Synthesis, characterization, and antimicrobial activity of silver carbene complexes derived from 4,5,6,7-tetrachlorobenzimidazole against antibiotic resistant bacteria

Silver N-heterocyclic carbene complexes have been shown to have great potential as antimicrobial agents, affecting a wide spectrum of both Gram-positive and Gram-negative bacteria. A new series of three silver carbene complexes (SCCs) based on 4,5,6,7-tetrachlorobenzimidazole has been synthesized, characterized, and tested against a panel of clinical strains of bacteria. The imidazolium salts and their precursors were characterized by elemental analysis, mass spectrometry, (1)H and (13)C NMR spectroscopy, and single crystal X-ray diffraction. The silver carbene complexes, SCC32, SCC33, and SCC34 were characterized by elemental analysis, (1)H and (13)C NMR spectroscopy, and single crystal X-ray diffraction. These complexes proved highly efficacious with minimum inhibitory concentrations (MICs) ranging from 0.25 to 6 μg mL(-1). Overall, the complexes were effective against highly resistant bacteria strains, such as methicillin-resistant Staphylococcus aureus (MRSA), weaponizable bacteria, such as Yersinia pestis, and pathogens found within the lungs of cystic fibrosis patients, such as Pseudomonas aeruginosa, Alcaligenes xylosoxidans, and Burkholderia gladioli. SCC33 and SCC34 also showed clinically relevant activity against a silver-resistant strain of Escherichia coli based on MIC testing.     

Linker Flexibility-Dependent Cluster Transformations and Cluster-Controlled Luminescence in Isostructural Silver Cluster-Assembled Materials (SCAMs)

Silver chalcogenolate clusters (SCCs) and silver cluster-assembled materials (SCAMs) are an important category of novel luminescent materials, the emission of which can be modulated by variation of the cluster nodes and linker species. Here, the successfully synthesis of two isostructural 2D SCAMs is reported: Ag₁₂bpa and Ag₁₂bpe are formed by using two linkers with different conformational freedom (bpa=1,2-bis(4-pyridyl)ethane, bpe=1,2-bis(4-pyridyl)ethylene), with dodenuclear silver chalcogenolate clusters as secondary building units (SBUs). Interestingly, nonluminescent Ag₁₂bpa at room temperature could quickly transform into 1D Ag₁₀bpa , with concomitant dissociation of two silver atoms and the remaining ten silver atoms rearranging in the cluster, thus exhibiting an intense yellow phosphorescence after being triggered by acetonitrile (CH₃CN). Similarly, stimulating Ag₁₂bpe with CH₃CN, by contrast, gave another 2D structure Ag₁₂bpe-1b with the distorted SBUs and different topology structure, and both of them are merely red-emissive at low temperature. To note, after exchanging ligands, room-temperature nonluminescent 2D Ag₁₂bpe-1b can be transformed into intensely luminescent 1D Ag₁₀bpa . This linker-flexibility-dependent structural transformation and cluster-based SBU controlled luminescence remains scarce. Our work provides new insights into structure–luminescence relationship in clustered metal–organic frameworks and intelligent stimulus-responsive luminescent materials.     

Effects of photodynamic therapy evaluated in a novel three-dimensional squamous cell carcinoma organ construct of the skin

Squamous cell carcinoma (SCC) of the skin is a malignant neoplasm that occurs in all ethnic groups primarily due to chronic sun exposure and constitutes a major health problem worldwide. Novel therapies for SCC are in development but as yet no in vitro models capable of screening these therapies and their mechanism of action before proceeding to clinical trials in human subjects have emerged. For this reason we have developed and characterized a novel three-dimensional human SCC construct and validated it using photodynamic therapy (PDT), a well-established modality for treating in situ SCCs. Histologic and immunohistochemical characterization of these SCC constructs revealed epidermal and dermal de-differentiation, increased cell proliferation and expression of immunohistochemical markers specific for cutaneous SCC. Application of PDT to these constructs led to tumor regression with widespread apoptosis and necrosis within 5 days. This in vitro model consistently reproduces the tumor development and dynamics of growing SCCs in vivo and provides a useful approach for screening new treatment modalities for this form of cutaneous cancer.     

A biologically friendly approach for silver nanoparticle formation and their in situ attachment to lecithin vesicles

There has been a keen interest for developing a biologically friendly approach for the preparation of silver nanoparticles for their application reasons. A biocompatible, single step method is established for the preparation of silver nanoparticles in lecithin (Egg phosphatidylcholine)/water systems where lecithin itself acts as a reductant for silver nitrate to form the silver nanoparticles. In another attempt, silver nanoparticles were successfully synthesized inside the lecithin vesicles and were found attached to the bilayers of lecithin vesicles. To the best of our knowledge, this is the first report where a biological surfactant has acted as a mild reducing agent for silver nitrate by itself to form silver nanoparticles.     

Subcellular Duplex DNA and G‐Quadruplex Interaction Profiling of a Hexagonal PtII Metallacycle

Metal‐driven self‐assembly afforded a multitude of fascinating supramolecular coordination complexes (SCCs) with applications as catalysts, host–guest, and stimuli‐responsive systems. However, the interest in the biological applications of SCCs is only starting to emerge and thorough characterization of their behavior in biological milieus is still lacking. Herein, we report on the synthesis and detailed in‐cell tracking of a Pt₂L₂ metallacycle. We show that our hexagonal supramolecule accumulates in cancer cell nuclei, exerting a distinctive blue fluorescence staining of chromatin resistant to UV photobleaching selectively in nucleolar G4‐rich regions. SCC co‐localizes with epitopes of the quadruplex‐specific antibody BG4 and replaces other well‐known G4 stabilizers. Moreover, the photophysical changes accompanying the metallacycle binding to G4s in solution (fluorescence quenching, absorption enhancement) also take place intracellularly, allowing its subcellular interaction tracking.     

Early events in UV carcinogenesis--DNA damage, target cells and mutant p53 foci

Skin carcinomas are the most common cancers in fair-skinned populations of North West European descent. The risk is closely related to sun (UV) exposure and susceptibility to sunburn. Induction of squamous cell carcinomas (SCCs) in the skin of hairless mice by daily UVB exposure appears to emulate the genesis of these tumors in humans quite well. The carcinomas, and the UVB signature mutations that they carry in their p53 genes, can be linked most specifically to the induction of cyclobutane pyrimidine dimers (CPDs). The wavelength dependence of the induction of carcinomas parallels that of CPD induction over the UVB and UVA2 spectral regions. Microscopic clusters of cells overexpressing p53 with UVB signature mutations ("p53 patches") can be detected in the interfollicular epidermis long before the skin tumors arise. DNA repair--more precisely nucleotide excision repair--is a crucial line of defense against UV-induced p53 patches and skin carcinomas. Although chemoprevention of UV carcinogenesis, e.g. with difluoromethylornithine, may be successful by inhibiting the outgrowth of tumors, it may be better to counter the initial steps in tumor development. As the p53 patches appear to be potential precursors of SCCs, regression of p53 patches in unexposed skin should lower subsequent development of SCCs. However, "holoclonal" p53 patches might persist. Ablation of the interfollicular epidermis would be expected to abrogate development of SCC, and negation of this expectation [Faurschou A. et al., Exp. Dermatol. 2007;16:485-489] would indicate that SCCs stem from deep-seated cells in the hair follicles. Careful examination of archival material showed that although most small p53 patches arise interfollicularly, some may actually arise high up in a follicle, in the infundibulum.     

Improved detection of lymphocyte membrane proteins in purified form and as a crude mixture using native and denaturing polyacrylamide gel electrophoresis by optimisation of coomassie brilliant blue and silver staining.

Optimised silver staining protocols were devised for the detection of membrane proteins in purified form and as a crude mixture. These were adduced in both sodium dodecyl sulphate (SDS) and native polyacrylamide gel electrophoresis and consisted of ethanol-acetic acid-formaldehyde fixation, Coomassie Brilliant Blue prestaining, Rapidfix pretreatment, formaldehyde enhancement and finally ammoniacal silver staining. With these modifications, numerous staining problems of membrane proteins were overcome. These included reduction in background staining, enhanced detection sensitivity in native gels, elimination of negative staining and the avoidance of metallic silver deposition on the gel surface. In overcoming these problems, some factors determining the colour and stainability of membrane proteins in their native state were determined. Both the anionic Coomassie Brilliant Blue dye and SDS detergent improved the sensitivity of silver staining in native gels, and ammoniacal silver was more sensitive than neutral silver, suggesting silver staining to be a charge dependent process.     

Modeling of finite diffusion impedance by <Emphasis Type="Italic">RC</Emphasis> two-terminal circuit

The Maxwell model consisting of three series capacitive circuits (SCCs) was employed for constructing an equivalent circuit of finite diffusion impedance (BW). The parameters of a low-frequency SCC were determined using a power series expansion of frequency dependences of BW capacitance and conductivity. All the further SCCs are calculated on the basis of the coincidence between BW and Warburg impedance at high-frequencies. Exact formulas are presented that allow extending an equivalent circuit by adding new SCCs, which is necessary for extension of the frequency range, in which the model and BW yield similar results.     

Silver technology for stabilization of simple (Z)-enethiols: stereoselective synthesis and reaction of silver (Z)-enethiolates

Reported here for the first time are the stereoselective synthesis and reaction of simple silver (Z)-enethiolates, which serve as stabilized (Z)-enethiol storage. In contrast to labile enethiols, silver (Z)-enethiolates are stable even in solutions, and their isolation and purification are very simple. The method for synthesis of silver (Z)-enethiolates involves an unusual vinylic SN2 reaction of (E)-vinyl-lambda3-iodanes with thiobenzamides yielding the inverted (Z)-S-vinylthioimidonium salts, followed by their regioselective C-S bond cleavage with silver acetate. Alkylation, arylation, and Michael addition of silver (Z)-enethiolates yielding (Z)-vinyl sulfides were dramatically accelerated by the addition of Bu4NI (LiI), which probably generates reactive ammonium (Z)-enethiolates with an increased nucleophilicity.     

Size-controlled synthesis of monodispersed silver nanoparticles capped by long-chain alkyl carboxylates from silver carboxylate and tertiary amine

Monodispersed silver nanoparticles capped by long-chain alkyl carboxylates were prepared by the reaction of silver carboxylate with tertiary amine at 80 degrees C for 2 h. This approach is a unique, size-controlled synthetic method for the large-scale preparation of silver nanoparticles. Long-chain alkyl carboxylate derived from a precursor acts as a stabilizer to avoid the aggregation of silver nanoparticles and to control particle size. In addition, amine plays an important role both as a reagent to form a thermally unstable, amine-coordinated intermediate, bis(amine)silver(I) carboxylate, and as a mild reducing agent for the intermediate to produce nanoparticles at a low temperature. The silver core and carboxylate-capping ligand of silver nanoparticles were characterized by various techniques such as transmission electron microscopy, optical absorption spectroscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, gas chromatograph mass spectroscopy, and thermogravimetric and differential thermal analysis. The diameter of the nanoparticles can be strongly influenced by the alkyl chain length and the structure of the carboxylate. The average diameters of the silver nanoparticles were controlled to less than 5 nm in the case of silver carboxylate with a single alkyl chain length of 13 or 17 carbon atoms. On the contrary, the average diameters of silver nanoparticles became large and polydisperse in the case of silver carboxylate with a chain length of 7 carbon atoms or a branched chain. In comparing triethylamine with trioctylamine, there was no obvious effect to regulate the size distribution of the nanoparticles because they could not function as a capping ligand of the nanoparticles due to their weak coordination to silver. In addition, the heat treatment of silver nanoparticles in solution rather than in the solid state was effective for the growth of particles while maintaining narrow size distributions.     

Synthesis and surface chemistry of nano silver particles

In this report, we present a simple wet chemical route to synthesize nano-sized silver particles, and their surface properties are discussed in detail. Silver nano particles of the size 40–80 nm are formed in the process of oxidation of glucose to gluconic acid by amine in the presence of silver nitrate, and the gluconic acid caps the nano silver particle. The presence of gluconic acid on the surface of nano silver particles was confirmed by XPS and FTIR studies. As the nano silver particle is encapsulated by gluconic acid, there was no surface oxidation, as confirmed by XPS studies. The nano silver particles have also been studied for their formation, structure, morphology and size using UV–Visible spectroscopy, XRD and SEM. Further, the antibacterial properties of these nano particles show promising results for E. Coli. The influence of the alkaline medium towards the particle size and yield was also studied by measuring the pH of the reaction for DEA, NaOH and Na₂CO₃.     

银纳米片的研究进展

金属纳米材料具有不同于宏观块体材料的特殊性质. 在银纳米结构中, 银纳米片因其独特的形貌依赖光学性质备受关注, 该特性已在离子检测、分子染色、表面增强拉曼光谱(SERS)、表面荧光增强、生物医学等领域显示了重要应用价值. 本文从银纳米片的制备方法入手, 首先综述了银纳米片的各种制备方法以及实验条件(如光照的波长、表面活性剂种类、还原剂种类)对产物形貌的影响. 其次介绍了银纳米片的奇特光学性质, 总结了银纳米片的几种重要生长机制, 最后介绍了银纳米片的应用价值, 并对银纳米片的研究前景做了展望.     

Potentiometric detection of halides and pseudohalides in anion chromatography

A small piece of silver wire, coated with an insoluble silver salt, can be used as a selective potentiometric detector for halides in ion chromatography. Several coated electrodes were examined by electron microscopy and their response to various anions evaluated in a flow-injection system. A silver/silver chloride was found to be a selective and reproducible detector for chloride, bromide, iodide, thiocyanate and thiosulfate separated by ion chromatography. Calibration curves were non-linear and had slopes ranging from 40 to 60 mV per concentration decade in the range 0.1–2 mM. A working range of 0.05–2 mM was used. This electrode is also satisfactory when gradient elution is used in ion chromatography.     

Remarks on the reactions of a tetracarboxylic porphyrin with gold and silver ions: A spectrophotometric,TEM and SEM study

The coproporphyrin-I (CPI) behaves as a reducing agent for silver and gold metal ions and as stabilizing agent for the formed colloidal metallic nanoparticles. The peculiarity of silver and gold nanoparticles obtained in the reactions of monomeric form of CPI with their metal ions has been studied. The optical properties of the colloidal forms of these metals have been investigated by UV–Vis spectrophotometry, and their morphology by TEM and SEM measurements. The structures and the size distributions of Ag and Au particles have been characterized and determined by computerized TEM images.     

电子显微镜技术表征聚乙二醇包覆的银纳米线的显微结构特征

以缓慢的水热合成法制备聚乙二醇(PEG)包覆的银纳米线,并用电子显微镜对其微观形貌和结构进行了表征。PEG是一种对银表面呈弱亲和性的水溶性聚合物,它在银纳米线合成中既作为Ag+的还原剂,又作为银线的包覆剂。扫描电镜和透射电镜表征显示,这种银纳米线的直径为80～300 nm,长度大于100μm;并且其中一部分银纳米线首尾相接形成了闭合纳米线圈,是首例以化学法制取的金属闭合纳米线圈。闭合环状纳米线的形成进一步支持了金属纳米线的融合生长机制。透射电镜和选区电子衍射以及银纳米线横截面切片的透射电镜表征显示,这种PEG包覆的银纳米线具有轴对称的五重挛晶结构。银纳米线经过长时间的水热孵化而保持其五重挛晶结构,这一点与某些文献报道的情况有所不同,说明银纳米线结构及其演化具有一定的复杂性。     

Silver polymeric nanocomposites as advanced antimicrobial agents: classification, synthetic paths, applications, and perspectives

Utilization of metallic nanoparticles in various biotechnological and medical applications represents one of the most extensively investigated areas of the current materials science. These advanced applications require the appropriate chemical functionalization of the nanoparticles with organic molecules or their incorporation in suitable polymer matrices. The intensified interest in polymer nanocomposites with silver nanoparticles is due to the high antimicrobial effect of nanosilver as well as the unique characteristics of polymers which include their excellent structural uniformity, multivalency, high degree of branching, miscellaneous morphologies and architectures, and highly variable chemical composition. In this review, we explore several aspects of antimicrobial polymer silver nanocomposites, giving special focus to the critical analysis of the reported synthetic routes including their advantages, drawbacks, possible improvements, and real applicability in antibacterial and antifungal therapy. A special attention is given to "green" synthetic routes exploiting the biopolymeric matrix and to the methods allowing preparing magnetically controllable antimicrobial polymers for targeting to an active place. The controversial mechanism of the action of silver against bacteria, fungi and yeasts as well as perspectives and new applications of silver polymeric nanocomposites is also briefly discussed.     

线状和树枝状银纳米结构、形成机理及表面增强拉曼散射性质(英文)

以聚丙烯酰胺(PAM)为模板,在液相中通过不同浓度的抗坏血酸还原硝酸银能够得到缠结的线状和树枝状银纳米结构.该方法合成条件温和(常温常压)、产率高、成本低、操作简单,并且得到了特殊形貌的缠结收光在谱一对起线的状线和状树银枝纳状米银结纳构.米通结过构透的射形电貌子和显性微质镜进(T行E了M)表,扫征描.研电究子表显明微,镜PA(SMEM对)线、拉形曼产光物谱的和形紫成外起?可了见决吸定性作用.在反应初期,大量新生成的银核被PAM链吸附,小颗粒逐渐长大,进而相连,导致生成了缠结的线状银纳米结构.另外,抗坏血酸的浓度越高,越不利于线状结构的生成.利用对巯基苯胺(PATP)为探针分子研究了银纳米结构的表面增强拉曼散射(SERS)活性,结果表明线状银纳米结构具有较强的表面增强拉曼散射效果.     

Complexes of silver(I) with peptides and proteins as produced in electrospray mass spectrometry

Silver(I) forms aqueous phase complexes with both sulfur and nonsulfur containing peptides and proteins. These complexes were introduced into the gas phase via electrospray, and their structures probed by means of tandem mass spectrometry. Experiments with di-, tri-, and oligopeptides show that the abundance of silver(I)-containing ions increases relative to that of proton-containing ions as peptide length increases. This increase is much more dramatic for methionine-containing peptides. Collision-induced dissociation of silver-peptide complexes yields a multitude of product ions that are silver containing. However, even for methioninecontaining peptides, very few of these product ions contain the methionine residue. The solution-phase structure and the gas-phase structure of the silver/peptide complex are not identical. The methionine sulfur acts as the silver anchoring point in solution. Desolvation in the gas phase leads to a rearrangement of the silver/peptide complex such that the silver ion becomes chelated to the nitrogen and oxygen atom on the peptide backbone in addition to the methionine sulfur. This rearrangement decreases the importance of the silver/sulfur bond to the extent that it is frequently broken upon collision activation and leads to the formation of silver/peptide product ions that are nonsulfur bearing.     

Silver ion liquid-chromatographic mobility of plant diacylglycerols as a function of their composition and spatial arrangement

Coordination complexes of unsaturated rac-1,2-diacylglycerols (DAGs) with silver ions were separated by adsorption and reversed-phase TLC (silver ion TLC and silver ion RP-TLC, respectively). During silver ion TLC, silver ion complexes are formed by an indeterminate number of coordination centers of various nature and only at the adsorbent surface; separation of the complexes proceeds according to an adsorption mechanism, and there is an inverse exponential relationship between DAG unsaturation and their mobility. With silver ion RP-TLC, the complexes are formed only with double bonds, only in solution, and at a 1:1 ratio; the complexes are fractionated by lipophilic partitioning between two liquid phases, and the relationship between the unsaturation of DAGs and their mobility is a direct linear one. Nevertheless, in spite of all these differences, the use of both methods demonstrated that DAG species characterized by a coiled acyl configuration always greatly exceeded in polarity those with the same unsaturation, but with the configuration close to an extended one; in the former group, this excess amounted to two- to three-fold and 30-40% for silver ion TLC and silver ion RP-TLC, respectively. In addition, for both versions of silver ion LC, these two groups of species differ from each other quantitatively, but not qualitatively, in the pattern of the relationship between the unsaturation and mobility of DAG complexes. Thus, under all conditions of silver ion LC studied here, the polarity of DAG complexes and, therefore, their mobility are conditional not only on the number of double bonds, but also on their configuration.     

Metal Extracts as Precursors for the Production of Metal Powders and Coatings via the Extraction-Pyrolytic Method

The extraction of copper, silver, bismuth, and nickel with carboxylic acids thus providing concentrated metal-containing organic solutions and their crystalline salts has been studied. Micron- and submicron-sized metal powders have been obtained via reduction of these metals carboxylates by heating in benzyl alcohol or ethylene glycol. The synthesis of aspherical silver nanoparticles has been achieved by the reduction of a liquid extract of silver neodecanoate in benzyl alcohol. The possibility of the use of concentrated silver-containing solutions as inks for obtaining of electroconductive images has been demonstrated.