组氨酸修饰普鲁士蓝的制备及与银离子的作用

利用水热法合成了组氨酸修饰的普鲁士蓝(HisPB). 通过扫描电子显微镜(SEM), X射线衍射(XRD)以及紫外-可见分光光度计(UV-Vis)等对合成的HisPB样品进行了形貌和结构表征. 与未经修饰的普鲁士蓝(PB)相比, 组氨酸修饰的普鲁士蓝粒子体积更大, 表面更光滑, 表面官能团增多, 这些因素显著提升了普鲁士蓝在碱性溶液中的稳定性. 确定了HisPB用于检测银离子的最佳pH值为10, 通过监测HisPB与银离子反应后其紫外光谱在800 nm处的吸收峰强度变化以及溶液颜色的改变, 实现了对6~40 μmol/L浓度范围内银离子的检测.     

Silver Ions in Non‐canonical DNA Base Pairs: Metal‐Mediated Mismatch Stabilization of 2′‐Deoxyadenosine and 7‐Deazapurine Derivatives with 2′‐Deoxycytidine and 2′‐Deoxyguanosine

Novel silver‐mediated dA?dC, dA*?dC, and dA*?dG base pairs were formed in a natural DNA double helix environment (dA* denotes 7‐deaza‐dA, 7‐deaza‐7‐iodo‐dA, and 7‐cyclopropyl‐7‐deaza‐dA). 7‐Deazapurine nucleosides enforce silver ion binding and direct metal‐mediated base pair formation to their Watson–Crick face. New phosphoramidites were prepared from 7‐deaza‐dA, 7‐deaza‐7‐iodo‐dA, and 7‐cyclopropyl‐7‐deaza‐dA, which contain labile isobutyryl protecting groups. Solid‐phase synthesis furnished oligonucleotides that contain mismatches in near central positions. Increased thermal stabilities (higher T_m values) were observed for oligonucleotide duplexes with non‐canonical dA*?dC and dA?dC pairs in the presence of silver ions. The stability of the silver‐mediated base pairs was pH dependent. Silver ion binding was not observed for the dA?dG mismatch but took place when mismatches were formed between 7‐deazaadenine and guanine. The specific binding of silver ions was confirmed by stoichiometric UV titration experiments, which proved that one silver ion is captured by one mismatch. The stability increase of canonical DNA mismatches might have an impact on cellular DNA repair.     

Modified silver staining for immobilized pH gradients.

Silver development of gels containing an immobilized pH gradient has proved difficult so far because the bonded buffers (especially the tertiary amino acrylamido derivatives) tend to absorb silver ions with a resultant heavy background of increasing darkness from the anode to the cathode. We report a variant of silver staining in which thiosulfate is used twice: (i) prior to silver impregnation, at the millimolar level, to enhance sensitivity, and (ii) during development, at the micromolar level, to decrease the background.     

Synthesis of copolymer-stabilized silver nanoparticles for coating materials

Silver ions being less toxic than silver nanoparticles, a more safe material can be obtained to be used as antimicrobial coating. This can be achieved by using thiol chemistry and covalently attach the silver nanoparticles in the coating. Our aim is to produce a coating having antimicrobial properties of silver ions but with the silver nanoparticles firmly attached in the coating. Here, we present a way to produce silver nanoparticles that can be used as a component in a coating or as such to produce an antimicrobial coating. The silver nanoparticles presented here are stabilized by a copolymer (poly(butyl acrylate–methyl methacrylate)) that is soft and has well-known good film-producing properties. The reversible addition-fragmentation chain transfer radical polymerization technique used to prepare the polymers provides conveniently a thiol group for effective binding of the silver nanoparticles to the polymers and thus to the coating.     

Handling (Nano)Silver as Antimicrobial Agent: Therapeutic Window,Dissolution Dynamics,Detection Methods and Molecular Interactions

Silver is an antimicrobial agent well known since antiquity. With the emergence of multiresistant bacteria, it has come back into the focus of research, and ionic as well as nano-sized silver have been studied in vitro and in vivo. The results are controversial, silver being discussed as the “silver bullet” or a “wolf in sheep's clothing”. A thorough search of literature from chemistry, materials and environmental science, biology and medicine led to this Review which summarizes the potential use of silver and its compounds in medicine, ongoing processes of dissolution and the different methods by which this usefulness can be evaluated. It also highlights the therapeutic window of silver, mechanistic interactions of silver and biological media as well as best practices for handling silver in a biomedical environment. This Review reflects the current knowhow and observations, and may thus give hints and guidelines to understand and interpret the observed effects.     

Chemical and Biological Aspects of Nutritional Immunity—Perspectives for New Anti‐Infectives that Target Iron Uptake Systems

Upon bacterial infection, one of the defense mechanisms of the host is the withdrawal of essential metal ions, in particular iron, which leads to “nutritional immunity”. However, bacteria have evolved strategies to overcome iron starvation, for example, by stealing iron from the host or other bacteria through specific iron chelators with high binding affinity. Fortunately, these complex interactions between the host and pathogen that lead to metal homeostasis provide several opportunities for interception and, thus, allow the development of novel antibacterial compounds. This Review focuses on iron, discusses recent highlights, and gives some future perspectives which are relevant in the fight against antibiotic resistance.     

Selective Synthesis of Silver Nanoparticles onto Potassium Hexaniobate: Structural Organisation with Bactericidal Properties

Silver‐based nanocomposites are known to act as biocides against a series of microorganisms and are largely studied as an alternative to substitute conventional antibiotics that show decreasing efficacy. In this work, an eco‐friendly method to synthesize silver nanoparticles assembled on the surface of hexaniobate crystals is reported. By means of ion exchange, K⁺ ions of layered potassium hexaniobate were partially substituted by Ag⁺ ions and the resulting material was exposed to UV light. The irradiation allowed the reduction of silver ions with consequent formation of silver nanoparticles located only on the hexaniobate surface, whereas Ag⁺ ions located in the interlayer space remained in the ionic form. Increasing UV‐light exposure times allowed controlling of the silver nanoparticle size. The antibacterial effects of the pristine potassium hexaniobate and of silver‐containing hexaniobate samples were tested against Escherichia coli (E. coli). The antibacterial efficacy was determined to be related to the presence of silver in hexaniobate. An increasing activity against E. coli was observed with the decrease in silver nanoparticles size, suggesting that silver nanoparticles of distinct sizes interact differently with bacterial cell walls.     

The Kalimantacin Polyketide Antibiotics Inhibit Fatty Acid Biosynthesis in Staphylococcus aureus by Targeting the Enoyl‐Acyl Carrier Protein Binding Site of FabI

The enoyl‐acyl carrier protein reductase enzyme FabI is essential for fatty acid biosynthesis in Staphylococcus aureus and represents a promising target for the development of novel, urgently needed anti‐staphylococcal agents. Here, we elucidate the mode of action of the kalimantacin antibiotics, a novel class of FabI inhibitors with clinically‐relevant activity against multidrug‐resistant S. aureus. By combining X‐ray crystallography with molecular dynamics simulations, in vitro kinetic studies and chemical derivatization experiments, we characterize the interaction between the antibiotics and their target, and we demonstrate that the kalimantacins bind in a unique conformation that differs significantly from the binding mode of other known FabI inhibitors. We also investigate mechanisms of acquired resistance in S. aureus and identify key residues in FabI that stabilize the binding of the antibiotics. Our findings provide intriguing insights into the mode of action of a novel class of FabI inhibitors that will inspire future anti‐staphylococcal drug development.     

Nanostructure,interactions, and conductivities of polymer electrolytes comprising silver salt and microphase‐separated graft copolymer

Silver polymer electrolytes were prepared by blending silver salt with poly(oxyethylene)₉ methacrylate)‐graft‐poly(dimethyl siloxane), POEM‐g‐PDMS, confining silver salts within the continuous ion‐conducting POEM domains of microphase‐separated graft copolymer. AgClO₄ polymer electrolytes exhibited their maximum conductivity at high silver concentrations as well as higher ionic conductivities than AgCF₃SO₃ electrolytes. The difference in conductivities of the two electrolytes was investigated in terms of the differences in the interactions of silver ions with ether oxygen of POEM and, hence, with the anions of salts. Upon the addition of salt in graft copolymer, the increase of T_g in AgClO₄ was higher than that in AgCF₃SO₃ electrolytes. Analysis of an extended configuration entropy model revealed that the interaction of ether oxygen/AgClO₄ was stronger than that of ether oxygen/AgCF₃SO₃ whereas the interaction of Ag⁺/ClO₄^? was weaker than that of Ag⁺/CF₃SO₃^?. These interactions are supported by the anion vibration mode of FT‐Raman spectroscopy. It is thus concluded that the higher ionic conductivity of AgClO₄ electrolytes was mostly because of higher concentrations of free ions, resulting from their strong ether oxygen/silver ion and weak silver ion/anion interactions. A small angle X‐ray scattering study also showed that the connectivity of the POEM phase was well developed to form nanophase morphology and the domain periodicities of graft copolymer electrolytes monotonically increased with the increase of silver concentration up to critical concentrations, after which the connectivity was less developed and the domain spacings remained invariant. This is attributed to the fact that silver salts are spatially and selectively incorporated in conducting POEM domains as free ions up to critical concentrations, after which they are distributed in both domains as ion pairs without selectivity. The increase of domain d‐spacing in AgClO₄ electrolytes was larger than that in AgCF₃SO₃, which again results from high concentrations of free ions in the former. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1018–1025, 2007     

Fluorogenic Ag+–Tetrazolate Aggregation Enables Efficient Fluorescent Biological Silver Staining

Silver staining, which exploits the special bioaffinity and the chromogenic reduction of silver ions, is an indispensable visualization method in biology. It is a most popular method for in‐gel protein detection. However, it is limited by run‐to‐run variability, background staining, inability for protein quantification, and limited compatibility with mass spectroscopic (MS) analysis; limitations that are largely attributed to the tricky chromogenic visualization. Herein, we reported a novel water‐soluble fluorogenic Ag⁺ probe, the sensing mechanism of which is based on an aggregation‐induced emission (AIE) process driven by tetrazolate‐Ag⁺ interactions. The fluorogenic sensing can substitute the chromogenic reaction, leading to a new fluorescence silver staining method. This new staining method offers sensitive detection of total proteins in polyacrylamide gels with a broad linear dynamic range and robust operations that rival the silver nitrate stain and the best fluorescent stains.     

The Vancomycin Group of Antibiotics and the Fight against Resistant Bacteria

A last line of defence against “superbugs” are the vancomycin group antibiotics. This review describes the determination of their mode of action, and a mechanism of resistance to them. Remarkably, this mechanism of resistance can be overcome without directly modifying the binding site of the antibiotics for the cell-wall precursors of pathogenic bacteria.     

Tris{2‐[N‐(diethylaminothiocarbonyl)benz(‐amidino;‐imidoxy;‐imidothio)‐N′‐yl]ethyl}amine – neue tripodale Liganden. Darstellung,Komplexstabilität und Extraktionsverhalten ihrer Silber(I)‐Komplexe

Tris{2‐[ N ‐(diethylaminothiocarbonyl)benz(‐amidino; imidoxy; ‐imidothio)‐ N ′‐yl]ethyl}amines – New Tripodal Ligands. Synthesis, Complex Stability, and Extraction Behaviour of their Silver(I) Complexes N‐(Thiocarbamoyl)‐benzimidoylchlorides react with trivalent nucleophiles to give four novel tripodal ligands. Two of them have been characterized by X‐ray methods. The ligands form with silver(I) cationic mononuclear complexes in which the three arms of the ligand are coordinated monodentately via sulfur. The results of FAB and ESI mass spectrometry as well as ESCA and NMR investigations verify this binding mode. The protonation constants of the ligands and the stability constants of silver(I) complexes have been determined potentiometrically. The novel tripodal compounds behave as powerful extractands for silver(I).     

Amperometric titration of palladium, silver and copper with benzimidazol-2-ylmethanethiol, and its application to non-ferrous materials

A method is described for the determination of mg amounts of palladium, silver and copper by amperometric titration with benzimidazol-2-ylmethanethiol in acetate buifer medium (pH 4-5) at an applied potential of -0.2 V vs. the saturated calomel electrode. Direct titrations are possible in the presence of a number of foreign ions. Copper and palladium interfere mutually and in the determination of silver. Mercury(I), mercury(II) and platinum(IV) also interfere. Silver does not interfere in the determination of copper and palladium if it is first precipitated as chloride. The method has been successfully applied to the analysis of non-ferrous materials.     

One-step synthesis of silver nanoparticles, nanorods, and nanowires on the surface of DNA network

Here, we describe a one-step synthesis of silver nanoparticles, nanorods, and nanowires on DNA network surface in the absence of surfactant. Silver ions were first adsorbed onto the DNA network and then reduced in sodium borohydride solution. Silver nanoparticles, nanorods, and nanowires were formed by controlling the size of pores of the DNA network. The diameter of the silver nanoparticles and the aspect ratio of the silver nanorods and nanowires can be controlled by adjusting the DNA concentration and reduction time.     

Temperature‐induced self‐assembly and metal‐ion stabilization of histidine functional block copolymers

Histidine functional block copolymers are thermally self‐assembled into polymer micelles with poly‐N‐isopropylacrylamide in the core and the histidine functionality in the corona. The thermally induced self‐assemblies are reversible until treated with Cu²⁺ ions at 50 °C. Upon treatment with 0.5 equivalents of Cu²⁺ relative to the histidine moieties, metal‐ion coordination locks the self‐assemblies. The self‐assembly behavior of histidine functional block copolymers is explored at different values of pH using DLS and ¹H NMR. Metal‐ion coordination locking of the histidine functional micelles is also explored at different pH values, with stable micelles forming at pH 9, observed by DLS and imaged by atomic force microscopy. The thermal self‐assembly of glycine functional block copolymers at pH 5, 7, and 9 is similar to the histidine functional materials; however, the self‐assemblies do not become stable after the addition of Cu²⁺, indicating that the imidazole plays a crucial role in metal‐ion coordination that locks the micelles. The reversibility of the histidine‐copper complex locking mechanism is demonstrated by the addition of acid to protonate the imidazole and destabilize the polymer self‐assemblies. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1964–1973     

Examination of a synthetic benzophenone membrane-targeted antibiotic

The enormous success of antibiotics is seriously threatened by the development of resistance to most of the drugs available on the market. Thus, novel antibiotics are needed that are less prone to bacterial resistance and are directed toward novel biological targets. Antimicrobial peptides (AMPs) have attracted considerable attention due to their unique mode of action and broad spectrum activity. However, these agents suffer from liability to proteases and the high cost of manufacturing has impeded their development. Previously, we have reported on a novel class of benzophenone-based antibiotics and early studies suggested that these agents might target the bacterial membrane. In this study, we present our work on the mechanism of action of these novel membrane targeted antibiotics. These compounds have good affinities to polyanionic components of the cell wall such as lipoteichoic acid (LTA) and lipopolysaccharide (LPS). We found that these agents release potassium ions from treated bacteria; thus, resulting in disruption of the bacterial membrane potential. Benzophenone-based membrane targeted antibiotics (BPMTAs) cause membrane disruption in synthetic lipid vesicles that mimic Gram-positive or Gram-negative bacteria. The compounds display no hemolytic activity up to a concentration that is 100 times the MIC values and they are capable of curing mice of a lethal MRSA infection. Repeated attempts to develop a mutant resistant to these agents has failed. Taken together, BPMTAs represent a promising new class of membrane-targeted antibacterial agents.     

Histidine‐modified organic‐silica hybrid monolithic column for mixed‐mode per aqueous and ion‐exchange capillary electrochromatography

A novel organic‐silica hybrid monolith was prepared through the binding of histidine onto the surface of monolithic matrix for mixed‐mode per aqueous and ion‐exchange capillary electrochromatography. The imidazolium and amino groups on the surface of the monolithic stationary phase were used to generate an anodic electro‐osmotic flow as well as to provide electrostatic interaction sites for the charged compounds at low pH. Typical per aqueous chromatographic behavior was observed in water‐rich mobile phases. Various polar and hydrophilic analytes were selected to evaluate the characteristics and chromatographic performance of the obtained monolith. Under per aqueous conditions, the mixed‐mode mechanism of hydrophobic and ion‐exchange interactions was observed and the resultant monolithic column proved to be very versatile for the efficient separations of these polar and hydrophilic compounds (including amides, nucleosides and nucleotide bases, benzoic acid derivatives, and amino acids) in highly aqueous mobile phases. The successful applications suggested that the histidine‐modified organic‐silica hybrid monolithic column could offer a wide range of retention behaviors and flexible selectivities toward polar and hydrophilic compounds.     

Positive Allosteric Control of Guests Encapsulation by Metal Binding to Covalent Porphyrin Cages

The allosteric control of the receptor properties of two flexible covalent cages is reported. These receptors consist of two zinc(II) porphyrins connected by four linkers of two different sizes, each incorporating two 1,2,3-triazolyl ligands. Silver(I) ions act as effectors, responsible for an on/off encapsulation mechanism of neutral guest molecules. Binding silver(I) ions to the triazoles opens the cages and triggers the coordination of pyrazine or the encapsulation of N,N′-dibutyl-1,4,5,8-naphthalene diimide. The X-ray structure of the silver(I)-complexed receptor with short connectors is reported, revealing the hollow structure with a cavity well-defined by two eclipsed porphyrins. Rather unexpectedly, the crystallographic structure of this receptor with pyrazine as a guest molecule showed that the cavity is occupied by two pyrazines, each binding to the zinc(II) porphyrin in a monotopic fashion.     

Surface recognition of a protein using designed transition metal complexes.

Each protein has a unique pattern of histidine residues on the surface. This paper describes the design, synthesis, and binding studies of transition metal complexes to target the surface histidine pattern of carbonic anhydrase (bovine erythrocyte). When the pattern of cupric ions on a complex matches the surface pattern of histidines of the protein, strong and selective binding can be achieved in aqueous buffer (pH = 7.0). The described method of protein recognition is applicable to proteins of known structures. With rapidly increasing number of solved protein structures, the method has wide applicability in purification, targeting, and sensing of proteins.     

Biosynthesis of silver nanoparticle using flowers of Calotropis gigantea (L.) W.T. Aiton and activity against pathogenic bacteria

Silver nanoparticles (AgNPs) from silver nitrate solution are carried out using the flower extract of Calotropis gigantea. Silver nanoparticles were characterized by UV–vis spectrophotometer, X-Ray diffractometer (XRD). Reduction of silver ions in the aqueous solution of silver during the reaction was observed by UV–vis spectroscopy. Crystalline nature of synthesized silver nanoparticles was studied by XRD pattern, refraction peak using the Scherrer’s equation. Antibacterial activity of the silver nanoparticles was performed by disc diffusion method against Bacillus subtilis, Pseudomonas putida and Escherichia coli. The antibacterial activity of synthesized silver nanoparticles by flower extract of C. gigantea was found against B. subtilis (10 mm). Synthesised AgNPs has the efficient antibacterial activity against Gram positive bacteria.