The properties of atomically monodisperse noble metal nanoclusters (NCs) are intricately intertwined with their precise molecular formula. The vast majority of size-specific NC syntheses start from the reduction of the metal salt and thiol ligand mixture. Only in gold was it recently shown that ligand-exchange could induce the growth of NCs from one atomically precise species to another; a process of yet unknown reversibility. Here, we present a process for the ligand-exchange-induced growth of atomically precise silver NCs, in a biphasic liquid-liquid system, which is particularly of interest because of its complete reversibility and ability to occur at room temperature. We explore this phenomenon in-depth using Ag 35 (SG) 18

Solving the atomic structure of metallic clusters is fundamental to understanding their optical, electronic, and chemical properties. Herein we present the structure of the largest aqueous gold cluster, Au146(p-MBA)57 (p-MBA: para-mercaptobenzoic acid), solved by electron diffraction (MicroED) to subatomic resolution (0.85 Å) and by X-ray diffraction at atomic resolution (1.3 Å). The 146 gold atoms may be decomposed into two constituent sets consisting of 119 core and 27 peripheral atoms. The core atoms are organized in a twinned FCC structure whereas the surface gold atoms follow a C2 rotational symmetry about an axis bisecting the twinning plane. The protective layer of 57 p-MBAs fully encloses the cluster and comprises bridging, monomeric, and dimeric staple motifs. Au146(p-MBA)57 is the largest cluster observed exhibiting a bulk-like FCC structure as well as the smallest gold particle exhibiting a stacking fault.

The structure and bonding of the gold-subhalide compounds Au144Cl60[z] are related to those of the ubiquitous thiolated gold clusters, or Faradaurates, by iso-electronic substitution of thiolate by chloride. Exact I-symmetry holds for the [z] = [2+,4+] charge-states, in accordance with new ESI-MS measurements and the predicted electron shell filling. The High symmetry facilitates analysis of the global structure as well as the bonding network, with some striking results.

Gold nanoclusters (AuNC) with well-defined structure and arrangement possess particular physical and functional properties. AuNC that differ only by less than 1 nm in diameter corresponding to one atomic layer show different structural, optical and physicochemical properties in a size-dependent mode, making their analytical characterization a challenge. An integrative approach with UV-Vis, dynamic light scattering and zeta-potential in combination with high-performance analytical techniques such as multi-wavelength analytical ultracentrifugation and electrospray ionization mass spectrometry were used to separate and determine their specific hydrodynamic diameter, partial abundance, molecular weight and

Collisional cooling rates of infrared excited ions are measured in a quadrupole ion trap (QIT) mass spectrometer at different combinations of temperature and pressure. Measurements are carried out by monitoring fragmentation efficiency of leucine enkephalin as a function of irradiation time by an infrared laser after a short excitation and incrementally increasing cooling periods. Cooling rates are observed to be directly related to bath gas pressure and inversely related to bath gas temperature. The cooling rate at typical ion trap operating pressure (1 mTorr) and temperature (room T) is faster than can be measured. At elevated temperature and the lowest pressure used for the studies, the rate of collisional cooling becomes negligible compared to the rate of radiative cooling. or many years, collisional cooling has been used to damp the kinetic energies of trapped ions to improve the performance of the quadrupole ion trap mass spectrometer [1][2][3]. After formation in, or injection into, the quadrupole ion trap, ions undergo collisions with the bath gas, causing their trajectory to shrink to the center of the ion trap. This more compact cloud of ions increases sensitivity and resolution when using mass-selective instability [2] or resonance ejection [4] for mass analysis. A bath gas pressure of 1 mTorr is the commonly used operating pressure, and all commercial ion traps operate at ambient temperature.Although collisional cooling of the ion's kinetic energy is helpful for ion trap performance, cooling of the ion's internal energy also occurs; this may or may not be desired. This internal cooling can reduce fragmentation efficiency and thus be a detriment when trying to dissociate ions using "slow heating" techniques [5] such as infrared multiphoton photodissociation (IRMPD). IRMPD has been successfully implemented in a quadrupole ion trap [6 -15]. IRMPD works by increasing the internal energy of an ion by multiple photon absorption. When a bath gas pressure of 1 mTorr is used, the transfer of the ion's internal energy to the bath gas via collisions may occur at a faster rate than the rate of energy-transfer to the ions by photon absorption. The ratio of the rate of energy loss via collisional cooling to energy gain via photon absorption depends on the ion's absorption cross-section, the power of the laser, trapping volume temperature, and pressure. If the rate of energy loss by collisions is greater than the rate of energy gained by photon absorption, the ions irradiated will not dissociate. It is due to this reason that IRMPD is not practical for peptide dissociation in a quadrupole ion trap at the typical operating pressure and roomtemperature [6,15]. Most of the examples of IRMPD in the quadrupole ion trap have been accomplished by lowering the bath gas pressure. At decreased pressures, however, the performance of the QIT is adversely affected. Sensitivity is decreased by approximately an order of magnitude [6], and resolution is also decreased.An alternate approach to overcome the problem of collisional c...

Experimental and theoretical evidence reveals the resilience and stability of the larger aqueous gold clusters protected with p-mercaptobenzoic acid ligands (pMBA) of composition Aun(pMBA)p or (n, p). The Au144(pMBA)60, (144, 60), or gold-144 aqueous gold cluster is considered special because of its high symmetry, abundance, and icosahedral structure as well as its many potential uses in material and biological sciences. Yet, to this date, direct confirmation of its precise composition and total structure remains elusive. Results presented here from characterization via high-resolution electrospray ionization mass spectrometry on an Orbitrap instrument confirm Au102(pMBA)44 at isotopic resolution. Further, what usually appears as a single band for (144, 60) in electrophoresis (PAGE) is shown to also contain the (130, 50), recently determined to have a truncated-decahedral structure, and a (137, 56) component in addition to the dominant (144, 60) compound of chiral-icosahedral structure. This finding is significant in that it reveals the existence of structures never before observed in all-aromatic water-soluble species while pointing out the path toward elucidation of the thermodynamic control of protected gold nanocrystal formation.

Short-thiolate-protected Au144(SR)60 clusters are capped by 12 distinct ligand types of 5-fold equivalence.

Here we report on the identification and applications of an aqueous 29-atom silver cluster stabilized with 12 lipoate ligands, i.e. Ag 29 (R-α−LA) 12 or (29,12), wherein R-α− LA = R-α-lipoic acid, a natural dithiolate. Its uniformity is checked by HPLC-ESI-MS and analytical ultracentrifugation, which confirms its small dimension (∼3 nm hydrodynamic diameter). For the first time, this cluster has been detected intact via electrospray ionization mass spectrometry, allowing one to confirm its composition, its [3-] charge-state, and the 8-electron shell configuration of its metallic silver core. Its electronic structure and bonding, including T-symmetry and profound chirality in the outer shell, have been analyzed by DFT quantum-chemical calculations, starting from the known structure of a nonaqueous homologue. The cluster is effective against Methicillin-Resistant Staphylococcus aureus bacteria (MRSA) at a minimum inhibitory concentration (MIC) of 0.6 mg-Ag/mL. A preformed Candida albicans fungal biofilm, impermeable to other antifungal agents, was also inhibited by aqueous solutions of this cluster, in a dose−response manner, with a half-maximal inhibitory concentration (IC 50 ) of 0.94 mg-Ag/mL. Scanning electron micrographs showed the post-treatment ultrastructural changes on both MRSA and C. albicans that are characteristic of those displayed after treatment by larger silver nanoparticles.