Subnanometer clusters exhibit unique properties not observed at the bulk or nanometer scale. Many applications, however, require clusters to be monodisperse in size and composition. While substantial progress has been made empirically on producing specific-sized gold clusters using different ligands, the mechanisms of cluster formation remain insufficiently understood. Using high mass-resolution electrospray ionization mass spectrometry, we characterized the formation of cationic triphenylphosphine-ligated gold clusters [Au x (PPh3) y z+] in solution. Our data provides evidence that small hydrogen-containing intermediate “building blocks” (i.e., Au2(PPh3)2H+, Au4(PPh3)4H+, and Au7(PPh3)7H5 2+) are responsible for the growth of larger gold clusters (i.e., Au6(PPh3)6 2+ and Au8(PPh3)7 2+) over several hours. In addition, intermediate degradation and cluster growth are shown to be dependent on irradiation of the reacting solution with light. Specifically, the rate of growth of large clusters is demonstrated to scale with the intensity of light exposure. Complementary theoretical calculations were also performed that provide molecular-level insight into the nature of the bonding between the hydrogens and gold atoms in the intermediate Au-phosphine clusters. Collectively, our joint experimental and theoretical findings advance the understanding of the factors at play in the size-selective synthesis of ligated gold clusters in solution.

Triphenylphosphine (PPh3)-ligated gold nanoclusters are valuable for a number of potential applications due to their relative ease of synthesis and usefulness in forming advanced cluster architectures. While previous studies have reported cationic PPh3-ligated gold clusters with core sizes of Au1–4, Au6–11, and Au13–14, there has not been definitive identification by mass spectrometry of many larger clusters in the Au12–25 range. Herein, we survey a polydisperse solution of cationic PPh3-ligated gold clusters using high-mass-resolution (M/ΔM = 60,000) electrospray ionization mass spectrometry (ESI-MS). To improve the sensitivity and mass resolution of larger clusters for unambiguous identification, we increased the number of scan averages and reduced the range of mass collection windows to 200 m/z, thereby mitigating potential mass and ion abundance bias resulting from smaller “building block” gold clusters that are present in much higher abundance in solution. In addition to the previously reported clusters, we identify several new species including Au5(PPh3)5 +, Au12(PPh3)9HCl2+, Au15(PPh3)9Cl2+, Au16(PPh3)10Cl2 2+, Au17(PPh3)11 3+, Au18(PPh3)10 2+, Au19(PPh3)10Cl2+, Au20(PPh3)12H3 3+, Au21(PPh3)10Cl2+, and Au22(PPh3)10Cl2 2+, indicating that a full range of clusters between Au1–22 may be observed in a single polydisperse solution. Considering all of the clusters observed, our findings provide evidence that the Au12–14 size range is a critical transition point in cluster nucleation. While smaller clusters exhibit a 1:1 gold-to-ligand ratio, larger clusters (beginning Au12–14) feature additional gold atoms without an equal number of accompanying ligands. Our results support previous evidence in the literature indicating that the “magic number” icosahedral Au13 geometry is the smallest cluster size where a ligand-less central gold atom is coordinated by a complete shell of 12 surrounding ligated gold atoms, thereby creating a stable “one-shell” cluster. Furthermore, our findings reinforce growing evidence that ligands may be used to actively direct gold cluster size and abundance during synthesis. While for PPh3-ligated systems the most abundant species are Au6–9 clusters, we find that for related methyldiphenylphosphine (PPh2Me) and dimethylphenylphosphine (PPhMe2)-ligated systems the most abundant cluster sizes are Au10–11 and Au12–14, respectively. Together, we demonstrate that reducing the range of m/z collection windows and increasing the number of scan averages dramatically improves instrument sensitivity for cationic gold clusters, enabling thorough characterization of polydisperse solutions that is not possible using conventional techniques.

We employ ion mobility spectrometry and density functional theory to determine the structure of Au7(PPh3)7H5 2+ (PPh3 = triphenylphosphine), which was recently identified by high mass resolution mass spectrometry. Experimental ion-neutral collision cross sections represent the momentum transfer between the ionic clusters and gas molecules averaged over the relative thermal velocities of the colliding pair, thereby providing structural insights. Theoretical calculations indicate the geometry of Au7(PPh3)7H5 2+ is similar to Au7(PPh3)7 +, with three hydrogen atoms bridging two gold atoms and two hydrogen atoms forming single Au–H bonds. Collision-induced dissociation products observed during IMS experiments reveal that smaller hydrogen-containing clusters may be produced through fragmentation of Au7(PPh3)7H5 2+. Our findings indicate that hydrogen-containing species like Au7(PPh3)7H5 2+ act as intermediates in the formation of larger phosphine ligated gold clusters. These results advance the understanding and ability to control the mechanisms of size-selective cluster formation, which is necessary for scalable synthesis of clusters with tailored properties.

For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprodTo order this and other USGS information products, visit http://store.usgs.gov Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. AbstractThis report, prepared in cooperation with the Pennsylvania Department of Environmental Protection (PaDEP), the Eastern Pennsylvania Coalition for Abandoned Mine Reclamation, and the Dauphin County Conservation District, provides estimates of water budgets and groundwater volumes stored in abandoned underground mines in the Western Middle Anthracite Coalfield, which encompasses an area of 120 square miles in eastern Pennsylvania. The estimates are based on preliminary simulations using a groundwater-flow model and an associated geographic information system that integrates data on the mining features, hydrogeology, and streamflow in the study area. The Mahanoy and Shamokin Creek Basins were the focus of the study because these basins exhibit extensive hydrologic effects and water-quality degradation from the abandoned mines in their headwaters in the Western Middle Anthracite Coalfield. Proposed groundwater withdrawals from the flooded parts of the mines and stream-channel modifications in selected areas have the potential for altering the distribution of groundwater and the interaction between the groundwater and streams in the area.Preliminary three-dimensional, steady-state simulations of groundwater flow by the use of MODFLOW are presented to summarize information on the exchange of groundwater among adjacent mines and to help guide the management of ongoing data collection, reclamation activities, and water-use planning. The conceptual model includes high-permeability mine voids that are connected vertically and horizontally 1 USGS Pennsylvania Water Science Center.2 Independent consultant (deceased). within multicolliery units (MCUs). MCUs were identified on the basis of mine maps, locations of mine discharges, and groundwater levels in the mines measured by PaDEP. The locations and integrity of mine barriers were determined from mine maps and groundwater levels. The permeability of intact barriers is low, reflecting the hydraulic characteristics of unmined host rock and coal.A steady-state model was calibrated to measured groundwater levels and stream base flow, the latter at many locations composed primarily of discharge from mines. Automatic parameter estimation used MODFLOW-2000 with manual adjustments to constrain parameter values to realistic ranges. The calibrated model supports the conceptua...

Category: Arthroscopy; Ankle; Hindfoot; Sports Introduction/Purpose: Haglund's syndrome is a common cause of posterior heel pain and can be associated with retrocalcaneal bursitis and degenerative Achilles tendinosis. Open approaches for resection of the Haglund's lesion have long been employed in patients that fail to improve with conservative treatment. This often involves partial elevation of the Achilles insertion with reattachment. More recently, endoscopic surgical techniques have evolved, enabling more rapid rehabilitation with less tendon disruption. The decision on the surgical approach is influenced by the degree of insertional Achilles tendinosis with endoscopic techniques preferred in the absence of insertional pathology. The primary objective of this investigation was to report on a large series of patients treated surgically for symptomatic Haglund's lesions. Methods: We reviewed the outcomes of Haglund's syndrome surgical cases at our institution over a five-year period. We included cases with insertional Achilles tendinosis and retrocalcaneal bursitis related to the Haglund's lesion, but excluded revisions and cases involving flexor hallucis longus tendon transfers. We recorded patient demographics, sport and activity level, comorbidities, BMI, duration of symptoms, surgical technique, tourniquet time, rehabilitation protocol, postoperative complications, and duration of postoperative follow-up. We also reviewed relevant preoperative imaging and recorded the presence of Achilles insertional degenerative calcification or an insertional calcaneal enthesophyte on radiographs. We then prospectively administered questionnaires regarding return to sport and patient-reported outcome measures including the SANE, PASS, VISA-A and PROMIS (Physical Function, Pain Interference and Global Health domains). Results: In total, 17 of the 77 (22%) included cases were performed with the endoscopic surgical technique. Six patients underwent bilateral Haglund surgeries during the study period, accounting for 12 of the 77 cases. The open Haglund resection group had a higher rate of concomitant Achilles insertional degenerative calcification on radiographs and MRI (72%). In addition, the open group was older than the endoscopic group (average age 54 vs 45), had a higher rate of comorbidities, higher rate of postoperative complications, and a higher rate of return to the operating room for revision surgery (11% vs 0% for endoscopic). Seventeen patients were elite distance running athletes and were preferentially treated by endoscopic techniques (11/17, 64%). At 24-month follow-up, the majority of patients report return to baseline activity. Conclusion: Patients treated surgically for Haglund's syndrome and insertional Achilles tendinopathy generally have good outcomes. Outcomes are better for endoscopically treated patients compared to open treatment, although these patients tend to be younger, healthier, and have less Achilles tendons disease. Still, some degree of Achilles tendinopathy and limited intrasubstance calcification can be successfully addressed with the endoscopic technique. We are endeavoring to better define indications for, and limitations of, the endoscopic technique for insertional Haglund's disease.