Central Au Research Articles

Selective recovery of Au from waste printed circuit board by water-soluble organic leaching: The key role of in situ bromine mediation and identificationof pathway

A large amount of gold in electronic waste (E-waste) is not properly recovered owing to the absence of efficient and safe leaching methods. Herein, we proposed the concept of ‘water-soluble organic Au leaching’ and created a new water-soluble organic leaching agent, WS NBS–DMF, by dissolving millimolar amounts of N-bromosuccinimide (NBS) and dimethylformamide (DMF) in water. Under mild conditions (25 ℃, pH 7.0), WS NBS–DMF achieved a 94.9 % leaching efficiency of Au for waste printed circuit board (WPCB) with limited leaching of base metals. The potent bromine radical (Br•) and ligands significantly contributed to Au complexation and oxidization via in situ bromine generation and radical initiation from WS NBS–DMF. The bidirectional hydrogen-bond effect of DMF facilitated the in situ bromine generation. Two Au(I) complexes ([AuBr2]- and [(NHS)AuBr]-) and an Au(III) complex ([(NHS)AuBr3]-) were confirmed as the Au leaching products by spectroscopy and mass spectrometry. Furthermore, reciprocal σ-donations between the Au center and ligands in the bonding orbitals enhanced the stability of the Au complexes, thereby promoting efficient Au leaching. Comparing with other leaching methods, this study of WS NBS–DMF provides a safe, economic and eco-friendly technique for efficient and selective gold recovery from e-waste.

Gold Tripyrrindione: Redox Chemistry and Reactivity with Dichloromethane.

The identification of ligands that stabilize Au(III) centers has led to the isolation of complexes for applications in catalysis, gold-based therapeutics, and functional materials. Herein, we report the coordination of gold by tripyrrin-1,14-dione, a linear tripyrrole with the scaffold of naturally occurring metabolites of porphyrin-based protein cofactors (e.g., heme). Tripyrrindione H3TD2 binds Au(III) as a trianionic tridentate ligand to form square planar complex [Au(TD2)(H2O)], which features an adventitious aqua ligand. Two reversible ligand-based oxidations of this complex allow access to the other known redox states of the tripyrrindione framework. Conversely, (spectro)electrochemical measurements and DFT analysis indicate that the reduction of the complex is likely metal-based. The chemical reduction of [Au(TD2)(H2O)] leads to a reactive species that utilizes dichloromethane in the formation of a cyclometalated organo-Au(III) complex. Both the aqua and the organometallic Au(III) complexes were characterized in the solid state by microcrystal electron diffraction (MicroED) methods, which were critical for the analysis of the microcrystalline sample of the organo-gold species. Overall, this study illustrates the synthesis of Au(III) tripyrrindione as well as its redox profile and reactivity leading to gold alkylation chemistry.

Study of charged particle multiplicity with centrality in Au+Au collisions at SNN = 200 GeV

We have carried out methods of study to find the correlation between charged particle multiplicity and collision centrality of Au+Au collisions at SNN = 200 GeV. We have studied the open data from the ALICE experiment and arrived at the conclusion that central collisions produced a greater number of charged particles than peripheral collisions. This is done by reconstructing the three silicon layers inside the inner tracking system of the detector and studying the change in two spatial variables between layers: pseudorapidity with range || < 1 and azimuthal angle with acceptance , which can then be input into the sideband method to find the final multiplicity of each event. The study provides an insight into the transient nature of the Quark Gluon Plasma (QGP) produced in collisions by exploring how collision aftermaths vary with different conditions of the partons, which hopefully adds to the understanding of matter under the strong force at extreme energy density.

Thermodynamic signatures and phase transitions in high-energy Au–Au collision

In this study, we systematically investigate the dynamics of various hadrons namely π +, π −, K +, K −, p, p¯ , Λ, Λ¯ , Ξ− and Ξ¯+ produced in central Au–Au collisions. We analyze data of AGS and RHIC, which span a broad range of collision energies, ranging from sNN = 1.9 to 200 GeV. To analyze the transverse momentum (p T ) and transverse mass (m T ) distributions, we employ a two-component standard distribution function, achieving a very good representation of the experimental data across these energy regimes. We extract key thermodynamic parameters, including the effective temperature T, the mean transverse momentum 〈p T 〉, and the initial temperature T i , and analyze their dependence on the values of collision energy and particle mass. Our findings reveal a distinct transition behaviour around sNN=19.6GeV . Below sNN=19.6GeV , the values of T, 〈p T 〉, and T i increase monotonically for all hadrons due to higher energy transfer into the system. Above this energy threshold, these extracted parameters plateau, suggesting that the additional energy is utilized as latent heat for phase transition rather than increasing the system’s temperature. These observations delineate two distinct regions: a hadron-dominated region at lower energies and a parton-dominated region at higher energies, each potentially indicative of different phases of matter, with the latter possibly signalling the onset of a quark–gluon plasma. The study thus provides critical insights into the complex interplay of thermodynamics, phase transitions, and particle interactions in high-energy Au–Au collisions.

DFT investigation on the application of a thiol-protected gold cluster Au12(SCH3)9+ toward adsorption of temozolomide

The adsorption behavior of a thiol-protected gold cluster Au12(SCH3)9+ to temozolomide (TMZ) has been investigated at the M06-2X-D3/6-311G(d, p)&LanL2dz//B3LYP-D3(BJ)/6-31G(d,p)&LanL2dz. Results show that TMZ prefers to combine with the central Au atom in the Au cluster via its O and N atoms, forming ionic Au–O and Au–N bonds, respectively. The calculated adsorption energies of TMZ on Au12(SCH3)9+ are − 44.43, −12.27, −43.59, and −10.01 kcal·mol−1 in the gas phase, water, acetic acid, and dimethyl sulfoxide, respectively. The interaction strength and mode between the TMZ drug and Au12(SCH3)9+ vary with different solution environments. Therefore, the solvent could influence the interaction of TMZ-Au12(SCH3)9+ complexes. Such a property of TMZ–Au12(SCH3)9+ could be applied to drug-delivery processes, which might contribute to improving the efficiency of this drug and reducing its toxic and side effects. Based on the natural population analysis and QTAIM analysis, noticeable charge transfer from TMZ to the Au cluster was observed, increasing the dipole moments of TMZ–Au12(SCH3)9+ complexes. We believe that this work could extend the applications of small Au-based clusters, especially thiol-protected gold clusters in drug-delivery processes.

Valence Tautomerism Induced Proton Coupled Electron Transfer:X-H Bond Oxidation with a Dinuclear Au(II) Hydroxide Complex.

We report the preparation and characterization of the dinuclear AuII hydroxide complex AuII 2(L)2(OH)2 (L=N,N'-bis (2,6-dimethyl) phenylformamidinate) and study its reactivity towards weak X-H bonds. Through the interplay of kinetic analysis and computational studies, we demonstrate that the oxidation of cyclohexadiene follows a concerted proton-coupled electron transfer (cPCET) mechanism, a rare type of reactivity for Au complexes. We find that the Au-Au σ-bond undergoes polarization in the PCET event leading to an adjustment of oxidation levels for both Au centers prior to C(sp3)-H bond cleavage. We thus describe the oxidation event as a valence tautomerism-induced PCET where the basicity of one reduced Au-OH unit provides a proton acceptor and the second more oxidized Au center serves as an electron acceptor. The coordination of these events allows for unprecedented radical-type reactivity by a closed shell AuII complex.

Valence Tautomerism Induced Proton Coupled Electron Transfer:X−H Bond Oxidation with a Dinuclear Au(II) Hydroxide Complex

AbstractWe report the preparation and characterization of the dinuclear AuII hydroxide complex AuII2(L)2(OH)2 (L=N,N′‐bis (2,6‐dimethyl) phenylformamidinate) and study its reactivity towards weak X−H bonds. Through the interplay of kinetic analysis and computational studies, we demonstrate that the oxidation of cyclohexadiene follows a concerted proton‐coupled electron transfer (cPCET) mechanism, a rare type of reactivity for Au complexes. We find that the Au−Au σ‐bond undergoes polarization in the PCET event leading to an adjustment of oxidation levels for both Au centers prior to C(sp3)−H bond cleavage. We thus describe the oxidation event as a valence tautomerism‐induced PCET where the basicity of one reduced Au−OH unit provides a proton acceptor and the second more oxidized Au center serves as an electron acceptor. The coordination of these events allows for unprecedented radical‐type reactivity by a closed shell AuII complex.

Calculation of momentum correlation functions between π, K , and p for several heavy-ion collision systems at sNN=39 GeV

Momentum correlation functions between π, K, and p are calculated for several heavy-ion collision systems, namely B510+B510, O816+O816, Ca2040+Ca2040, and Au79197+Au79197 in central collisions as well as Au79197+Au79197 collision in different centralities at center-of-mass energy sNN=39 GeV within the framework of a multiphase transport model complemented by the Lednický and Lyuboshitz analytical method. The results present the centrality and system-size dependence of the momentum correlation functions among pairs of π, K, and p, from which the emission source-size can be deduced. It is found that the deduced source sizes increase with the decreasing of centrality for Au + Au system or with the increasing of system size in central collisions with different nuclear size. In addition, through the momentum correlation functions of nonidentical particle pairs gated on velocity, the average emission sequence of nonidentical particles can be indicated. The results illustrate that in the small relative momentum region, protons are emitted in average earlier than π+ and K+, and K+ are emitted averagely earlier than π+. Furthermore, it seems that larger interval of the average emission order among them is exhibited for smaller collision systems. The present study sheds light on the dynamics of light particle emission at RHIC energy. Published by the American Physical Society 2024

DFT-Enabled Development of Hemilabile (P∧N) Ligands for Gold(I/III) RedOx Catalysis: Application to the Thiotosylation of Aryl Iodides.

Ligand-enabled oxidative addition of Csp2-X bonds to Au(I) centers has recently appeared as a valuable strategy for the development of catalytic RedOx processes. Several cross-coupling reactions that were previously considered difficult to achieve were reported lately, thus expanding the synthetic potential of gold(I) complexes beyond the traditional nucleophilic functionalization of π-systems. MeDalPhos has played an important role in this development and, despite several studies on alternative structures, remains, so far, the only general ligand for such process. We report herein the discovery and DFT-enabled structural optimization of a new family of hemilabile (P∧N) ligands that can promote the oxidative addition of aryl iodides to gold(I). These flexible ligands, which possess a common 2-methylamino heteroaromatic N-donor motif, are structurally and electronically tunable, beyond being easily accessible and affordable. The corresponding Au(I) complexes were shown to outperform the reactivity of (MeDalPhos)Au(I) in a series of alkoxy- and amidoarylations of alkenes. Their synthetic potential and comparatively higher reactivity were further highlighted in the thiotosylation of aryl iodides, a challenging unreported C-S cross-coupling reaction that could not be achieved under classical Pd(0/II) catalysis and that allows for general and divergent access to aryl sulfur derivatives.

Synthesis and crystal structure of [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene](isocyanato-κN)gold(I)

The title complex, [Au(NCO)(C27H36N2)], was synthesized by ligand metathesis from [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene]gold(I) chloride and sodium cyanate in anhydrous tetrahydrofuran and crystallized from toluene at 233 K in the orthorhombic space group P212121, as a neutral complex with the central Au atom di-coordinated by an N-heterocyclic carbene [Au—C = 1.963 (2) Å] and an isocyanate [Au—N 1.999 (2) Å] ligands, with a linear CAuNCO moiety. The crystal packing is consolidated by C—H...O hydrogen bonds.

Three-Dimensional Au Octahedral Nanoheptamers: Single-Particle and Bulk Near-Field Focusing for Surface-Enhanced Raman Scattering.

Herein, we present a synthetic approach to fabricate Au nanoheptamers composed of six individual Au nanospheres interconnected through thin metal bridges arranged in an octahedral configuration. The resulting structures envelop central Au nanospheres, producing Au nanosphere heptamers with an open architectural arrangement. Importantly, the initial Pt coating of the Au nanospheres is a crucial step for protecting the inner Au nanospheres during multiple reactions. As-synthesized Au nanoheptamers exhibit multiple hot spots formed by nanogaps between nanospheres, resulting in strong electromagnetic near-fields. Additionally, we conducted surface-enhanced Raman-scattering-based detection of a chemical warfare agent simulant in the gas phase and achieved a limit of detection of 100 ppb, which is 3 orders lower than that achieved using Au nanospheres and Au nanohexamers. This pseudocore-shell nanostructure represents a significant advancement in the realm of complex nanoparticle synthesis, moving the field one step closer to sophisticated nanoparticle engineering.

3-dimensional flow analysis: A novel tool to study the collision geometry and the equation-of-state

We propose to extend the commonly known flow analysis in the transverse px-py plane to novel flow coefficients based on the angular distribution in the px-pz and py-pz planes. The new flow coefficients, called un and wn (in addition to vn), turn out to be also highly sensitive to the nuclear Equation-of-State and can be used to explore the EoS in more detail than is possible using only vn. As an example to quantify the effect of the EoS, the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model is used to investigate 20-30% central Au+Au collisions at E=lab1.23AGeV.

Reactivity Studies of Cyclic Alkyl(Amino) Carbene (cAAC)‐Supported Phosphinidenide with AuCl

AbstractA neutral octa‐nuclear AuI‐cluster (2) with molecular formula [(Cy‐cAACPAu)4(AuCl)4] [Cy‐cAAC=:C(N‐2,6‐iPr2C6H3)(C6H10)(CMe2)(CH2)] has been isolated, and structurally characterized by single‐crystal X‐ray diffraction. 2 has been further studied by NMR and ESI‐MS. The μ3‐P bridged AuI‐cluster 2 possesses a C2 axis that passes through the two Au atoms positioned oppositely of the central AuI4P4 core, and two carbene‐P chromophores. The emission spectrum of 2 exhibited a broad band with λem at 720 nm, and an average lifetime of 3.36 ns when excited at 388 nm in solid state at room temperature. Cyclic voltammetry (CV) studies revealed that 2 can undergo reversible one‐electron oxidation at 0.76 V. The electronic transition in 2 has been further studied by computational methods.

Energy dependence of intermittency for charged hadrons in Au+Au collisions at RHIC

Density fluctuations near the QCD critical point can be probed via an intermittency analysis in relativistic heavy-ion collisions. We report the first measurement of intermittency in Au+Au collisions at sNN = 7.7-200 GeV measured by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The scaled factorial moments of identified charged hadrons are analyzed at mid-rapidity and within the transverse momentum phase space. We observe a power-law behavior of scaled factorial moments in Au+Au collisions and a decrease in the extracted scaling exponent (ν) from peripheral to central collisions. The ν is consistent with a constant for different collisions energies in the mid-central (10-40%) collisions. Moreover, the ν in the 0-5% most central Au+Au collisions exhibits a non-monotonic energy dependence that reaches a minimum around sNN = 27 GeV. The physics implications on the QCD phase structure are discussed.

Dimetal-Binding Scaffold 2-(Pyridin-2-yl)imidazo[1,5-b]pyridazine-7-ylidene: Synthesis of Trinuclear Heterobimetallic Complexes Involving Gold-Metal Interactions.

As a dimetal-binding rigid scaffold, 2-(pyridin-2-yl)imidazo[1,5-b]pyridazine-7-ylidene was introduced. The scaffold was first converted into a meridional Au,N,N-tridentate ligand through binding of a Au(I)Cl moiety at the carbene center. The Au(I) center and the N,N-chelating moiety were expected to function as metallophilic and 4e-σ-donative interaction sites, respectively, in the binding of the second metal center. In this manner, various trinuclear heterobimetallic complexes were synthesized with different 3d-metal sources, such as cationic CuI, CuII, NiII, and CoII salts. SC-XRD analysis showed that the mono-3d-metal di-gold(I) trinuclear heterobimetallic complexes were constructed through gold(I)-metal interactions. Metallophilic interactions were also investigated by quantum chemical calculations including the AIM and IGMH methods.

Defective Au nanoparticles manipulated by Au-MgxAl-LDH interplay for alkali-free oxidation of benzyl alcohol

Supported gold catalyst, especially in terms of nanosized particles with defective surface and low-coordinated structure, plays a vital role in the heterogeneous catalysis. However, such defective Au nanoparticles are hardly acquired when supporting on non-reducible metal oxides/hydroxides due to insufficient Au-support interaction. In this work, we found that the defective Au NPs could be fabricated via the strong interplay between Au and crystal lattices of layered double hydroxides-MgxAl-LDH. Experimental and theoretical evidences revealed that the formation of a preferential-oriented LDH(015) plane enabled the surface configuration for defective Au centers with the maximized number of step sites at Mg/Al ratio of 3.0–3.5. The optimized Au/Mg3.5Al-LDH catalyst shows a boosting catalytic activity for benzyl alcohol oxidation (TOF, 1008 h−1) at only 80 °C with the lowest activation energy in the absence of alkali. The work provides a new insight for manipulating the defective-enriched Au particles via the fine-tuning Au-LDH interplay for alkali-free selective oxidations.

Large-scale assembly of geometrically diverse metal nanoparticles-based 3D plasmonic DNA nanostructures for SERS detection of PNK in cancer cells

The organization of geometrically diverse metal nanoparticles into a core/satellite structure at a large scale is a promising strategy for improve SERS performance due to hot spots localized enrichment and signal increase. However, due to the lack of extensional frames and strong electrostatic repulsion between plasma NPs, the fabrication of such 3D architectures with a high-density periodic hotspot in the focus volume has proven exceedingly difficult. Herein, we demonstrate a facile large-scale assembly of geometrically diverse metal nanoparticles strategy for constructing spatially extended 3D plasmonic nanostructures resembling “signal towers” based on RCA-mediated periodic organization of gold nanospheres (GNS) surrounding gold nanorods (GNRs). Using cancer cell T4 PNK as a model, a padlock probe with 5′- hydroxyl (P-circle) was designed as the T4 PNK substrate. The center Au nanorod was coated with P1 and served as a “pedestal” to allow substantial loading of P-circle after target phosphorylation to initiate the rolling ring amplification reaction (RCA). The resultant DNA nanowire serves as an “antenna” to successively lock numerous Raman reporter P2 (Cy3-P2-SH) through base pairing at regular intervals. Finally, the 3D plasma DNA nanostructures that resemble “signal towers” could be obtained by placing a large number of GNS with a strong affinity for Au–S. The proposed 3D SERS sensor exhibited a sensitivity of LOD as low as 0.274 mU/mL, which was attributed to a substantial electromagnetic field enhancement at the inter-nanoparticle gaps between the adjacent pedestal and antenna. Moreover, by exploiting the synergistic effect of the periodically extended DNA scaffold generated by RCA amplification and the co-assembly of thiol ligand, the loaded GNS can be extended to three-dimensional space, forming a high-density periodic hotspot in the focal volume, thereby ensuring high enhancement and high reproducibility of Raman signals. In addition, this method can be used to quantify T4 PNK in HeLa cells, demonstrating its applicability in diagnosing and estimating PNK-related diseases in complex fluids.

Neural-Network-Based Quark–Gluon Plasma Trigger for the CBM Experiment at FAIR

Algorithms optimized for high-performance computing, which ensure both speed and accuracy, are crucial for real-time data analysis in heavy-ion physics experiments. The application of neural networks and other machine learning methodologies, which are fast and have high accuracy, in physics experiments has become increasingly popular over recent years. This paper introduces a fast neural network package named ANN4FLES developed in C++, which has been optimized for use on a high-performance computing cluster for the future Compressed Baryonic Matter (CBM) experiment at the Facility for Antiproton and Ion Research (FAIR, Darmstadt, Germany). The use of neural networks for classifying events during heavy-ion collisions in the CBM experiment is under investigation. This paper provides a detailed description of the application of ANN4FLES in identifying collisions where a quark–gluon plasma (QGP) was produced. The methodology detailed here will be used in the development of a QGP trigger for event selection within the First Level Event Selection (FLES) package for the CBM experiment. Fully-connected and convolutional neural networks have been created for the identification of events containing QGP, which are simulated with the Parton–Hadron–String Dynamics (PHSD) microscopic off-shell transport approach, for central Au + Au collisions at an energy of 31.2 A GeV. The results show that the convolutional neural network outperforms the fully-connected networks and achieves over 95% accuracy on the testing dataset.

Crystal Design, Antitumor Activity and Molecular Docking of Novel Palladium(II) and Gold(III) Complexes with a Thiosemicarbazone Ligand.

The current research describes the synthesis and characterization of 2-acetylpyridine N(4)-cyclohexyl-thiosemicarbazone ligand (HL) and their two metal complexes, [Au(L)Cl][AuCl2] (1) and [Pd(L)Cl]·DMF (2). The molecular structures of the compounds were determined by physicochemical and spectroscopic methods. Single crystal X-ray diffraction was employed in the structural elucidation of the new complexes. The complexes showed a square planar geometry to the metal center Au(III) and Pd(II), coordinated with a thiosemicarbazone molecule by the NNS-donor system and a chloride ion. Complex (1) also shows the [AuCl2]- counter-ion in the asymmetric unit, and complex (2) has one DMF solvent molecule. These molecules play a key role in the formation of supramolecular structures due to different interactions. Noncovalent interactions were investigated through the 3D Hirshfeld surface by the dnorm function and the 2D fingerprint plots. The biological activity of the compounds was evaluated in vitro against the human glioma U251 cells. The cytotoxicity results revealed great antitumor activity in complex (1) compared with complex (2) and the free ligand. Molecular docking simulations were used to predict interactions and properties with selected proteins and DNA of the synthesized compounds.

Exploring light nuclei production at RHIC and LHC energies with A Multi-Phase Transport model and a coalescence afterburner

In heavy-ion collisions, understanding how light nuclei species are produced can provide insight into the nature of hadronic interactions in extreme conditions. It can also shed light on understanding the matter-antimatter asymmetry and dark matter searches in astrophysical processes. To investigate the production mechanism of light nuclei such as deuteron, triton, and helium-3, we use a naive coalescence afterburner coupled to the well-known “A Multi-Phase Transport model” (AMPT). We focus on studying the production of light nuclei in central Au+Au collisions at different center of mass energies (sNN = 19.6, 39, and 200 GeV) and in Pb+Pb collisions at sNN = 2.76 TeV, at mid-rapidity. We generate events with the string melting version of AMPT, and feed the information of the nucleons with spatial and momentum conditions into the coalescence afterburner. Our study reports differential and integrated yields in transverse momentum (pT) of the light nuclei in different center of mass energies. We also estimate the coalescence parameters (BA) as a function of pT and collision energy for (anti-)deuterons, tritons and helium-3s for Au+Au and Pb+Pb collisions, which are compared to other light nuclei production studies. All results are compared with measurements from the STAR and ALICE experiments.