Thiolate Ligands Research Articles

Obviating Ligand Exchange Preserves the Intact Surface of HgTe Colloidal Quantum Dots and Enhances Performance of Short Wavelength Infrared Photodetectors.

A large volume, scalable synthesis procedure of HgTe quantum dots (QDs) capped initially with short-chain conductive ligands ensures ligand exchange-free and simple device fabrication. An effective n- or p-type self-doping of HgTe QDs is achieved by varying cation-anion ratio, as well as shifting the Fermi level position by introducing single- or double-cyclic thiol ligands, that is, 2-furanmethanethiol (FMT) or 2,5-dimercapto-3,4-thiadiasole (DMTD) in the synthesis. This allows for preserving the intact surface of the HgTe QDs, thus ensuring a one order of magnitude reduced surface trap density compared with HgTe subjected to solid-state ligand exchange. The charge carrier diffusion length can be extended from 50 to 90nm when the device active area consists of a bi-layer of cation-rich HgTe QDs capped with DMTD and FMT, respectively. As a result, the responsivity under 1340nm illumination is boosted to 1 AW-1 at zero bias and up to 40 AW-1 under -1V bias at room temperature. Due to high noise current density, the specific detectivity of these photodetectors reaches up to 1010 Jones at room temperature and under an inert atmosphere. Meanwhile, high photoconductive gain ensures a rise in the external quantum efficiency of up to 1000% under reverse bias.

Single Atom Alloys Segregation in the Presence of Ligands.

Single atom alloys (SAAs) have gained remarkable attention due to their tunable properties leading to enhanced catalytic performance, such as high activity and selectivity. The stability of SAAs is dictated by surface segregation, which can be affected by the presence of surface adsorbates. Research efforts have primarily focused on the effect of commonly found catalytic reaction intermediates, such as CO and H, on the stability of SAAs. However, there is a knowledge gap in understanding the effect of ligands from colloidal nanoparticle (NP) synthesis on surface segregation. Herein, we combine density functional theory (DFT) and machine learning to investigate the effect of thiol and amine ligands on the stability of colloidal SAAs. DFT calculations revealed rich segregation energy (Eseg) data of SAAs with d8 (Pt, Pd, Ni) and d9 (Ag, Au, Cu) metals exposing (111) and (100) surfaces, in the presence and absence of ligands. Using these data, we developed an accurate four-feature neural network using a multilayer perceptron regression (NN MLP) model. The model captures the underlying physics behind surface segregation in the presence of adsorbed ligands by incorporating features representing the thermodynamic stability of metals through the bulk cohesive energy, structural effects using the coordination number of the dopant and the ligands, the binding strength of the adsorbate to the metals, strain effects using the Wigner-Seitz radius, and electronic effects through electron affinities. We found that the presence of ligands makes the thermodynamics of segregation milder compared to the bare (nonligated) SAA surfaces. Importantly, the adsorption configuration (e.g., top vs bridge) and the binding strength of the ligand to the SAA surface (e.g., amines vs thiols) play an important role in altering the Eseg trends compared to the bare surface. We also developed an accurate NN MLP model that predicts Eseg in the presence of ligands to find thermodynamically stable SAAs, leading to the rapid and efficient screening of colloidal SAAs. Our model captures several experimental observations and elucidates complex physics governing segregation at nanoscale interfaces.

Functionalization of Polymer-Wrapped Silver Nanoclusters and Potential Applications as Antimicrobial Mask Materials.

The poly(methacrylic acid) (PMAA) polymer stabilized silver nanoclusters Agn (n = 2-9), synthesized in aqueous solution by the selected light wavelength irradiation photolysis approach, have been functionalized with thiol and amine ligands and successfully transferred from aqueous to organic media. Low- or high-resolution positive mass spectra showed constant species composites with the molecular formula AgnLn-1 [n = 2 to ∼9, L = butylmercaptan (C4H9S), thiolphenol (C6H5S), or dodecanethiol (C12H25S)] and proved that the molecules consist of deprotonated sulfur ligands in each species with one positive charge. Fourier transform infrared and X-ray photoelectron spectroscopy are consistent, indicating deprotonated sulfur, while silver has a zero valence value. The composition of the functionalized silver clusters is in agreement with that observed from polymer-wrapped "naked" silver clusters, which strongly indicates their real existence. For the silver cluster amine systems (heptylamine, dodecylamine, and oleylamine), only "naked" silver cluster species were detected from mass spectroscopy, similar to the polymer-wrapped case, indicating they are not stable enough in the gas phase. The development of a new antibacterial mask material is very important. The dodecylamine-capping silver nanoclusters were selected by coating the coffee filter surface to conduct antibacterial tests with Staphylococcus aureus and Escherichia coli, demonstrating very efficient antimicrobial properties even with organic capping ligands. Experiments also show that they work on mask material. One nanowire assembly with polystyrene and dodecylamine-capping silver nanoclusters was prepared, showing uniform nanofibers generated via the electrospray technique.

Activity of Different AunSn+1 Staples in the Ligand Exchange of Au23(SR)16- with a Single Foreign Thiolate Ligand.

Ligand exchange has been widely used to synthesize novel thiolated gold nanoclusters and to regulate their specific properties. Herein, density functional theory (DFT) calculations were conducted to investigate the kinetic profiles of the ligand exchange of the [Au23(SCy)16]- nanocluster with an aromatic thiolate (2-napthalenethiol). The three types of staple motifs (i.e., trimetallic Au3S4, monometallic AuS2, and the bridging thiolates) of the Au23 cluster precursor could be categorized into eight groups of S sites with different chemical environments. The ligand exchange of all of them occurs favorably via the SN1-like pathway, with one site starting with the Au-S dissociation and seven other sites starting with the H-transfer steps. By contrast, the SN2-like pathway (i.e., the synergistic SCy-to-SAr exchange prior to the H-transfer step) is unlikely in the target systems. Meanwhile, the Au-S bond on the capping Au atom of the bicapped icosahedral Au15 core is the most active one, while the S sites on Au3S4 (except for the one remote from the metallic core) are all competitive exchanging sites. The ligand exchange activity of the bridging thiolate and the remote S site on Au3S4 is significantly less reactive. The calculation results correlate with the multiple ligand exchange within only a few minutes and the preferential etching of the AuS2 staple with the foreign ligands reported in earlier experiments. The relative activity of different staples might be helpful in elucidating the inherent principles in the ligand exchange-induced size-evolution of metal nanoclusters.

Catalytic Hydrogenation of Nitroarenes over Ag33 Nanoclusters: The Ligand Effect.

Using ligand-protected metallic nanoclusters with atomic precision as catalysts and elucidating its ligand effect in the catalysis are the prerequisites to deepen the structure-catalysis relationship of nanoclusters at the molecular level. Herein, a series of Ag33 nanoclusters protected with different thiolate ligands (2-phenylethanethiol, 4-chlorobenzyl mercaptan, and 4-methoxybenzyl mercaptan as precursors) were synthesized and used as heterogeneous catalysts for the conversion of nitroarenes to arylamine with NaBH4 as reductant. The obtained nanoclusters exhibited ligand-dependent catalytic activity, with benzyl thiolate ligands distinctly superior to the phenethyl thiolate ligands. DFT calculations revealed that the ligand regulated catalytic activity of the nanoclusters was ascribed to the H-π and π-π interactions between the ligands and the substrates, owing to the presence of phenyl rings in these structures. This work highlighted the importance of the ligands on the metallic nanoclusters in catalysis and provides a strategy to regulate the catalytic activity by utilizing weak interactions between the catalysts and the substrates.

Towards Copper(I) Clusters for Photo-Induced Oxidation of Biological Thiols in Living Cells.

The cell redox balance can be disrupted by the oxidation of biological peptides, eventually leading to cell death, which provides opportunities to develop cytotoxic drugs. With the aim of developing compounds capable of specifically inducing fatal redox reactions upon light irradiation, we have developed a library of copper compounds. This metal is abundant and considered essential for human health, making it particularly attractive for the development of new anticancer drugs. Copper(I) clusters with thiol ligands (including 5 novel ones) have been synthesized and characterized. Structures were elucidated by X-ray diffraction and showed that the compounds are oligomeric clusters. The clusters display high photooxidation capacity towards cysteine - an essential amino acid - upon light irradiation in the visible range (450 nm), while remaining completely inactive in the dark. This photoredox activity against a biological thiol is very encouraging for the development of anticancer photoredox drugs.The in vitro assay on murine colorectal cancer cells (CT26) did not show any toxicity - whether in the dark or when exposed to 450 nm light, likely because of the poor solubility of the complexes in biological medium.

The Effect of Peroxynitrite and tert-Butyl Hydroperoxide on Thiol Ligands of Dinitrosyl Iron Complexes

The Effect of Peroxynitrite and tert-Butyl Hydroperoxide on Thiol Ligands of Dinitrosyl Iron Complexes

Effect of Peroxynitrite and <i>tert</i>-Butyl Hydroperoxide on Thiol Ligands of Dinitrosyl Iron Complexes

Low molecular weight dinitrosyl iron complexes (DNICs) with thiol-containing ligands are a physiological form for deposit and transport of nitric oxide (NO) in the organism, herewith DNICs can exhibit antioxidant and antiradical properties. It was that DNICs containing cysteine, glutathione and lipoic acid as ligands, decreased the rate of dihydrodamine oxidation by peroxynitrite formed during 3-morpholinononymine decomposition. Thiol (sulfhydryl) ligands are present in DNICs in the form of thiolate anions (R-S−), which protects these groups from oxidation by peroxynitrite. When tert-butyl peroxide was used as an oxidizer at low concentration, the protective effect of DNICs on their SH-groups was observed for complexes with lipoic acid (LA-DNIC) and with glutathione (GS-DNIC). LA-DNIC was more resistant to oxidizing agents and more effective peroxynitrite trap than other DNICs. DNICs associated with bovine serum albumin had a negligible protective effect on cysteine residue during oxidation by peroxynitrite and tert-butyl hydroperoxide. The obtained results allow us to consider low molecular weight DNICs with thiol ligands as peroxynitrite traps and thiol residues protectors in proteins.

Tuning Ligands Ratio Allows for Controlling Gold Nanocluster Conformation And Activating A Nonantimicrobial Thiol Fragrance for Effective Treatment of MRSA-induced Keratitis.

Bacterial keratitis is a serious ocular disease that affects millions of people worldwide each year, among which ∼25% are caused by Staphylococcus aureus. With the spread of bacterial resistance, refractory keratitis caused by methicillin-resistant Staphylococcus aureus (MRSA) affects ∼120-190 thousand people annually and has become a significant cause of infectious blindness. Atomically precise gold nanoclusters (GNCs) have recently emerged as promising antibacterial agents, although how GNC structure and capping ligands control its antibacterial properties remain largely unexplored. In this study, by adjusting the ratio of a "bulky" thiol fragrance to a linear zwitterionic ligand, the GNC conformation is transformed from Au25 (SR)18 to Au23 (SR)16 species, simultaneously converting both inactive thiol ligands into potent antibacterial nanomaterials. Surprisingly, mixed-ligand capped Au23 (SR)16 GNCs exhibit superior antibacterial potency compared to their mono-ligand counterparts. The optimal GNC is highly potent against MRSA, showing >1024-fold lower minimum inhibitory concentration than the corresponding free ligands. Moreover, it displays excellent potency in treating MRSA-induced keratitis in mice with greatly accelerated corneal recovery (by ∼9-fold). Thus, this study establishes a feasible method to synthesize antibacterial GNCs by adjusting the ligand ratio to control GNC conformation and active non-antibacterial ligands, thereby greatly increasing the repertoires for combating multidrug-resistant bacterial infections. This article is protected by copyright. All rights reserved.

Enhancement of cellular uptake by increasing the number of encapsulated gold nanoparticles in polymeric micelles

We apply a combination of polycaprolactone (PCL)-thiol ligand functionalization with flow-controlled microfluidic block copolymer self-assembly to produce biocompatible gold nanoparticle (GNP)-loaded micellar polymer nanoparticles (GNP-PNPs) in which GNPs are encapsulated within PCL cores surrounded by an external layer of poly(ethylene glycol) (PEG). By varying both the relative amount of block copolymer and the microfluidic flow rate, a series of GNP-PNPs are produced in which the mean number of GNPs per PNP in the < 50-nm fraction (Zave,d< 50 nm) varies between 0.1 and 1.9 while the external PEG surface is constant. Zave,d< 50 nm values are determined by statistical analysis of TEM images and compared with the results of cell uptake experiments on MDA-MB-231 cancer cells. For Zave,d< 50 nm ≤ 1 (including a control sample of individual GNPs also with a PEG surface layer), cell uptake is relatively constant, but increases sharply for Zave,d< 50 nm > 1, with a factor of 7 enhancement as Zave,d< 50 nm increases from 1 to ∼2. Enabled by the shear processing control provided by the microfluidic chip, these results provide the first evidence that cellular uptake can be enhanced specifically by increasing the number of GNPs per vector, with other parameters, including polymeric material, internal structure, and external surface chemistry, held constant. They also demonstrate a versatile platform for packaging GNPs in biocompatible polymeric carriers with flow-controlled formulation optimization for various therapeutic and diagnostic applications.

Controllably partial removal of thiolate ligands from unsupported Au25 nanoclusters by rapid thermal treatments for electrochemical CO2 reduction

Colloidal synthesis of metal nanoclusters will inevitably lead to the blockage of catalytically active sites by organic ligands. Here, taking [Au25(PET)18]− (PET = 2-phenylethanethiol) nanocluster as a model catalyst, this work reports a feasible procedure to achieve the controllably partial removal of thiolate ligands from unsupported [Au25(PET)18]− nanoclusters with the preservation of the core structure. This procedure shortens the processing duration by rapid heating and cooling on the basis of traditional annealing treatment, avoiding the reconfiguration or agglomeration of Au25 nanoclusters, where the degree of dethiolation can be regulated by the control of duration. This work finds that a moderate degree of dethiolation can expose the Au active sites while maintaining the suppression of the competing hydrogen evolution reaction. Consequently, the activity and selectivity towards CO formation in electrochemical CO2 reduction reaction of Au25 nanoclusters can be promoted. This work provides a new approach for the removal of thiolate ligands from atomically precise gold nanoclusters.

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.

μ-1,2-Bis(dipheylphosphino)ethane-κ2P,P’]bis(3-mercapto-1,2-propanediolato-κS-gold(I))

A new dinuclear gold(I) complex, possessing a bridging diphosphine ligand (1,2-bis(diphenylphosphino)ethane) and two terminal thiol ligands (1-thioglycerol), was synthesized and fully characterized by IR, 1H and 31P NMR, fluorescence, ESI-mass, and diffuse reflection spectroscopy, together with X-ray diffraction and elemental analyses. The compound formed a 1D chain supramolecular structure through intermolecular aurophilic interactions in the crystal structure, leading to photoluminescence in the solid state.

Phosphine‐Triggered Structural Defects in Au44 Homologues Boost Electrocatalytic CO2 Reduction

AbstractThe systematic induction of structural defects at the atomic level is crucial to metal nanocluster research because it endows cluster‐based catalysts with highly reactive centers and allows for a comprehensive investigation of viable reaction pathways. Herein, by substituting neutral phosphine ligands for surface anionic thiolate ligands, we establish that one or two Au3 triangular units can be successfully introduced into the double‐stranded helical kernel of Au44(TBBT)28, where TBBT=4‐tert‐butylbenzenethiolate, resulting in the formation of two atomically precise defective Au44 nanoclusters. Along with the regular face‐centered‐cubic (fcc) nanocluster, the first series of mixed‐ligand cluster homologues is identified, with a unified formula of Au44(PPh3)n(TBBT)28−2n (n=0–2). The Au44(PPh3)(TBBT)26 nanocluster having major structural defects at the bottom of the fcc lattice demonstrates superior electrocatalytic performance in the CO2 reduction to CO. Density functional theory calculations indicate that the active site near the defects significantly lowers the free energy for the *COOH formation, the rate‐determining step in the whole catalytic process.

Phosphine-Triggered Structural Defects in Au44 Homologues Boost Electrocatalytic CO2 Reduction.

The systematic induction of structural defects at the atomic level is crucial to metal nanocluster research because it endows cluster-based catalysts with highly reactive centers and allows for a comprehensive investigation of viable reaction pathways. Herein, by substituting neutral phosphine ligands for surface anionic thiolate ligands, we establish that one or two Au3 triangular units can be successfully introduced into the double-stranded helical kernel of Au44 (TBBT)28 , where TBBT=4-tert-butylbenzenethiolate, resulting in the formation of two atomically precise defective Au44 nanoclusters. Along with the regular face-centered-cubic (fcc) nanocluster, the first series of mixed-ligand cluster homologues is identified, with a unified formula of Au44 (PPh3 )n (TBBT)28-2n (n=0-2). The Au44 (PPh3 )(TBBT)26 nanocluster having major structural defects at the bottom of the fcc lattice demonstrates superior electrocatalytic performance in the CO2 reduction to CO. Density functional theory calculations indicate that the active site near the defects significantly lowers the free energy for the *COOH formation, the rate-determining step in the whole catalytic process.

Synthesis and Structure of Polyhydrido Copper Nanocluster [Cu14H10(PPh3)8(SPhMe2)3]+: Symmetry-Breaking by Thiolate Ligands to form Racemic Pairs of Chiral Clusters in Solid-State

A polyhydrido copper nanocluster, [Cu14H10(PPh3)8(SR)3]+ (HSR = 2,4-dimethylbenzenethiol), adopting a distorted fcc structure, is reported. One cube-vertex copper atom, coordinated by the three thiolate ligands and a PPh3, protrudes outwards from the fcc metal framework. The twisting of the three thiolate ligands about the threefold axis lowers the symmetry from Oh (Cu14) to C3, forming racemic pairs of intrinsic chiral clusters in crystalline solid-state.Graphical

Hexakis(μ-3-aminopropanethiolato-1κ6N,S:2κ3S;3κ6N,S:2κ3S)cadmium(II)dirhodium(III) Dibromide Tetrahydrate

Cadmium(II) complexes with thiolate ligands have received considerable attention because of their intriguing structural features and relevance to metalloproteins. In this study, a new cadmium(II)–rhodium(III) trinuclear complex, [Cd{Rh(apt)3}2]Br2·4H2O (1, apt = 3-aminopropanethiolate), was synthesized by the reaction of fac-[Rh(apt)3] with cadmium bromide. Compound 1 was characterized using elemental analysis, X-ray fluorescence and IR spectroscopies, and powder X-ray diffraction study. Single-crystal X-ray analysis revealed that the cadmium(II) center in 1 was surrounded by six thiolato S atoms from two fac-[Rh(apt)3] units.

The chemistry of rhenium and manganese carbonyl complexes bearing heterocyclic thiolate ligands: Mono‒, di‒, tri‒, and tetranuclear complexes

The chemistry of rhenium and manganese carbonyl complexes bearing heterocyclic thiolate ligands: Mono‒, di‒, tri‒, and tetranuclear complexes

All-Solution-Processed Perovskite Light-Emitting Diodes Based on a Thiol-Modified ZnO Electron-Transporting Layer.

All-solution-processed perovskite light-emitting diodes (LEDs) have the potential to be inexpensive and easily manufactured on a large scale without requiring vacuum thermal deposition of the emissive and charge transport layers. Zinc oxide (ZnO), which possesses superior optical and electronic properties, is commonly used in all-solution-processed optoelectronic devices. However, the polar solvent of ZnO inks can corrode the perovskite layer and cause severe photoluminescence quenching. In this work, we report the successful dispersion of ZnO nanoparticles in nonpolar n-octane by controlling the surface ligands from acetates to thiols. The nonpolar ink prevents the destruction of perovskite films. In addition, thiol ligands upshift the conduction band energy level, which also helps inhibit exciton quenching. Consequently, we demonstrate the fabrication of high-performance all-solution-processed green perovskite LEDs with a brightness of 21 000 cd/m2 and an external quantum efficiency of 6.36%. Our work provides a ZnO ink for fabricating efficient all-solution-processed perovskite LEDs.

Fully Reduced and Mixed-Valent Multi-Copper Aggregates Supported by Tetradentate Diamino Bis(thiolate) Ligands.

Tetradentate diamino bis(thiolate) ligands (l-N2S2(2-)) with saturated linkages between heteroatoms support fully reduced [(Cu(l-N2S2))2Cu2] complexes that bear relevance as an entry point toward molecules featuring the Cu2ICu2II(μ4-S) core composition of nitrous oxide reductase (N2OR). Tetracopper [(Cu(l-N2(SMe2)2))2Cu2] (l-N2(SMe2H)2 = N1,N2-bis(2-methyl-2-mercaptopropane)-N1,N2-dimethylethane-1,2-diamine) does not support clean S atom oxidative addition but undergoes Cl atom transfer from PhICl2 or Ph3CCl to afford [(Cu(l-N2(SMe2)2))3(CuCl)5], 14. When introduced to Cu(I) sources, the l-N2(SArH)2 ligand (l-N2(SArH)2 = N1,N2-bis(2-mercaptophenyl)-N1,N2-dimethylethane-1,2-diamine), made by a newly devised route from N1,N2-bis(2-fluorophenyl)-N1,N2-dimethylethane-1,2-diamine, ultimately yields the mixed-valent pentacopper [(Cu(l-N2SAr2))3Cu2] (19), which has 3-fold rotational symmetry (D3) around a Cu2 axis. The single CuII ion of 19 is ensconced within an equatorial l-N2(SAr)2(2-) ligand, as shown by 14N coupling in its EPR spectrum. Formation of 19 proceeds from an initial, fully reduced product, [(Cu(l-N2SAr2))3Cu2(Cu(MeCN))] (17), which is C2 symmetric and exceedingly air-sensitive. While unreactive toward chalcogen donors, 19 supports reversible reduction to the all-cuprous state; generation of [19]1- and treatment with S atom donors only return 19 because structural adjustments necessary for oxidative addition are noncompetitive with outer-sphere electron transfer. Oxidation of 19 is marked by intense darkening, consistent with greater mixed valency, and by dimerization in the crystalline state to a decacopper species ([20]2+) of S4 symmetry.