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Redox-active metal complexes of sterically hindered phenolic ligands: Antibacterial activity and reduction of cytochrome c. Part IV. Silver(I) complexes with hydrazone and thiosemicarbazone derivatives of 4,6-di-tert-butyl-2,3-dihydroxybenzaldehyde
... Meanwhile, the presence of a methoxy group at the -meta position in P6 caused a higher SI value of 0.393 than that of P3. Based on the results of previous studies, the insertion of methyl [28] and hydroxyl [29][30] groups into the compounds enhanced the antiplasmodial activity. Nonetheless, it remained uncertain for the role of each functional group in improving the selectivity of the silver complexes. ...
A series of six sulfur-bridged dinuclear silver(I) thiosemicarbazone complexes were synthesized through the reaction of silver(I) nitrate with 4-phenyl-3-thiosemicarbazone derivatives together with triphenylphosphine (PPh3) (in a 1:1:2 molar ratio). Following structural characterizations using various techniques such as elemental analysis, Fourier-transform infrared (FTIR) spectroscopy, as well as 1H, 13C, 31P{1H}s, COSY, and 1H-13C nuclear magnetic resonance (NMR) spectroscopy, it was found that the thiosemicarbazone ligand exists in the form of a thione rather than thiol tautomer. Subsequently, MDA-MB-231 and MCF-7 breast cancer cell lines, as well as the HT-29 colon cancer cell lines, were used to investigate the in vitro antiproliferative activities of these complexes. In all cases, the IC50 values were in the potent micromolar range. Besides, the aforementioned complexes also had good antiplasmodial activity against chloroquine-resistant P. falciparum, as per the results of histidine-rich protein 2 (HRP2) assays and cytotoxicity evaluations of MDBK cells.
... The X-ray diffraction analysis (XRD) was carried out using DRON-2 (CuKα-emission). The redox-properties of Ni(II) complexes were evaluated by the means of the cyclic voltammetry method in the potential range from -2.2 to +2.2 V, using a de-aerated acetonitrile solution of these compounds [16][17][18][19]. The lipophilicity test was made by determining the n-octanol/water partition coefficient (Pow) [20]. ...
... The biological importance of these Schiff's base chelates of thiosemicabazides involved the researchers greater than before to develop fresh ligands as antibacterial [16], antimicrobial [17][18][19], antifungal [20,21], antiparasitic [22], antitumor [23], anticancer [24][25][26], antioxidant [27,28], anti-inflammatory [29], anti-HIV [30], antiproliferative [31], antileishmanial activities [32] and antiviral [33]. Tetradentate thiosemicabazone with strong DNA-binding ability was isolated after the condensation of pyruvaldehyde with 4-(aryl)-thiosemicarbazones [34]. ...
Due to their borad profiles of biological activities, transition metal complexes containing semicarbazones and thiosemicarbazones become largely appealing. This mini review focused on the recent developments in last 5 years on the biological applications of Co(II) and Ni(II) complexes of semicarbazones and thiosemicarbazones.
... This effect is less pronounced for the hydrazone sulphonylimine (Y = NNR; 1 and 2) than for the imine sulphonylimine complexes (Y = NR; 3). The opposite effect (charge transfer from the ligand to the metal) is considered responsible for the Ag(I)→ Ag(0) process not having been observed in the phenolic hydrazone Ag(I) complex, and in the case of the related phenolic thiosemicarbazone Ag(I) complex (−0.14 V) the potential is considerably lower [26] than the values herein reported. ...
Camphorsulphonylimine complexes [Ag(NO3)(IL)2] (IL = C12H19N3SO2, 1) and [(AgNO3)2(IIL)] (IIL = C22H23N3SO2, 2) were synthesized and characterized by elemental analysis, spectroscopy (IR, NMR) and cyclic voltammetry. [Ag(NO3)(IL)2] crystalizes in the monoclinic C2 space group with a triangular geometry assuming a chalice-type shape. The anti-proliferative properties of the new complexes 1 and 2 and those of the previously reported [(AgNO3)2(IIIL)] (IIIL = C16H18N3SO2, 3) were assessed against the human ovarian cancer cells (cisplatin-sensitive A2780, cisplatin-resistant A2780cisR) and the non-tumoral human HEK 293 cell line, using the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. The NR (3-amino-7-dimethylamino-2-methylphenazine hydrochloride) assay was alternatively used to assess the cytotoxicity on the A2780 cells. Results from the MTT assay (48 h exposure) show that the complexes display IC50 values lower (by at least one order of magnitude) than cisplatin, while the cytotoxicity of AgNO3 is of the same order of cisplatin. The camphorsulphonylimine ligands display irrelevant (IL, IIIL) or no cytotoxicity (IIL). The highest cytotoxicity (lower IC50) was found for [(AgNO3)2(IIL)]. The binding ability of the complexes to calf thymus-deoxyribonucleic acid (CT-DNA) was studied by fluorescence. Constants (Ksv, Ka) and the number (n) of binding centres to DNA were calculated showing that DNA intercalation possibly occurs in the cases of complexes 2 and 3, while a more complicated process operates for 1. As expected from the cytotoxicity, [(AgNO3)2(IIL)] displays the highest binding affinity (Ka = 1.61 × 105 M− 1). No binding to DNA was detected for AgNO3 or IIL under the experimental conditions used. The binding trend to CT-DNA found by fluorescence was corroborated by cyclic voltammetry.
N-Benzylation of acylhydrazones of the hydroxybenzaldehyde series with 3,5-di-tert-butyl-4-hydroxybenzyl acetate was performed at room temperature in the absence of acid or base catalysts. Carboxamides do not react with 3,5-di-tert-butyl-4-hydroxybenzyl acetate under similar conditions. N-Benzylation of isoniazid and (diphenylphosphoryl)acetic acid hydrazones was shown to be an efficient method for the synthesis of new hybrid compounds containing moieties of biologically active acylhydrazones and sterically hindered phenols. N-Benzyl derivatives of isoniazid and (diphenylphosphoryl)acetic acid hydrazones containing a hydroxy group at the ortho position of the aromatic ring are formed as individual E isomers with respect to the C-N double bond.
Rare earth elements (La-Lu, Sc, and Y) exhibit unique magnetic and optical properties that make them irreplaceable components of many technologies. Concerns over the rare earth supply chain have focused efforts toward recycling rare earths from end of life technology. Less than 1% of the rare earth elements are currently recycled. This situation is due to the high cost of implementing solvent extraction methods to purify these elements from mixtures, compared to the costs associated with primary mining and purification operations. This dissertation describes work on the development of novel ligands that form water- and oxygen-stable rare earth complexes, to facilitate the separation of rare earth mixtures into purified elements to enable recycling. Derivatization of a tripodal hydroxylamine ligand demonstrated that changing the steric and electronic properties of rare earth complexes impacted their solubility properties and stability to water. A tripodal hydroxypyridonate ligand system with pH-dependent precipitation of the rare earths was achieved. The precipitation separation performance was quantified as a function of pH and ligand equivalents through the development of a high-throughput experimentation screen. The screening results determined optimal rare earth separations conditions that were applied on lab-scale to afford aqueous rare earth separations in a single chelation and separation step. Development of a tripodal catecholate ligand formed homobimetallic rare earth complexes with rare earth-dependent redox properties, determined using cyclic voltammetry, and informed ligand design for future redox-driven separations processes.
Four new heteroleptic silver(I) complexes with the general formula [Ag(L1–4)(nap)] (1–4), where L1–4 = 2-(1-(4-substitutedphenyl)ethylidene)hydrazinecarbothioamide and nap = naproxen, have been synthesized and characterized. The geometric parameters determined from density functional theory and UV-Vis studies indicate distorted tetrahedral geometry around silver(I) ion. Fourier transform infrared (FT IR) spectra evidenced asymmetric bidentate coordination mode of carboxyl oxygen atoms of naproxen with silver(I) ion. The complexes are stable for 72 h and biocompatibility was analysed towards normal human dermal fibroblast cells, which showed non-toxic nature up to 100 ng/ml. In vitro anti-proliferative activity of the complexes by MTT assay was tested against three human cancerous cell lines and one non-tumorigenic human breast epithelial cell line (MCF-10a) in which the complex 4 exhibited enhanced activity. The morphological changes observed by acridine orange/ethidium bromide and Hoechst 33258 staining method reveal apoptosis-inducing ability of the complexes. The molecular docking studies suggest hydrogen bonding, hydrophobic and π-pair interactions with the active site of epidermal growth factor receptor, vascular endothelial growth factor receptor 2 and lipoxygenase receptors.
An environmentally benign electrochemically enabled chemoselective sulfonylation and hydrazination of C2,C3-unsubstituted indoles with arylsulfonyl hydrazide in the presence of ammonium bromide as redox catalyst and electrolyte was demonstrated in this work. Under mild electro-oxidation conditions, a series of indole hydrazination products with pharmacological activity were obtained. In vitro, the hydrazination products exhibited a better anti-cancer activity compared with the diazotization products. Further mechanistic studies showed that the compound 3ae inhibits cell migration and tubulin aggregation in T-24 cells, thereby leading to cell apoptosis.
Background
In this review article a brief overview of novel metallotherapeutic agents (with an emphasis on the complexes of essential biometals) promising for medical application is presented. We have also focused on recent work carried out by our research team, specifically the development of redox-active antimicrobial complexes of sterically hindered diphenols with some essential biometals (copper, zinc, nickel).
Results
The complexes of essential metals (manganese, iron, cobalt, nickel, copper, zinc) described in the review show diverse in vitro biological activities, ranging from antimicrobial and anti-inflammatory to antiproliferative and enzyme inhibitory. It is necessary to emphasize that the type of organic ligands in these metal complexes seems to be responsible for their pharmacological activities. In the last decades there has been a significant interest in synthesis and biological evaluation of metal complexes with redox-active ligands. A substantial step in the development of these redox-active agents is the study of their physico-chemical and biological properties, including investigations in vitro of model enzyme systems, which can provide evidence on a plausible mechanism underlying the pharmacological activity. When considering the peculiarities of the pharmacological activity of the sterically hindered diphenol derivatives and their nickel(II), copper(II) and zinc(II) complexes synthesized, we took into account their being potential antioxidants, their antimicrobial activity possibly resulting from their affecting the electron-transport chain.
Conclusion
We have obtained novel data demonstrating that the level of antibacterial and antifungal activity in the series of the above-mentioned metal-based antimicrobials depends not only on the nature of the phenolic ligands and complexing metal ions, but also on the lipophilicity and reducing ability of the ligands and metal complexes, specifically regarding the potential biotargets of their antimicrobial action – ferricytochrome c and the superoxide anion radical. The combination of antibacterial, antifungal and antioxidant activity allows one to consider these compounds as promising substances for developing therapeutic agents with a broad spectrum of activity.
Five new silver(I) complexes were synthesized with mixed ligands of thiosemicarbazone derivatives and diphenyl(p-tolyl)phosphine in search of new biologically active compounds. A CHN elemental analysis, powder X-ray diffraction data (PXRD) as well as several spectroscopic techniques such as FT-IR, energy-dispersive X-ray (EDX), ¹H, ¹³C, and ³¹P{¹H} NMR were performed to elucidate the structure of these complexes. Elemental analysis suggested that the stoichiometry of the complexes formed by the reaction of silver nitrate with thiosemicarbazone in the presence of (p-tolyl)PPh2 was indeed 1:2:1 molar ratio. The silver ions were discovered to be coordinated to the sulfur of thiosemicarbazone and phosphorus of (p-tolyl)PPh2, having a tetrahedral geometry based on the spectroscopic data obtained. The PXRD patterns were studied to see the degree of crystallinity of the complexes. The in vitro antiproliferative activity of these complexes was investigated towards the MDA-MB-231 and MCF-7 breast cancer cell lines, as well as the HT-29 colon cancer cell line, which yielded IC50 values in low micromolar range. The antiplasmodial activity of these complexes was also examined against chloroquine-resistant P. falciparum parasite which demonstrated good activity and further tested for their selectivity index.
A series of Mn(II) and Co(II) complexes were obtained after the condensation of ligand methylcarbamatethiosemicarbazone (L) and corresponding metal salt. The ratio of metal salt to nitrogen and sulphur donor atom containing ligand was 1:2. The conventional condensation reaction was employed to synthesize the multi-donor ligand by refluxing methylcarbamate and thiosemicarbazide in 1:1 ratio. The mode of bonding and geometry of the synthesized complexes were confirmed by elemental analysis, magnetic susceptibility, molar conductance, IR, 1H-NMR, mass, electronic spectra, EPR and molecular modeling. The general composition ML2X2 is assigned to transition metal complexes, where M = Mn(II) and Co(II), L = methylcarbamatethiosemicarbazone and X = Cl−, CH3COO−. The non-electrolytic nature of metal complexes was confirmed by molar conductance. The spectral studies suggested six-coordinated geometry for the synthesized complexes. Molecular modeling of ligand and complexes was also done by using Gaussian. The bacterial activities of all the synthesized compounds were also evaluated against E. coli and S. aureus. Based on antimicrobial results, it was concluded that metal complexes exhibited higher inhibition potential than free Schiff’s base ligand.
Hydrazones are a class of organic compounds with the general structure –C=N–NH–, resulting from the condensation of carbonylated substances with amines. The synthesis of this functional group generally occurs by the condensation of hydrazines or hydrazides with aldehydes and ketones. In recent years, the functional group hydrazone has been gaining prominence in medicinal chemistry, due mainly to its wide spectrum of applications and chemical and biological properties, as well as its structural versatility. Thus, this systematic review is aimed to investigate the biological potential of hydrazones obtained synthetically in the last decade. Among the papers included in this study, over 80% of them exhibit promising results for the evaluation activity, and less than 15% of these had unimpressive results. In addition, the relationship and importance of the coordination properties of the hydrazonic derivatives for the evaluated activities became apparent. Moreover, synthetic hydrazones are promising organic substances for the research and development of new chemical prototypes for the discovery of new drugs.
Features of the formation of silver nanoparticles (Ag-NPs) via intramolecular redox transformation of the Ag(I) complex of 4,6-di-tert-butyl-2,3-dihydroxybenzaldehyde isonicotinoylhydrazone in organic solvents with donor numbers DN > 19 were studied. The stability of the organic sols depended on the nature of the dispersion medium and the presence of oxygen and water in it. The physical chemistry and morphology of the Ag-NP in the organic sol were investigated using molecular absorption spectroscopy, transmission electron microscopy, and atomic force microscopy. The silver sol consisted of spherical Ag-NPs 5–20 nm in size with a characteristic absorption band near 440 nm. It was found that the silver complex with valence tautomerism was a promising precursor for Ag-NPs. The synthesized Ag-NPs showed high antimicrobial activity compared with standard antibiotics and Ag-containing agents (MIC = 0.007 μmol/mL).
The compositions and geometries of coordination polyhedra in Cu(II) and Mn(II) complexes with Mannich bases were determined using IR, EPR, and electron spectroscopy. It was shown that bidentate ligands were coordinated to the metal ions in these complexes. The coordination polyhedra of mononuclear Cu(II) and Mn(II) complexes consisted of two mono-anionic ligands. Polyhedra of the Mn(II) complexes also contained two water molecules. The Cu(II) complexes had characteristic square-planar [CuN2O2] coordination polyhedra; Mn(II) complexes, [MnN2O4] octahedra.
A series of heterocycle-attached methylidenebenzenesulfonohydrazone derivatives were synthesized and evaluated for their antifungal activities against seven phytopathogenic fungi such as Fusarium graminearum, Alternaria solani, Valsa mali, Phytophthora capsici, Fusarium solani, Botrytis cinerea, and Glomerella cingulata. Compounds 7b, 8d, 9a, 9b and 9d exhibited a good and broad-spectrum of antifungal activities against at least five phytopathogenic fungi at the concentration of 100μg/mL. It demonstrated that addition of one double bond between the phenylsulfonylhydrazone fragment and the furan ring of 6a,b,d could afford more active compounds 9a,b,d; however, introduction of the nitro group on the phenyl ring of 6a-9a gave less potent compounds 6e-9e.
Ag(I) complexes formed by polydentate phenolic derivatives of thioglycolic and thiopropionic acids with Ag(I) ions could be a promising field of search for potential chemotherapeutic agents. Convenient synthetic methods to prepare these ligands have been developed on the basis of addition reactions occurring between S-nucleophiles and obenzoquinones. The results are presented of physicochemical investigation of Ag(I) ions complexation with phenolic ligands, which made it possible to determine ionic and redox ligand forms with high nucleophilicity of metal-ion binding sites, the peculiarities of the structural organization of the coordination cores of the newly synthesized complexes. The investigation of the molecular and electronic structure of Ag(I) complexes has been performed within the density functional theory framework. On the basis of the pharmacological screening results the selection is justified of a lead compound possessing antibacterial, antifungal and antiherpetic activity comparable to those of some standard drugs to develop effective pharmaceuticals for combination therapy of mixed infections. Data have been obtained on the ability of some phenolic derivatives of thioglycolic and thiopropionic acids as well as their Ag(I) complexes to reduce bovine cytochrome c.
Highly luminescent single colloidal silver nanoparticles under blue excitation were detected. The intense luminescence observed from the single particles is attributed to different emissive centers. Picosecond lifetimes of those single nano-objects have been measured. Comparison with colloidal particles emission formed in aqueous solution, using polyacrylate polyanion as stabilizer is drawn. The optical properties of silver colloidal particles in solution are observed while their surface is changed by deposition of silver ion. A large visible emission under UV or surface plasmon region excitations is observed for Agn@Ag+, while no fluorescence emission was found for Agn or Ag+ systems. The intense visible light emission changes should primarily come from chemical surface active sites. It was observed that the oligomeric clusters, composed of only few atoms Ag4+x x+ and Ag7 3+, have a substantial emission in the same visible region. A model which ascribes the photoemission of the chemically modified silver colloidal particle to oligomeric clusters on the Ag particle surface is proposed. Those emissive water soluble silver clusters have potential for biological labelling, and light emitting sources in nanoscale optoelectronics applications.
The kinetics of reduction of cytochrome c by catechol(s), quinol(s) and related compounds were investigated by stopped-flow spectrophotometry. Studies on the influence of pH on the rates indicate that only deprotonated forms of these compounds act as reducing agents, with the dianionic forms being the most effective. The pH-independent second-order rate constants are reported. Hammett treatment of the effects of substituents on the aromatic ring structure of the reductants show that for electron transfer to occur the charge on the deprotonated species must not be withdrawn on to the substituents. Possible sites for electron donation to cytochrome c are discussed, and the results indicate that the haem edge is a likely candidate.
Mycobacterium smegmatis is a fast-growing nonpathogenic species particularly useful in studying basic cellular processes of relevance to pathogenic
mycobacteria. This study focused on the d-alanine racemase gene (alrA), which is involved in the synthesis of d-alanine, a basic component of peptidoglycan that forms the backbone of the cell wall. M. smegmatis alrA null mutants were generated by homologous recombination using a kanamycin resistance marker for insertional inactivation.
Mutants were selected on Middlebrook medium supplemented with 50 mM d-alanine and 20 μg of kanamycin per ml. These mutants were also able to grow in standard and minimal media without d-alanine, giving rise to colonies with a drier appearance and more-raised borders than the wild-type strain. The viability
of the mutants and independence of d-alanine for growth indicate that inactivation of alrA does not impose an auxotrophic requirement for d-alanine, suggesting the existence of a new pathway of d-alanine biosynthesis in M. smegmatis. Biochemical analysis demonstrated the absence of any detectable d-alanine racemase activity in the mutant strains. In addition, the alrA mutants displayed hypersusceptibility to the antimycobacterial agent d-cycloserine. The MIC of d-cycloserine for the mutant strain was 2.56 μg/ml, 30-fold less than that for the wild-type strain. Furthermore, this hypersusceptibility
was confirmed by the bactericidal action of d-cycloserine on broth cultures. The kinetic of killing for the mutant strain followed the same pattern as that for the wild-type
strain, but at a 30-fold-lower drug concentration. This effect does not involve a change in the permeability of the cell wall
by this drug and is consistent with the identification of d-alanine racemase as a target of d-cycloserine. This outcome is of importance for the design of novel antituberculosis drugs targeting peptidoglycan biosynthesis
in mycobacteria.
The Cu2+ complexes of the 1-16 and the 1-20 fragments of the Alzheimer's disease-related beta-amyloid peptide (CuAbeta) show significant oxidative activities toward a catechol-like substrate trihydroxylbenzene and plasmid DNA cleavage. The latter reflects possible oxidative stress to biological macromolecules, yielding supporting data to the pathological role of these soluble Abeta fragments. The former exhibits enzyme-like kinetics and is dependent on [H2O2], exhibiting k(cat) of 0.066 s-1 (6000-fold higher than the reaction without CuAbeta) and k(cat)/Km of 37.2 m-1s-1 under saturating [H2O2] of approximately 0.24%. This kinetic profile is consistent with metal-centered redox chemistry for the action of CuAbeta. A mechanism is proposed by the use of the catalytic cycle of dinuclear catechol oxidase as a working model. Trihydroxylbenzene is also oxidized by CuAbeta aerobically without H2O2, affording rate constants of 6.50x10(-3) s-1 and 3.25 m-1s-1. This activity is also consistent with catechol oxidase action in the absence of H2O2, wherein the substrate binds and reduces the Cu2+ center first, followed by O2 binding to afford the mu-eta2:eta2-peroxo intermediate, which oxidizes a second substrate to complete the catalytic cycle. A tetragonally distorted octahedral metal coordination sphere with three coordinated His side chains and some specific H-bonding interactions is concluded from the electronic spectrum of CuAbeta, hyperfine-shifted 1H NMR spectrum of CoAbeta, and molecular mechanics calculations. The results presented here are expected to add further insight into the chemistry of metallo-Abeta, which may assist better understanding of the neuropathology of Alzheimer's disease.
There are an astonishing number and variety of roles that metals play in contemporary medicine. This book contains information on the medicinal uses of inorganics, that is, of elements such as boron, lithium, selenium, to name a few, as well as metal-containing species. In keeping with the notion that healthy mammals rely on (bio-essential) metals for the normal functioning of approximately a third of their proteins and enzymes, a large number of drugs are metal-based and considerable effort is being devoted to developing both second- and third-generation drugs as well as generating novel metal-based drugs. While there is no doubt that there is an emphasis on 'Metallotherapeutics' throughout the volume, the use of metals in medicine is not restricted to metal-based drugs. The following are also covered: non-invasive radiopharmaceuticals Magnetic Resonance Imaging (MRI) mineral supplements.
Origin of Molecular Spectra Origin of Infrared and Raman Spectra Vibration of a Diatomic Molecule Normal Coordinates and Normal Vibrations Symmetry Elements and Point Groups Symmetry of Normal Vibrations and Selection Rules Introduction to Group Theory The Number of Normal Vibrations for Each Species Internal Coordinates Selection Rules for Infrared and Raman Spectra Structure Determination Principle of the GF Matrix Method Utilization of Symmetry Properties Potential Fields and Force Constants Solution of the Secular Equation Vibrational Frequencies of Isotopic Molecules Metal–Isotope Spectroscopy Group Frequencies and Band Assignments Intensity of Infrared Absorption Depolarization of Raman Lines Intensity of Raman Scattering Principle of Resonance Raman Spectroscopy Resonance Raman Spectra Theoretical Calculation of Vibrational Frequencies Vibrational Spectra in Gaseous Phase and Inert Gas Matrices Matrix Cocondensation Reactions Symmetry in Crystals Vibrational Analysis of Crystals The Correlation Method Lattice Vibrations Polarized Spectra of Single Crystals Vibrational Analysis of Ceramic Superconductors References
One of the topical directions of modern medical chemistry is the preparation of new pharmaceuticals to fight infections causing more than 20 % of overall number of lethal outcomes. Furthermore, the development of novel pharmaceuticals with a broad activity spectrum acquires a paramount importance because of the resistance of microorganisms to commonly used antibiotics. A crucially new method of attacking these problems is based on the suggestion that many bioactive compounds act in the human body as complexing agents, and most of them can exert pharmacological activity only upon interaction with metal ions. Thus, functional modifying of biologically active substances and pharmaceuticals by binding them into metal complexes in order to increase their pharmacological effect and minimize their toxicity and side effects appears quite worthwhile. Metal complexes of derivatives of sterically hindered o-diphenols and oaminophenols present a promising field of search for compounds useful in producing novel chemotherapeutic agents with a broad activity spectrum, the said ligands being able to inhibit free-radical reactions of fragmentation of essential biomolecules, exhibit antioxidant and antiviral activity while demonstrating low toxicity. We studied the complexation of derivatives of sterically hindered o-diphenols and oaminophenols with Cu(II), Co(II), Ni(II) and Zn(II) ions and estimated the level of antimicrobial activity of the metal complexes separated in crystalline form as compared to the ligands and some antibiotics. Acid-base properties of the ligands were examined, and the stability constants of the metal complexes were determined. A procedure of synthesis of the complexes and their separation as crystalline powders was developed, the composition and physico-chemical characteristics of the complexes as well as the composition and structure of coordination cores were determined. The reducing properties of the ligands and their metal complexes were examined by cyclic voltammetry. Cu(II) ions were found to form complexes in crystalline state with most of the ligands under investigation, while Co(II), Ni(II), and Zn(II) ions - predominantly with sulfurcontaining o-diphenol derivatives. Most of the metal complexes synthesized have the composition described by the general formula ML2. The next ways of ligand coordination were found: monodentate, bidentate and tridentate, square planar (M{cyrillic}O4, M{cyrillic}O2S2, M{cyrillic}O2N2) and octahedral (M{cyrillic}O4S2, M{cyrillic}O5S) coordination cores being characteristic of the metal complexes. Relying on the results of pharmacological screening, metal complexes were selected which may be considered as potential chemotherapeutic agents with antimicrobial activity comparable to those of commonly used antibiotics (tetracycline, streptomycin, nystatin, terbinafine).
Convenient synthetic methods to prepare sulphur-and phosphorus-containing 1,2- dihydroxybenzene derivatives have been developed on the basis of addition reactions occurring between S-nucleophiles or dialkylphosphites and o-benzoquinones. A series of o-aminophenol derivatives has been prepared by reactions of sterically hindered 1,2- dihydroxybenzene derivatives with aromatic and cyclic amines. Functionalization of the compounds synthesized allowed new polydentate ligands to be obtained for preparation of their respective bioactive metal complexes. Complexes formed by derivatives of sterically hindered 1,2-dihydroxybenzene and o-aminophenol derivatives with some biometals could be a promising field of search for potential chemotherapeutic agents, since the free ligands of this type were shown to display antioxidant and antiviral activities. Synthetic procedures for the complexes of sterically hindered 1,2- dihydroxybenzene and o-aminophenol derivatives with ferrous and manganous ions have been worked out, and composition, geometry as well as physico-chemical characteristics of the complexes have been determined. Pharmacological screening revealed some phenolic compounds and metal complexes that may be considered as potential chemotherapeutic agents with activities comparable to those of some standard antibiotics (streptomycin, ampicillin, nystatin, terbinafin). The direct correlation that we have discovered between antimicrobial properties of the most active compounds, evaluated by pharmacological screening, and their reducing ability determined electrochemically deserves particular attention. Based on these results, an assumption can be made that biological redox processes and the enzymes catalyzing them (oxidoreductases) would be closely related to pharmacological properties of the compounds studied. Data have been obtained on the ability of some phenolic compounds, as well as their metal complexes, to reduce bovine cytochrome c, and on catalysis of this process by human NADPH: cytochrome P450-reductase (P450R). This provides reasons to believe that these oxidoreductases belong to the factors responsible for certain pharmacological properties of the compounds under study, in particular, for metabolism and side effects. Some oxidoreductases being present in bacteria and yeasts and performing a number of important biological functions (cellular respiration, protection from oxidative stress and reactive oxygen species, etc.) are similar to cytochrome c and P450R as regards structural and functional characteristics. On this basis, it is quite acceptable to use cytochrome c and P450R as models of enzymes present in microorganisms for investigating possible mechanisms of antimicrobial activity of sterically hindered 1,2-dihydroxybenzene and oaminophenol derivatives and their metal complexes.
The bipyridyl adduct of tetrameric [Co(3,5-DBSQ)2]4 has been formed by treating the parent Co(II) complex with bipyridine in toluene solution. Structural features within the inner coordination sphere are consistent with a Co(III) metal center. One of the independent quinone ligands is coordinated as a semiquinone and the other as a catecholate. In toluene solution the results of magnetic, EPR, NMR, and spectral experiments suggest an equilibrium between a Co(II) species Co(3,5-DBSQ)2(bpy) and the Co(III) form found in the solid state, Co(3,5-DBCat)(3,5-DBSQ)(bpy). These two forms of the complex are related by the transfer of an electron between the metal ion and one of the quinone ligands.
The influence of glass composition on the sensitivity to ionizing radiation as well as on the radiophotoluminescence ‘build-up’ kinetics is studied in silver doped glass system XNaPO3, (100 - X)Ca(PO3)2, where X varied from 0 to 100 mol%. Concentration of Ag2O was 0.1 wt%. All glass compositions were prepared in a globar-heated furnace at 1000–1200°C. Gamma-irradiated glasses, containing radiation-induced paramagnetic centers of photoluminescence, were investigated by electron spin resonance and luminescence spectroscopic methods. The variation of NaPO3 concentration from 100 to 40 mol% have decreased the glass sensitivity to gamma-radiation more than 800 times and simultaneously have increased the ‘build-up’ time of radiophotoluminescent centers. Room temperature stable Ag0 atoms were detected in the glass, containing 40 mol% NaPO3 and less. Results are discussed based on the model of post-radiational relaxation. It is shown that all effects found in this work are caused by the decrease of Ag+ ion mobilities with decrease of alkali content in the glass.
Ag(I) and Cu(II) complexes with 2-(4,6-di-tert-butyl-2,3-dihydroxyphenylsulfanyl)acetic acid ligands (L) have been synthesized and characterized using a combination of methods, including x-ray powder diffraction, elemental analysis, TG/DTA, FT-IR, and EPR. The antimicrobial properties of 2-(4,6-di-tert-butyl-2,3-dihydroxyphenylsulfanyl]acetic acid and its complexes with Ag(I) and Cu(II) were tested against standard E. coli, Ps. aeruginosa, C. albicans, B. subtilis, St. aureus, and Pr. vulgaris strains.
The synthesis and physico-chemical characterization of Fe(II) and Mn(II) complexes of 2-[4,6-di(tert-butyl)-2,3-dihydroxyphenylsulfanyl]acetic acid (HLI) and 2-[4,6-di(tert-butyl)-2,3-dihydroxyphenylsulfinyl]acetic acid (HLII) were carried out. The investigation of the molecular and electronic structure of Cu(II), Ni(II), Zn(II), Fe(II) and Mn(II) complexes has been performed within the density functional theory (DFT) framework. The computed properties were compared to the experimental ones, and molecular structures of the compounds were proposed based on the array of spectral data and quantum chemical calculations. Antibacterial activity of the Fe(II) and Mn(II) complexes was evaluated in comparison with Cu(II), Co(II), Ni(II) and Zn(II) complexes and three standard antibiotics; it was found to follow the order: (1) Сu(LI)2 > Mn(LI)2 > HLI > Ni(LI)2 > Zn(LI)2 > Fe(LI)2 > Co(H2O)2LI; (2) Cu(LII)2 > Сo(LII)2 > Ni(LII)2 > Mn(H2O)2(LII)2 > Fe(LII)2 > HLII > Zn(LII)2; their reducing ability (determined electrochemically) followed the same order. Spectrophotometric investigation was carried out in order to estimate the rate of the reduction of bovine heart сytochrome c with the ligands and their metal(II) complexes. The complexes Сu(LI)2, Mn(LI)2 and Co(LII)2 with the high reducing ability were found to be characterized by the highest rates of Cyt с reduction. NADPH:cytochrome P450-reductase had no substantial effect on the rate of сytochrome c reduction with HLI and HLII ligands.
The synthesis and physico-chemical characterization of Fe(II) and Mn(II) complexes of 4,6-di-tert-butyl-3[(2-hydroxyethyl)sulphanyl]-1,2-dihydroxybenzene (HL I) and 2-amino-4,6-di-tert-butylphenol (HL II) were carried out. Antibacterial activity of the Co(II), Fe(II) and Mn(II) complexes was evaluated in comparison with Cu(II) complexes and three common antibiotics; it was found to follow the order: (1) Cu(L I) 2 > Co(L I) 2 > Fe(L I) 2 P Mn(L I) 2 > HL I ; (2) Cu(L II) 2 > Co(L II) 2 > HL II > Fe(L II) 2 P Mn(L II) 2 ; and their reducing ability (determined electrochemically) followed the same order. Spectrophotometric investigation was carried out in order to estimate the rate of the reduction of bovine heart cytochrome c with the ligands and their metal(II) complexes. NADPH:cytochrome P450-reductase was found to increase the rate of cytochrome c reduction with HL I and HL II ligands, while adrenodoxin in couple with NAD(P)H: adre-nodoxin reductase had no substantial effect thereon. It was shown that the reduction of cytochrome c with these compounds cannot be related solely to the facility of their oxidation or ionization.
Specific features of the formation of silver nanoparticles upon the decomposition of the complex of Ag(I) with 2-[4,6-di(tert-butyl)-2,3-dihydroxyphenylsulfanyl]acetic acid in organic solvents characterized by large donor numbers (27–34) are studied.
It is established that the stability of prepared organosols depends to a significant extent on the nature of a dispersion
medium and the presence of water and oxygen in this medium. The Ag(I) complex is a solid precursor for the preparation of
silver nanoparticles.
Quinone complexes of nickel have been prepared by treating Ni(CO)4 with 3,6-di-tert-butyl-1,2-benzoquinone (3,6-DBBQ). Reactions carried out with stoichiometric quantities of 3,6-DBBQ lead to the formation of monomeric, square planar Ni(3,6-DBSQ)2. Spins of the radical semiquinone ligands are coupled antiferromagnetically to result in near diamagnetism. Electrochemical characterization has shown that the complex undergoes reduction in two one-electron steps. Chemical reduction with CoCp2 results in the formation of (CoCp2)[Ni(3,6-DBCat)2]. EPR spectra recorded on this product show anisotropy that is consistent with the Ni(III) formulation. Reactions carried out with Ni(CO)4 and an excess of 3,6-DBBQ lead to the formation of Ni)3,6-DBBQ)(3,6-DBCQ)2. Crystalligraphic characterization Ni(3,6-DBBQ)(3,6-DBSQ)2. Crystallographic characterization (Ni(3,6-DBBQ) (3,6-DBSQ)2: orthorhombic, Ccca, a = 20.092(6), b = 24.335(8), c = 18.340(4) Å, V = 8967(4) Å3, Z = 4) has shown that the metal is octahedral and that the benzoquinone and semiquinone ligands are differentiable by characteristic CO, CC and Ni bond lengths. Magnetic properties are slightly temperature dependent due to either weak antiferromagnetic NiSQ exchange or offsetting NiSQ (ferromagnetic) and SQSQ (antiferromagnetic) exchange interactions.
The interaction between silver(I) ions with 3,5-di(tert-butyl)-1,2-benzenediol (I) and sulfur-containing derivatives of sterically hindered diphenols: 4,6-di(tert-butyl)-3-(2-hydroxyethylsulfanyl)-1,2-benzenediol (II), 2-(2,5-dihydroxyphenylsulfanyl)acetic acid (III), 2-(2,5-dihydroxy-3,4,6-trimethylphenylsulfanyl)acetic acid (IV), 2-[4,6-di(tert-butyl)-2,3-dihydroxyphenylsulfanyl]acetic acid (V), 5,7-di(tert-butyl)-8-hydroxy-2,3-dihydro-1,4-benzoxathiin-2-one (VI), 3-[4,6-di(tert-butyl)-2,3-dihydroxyphenylsulfanyl]-2-methyl-carboxyamidopropanoic acid (VII) was studied. A competition of redox process and complexation is possible when these organic compounds interact with silver(I) ions. I–IV, VI and VII were found to reduce Ag(I) to Ag(0), silver sol formation being possible under certain conditions. The sols were examined by TEM and optical spectroscopy methods. The interaction of V with silver(I) ions is not accompanied by a redox reaction, the latter being hindered by complexation. The complexation was studied by potentiometric titration, and the complex of V with Ag(I) was characterized by the means of X-ray powder diffraction, elemental analysis, TG/DTA and IR spectroscopy. The antimicrobial activities of V and its Ag(I) complex, evaluated by minimum inhibitory concentration (MIC), were also tested.
Cationic silver clusters formed in γ-irradiated Ag+-exchanged zeolite rho have been studied by electron spin resonance (ESR) spectroscopy. It was found that dehydrated Ag-rho zeolites show a remarkable tendency for stabilization of Ag43+ clusters. In dehydrated samples tetrameric silver is stable for months at room temperature and is still observed at 100°C. It is postulated that Ag43+ clusters are located in distorted octagonal prisms which appear to be very effective trapping sites. In hydrated rho zeolite framework distortions are removed and silver tetramers decay below room temperature.
A practical, easily accessible guide for bench-top chemists, this book focuses on accurately applying computational chemistry techniques to everyday chemistry problems.
Provides nonmathematical explanations of advanced topics in computational chemistry.
Focuses on when and how to apply different computational techniques.
Addresses computational chemistry connections to biochemical systems and polymers.
Provides a prioritized list of methods for attacking difficult computational chemistry problems, and compares advantages and disadvantages of various approximation techniques.
Describes how the choice of methods of software affects requirements for computer memory and processing time.
This paper reports the synthesis and characterization of six compounds of copper(I), stabilized in its reduced state by two triphenylphosphines, in which 4-fluorobenzaldehyde thiosemicarbazone and N-methylthiosemicarbazone act as chelating through their sulfur and imino nitrogen. The three oxoanions that have been chosen, NO3−, SO42− and CH3COO−, play an important role: their oxygens are bad competitors with the imino nitrogen of the thiosemicarbazone moiety and moreover they form strong charge assisted hydrogen bondings that stabilize the neutral form of the ligand. The overall packing is determined by intermolecular phenyl–phenyl van der Waals interactions.
Ab initio effective core potentials (ECP’s) have been generated to replace the innermost core electron for third‐row (K–Au), fourth‐row (Rb–Ag), and fifth‐row (Cs–Au) atoms. The outermost core orbitals—corresponding to the ns2np6 configuration for the three rows here—are not replaced by the ECP but are treated on an equal footing with the nd, (n+1)s and (n+1)p valence orbitals. These ECP’s have been derived for use in molecular calculations where these outer core orbitals need to be treated explicitly rather than to be replaced by an ECP. The ECP’s for the forth and fifth rows also incorporate the mass–velocity and Darwin relativistic effects into the potentials. Analytic fits to the potentials are presented for use in multicenter integral evaluation. Gaussian orbital valence basis sets are developed for the (3s, 3p, 3d, 4s, 4p), (4s, 4p, 4d, 5s, 5p), and (5s, 5p, 5d, 6s, 6p) ortibals of the three respective rows.
Invasive mycoses are important causes of morbidity and mortality among neutropenic and other immunocompromised patients. Candidiasis and aspergillosis are the most frequent mycoses but many other opportunistic fungal infections are emerging. The lack of appropriate diagnostic tools for an early diagnosis often implies that many patients receive empirical antifungal therapy or that therapy is started when the disease is in an advanced stage with only a remote possibility for cure. Moreover, there is a relative shortage of antifungal agents for treating these life-threatening mycoses. Nowadays, a formidable technical challenge is faced by the pharmaceutical industry in the discovery of new antifungal targets and the development of effective antifungal drugs. The number of new antifungal agents at different stages of the development pipeline is high in a clear contrast to the fact that during more than four decades, amphotericin B has been nearly the unique available therapy for invasive mycoses. This review will summarise the advances in the field of new antifungal agents, including those agents in the development process, with particular emphasis on antifungal agents currently used in the therapy of superficial and invasive fungal infections, and the increasing recognition of the importance of fungal biofilms in the outcome of treatment.
Treatment of Ag6(tsac)6 (tsac=thiosaccharinate anion) with pyridine (py) and 1,10-phenanthroline (o-phen) each affords two novel silver(I)-thiosaccharinate complexes: dinuclear [Ag2(tsac)2py] (1) and polynuclear [Ag(tsac)(o-phen)]n (2). Both crystal structures have been determined by X-ray diffraction and spectroscopic structural analysis (IR and Raman, UV–Vis, 1H and 13C NMR) have also been made for both compounds. Thermal stability analysis (TGA and DTA) of complex 1 are used to confirm the strength of the pyridine coordination to the silver ion. The molecular structure of complex 1 shows some astonishing characteristics. The two silver atoms are in different environments: one of them is surrounded by two S atoms, while the other completes its coordination sphere by three N atoms, two from the thiosaccharinate anions and the third from a pyridine molecule. The short Ag(1)–Ag(2) contact distance, 2.9681(8)Å, indicates an interaction between the two silver metal atoms exists. Complex 2 shows a thiosaccharinate molecule bridging two silver atoms through the exocyclic S atom while the o-phenanthroline ligand is coordinated as a bidentate N,N chelate, forming a polynuclear chain. Quantum chemical calculations confirm the argentophilic character of the Ag–Ag interaction in complex 1, and its structure and vibrational assignments were correlated and confirmed theoretically.
Chapter 24 discusses the computation of solvation effects. A discussion of the physical basis for solvation effects is presented.
6-Aminocoumarin reacts with pyridine-2-carboxaldehyde and has synthesized N-[(2-pyridyl)methyliden]-6-coumarin (L). The ligand, L, reacts with [Cu(MeCN)(4)]ClO4/AgNO3 to synthesize Cu(I) and Ag(I) complexes of formulae, [Cu(L)(2)]ClO4 and [Ag(L)(2)]NO3, respectively. While similar reaction in the presence of PPh3 has isolated [Cu(L)(PPh3)(2)]ClO4 and [Ag(L)(PPh3)(2)]NO3. All these compounds are characterized by FTIR, UV-Vis and H-1 NMR spectroscopic data. In case of [Cu(L)(PPh3)(2)]ClO4 and [Ag(L)(PPh3)(2)]NO3, the structures have been confirmed by X-ray crystallography. The structure of the complexes are distorted tetrahedral in which L coordinates in a N,N' bidentate fashion and other two coordination sites are occupied by PPh3. The ligand and the complexes are fluorescent and the fluorescence quantum yields of [Cu(L)(PPh3)(2)]ClO4 and [Ag(L)(PPb3)(2)]NO3 are higher than [Cu(L)(2)]ClO4 and [Ag(L)(2)]NO3. Cu(I) complexes show Cu(II)/Cu(I) quasireversible redox couple while Ag(I) complexes exhibit deposition of Ag(0) on the electrode surface during cyclic voltammetric experiments. GAUSSIAN 03 computations of representative complexes have been used to determine the composition and energy of molecular levels. An attempt has been made to explain solution spectra and redox properties of the complexes.
A novel triazole-bridging polynuclear silver(I) complex, [Ag4(ptr)6](NO3)4 · 4H2O (1), was synthesized with (m-phenol)-1,2,4-triazole (ptr), which is the first discrete tetranuclear complex containing 4-substituted triazoles. The compound features blue fluorescence with a broad emission at 432 nm excited at 363 nm, possibly originating from the π–π∗ transition of the triazole ring.
The peculiarities have been studied of silver organosol formation in the breakdown of Ag(I) complex (synthesized by us) with 2-[4,6-di(tert-butyl)-2,3-dihydroxyphenylsulfanyl]-acetic acid in solvents (dimethyl formamide, methanol, ethanol, propanol-2, butanol-1) of a high donor number (DN = 27–34). The dispersiveness and assembly peculiarities of silver nanoparticles in organosols were examined by means of absorbance spectroscopy, TEM and AFM. The organosol stability essentially depends on the nature of the dispersive medium, and on whether water and/or oxygen are present therein. The Ag(I) complex was shown to be a promising solid precursor in production of silver nanoparticles. Employing this precursor a new method of forming silver nanoparticles in polyelectrolyte capsule walls is proposed.
Chapter four discusses the fundamental approximations behind many common semiempirical methods. The relative merits of these methods are also discussed.
Surface-enhanced Raman scattering (SERS) and UV–vis absorption techniques were used to monitor the faradaic reduction of 2-formylpyridine thiosemicarbazone (PATS2) at a silver electrode in methanol solution. Using these spectroscopic techniques coupled with cyclic voltammetry it was possible to identify the reduction products of PATS2 as thiourea and 2-picolylamine, giving support for one of the proposed mechanisms presented in the literature.
La 1ª ed. fue publicada bajo el título: Advances in infrared group frequencies Incluye índice
Structural modification of the frontline antitubercular isonicotinic acid hydrazide (INH) provides lipophilic adaptations (3-46) of the drug in which the hydrazine moiety of the parent compound has been chemically blocked from the deactivating process of N(2)-acetylation by N-arylaminoacetyl transferases. As a class, these compounds show high levels of activity against Mycobacterium tuberculosis in vitro and in tuberculosis-infected macrophages. They provide strong protection in tuberculosis-infected mice and have low toxicity. With some representatives of this class achieving early peak plasma concentrations approximately three orders of magnitude above minimum inhibitory concentration, they may serve as tools for improving our understanding of INH-based treatment modalities, particularly for those patients chronically underdosed in conventional INH therapy.
Cytochrome c was reduced when superoxide was generated from xanthine oxidase in the presence of alloxan, and by the reaction of alloxan and with reduced glutathione. In each case, most of the reduction was inhibited by superoxide dismutase, but considerably more enzyme was required than with superoxide alone. This indicates that the superoxide dismutase-inhibitible cytochrome c reduction was mainly due to a direct reaction with the alloxan radical, and implies that other reactions that are inhibited by superoxide dismutase could be due to either alloxan radicals or superoxide.
Acetylpyridine benzoyl hydrazone (APBH) 1 and its copper complex [[(APBH)CuCl](2)].(EtOH) 2 were structurally characterized by elemental analysis, magnetic measurements, spectroscopy, electrochemistry and single crystal X-ray diffraction studies. The ligand assumes Z-isomeric form and planar geometry in solid state, coordinating through pyridyl nitrogen, azomethine nitrogen and the carbonyl oxygen of the benzoyl group. The copper complex is dimeric and has a distorted octahedral geometry in which the two copper atoms are bridged by two chloride atoms. Antimycobacterial screening of ligand and its copper compound against Mycobacterium smegmatis shows clear enhancement in the antitubercular activity upon copper complexation.
Antibiotics are failing and drug companies have all but stopped developing new ones. Will conquered diseases come back to haunt us? Martin Leeb examines one plan to avert the crisis.
The peculiar redox-active character of quinonoid metal complexes makes them extremely appealing to design materials of potential technological interest. We show here how the tuning of the properties of these systems can be pursued by using appropriate molecular synthetic techniques. In particular, we focus our attention on metal polyoxolene complexes exhibiting intramolecular electron transfer processes involving either the ligand and the metal ion or the two dioxolene moieties of a properly designed ligand thus inducing electronic bistability. The transition between the two metastable electronic states can be induced by different external stimuli such as temperature, pressure, light, or pH suggesting the use of these systems for molecular switches.
Silver products have been used for thousands of years for their beneficial effects, often for hygiene and in more recent years as antimicrobials on wounds from burns, trauma, and diabetic ulcers. Silver sulfadiazine creams (Silvazine and Flamazine) are topical ointments that are marketed globally. In recent years, a range of wound dressings with slow-release Ag compounds have been introduced, including Acticoat, Actisorb Silver, Silverlon, and others. While these are generally accepted as useful for control of bacterial infections (and also against fungi and viruses), key issues remain, including importantly the relative efficacy of different silver products for wound and burn uses and the existence of microbes that are resistant to Ag+. These are beneficial products needing further study, although each has drawbacks. The genes (and proteins) involved in bacterial resistance to Ag have been defined and studied in recent years.
Silver has a long and intriguing history as an antibiotic in human health care. It has been developed for use in water purification, wound care, bone prostheses, reconstructive orthopaedic surgery, cardiac devices, catheters and surgical appliances. Advancing biotechnology has enabled incorporation of ionizable silver into fabrics for clinical use to reduce the risk of nosocomial infections and for personal hygiene. The antimicrobial action of silver or silver compounds is proportional to the bioactive silver ion (Ag(+)) released and its availability to interact with bacterial or fungal cell membranes. Silver metal and inorganic silver compounds ionize in the presence of water, body fluids or tissue exudates. The silver ion is biologically active and readily interacts with proteins, amino acid residues, free anions and receptors on mammalian and eukaryotic cell membranes. Bacterial (and probably fungal) sensitivity to silver is genetically determined and relates to the levels of intracellular silver uptake and its ability to interact and irreversibly denature key enzyme systems. Silver exhibits low toxicity in the human body, and minimal risk is expected due to clinical exposure by inhalation, ingestion, dermal application or through the urological or haematogenous route. Chronic ingestion or inhalation of silver preparations (especially colloidal silver) can lead to deposition of silver metal/silver sulphide particles in the skin (argyria), eye (argyrosis) and other organs. These are not life-threatening conditions but cosmetically undesirable. Silver is absorbed into the human body and enters the systemic circulation as a protein complex to be eliminated by the liver and kidneys. Silver metabolism is modulated by induction and binding to metallothioneins. This complex mitigates the cellular toxicity of silver and contributes to tissue repair. Silver allergy is a known contra-indication for using silver in medical devices or antibiotic textiles.
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