Sensitive determination of nitrite by means of a Landolt-type reaction in fluorescent aggregates of a binaphthyl-based amphiphile

The iodine quenching effect on the fluorescence of a binaphthyl-based amphiphile, C₈BNC₆N, was used for monitoring the Landolt-type reaction between nitrite, iodide, and thiosulfate. Due to the possibility of iodine detection in the 10^–8–10^–7 M range, and to the effective concentration of anionic reagents on the surface of cationic aggregates, the indicator reaction can be monitored using reagents at concentration levels as low as 10^–7 M. To optimize the analytical system, the effect of pH and reagent concentrations on the rate of indicator reaction were studied. The influence of the matrix of water samples and effect of side-reactions increasing the value of a blank test were examined. A procedure for nitrite determination in water was developed, using the diazo reaction for selective nitrite removal to provide a reference solution, which avoided possible effects of the matrix components. The usefulness of this method was tested by determining trace amounts of nitrite in water samples. The procedure allows determination of nitrite down to 5 ng/ml (detection limit about 2ng/ml) with r.s.d. of 10% in the 20–250 ng/ml range.     

The acidity functionsH 0 s of HCl solutions in EtOH with low water content

The acidity functionsH ₀ ^s of HCl solutions in EtOH-H₂O solvents containing 1.09, 3.0, and 5.0% water have been measured at 25 and 40 °C by the indicator method. The concentration of HCl changes from 10^–2 to 36m. Nitroanilines, for which a protonation mechanism is realized in the studied systems, were used as indicators.For each solvent,H ₀ ^s is temperature independent atm _HCl < 4, and acidity atm _HCl > 4 mol L^–1 increases more rapidly at 25 °C than at 40 °C. The acidity functions of aqueous and water-ethanol solutions of HCl were compared, and the concentrations of proton solvates of different compositions and their relative protonating ability were evaluated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1722–1725, October, 1994.This work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-18356).     

The acidity scale of HCl solutions in N,N-dimethylformamide

The scale of the thermodynamic acidity of HCl solutions in DMF has been measured at 25 and 39.5 °C up to 15 mol L^–1 acid concentration by the indicator method. It is shown that in the HCl-DMF system the ionization of the nitroaniline-derived indicators occurs by the ion pair mechanism. Within the temperature range studied acidity is independent of temperature. Indicators of the nitroaniline series are used.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1025–1028, June, 1994.     

Micellar Solubilization of Biopolymers in Hydrocarbon Solvents III. Empirical Definition of an Acidity Scale in Reverse Micelles

This paper deals with the problem of defining, and measuring, the pH inside the water pool (which we define as pH_wp) of reverse micelles, i.e. micelles formed by surfactants dissolved in apolar solvents in the presence of minimal amounts of water. The conceptual and experimental difficulties are discussed, and it is argued that no absolute determination of pH_wp is possible, mostly because water in the water pools of reverse micelles is a new solvent, for which no standardization of acidity is available. The problem can be approached only on the basis of an empirical acidity scale. An empirical acidity scale for water pools in reverse micelles of bis (2-ethyl-hexyl) sodium sulfosuccinate (AOT) in isooctane has been defined by measuring the ³¹P-chemical shifts of phosphate buffers. The chemical shifts in bulk water were compared to those found in reverse micelles under the assumption that the pK of phosphate ion is the same in the two systems. It was found that in most cases there was little difference (less than 0.4 pH units) between pH_wp and the pH of the starting buffer in bulk water (which we define as pH_st). However, this difference between pH_wp and pH_st may become much larger in certain cases. The difference (pH_wp–pH_st) is measured under a variety of conditions, and this permits the determination of an operational acidity in the micelle water pools as a function of the pH_st with which the aqueous micelles are prepared. The significance of such data for interpreting the behaviour of enzymes confined in the micelles water pool is discussed. Based on the pH_wp scale, the apparent pK_a of phenol-red and 4-nitrophenol were determined in reverse micelles containing different buffers and different water content. The pK_a values obtained were rather sensitive to changes of both these factors, which was taken to signify that organic dies have only a very limited applicability to measure the acidity of the water pools of reverse micelles.     

Hydrolysis of bis(chloromethyl)phosphonic acid p-nitroanilide in aqueous micellar surfactant solutions

The hydrolysis of bis(chloromethyl)phosphonic acid p-nitroanilide has been studied in the pH range 6.86–13.0 and the effects of ionic surfactant micelles on this process have also been examined. The nature of the micellar effects of cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS) on this reaction lead us to conclude that both the neutral and anionic forms of the substrate are reactive, and that in the range of pH > pK_a hydrolysis of the ionic form of the anilide predominates, while at pH < pK_a the reaction of the neutral form is predominant. The binding constants for both the neutral and anionic forms of bis(chloromethyl)phosphonic acid p-nitroanilide in micellar CTAB and SDS solutions have been determined using a kinetic method, as well as by measuring the changes in the acid-base properties of the substrate resulting from the influence of micelles.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1718–1722, August, 1990.     

Condensation of <Emphasis Type="Italic">p</Emphasis>-Dimethylaminocinnamaldehyde with Aniline and Substituted Anilines in Micellar Media

Optimal conditions were found for the reactions of aniline and its hydroxy-, carboxy-, methyl-, and nitro-substituted derivatives with p-dimethylaminocinnamaldehyde in the presence of sodium dodecyl sulfate micelles in the pH range 1–6. A correlation was revealed between the optimal pH value pK _a of aromatic amines. The reaction in the model system aniline-p-dimethylaminocinnamaldehyde-sodium dodecyl sulfate in micelles formed by anionic surfactants is accelerated more than 1000-fold due to increased concentration of the reactive species in sodium dodecyl sulfate micelles.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 2, 2005, pp. 288–294.Original Russian Text Copyright © 2005 by Doronin, Chernova, Gusakova.     

Anodic Dissolution of Gold in Cyanide Solutions Containing Lead Ions: Effect of the Solution pH

The effect of the electrode potential on the gold dissolution rate in alkali–cyanide solutions with and without 10^–5 M of hydroxy compounds of lead is studied. With the compounds, the process rate passes through a maximum, whose potential E _m shifts in the negative direction and whose height drops with increasing pH. The pH dependence of E _m is linear, with the slope dE _m/dpH = –71 ± 5 mV, and correlates with that of the potential at which lead adatoms start to undergo desorption from the gold surface in alkali solutions. Without the compounds, the gold dissolution rate in alkali–cyanide solutions is independent of the solution pH at E < 0. Thus, the effect of the solution pH in this potential range is connected not with a direct participation of hydroxide ions in the anodic process but is of a secondary nature caused by the dependence of the region of adsorption of catalytically active lead adatoms on the hydroxide ion content in solution.     

Removal, preconcentration and determination of Mo(VI) from water and wastewater samples using maghemite nanoparticles

Removal and recovery of Mo(VI) from aqueous solutions were investigated using maghemite (γ-Fe₂O₃) nanoparticles. Combination of nanoparticle adsorption and magnetic separation was used to the removal and recovery of Mo(VI) from water and wastewater solutions. The nanoscale maghemite with mean diameter of 50 nm was synthesized by reduction coprecipitation method followed by aeration oxidation. Various factors influencing the adsorption of Mo(VI), e.g. pH, temperature, initial concentration, and coexisting common ions were studied. Adsorption reached equilibrium within <10 min and was independent of initial concentration of Mo(VI). Studies were performed at different pH values to find out the pH at which maximum adsorption occurred. The maximum adsorption occurred at pHs between 4.0 and 6.0. The Langmuir adsorption capacity (q_max) was found to be 33.4 mg Mo(VI)/g of the adsorbent. The results showed that nanoparticle (γ-Fe₂O₃) is suitable for the removal of Mo(VI), as molybdate, from water and wastewater samples. The adsorbed Mo(VI) was then desorbed and determined spectrophotometrically using bromopyrogallol red as a complexation reagent. This allows the determination of Mo(VI) in the range 1.0–86.0 ng mL⁻¹.     

Separation of fluoride ion by extraction with triphenyltin chloride. Application for NAA of fluorine by means of 14-MeV neutrons

The separation of fluoride by extraction with toluene solution of triphenyltin chloride has been studied. Quantitative isolation of fluoride from solutions with a wide acidity range (pH 4.0–11.5) has been established. It is suggested that interferences by Ca, Mg, Fe, and Al can be avoided by masking these elements using sulfate and hydroxyde ions. Interference by phosphate ions can be overcome in a similar fashion. The halogenated species can be masked by mercury nitrate. Detection limit for fluorine determination is about 3 g for a neutron generator flux of 2·11¹¹ n·cm^–1·s^–1. A method for fluorine assay in water using a neutron generator with a detection limit of 1 ppm has been developed.     

Surface charge modulation of poly(ethylene glycol)–poly( , -lactide) block copolymer micelles: conjugation of charged peptides

Block copolymer micelles with aldehyde functionality were prepared in aqueous medium by dialyzing the N,N-dimethylacetamide solution of α-acetoxy-poly(ethylene glycol)-poly( , -lactide) block copolymer (acetal-PEG–PDLLA) against water, followed by mild acid treatment to convert the acetal moiety of the micelle to the aldehyde group. Peptidyl ligands (phenylalanine (Phe) and tyrosyl–glutamic acid (Tyr–Glu)) were then chemically conjugated to the micelle through Schiff base formation and successive reductive amination using NaBH₃CN. Micelles with peptidyl ligands thus prepared have a size of approximately 40 nm with extremely narrow distribution (μ₂/ ²<0.1) based on cumulant analysis of dynamic light scattering. A maximum 53% of the PEG-chain end of the micelle could be converted into peptidyl groups. Zeta potential values of Tyr–Glu derivatized micelles were well correlated with the amount of conjugated ligands, controllable over the range of 0 to−9 mV in sodium phosphate buffer (pH 7.4, 10 mM). These micelles with peptidyl ligands may have a utility for exploring the effect of the surface charge on the pharmacokinetic behavior of particulate systems as well as for modulated drug delivery where cellular peptidyl receptors play a substantial role.     

Ionic Equilibria of Chromophoric Reagents in Microemulsions

Protolytic equilibria of twenty chromophoric acid–base indicators from different classes, namely, sulfophthaleins, hydroxyxanthenes, azo compounds, and others, were studied in direct microemulsions of benzene–pentanol-1–surfactant–water at volume fractions of the dispersed phase of up to 13%. Cetylpyridinium chloride, sodium dodecylsulfate, and certain nonionic surfactants were used. Apparent acidity constants (pK _a) of indicators were determined under the conditions of their complete binding by microdroplets (pK _a ^ac). The strong differentiating effect of the dispersed phase of microemulsions of different types on the acid–base properties of indicators was revealed. The effect of the ionic strength of the continuous phase (0.025–1.0) on the values of pK _a ^ac was studied. The partition constants of Bromothymol Blue anions between water and negatively charged microdroplets were estimated. Similarities and differences were revealed in the action of microemulsions and micellar solutions of the corresponding surfactants on the state of the studied chromophoric reagents.     

Coated,Wire-Based,New Schiff Base Potentiometric Sensor for Lead(II) Ion

An ion-selective electrode for lead(II) based on a dispersion of N,N"-bis(3-methyl salicylidine)-p-phenyl methane diamine particles into a polymeric membrane using coated-wire configuration is described. Membranes based on polyvinyl chloride containing different amounts of plasticizer and ionophore are studied. The best performance in terms of slope (30.3 ± 0.6 mV per decade) and response time (<15 s) is displayed. The sensor shows a Nernstian response for Pb(II) ions over a wide concentration range of 2.0 × 10^–5 to 0.10 M. The sensors can be used for more than three months without any considerable divergence in potentials. The selectivity is also good towards the most common univalent and divalent cations and the signal is constant in the pH range 1.6–6.0. An application to lead determination in mineral rocks and wastewater proved to be a success, and it was employed as an indicator electrode in potentiometric titration of CrO^2– ₄ with lead ions.     

Molarity and ionic strength of focused carrier ampholytes in isoelectric focusing

Focused 1% carrier ampholytes in the pH range 3.5–10 have a molarity of 9–1 0 mM, as determined by osmolarity measurements of fractions focused in free water. From electrophoretic and isoelectric focusing data of red blood cells, it has been demonstrated that the corresponding ionic strength is 0.5 mg-ions/1. Also theoretical considerations and conductivity measurements point to a value in the range of 0.5–1.0 mg-ions/1. The following equations for ionic strength (I) calculations have been derived:I = _amph + C_Hin the pH range 2.5–7 andI = _amph + C_OHin the pH range 7–11.     

Investigations of Cobalt, Nickel, and Copper Diethyldithiocarbamates Using Thermal Lens Spectrometry

Thermal lens spectrometry was used to study the dissociation kinetics of diethyldithiocarbamate complexes of copper(II), cobalt(III), and nickel(II) as a function of pH in the presence of chloride and sulfate ions. It is shown that, as distinct from conventional spectrophotometric and potentiometric measurements, the reversible dissociation of the test complexes and the irreversible oxidation of the ligand can be studied separately (at a level of n × 10^–8–n × 10^–6 M) using thermal lens spectrometry. Because of work in more dilute solutions and due account of the kinetic features of the systems in question, thermal lens spectrometry provides a higher accuracy of the determination of stability constants for diethyldithiocarbamate complexes of copper(II), cobalt(III), and nickel(II). The adsorption of the diethyldithiocarbamate complexes in question from water–ethanol solutions (1 : 3) on Silasorb C₁₈ silica is studied, and the adsorption constants are determined. The limits of detection of copper(II), cobalt(III), and nickel(II) diethyldithiocarbamates obtained in extraction–thermal-lens determination are n × 10^–8 M.     

Dielectric Properties and Structure of Aqueous Decaoxyethylene p-Isononylphenyl Ether Solutions

The static permittivity _s of aqueous decaoxyethylene p-isononylphenyl ether (NOP-10 grade) solutions is measured at surfactant concentrations of 1.14 and 4.97 wt % within 275–351 K temperature range; at concentrations of 9.96, 20, and 30 wt %, within 275–313 K range. Data on _s are analyzed, using the models of dilute disperse systems of oil–water type containing spherical particles, oblate and prolate spheroids. At 30, 20, and 9.96 wt % NOP-10 content, fragments of hexagonal mesophase are still retained in the isotropic phase near the interface, where there is a certain orientation of micelles acquiring the shape of prolate spheroids instead of cylindrical micelles. Upon heating up to 313 K, micelles are disoriented and their shape changes in prolate spheroid spherical micelle oblate spheroid sequence. With a further rise in water content, the fragments of lamellar mesophase appear in the isotropic phase at 4.97 and 1.14 wt % NOP-10 near the melting points of these solutions. They can exist with equal probability as the regions where either spherical micelles are located in the nodes of cubic lattice or oblate spheroidal micelles are distributed at random. As the temperature approaches the cloud point of dilute solutions, the randomly oriented oblate spheriodal micelles tend to acquire the disc-like shape.     

Micellar effects of cation-active surfactants on the reaction of (o-aminomethyl)phenols with ethylp-nitrophenyl chloromethylphosphonate

The reaction of (o-aminomethyl)phenols with ethylp-nitrophenyl chloromethylphosphonate in aqueous micellar solutions of cation-active surfactants has been studied. The effect of the structure of the surfactant and the nucleophile, pH of the medium, and temperature on the reaction rate in the micellar phase has been investigated. The rate constants in micelles are much higher than those in water.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2065–2068, December, 1993.     

Self aggregation of binary mixtures of sodium dodecyl sulfate and polyoxyethylene alkyl ethers in aqueous solution

The mixed micelles of sodium dodecyl sulphate (SDS) with Brij35 and Brij 97 were studied separately by fluorescence measurement using pyrene as fluorescent probe. In the range of 0–1.0 mole fraction (X) of added SDS to Brij solutions, the cmc value of the mixed micelles varies from 0.085 to 8 mmol with Brij 35 and 0.04 to 8 mmol with Brij 97. The aggregation number also changes. A measure of the stability of mixed micelles is also presented. The interaction parameter ₁₂ and the chain–chain contribution parameter (B₁) are extracted from the analysis of the results. This parameter B₁ is related to the standard free energy change associated with the introduction of one ionic species into a nonionic micelle coupled with the release of one nonionic species from the micelle. The clouding behaviour of Brij 97 in the presence of SDS was investigated and the associated thermodynamic parameters of clouding were generated and discussed.     

Effects of Nonionic, Cationic, and Mixed Nonionic-Cationic Surfactants on the Acid-Base Behavior of Phenyl Salicylate

The effects of Brij 35 micelles, CTABr micelles, and mixed Brij 35–CTABr micelles on the acid–base behavior of phenyl salicylate (PST) have been studied in aqueous solution containing 2% v/v acetonitrile. The apparent pK_b (pK^app_b) of PST is decreased by 1.5 pK units with the increase in [Brij 35] from 0 to 0.02 M which is attributed to micellar medium effect. The values of pK^app_b remain almost independent of [CTABr] within its range 0.01–0.03 M. The increase in [CTABr] from 0 to 0.03 M in aqueous solution containing 0.02 M Brij 35 has not resulted in a change in pK^app_b. This shows that the characeristic structural features of nonionic Brij 35 micelles remain essentially unchanged on addition of CTABr under the present experimental conditions.     

Ionizing properties of complexes with strong symmetrical hydrogen bonds in acid solutions in aprotic solvents

The acidity functions H₀ of solutions of trifluoroacetic acid (TFA) in DMF and methanesulfonic acid (MSA) in 2-pyrrolidone over an acid (HA) concentration range of 0–100% and of H₂SO₄ solutions in 2-pyrrolidone (66.7–100 mol % HA) at 25°C were determined using the indicator method. Data were obtained on the relative ionizing powers of the quasi-ion pairs S· · · H· · ·A (S is a solvent molecule) formed by DMF with acids (HCl, MSA, and TFA) and by MSA with DMF and 2-pyrrolidone. The effects of the acid anion (with MSA and H₂SO₄ solutions in 2-pyrrolidone acting as examples) and the counterion SH⁺ (with MSA solutions in DMF and 2-pyrrolidone acting as examples) on the ionizing power of (Ä · · ·H· · ·A)^– ions with strong symmetrical H-bonds were studied. It was found that, under comparable conditions, the replacement of a 2-pyrrolidone molecule by a DMF molecule in the SH⁺ cation insignificantly decreased the acidity of solution, whereas the (Ä· · ·H· · ·A)^– ions in H₂SO₄ solutions exhibited a much higher ionizing power than that of structurally similar anions in MSA solutions.Translated from Kinetika i Kataliz, Vol. 46, No. 1, 2005, pp. 44–49.Original Russian Text Copyright © 2005 by Kislina, Sysoeva, Librovich.     

Solubilization of Perfluorodecalin in Aqueous Solutions of Dodecaethoxylated Nonylphenol

The solubilization of perfluorodecalin in aqueous solutions of dodecaethoxylated nonylphenol (Neonol AF_9–12) was studied by spectrometry, dynamic light scattering, and precision tensiometry. The aggregation numbers of Neonol AF_9–12 micelles, as well as the composition of micelles containing perfluorodecalin were determined. Within the framework of the pseudophase model, the partial coefficient of solubilizate distribution between micellar and aqueous phases and the standard Gibbs free energy of solubilization were calculated for the systems studied. It was shown that mixing of perfluorodecalin with Neonol AF_9–12 hydrocarbon radicals in micelle core is non-ideal.