Complexation Of Silver Ions Research Articles

Silver (I) complexes of imidazolium based N-heterocyclic carbenes for antibacterial applications

Abstract Imidazolium-based novel ionic liquids (ILs) and their silver complexes were synthesized and evaluated for antibacterial properties. In current endeavor, we have designed novel ILs and prepared their neutral and ionic silver complexes where their formation is influenced by the polarity of solvent as evidenced by NMR, FT-IR, and EI-MS data followed by investigating the antimicrobial activity, MIC determination and stability studies against microbial growth. The most potent compound NS-11 and IS-11 inhibited the microbial growth with MIC value of 6.25 μM against S. aureus and NS-11 displayed MIC of 25 μM against S. enterica showing an efficient growth inhibition even up to 21 d. The relative potency amongst the test compounds was assigned using optical density measurement at 600 nm. The cell morphology when monitored with SEM, showed the rupture of bacterial cell wall and thereby indicating cell wall as a site of action resulting in the ceasing of bacterial growth. The side chain in ligands as well as metal complexes was varied as biphenyl carbonitrile, benzyl, butyl and methyl in order to investigate the effects of steric properties and hydrophobicity on biological activity reflecting a direct correlation. The variation of side chain gives clear insight into the essence of substitutions to contribute towards enhanced stability against bacterial growth.

Structural and spectral studies of silver(I) complexes with new Schiff bases derived from 2-thiopheneethylamine and their application in thin layer deposition by spin and dip coating techniques

New Schiff bases were obtained in the reaction of 2-thiopheneethylamine with 3-methyl-2-thiophenecarboxaldehyde (for thet(3-methca), L1) or 5-bromo-2-thiophenecarboxaldehyde (for thet(5-Brthca), L2) and characterized by 1H, 13C and 15N NMR spectra and a 1H differential Nuclear Overhauser Effect (NOE diff.) experiment. The synthesized ligands were used for the complexation of silver(I) ions, resulting in new complexes of the formula [Ag(thet(3-methca))2(NO3)] (1) and [Ag(thet(5-Brthca))2(NO3)] (2). The X-ray crystal structure analysis of (1) revealed a distorted tetrahedral geometry of the coordination sphere with two monodentately N bonded Schiff base (L1) molecules and a bidentately coordinated nitrate anion. In [Ag(thet(5-Brthca))2(NO3)] (2), a twofold [y,x,−z] symmetry of the molecule is found, with the symmetry axis coinciding with the double NO bond in the nitrate ligand. The silver(I) ion binds the Schiff base and nitrate anion identically to that in (1), but also bonds to two sulfur donors, thereby having a strongly deformed octahedral coordination sphere. 1H NOE diff. spectra revealed a significant NOE enhancement for the imine hydrogen atoms and the hydrogen atoms in the aromatic rings in closest proximity. The UV–Vis and fluorescence spectra of the ligands and complexes were measured. All the compounds exhibit a higher intensity fluorescence in the solid state than in solution. The geometries of the complexes, optimized in DFT simulations, have been used to assist in the interpretation of the fluorescence experiments and absorption spectra. The obtained complexes have been used for preparation of thin layers on Si(111) to test the possibility of their use as fluorescent materials. Thin layers of the complexes were deposited by spin and dip coating techniques on Si(111) substrates and were characterized by scanning electron microscopy (SEM/EDX) and atomic force microscopy (AFM). The fluorescence spectra of [Ag(thet(3-methca))2(NO3)] (1)/Si and [Ag(thet(5-Brthca))2(NO3)] (2)/Si layers revealed the highest fluorescence intensity when a multistage deposition was applied at different spin rates and deposition times. The obtained layers have better parameters than materials which were used successfully as gas sensing materials.

UV light induces Ag nanoparticle formation: roles of natural organic matter, iron, and oxygen

Nanoparticles occurring in the environment originate either from engineered, synthetically produced nanoparticles, or from naturally produced nanoparticles. The latter can be formed in natural media by light-induced reduction of metal ions in presence of natural organic matter, such as humic substances occurring widely in waters, soils and sediments. There is actually few knowledge on the effect of sunlight and of the nature of organic matter on nanoparticle formation. Therefore, we studied here the photoreduction of silver(I) ion to silver nanoparticles with and without ferrous ion under oxic and anoxic conditions, using humic and fulvic acids as proxies of natural organic matter. UV light-induced formation of silver nanoparticles was monitored up to 60 min by measuring surface plasmon resonance in air-saturated mixture and nitrogen-saturated mixture of silver(I) ion–organic matter. Results show that the surface plasmon resonance intensity was about 2.5 times higher in the nitrogen-purged solution mixture than the air-saturated solution. This finding suggests the oxygen-containing species had no major role in forming silver nanoparticles. Therefore, photo-driven formation of silver nanoparticles most likely involved photoactivation of silver(I) ion and natural organic matter complexes. We observed also that both iron(II) and iron(III) ions highly modified the surface plasmon resonance spectra of the particles with broader features. Results also reveal that in the presence of humic acid, the intensity of the surface plasmon resonance peak decreased by at least 50 %, while almost no change in the intensity was seen when fulvic acid was used. Overall, our findings demonstrate that the ligand–metal charge transfer process, affected by the nature of organic matter, i.e., humic acid versus fulvic acid, was influenced by redox iron species.

Extraction of squalene from camellia oil by silver ion complexation

Abstract Separation of squalene, a type of terpenoid hydrocarbons with important biological properties, from camellia oil by silver ion complexation was studied. We showed that the UV–visible absorption wavelength of squalene in AgNO3-methanol solution was obviously red-shifted, and the infra-red vibration wavelength of C C bond slightly decreased, indicating that complexation between squalene and Ag+ took place. The distributions of squalene in AgNO3 methanol solution/petroleum ether under different conditions were further investigated. We found that the fraction of squalene in AgNO3-methanol phase was enhanced with increased percentage of methanol and AgNO3 concentration and decreased extraction temperature. The distribution coefficient of squalene was up to 7.87 under optimum extraction conditions with 70% methanol (v/v), 0.6 mol/L AgNO3, reaction time of 12 h, and at the temperature of 0 °C. Furthermore, under the optimum conditions, extraction of squalene from the unsaponifiable portion of camellia oil exhibited high selectivity with a raffinate rate and a back-extraction rate of 73.9% and 72.5%, respectively. The purity of extracted squalene was 37.8%, 108 times more concentrated than that in the starting material.

In Situ Cell Surface Modification for Surface-enhanced Raman Analysis of Cell Membrane

We report in situ cell surface modification for surface-enhanced Raman analysis of cell membrane. Our method can produce silver metals on cell membrane via the formation of complex of silver ions a...

Doped sol–gel films vs. powders TiO2: On the positive effect induced by the presence of a substrate

SiO2 and Ag–SiO2 doped TiO2 films and powders have been produced using a controlled sol–gel process. The dopant has been introduced using an alkoxysilane-functionalized ligand, with or without complexed silver ions. The influence of dopants on physico-chemical properties of the catalysts is studied by XRD, TEM–EDX, DRUV–vis analyses in the case of powders, while GIXRD, XPS, profilometry, UV–vis absorption analyses have been used for thin films. The photocatalytic activity has been evaluated from the degradation of methylene blue under UV-A light in the presence of the different catalysts over a period of 24h. The detailed comparison between powders and films highlights a surprising positive effect in the case of films due to the presence of the substrate. In the case of photocatalytic powders, the presence of SiO2 or Ag–SiO2 into the TiO2 matrix has a detrimental effect on the photocatalytic activity while the opposite tendency is observed in the case of films, with best activities obtained with Ag–SiO2 doping. Different factors, in particular crystallinity modification between powders and films, have been studied to explain these opposite behaviors. In the case of powders, crystallization is hindered by SiO2 and Ag particles incorporation into the TiO2 matrix, leading to a decrease of the photocatalytic activity. In the case of thin films, probably because of the presence of a substrate, crystallization is not influenced by the presence of SiO2 and Ag particles. Therefore, the latter ones can fully play their role of electron traps leading to an enhanced photocatalytic activity.

ChemInform Abstract: Review: Multimetallic Silver(I)‐Pyridinyl Complexes: Coordination of Silver(I) and Luminescence

AbstractReview: 221 refs.

Synthesis of polystyrene@(silver–polypyrrole) core/shell nanocomposite microspheres and study on their antibacterial activities

We reported the synthesis of polystyrene@(silver–polypyrrole) (PS@(Ag–PPy)) nanocomposite microspheres with the well-defined core/shell structure, in which the functionalized PS microspheres by the sulfonic acid groups were employed as template. The diameter of the synthesized PS microsphere template and AgNP was 1.26 μm and 50 nm, respectively. In order to well control the redox reaction between Ag+ and Py monomer and to avoid the accumulation of these AgNPs during synthesis process, the complexation of triethanolamine (TEA) and silver ion ([Ag(TEA)2]+) was employed as the oxidant, so that the generation rate of AgNPs was in turn decreased. Moreover, compared with the redox reaction between AgNO3 and Py, the introduction of [Ag(TEA)2]+ ions resulted in the improved coverage and distribution of AgNPs around the surface of PS microspheres. Meanwhile, the loading amount of Ag–PPy nanocomposites on the final microspheres was adjustable. The increasing concentrations of Py monomer and [Ag(TEA)2]+ ions resulted in the increase of Ag–PPy nanocomposite loading. The results of antibacterial experiment suggested that the synthesized PS@(Ag–PPy) composite microspheres showed the prominent antibacterial properties against both the Gram-negative bacteria of Escherichia coli and the Gram-positive bacteria of Staphylococcus aureus. For the bacteria with concentration at 1 × 105 – 9×105 cfu/mL, the microspheres can kill the bacteria above 3-log reduction with the concentration of PS@(Ag–PPy) composite microspheres at 50 μg/mL, in which the weight fraction of Py in the composite microspheres was above 10 wt%. When the weight fraction of Py in the composite microspheres was at 5 wt%, the 2-log reduction of in bacterial viability could also be obtained.

Carboxymethyl cellulose assisted immobilization of silver nanoparticles onto cellulose nanofibers for the detection of catechol

We report a facile approach to synthesize and immobilize silver nanoparticles (AgNPs) onto carboxymethyl cellulose (CMC)-modified electrospun cellulose nanofibers and demonstrate the potential application of as-prepared AgNPs-CMC/cellulose composite nanofibrous mats as effective biosensor substrate materials. Cellulose nanofibers were prepared by the combination of electrospinning with deacetylation. Then, CMC was adsorbed onto cellulose nanofibers to complex silver ions through the chemical binding with the free carboxyl groups of CMC for subsequent reductive formation of AgNPs. The AgNPs-CMC/cellulose nanofibers immobilized with laccase (Lac) by electrostatic interactions were used as biosensor substrate materials for catechol detection. The cyclic voltammetries revealed that the AgNPs-CMC/cellulose nanofibers was beneficial to the immobilization of Lac and facilitated the direct electron transfer between Lac and electrode. Lac/AgNPs-CMC/cellulose/glassy carbon electrode exhibited a detection limit of 1.64μM (S/N=3), and a wide linear range from 4.98μM to 3.65mM, as well as good repeatability, reproducibility, stability, and selectivity. The CMC/cellulose nanofibrous mats have great potential applications as substrate materials for different biosensors by immobilizing other different functional nanoparticles or enzyme on them.

Biogenic silver nanoparticles associated with silver chloride nanoparticles (Ag@AgCl) produced by laccase from Trametes versicolor.

In the present study, semi-purified laccase from Trametes versicolor was applied for the synthesis of silver nanoparticles, and the properties of the produced nanoparticles were characterized. All of the analyses of the spectra indicated silver nanoparticle formation. A complete characterization of the silver nanoparticles showed that a complex of silver nanoparticles and silver ions was produced, with the majority of the particles having a Ag2+ chemical structure. A hypothetical mechanistic scheme was proposed, suggesting that the main pathway that was used was the interaction of silver ions with the T1 site of laccase, producing silver nanoparticles with the concomitant inactivation of laccase activity and posterior complexing with silver ions.

Hybrid systems of gold and silver nanoparticles generated on cellulose surfaces

Developing methods for immobilizing metallic nanoparticles (NP) onto different surfaces is a subject of fundamental interest, as nanometric structures enable the appearance of novel properties, absent in bulk or even in micrometric dimensions. In fact, the presence of NP with different size and shape on surfaces can induce substantial modifications on their electronic, optical, magnetic, physical or chemical proprieties. This will be very useful for many applications in different areas ranging from electronics to biomedicine.In this work, we use a simple, reproducible and economic method to grow metallic gold and silver NP directly on cellulose surfaces. A prior chemical activation of the alcohol groups on the cellulose surface is needed for grafting amino functions, which will complex silver and gold ions. Therefore, NP nucleation is only allowed and selectively accomplished on these seed coordination sites. The growth of NP is achieved by the interaction of aqueous dilute solutions of AgNO3 or NaAuCl4 with the cellulose surface. The procedure limits the generation of NP only to the cellulose surface, keeping the dispersion medium completely exempt of them. The resulting NP are, consequently chemically immobilized on the cellulose surface. The chemical anchoring of the NP to the surface avoids particle desorption and extends the lifetime of the resulting hybrid materials. Following this procedure, silver and gold NP could be successfully created on cellulose and this was supported by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM).The present AFM (Figure 1) study enabled to characterize the size and shape of silver NP: they are spherical and have a diameter of ~15 nm. SEM image of Ag NP (Figure 2) display the existence of NP agglomerates. Comparison of the two images suggests size and spatial distributions strongly non- uniform. It is now a challenge to deposit nanoparticles in an organized manner, achieving a regular surface functionalization of cellulose. In TEM (Figure 3) we see a sample where Ag and Au salts interacted simultaneously with the cellulose surface. Crossing the images with other information from analytical techniques, it seems that Ag NP and Au NP form mainly separately instead of presenting a core-shell structure. Also, there is evidence that larger NP are the ones made of silver which suggests that the final result is kinetically (and not thermodynamically) controlled.The authors acknowledge FCT for A.M. Ferraria Grant SFRH/BPD/26239/2006, for A. P. Carapeto Grant SFRH/BD/75734/2011 and strategic projects PEst-OE/CTM/LA0024/2011 and PEst-OE/CTM-UI0084/2011.

Numerical simulation and experiment in the systems of labile complexes of metals. Silver reduction from the thiourea electrolyte

Voltammograms of silver reduction from complex thiourea electrolytes with the ligand to metal concentration ratio varied from 1 to 50 were measured on the freshly prepared surface of silver electrode. The results were analyzed using the numerical model of this electrode process which takes into account homogeneous chemical reactions proceeding in solution, diffusion–migration transfer of the species present in solution, and electrode reactions participated by electroactive components of the electrolyte. We estimated the values of standard exchange current density for partial electrode reactions in which silver complexes with different number of ligands can take part. The highest electrochemical activity is exhibited in solutions with the low concentration of complex-forming agent – by silver aqua complexes, while in solutions with high thiourea concentration – by silver complexes with one ligand. It was found that kinetic hindrances to discharge of the thiourea silver complexes unlikely to be due to the adsorption of thiourea molecules blocking the growth sites or to the adsorption of complex silver ions. The results admit interpretation of the mechanism of electrode process either from the viewpoint of simultaneous discharge of all the complex silver ions present or from the viewpoint of discharge of silver complex with one ligand in combination with rapid chemical reactions of dissociation of other, non-discharging silver complexes.

Comparative Study of Loading of Anodic Porous Alumina with Silver Nanoparticles Using Different Methods.

Three different routes were used to infiltrate the pores of anodic porous alumina templates with silver nanoparticles, selected as an example of a bioactive agent. The three methods present a continuous grading from more physical to more chemical character, starting from ex situ filling of the pores with pre-existing particles, moving on to in situ formation of particles in the pores by bare calcination and ending with in situ calcination following specific chemical reactions. The resulting presence of silver inside the pores was assessed by means of energy dispersive X-ray spectroscopy and X-ray diffraction. The number and the size of nanoparticles were evaluated by scanning electron microscopy of functionalized alumina cross-sections, followed by image analysis. It appears that the best functionalization results are obtained with the in situ chemical procedure, based on the prior formation of silver ion complex by means of ammonia, followed by reduction with an excess amount of acetaldehyde. Elution of the silver content from the chemically functionalized alumina into phosphate buffer saline has also been examined, demonstrating a sustained release of silver over time, up to 15 h.

Doubly-bridged PNP-lariat ethers and their complexes with silver(i) ions in methanol solution

We report the preparation of four new double-bridged PNP-lariat ether derivatives L1–L4 synthesized from precursor 1 by the subsequent substitution of chlorine atoms. The process consists of two steps. In the first one two reactive chlorine atoms of the –PCl2 exocyclic moiety are substituted with respective nucleophiles: 2,2′-thiodiethanethiol 2 and 2,2′-oxydiethanethiol 3. In the second step the other chlorine atoms are substituted by aziridynyl 6 and pyrrolidinyl 7 groups, respectively. Their structures were established by MS, 1H NMR, 31P NMR, 13C NMR spectroscopy. Furthermore, this work includes the investigation of complexation of silver(I) ions with the new ligands L1–L4 in methanol solution. The formation of the novel tetra-nuclear silver(I) complexes were observed. Stability constants were determined using a simple potentiometric titration. 1H NMR, 31P NMR, 13C NMR spectra were recorded to investigate how the complexation of silver(I) ions by the investigated macrocyclic ligands occurs.

Synthesis, structure, and photocatalytic properties of new dinuclear helical complex of silver(I) ions

The 6′,6″-(2-phenylpyrimidine-4,6-diyl)bis(6-methyl-2,2′-bipyridine) ligand L reacts with trifluoromethanesulfonate silver(I) to give dinuclear helical complex [Ag2L2](CF3SO3)2·H2O in which metal ions are in approximately heavily flattened tetrahedron coordination geometry. The complex has been characterized by spectroscopic techniques, elemental analysis, transmission and scanning electron microscopies, and thermogravimetry. The solid state structure of complex has been determined by X-ray diffractometry. The methylene blue (MB) degradation was studied with UV–Vis spectrophotometry. A maximum degradation efficiency of 90% of the dye has been achieved. Photodegradation of the dye follows second-order kinetics. [Ag2L2](CF3SO3)2·H2O is active photocatalyst of MB degradation under UV–Vis and sunlight irradiation.

High current density electrodeposition from silver complex ionic liquids

Liquid metal salts are electrolytes with the highest possible metal concentration for electrodeposition, because the metal ion is an integral part of the solvent. This paper introduces the new ionic silver complexes [Ag(MeCN)(4)](2)[Ag(Tf(2)N)(3)], [Ag(MeCN)][Tf(2)N] and [Ag(EtIm)(2)][Tf(2)N], where MeCN stands for acetonitrile, EtIm for 1-ethylimidazole and Tf(2)N is bis(trifluoromethylsulfonyl)imide. These complexes have been characterized by differential scanning calorimetry, single crystal X-ray crystallography, thermogravimetrical analysis, Raman spectroscopy and cyclic voltammetry. [Ag(MeCN)(4)](2)[Ag(Tf(2)N)(3)] is a room temperature ionic liquid. Smooth silver layers of good quality could be deposited from it, at current densities of up to 25 A dm(-2) in unstirred solutions. [Ag(EtIm)(2)][Tf(2)N] melts at 65 °C and can be used as an electrolyte for silver deposition above this temperature. [Ag(MeCN)][Tf(2)N] has a melting point that is too high to be useful in electrodeposition. Addition of thiourea or 1H-benzotriazole to the electrolyte decreased the surface roughness of the silver coatings. The morphology of the metal layers was investigated by atomic force microscopy (AFM). Adsorption of 1H-benzotriazole on the silver metal surface has been proven by Raman spectroscopy. This work shows the usefulness of additives in improving the quality of metal films electrodeposited from ionic liquids.

Complexes of silver(i) ions with tetrapyrrolidinyl- and tetramorpholinyl-PNP-lariat ethers in acetonitrile and methanol solutions

This work concerns the investigation of stability constants of silver(I) ions with the tetrapyrrolidinyl-PNP-lariat ether L1 in acetonitrile solution and tetramorpholinyl-PNP-lariat ether L2 in acetonitrile and methanol solutions. The new tetramorpholinyl-PNP-lariat ether L2 was synthesized on the basis of the procedure described in a previous publication. Stability constants of complexes with silver ions were determined using a simple potentiometric titration. Furthermore, NMR spectra were obtained to investigate how the complexation of silver(I) ions by the investigated macrocyclic ligand occurs. Spectrometric data analyses and potentiometric measurements indicate that complexation of Ag+ involves participation of the endocyclic nitrogen atom of the cyclophosphazene ring and polyether oxygen donors. As regards L1 the stability of the obtained complex is influenced by pyrrolidinyl groups. On the other hand, L2 includes the morpholinyl subunits attached to the exocyclic P atom, having in their structure the oxygen atom, which pulls out the electrons of the cyclophosphazene ring and thereby destabilizes the formation of a coordination system.

Adsorption and gas-chromatographic properties of silver-modified silicas

Ag0 and Ag(I) nanoparticles are immobilized on the surface of a macroporous silica and amino silica. The adsorption kinetics of a basic dye, methylene blue (MB), from aqueous solutions and the adsorption isotherms of alkyne phenylacetylene from an octane solution are measured. The dependence of the rate constants of MB adsorption on the conditions of immobilization and silver reduction is considered. Silica containing immobilized Ag(I) is shown to have a high adsorption activity with respect to phenyl acetylene. By gas chromatography, it is shown that silver-modified silica has a higher selectivity with respect to alkenes. The reduction of silver on the silica surface and the complexation of silver ions with aminopropyl groups of amino silica lead to a significant decrease in the selectivity of composites.

Structural and Conductivity Studies of Poly(Ethylene Oxide) – Silver Triflate Polymer Electrolyte System

Film of PEO containg AgCF3SO3 were prepared by the solution casting technique. Fourier transform infrared (FTIR) spectroscopy have been carried out on a series of complexes containing poly (ethylene oxide) PEO and silver triflate (AgCF3SO3) salt. Spectral analysis of all the samples has revealed the complexation of silver ions with oxygen in PEO. The ac conductivity and electrical modulus of the samples prepared have been analyzed. The ac conductivity was observed to obey the Universal power law. The temperature dependence of the power law exponent n is reasonably interpreted by the overlapping large polaron tunneling (OLPT) model. The imaginary part, M” of electrical modulus shows the formation of dispersion peak. The plot of log conductivity relaxation times and log sigma as a function of salt concentration was in accordance with each other.

Circular dichroism and UV-Vis absorption spectroscopic monitoring of production of chiral silver nanoparticles templated by guanosine 5′-monophosphate

Herein we report the chemical reduction of silver ions incorporated into chiral supramolecular nanostructures by NaBH(4) in buffered (basic) and unbuffered conditions. In situ self-assembly of guanosine 5'-monophosphate (5'-GMP) templated by Ag(I) and generation of silver nanoparticles (NPs) were continuously monitored by CD and UV-Vis spectroscopy measurements. 5'-GMP has been identified as an efficient chiral organic ligand to complex silver ions into a hierarchical helical nanostructure and is a useful capping agent for stabilizing silver NPs with a size diameter lower than 20 nm. The observation of opposite signed bands in the CD spectra of Ag(I)/5'-GMP complexes at different pH has suggested the existence of opposite-handed supramolecular helical structures depending on pH. Both helical supramolecular structures induce chirality in the silver NPs during their growth of the same handedness as shown by the CD signals in the plasmon resonance band.