Metal Complexes as Antifungals? From a Crowd-Sourced Compound Library to the First In Vivo Experiments.

There are currently fewer than 10 antifungal drugs in clinical development, but new fungal strains that are resistant to most current antifungals are spreading rapidly across the world. To prevent a second resistance crisis, new classes of antifungal drugs are urgently needed. Metal complexes have proven to be promising candidates for novel antibiotics, but so far, few compounds have been explored for their potential application as antifungal agents. In this work, we report the evaluation of 1039 metal-containing compounds that were screened by the Community for Open Antimicrobial Drug Discovery (CO-ADD). We show that 20.9% of all metal compounds tested have antimicrobial activity against two representative Candida and Cryptococcus strains compared with only 1.1% of the >300,000 purely organic molecules tested through CO-ADD. We identified 90 metal compounds (8.7%) that show antifungal activity while not displaying any cytotoxicity against mammalian cell lines or hemolytic properties at similar concentrations. The structures of 21 metal complexes that display high antifungal activity (MIC ≤1.25 µM) are discussed and evaluated further against a broad panel of yeasts. Most of these have not been previously tested for antifungal activity. Eleven of these metal complexes were tested for toxicity in the Galleria mellonella moth larva model, revealing that only one compound showed signs of toxicity at the highest injected concentration. Lastly, we demonstrated that the organo-Pt(II) cyclooctadiene complex Pt1 significantly reduces fungal load in an in vivo G. mellonella infection model. These findings showcase that the structural and chemical diversity of metal-based compounds can be an invaluable tool in the development of new drugs against infectious diseases.

Conceptual Developments of Aryldiazonium Salts as Modifiers for Gold Colloids and Surfaces.

Modified colloids and flat surfaces occupy an important place in materials science research due to their widespread applications. Interest in the development of modifiers that adhere strongly to surfaces relates to the need for stability under ambient conditions in many applications. Diazonium salts have evolved as the primary choice for the modification of surfaces. The term "diazonics" has been introduced in the literature to describe "the science and technology of aryldiazonium salt-derived materials". The facile reduction of diazonium salts via chemical or electrochemical processes, irradiation stimuli, or spontaneously results in the efficient modification of gold surfaces. Robust gold-aryl nanoparticles, where gold is connected to the aryl ring through bonding to carbon and films modified by using diazonium salts, are critical in electronics, sensors, medical implants, and materials for power sources. Experimental and theoretical studies suggest that gold-carbon interactions constructed via chemical reactions with diazonium salts are stronger than nondiazonium surface modifiers. This invited feature article summarizes the conceptual development of recent studies of diazonium salts in our laboratories and others with a focus on the surface modification of gold nanostructures, flat surfaces and gratings, and their applications in nanomedicine engineering, sensors, energy, forensic science, and catalysis.

The influence of gold(i) on the mechanism of thiolate, disulfide exchange.

The mechanism of gold(i)-thiolate, disulfide exchange was investigated by using initial-rate kinetic studies, 2D ((1)H-(1)H) ROESY NMR spectroscopy, and electrochemical/chemical techniques. The rate law for exchange is overall second order, first order in gold(i)-thiolate and disulfide. 2D NMR experiments show evidence of association between gold(i)-thiolate and disulfide. Electrochemical/chemical investigations do not show evidence of free thiolate and are consistent with a mechanism involving formation of a [Au-S, S-S], four-centered metallacycle intermediate during gold(i)-thiolate, disulfide exchange.

The influence of zinc(II) on thioredoxin/glutathione disulfide exchange: QM/MM studies to explore how zinc(II) accelerates exchange in higher dielectric environments.

QM/MM studies were performed to explore the energetics of exchange reactions of glutathione disulfide (GSSG) and the active site of thioredoxin [Cys32-Gly33-Pro34-Cys35] with and without zinc(II), in vacuum and solvated models. The activation energy for exchange, in the absence of zinc, is 29.7 kcal mol(-1) for the solvated model. This is 3.3 kcal mol(-1) higher than the activation energy for exchange in the gas phase, due to ground state stabilization of the active site Cys-32 thiolate in a polar environment. In the presence of zinc, the activation energy for exchange is 4.9 kcal mol(-1) lower than in the absence of zinc (solvated models). The decrease in activation energy is attributed to stabilization of the charge-separated transition state, which has a 4-centered, cyclic arrangement of Zn-S-S-S with an estimated dipole moment of 4.2 D. A difference of 4.9 kcal mol(-1) in activation energy would translate to an increase in rate by a factor of about 4000 for zinc-assisted thiol-disulfide exchange. The calculations are consistent with previously reported experimental results, which indicate that metal-thiolate, disulfide exchange rates increase as a function of solvent dielectric. This trend is opposite to that observed for the influence of the dielectric environment on the rate of thiol-disulfide exchange in the absence of metal. The results suggest a dynamic role for zinc in thiol-disulfide exchange reactions, involving accessible cysteine sites on proteins, which may contribute to redox regulation and mechanistic pathways during oxidative stress.

An infrared spectroscopic based method for mercury(II) detection in aqueous solutions.

A new method that uses solid phase extraction (SPE) coupled with FTIR spectroscopy to detect Hg(II) in aqueous samples is described. The technique is envisioned for on-site, field evaluation rather than lab-based techniques. This paper presents the "proof of principle" of this new approach toward measurements of Hg(II) in water and identifies mass transport issues that would need to be overcome in order to migrate from a lab based method to field operation. The SPE material supported on a Si wafer is derivatized with an acylthiosemicarbazide, which undergoes a reaction in the presence of aqueous Hg(II) to form an oxadiazole ring. The progress of the reaction is monitored by IR spectroscopy. Following EPA guidelines, the method of detection limit (MDL) for the SPE/IR was 5 µg of Hg(II)cm(-2). In a 1L sample and a 1cm(2) Si wafer, this translates to a detection limit of 5 ppb. This system shows a high selectivity toward aqueous Hg(II) over other thiophilic heavy metal ions such as Pb(II), Cd(II), Fe(III), and Zn(II) and other metal ions such as Ni(II), Mn(II), Co(II), Cu(II), In(III), Ru(III), Na(I), and Ag(I) in aqueous solutions.

Luminescence, structural, and bonding trends upon varying the halogen in isostructural aurophilic dimers.

The preparation of three isonitrile complexes (p-tosyl)CH(2)NCAu(I)X (X = Cl, Br, and I) along with their structural, spectral, and computational characterization are reported. X-Ray crystallography reveals that these complexes all crystallize in the same space group, C2/c, and have closely related supramolecular structures. The three complexes exhibit crossed-dimer structures with short Au...Au aurophilic distances of 3.0634(4) A, 3.1044(7) A, and 3.1083(5) A, for X = Cl, Br, and I, respectively. These distances are among the shortest ligand-unassisted Au...Au interactions reported. While RNCAuX complexes that we reported earlier associate as anti-parallel, one-dimensional aurophilic polymers with long Au...Au distances (approximately 3.6 A) and exhibit orange-red phosphorescence, the analogous aurophilic dimers herein show seemingly counter-intuitive blue-green emissions despite having much shorter Au...Au distances. DFT computations are used to augment experiment and study the T(1) phosphorescent excited state of [RNCAuX](n) in parallel, anti-parallel, and staggered conformations. Excimeric bonding and large Stokes shifts are predicted for all models, the extent of which is sensitive to both "n" and conformation with trends commensurate with experimental luminescence data. Calculations for the three [MeNCAuX](2) dimeric complexes reveal blue-green phosphorescence with a red shift as a function of increasing halide softness, consistent with experimental data for (p-tosyl)CH(2)NCAu(I)X (Cl > Br > I). The overall experimental and theoretical work signifies the central role of ground-state aurophilic bonding and excited-state excimeric bonding on the electronic structure, hence facilitating development of structure-luminescence relations that may assist in the rational design of novel optoelectronic devices.

Novel metallamacrocyclic gold(I) thiolate cluster complex: structure and luminescence of [Au9(mu-dppm)4(mu-p-tc)6](PF6)3.

The structure of a novel metallamacrocyclic phosphine gold(I) thiolate cluster, [Au9(mu-dppm)4(mu-p-tc)6](PF6)3, where dppm = bis(diphenylphosphine)methane and p-tc = p-thiocresolate, is reported and shows AuAu attractions of approximately 3.0 A and gold(I) atoms linked to thiolate and phosphine ligands in distorted trigonal and nearly linear geometries.

Mu-biphenyl-2,2'-dithiolato-kappa2S:S'-bis[(triphenylphosphine-kappaP)gold(I)].

The reaction of ClAuPPh3 and 1,1'-biphenyl-2,2'-dithiol in the presence of trimethylbenzylammonium chloride and K2CO3 in a tetrahydrofuran/methanol solution gives the title complex, [Au2(C12H8S2)(C18H15P)2]. The molecule contains P-Au-S units which 'cross' with torsion angles of approximately 90 degrees [P-Au-Au-P = 86.23 (5) degrees and S-Au-Au-S = 95.62 (5) degrees]. The intra- and intermolecular Au.Au distances [3.9064 (3) and 6.3797 (5) A, respectively] are outside the range for typical Au...Au interactions. However, the Au atoms appear to be drawn together, leading to a significant bending of the P-Au-S angles [170.24 (5) and 169.52 (5) degrees].

Formation of a cationic gold(I) complex and disulfide by oxidation of the antiarthritic gold drug auranofin.

The mechanism of action of auranofin, an antiarthritic gold(I) drug, is unknown, but several studies suggest that oxidation may be important for its biochemical effect. Bulk electrolysis studies on auranofin [(Et(3)P)Au(TATG); TATG = 2,3,4,6-tetraacetyl-1-thio-d-glucopyranosato] at +1.2 and +1.6 V versus Ag/AgCl in 0.1 M Bu(4)NBF(4)/CH(2)Cl(2) results in n values of 0.5 and >2 electrons, respectively. Oxidation of auranofin with the mild oxidant, Cp(2)Fe(+), results in formation of disulfide and a digold(I) cation with a bridging thiolate ligand, [(Et(3)PAu)(2)(mu-TATG)](+) (1). The X-ray structure of the PMe(3) analogue, [(Me(3)PAu)(2)(mu-TATG)](NO(3)) (2), is reported. Compound 2 forms a tetranuclear cluster containing an almost perfect square of four gold atoms with Au.Au distances averaging 3.14 A. The complex crystallizes in the tetragonal space group P4(2)2(1)2 with cell constants a = 26.1758(6) A, b = 26.1758(6) A, c = 9.7781(3) A, alpha = beta = gamma = 90 degrees, V = 6699.7(3) A(3), Z = 4, R1 = 0.0644, and wR2 = 0.1152. A mechanism for oxidation of auranofin and possible biological implications are discussed.

[Mu-o-phenylenebis(diphenylphosphine)-kappa2P:P']bis[chlorogold(I)], dppbz(AuCl)2.

The Au...Au distance in the title compound, [Au(2)Cl(2)(C(30)H(24)P(2))], is 2.996 (1) A, typical of an Au...Au interaction. The two P-Au-Cl arms 'cross' at the Au centers, with a Cl-Au...Au-Cl torsion angle of -63.92 (7) degrees. Only a small deviation from linearity is observed in the coordination around the Au atoms. Related phosphine-gold(I) chloride structures with intra- and intermolecular Au...Au interactions are surveyed.