Antimicrobial and anticancer activity of tetrahedral, chelated, diphosphine silver(I) complexes: comparison with copper and gold

Tetrahedral, bischelated Ag(I) diphosphine complexes [Ag(P-P)2]NO3, where P-P is Ph2P(CH2)2PPh2 (dppe), Et2P(CH2)2PPh2 (depe), and cis-Ph2P(CH = CH)PPh2 (dppey), are potently cytotoxic to B16 melanoma cells in vitro (IC50 4 microM) and exhibit good activity against ip P388 leukemia in mice. The complex [Ag(dppe)2]NO3 is active against M5076 reticulum cell sarcoma. The antibacterial and antifungal activities of Ag(I) diphosphine and related Cu(I) and Au(I) complexes were assessed. The complexes [Au(dppey)2]Cl, [Au(dppp)2]Cl and (CuCl)2(dppe)3 show modest activity against three of the 12 bacterial strains tested, but all complexes exhibit antifungal activity against three strains of C. albicans in a "defined" medium, [Ag(depe)2]NO3 and [Au(dppp)2]Cl having comparable activity to fungizone. Antifungal activity of the complexes is reduced in Sabouraud's broth medium, and lost altogether for the Ag(I) complexes. Reactions of some of the Ag(I) complexes with glutathione and blood plasma were studied by 31P NMR.     

Synthesis, structure, and catalytic activity of chiral silver(I) and copper(II) complexes with biaryl-based nitrogen-containing ligands

A series of chiral Ag(I) and Cu(II) complexes have been prepared from the reaction between AgX (X = NO₃, PF₆, OTf) or CuX₂ (X = Cl, ClO₄) and chiral biaryl-based N-ligands. The rigidity of the ligand plays an important role in the Ag(I) complex formation. For example, treatment of chiral N₃-ligands 1-3 with half equiv of AgX (X = NO₃, PF₆, OTf) gives the chiral bis-ligated four-coordinated Ag(I) complexes, while ligand 4 affords the two-coordinated Ag(I) complexes. Reaction of AgX with 1 equiv of chiral N₄-ligands 5, 7, 8 and 10 gives the chiral, binuclear double helicate Ag(I) complexes, while chiral mono-nuclear single helicate Ag(I) complexes are obtained with N₄-ligands 6 and 9. Treatment of either N₃-ligand 1 or N₄-ligand 9 or 10 with 1 equiv of CuX₂ (X = Cl, ClO₄) gives the mono-ligated Cu(II) complexes. All the complexes have been characterized by various spectroscopic techniques, and elemental analyses. Seventeen of them have further been confirmed by X-ray diffraction analyses. The Cu(II) complexes do not show catalytic activity for allylation reaction, in contrast to Ag(I) complexes, but they do exhibit catalytic activity for Henry reaction (nitroaldol reaction) that Ag(I) complexes do not.     

Synthesis of a new tetradentate bis(imino-phosphine) ligand and its complexation with copper(I) ions

Schiff base condensation of m-phenylenediamine with two equivalents of o-(diphenylphophino)benzaldehyde products the potentially tetradentate molecule 1,3-(Ph₂P(o-C₆H₄)CHN)₂C₆H₄ (1) in high yield. The reaction of 1 and [Cu(NCMe)₄]BF₄ affords the dinuclear complex [(1,3-(Ph₂P(o-C₆H₄)CHN)₂C₆H₄)₂Cu₂](BF₄)₂ (2) through coordination of the imino-phosphine groups. The structure of 2 has been determined by an X-ray diffraction study.     

Bio-guided search of active indole alkaloids from Tabernaemontana catharinensis: Antitumour activity,toxicity in silico and molecular modelling studies

Active plant metabolites have been used as prototype drugs. In this context, Tabernaemontana catharinensis (Apocynaceae) has been highlighted because of the presence of active indole alkaloids. Thus, this study aims the bio-guided search of T. catharinensis cytotoxic alkaloids. The chemical composition was identified by high-resolution mass spectrometry, and fractionation was performed by open column and preparative thin-layer chromatography, from plant stems. The enriched fractions were tested in vitro in tumour cells A375 (melanoma cell line) and A549 (adenocarcinomic human alveolar basal epithelial cells), and non-tumour Vero cells (African green monkey kidney epithelial cells). The alkaloids identified as active were submitted to in silico toxicity prediction by ADME-Tox and OSIRIS programs and, also, to molecular docking, using topoisomerase I (PDB ID: 1SC7) by iGEMDOCK. As a result, six sub-fractions were obtained, which were identified as containing 16-epi-affinine, 12-methoxy-n-methyl-voachalotine, affinisine, voachalotine, coronaridine hydroxyindoline and ibogamine, respectively. The affinisine-containing sub-fraction showed selective toxicity against A375, with an IC₅₀ of 11.73 µg mL⁻¹, and no cytotoxicity against normal cells (Vero). From the in silico toxicity test results, all indole alkaloid compounds had a low toxicity risk. The molecular docking data provided structural models and binding affinities of the plant’s indole alkaloids and topoisomerase I. In summary, this bio-guided search revealed that the indole alkaloids from T. catharinensis display selective cytotoxicity in A375 tumour cells and toxicity in silico. Particularly, affinisine might be a chemotherapeutic for A375 melanoma cells.     

Secondary ion mass spectrometry of nonvolatile isocyanide complexes of silver(I) and copper(I)

A series of silver and copper coordination complexes has been studied using secondary ion mass spectrometry (SIMS). Results are presented for the monomeric silver(I) complexes [Ag(CNR)₄]X, where R = cyclohexyl for X  ClO₄⁻, and R = methyl or t-butyl for X  PF₆⁻. Likewise, Cu(I) complexes [Cu(CNR)₄]PF₆, where R =methyl, t-butyl, or cyclohexyl, were examined. The presence of AgL₂⁺ (L represents the intact RNC ligand) and the absence of AgL₃⁺ and AgL₄⁺ species attests to the gas phase stability of two-coordinate silver(I). Similar results to these were obtained for the Cu(I) complexes, with the exception of [Cu(CNCH₃)₄]PF₆ whose spectrum contains CuL₄⁺, CuL₃⁺, CuL₂⁺, CuL⁺, and Cu⁺ ions. The latter result reflects the enhanced stability of the tetrahedral Cu(I) geometry compared to Ag(I) in the gas phase. Cross labeling experiments and isotopic labeling studies have provided insights into fragmentation mechanisms. Ligand exchange occurs when mixtures are examined. These exchange reactions provide evidence for extensive molecular mixing which can accompany SIMS even under low primary ion dose conditions. Cluster ion formation as well as the observation of α-cleavage of the NC bonds of RNC ligands have been observed and these results are discussed. Granulated graphite and ammonium chloride were employed to study matrix effects. Granulated graphite enhanced NC cleavage for the silver complexes but had little effect on the relative abundance of silver cluster ions. On the other hand, copper cluster ions were more sensitive to matrix effects.     

Structure and antibacterial activity of the silver(I) complex of 2-aminophenoxazine-3-one

The crystal structure and antibacterial activity of the first metal complex of 2-aminophenoxazine-3-one is reported. We describe the silver(i) complex of this important biological molecule and show that the binding mode is through the phenoxazine ring nitrogen. A new synthetic route to 2-aminophenoxazine-3-one is also reported.     

Novel organic-inorganic molecular assembly: a copper(I) and copper(II) mixed-valent cluster with bromide bridges and paramagnetic ligands

Complex pbt₂Cu₈Br₁₂ [pbt=pyridine-2,6-diylbis(methyleneamino-TEMPO)] was synthesized from CuBr₂ and a new ligand pbt, and characterized by means of X-ray crystal structure analysis and magnetic measurements. The centrosymmetric molecule consists of a Cu₆Br₁₀ cluster sandwiched with two pbt·CuBr complexes. Detailed geometrical analysis and magnetic analysis reveal the presence of four copper(I) and four copper(II) ions in a molecule. Antiferromagnetic couplings observed can be attributed to the intermolecular radical?radical and intramolecular copper(II)?copper(II) interactions.     

Gold(I) complexes with thiosemicarbazones: cytotoxicity against human tumor cell lines and inhibition of thioredoxin reductase activity

Complexes [Au(H2Ac4DH)Cl]?MeOH (1) [Au(H₂2Ac4Me)Cl]Cl (2) [Au(H₂2Ac4Ph)Cl]Cl?2H₂O (3) and [Au(H₂2Bz4Ph)Cl]Cl (4) were obtained with 2-acetylpyridine thiosemicarbazone (H2Ac4DH), its N(4)-methyl (H2Ac4Me) and N(4)-phenyl (H2Ac4Ph) derivatives, as well as with N(4)-phenyl 2-benzoylpyridine thiosemicarbazone (H2Bz4Ph). The compounds were cytotoxic to Jurkat (immortalized line of T lymphocyte), HL-60 (acute myeloid leukemia), MCF-7 (human breast adenocarcinoma) and HCT-116 (colorectal carcinoma) tumor cell lines. Jurkat and HL-60 cells were more sensitive than MCF-7 and HCT-116 cells. Upon coordinating to the gold(I) metal centers in complexes (2) and (4), the cytotoxic activity of the H2Ac4Me and H2Bz4Ph ligands increased against the HL-60 and Jurkat tumor cell lines. 2 was more active than auranofin against both leukemia cells. Most of the studied compounds were less toxic than auranofin to peripheral blood mononuclear cells (PBMC). All compounds induced DNA fragmentation in HL-60 and Jurkat cells indicating their pro-apoptotic potential. Complex (2) strongly inhibited the activity of thioredoxin reductase (TrxR), which suggests inhibition of TrxR to be part of its mechanism of action.     

Coordination modes of N-(2-hydroxyphenyl)methyl-bis-(2-pyridylmethyl)amine with copper (I) and (II) halides

The title ligand, N-(2-hydroxyphenyl)methyl-bis-(2-pyridylmethyl)amine, was prepared via a condensation-reduction synthetic route. The compounds, CuCl(C₁₉H₁₉N₃O) and [CuBr(C₁₉H₁₉N₃O)]⁺Br⁻ · 3H₂O, were readily synthesized from the reaction of CuCl or CuBr₂ and the ligand in acetonitrile. The title copper(I) compound is an O-H ? Cl hydrogen-bonded linear chain of tetrahedrally coordinated copper centers, and the title copper(II) compound exists as two strongly tetragonally distorted dibromide bridged metal cations in a dimer with the phenol hydroxyl groups weakly bound in a trans-fashion to one of the bridging bromides. In the copper(I) complex the phenoxy group acts only as a hydrogen bond donor, whereas in the copper(II) complex it acts both as a ligand and a hydrogen bond donor.     

Molecular design, crystal structure, antimicrobial activity and reactivity of light-stable and water-soluble Ag-O bonding silver(I) complexes, dinuclear silver(I) N-acetylglycinate

The reaction in water of silver oxide with N-acetylglycine (H₂acgly) possessing the partial structure, i.e. the OC-N-C-COOH moiety, afforded light-stable and water-soluble dinuclear silver(I) complex _∞{[Ag(Hacgly)]₂} (complex 1). X-ray crystallography revealed that complex 1 in the solid state formed a ladder polymeric structure based on bis(carboxylato-O,O′)-bridged centrosymmetric Ag₂O₄ core, which was different from the two previously reported structures of silver(I) glycinate. Complex 1 which only comprises labile Ag-O bonding showed a wide range of antimicrobial activities against selected bacteria, yeasts and molds. Complex 1 can also work as an useful silver(I) precursor for novel silver(I) cluster synthesis.     

Crystal and molecular structure of bis(tricyclohexylphosphine)silver(I)nitrate and bis(tricyclohexylphosphine)silver(I)perchlorate; correlation of the structures with the silver-phosphorus coupling constants

Two (1:2) silver monophosphine complexes have been studied by X-ray diffraction methods and in solution by P NMR spectroscopy. Both are monomeric and tricoordinated in the solid state but one of them, the perchlorate compound, is probably associated as a dimer species in solution from the lower ¹J(¹⁰⁷Ag³¹P) value when compared to the nitrate analogue. Previous structural correlations found in other silver-phosphine complexes have been confirmed for these new compounds. Thus, larger PAgP bond angles are associated with shorter AgP bond distances, longer Aganion bond distances and lower Lewis basicity of the anions. Selected structural data are: PAgP bond angle of 139.04(9)°, AgP bond lengths of 2.440(3) and 2.445(3) Å for the nitrate complex and 147.34(3)°, 2.429(1) Å and 2.432(1) Å, for the perchlorate one. J(¹⁰⁷Ag³¹P) is 457 Hz and 447 Hz, respectively. The complexes are triclinic, Z = 2, with the parameters: a = 9.258(2), b = 9.828(2), c = 23.385(5) Å, α = 94.73(2)°, β = 96.35(2)°, γ = 116.42(1)° (nitrate) and a = 9.505(2), b = 9.790(2), c = 23.667(6) Å, α= 99.03(2) β = 95.44(2) γ = 115.97(1)° (perchlorate).     

Effect of treatment with silver(I) complex of metronidazole on ocular rosacea: Design and formulation of new silver drug with potent antimicrobial activity

BackgroundMetronidazole with well-soluble silver nitrate forms a complex with potent activity (synergism) against bacterial strains and fungi with simultaneous lower side effect than in the case of the two agents administered separately.This study aimed to establish effectiveness in the treatment of ocular rosacea with new formulation of drops and ointment with silver(I) complex of metronidazole.MethodsThree patients suffering from serious ophthalmic complications of acne rosacea were treated with drops and ointments applied 3 times a day for 3 months. The uncorrected visual acuity testing (UCVA), pachymetry as well as subjective and objective tear film assessment were evaluated.ResultsIn all patients, we have improved UCVA as well as objective and subjective evaluation of the tear film parameters. No significant differences in corneal thickness were observed.ConclusionWell soluble silver(I) complex of metronidazole might be an alternative method in ophthalmic complications of acne rosacea treatment.     

Gold(I) and silver(I) complexes of 2,3-bis(diphenylphosphino)maleic acid: Structural studies and antitumour activity

The 2:1 and 1:2 adducts of Au(I) and 1:2 adducts of Ag(I) with the diphosphine 2,3-bis(diphenylphosphino)maleic acid (dpmaa) have been prepared in high yields. Crystal structures have been determined for the neutral digold complex (AuCl)₂(dpmaa) · 2thf (1) and the bis-chelated complex [Au(dpmaa)₂]Cl · H₂O · CH₃OH (2). For 1, conformational rigidity imposed by the ethylenic bridge facilitates the formation of short intramolecular Au-Au contacts with no evidence of similar intermolecular contacts. Complex 2 crystallizes with [Au(dpmaa)₂]⁺ cations hydrogen bonded through the carboxyl groups to a water molecule and chloride anion to form a H-bonded chain along the a axis. ³¹P NMR titration of 1 with dpmaa in acetone shows conversion to 2 at Au:P-P ratios less than 1:1 indicating similar high thermodynamic and kinetic stabilities to other bis-chelated [Au(P-P)₂]⁺ complexes containing 5- or 6-membered chelate rings. The ionic Au(I) complex 2 and the analogous Ag(I) complex [Ag(dpmma)₂]NO₃ (3) are highly water soluble. The in vitro cytotoxic activity of 2 was assessed against eight different cell lines and no significant activity was found. The solubility properties and solution behaviour of the complexes are compared to the analogous 1,2-bis(diphenylphosphino)ethane (dppe) complexes and the potential significance of these results to the antitumour properties of chelated 1:2 Au(I)diphosphine complexes are discussed.     

Crystal structures of multicopper oxidase CueO bound to copper(I) and silver(I): functional role of a methionine-rich sequence

The multicopper oxidase CueO oxidizes toxic Cu(I) and is required for copper homeostasis in Escherichia coli. Like many proteins involved in copper homeostasis, CueO has a methionine-rich segment that is thought to be critical for copper handling. How such segments function is poorly understood. Here, we report the crystal structure of CueO at 1.1 Å with the 45-residue methionine-rich segment fully resolved, revealing an N-terminal helical segment with methionine residues juxtaposed for Cu(I) ligation and a C-terminal highly mobile segment rich in methionine and histidine residues. We also report structures of CueO with a C500S mutation, which leads to loss of the T1 copper, and CueO with six methionines changed to serine. Soaking C500S CueO crystals with Cu(I), or wild-type CueO crystals with Ag(I), leads to occupancy of three sites, the previously identified substrate-binding site and two new sites along the methionine-rich helix, involving methionines 358, 362, 368, and 376. Mutation of these residues leads to a ∼4-fold reduction in k_cat for Cu(I) oxidation. Ag(I), which often appears with copper in nature, strongly inhibits CueO oxidase activities in vitro and compromises copper tolerance in vivo, particularly in the absence of the complementary copper efflux cus system. Together, these studies demonstrate a role for the methionine-rich insert of CueO in the binding and oxidation of Cu(I) and highlight the interplay among cue and cus systems in copper and silver homeostasis.     

Macrocyclic copper(II) complexes: superoxide scavenging activity, structural studies and cytotoxicity evaluation

Synthetic superoxide dismutase mimetics have emerged as a potential novel class of drugs for the treatment of oxidative stress related diseases. Among these agents, metal complexes with macrocyclic ligands constitute an important group. In this work we synthesized five macrocyclic copper(II) complexes and evaluated their ability to scavenge the superoxide anions generated by the xanthine-xanthine oxidase system. Two different endpoints were used, the nitro blue tetrazolium (NBT) reduction assay (colorimetric method) and the dihydroethidium (DHE) oxidation assay (fluorimetric method). IC(50) values in the low micromolar range were found in four out of five macrocyclic complexes studied, demonstrating their effective ability to scavenge the superoxide anion. The IC(50) values obtained with the NBT assay for the macrocyclic copper(II) complexes, were consistently higher, approximately threefold, than those obtained with the DHE assay. Spectroscopic and electrochemical studies were performed in order to correlate the structural features of the complexes with their superoxide scavenger activity. Cytotoxicity assays were also performed using the MTT method in V79 mammalian cells and we found that the complexes, in the range of concentrations tested in the superoxide scavenging assays were not considerably toxic. In summary, some of the presented macrocyclic copper(II) complexes, specially those with a high stability constant and low IC(50), appear to be promising superoxide scavenger agents, and should be considered for further biological assays.     

Tetrameric 1:1 and monomeric 1:3 complexes of silver(I) halides with tri(p-tolyl)-phosphine: A structural and biological study

Silver(I) halides react with tri(p-tolyl)phosphine (tptp, C₂₁H₂₁P) in MeOH/MeCN solutions in 1:1 or 1:3 molar ratios to give complexes of formulae {[AgCl(tptp)]₄} (1) or [AgX(tptp)₃] (X = Cl (2), Br (3), I (4)), respectively. The complexes were characterized by elemental analyses, and FT-IR far-IR, FT-Raman, TG and ¹H, ¹³C, ³¹P NMR spectroscopic techniques. Crystal structures of complexes 2-4 were determined by X-ray diffraction at room temperature (rt). The crystal structure of 1 and 4 was also determined at 100(1) and 140(2) K (lt), respectively. In complex 1 four μ3-Cl ions are bonded with four Ag(I) ions forming a cubane while the coordination sphere of silver(I) ions is completed by one P atom from a terminal tri(p-tolyl)phosphine ligand. In complexes 2-3 one terminal halogen and three P atoms from phosphine ligands form a tetrahedral arrangement around the metal ion. Complexes 1-4 were tested for in vitro cytostatic activity against sarcoma cancer cells (mesenchymal tissue) from the Wistar rat, polycyclic aromatic hydrocarbons (PAH, benzo[a]pyrene) carcinogenesis and against murine leukemia (L1210) and human T-lymphocyte (Molt4/C8 and CEM) cells. The silver(I) complexes 1-4 show strong activity.     

Structure and luminescence of copper(I) cyanide-amine and -sulfide networks

Copper(I) cyanide reacts with various liquid amines and sulfides (L) under solvent-less conditions to form (CuCN)L_n, n = 0.5, 0.57, 0.75, 0.8, 1, 1.25, 1.5, 2. New X-ray structures are reported for L = Py (Py = pyridine, n = 0.57), 2-MePy (n = 1), 3-EtPy (n = 1.5), 2-ClPy (n = 1), 3-ClPy (n = 2), 3-MeOPy (n = 2), 4-^tBuPy (n = 1.5), piperidine (n = 1.25), N-methylmorpholine (n = 1), N,N-dimethylcyclohexylamine (n = 1), 1-methylimidazole (n = 3), Me₂S (n = 1), and tetrahydrothiophene (n = 1). The amine structures (except for the monomeric 1-methylimidazole complex) reveal 1D CuCN chains decorated with 0-2 L per metal atom. Chain structures observed include zigzag, helical and figure-8 helical. The CuCN-sulfide structures show sulfur-bridging of CuCN chains. In some cases (CuCN)L_?1.5 species are transformed to (CuCN)L under vacuum. Thermal analysis shows facile release of ligand, yielding CuCN. Most of the (CuCN)L_n products are photoluminescent, emitting in the visible region. In some cases, coordination of very similar amines results in remarkably different emission spectra.     

Design,synthesis, biological evaluation and molecular modelling studies of indole glyoxylamides as a new class of potential pancreatic lipase inhibitors

A series of eighteen indole glyoxylamide analogues were synthesized, characterized and evaluated for their pancreatic lipase inhibitory activity. Porcine pancreatic lipase (Type II) was used with 4-nitrophenyl butyrate (as substrate) for the in vitro assay. Compound 8f exhibited competitive inhibition against pancreatic lipase with IC₅₀ value of 4.92 µM, comparable to that of the standard drug, orlistat (IC₅₀ = 0.99 µM). Compounds 7a-i and 8a-i were subjected to molecular docking into the active site of human PL (PDB ID: 1LPB) wherein compound 8f possessed a potential MolDock score of −153.037 kcal/mol. Molecular dynamics simulation of 8f complexed with pancreatic lipase, confirmed the role of aromatic substitution in stabilizing the ligand through hydrophobic interactions (maximum observed RMSD = 3.5 Å).     

Synthesis and characterization of copper(I) and silver(I) complexes with heterocyclic bidentate ligands (N, X), X = S, Se

The synthesis and structural characterization of series of copper and silver homoleptic complexes [M(R-pyX)], M = Cu, Ag, X = S, Se; R = H, 3-CF₃, 5-CF₃ (not all combinations), is described. The copper compounds, as well as [Ag(pySe)] and [Ag(3-CF₃-pySe)], were synthesised by electrochemical oxidation of anodic metal in a cell containing an acetonitrile solution of the corresponding proligand. The other homoleptic silver complexes were obtained by direct reaction between AgNO₃ and the salt of the corresponding ligand in methanol. In addition, the reaction of the metal thiolate compounds with bis(diphenylphosphino)ethane (dppe) in acetone allowed the synthesis of heteroleptic compounds [M₂(R-pyX)₂(dppe)₃]. The compounds obtained have been characterized by microanalysis, IR spectroscopy and mass spectrometry and, in cases where the complexes were sufficiently soluble, by ¹H NMR spectroscopy. The proligands (3-CF₃pySe)₂ (1), (5-CF₃-pySe)₂ (2) and (5-CF₃-pySe-DMF) (3) and the complexes [Cu(3-CF₃-pyS)] (4), [Ag(3-CF₃-pyS)] (5) and [Cu₂(5-CF₃-pyS)₂(dppe)₃] (6) were obtained as crystalline products and were studied by X-ray diffraction methods.     

Ionic metallomesogens derived from silver(I) bis-amine complexes: Structure and mesogenic behavior

Complexes [Ag(NH₂R)₂]X, (X = NO₃, R = -C₆H₄-C_nH_2n+1-p, -C₆H₄-O-C_nH_2n+1-p, -CH₂-C₆H₄-O-C_nH_2n+1-p, n = 6, 8, 10, 12, 14; X = BF₄, R = -CH₂-C₆H₄-O-C_nH_2n+1-p, n = 6, 8, 10, 12, 14; X = OAc, R = -CH₂-C₆H₄-O-C₁₀H₂₁-p; X = CF₃SO₃, R = -CH₂-C₆H₄-O-C₁₀H₂₁-p) have been prepared. They all show S_A mesophases corresponding to two kinds of structures, already present in the solid state. The alkylaniline and alkoxyaniline derivatives adopt a bilayered structure where the cation has an extended centrosymmetric conformation. The benzylamine derivatives contain U-shaped cations giving rise to a bilayered structure which allows microsegregation of the organic part of the molecule from the inorganic Ag?(anion) part. Some degree of interdigitation of the terminal chains is observed for all the complexes with aryl containing ligands.