Effect of sodium salicylate, sodium oxalate, and sodium chloride on the micellization and adsorption of sodium deoxycholate in aqueous solutions

The salicylate ion increases the rate of bile flow (choleretic effect) and bile salts are known to affect the colonic absorption of oxalate. Owing to this physiological relevance of salicylate and oxalate ions, critical micelle concentration (cmc) values of sodium deoxycholate (NaDC) were determined in aqueous sodium oxalate, sodium salicylate, and sodium chloride solutions by using surface tension, fluorescence, and EMF methods. The results indicate, besides a counterion effect, the influence of coanions on the cmc. In the range from 25 to 40 °C, cmc increases almost linearly with temperature. In the temperature range from 30 to 40 °C, the counterion binding constant β of NaDC micelles has the same value (0.17±0.01) in the presence of sodium chloride and sodium salicylate. On the other hand, in sodium oxalate solution β=0.05±0.02 when oxalate concentration is less than or equal to c* and β=0.48±0.04 above c*, where c*≈0.038 mol kg(-1). EMF measurements also supported this type of counterion binding to NaDC micelles in sodium oxalate solutions. In sodium oxalate solution, at c* a change in the shape of deoxycholate micelles is expected to take place. Salicylate, oxalate, and chloride coanions have a similar effect on the adsorption of NaDC. This study reveals that the choleretic effect of salicylate is not due to the influence of salicylate ions on the micellization of NaDC.     

Synthesis of amphiphilic silver nanoparticles in nanoreactors from invertible polyester

A silver complex is transformed into amphiphilic nanoparticles at room temperature using nanoreactors formed from an amphiphilic polyester. It takes a few minutes to form silver nanocolloids with a narrow particle size distribution. Developed silver forms a stable dispersion in both polar and nonpolar media. The amphiphilic polyester acts as a reducing and stabilizing agent simultaneously. The size of the synthesized amphiphilic silver nanoparticles depends on the concentration of the invertible polyester and solvent polarity.     

FT-Raman, FT-IR and surface enhanced Raman scattering spectra of sodium salicylate

FT-IR and FT-Raman spectra of sodium salicylate were recorded and analysed. Surface enhanced Raman scattering (SERS) spectrum was recorded is silver colloid. Comparisons of the SERS spectrum with the spectra in solution and of the solid sample are made. Sodium salicylate (an O donor ligand) is thought to adsorb in a somewhat 'tilted side on orientation' with respect to the silver surface.     

Direct spectrophotometry of silver in a non-aqueous medium

Silver in the range 0.01–10 p.p.m. is extracted from aqueous solution containing anthranilic acid diacetic acid into methyl isobutyl ketone as silver di-n-butylammonium salicylate without interference from 10-fold amounts of Mg, Ca, Zn, Pb, Al, Cu(II), Ni Co(II), Mn(II), Fe(III), Bi or any compatible common anion. Hg(II) is co-extracted slightly but can be retained in the aqueous phase with EDTA. Spectrophotometric determination of the extracted silver is done with pyrogallol red at 390 mμ in 4-cm cuvettes. The colour system is stable and reproducible. No special purification of reagents is necessary even for the lowest concentrations of silver.     

Thermodynamics of silver salicylate in water and water + 10, + 20, and + 40 mass percent of dioxane at different temperatures

The solubility studies on silver salicylate at different temperatures were made to derive (a) the standard electrode potential of the silver—silver salicylate electrode, (b) the mean activity coefficient of silver salicylate, (c) the dissociation constant of salicylic acid, and (d) the standard thermodynamic quantities, ΔG⁰_t, ΔH⁰_t, ΔS⁰_t, and δC⁰_pt, for the transfer of silver salicylate from the standard state in water to the standard state in water + 10, + 20, and + 40 mass percent of dioxane. The results are discussed in terms of the preferential solvation of the ions.     

An aqueous colloidal silver solution stabilized with carbonate ions

A method has been developed for the preparation of a stable “pure” silver hydrosol containing nanoparticles with an average size of 10 nm and stabilizing carbonate ions. The method consists in the photochemical reduction of silver ions with oxalate ions, which simultaneously generate carbonate ions. Optical spectroscopy, electron microscopy, and dynamic light scattering are used to study the hydrosol     

Mild Silver‐Mediated Geminal Difluorination of Styrenes Using an Air‐ and Moisture‐Stable Fluoroiodane Reagent

An air‐ and moisture‐stable fluoroiodane in the presence of AgBF₄ is suitable for selective geminal difluorination of styrenes under mild reaction conditions. One of the C? F bonds is formed by transfer of electrophilic fluorine from the hypervalent iodine reagent, while the other one arises from the tetrafluoroborate counterion of silver. Deuterium‐isotope‐labelling experiments and rearrangement of methyl styrene substrates suggest that the reaction proceeds through a phenonium ion intermediate.     

The stabilization of nanodisperse silver in a sulfo cation exchanger

Silver-ion exchanger (electron ion exchanger, EI) composites with equivalent silver and hydrogen counterion contents were prepared by chemical deposition. Microscopic and X-ray data showed that silver nanoparticles and their ensembles isolated from each other and stabilized by a polymeric matrix were formed. Contact of Ag⁰-EI in the H⁺ form with solutions of silver salts caused the occurrence of two processes, ion exchange and metal recrystallization. These processes were interrelated because they involved one common particle, the silver counterion. Recrystallization proceeded by the electron-ion mechanism, but, because of matrix isolation of silver particles, electron transfer occurred inside separate structural elements (ensembles of particles) rather than over the whole composite volume. The transfer of silver ions largely occurred over ionogenic matrix centers, which substantially decreased their mobility. The low electronic conductivity of the composite and limited mobility of counterions were charge stabilization factors, which hindered recrystallization and, along with matrix stabilization, contributed to the retention of nanosized silver particles.     

Counterion specificity in the phase behavior of tetradecyldimethylamine oxides at different degrees of protonation

Effects of counterion species on the aggregate structure of tetradecyldimethylamine oxide (C14DMAO) accompanying the protonation were examined by viscoelastic properties and phase behavior observations. Different extents of the synergetic behavior between protonated and non-protonated amine oxides were observed depending on the counterion species, which follow the Hofmeister, or the lyotropic, series. The efficacy of monovalent anions with respect to the increasing the surfactant packing parameter was as follows: salicylate>perchlorate>nitrate>bromide>chloride, formate. Vesicle formation was found in the case of salicylate and perchlorate anions and elongation of rodlike micelles was observed for nitrate, bromide, sulfate, tartronate and tartrate anions but little effects in the case of chloride and formate anions. The observed ionic specificity is well correlated with the free energy of hydration of counterions.     

Stabilized Silver Nanoparticles and Nanoclusters Ag<Subscript>n</Subscript> in Humic-Based Bioactive Nanocomposites

Silver-containing nanocomposites synthesized from the compounds of a humic series have been studied using modern physical–chemical methods (EPR, TEM, IR and XRD, etc.). It is shown that the humic substances with different functional groups and isolated from different sources have also different ability of stabilizing the silver nanoparticles. Long-term stable nanoparticles and silver clusters have been found. A multiplet, observed in the EPR spectra of silver-containing nanocomposites, which are obtained from humic substances isolated from therapeutic muds and shales, is assigned to the formed Ag_n nanoclusters. Formation of the silver molecular clusters depends on the kind of humic substances and depth of their decomposition.     

Formation of silver bromide precipitate of nanoparticles in a single microemulsion utilizing the surfactant counterion

Silver bromide precipitate of nanoparticles was prepared by addition of silver nitrate aqueous solution to a single microemulsion system consisting of dioctyldimethylammonium bromide, n-decanol, and water in isooctane. The silver ion reacted readily with the surfactant counterion, bromide, to form the precipitate of nanoparticles, which was stabilized in the water pools. The use of the surfactant counterion as a reactant is a new approach to nanoparticle preparation in microemulsions. It is characterized by high reactivity and less dependency on the intermicellar exchange of solubilizate. The effects of the surfactant and the cosurfactant concentrations, the amount of silver nitrate, and the water to surfactant mole ratio, R, were evaluated. Increasing the surfactant concentration at fixed R and amount of silver nitrate enhanced the role of intermicellar nucleation and resulted in the formation of larger particles, while increasing the amount of silver nitrate at fixed values of all the other variables enhanced the direct nucleation and resulted in the formation of smaller particles. Particle aggregation and flocculation took place when the concentration of n-decanol or the value of R was increased. Particle aggregation and flocculation were attributed to the decrease in the interaction between the surfactant protective layer and the nanoparticles in the water pools.     

Vibrational study of the salicylate interaction with metallic ions and surfaces

Infrared and Raman spectroscopy are used in this work to study the metallic complexes of salicylic acid with silver and copper, comparing the interaction between salicylate and the cations (Ag+ and Cu2+) in the metal complexes with the SERS spectra when adsorbed on colloidal metal surfaces of the same metals. The salicylate complexes with the above metals were compared to those of Na+, Fe3+ and Al3+ cations. A different interaction mechanism is deduced for salicylate in the metal complex and when adsorbed on the metal surface.     

Role of phosphates in promotion of silver catalysts for partial oxidation: II. Formation of active sites in the structure of silver phosphate under the action of a reductive medium

The morphology and chemical composition of the surface of silver phosphate are studied. The qualitative and quantitative compositions of silver phosphate are quite the same as those of the surface of the phosphorus-promoted silver catalyst. Silver particles surrounded by silver phosphate form in the subsurface region upon treatment of the sample with hydrogen. As a result, a complex catalytic system is formed in which silver phosphate is both the precursor of the reactive component (metallic silver particles) and the stabilizing matrix for this component. The system obtained is stable toward high temperature and redox reaction media.Translated from Kinetika i Kataliz, Vol. 46, No. 1, 2005, pp. 161–166.Original Russian Text Copyright © 2005 by Knyazev, Magaev, Vodyankina, Titkov, Salanov, Koshcheev, Boronin.     

Geometrical factors in the capacity of the electrical double layer

A method for determination of double layer capacities at silver iodide-solution interfaces is presented. The influence of counterion on capacity is subjected to special study in the present work. Capacities at the silver iodide interface are compared with those at the mercury interface (Grahame) and interpreted in terms of theGouy-Stern double layer model. Some characteristic differences between capacities at mercury and silver iodide interfaces are explained in terms of different structural factors.     

Resistance of polyvinyl alcohol blends stabilized by sodium and ammonium salts of lignite humic acids against γ-irradiation

The dried blends containing sodium and ammonium salts of lignite humic acids (humates, 0.5–10% w/w) in polyvinyl alcohol (PVA) were exposed to high dosage of γ-irradiation in the range of doses 127–806 kGy. Resulted products were then tested for their stability using thermogravimetrical analysis. As a reference the non-treated blends were used since the pure PVA exposed to γ-irradiation very quickly lost its stability and resulting consistence did not allow the stability tests. Stabilities showed a strong concentration and counterion dependency. While sodium counterion caused mostly destabilization with increasing dose, the ammonium counterion acted in an opposite way. The tests carried out in a moisturizing container revealed the changes in water absorbing capacity of irradiated samples and allowed partial explanation of humate stabilizing effect. Generally, at lower concentration of a humate the increase was observed with an increase in the γ-irradiation dose and vice versa. The results confirmed the antioxidant and stabilizing effect of humic acids added to some synthetic polymers and their applicability in materials exposed to γ-irradiation.     

Synthesis of nanosized silver colloids by microwave dielectric heating

Silver nanosized crystallites have been synthesized in aqueous and polyols viz., ethylene glycol and glycerol, using a microwave technique. Dispersions of colloidal silver have been prepared by the reduction of silver nitrate both in the presence and absence of stabilizer poly(vinylpyrolidone) (PVP). It was observed that PVP is capable of complexing and stabilizing Ag nanoparticles formed through the reduction of Ag⁺ ions in water and ethylene glycol. In the case of ethylene glycol, it has been shown that the use of PVP leads to particles with a high degree of stability. The colloids are stable in glycerol for months even in the absence of stabilizer.     

Rapid Synthesis of Silver Nanoparticles by Microwave-Polyol Method with the Assistance of Latex Copolymer

Highly stable and monodispersed silver nanoparticles with uniform morphology have been successfully prepared by microwave (MW) irradiation within a few seconds from the mixture of silver nitrate, ethanol and latex copolymer. The aqueous emulsion of latex copolymer acts as both reducing and stabilizing agent. To the best of our knowledge, it was the first time that the effect of MW irradiation time and latex concentration on the silver nanoparticle preparation and properties was analyzed. The formation of silver nanoparticles was confirmed by Ultraviolet–visible spectroscopy and transmission electron microscopy (TEM). The UV–Vis spectra are marked by the characteristic surface plasmon absorption band in the range 410–420 nm. From TEM images, silver nanoparticles were observed to be spherical with sizes ranging from 4 to 10 nm. Electron diffraction patterns on selected area, indicated that the silver nanoparticles are crystalline with face centered cubic structure.     

Synthesis of highly stable silver nanoparticles by photoreduction and their size fractionation by phase transfer method

In this report we demonstrate a green chemical approach for the synthesis of stable silver nanoparticles in aqueous medium using tyrosine as an efficient photoreducing agent. A narrow size distribution of silver nanoparticles can be achieved by this simple photoirradiation method without using any additional stabilizing agents or surfactants. Two different irradiation sources have been explored resulting in a different particle size distribution pattern in each case. Further, we show that starting from a polydisperse tyrosine synthesized silver nanoparticles sample, it is also possible to fractionate them into different size ranges. The size fractionation was achieved by a 2 stage phase transfer method employing different organic solvents. The nanoparticles synthesized were characterized using UV-vis spectroscopy, Transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques.     

7]-Helicene: a chiral molecular tweezer for silver(I) salts

We have unambiguously demonstrated the binding of the silver(I) ion in the central cavity of [7]-helicene, given that the counterion is weakly coordinating. In such a binding mode, the helicene is functioning as a chiral molecular tweezer.     

Influence of adsorbing species on properties of equilibrium silver iodide clusters

Thermodynamically stable AgI clusters were studied in the presence of high- and low-molecular-weight additives: polyethyleneimine (PEI) and dimethylformamide (DMF), respectively. Clusters containing up to 20 silver iodide pairs, roughly twice as many as in the system without PEI or DMF, have been observed. We show that the mechanism stabilizing these clusters is mixed adsorption with iodide ions at the AgI-electrolyte interface. We make it plausible that more strongly adsorbing additives give rise to ultralow interfacial tensions of the AgI-electrolyte interface, with perspectives for "reversible colloids."