Ag(I)-N bond-containing compound showing wide spectra in effective antimicrobial activities: polymeric silver(I) imidazolate

Mechanochemical Preparation, Solid-State Characterization, and Antimicrobial Performance of Copper and Silver Nitrate Coordination Polymers with L- and DL-Arginine and Histidine

The antimicrobial activity of the novel coordination polymers obtained by co-crystallizing the amino acids arginine or histidine, as both enantiopure L and racemic DL forms, with the salts Cu(NO3)2 and AgNO3 has been investigated to explore the effect of chirality in the cases of enantiopure and racemic forms. The compounds [Cu·AA·(NO3)2]CPs and [Ag·AA·NO3]CPs (AA = L-Arg, DL-Arg, L-His, DL-His) were prepared by mechanochemical, slurry, and solution methods and characterized by X-ray single-crystal and powder diffraction in the cases of the copper coordination polymers, and by powder diffraction and by solid-state NMR spectroscopy in the cases of the silver compounds. The two pairs of coordination polymers, [Cu·L-Arg·(NO3)2·H2O]CP and [Cu·DL-Arg·(NO3)2·H2O]CP, and [Cu·L-Hys·(NO3)2·H2O]CP and [Cu·DL-His·(NO3)2·H2O]CP, have been shown to be isostructural in spite of the different chirality of the amino acid ligands. A similar structural analogy could be established for the silver complexes on the basis of SSNMR. The activity against the bacterial pathogens Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus was assessed by carrying out disk diffusion assays on lysogeny agar media showing that, while there is no significant effect arising from the use of enantiopure or chiral amino acids, the coordination polymers exert an appreciable antimicrobial activity comparable, when not superior, to that of the metal salts alone.

Ostwald Ripening and Antibacterial Activity of Silver Nanoparticles Capped by Anti-Inflammatory Ligands

Silver nanoparticles (AgNPs) have been extensively studied during recent decades as antimicrobial agents. However, their stability and antibacterial activity over time have yet to be sufficiently studied. In this work, AgNPs were coated with different stabilizers (naproxen and diclofenac and 5-chlorosalicylic acid) in different concentrations. The suspensions of nanostructures were characterized by transmission electron microscopy, UV-Vis and FT-IR spectroscopic techniques. The antibacterial activity as a function of time was determined through microbiological studies against Staphylococcus aureus. The AgNPs show differences in stabilities when changing the coating agent and its concentration. This fact could be a consequence of the difference in the nature of the interaction between the stabilizer and the surface of the NPs, which were evaluated by FT-IR spectroscopy. In addition, an increase in the size of the nanoparticles was observed after 30 days, which could be related to an Ostwald maturation phenomenon. This result raises new questions about the role that stabilizers play on the surface of NPs, promoting size change in NPs. It is highly probable that the stabilizer functions as a growth controller of the NPs, thus determining an effect on their biological properties. Finally, the antibacterial activity was evaluated over time against the bacterium Staphylococcus aureus. The results showed that the protective or stabilizing agents can play an important role in the antibacterial capacity, the control of the size of the AgNPs and additionally in the stability over time.

One pot synthesis of two potent Ag(I) complexes with quinoxaline ligand, X-ray structure, Hirshfeld analysis, antimicrobial, and antitumor investigations

In one pot, the self-assembly of AgNO₃ and 2-chloroquinoxaline (2Cl-quinox) in water-ethanol mixture afforded two novel crystalline Ag(I) complexes. The major product is the polymeric complex [Ag(2Cl-quinox)(NO₃)]_n; (1), while the minor product (2) comprises two molecules which are the monomeric [Ag(2Cl-quinox)₂(NO₃)]; (2a) and polymeric [Ag(2Cl-quinox)(NO₃)]_n; (2b) complexes. The single crystal X-ray structure revealed that 1 and 2b are made up of two-dimensional infinite sheets. In contrast, 2a is a monomeric complex which has a highly distorted tetrahedral geometry around Ag(I) center. In all cases, the 2Cl-quinox molecule acts as a terminal monodentate ligand. Complexes 1 and 2b have similar molecular structures and also have almost similar crystal packing. Using Hirshfeld surface analysis, the O…H hydrogen bonds and π-π stacking interactions contributed significantly to the molecular packing. Both complexes have broad-spectrum action towards multi drug-resistance bacteria. The most effective function of 2 is against Proteus morganii, with a MIC value of 8 μg/mL. Complex 2 (IC₅₀ = 5.93 ± 0.52 μg/mL) has remarkably greater cytotoxic effect against lung carcinoma (A-549) than cis-platin (IC₅₀ = 7.5 ± 0.69 μg/mL) and AgNO₃ (IC₅₀ = 14.7 ± 0.53 μg/mL). The higher Ag-content in 2 could be the main reason for its higher cytotoxicity than 1.

Silver Itaconate as Single-Source Precursor of Nanocomposites for the Analysis of Chloride Ions

At present, conjugated thermolysis of metal-containing monomers is widely used as single-source precursors to obtain new metal- and metal oxide-containing nanocomposites. In this study, a detailed analysis of the main stages of conjugated thermolysis of silver itaconate was carried out. The obtained nanocomposites containing silver nanoparticles are evenly distributed in a stabilizing carbon matrix. The structural characteristics and properties of the resulting nanomaterials were studied using X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). We have developed a method of test analysis of chlorides using paper modified with the obtained silver-containing nanocomposites. The analysis technique is based on the in situ conversion of chlorides to molecular chlorine, its dynamic release, and colorimetric detection using NP-modified paper test strips. A simple installation device is described that allows this combination to be realized. The proposed approach seems promising for nanoparticle-based determinations of other analytes that can be converted into volatile derivatives.

Antimicrobial Properties of Amino-Acid-Derived N-Heterocyclic Carbene Silver Complexes

Complexes {Ag[NHC^Mes,R]}_n (R = H, 2a; Me, 2b and 2b’; ⁱPr, 2c; ⁱBu, 2d), were prepared by treatment of imidazolium precursor compounds [Im^Mes,R] (2-(3-mesityl-1H-imidazol-3-ium-1-yl)acetate, 1a, (S)-2-alkyl(3-mesityl-1H-imidazol-3-ium-1-yl)acetate, 1b–d, and (R)-2-methyl(3-mesityl-1H-imidazol-3-ium-1-yl)acetate, 1b’, with Ag₂O under appropriate conditions. They were characterised by analytical, spectroscopic (IR, ¹H, and ¹³C NMR and polarimetry), and X-ray methods (2a). In the solid state, 2a is a one-dimensional coordination polymer, in which the silver(I) cation is bonded to the carbene ligand and to the carboxylate group of a symmetry-related Ag[NHC^Mes,H] moiety. The coordination environment of the silver centre is well described by the DFT study of the dimeric model {Ag[NHC^Mes,H]}₂. The antimicrobial properties of these complexes were evaluated versus Gram-negative bacteria E. coli and P. aeruginosa. From the observed MIC and MBC values (minimal inhibitory concentration and minimal bactericidal concentration, respectively), complex 2b’ showed the best antimicrobial properties (eutomer), which were significantly better than those of its enantiomeric derivative 2b (distomer). Additionally, analysis of MIC and MBC values of 2a–d reveal a clear structure–antimicrobial effect relationship. Antimicrobial activity decreases when the steric properties of the R alkyl group in {Ag[NHC^Mes,R]}_n increase.

Homochiral imidazolium-based dicarboxylate silver(I) compounds: synthesis, characterisation and antimicrobial properties

Complexes [Ag(LR)], 2 (LR = 2,2'-(imidazolium-1,3-diyl)di(2-alkylacetate)), were prepared by treatment of compounds HLR, 1, with Ag2O. They were characterised by analytical, spectroscopic (IR, 1H and 13C NMR and polarimetry) and...

Water-Stable Silver-Based Metal-Organic Frameworks of Quaternized Carboxylates and Their Antimicrobial Activity

Three-dimensional (3D) and two-dimensional (2D) Ag-based zwitterionic metal-organic frameworks (MOFs) [Ag₂(Cedcp)]_n (1, 3D, H₃CedcpBr denotes N-(carboxyethyl)-(3,5-dicarboxyl)-pyridinium bromide) and {[Ag₄(Cmdcp)₂(H₂O)₄]·4H₂O}_n (2, 2D, H₃CmdcpBr denotes N-(carboxymethyl)-(3,5-dicarboxyl)-pyridinium bromide) have been prepared and investigated for antimicrobial activity via minimal inhibition concentration (MIC) test and killing kinetic assay. Both MOFs 1 and 2 show good water stability and solubility ascribed to their characteristic aromatic rings and positively charged pyridinium of the ligands, as well as the presence of Ag⁺ on their surface, leading to strong antimicrobial activity and a wide antimicrobial spectrum toward Gram-negative and positive bacteria. The results indicated that MOF 2 possesses a faster antibacterial activity (60 min) than MOF 1 (120 min). Scanning electron microscopy analysis further suggests that the Ag-based MOFs are capable of rupturing the bacterial membrane, leading to cell death. Moreover, both MOFs exhibit little hemolytic activity against mouse erythrocytes and show good biocompatibility in vitro, rendering MOFs 1 and 2 potential therapeutic agents for diseases caused by bacteria.

New Antibacterial Silver(I) Coordination Polymers Based on a Flexible Ditopic Pyrazolyl-Type Ligand

In the last two decades, a tremendous amount of attention has been directed towards the design of antibacterial silver(I)-based materials, including coordination polymers (CPs) built up with a great variety of oxygen and nitrogen-containing ligands. Herein, a family of six new silver(I)-based CPs, having the general stoechiometric formula [Ag(H₂DMPMB)(X)] (X = NO₃, 1; CF₃CO₂, 2; CF₃SO₃, 3; BF₄, 4; ClO₄, 5; and PF₆, 6) and incorporating the flexible ditopic pyrazolyl-type ligand 4,4'-bis((3,5-dimethyl-1H-pyrazol-4-yl)methyl)biphenyl (H₂DMPMB), has been prepared by the chemical precipitation method involving the reaction of silver(I) salts with H₂DMPMB in the 1:1 molar ratio, in alcohols, or acetonitrile at room temperature for two-hours. The new silver(I)-based polymeric materials were characterized by means of Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA), and thermogravimetric analysis (TGA), allowing for the proposition that their structures comprise one-dimensional chains, with the silver(I) ions mostly assuming a T-shapped stereochemistry completed by the exo-bidentate ligands and counter-anions. The obtained silver(I) CPs showed a remarkable light insensitivity and stability in the air, are insoluble in water and in most common organic solvents, and possess appreciable thermal stabilities spanning the range 250-350 °C. The antibacterial activity of the obtained silver(I) CPs was tested against the Gram-negative bacteria Escherichia coli (E. coli) and Gram-positive bacteria Staphylococcus aureus (S. aureus) using the Tetrazolium/Formazan test (TTC), by measuring the bacterial viability at different time intervals. The complete reduction of both bacterial strains occurred after 24 h of exposure to all silver(I) CPs, the bacterial viability values for S. aureus reaching 8% for compounds 3, 5, and 6 after only two-hours.

Capping of silver nanoparticles by anti-inflammatory ligands: Antibacterial activity and superoxide anion generation

Silver nanoparticles (AgNPs) have been widely recognized as antibacterial agents. However, its stability and activity over time have been poorly studied. In this work, the properties and characteristics of differently stabilized AgNPs were evaluated during a span of time. The surface capping agents were diclofenac (d), and ketorolac (k), which currently are used as anti-inflammatory in human medicine. On evaluating the size variation over time, it was observed that the AgNPs-k are the most stable, unlike the non-capped nanoparticles agglomerate and precipitate. UV-Vis spectroscopy analysis showed that the absorbance during time decreases for the three types of nanoparticles, but the decrease is less marked for the two types of anti-inflammatory-capped AgNPs. The rapid loss of the optical prop- erties of bare AgNPs, is mainly due to oxidation, agglomeration, and precipitation of this nanoparticles. The potential cytotoxicity of the AgNPs, evaluated through the formation of the superoxide anion using XXT, showed that both, AgNPs-k and AgNPs-d, generate the radical anion when the samples are irradiated with UV light at 365 nm. This effect appears associated with the capping agents, since the bare nanoparticles did not promote the formation of the superoxide anion. The antibacterial activity of the AgNPs throughout time, against two microorganisms (Escherichia coli and Staphylococcus aureus), was also evaluated. The results showed that capping agents played a decisive role in the antibacterial ability of AgNPs and also in enhancing the antibacterial activity over time.

Mononuclear silver(I) complexes with 1,7-phenanthroline as potent inhibitors of Candida growth

Mononuclear silver(I) complexes with 1,7-phenanthroline (1,7-phen), [Ag(NO₃-O,O') (1,7-phen-N7)₂] (1) and [Ag(1,7-phen-N7)₂]X, X = ClO₄^- (2), CF₃SO₃^- (3), BF₄^- (4) and SbF₆^- (5) were synthesized and structurally characterized by NMR (¹H and ¹³C), IR and UV-Vis spectroscopy and ESI mass spectrometry. The crystal structures of 1, 3 and 4 were determined by single-crystal X-ray diffraction analysis. In all these complexes, 1,7-phen coordinates to the Ag(I) ion in a monodentate fashion via the less sterically hindered N7 nitrogen atom. The investigation of the solution stability of 1-5 in DMSO revealed that they are sufficiently stable in this solvent at room temperature. Complexes 1-5 showed selectivity towards Candida spp. in comparison to bacteria, effectively inhibiting the growth of four different Candida species with minimal inhibitory concentrations (MIC) between 1.2 and 11.3 μM. Based on the lowest MIC values and the lowest cytotoxicity against healthy human fibroblasts with selectivity index of more than 30, the antifungal potential was examined in detail for the complex 1. It had the ability to attenuate C. albicans virulence and to reduce epithelial cell damage in the cell infection model. Induction of reactive oxygen species (ROS) response has been detected in C. albicans, with fungal DNA being one of the possible target biomolecules. The toxicity profile of 1 in the zebrafish model (Danio rerio) revealed improved safety and activity in comparison to that of clinically utilized silver(I) sulfadiazine.

Silver(I) Complexes of Diphenylpyridines: Crystal Structures, Luminescence Studies, Theoretical Insights, and Biological Activities

A series of simple two-coordinated cationic silver(I) complexes, namely, [Ag{4-(4-R¹ -phenyl)-2,6-diphenylpyridine}₂ ]X (X=ClO₄ ^- , BF₄ ^- , or SO₃ CF₃ ^- ), with different electron-donating or -withdrawing groups (e.g., R¹ =N(Me)₂ , Me, H, Cl, and Br) on the phenyl ring, were successfully prepared. Extensive characterization of these complexes by various NMR spectroscopy techniques and mass spectrometry was further corroborated by single-crystal XRD analyses. Detailed photophysical investigations of [Ag{4-(4-N,N-dimethylaminophenyl)-2,6-diphenylpyridine}₂ ]ClO₄ (C1) displayed a strong room-temperature fluorescence in solution with an anomalously high luminescence quantum yield of 0.83. The effects of distinct substituent groups (C2-C5), π-conjugated aromatic rings (C6 and C7), and anions (C8 and C9) on the photoluminescence properties were evaluated. Furthermore, DFT and time-dependent DFT calculations were performed to discern the composition of the excited state, as well as to confirm the obtained relative emission energies upon substitution with electronically different ligands. These results indicated that the strong electron-donating substituent of N,N-dimethylamine played an important role in the unprecedented high luminescence quantum yield of C1. In addition, preliminary antimicrobial studies and confocal microscopy fluorescent imaging of HeLa cells labeled with these complexes reveal their potential applications in biological activities.

Biopolymeric self-assembled nanoparticles for enhanced antibacterial activity of Ag-based compounds

Microbial infections still remain one of the main issues for human health. The rapid development of resistance towards the most common antimicrobial drugs in bacteria represents today a challenge in the infections management. In the present work we have investigated the antibacterial activity of a group of compounds, namely silver N-heterocyclic carbene complexes, against a broad spectrum of bacteria. For the most promising compound, a biopolymeric nanocarrier has been developed, in order to potentiate the metal complex activity against both Gram +ve and Gram -ve. The polymeric nanovehicle is based on dextran, modified with oleic acid residues, that confer amphiphilic properties to the polysaccharide. We have characterized the obtained biomaterial and studied its ability to self-assemble into nanoparticles in aqueous environment. Next, the transdermal diffusion analyses have been carried out to evaluate the ability of the polymeric particles to penetrate tissues. Thanks to the strategy adopted, we have fabricated an antibacterial system to which K. pneumoniae and E. coli are the most sensitive.

Linkage Isomerism in Silver Acylpyrazolonato Complexes and Correlation with Their Antibacterial Activity

Novel silver(I) acylpyrazolonato coordination polymers of formula [Ag(Q(R))]n (1-3) have been synthesized by interaction of silver nitrate with HQ(R) in methanol in the presence of an equivalent quantity of KOH (in general HQ(R) = 1-phenyl-3-methyl-4-RC(═O)-5-pyrazolone, in detail HQ(fb), R = -CF2CF2CF3; HQ(cy), R = -cyclo-C6H11; HQ(be), R = -C(H)═C(CH3)2). [Ag(Q(R))]n react with 2-ethylimidazole (2EtimH), 1-methylimidazole (Meim), and triphenylphosphine (PPh3), affording the mononuclear Ag(Q(fb))(EtimH) (4), Ag(Q(cy))(Meim)2 (5), Ag(Q(be))(Meim) (6), and Ag(Q(R))(PPh3)2 (7-9). All complexes have been analytically and spectroscopically characterized, and for some of them the X-ray crystal structure has been resolved. In particular, the single crystal molecular structure determination of Ag(Q(fb))(EtimH) and Ag(Q(be))(PPh3)2 has confirmed the different coordination modes of the HQ(fb) and HQ(be) acylpyrazolone ligands, the former being bound to the silver(I) ion in a monodentate fashion while the latter in the O2-chelating mode. Density functional theory computations suggest new insights about metal-ligand interactions and the observed linkage isomerism. While phosphine-containing complexes Ag(Q(R))(PPh3)2 (7-9) seem not to be able to efficiently inhibit the growth of Escherichia coli and Staphylococcus aureus, the polynuclear complexes [Ag(Q(R))]n (1-3) and the mononuclear Ag(Q(fb))(EtimH) (4), Ag(Q(cy))(Meim)2 (5), and Ag(Q(be))(Meim) (6) show a high and almost steady in time antibacterial activity, comparable to that of AgNO3. This activity is likely related to the degree of saturation of the silver center and to the presence of different ancillary ligands in the diverse typologies of complexes.

Antibacterial effect of silver (I) carbohydrate complexes on oral pathogenic key species in vitro

Background

It was the aim of this study to evaluate the antibacterial impact of two silver(I) carbohydrate complexes with tripodal thioglycosides, namely tris[2-(β-D-thio-glucopyranosyl)ethyl]-amine-silver(I)-nitrate (3) and tris[2-(α-D-thio-manno-pyranosyl)ethyl]-amine-silver(I)-nitrate (4), on five oral pathogenic bacterial strains. Furthermore, cytocompatibility was tested using human gingival fibroblasts (HGF).

Methods

Minimum inhibitory concentrations (MIC) were determined on five oral pathogenic bacterial strains by using the broth microdilution method: Fusobacterium nucleatum (ATCC 10953), Aggregatibacter actinomycetemcomitans (ATCC 33384), Porphyromonas gingivalis (ATCC 33277), Streptococcus mutans (ATCC 25175) and Enterococcus faecalis (DSMZ 20376). Furthermore, antimicrobial efficiency was tested using agar diffusion assays. To evaluate cytocompatibility, human gingival fibroblasts (HGFs) were exposed to AgNO₃ and complex 3 followed by a live/dead staining.

Results

MIC of the silver(I) complexes ranged between 0.625 and 5.0 mmol/L. The silver complexes 3 and 4 showed higher antibacterial efficiency against all tested species than AgNO₃. Antibacterial efficiency of complexes 3 and 4 on F. nucleatum (≥18 mm) and A. actinomycetemcomitans (≥23 mm) was more pronounced than against P. gingivalis (≥15 mm). Complex 3 (20 mM) induced the largest inhibition zones (30 to 31 mm) on Gram-negative strains. For Gram-positive strains, the largest inhibition zones were achieved by complex 3 (20 mM/S. mutans: 28 mm, E. faecalis: 18 mm). Complex 3 had a lower cytotoxic impact on HGFs compared to AgNO₃ by the power of ten.

Conclusions

The findings suggest that silver(I) carbohydrate complexes 3 and 4 might function as novel antimicrobial agents for the treatment of periodontal, carious or endodontic diseases.

Silver(i) complexes with quinazoline and phthalazine: synthesis, structural characterization and evaluation of biological activities

New silver(i) complexes with quinazoline and phthalazine have been synthesized, characterized and evaluated for their antimicrobial activity and their effect on the viability of fibroblasts and the development of zebrafish embryos.

Silver release and antimicrobial properties of PMMA films doped with silver ions, nano-particles and complexes

Materials prepared on the base of bioactive silver compounds have become more and more popular due to low microbial resistance to silver. In the present work, the efficiency of polymethylmethacrylate (PMMA) thin films doped with silver ions, nanoparticles and silver-imidazole polymer complex was studied by a combination of AAS, XPS and AFM techniques. The biological activities of the proposed materials were discussed in view of the rate of silver releasing from the polymer matrix. Concentrations of Ag active form were estimated by its ability to interact with l-cysteine using electronic circular dichroism spectroscopy. Rates of the released silver were compared with the biological activity in dependence on the form of embedded silver. Antimicrobial properties of doped polymer films were studied using two bacterial strains: Staphylococcus epidermidis and Escherichia coli. It was found that PMMA films doped with Ag(+) had greater activity than those doped with nanoparticles and silver-imidazole polymeric complexes. However, the antimicrobial efficiency of Ag(+) doped films was only short-term. Contrary, the antimicrobial activity of silver-imidazole/PMMA films increased in time of sample soaking.