Hexazamacrocycle assisted sensing of silver ion through facile synthesis of silver nanoparticles

The ease of generation of silver nanoparticles by using hexazamacrocycle ligand, L1 is utilized for the visual detection of the presence of silver ions at lower concentrations.     

Kinetics of protein aggregation with formation of unreactive intermediates

Irreversible protein aggregation resulting in formation and deposition of insoluble fibrils or amorphous precipitates is usually assumed to occur via sequential attachment of monomers to soluble intermediates. We complement this scheme by slow conversion of the intermediates to a relatively stable form so that they do not react with monomers but can be trapped by precipitates. For reasonable values of parameters, our model predicts that the aggregation kinetics order may be between 2.0 and 2.5. In particular, the model can be used to explain the reaction order, 2.17 +/- 0.09, observed for aggregation of recombinant human granulocyte colony stimulating factor.     

Kinetics of the formation of silver dimers: early stages in the formation of silver nanoparticles

Silver clusters too small to support a plasmon band possess interesting fluorescence properties as well as being a convenient route to studying the early stages of nanoparticle formation. Fluorescent silver clusters are synthesized in toluene solution, and the formation is monitored herein by laser flash photolysis (LFP). Kinetic analysis of the formation of the Ag clusters is consistent with the formation of the smallest possible clusters, silver dimers (Ag(2)), whereby a mechanism for the formation of these clusters is provided as well as the first reported extinction coefficient and association constant for Ag(0) to form Ag(2). The formation of Ag(2) clusters is contrasted with the formation of Ag nanoparticles in aqueous media, and the particular stability and selectivity toward Ag(2) in this system is also studied using LFP.     

A novel silver ion assisted cleavage of a trichlorocyclopropane.

Ag⁺ assisted solvolysis of the trichlorocyclopropane (2) gives (3). Assisted cleavage of the initially formed cyclopropachroman-4-ol with subsequent oxidation is suggested as a possible mechanism.     

Mercaptothiazolinyl functionalized hexapodal and tripodal receptors on benzene platform: formation of silver ion assisted hexanuclear metallocage vs metal-organic polymer

Mercaptothiazolinyl functionalized hexapodal (L(1)) and tripodal (L(2)) receptors on the benzene platform have been synthesized easily in good yields and structurally characterized by a single-crystal X-ray crystallographic study. In the solid state, L(1) shows an orientation of six arms in 1,3,5 vs 2,4,6 facial steric gearing fashion, whereas L(2) adopted C(2v) symmetry where two of its thiazolinyl arms are oriented in one direction and the third arm in the another direction. Two silver complexes of L(1), 1 ([2(L(1))·6(AgClO(4))·2(CHCl(3))·HClO(4)]) and 2 ([2(L(1))·6(AgClO(4))]), that are suitable for single-crystal X-ray studies are isolated upon the slow diffusion of a dimethylformamide solution of AgClO(4) to the solution of L(1) in chloroform and dichloromethane, respectively. Similarly, upon the slow diffusion of an acetonitrile solution of AgClO(4) to the chloroform solution of L(2), colorless crystals of the silver complex of L(2), 3, are successfully isolated. The structural analyses of 1 and 2 show the formation of a silver ion assisted hexanuclear metallocage Ag(6)(L(1))(2) via dimeric assembly of L(1) with multiple clefts and pockets toward guests binding. In 1, two chloroform molecules sit in top and bottom pockets, whereas six perchlorate counteranions are bound in six clefts between the silver ion pillared side arms of the metallocage. Though complex 2 shows the formation of a metallocage like 1, the single crystal structural analysis depicts perchlorate counteranions bonded to the silver atoms of the metallocage. On the contrary, the silver complex of tripodal receptor L(2), 3, shows the formation of a metallo-organic polymeric network of L(2) and Ag(+). To the best of our knowledge, this work represents the first report on the formation of an M(6)L(2) type metallosupramolecular cage topology with multiple clefts for guest binding by a semirigid hexapodal receptor.     

Triplet state formation of aromatic hydrocarbons quenched with silver ion in ethanol

Fluorescence quenching rate constants of aromatic hydrocarbons by silver ions are determined. The values obtained are not well interpreted with thermodynamical considerations based on an electron transfer mechanism, but related to the intersystem crossing rate constant of the fluorescer. Triplet state formation in the course of quenching has been confirmed by laser photolysis studies.     

Kinetics of complex formation of 2‐methoxyphenol with ferric ion and hexacyanoferric ion

Complexes containing one molecule of organic ligand have been formed in the reaction of 2 methoxyphenol with ferric ion or hexacyanoferric ion. Kinetic investigations showed that the reaction order with respect to ferric ion or hexacyanoferric ion is close to one. The reaction order with respect to 2‐methoxyphenol is 0.8 in the reaction with ferric ion and close to 0 in the reaction with hexacyanoferric ion. The reaction mechanism, based on kinetic investigations, involves the decomposition of the initial complex, formed with the pentacoordinated complex and water or cyanide ion. In a second stage of the reaction, the pentacoordinated complex adds 2‐methoxyphenol; and one molecule of initial ligand, water, or cyanide ion, comes off. Some ratios of rate constants of elementary reactions have been calculated. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 184–191, 2000     

Kinetics of radiation-induced formation and thermal annealing of the nitrite ion in potassium picrate

The formation kinetics of the nitrite ion in solid potassium picrate in a γ-radiation field was studied. It was found that nitrite ions accumulate by a complex law having some features of an oscillating process. The thermal stability of NO ₂ ^- was examined, a part of nitrite ions decay following a complex law upon annealing. This phenomenon is rationalized in terms of the scheme suggesting that radiation-induced NO ₂ ^- is formed in two states, the metastable NO ₂ ^- species and the KNO₂ phase.     

Characterization of reaction intermediates by ion spectroscopy

In the last decade, we have experienced massive progress in spectroscopic methods for mass-selected ions. The aim of this tutorial review is to present action spectroscopy as a powerful tool for the investigation of ionic reaction intermediates. Examples span from ultraviolet and infrared photodissociation spectroscopy of model reaction intermediates to applications of infrared multiphoton dissociation spectroscopy (IRMPD) to intermediates directly sampled from reaction mixtures. The first example of double resonance IR-UV spectroscopy of model intermediates in an organometallic reaction is also mentioned.     

Kinetics of silver anodic dissolution in thiosulfate electrolytes

The regularities of silver anodic dissolution are studied by using the voltammetry (at the potential scan rates from 5 to 1000 mV/s) on the electrode, which was renewed immediately in the solution by cutting-off a thin surface metal layer, and quartz microgravimetry, for various concentrations of sodium thiosulfate (0.05–0.2 M). It is shown that, in the potential range from 0 to 0.4 V (normal hydrogen electrode), the polarization curves reflect the silver dissolution, whereas the contribution of oxidation of S₂O₃²⁻ ions is insignificant. At low potential scan rates, the process kinetics is of mixed nature. The kinetics and mechanism of anodic process are studied by using the measurements at high potential scan rates (100–200 mV/s) and the calculations of equilibrium composition of near-electrode layer. It is found that the exchange current in the electrolytes studied is 5 × 10⁻⁵ A/cm², the transfer coefficient α is approximately 0.5, and both parameters are virtually independent of the concentration of S₂O₃²⁻ ions. The reaction order of silver dissolution with respect to the ligand $ \left. {\frac{{\partial logi}} {{\partial logc}}} \right|_E $ \left. {\frac{{\partial logi}} {{\partial logc}}} \right|_E is close to unity and is independent of potential. With regard for the literature data on the adsorption of thiosulfate ions on silver, this result is interpreted as the evidence for the involvement of one S₂O₃²⁻ ion from bulk solution, along with adsorbed ligands, in the elementary act of metal dissolution.     

Flame atomic absorption spectrometry of silver and gold in copper intermediates

The effect of hydrochloric acid and salts from the sample on the solubility of methyl isobutyl ketone (MIBK) in aqueous phase and the effect of hydrochloric acid concentration on the MIBK extraction of iron(III) and gold(III) were studied. As a result, an improved method by flame atomic absorption sepctrometry for determination of silver and gold in copper intermediates was developed, employing a more efficient removal of iron and special standards depending upon the concentration of salts introduced by different samples.     

Complex formation of silver(I) with glycinate ion in aqueous ethanol and dimethyl sulfoxide solutions

The complex formation reaction of silver(I) with glycinate ion in aqueous ethanol and dimethyl sulfoxide solutions of variable compositions was studied by potentiometric titration at 298 K. The stabilities of Ag(I) glycinate complexes were found to increase with the increasing content of the organic cosolvent. The contribution of ΔG° of the reagent resolvation to the change in the Gibbs energy of the complex formation reaction was estimated using the literature data. The change in the ligand solvate state was shown to give the main contribution to the stability of the title complexes in water-organic solvents.     

Kinetics and mechanism of formation of penta-ammineglycinecobalt(III) ion from aquopenta-amminecobalt(III) ion and glycine in acid media

The rates of formation of penta-ammineglycinecobalt(III) ion from aquopenta-amminecobalt(III) ion and glycine in acidic media have been studied spectrophotometrically at different glycine concentration and different pH in the range of 50–70°C. The ΔH≠ and ΔSz≠ values are 27.6 kcal mole^?1 and +5.2 e. u. respectively, and increase in ionic strength causes only a slight acceleration of the rate. The results are consistent with a mechanism involving outer-sphere association between the aquopenta-amminecobalt(III) complex and glycine, followed by its transformation into the product by an essentially dissociative process in which rupture of the Co(III)? OH₂ bond is primarily important in the transition state (S_N1IP mechanism).     

Kinetics of oxygen adsorption on silver films

Kinetics of oxygen adsorption on silver films prepared by metal vacuum evaporation and condensation technique has been studied. The adsorption proceeds in accordance with the kinetic law of Zeldovich-Roginskii. Oxygen dissolution in the silver subsurface layers result in a decrease of the initial adsorption rate and an enhanced exponential decrease of the adsorption rate as a function of surface coverage.     

Kinetics of styrylquinolinc formation

A comprehensive kinetic investigation of reactions occurring in the formation of styryl-quinolines has been conducted. Specific rate data such as rate equations, rate constants, and thermodynamic activation values have been determined and utilized in a study of which factors are of greatest importance in the reactions forming 2-styrylquinolines. A mechanism has been proposed for the condensation reaction which agrees with rate relationships found. Gas-liquid partition chromatography was used to follow the kinetics of the condensation reactions. A rate constant of 5.41 × 10^?2M^?1min^?1 was found for the reaction of benzaldehyde with 2-methyl-quinoline using zinc chloride as a catalyst at 104.0°. Rate constants of 1.28 × 10^?2 MT^?1 min^?1 and 1.05 × 10^?2 M^?1 min^?1 were found for the reactions of p-methylbenzaldehyde and p-methoxybenzaldehyde with quinaldine to form 2-(p-methylstyryl)quinoline and 2-(p-methoxystyryl)-quinoline, respectively at 92.4°. A linear relationship was found using the Hammett equation. An Arrhenius plot was constructed from rate constants determined at five different temperatures for the reaction of benzaldehyde and quinaldine to form 2-styrylquinoline, using zinc chloride as a catalyst. The energy of activation, E_a, was found to be 22.2 kcal/mole for this reaction. The enthalpy of activation, ΔH?, free energy of activation, ΔF?, and entropy of activation, ΔS?, were found to be 21.4 kcal/mole, 27.7 kcal/mole and -16.7 eu/mole, respectively, at 104.0°. The mechanism proposed in the formation of 2-styrylquinoline involves the fast formation of a carbanion-zinc chloride complex, which then attacks, in the rate determining step, the aldehyde utilized in the reaction. The lack of reaction of certain methylquinolines is attributed to the inadequacy of the carbanion formed and not to the difficulty involved in the initial formation of the carbanion.