDI conditions. It was noted that considerable reduction of Ag ϩ takes place in the plume and the matrices enhance the formation of silver clusters. As a continuation of our work, we utilized this method for the generation of pure gold clusters and for the production of mixed binary goldsilver clusters. To our best knowledge we are the first to apply the MALDI method to produce pure gold and bimetallic Au-Ag cluster ions. The present report shows that the resulting distribution of the binary gold-silver clusters can be effectively chan...

Clusters of Monoisotopic Elements for Calibration in (TOF) Mass Spectrometry

“…Clusters of monoisotopic elements provide simple spectra with many monoisotopic peaks covering the mass range of interest with regular mass spacing. In this work, we discuss the calibration of mass spectra by clusters of red phosphorus, which is already established in our laboratory [6,[10][11][12][13][14][15][16], and compare it with calibration by gold clusters generated directly on the target by laser desorption ionization (LDI)-MS of various materials, including gold foil [17], various types of gold nanoparticles (AuNPs), chloroauric acid (HAuCl 4 ), a mixture of 2-(4-hydroxyphenylazo) benzoic acid and HAuCl 4 [18], and polyvinylpyrrolidone-stabilized AuNPs [19]. Gold clusters provide simple and fast determination of accurate mass compared with common calibration standards, such as peptides or proteins.…”

“…Kéki et al described the generation of positively charged gold clusters up to m/z 18,000 in positive reflectron ion mode, but they identified only single isotopic peaks for clusters with masses up to 3000 Da and reported the presence of hydride-type ions like Au n H + [18]. Furthermore, they did not provide a detailed evaluation and statistical analysis.…”

Mild route to generate gaseous metal anions

“…The formation of gaseous metal anions by decomposition of a salt in which the metal is initially present in cationic form is a rare chemical process. [6] Metal anions emerging from the linear quadrupole region of the mass spectrometer according to the procedure described bear lower kinetic energies than the anions generated by other high-energy processes. [7][8][9][10][11][12][13] Most previously described alkali anion generating methods require sophisticated instrumentation therefore not amenable to simple bench-top applications.…”

Binding Interactions and Raman Spectral Properties of Pyridine Interacting with Bimetallic Silver–Gold Clusters

“…[5] Three studies of anionic photoelectron spectroscopy (PES) on Au m Ag n À clusters have been reported very recently. [6][7][8] Theoretical studies of neutral gold-silver clusters have been reported recently by Bonacic-Koutecky et al [2,9,10] and Kim and co-workers, [11] who investigated the geometric and electronic structures of such bimetallic clusters. On the basis of density functional theory (DFT) calculations, they noted two effects in bimetallic clusters: 1) stable structures of small bimetallic clusters tend to remain planar; 2) the difference in electronegativity results in charge transfer (CT) from silver to gold atoms, resulting in a partial positive charge residing on the silver atoms.…”