A 2D Acridine-Based Covalent Organic Framework for Selective Detection and Efficient Extraction of Gold from Complex Aqueous-Based Matrices.

Developing candidate materials which possess the ability of both selective detection and efficient capture of precious metal gold is highly desirable for environment and economy. However, most of reported materials only focus on single function, which seriously restricts their practical application as probes or adsorbents. Herein, a two dimensional (2D) acridine-based covalent organic framework (TpDa-COF) is prepared via the linkage of imine bonds for gold detection and adsorption. The synthesized COF can achieve both fluorescence and colorimetric dual sensing for Au3+ in a low concentration range (0.1-1.5 ppm) with the limit of detection (LOD) of 0.036 ppm. Impressively, the selectivity of TpDa-COF for the detection of Au3+ is admirable (Fe3+, Fe2+ and Cu2+ for negligible influence on its fluorescence). In addition, TpDa-COF exhibits ultrahigh adsorption capacity of 982.5 mg ⋅ g-1 for gold at pH=4, which is attributed the synergistic effect of both selective coordination and reductive process of Au(III) to Au(0). Meanwhile, both positive entropy change (ΔS=76.07 J ⋅ mol-1 ⋅ K-1) and high distribution coefficient (Kd=12484.8 mL ⋅ g-1) confirm the good affinity between TpDa-COF framework and gold. This work gives us a new insight to prepare COF with pyridine nitrogen sites for gold detection and adsorption.

Gold-Catalyzed Alkoxy-Carbonylation of Aryl and Vinyl Iodides.

Herein, for the first time, we disclose the gold-catalyzed alkoxy-carbonylation of aryl and vinyl iodides utilizing ligand-enabled Au(I)/Au(III) redox catalysis. The present methodology is found to be general, efficient, employs mild reaction conditions and showcases a broad substrate scope even with structurally complex molecules. Density functional theory (DFT) calculations revealed mechanistic pathways distinct from those of conventional transition metal-catalyzed carbonylation reactions.

Rapid Detection and Selective Extraction of Au(III) from Electronic Waste Using an Oxime Functionalized MOF-on-MOF Heterostructure.

Gold is not only a precious resource for many industries but also a global contaminant as a result of the discharge of gold-containing waste. Designing appropriate materials for the detection and extraction of gold is of great significance for the economy and environment. However, most reports only focus on sensing or adsorption for gold because of the difficulty of combining two functions in a single material. Herein, an oxime-functionalized MOF-on-MOF heterostructure (MOF-808@ZIF-90-XE) for the simultaneous detection and recovery of Au3+ is first demonstrated. The constructed hybrid material exhibits good stability, ultra-fast response time (3.6 s) as well as excellent sensitivity for the detection of Au3+ . Experimental characterizations and theoretical calculations suggest that dynamic quenching and competitive adsorption may be possible sensing mechanisms. In addition, MOF-808@ZIF-90-XE shows outstanding selectivity and admirable adsorption capacity (1575 mg g-1 ) for the capture of Au3+ owing to high surface area and abundant active adsorption sites. This paper provides a new strategy by designing a hybrid MOF-on-MOF heterostructure for the detection and extraction of gold.

Encapsulation of Au(III) Complex Using Lactoferrin Nanoparticles to Combat Glioma.

Metal-based drugs have been used for decades to treat solid cancers; however, these drugs have no significant therapeutic effect on glioma because they cannot effectively cross the blood-brain barrier (BBB). To develop a novel metal-based agent that can cross the BBB to target glioma, we synthesized an Au complex (C2) with remarkable glioma cytotoxicity and fabricated lactoferrin (LF)-C2 nanoparticles (LF-C2 NPs) as a novel therapy. We confirmed that C2 kills glioma cells by inducing apoptosis and autophagic death. The LF-C2 NPs cross the BBB, inhibit glioma growth, and selectively accumulate in the tumor tissue, significantly decreasing the side effects of C2. This study provides a novel strategy for applying metal-based agents to targeted therapy for glioma.

Construction of Porous Polyureas and Polyamides via Domino Polymerization and Their High-Efficiency Au(III) Adsorption.

The adoption of new synthesis strategy and monomers significantly promotes the construction of porous organic polymers (POPs) and their promising applications. A fabricating method of porous polyimides is developed via sequential imidization and cross-linking reaction among self-condensable building blocks, as reported in the authors' previous manuscript. Herein, porous polyureas (A-POPs) are prepared starting from 4-ethynylaniline and diisocyanate monomers, while porous polyamides (B-POPs) are synthesized from 4-ethynylbenzoic acid and diisocyanate monomers. It is found that decreasing the monomer content in solvent can effectively inhibit the premature phase separation and facilitate the evolution of integrated network. Eventually, a maximum surface area of 425 m2  g-1 is achieved for porous polyureas when the content of monomers is 10%. To the best knowledge, A-POPs are the porous polyureas with the highest surface areas reported up to now. The as-prepared porous polyurea (AN-POP) exhibits the maximum adsorption capacity of 1093.87 ± 5.23 mg g-1 and removal rate of 99.96% for Au(III), due to its high surface area and the coordination between the heteroatoms (N and O) in A-POPs and metal ions. Besides, the porous polyurea also exhibits excellent renewable efficiency and high selectivity to Au(III).

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.

Highly efficient metal-organic frameworks adsorbent for Pd(II) and Au(III) recovery from solutions: Experiment and mechanism.

With the boom of modern industry, the demand for precious metals palladium (Pd) and gold (Au) is increasing. However, the discharge of Pd(II) and Au(III) wastewater has caused environmental pollution and shortage of resources. Here, a new metal-organic frameworks adsorbent (MOF-AFH) was synthesized to efficiently separate Pd(II) and Au(III) from the water. The adsorption behavior of Pd(II) and Au(III) was explored at the same time. When gold and palladium are adsorbed separately, the adsorption capacity of gold and palladium is 389.02 mg/g and 191.27 mg/g, respectively. The equilibration time is 3 h. When gold and palladium coexist, the adsorption capacities of Au(III) and Pd(II) are 238.71 and 115.02 mg/g, respectively. The experimental results show that the adsorption of Pd(II) and Au(III) on MOF-AFH is a single-layer chemical adsorption, which is an endothermic process. MOF-AFH has excellent selectivity and after MOF-AFH is repeatedly used 4 times, the removal effect can still reach more than 90%. The adsorption mechanisms include reduction reaction and chelation with N and O-containing functional groups on the adsorbent. There is also electrostatic interaction for Au(III) adsorption. The adsorbent can be used to efficiently recover gold and palladium from wastewater.

DNA interaction, anticancer, cytotoxicity and genotoxicity studies with potential pyrazine-bipyrazole dinuclear µ-oxo bridged Au(III) complexes.

Pyrazine-bipyrazole-based µ-oxo bridged dinuclear Au(III) complexes were synthesized and characterized by various spectrometric (1H-NMR, 13C (APT) NMR, FT-IR, Mass spectrometry) and analytical techniques (elemental analysis and conductance measurement). The evaluation of DNA binding activity by UV-Vis absorption spectra and viscosity measurement demonstrated that all the compounds intercalate in between the stacks of DNA base pair and the binding constant values were observed in the range of 5.4 × 104-2.17 × 105 M-1. The molecular docking study also supports the intercalation mode of binding. The anti-proliferation activity of complexes on A549 (Lung adenocarcinoma) cells by MTT assay demonstrated IC50 values in the range of 47.46 -298.12 µg/mL. The genotoxicity of compounds was checked by smearing observed in the DNA of S. pombe cell under the influence of complexes. The in vivo cytotoxicity of compounds against brine shrimp demonstrated the LC50 values in the range of 4.59-27.22 µg/mL. The promising results of the Au(III) complexes received significant attention and make them suitable for the new metallodrugs after the detailed mechanistic biological study.

Gold (III) Derivatives in Colon Cancer Treatment.

Cancer is one of the leading causes of morbidity and mortality worldwide. Colorectal cancer (CRC) is the third most frequently diagnosed cancer in men and the second in women. Standard patterns of antitumor therapy, including cisplatin, are ineffective due to their lack of specificity for tumor cells, development of drug resistance, and severe side effects. For this reason, new methods and strategies for CRC treatment are urgently needed. Current research includes novel platinum (Pt)- and other metal-based drugs such as gold (Au), silver (Ag), iridium (Ir), or ruthenium (Ru). Au(III) compounds are promising drug candidates for CRC treatment due to their structural similarity to Pt(II). Their advantage is their relatively good solubility in water, but their disadvantage is an unsatisfactory stability under physiological conditions. Due to these limitations, work is still underway to improve the formula of Au(III) complexes by combining with various types of ligands capable of stabilizing the Au(III) cation and preventing its reduction under physiological conditions. This review summarizes the achievements in the field of stable Au(III) complexes with potential cytotoxic activity restricted to cancer cells. Moreover, it has been shown that not nucleic acids but various protein structures such as thioredoxin reductase (TrxR) mediate the antitumor effects of Au derivatives. The state of the art of the in vivo studies so far conducted is also described.

Steric and Electronic Effects in N-Heterocyclic Carbene Gold(III) Complexes: An Experimental and Computational Study.

A series of neutral acridine-based gold(III)-NHC complexes containing the pentafluorophenyl (-C6F5) group were synthesized. All of the complexes were fully characterized by analytical techniques. The square planar geometry around the gold center was confirmed by X-ray diffraction analysis for complexes 1 (Trichloro [1-methyl-3-(9-acridine)imidazol-2-ylidene]gold(III)) and 2 (Chloro-bis(pentafluorophenyl)[1-methyl-3-(9-acridine)imidazol-2-ylidene]gold(III)). In both cases, the acridine rings play a key role in the crystal packing of the solid structures by mean of π-π stacking interactions, with centroid-centroid and interplanar distances being similar to those found in other previously reported acridine-based Au(I)-NHC complexes. A different reactivity when using a bulkier N-heterocyclic carbene ligand such as 1,3-bis-(2,6-diisopropylphenyl)-2-imidazolidinylidene (SIPr) was observed. While the use of the acridine-based NHC ligand led to the expected organometallic gold(III) species, the steric hindrance of the bulky SIPr ligand led to the formation of the corresponding imidazolinium cation stabilized by the tetrakis(pentafluorophenyl)aurate(III) [Au(C6F5)4]- anion. Computational experiments were carried out in order to figure out the ground state electronic structure and the binding formation energy of the complexes and, therefore, to explain the observed reactivity.

Construction of MoS2 nanoarrays and MoO3 nanobelts: Two efficient adsorbents for removal of Pb(II), Au(III) and Methylene Blue.

Toxic heavy metal ions, valuable noble metal ions and organic dyes are significant concerns in wastewater treatment. In this work, MoO3 nanobelts (MoO3 NBs) prepared by solvothermal method and MoS2 nanoarrays (MoS2 NAs) constructed using MoO3 NBs precursor were proposed to effectively remove heavy/noble metal ions and organic dyes, such as Pb(II), Au(III) and Methylene Blue (MB). The two adsorbents exhibited the excellent adsorption capacity towards Pb(II), Au(III) and MB. The maximum removal capacity of Pb(II) and MB on MoO3 NBs was 684.93 mg/g and 1408 mg/g, respectively, whereas that of Au(III) and MB on MoS2 NAs was 1280.2 mg/g and 768 mg/g, respectively. Furthermore, the thermodynamic parameters were calculated from the temperature-dependent curves, suggesting that the removal of Pb(II) and Au(III) on both adsorbents was spontaneous and endothermic. The new adsorbents introduced here were high adsorption activity, ease of fabrication, high scalability, good chemical stability, great repeatability and abundant and cheap supply, which were highly attractive for wastewater treatment.

Computational Analysis of Photophysical Properties and Reactivity of a New Phototherapeutic Cyclometalated Au(III)-Hydride Complex.

Gold(III) complexes have recently emerged as new versatile and efficacious metal containing anticancer agents. In an attempt to reconcile the specific affinity of such complexes for target sulfur containing biomolecules with their capability to strongly bind thiol-containing compounds widely distributed in non-tumoral cells, a new series of cyclometalated Au(III)-hydride complexes has been proposed as photoactivatable anticancer prodrugs. Here, the computational exploration of the photophysical properties and reactivity in dark and under light irradiation of the first member of the series, named 1 a, is reported. Complex 1 a low hydricity in dark together with facile hydride substitution leading to H2 elimination under excitation by visible light have been examined by means of DFT and TD-DFT computations. Both singlet and triplet excited states have been characterized, allowing the identification of the active species involved in photoactivation pathways leading to the controlled detachment of the hydride ligand. Also the viable two-photon activation at the ideal phototherapeutic window has been investigated.

Computational Studies of Au(I) and Au(III) Anticancer MetalLodrugs: A Survey.

Owing to the growing hardware capabilities and the enhancing efficacy of computational methodologies, computational chemistry approaches have constantly become more important in the development of novel anticancer metallodrugs. Besides traditional Pt-based drugs, inorganic and organometallic complexes of other transition metals are showing increasing potential in the treatment of cancer. Among them, Au(I)- and Au(III)-based compounds are promising candidates due to the strong affinity of Au(I) cations to cysteine and selenocysteine side chains of the protein residues and to Au(III) complexes being more labile and prone to the reduction to either Au(I) or Au(0) in the physiological milieu. A correct prediction of metal complexes' properties and of their bonding interactions with potential ligands requires QM computations, usually at the ab initio or DFT level. However, MM, MD, and docking approaches can also give useful information on their binding site on large biomolecular targets, such as proteins or DNA, provided a careful parametrization of the metal force field is employed. In this review, we provide an overview of the recent computational studies of Au(I) and Au(III) antitumor compounds and of their interactions with biomolecular targets, such as sulfur- and selenium-containing enzymes, like glutathione reductases, glutathione peroxidase, glutathione-S-transferase, cysteine protease, thioredoxin reductase and poly (ADP-ribose) polymerase 1.

Au(III) complexes with tetradentate-cyclam-based ligands.

Chiral cyclam (1,4,8,11-tetraazacyclotetradecane) derivatives were synthesized stepwise from chiral mono-Boc-1,2-diamines and (dialkyl)malonyl dichloride via open diamide-bis(N-Boc-amino) intermediates (65-91%). Deprotection and ring closure with a second malonyl unit afforded the cyclam tetraamide precursors (80-95%). The new protocol allowed the preparation of the target cyclam derivatives (53-59%) by a final optimized hydride reduction. Both the open tetraamine intermediates and the cyclam derivatives successfully coordinated with AuCl3 to give moderate to excellent yields (50-96%) of the corresponding novel tetra-coordinated N,N,N,N-Au(III) complexes with alternating five- and six-membered chelate rings. The testing of the catalytic ability of the cyclam-based N,N,N,N-Au(III) complexes demonstrated high catalytic activity of some complexes in selected test reactions (full conversion in 1-24 h, 62-97% product yields).

Reactivity of the [Au(C

Gold complexes are promising compounds used in cancer chemotherapy. Besides their steric features, which enable biomolecule interactions, the redox instability and the high affinity of gold with cellular nucleophiles influence the biological action in these complexes. Both features were herein theoretically investigated for the [Au(C^N^C)Cl] probe complex (C^N^C = 2,6-diphenylpyridine) using H2O, CH3SH/CH3S-, CH3Se- and meim-4-H (4-methylimidazole) as biomimetic nucleophiles. Based on the results, the lowest energy reaction path followed two consecutive steps: (1) chloride-exchange ([Formula: see text] = 4.14 × 107 M-1 s-1) and (2) reduction of the resulting Au(III) metabolite to the corresponding Au(I) analog with chelate ring-opening ([Formula: see text] =+0.15 V-data based on the reaction with CH3Se-). These findings bring new insights about the mechanism of the Au(III) complex/biomolecule interaction in the cell, which is responsible for triggering biological responses.

Effective and selective recovery of Au(III) from WPCBs using quaternary phosphonium adsorbent synthesized by adjusting steric hindrance.

With the gradual depletion of natural gold ore, waste printed circuit boards (WPCBs) have become one of the most attractive alternatives to gold ore. Here, a series of quaternary phosphonium adsorbents with a large size were successfully synthesized by adjusting the number of functional groups and carbon chain length of functional monomers, which can be used for selective recovery of gold(III) from WPCBs leaching solution. The quaternary phosphonium adsorbent (PS-TEP) prepared by the nucleophilic substitution reaction between triethyl phosphine with the smallest volume and chloromethylated polystyrene (PS-Cl) exhibited the best gold loading capacity (617.90 mg g-1). The adsorption mechanism of gold(III) on PS-TEP surface mainly involves anion exchange between AuCl4- and Cl- in the adsorbent. The charge level of the H atom closest to -CH2-P+ group directly determines the strength of the interaction between the adsorbent and the gold ion. Multiwfn and VMD programs visually confirm the weak interaction between PS-TEP+ and AuCl4-. After 5 adsorption-stripping cycles, the adsorption rate of gold(III) in solution remained at about 99 %. In addition, PS-TEP exhibited good gold(III) selectivity in both simulated and actual WPCBs gold leaching solutions. These results indicate that the large-particle PS-TEP with high capacity is suitable for selective gold recovery from WPCBs leaching solution.

An O/N/S-rich porous Fe-based metal-organic framework (MOF) for gold recovery from the aqueous phase with excellent performance.

Recovering gold from wastewater has both economic and environmental benefits. However, how to effectively recover it is challenging. In this work, a novel Fe-based metal-organic framework (MOF) was synthesized and decorated with 2,5-thiophenedicarboxylic acid to have a well-developed porous architecture to effectively recover Au(III) from water. The maximum Au(III) sorption capacity by the finally-synthesized porous material MIL-101(Fe)-TDCA reached 2350 mg/g at pH = 6.00 ± 0.15, which is one of the highest among all literature-reported relevant materials including MOFs, and high sorption strength can be maintained within a wide pH range from 2.0 to 10.0. Besides, Au(III) sorption efficiency at low concentrations (i.e., 3.5 × 104 mg/mL) reached over 99%. Mechanically, outstanding Au(III) sorption by MIL-101(Fe)-TDCA resulted from the O/N/S-containing moieties on its surface, large surface area and porosity. The N- and S-containing functionalities (CS, CONH) served as electron donors to chelate Au(III). The O-containing (FeOFe, COFe, COOH, and coordinated H2O) and N-containing (CONH) moieties on MIL-101(Fe)-TDCA interacted with OH groups on the hydrolyzed species of Au(III) (AuCl3(OH)-, AuCl2(OH)2-, and AuCl(OH)3-) by hydrogen bond, which further increased Au(III) sorption. Furthermore, about 45.71% of Au(III) was reduced to gold nanoparticles by CS groups on the decorated 2,5-dithiophene dicarboxylic acid during sorption on MIL-101(Fe)-TDCA. Over 98.35% of Au(III) was selectively sorbed on MIL-101(Fe)-TDCA at pH 4.0, much higher than that of the coexisting heavy metal ions including Cu(II), Zn(II), Pb(II), and Ni(II) (< 5%), despite their same concentration at 0.01 mg/mL. Although sorption selectivity of a noble metal Pt(IV) by MIL-101(Fe)-TDCA is relatively poor (68.23%), it could be acceptable. Moreover, reusability of MIL-101(Fe)-TDCA is also excellent, since above 90.5% Au(III) still can be sorbed after two sorption-desorption cycles. Overall, excellent sorption performance and the roughly-calculated gold recycling benefits (26.30%) highlight that MIL-101(Fe)-TDCA is a promising porous material for gold recovery from the aqueous phase.

Revisited UV- spectra of chlorohydroxoaurate anions.

The most important ionic precursor of gold, [AuCl4]-, is used in aqueous solution leading to chlorohydroxoaurates species, [AuCl4-x(OH)x]- (x = 1-4) due to partial hydrolysis. Their UV spectral signatures are still relatively unknown though very useful in many domains of application. Individual spectra of each of them are determined for the first time thanks to a thorough experimental investigation comprising the range 200-250 nm, surpringly ignored up to now. New isosbestic points useful for species partition analysis are evidenced. Electronic transition attribution is obtained from quantum chemical calculations based on TD-DFT. The prediction of the experimental blueshifted bands of the [AuCl4-x(OH)x]-1 anions was possible only after applying energy corrections calibrated on the full UV range two-band spectrum of the [AuCl4]- complex.

Efficient and selective capture of Au(III) from PCBs by pentaethylenehexamine-modified chloromethylated polystyrene beads.

Recycling of gold promotes solving the problems of resource waste and environmental pollution. In this work, pentaethylenehexamine (PEHA)-modified chloromethylated polystyrene beads (PEHA-CMPS) was synthesized for the recovery of Au(III) from actual printed circuits boards (PCBs) leaching solution. PEHA-CMPS exhibited excellent adsorption efficiency at a wide pH range. It was discovered that the pseudo-second-order and Langmuir model provided a superior match for the Au(III) adsorption process. The maximum adsorption capacity for Au(III) was 1186 mg/g. Furthermore, PEHA-CMPS was able to selectively capture trace Au(III) with recovery efficiencies of above 80% from the actual PCBs leaching solution. In addition, the column separation approach was utilized to better assess the practical applications for PEHA-CMPS, proving that the prepared adsorbent exhibited great prospects in industrial applications. The adsorption efficiency still maintained 95% after five adsorption-desorption cycles. The FTIR, XRD, and XPS analyses demonstrated that Au(III) uptake on PEHA-CMPS was a collaborative process involving electrostatic interaction, chelation, and oxidation-reduction. The PEHA-CMPS provided a promising strategy in Au(III) recovery and environmental remediation.

Immobilization of tannin onto dialdehyde chitosan as a strategy for highly efficient and selective Au(III) adsorption.

Recycling of Au(III) from wastewater can not only increase resource utilization but also reduce environmental pollution. Herein, a chitosan-based bio-adsorbent (DCTS-TA) was successfully synthesized via crosslinking reaction between tannin (TA) and dialdehyde chitosan (DCTS) for the recovery of Au(III) from the solution. The maximum adsorption capacity for Au(III) was 1146.59 mg/g at pH 3.0, which fitted well with the Langmuir model. The XRD, XPS, and SEM-EDS analyses demonstrated that Au(III) adsorption on DCTS-TA was a collaborative process involving electrostatic interaction, chelation, and redox reaction. Existence of multiple coexisting metal ions did not significantly affect the Au(III) adsorption efficiency, with >90 % recovery of DCTS-TA obtained after five cycles. DCTS-TA is a promising candidate for Au(III) recovery from aqueous solutions due to its easy preparation, environmental-friendliness, and high efficiency.