Hemoglobin co-immobilized with silver–silver oxide nanoparticles on a bare silver electrode for hydrogen peroxide electroanalysis

Hemoglobin (Hb) and silver–silver oxide (Ag–Ag₂O) nanoparticles were co-immobilized on a bare silver electrode surface by cyclic voltammetry, and were characterized by UV–vis reflection spectroscopy, scanning electron microscopy, and electrochemical impedance spectroscopy. The immobilized Hb was shown to maintain its biological activity well. Direct electron transfer between Hb and the resulting electrode was achieved without the aid of any electron mediator. The reduction currents to hydrogen peroxide (H₂O₂) at co-immobilized electrodes showed a linear relationship with H₂O₂ concentration over a concentration range from 6.0?×?10^?6 to 5.0?×?10^?2 mol L^?1, and a detection limit of 2.0?×?10^?6 mol L^?1 (S/N?=?3).     

Temporal stability of standard potentials of silver–silver chloride reference electrodes

The four-year evolution of standard potential of a silver?Csilver chloride reference electrode (denoted further in the text as an Ag/AgCl electrode) is presented together with some suggestions for the improvement of pH primary measurement procedure.     

Zeolite-supported silver and silver�Ciron nanoclusters and their activities as photodecomposition catalysts

Catalysts containing nanoclusters of Ag(I) and Fe₂O₃ as dopants with sodalite and Y zeolite supports have been investigated in order to develop a more efficient catalyst for photodecomposition of the pesticide carbaryl and to gain insight about the reaction mechanism. Ag(I)?Csodalite, Ag(I)/Fe₂O₃?Csodalite, Ag(I)?CY zeolite, and Ag(I)/Fe₂O₃?CY zeolite were synthesized by ion-exchange techniques and characterized by powder X-ray diffraction (XRD), solid-state luminescence, UV?Cvisible absorption, and atomic absorption spectroscopy measurements. The luminescence activity of the sodalite-supported and Y zeolite-supported catalysts was significantly different. Catalyst performance studies were conducted using carbaryl as the target compound and specific wavelengths of UV light as photon sources for the experiments. The studies showed that each catalyst??s performance was determined primarily by the specific wavelength of the UV light with which the system was irradiated. The studies also showed that inclusion of Fe₂O₃ as dopant enhanced the reactivity of the catalysts in several instances, with the Ag(I)/Fe₂O₃?Csodalite catalyst and 298 nm irradiation being the most reactive of the systems studied. Additional reactions using each catalyst and 298 nm irradiation, and including either sodium bicarbonate as hydroxyl radical scavenger or D₂O as solvent, showed that hydroxyl radicals were likely intermediates in the catalyzed photodecomposition reaction.     

Defect of nanocrystalline copper and silver

Ｎａｎｏｓｃａｌｅｍａｔｅｒｉａｌｓａｒｅｔｈｅｉｍｐｏｒｔａｎｔｐａｒｔｏｆｎａｎｏｓｃｉｅｎｃｅａｎｄｔｅｃｈｎｏｌｏｇｙ.Ｔｈｅｓｔｕｄｙｏｆｎａｎｏｃｒｙｓｔａｌｌｉｎｅｍａｔｅｒｉａｌｓ’ｓｔｒｕｃｔｕｒｅｉｓｃｌｏｓｅｌｙｃｏｎｎｅｃｔｅｄｗｉｔｈｔｈｅｉｒａｐｐｌｉｃａｔｉｏｎ.Ｔｈｅｒｅｆｏｒｅ,ｔｈｅｓｔｒｕｃｔｕｒｅｓｔｕｄｙｏｆｎａｎｏｃｒｙｓｔａｌｌｉｎｅｍａｔｅｒｉａｌｓａｔｔｒａｃｔｓｐａｒｔｉｃｕｌａｒｉｎｔｅｒｅｓｔｉｎｔｈｅｒａｐｉｄｄｅｖｅｌｏｐｍｅｎｔｏｆｈｉ…     

A novel shape-selective fabrication of nanostructured silver

A novel protection-reduction technique is developed for the preparation of silver nanoparticles, nanorods and wheatear-like supramolecular nanostructures at room temperature using silver potassium cyanide [KAg(CN)2] as a silver source, vitamin C (Vc) as a reducing agent and polyvinylpyrrolidone (PVP) as a protecting agent. The concentration of KAg(CN)2, the mole ratios of PVP/Vc and KAg(CN)2/Vc have significant effects on the formation and growth of these novel nanostructures. This method may be extended to prepare novel nanostructures of other metals.     

Solvent extraction of silver trifluoromethanesulfonate from water into nitrobenzene in the presence of silver ionophore?IV

Abstract  

From extraction experiments in the two-phase water/nitrobenzene system, the stability constant of the silver ionophore IV (i.e., 5,11,17,23-tetra-tert-butyl-25,27-bis[2-(methylthio)ethoxy]calix[4]arene)–Ag⁺ complex in nitrobenzene saturated with water was determined. Furthermore, the most probable structure of the resulting complex was derived by means of density functional level of theory calculations.     

Preparation and characterization of polyacrylamide–silver nanocomposites

Polyacrylamide–silver nanocomposites are successfully prepared by irradiating the aqueous solution of AgNO₃ and acrylamide monomer with ⁶⁰Co γ-ray. The composites are found to contain nanometer silver particles with a narrow size distribution and a homogeneous dispersion. The existing of isopropanol (as a hydroxyl radical scavenger and chain transfer agent) in system affects the properties of both the dispersed phase and matrix of the nanocomposites. The fast-formed polymer chains probably play a key role in preventing the aggregation of silver particles which are reduced later.     

Review: Multimetallic silver(I)–pyridinyl complexes: coordination of silver(I) and luminescence

This review highlights some structural features and luminescent properties of homo- and hetero-multinuclear silver(I)–pyridinyl complexes. It focuses on the coordination and geometry of the silver(I) ions to the pyridinyl-nitrogen. For this reason, we have considered only pyridinyl-N–Ag(I) complexes whose crystal data are available. In addition, this review does not consider mononuclear silver(I)–pyridinyl complexes as these have been reviewed elsewhere. This is motivated by the fact that multinuclear silver(I)–pyridinyl complexes have been shown to be more stable in solution, possess enhanced properties, and have fascinating structures compared to their mononuclear counterparts. The introduction highlights pyridinyl ligands used in complexation of silver(I) ions. The main body highlights complexation of silver(I) through pyridinyl nitrogen and the interactions found in the multinuclear silver(I)–pyridinyl complexes as well as the coordination number and geometry of silver(I) centers. Though silver(I) has been flaunted to prefer linear twofold coordination geometry, from this review, it is clear that higher coordination numbers in varied geometries are possible. These include distorted trigonal planar, T-shaped, distorted tetrahedral, trigonal bipyramidal, and octahedral geometries. Coordination of silver(I) to pyridinyl ligands and their metalloligands has been observed to impart or enhance luminescent properties in the ensuing complexes.     

SERS studies of some α-aminoanthraquinones in silver sol

Surface enhanced Raman scattering (SERS) studies of 1-aminoanthraquinone (AAQ), 1-methylaminoanthraquinone (MAAQ) and 1-propanolaminoanthraquinone (PAAQ) adsorbed on silver colloidal particles have been made. The observed SERS spectra have 8, 8 and 11 new bands for AAQ, MAAQ and PAAQ, respectively. The procedure used to prepare the silver sol has an effect on the quality of the SERS spectra. In all the three samples, the intensity of bands due to carbonyl stretching and ring breathing modes is more pronounced. It is found that there is a downward shift in the frequency of the ring breathing mode in PAAQ due to bulky substitution.     

Deposition of silver nanoparticles into porous system of sol–gel silica monoliths and properties of silver/porous silica composites

Porous monolithic gels based on silica with pore size from 16 nm to 3–5 μm have been synthesized using sol–gel technology. Parameters of porous structure are determined by the components molar ratio in the reaction mixture. The reduction processes of silver ions by formamide in the synthesized porous gel were studied. It has been shown that at the initial stage of the reaction, silver particles with size up to 10 nm are formed in the absence of any stabilizers. The composites Ag/SiO₂ were synthesized by means of the threefold impregnation of porous monoliths using the solution of silver nitrate in the mixture of methanol and formamide. Their catalytic activity in the CO oxidation was studied. It was discovered that after activation in oxygen and hydrogen the samples display a low temperature activity, which depends on the number of Si–O-nonbridging oxygen groups on the surface of silica porous monoliths.     

The preparation of conducting polyaniline–silver and poly(p-phenylenediamine)–silver nanocomposites in liquid and frozen reaction mixtures

The oxidation of aniline with silver nitrate in 1 mol L⁻¹ acetic acid at 20 °C yielded a composite of two conducting components, polyaniline and silver; the acceleration with 1 mol% of p-phenylenediamine is needed for efficient synthesis. The yield and molecular weight increased when aniline was copolymerized with 10 mol% p-phenylenediamine. Such product displayed metallic conductivity below 180 K and semiconductor type above this temperature. As the result, the conductivity was the same at 100 and 300 K. The oxidation of p-phenylenediamine alone with silver nitrate also produced a conducting composite having the conductivity of 1,750 S cm⁻¹ despite the assumed nonconductivity of poly(p-phenylenediamine). The present study demonstrates that all oxidations proceeded also in frozen reaction mixtures at −24 °C, i.e., in the solid state. In most cases, molecular weights of polymer component increased, the conductivity of composites with silver improved, to 2,990 S cm⁻¹ for poly(p-phenylenediamine)–silver, and remained high after deprotonation with 1 mol L⁻¹ ammonium hydroxide.

     

γ-Ray synthesis of starch-stabilized silver nanoparticles with antibacterial activities

Silver nanoparticles (Ag NPs) are fabricated through γ-irradiation reduction of silver ions in aqueous starch solutions. The UV–vis analyses show smaller sizes of Ag NPs produced, with higher yields, as the irradiation doses and/or Ag⁺ concentrations are increased. Higher concentrations of starch enhance the yields of Ag NPs, with no significant effects on their size. The most economical Ag NPs are produced at 5 kGy γ-irradiation of a 2×10⁻³ M solution of AgNO₃ containing 0.5% starch. They show a relatively narrow size distribution, indicated by TEM and its corresponding size distribution histogram. The XRD pattern confirms the face-centered cubic (fcc) Ag NPs embedded in starch molecules. Interactions between these nanoparticle surfaces and starch oxygen atoms are indicated by FT–IR. Antibacterial activities of Ag NPs against Escherichia coli appear dependent on the γ-ray doses applied.     

Thermodynamics of oxygen in dilute liquid silver–tellurium alloys

Abstract  

The activity coefficient of oxygen in liquid Ag and binary Ag–Te dilute alloys were determined between 1,285 and 1,485 K by coulometric titration using the electrochemical cell (Ir, [O] in liquid metal or alloy | yttria stabilized zirconia | air, Pt). The experimental and evaluation procedures described in the literature were adopted. The oxygen activity coefficient was determined in pure liquid silver to be . Next, the oxygen activity coefficient in dilute Ag–(Te)–O alloys for variable X _Te content (from 0.01 to 0.06) was measured. From the obtained results, Wagner’s interaction parameter as a function of temperature was derived in the form . The electrochemical coulometric titration method seems to be very useful to study the thermodynamics of oxygen interaction in liquid silver and its alloys.     

Chiral silver phosphate-catalyzed cycloisomeric kinetic resolution of α-allenic alcohols

A kinetic resolution of α-allenic alcohols is realized through chiral silver phosphate-catalyzed cycloisomerization with high stereoselectivity (selectivity factor up to 189) and tolerance of a variety of functional groups. A mechanistic model is proposed to interpret the origin of the high stereoselectivity and broad substrate scope.     

Application of silver electrode to the electrochemical studies of hemoglobin

Several aspects of the application of silver electrode to the electrochemical studies of hemoglobin have been discussed in this paper . The silver electrode could not only be used directly as the electrode for the electrochemical studies of hemoglobin, but also react with phenothiazine and benzimidazole to give stable and useful mediator-coated electrodes. In addition, the silver electrode could help sodium dodecyl sulfate to give full play to its promoting effect on the protein.     

“Blue silver”: transformation of clusters and metal coagulation

The formation and transformations of blue silver ( _max 700 nm) during -irradiation of a weakly alkaline (pH 9) aqueous solution containing AgClO₄, polyacrylic acid (PAA), and isopropanol were studied. We believe that blue silver is a linear silver cluster stabilized on a polymeric molecule. During radiation-chemical reduction the cluster is transformed into new clusters ( _max = 365 and 460 nm). When all of the Ag⁺ ions present in the solution have been reduced, clusters coalesce and a new phase,i.e., colloidal silver particles, forms. The mechanism of the radiation-chemical transformations is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 35–37, January, 1995.     

Synthesis and characterization of silver—poly(methylmethacrylate) nanocomposites

The optical properties of silver nanoparticles embedded in poly(methylmethacrylate) (PMMA) was investigated as well as the influence of silver nanoparticles on the thermal properties of polymer matrix. The average size and particle size distribution of silver nanoparticles was determined using transmission electron microscopy. The obtained transparent nanocomposite films were optically characterized using UV-Vis and FTIR spectroscopy. Thermal stability of polymer matrix was improved upon incorporation of small amount of silver nanoparticles. Also, silver nanoparticles have pronounced effect on thermo-oxidative stability of PMMA matrix. The glass transition temperatures of nanocomposites are lower compared to the pure polymer.     

Electrocatalytic studies using silver–clay composite — a novel material

A clay-modified electrode (CME) consisting of novel colloidal silver–montmorillonite clay composite material (Ag⁰_n–MM) has been prepared and characterized. The study on its ability to enhance the redox reactions of phenothiazine dyes reveals that the nanosize particle nature of the silver is retained in the film, as reflected from cyclic voltammograms and photogalvanic studies. The photogalvanic current observed for the dyes in this composite material shows an enhanced anodic photocurrent versus the case in ion-exchanged CMEs, where the dyes show a cathodic photocurrent. The unique behavior is explained by a suitable mechanism.     

Antifungal activity of silver nanoparticle-encapsulated β-cyclodextrin against human opportunistic pathogens

Silver nanoparticles were synthesised by reducing silver acetate with a long-chain aliphatic amine. β-Cyclodextrin (CD)-stabilised silver nanoparticles were successfully synthesised and characterised by the UV–vis spectroscopy and scanning electron microscopy analysis. This system was examined for their antifungal activity against opportunistic human pathogens such as Aspergillus fumigatus, Mucor ramosissimus and Chrysosporium species. This study clearly demonstrates that the present system is a powerful antifungal agent against human opportunistic pathogenic fungi.