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In a search for novel antimicrobial metal-based therapeutic agents, mononuclear gold(III) complexes 1-7 of the general formula [AuCl3(azole)], where azole stands for imidazole (im, 1), 1-isopropylimidazole (ipim, 2), 1-phenylimidazole (phim, 3), clotrimazole (ctz, 4), econazole (ecz, 5), tioconazole (tcz, 6) and voriconazole (vcz, 7) were synthesized, characterized and biologically evaluated. In all complexes, the corresponding azole ligand is monodentately coordinated to the Au(III) via the imidazole or triazole nitrogen atom, while the remaining coordination sites are occupied by chloride anions leading to the square-planar arrangement. In vitro antimicrobial assays showed that the complexation of inactive azoles, imidazole, 1-isopropylimidazole and 1-phenylimidazole, to the Au(III) ion led to complexes 1-3, respectively, with moderate activity against the investigated strains and low cytotoxicity on the human normal lung fibroblast cell line (MRC-5). Moreover, gold(III) complexes 4-7 with clinically used antifungal agents clotrimazole, econazole, tioconazole and voriconazole, respectively, have, in most cases, enhanced antimicrobial effectiveness relative to the corresponding azoles, with the best improvement achieved after complexation of tioconazole (6) and voriconazole (7). The complexes 4-7 and the corresponding antifungal azoles inhibited the growth of dermatophyte Microsporum canis at 50 and 25 mu g mL(-1). Gold(III) complexes 1-3 significantly reduced the amount of ergosterol in the cell membrane of Candida albicans at the subinhibitory concentration of 0.5 x MIC (minimal inhibitory concentration), while the corresponding imidazole ligands did not significantly affect the ergosterol content, indicating that the mechanism of action of the gold(III)-azole complexes is associated with inhibition of ergosterol biosynthesis. Finally, complexes 5 and 6 significantly reduced the production of pyocyanin, a virulence factor in Pseudomonas aeruginosa controlled by q

Five novel copper(ii) complexes with pyridine-4,5-dicarboxylate esters as ligands, [Cu(NO3)(py-2tz)(H2O)(3)]NO3 (1), [Cu(NO3)(2)(py-2metz)(H2O)] (2), [Cu(NO3)(2)(py-2py)(H2O)]center dot H2O (3), [CuCl2(py-2tz)](2) (4) and [CuCl2(py-2metz)](n) (5) (py-2tz is dimethyl 2-(thiazol-2-yl)pyridine-4,5-dicarboxylate, py-2metz is dimethyl 2-(4-methylthiazol-2-yl)pyridine-4,5-dicarboxylate and py-2py is dimethyl 2,2 '-bipyridine-4,5-dicarboxylate), were synthesized and structurally characterized by different spectroscopic and electrochemical methods. The structure of these complexes was determined by single-crystal X-ray diffraction analysis, confirming the bidentate coordination mode of the corresponding pyridine-4,5-dicarboxylate ester to the Cu(ii) ion through the nitrogen atoms. The antimicrobial potential of copper(ii) complexes 1-5 was assessed against two bacterial and two Candida species. These complexes showed better growth inhibiting activity against Candida spp. with respect to the tested bacterial species, also being moderately toxic towards normal human lung fibroblast cells (MRC-5). Complexes 1 and 4 showed the greatest ability to inhibit the filamentation of C. albicans, which is an important process during fungal infection, and these two complexes efficiently inhibited the biofilm formation of C. albicans at subinhibitory concentrations. Complex 4 also successfully prevented the adhesion of C. albicans in an in vitro epithelial cell model. The mechanism of the antifungal activity of copper(ii) complexes 1-5 was studied through their interaction with ct-DNA, as one of the possible target biomolecules, by fluorescence spectroscopy and gel electrophoresis. Finally, the ability of these complexes to bind to bovine serum albumin (BSA) was studied by fluorescence emission spectroscopy.

In order to develop a novel antifungal agent, we synthesized and completely structurally characterized the silver(I) complex with the known antimycotic itraconazole (itraco), [Ag(itraco-N)(2)]NO3 center dot H2O (Agitraco). The spectroscopic and crystallographic results revealed that, in this complex, two itraco ligands are monodentately coordinated to the Ag(I) ion via the triazole nitrogen atom forming a cationic [Ag(itraco-N)(2)]+ part, which is neutralized by the nitrate anion. The antifungal effect of silver(I) complex and itraconazole was evaluated against four different Candida species (C. albicans, C. glabrata, C. parapsilosis and C. krusei) by means of minimal inhibitory concentrations (MICs). Agitraco complex shows enhanced antifungal activity than itraco, being 2.3- and 4.5-fold more active against C. albicans and C. glabrata, respectively. The complex was also more efficient in inhibiting yeast to hyphae transition process in C. albicans, which is an important step in its pathogenesis. Part of the improved activity of Agitraco could be attributed to the greater induction of reactive oxygen species in Candida spp. with respect to itraco. The toxicity evaluation in the zebrafish model (Danio rerio) suggests that the Agitraco complex has better therapeutic profile and improved antifungal efficacy with respect to the parent drug, which were also proven in vivo using the zebrafish model of lethal disseminated candidiasis. Interaction of Agitraco with bovine serum albumin (BSA) was investigated with the aim to assess its binding affinity toward this biomolecule.

Copper(II) and zinc(II) complexes with clinically used antifungal drug fluconazole (fcz), {[CuCl2(fcz)(2)](.)5H(2)O}(n), 1, and {[ZnCl2(fcz)(2)]Greek ano teleia2C(2)H(5)OH}(n), 2, were prepared and characterized by spectroscopic and crystallographic methods. The polymeric structure of the complexes comprises four fluconazole molecules monodentately coordinated via the triazole nitrogen and two chlorido ligands. With respect to fluconazole, complex 2 showed significantly higher antifungal activity against Candida krusei and Candida parapsilosis. All tested compounds reduced the total amount of ergosterol at subinhibitory concentrations, indicating that the mode of activity of fluconazole was retained within the complexes, which was corroborated via molecular docking with cytochrome P450 sterol 14 alpha-demethylase (CYP51) as a target. Electrostatic, steric and internal energy interactions between the complexes and enzyme showed that 2 has higher binding potency to this target. Both complexes showed strong inhibition of C. albicans filamentation and biofilm formation at subinhibitory concentrations, with 2 being able to reduce the adherence of C. albicans to A549 cells in vitro. Complex 2 was able to reduce pyocyanin production in Pseudomonas aeruginosa between 10% and 25% and to inhibit its biofilm formation by 20% in comparison to the untreated control. These results suggest that complex 2 may be further examined in the mixed Candida-P. aeruginosa infections.

New silver(I) complex with thianthrene (tia), [Ag(NO3)(tia)(H2O)]n, was synthesized by the reaction of AgNO3 with an equimolar amount of tia in ethanol/dichloromethane (v/v 1:1) at room temperature, and characterized by NMR, IR and UV-Vis spectroscopy and single-crystal X-ray diffraction analysis. The antimicrobial activity of the synthesized complex was evaluated against the broad panel of Gram-positive and Gram-negative bacteria and Candida spp. This complex showed significant activity toward important human pathogens Gram-positive Staphylococcus aureus and Candida parapsilosis with minimal inhibitory concentrations (MICs) being 3.91 µg/mL. The interaction of [Ag(NO3)(tia)(H2O)]n with calf thymus DNA (ct-DNA) and bovine serum albumin (BSA) was studied to evaluate the binding affinity towards these biomolecules for possible insights on the mode of antimicrobial activity. The binding affinity of the investigated complex to BSA is higher than that for DNA, indicating that proteins could be more favorable binding sites for this complex in comparison to the nucleic acids.

In a continuing search for a novel metal-containing antimicrobial agents, the present study reports the synthesis, characterization and biological evaluation of two silver(I) complexes with 1,10-phenanthroline-based ligands, [Ag(1,10-phen)(2)]CF3COO center dot H2O (Ag1) and [Ag(CF3COO)(5,6-epoxy-1,10-phen)](2)(Ag2), 1,10-phen is 1, 10-phenanthroline and 5,6-epoxy-1,10-phen is 5,6-epoxy-5,6-dihydro-1,10-phenanthroline. The complexes were characterized by different spectroscopic techniques (IR, H-1 and C-13 NMR and UV-Vis), while the crystal structure of Ag2 complex was determined by a single-crystal X-ray diffraction analysis. The spectroscopic data confirmed that the structure of Ag1 complex, with silver(I) ion tetrahedrally coordinated by two bidentate 1, 10-phen ligands, is in accordance to the previous report (S.E. Paramonov et al., 2003). The crystallographic results showed that in dinuclear Ag2 complex, both Ag(I) ions are coordinated bidentately by 5,6-epoxy-1, 10-phen and monodentately by trifluoroacetate, with presence of the short Ag center dot center dot center dot Ag contact of 2.963 angstrom. Both silver (I) complexes were evaluated in vitro for antimicrobial activity against four bacterial and four Candida species, showing selectivity towards the investigated species of Candida with minimal inhibitory concentrations (MICs) between 0.9 and 12.5 mu M. Moreover, Ag2 complex manifested significant antiproliferative properties in the case of a range of human cell lines, including human breast cancer (MDA-MB 231), which resulted from the presence of epoxy functional group in the ligand. The gel electrophoresis results obtained from the studies of Ag1 and Ag2 interactions with bacteriophage lambda DNA (XDNA) suggested that these complexes did not cause DNA degradation.

1,2-Bis(4-pyridyl)ethane (bpa) and 1,2-bis(4-pyridyl)ethene (bpe) were used for the synthesis of polynuclear silver(I) complexes, {[Ag(bpa)]NO3}(n) (1), {[Ag(bpa)(2)](CF3SO3H2O)-H-.}(n) (2) and {[Ag(bpe)]CF3SO3}(n) (3). In complexes 1-3, the corresponding nitrogen-containing heterocycle acts as a bridging ligand between two Ag(I) ions. In vitro antimicrobial activity of these complexes, along with the ligands used for their synthesis, was evaluated against the broad panel of Gram-positive and Gram-negative bacteria and fungi. The silver(I) complexes 1-3 showed selectivity towards Candida spp. and Gram-negative Escherichia coli in comparison to the other investigated bacterial strains, effectively inhibiting the growth of four different Candida species with minimal inhibitory concentrations (MICs) between 2.5 and 25 mu g/mL and the growth of E. coli, with MIC value being 12.5 mu g/mL. Importantly, complex 2 significantly reduced C. albicans filamentation, an essential process for its pathogenesis. Antiproliferative effect on the normal human lung fibroblast cell line MRC-5 was also evaluated with the aim of determining the therapeutic potential of the complexes 1-3. The interactions of these complexes with calf thymus DNA (ctDNA) and bovine serum albumin (BSA) were studied to evaluate their binding activities towards these biomolecules for possible insights on their mode of action.

Infections of the cow udder leading to mastitis and lower milk quality are one of the biggest problems in the dairy industry worldwide. Unfortunately, therapeutic options for the treatment of cow mastitis are limited as a consequence of the development of pathogens that are resistant to conventionally used antibiotics. In the search for agents that will be active against cow mastitis associated pathogens, in the present study, five new silver(I) complexes with different chelating pyridine-4,5-dicarboxylate types of ligands, [Ag(NO3)(py-2py)](n) (1), [Ag(NO3)(py-2metz)](n) (2), [Ag(CH3CN)(py-2py)]BF4 (3), [Ag(py-2tz)(2)]BF4 (4) and [Ag(py-2metz)(2)]BF4 (5), py-2py is dimethyl 2,2'-bipyridine-4,5-dicarboxylate, py-2metz is dimethyl 2-(4-methylthiazol-2-yl)pyridine-4,5-dicarboxylate and py-2tz is dimethyl 2-(thiazol-2-yl)pyridine-4,5-dicarboxylate, were synthesized, structurally characterized and assessed for in vitro antimicrobial activity using both standard bioassay and clinical isolates from a contaminated milk sample obtained from a cow with mastitis. These complexes showed remarkable activity against the standard panel of microorganisms and a selection of clinical isolates from the milk of the cow diagnosed with mastitis. With the aim of determining the therapeutic potential of silver(I) complexes, their toxicity in vivo against the model organism, Caenorhabditis elegans (C. elegans), was investigated. The complexes that had the best therapeutic profile, 2 and 5, induced bacterial membrane depolarization and the production of reactive oxygen species (ROS) in Candida albicans cells and inhibited the hyphae as well as the biofilm formation. Taken together, the presented data suggest that the silver(I) complexes with pyridine ligands could be considered for the treatment of microbial pathogens, which are causative agents of cow mastitis.

The reactions between equimolar amounts of CuX2 (X = NO3− and CF3SO3−) and two aromatic nitrogen-containing heterocycles differing in the position of nitrogen atoms, 1,7- and 4,7-phenanthroline (1,7- and 4,7-phen), were performed in ethanol/methanol at room temperature. When CuX2 salts were mixed with 4,7-phen, two copper(II) complexes, [Cu(NO3)2(4,7-Hphen)2](NO3)2 (1) and [Cu(CF3SO3)(4,7- phen)2(H2O)2]CF3SO3 (2), were formed. On the other hand, in the reaction of CuX2 salts with 1,7-phen, only 1,7-HphenNO3 (3a/b) and 1,7-HphenCF3SO3 (4) were obtained as the final products. The obtained products 1–4 were characterized by spectroscopic and X-ray diffraction techniques. In the copper(II) complexes 1 and 2, the coordination geometry around the Cu(II) ion is distorted octahedral and square pyramidal, respectively. The antimicrobial potential of the copper(II) complexes 1 and 2 and corresponding compounds used for their synthesis were assessed against four different bacterial species and Candida albicans, displaying moderate growth inhibiting activity. The cytotoxic properties of the investigated complexes were also evaluated against the normal human lung fibroblast cell line (MRC-5) indicating moderate, yet more pronounced cytotoxicity than antimicrobial properties.

The reactions between equimolar amounts of CuX2 (X = NO3− and CF3SO3−) and two aromatic nitrogen-containing heterocycles differing in the position of nitrogen atoms, 1,7- and 4,7-phenanthroline (1,7- and 4,7-phen), were performed in ethanol/methanol at room temperature. When CuX2 salts were mixed with 4,7-phen, two copper(II) complexes, [Cu(NO3)2(4,7-Hphen)2](NO3)2 (1) and [Cu(CF3SO3)(4,7- phen)2(H2O)2]CF3SO3 (2), were formed. On the other hand, in the reaction of CuX2 salts with 1,7-phen, only 1,7-HphenNO3 (3a/b) and 1,7-HphenCF3SO3 (4) were obtained as the final products. The obtained products 1–4 were characterized by spectroscopic and X-ray diffraction techniques. In the copper(II) complexes 1 and 2, the coordination geometry around the Cu(II) ion is distorted octahedral and square pyramidal, respectively. The antimicrobial potential of the copper(II) complexes 1 and 2 and corresponding compounds used for their synthesis were assessed against four different bacterial species and Candida albicans, displaying moderate growth inhibiting activity. The cytotoxic properties of the investigated complexes were also evaluated against the normal human lung fibroblast cell line (MRC-5) indicating moderate, yet more pronounced cytotoxicity than antimicrobial properties.