Synthesis, structures, and electrochemistry of gold(III) ethylenediamine complexes and interactions with guanosine 5'-monophosphate

Structural characterization and plasmonic properties of manganese oxide-coated gold nanorods

The preparation of metal@(dielectric or semiconductor) core@shell hybrid materials have been shown promising for both SERS and SEF applications due to improved stability in the presence of ions and the adsorbate compared to non-covered metallic nanoparticles. However, fine control over the thickness of the covering layer is essential to maximize the intrinsic trade-off between the plasmonic enhancement and the chemical stability improvement. Here, the preparation of manganese dioxide ultrathin layers covered gold nanorods (AuNR@MnO₂) with varying thicknesses of the MnO₂ layer is reported, and the characterization and evaluation of the resulting materials as SERS and SEF substrate. The MnO₂ layer over the AuNR was prepared by reducing potassium permanganate by sodium oxalate in a basic medium. The AuNR@MnO₂ hybrid material was characterized by UV-Vis spectroscopy, transmission electron microscopy, X-ray powder diffraction, and cyclic voltammetry. It was studied the SEF effect of the cyanine dye IR-820 excited at 785 nm with high performance for several thicknesses of the MnO₂ ultrathin film. The enhancement factor increased for thicker oxide layers. The SERS effect of the IR-820 dye excited at 633 nm showed the most significant enhancement factor for thinner layers. The seemly opposite behavior of the two plasmonic effects may be assigned to the distance dependence of the electromagnetic field generated in the AuNR, which results in decreasing SERS performance. For SEF, the thinner layers resulted in the Au nanoparticles' emission quenching, so a more significant distance was necessary to observe enhancement.

Synthesis, X-ray characterization and regium bonding interactions of a trichlorido(1-hexylcytosine)gold(iii) complex

Herein we report the synthesis and X-ray characterization of a gold(iii) complex of 1-hexylcytosine via N(3). The AuCl₃N complexes stack on top of each other by reciprocal [AuCl] regium bonding interactions. After the first example 35 years ago, this is the second available structure of a cytosine nucleobase model complexed to gold(iii).

Gold(I/III)-Phosphine Complexes as Potent Antiproliferative Agents

The reaction of gold reagents [HAuCl₄•3H₂O], [AuCl(tht)], or cyclometalated gold(III) precursor, [C^NAuCl₂] with chiral ((R,R)-(-)-2,3-bis(t-butylmethylphosphino) quinoxaline) and non-chiral phosphine (1,2-Bis(diphenylphosphino)ethane, dppe) ligands lead to distorted Au(I), (1, 2, 4, 5) and novel cyclometalated Au(III) complexes (3, 6). These gold compounds were characterized by multinuclear NMR, microanalysis, mass spectrometry, and X-ray crystallography. The inherent electrochemical properties of the gold complexes were also studied by cyclic voltammetry and theoretical insight of the complexes was gained by density functional theory and TD-DFT calculations. The complexes effectively kill cancer cells with IC₅₀ in the range of ~0.10–2.53 μΜ across K562, H460, and OVCAR8 cell lines. In addition, the retinal pigment epithelial cell line, RPE-Neo was used as a healthy cell line for comparison. Differential cellular uptake in cancer cells was observed for the compounds by measuring the intracellular accumulation of gold using ICP-OES. Furthermore, the compounds trigger early – late stage apoptosis through potential disruption of redox homeostasis. Complexes 1 and 3 induce predominant G1 cell cycle arrest. Results presented in this report suggest that stable gold-phosphine complexes with variable oxidation states hold promise in anticancer drug discovery and need further development.

Revisiting the reactivity of tetrachloroauric acid with N,N-bidentate ligands: structural and spectroscopic insights

The reactivity of tetrachloroauric acid (HAuCl4) with readily accessible bidentate N-donor ligands affords N,N-ligated Au(iii) center complexes. These compounds are useful precursors of stable catalysts, anticancer agents, and building blocks for materials. This report provides detailed insight into intermediates, equilibria, the counter anion effect, and structural variability, using spectroscopy, crystallography and computational tools. Novel mixed-valence Au(i) and Au(iii) complexes [Au(o-phen)Cl2]2[AuCl2][AuCl4] and [Au(o-phen)Cl2][AuCl2] having AuCl2- and AuCl4- anions linearly arranged in the axial sites of the square-planar Au(o-phen)Cl2 cation were discovered. Other competing side products of the reaction studied revealed protonated N,N-bidentate ligands with AuCl4- anions. Quantitative variable temperature NMR studies reveal that for a mixture of target Au(iii) salt and the protonated ligand, the reaction favors the irreversible formation of the side product. Using a rapid (30 min) temperature controlled protocol, the desired coordinated species is accessible in respectable yields while avoiding side products.

Au(III) and Pt(II) Complexes of a Novel and Versatile 1,4-Disubstituted 1,2,3-Triazole-Based Ligand Possessing Diverse Secondary and Tertiary Coordinating Groups

A novel 1,4-disubstituted 1,2,3-triazole-based ligand, 2-(4-(pyridin-2-yl)-1 H-1,2,3-triazol-1-yl)propane-1,3-diamine (ptpd), which possesses pyridyl and diamino secondary and tertiary coordinating groups was synthesized in excellent yield. The reactivity of 2-(1-phenyl-1 H-1,2,3-triazol-4-yl)pyridine (ptp), di- tert-butyl (2-azidopropane-1,3-diyl)dicarbamate (Boc₂-ptpd), and ptpd·3HCl was investigated with Au(III) and Pt(II) precursors. Analysis including X-ray crystal structures of [Au(III)Cl₃(ptp)] (1), [Au(III)Cl₂(ptpd)][Au(I)Cl₂][OH]{[NaAuCl₄·2H₂O]} n (3), and [Pt(II)Cl₂(ptpdH₂)][PtCl₄] (4) revealed that ptpd (i) serves as a monodentate ligand for Au(III) coordinating to the metal center via the pyridine nitrogen only, (ii) preferentially coordinates Au(III) via the bidentate diamino group over the monodentate pyridine group, (iii) can coordinate Pt(II) in a bidentate fashion via the pyridyl nitrogen and the triazole N-3, and (iv) can bridge two Pt(II) centers through bidentate chelation at the diamino group and bidentate chelation via the pyridyl nitrogen and the triazole N-3. ptpd represents a versatile ligand template for the development of mixed metal complexes.

Controlling gold nanoparticle seeded growth in thermophilic ferritin protein templates

Ferritin protein cages provide templates for inorganic nanoparticle synthesis in more environmentally-friendly conditions. Thermophilic ferritin from Archaeoglobus fulgidus (AfFtn) has been shown to encapsulate pre-formed 6-nm gold nanoparticles (AuNPs) and template their further growth within its 8-nm cavity. In this study, we explore whether using a gold complex with electrostatic complementarity to the anionic ferritin cavity can promote efficient seeded nanoparticle growth. We also compare wt AfFtn and a closed pore mutant AfFtn to explore whether the ferritin pores influence final AuNP size.

The mechanism of aquaporin inhibition by gold compounds elucidated by biophysical and computational methods

The mechanism of inhibition of water and glycerol permeation via human aquaglyceroporin-3 (AQP3) by gold(iii) complexes has been described, for the first time, using molecular dynamics (MD), combined with density functional theory (DFT) and electrochemical studies.

Synthesis, structural characterization, electrochemical behavior and anticancer activity of gold(iii) complexes of meso-1,2-di(1-naphthyl)-1,2-diaminoethane and tetraphenylporphyrin

Gold(iii) complexes were tested for in vitro antiproliferative activity against three human tumor cell lines. All complexes exhibited remarkable cytotoxicity.

UV-Light-Induced Improvement of Fluorescence Quantum Yield of DNA-Templated Gold Nanoclusters: Application to Ratiometric Fluorescent Sensing of Nucleic Acids

The use of DNA as a template has been demonstrated as an effective method for synthesizing different-sized silver nanoclusters. Although DNA-templated silver nanoclusters show outstanding performance as fluorescent probes for chemical sensing and cellular imaging, the synthesis of DNA-stabilized gold nanoclusters (AuNCs) with high fluorescence intensity remains a challenge. Here a facile, reproducible, scalable, NaBH4-free, UV-light-assisted method was developed to prepare AuNCs using repeats of 30 adenosine nucleotides (A30). The maximal fluorescence of A30-stabilized AuNCs appeared at 475 nm with moderate quantum yield, two fluorescence lifetimes, and a small amount of Au(+) on the surface of the Au core. Results of size-exclusion chromatography revealed that A30-stabilized AuNCs were more compact than A30. A series of control experiments showed that UV light played a dual role in the reduction of gold-ion precursors and the decomposition of citrate ions. A30 also acted as a stabilizer to prevent the aggregation of AuNCs. In addition, single-stranded DNA (ssDNA) consisting of an AuNC-nucleation sequence and a hybridization sequence was utilized to develop a AuNC-based ratiometric fluorescent probe in the presence of the double-strand-chelating dye SYBR Green I (SG). Under conditions of single-wavelength excitation, the combination of AuNC/SG-bearing ssDNA and perfectly matched DNA emitted fluorescence at 475 and 525 nm, respectively. The formed AuNC/SG-bearing ssDNA enabled the sensitive, selective, and ratiometric detection of specific nucleic acid targets. Finally, the AuNC-based ratiometric probes were successfully applied to determine specific nucleic acid targets in human serum.

Dense Deposition of Gold Nanoclusters Utilizing a Porphyrin/Inorganic Layered Material Complex as the Template

We examined the deposition of gold clusters through the reduction of a gold precursor sensitized by nonaggregated, assembled porphyrin molecules on an inorganic layered material surface in order to develop a novel strategy for constructing assemblies of gold clusters. Visible light irradiation on nonaggregated, assembled porphyrin on the inorganic surface in the presence of the gold precursor and an electron donor induced the deposition of gold NPs on the surface of the inorganic layered material. Uniform gold clusters, with an average diameter of 1.5 nm, were deposited on the surface without aggregation. The average interparticle distance between adjacent gold clusters (center to center) was 2.3 nm, which agrees well with the average intermolecular distance of the nonaggregated, assembled porphyrin molecules on the inorganic surface. Thus, the generated gold clusters appear to reflect the nonaggregated, assembled structure of the porphyrin molecules on the inorganic surface. This method, termed the photosensitized template reduction (PTR) method, is a useful and novel technique for the deposition of metal nanoparticles on the surfaces of supporting materials.

Highly transparent Au-coated Ag nanowire transparent electrode with reduction in haze

Ag nanowire transparent electrode has excellent transmittance and sheet resistance, yet its optical haze still needs to be improved in order for it to be suitable for display applications. Ag nanowires are known to have high haze because of the geometry of the nanowire and the high light scattering characteristic of the Ag. In this study, a Au-coated Ag nanowire structure was proposed to reduce the haze, where a thin layer of Au was coated on the surface of the Ag nanowires using a mild [Au(en)2]Cl3 galvanic displacement reaction. The mild galvanic exchange allowed for a thin layer of Au coating on the Ag nanowires with minimal truncation of the nanowire, where the average length and the diameter were 13.0 μm and 60 nm, respectively. The Au-coated Ag nanowires were suspended in methanol and then electrostatically sprayed on a flexible polycarbonate substrate that revealed a clear reduction in haze with a 2-4% increase in total transmittance, sheet resistance ranges of 80-90%, and 8.8-36.8 Ohm/sq. Finite difference time domain simulations were conducted for Au-coated Ag nanowires that indicated a significant reduction in the average scattering from 1 to 0.69 for Au layer thicknesses of 0-10 nm.

Synthesis, spectroscopic characterization, electrochemical behavior and computational analysis of mixed diamine ligand gold(III) complexes: antiproliferative and in vitro cytotoxic evaluations against human cancer cell lines

The gold(III) complexes of the type [(DACH)Au(en)]Cl3, 1,2-Diaminocyclohexane ethylenediamine gold(III) chloride [where 1,2-DACH = cis-, trans-1,2- and S,S-1,2diaminocyclohexane and en = ethylenediamine] have been synthesized and characterized using various analytical and spectroscopic techniques including elemental analysis, UV-Vis and FTIR spectra; and solution as well as solid-state NMR measurements. The solid-state (13)C NMR shows that 1,2-diaminocyclohexane (1,2-DACH) and ethylenediamine (en) are strongly bound to the gold(III) center via N donor atoms. The stability of the mixed diamine ligand gold(III) was determined by (1)H and (13)C NMR spectra. Their electrochemical behavior was studied by cyclic voltammetry. The structural details and relative stabilities of the four possible isomers of the complexes were also reported at the B3LYP/LANL2DZ level of theory. The coordination sphere of these complexes around gold(III) center adopts distorted square planar geometry. The computational study also demonstrates that trans- conformations is slightly more stable than the cis-conformations. The antiproliferative effects and cytotoxic properties of the mixed diamine ligand gold(III) complexes were evaluated in vitro on human gastric SGC7901 and prostate PC3 cancer cells using MTT assay. The antiproliferative study of the gold(III) complexes on PC3 and SGC7901 cells indicate that complex 1 is the most effective antiproliferative agent among mixed ligand based gold(III) complexes 1-3. The IC50 data reveal that the in vitro cytotoxicity of complexes 1 and 3 against SGC7901 cancer cells are fairly better than that of cisplatin.

Underpotential Co-deposition of Au-Cu alloys: switching the underpotentially deposited element by selective complexation

Underpotential deposition and monolayer replacement processes are widely used for the synthesis of core/shell catalysts and heterointerfaces. Conventionally, only the more noble metal can be underpotentially deposited on or replace the less noble metal, limiting the number of accessible material configurations. We show here that the reverse process is possible, using the Au-Cu pair as a model system. By tuning the redox potentials of the two components via use of strong, selective metal ion complexes, Au-Cu alloys could be synthesized at will by (i) conventional underpotential co-deposition, whereby Cu is reduced at underpotential in parallel with the overpotential deposition of Au, or (ii) the reverse process, where Au is reduced at underpotential, while Cu is deposited at overpotential. Selective complexation also draws the redox potential of Au and Cu closer, resulting in co-deposition under activation control for the noble metal and precise alloy composition control by the applied potential, enabling in principle the formation of arbitrary metal or alloy interfaces. The alloys resulting from the two processes exhibit distinct enthalpy of mixing, suggesting different degrees of short-range order and dissimilar atomic configurations. These findings open new perspectives on underpotential deposition phenomena and possibly new synthetic opportunities in electrodeposition.

Histological changes in kidney and liver of rats due to gold (III) compound [Au(en)Cl(2)]Cl

Introduction

Development of novel metallodrugs with enhanced anti-proliferative potential and reduced toxicity has become the prime focus of the evolving medicinal chemistry. In this regards, gold (III) complexes with various ligands are being extensively investigated. In the current study renal and hepatic toxicity of a newly developed gold (III) compound [Au(en)Cl₂]Cl was assessed by histopathological evaluation of liver and kidney specimens of rats exposed to the compound.

Methods

Male rats (n = 42) weighing 200–250 gram were injected single, varying doses of gold (III) compound [(dichlorido(ethylenediamine)aurate((III)]chloride [Au(en)Cl₂]Cl in the acute toxicity component of the study. In the sub-acute toxicity part, a dose of 32.2 mg/kg (equivalent to 1/10 of LD50) was administered intraperitoneally for 14 consecutive days before sacrificing the animals. After autopsy, the renal and hepatic tissues were preserved in buffered formalin. Processing of the samples was followed by histopathological evaluation. The results were compared with the normal controls (n = 11).

Results

A dose of 32.2 mg/kg (1/10 of LD₅₀) revealed no renal tubular necrosis. The predominant histopathological finding was mild pyelitis, a prominence of eosinophils and mild congestion. The hepatic lesions comprised varying extents of ballooning degeneration with accompanying congestion and focal portal inflammation.

Conclusion

Gold (III) compound [Au(en)Cl₂]Cl causes minimal histological changes in kidney and liver of rats, reflecting its relative safety as compared to other clinically established antineoplastic drugs.

Synthesis of gold nanocubes in aqueous solution with remarkable shape-selectivity

This paper reports a facile method to prepare gold nanocubes with an average size length of 13 ± 2 nm, a shape selectivity >90%, and a very good reproducibility. The gold nanocubes were prepared by photocatalytic reduction of Au(III) using a cationic, water soluble porphyrin as the photocatalyst, and cetyltrimethylammonium bromide as the capping agent. The synthesis is performed in water, at pH 7, and room temperature. The nanocubes were characterized by transmission electron microscopy, scanning electron microscopy, atomic force microscopy, and X-ray phototelectron spectroscopy. Shape selectivity for the synthesis of nanocubes is due to a different rate of growth of the (100) and (111) facets of the nanoparticles, and such control in this synthesis is achieved by careful selection of the initial gold precursor for the photocatalytic cycle.

Synthesis, characterization and anti proliferative effect of [Au(en)2]Cl3 and [Au(N-propyl-en)2]Cl3 on human cancer cell lines

Two Au(III) complexes of the type [Au(en)2]Cl3 (2a) and [Au(N-pr-en)2]Cl3 (3a) were synthesized by reacting Auric acid (HAuCl(4)·3H2O) with 2 equiv. ethylenediamine (en) or N-alkyl substituted ethylenediamine ligands. This metallodrug was characterized by various analytical and spectroscopic techniques such as elemental analysis, UV-Vis, Far-IR, 1H NMR and solution 13C as well as solid 13C and 15N NMR. Potentiality of [Au(en)2]Cl3 and [Au(N-pr-en)2]Cl3 as an anti-cancer agent were investigated by measuring some relevant physicochemical and biochemical properties such as stability of Au-N bonds by vibrational stretching from Far IR as well as cytotoxicity and stomach cancer cell inhibiting effect, respectively. The solid-state 15N NMR chemical shift shows that the ligand is strongly bound to gold(III) centre via N atoms. The computational study of 2a shows that the gold coordination sphere adopts distorted square planar geometry with bidentate ethylenediamine ligands acting as a tetradentate chelate. While stable in the solution state, the in vitro biological studies performed with these compounds 2a in solution showed higher activity towards the inhibitory effects of the human cancer cell lines such as prostate cancer (PC-3) and gastric carcinoma (SGC-7901) than that of the N-substituted gold(III) complex (3a). Cytotoxicity of the new compounds has also been estimated in PC-3 and SGC-7901 cells.

Crystal and Molecular Structure of Dichloro(ethylenediamine)gold(III) Nitrate: [Au(NH2CH2CH2NH2)Cl2]NO3

The gold(III) atom in [Au(NH2CH2CH2NH2) Cl2]NO3 is chelated by the ethylenediamine (en) ligand and the approximately square planar geometry is completed by two chloride atoms. Weak Au⋯O and Au⋯Cl contacts are noted above and below the square plane leading to a tetragonally distorted octahedron for the gold(III) center. Extensive charge-assisted hydrogen bonding of the type N-H⋯O leads to the formation of a 2-D array and layers are consolidated into a 3-D network via C-H⋯O and C-H⋯Cl contacts. The compound crystallizes in the orthorhombic space group Pbca with a = 10.3380(11) Å, b = 8.2105(7) Å, c = 19.625(2) Å, and Z = 8.