Spectrophotometric study of acidity constants of Alizarine Red S in various water-organic solvent

The acidity constants of Alizarine Red S were determined spectrophotometrically at 25 degrees C and at constant ionic strength 0.1 M (KNO3) in pure water as well as in aqueous media containing variable mole percentages (5-70%) of organic solvents. The organic solvents used were methanol, ethanol, N,N-dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), acetonitrile and dioxan. The acidity constants of all related equilibria are estimated using the whole spectral fitting of the collected data to an established factor analysis model. DATAN program was applied for determining of acidity constants and pure spectra of different form of Alizarine Red S. The obtained results indicated that acidity constants decrease as the content of an organic solvent in the medium increases. There are linear relationship between acidity constants and the mole fraction of various organic solvents in the solvent mixtures. Effect of various solvents on acidity constants and pure spectrum of each component are also discussed.     

渐进因子分析－pH－分光法测定多元酸的离解常数

根据多元酸平衡体系中型体具有先出现先消失的特点,提出了用渐进因子分析与化学平衡结合迭代,从pH-分光矩阵中求解多元酸离解常数的新方法。用该法测定了多元酸茜素S和铬天青S的离解常数,并讨论了确定型体存在区域的经验式。结果表明该方法稳定、可靠、算法收敛快,所测得的离解常数与文献值吻合。     

Optical pH Sensor Based On Chemical Modification of Polymer Film

A new low-cost pH sensor developed by immobilizing a direct indicator dye to porous and transparent acetylcellulose film. This sensor was fabricated by binding α-Naphthyl Red and Alizarine Yellow GG to a cellulose acetate film that had previously been subjected to an exhaustive base hydrolysis. The membranes have good durability (>12 months) and a short response time (<5 s). The method is easy to perform and uses acetylcellulose as a carrier. The reagents used for the activity of the cellulose support are inexpensive, nontoxic, and widely available. The Alizarine Yellow GG sensor can be used for direct determination of pH in alkaline media without any alkaline error.     

Spectrophotometric study of the effects of surfactants and ethanol on the acidity constants of fluorescein

In the present paper, a sensitive, fast and suitable method for the calculation of pK(a) values of fluorescein is proposed. The effects of sodium dodecyl sulfate (SDS) and Triton X-100 (TX-100) as a surface-active agent on the acidic and basic forms, and the spectral properties of fluorescein were studied by the spectrophotometric method. The study was performed in sub-micelle surfactant concentration, and absorption spectra at 300-550 nm intervals were recorded. Stepwise acidity constants of fluorescein at pH range 1.50-10.00 and at constant ionic strength 0.1M and 25 degrees C were determined using DATAN program using pH-spectrophotometric titration data. The method is efficient, however the component spectra showed intensive overlapping. The calculated acidity constants of fluorescein in water at ionic strength 0.1 are pK(a1)=2.20, pK(a2)=4.30 and pK(a3)=6.43. The acidity constants of the dye in ethanol-water solution were studied by the same procedure. Effect of surfactants and ethanol on acidity constants and pure spectrum of each component are also discussed.     

Chemical Interaction between Nonionic Surfactants and an Acid Dye

Complexation of the dye Direct Red 1 with a series of laurylamine surfactants with varying number of ethylene oxide units has been studied by voltammetry. From the measurement of the cathodic current of both dye and surfactant, the stability constants of the established equilibrium between the dye D, the surfactant S, and the dye-surfactant complex D-S can be calculated. The values of the stability constant K at 25 degrees C calculated for a defined dye-surfactant stoichiometry depend on the number of ethylene oxide units incorporated by the surfactant. These constants decrease by one order of magnitude at 60 degrees C maintaining the dependence on the number of ethylene oxide units. Copyright 2001 Academic Press.     

Removal of Disperse Dyes from Water Using Surfactant Treated Alumina

An alumina surface was modified by adsorption of an anionic surfactant, sodium dodecyl sulfate (SDS). Typical S‐shaped isotherm of surfactant on alumina was observed. The adsorption of Disperse Red‐11, Disperse Blue‐26 and Disperse Red‐156 on alumina and surfactant treated alumina has been investigated. The enhancement in adsorption of these disperse dyes on surfactant treated alumina is observed, which may be attributed to their solubilization in surfactant aggregates formed at the solid/liquid interface. The effect of pH on adsorption has been studied. The adsorption is greatly influenced by pH of the medium. The applicability of the Langmuir model and the Dual‐Mode sorption model (DSM) were tested for equilibrium data.     

Determination of dibenzo [b,f]-1,4-oxazepine by extraction spectrophotometry

The spectrophotometric determination of the substance dibenzo [b,f]-1,4-oxazepine (CR) the form of an ionic associate with the anionactive dyes of the type of azo dyes, sulphonephthaleins and anthraquinones after extraction with chloroform was worked out. Conditional extraction constants K'(ex) were calculated and equilibrium ratios D and extraction yields E of ionic associates were determined. On the basis of detection limit L(Q), the dyes Alizarine Black S (0.7 microg/ml) and Orange II (0.8 microg/ml) were recommended for extractive spectrophotometric determination of the substance CR.     

Spectrophotometric determination of acidity constants of 4-(2-pyridylazo)resorcinol in binary methanol-water mixtures

The acidity constants of 4-(2-pyridylazo)resorcinol (PAR, Scheme 1) in binary mixtures of methanol-water at 25 °C and an ionic strength of 0.1 M have been determined spectrophotometrically. DATa ANalysis (DATAN) program applied for determination of acidity constants. As percent of methanol increases in solvent mixtures the pK_a constants also increased. There is linear relationship between acidity constants and the mole fraction of methanol in the solvent mixtures. Effect of solvent composition on acidity constants and pure spectrum of each component are also discussed.     

Enzyme-like kinetics of ferryloxy myoglobin formation in films on electrodes in microemulsions

Covalently linked films of the ferric heme protein myoglobin and poly-L-lysine on pyrolytic graphite electrodes reacted with tert-butylhydroperoxide (tBuOOH) to form ferryloxy protein species according to Michaelis-Menten enzyme kinetics. Rotating disk voltammetry data obtained in microemulsions, micellar solution, and buffers revealed a strong influence of water phase acidity on kinetic parameters. Microemulsion and surfactant type had a much smaller influence on reaction kinetics, possibly because the reaction takes place entirely in a water environment surrounding Mb in the films in all fluids. A large apparent Michaelis kcat in microemulsions with neutral water phases was offset by much weaker binding as shown by larger protein-substrate dissociation constants (Km). Acidic SDS microemulsions and pH 2 buffer provided the most efficient reaction conditions as judged by the ratio kcat/Km. Apparent kinetic constants are most likely governed by acidity-controlled protein conformations and their binding with tBuOOH in the intermediate protein-substrate complex.     

Spectrophotometric determination of acidity constants of 4-(2′-thiazolylazo)-resorcinol (TAR) in water-organic mixtures

<正>The acidity constants of TAR in different water-organic solvent binary mixtures at 25℃have been determined spectrophotometrically. DATa ANalysis(DATAN) program was used for calculations of the acidity constants and pure spectra of all formed species and their concentration distribution diagram in applied pH interval.Results show that there are a fairly inverse relationship between acidity constants and the mole fraction of the organic solvent in the binary mixtures.Effects of solvent composition on the pK_as and pure spectrum of each component are also discussed.     

Pseudo-homogeneous micelle extraction of ion-associates formed between tetrabutylammonium ion and some aromatic sulfonate ions into nonionic surfactant micelle studied through the mobility measurements in capillary zone electrophoresis

Ion-association extraction of some aromatic sulfonate ions including alkylbenzene sulfonates with tetrabutylammonium ion (TBA+) into nonionic surfactant micelle has been investigated through the changes in the electrophoretic mobility. Nonionic surfactants of Brij 35 and Brij 58 were used as micelle substrates to which the ion-associates formed could distribute. The electrophoretic mobility of the aromatic sulfonate ions was measured by capillary zone electrophoresis in the presence of TBA+ and/or the nonionic surfactant to determine ion-association constants (K(ass)), binding constants of the anions to the nonionic surfactant micelle (K(B)), and binding constants of the ion-associates to the nonionic surfactant micelle (K(B,IA)). Nonlinear phenomena induced with the alkyl chain moiety were observed on K(ass) and K(B) by its linear structure and the mixed micelle formation, respectively. Larger K(B) values were obtained with Brij 58 as micelle matrix than with Brij 35, while the differences in K(B,IA) were small between Brij 58 and Brij 35.     

Insoluble mixed monolayers : II. Protolytic equilibria and the influence of the pH on the collapse pressure

A general thermodynamic treatment is given for the protolytic equilibria in an insoluble monolayer, containing surfactant molecules with n ionizable protons and able to accept m more protons, and being spread at the liquid/gas interface. The correlation between the pH of the subphase liquid and the collapse pressure of the monolayer is discussed. By using the approximation of perfect solutions and of binary surface systems (protonated and deprotonated molecular species of the surfactant) several methods are proposed for deriving apparent surface acidity constants from experimental collapse pressure vs pH curves, in the case of both miscible in monolayer miscible in collapsed bulk phase and miscible in monolayer immiscible in collapsed bulk phase, type systems. Some of these methods are based on a complete perfect solution approximation (CA) taking into account the molar fraction of the subphase liquid in the monolayer and the others use “surfactant” approximation (SA), neglecting this molar fraction. The methods proposed are tested on monolayers of carotenoid pigments spread at aqueous solution/air interfaces. Results obtained by the different methods are rather close to each other, but the approximation CA is better than SA. The apparent surface acidity constants of different carotenoids are compared with each other and discussed in terms of molecular structure and electronic effects.     

The effect of surfactants on the dissociation constants of phenothiazine derivatives Alkalimetric determination of diethazine and chlorpromazine

The effect of a cationic, an anionic and a non-ionic surfactant on the acid-base equilibria of the phenothiazine derivatives, diethazine hydrochloride and chlorpromazine hydrochloride, has been studied. It has been found that the presence of cationic and non-ionic surfactants strongly enhances the dissociation of the two derivatives, whereas the anionic surfactant decreases the dissociation constant. These effects are in agreement with a theory based on a pseudophase, ion-exchange model of micelles. From the dissociation-constant values as a function of the surfactant concentration, the binding constants for diethazine and chlorpromazine with the surfactants Septonex and sodium dodecylsulphate have been calculated. The ability of cationic surfactants to solubilize the free bases of the phenothiazine derivatives and to increase their dissociation constants has been utilized to develop a new method for alkalimetric determination of the derivatives in a micellar medium. The method has been applied to determination of the content of the active component in pharmaceutical preparations.     

Change in the acid hydrolysis mechanism of esters enforced by strongly acid microemulsions

A kinetic study was carried out on the acid hydrolysis of 4-nitrophenylacetate and 4-nitrophenyllaurate in water/HOT/isooctane microemulsions. The substitution of Na+ in the sodium salt of bis(2-ethylhexyl)sulfosuccinate by H+ has permitted us to obtain a functionalized surfactant (HOT) and, consequently, strongly acid microemulsions. The use of HOT-based microemulsions allows us to reach concentrations of H+ in the aqueous core corresponding to a Hammett acidity function of H0 = -2. The rate constant at the interface and the distribution constants of the carboxylic esters throughout the different microenvironments of the microemulsion have been quantified by application of the pseudophase formalism. The results obtained show that the hydrolysis rate constant at the interface increases as the water content of the system decreases. The correlation of the rate constants at the interface of the microemulsion with the Hammett acidity function, H0 (on the basis of the Bunnett-Olsen criterion), has allowed us to confirm that the hydrolysis process takes place via an A2 mechanism for high water contents and through an A1 mechanism for values of W 相似文献   

Numerical evaluation of overlapping acidity constants from the ratio of absorbances at two wavelengths

A numerical method for the evaluation of overlapping acidity constants is proposed in this paper. The method is based on the ratio of absorbances measured at two wavelengths and is rather simpler than the successive approximation methods described by others. The method has been applied to evaluation of the acidity constants of isonicotinic acid.     

Spectrophotometric determination of acidity constants by two-rank annihilation factor analysis

Annihilation of the contribution of one chemical component from the original data matrix is a general method in rank annihilation factor analysis (RAFA). However, RAFA is not applicable for studying the protonation equilibria of multiprotic acids. In this work, a two-rank annihilation factor analysis (TRAFA) method was proposed for determination of the acidity constants of diprotic acids. After recording the electronic absorbance spectra of the acids at different pH, the contributions of both H₂A and A²⁻ were annihilated from the absorbance data, which made feasible the determination of two successive acidity constants. The method was validated by analysis of simulated data and its application to the determination of the acidity constants of calmagite, as a reference compound. A close agreement was obtained between the resulted values by TRAFA and the declared values. Indeed, the method was used for determination of the acidity constants of two new chromenone derivatives in binary solvents mixtures of methanol and water. The effects of changing solvent composition on acidity constant data were explained by linear solvation free energy relationships (LSFER) utilizing solvatochromic parameters.     

Inhibition effect of {surfactant–substrate} aggregation on the rate of oxidation of reducing sugars by alkaline hexacyanoferrate(III)

The effect of cationic (cetyltrimethylammonium bromide, CTAB), anionic (sodium lauryl sulfate, NaLS), and nonionic (Brij‐35) surfactants on the rate of oxidation of some reducing sugars (xylose, glucose, and fructose) by alkaline hexacyanoferrate(III) has been studied in the temperature range from 35 to 50°C. The rate of oxidation is strongly inhibited in the presence of surfactant. The inhibition effect of surfactant on the rate of reaction has been observed below critical micelle concentration (CMC) of CTAB. In case of NaLS and Brij‐35, the inhibition effect was above CMC, at which the surfactant abruptly associates to form micelle. The kinetic data have been accounted for by the combination of surfactant molecule(s) with a substrate molecule in case of CTAB and distribution of substrate into micellar and aqueous pseudophase in case of NaLS and Brij‐35. The binding parameters (binding constants, partition coefficients, and free‐energy transfer from water to micelle) in case of NaLS and Brij‐35 have been evaluated with the help of Menger and Portnoy model reported for micellar inhibition. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 595–604, 2007     

Micellar medium for the analysis of complex mixtures of molybdenum and tungsten by derivative synchronous spectrofluorimetry in steels

The cationic surfactant hexadecyltrimethylammonium bromide enhances the fluorescence intensity of both molybdenum and tungsten complexes obtained with Alizarin Red S. This characteristic has been used for a sensitive simultaneous spectrofluorimetric determination of both ions over the range 32-4000 ng/ml and 49-2500 ng/ml for Mo and W, respectively. Good selectivity is achieved applying the well known synchronous derivative technique with a minucious pH selection. The proposed method has been applied to a certified steel sample with recoveries between 96 and 102%.     

Effect of CTAB and SDS micelles on the excited state equilibria of some indole probes

The absorption and fluorescence spectral characteristics of some biologically active indoles have been studied as a function of acidity and basicity (H_/pH/H(o)) in cationic (cetyltrimethylammonium bromide, CTAB), anionic (sodium dodecylsulphate, SDS) and aqueous phases at a given surfactant concentration. The prototropic equilibrium reactions of these probes have been studied in aqueous and micellar phases and apparent excited state acidity constant (pK(a)(*)) values are calculated. The probes show formation of different species on changing pH. Various species present in water, CTAB and SDS have been identified and the equilibrium constants have been determined by Fluorimetric Titration method. The fluorescence spectral data suggest the formation of oxonium ion through the excited state proton transfer reaction in highly acidic media and formation of photoproducts due to the base catalyzed auto-oxidative reaction in basic aqueous solutions. Variations in the apparent pK(a)(*) value have been observed in different media. The change in the apparent pK(a) values depends upon the solubilising power of the micelles, as well as on the location of the protonating site in the molecule. The observation about increase in pK(a)(*) values in SDS and decrease in CTAB compared to pure water for various equilibria is consistent with the pseudophase ion-exchange (PIE) model.     

Multiwavelength spectrophotometric determination of acidity constants of 1-（2-thiazolylazo）-2-naphthol in methanol-water mixtures

The acid-base properties of 1-(2-thiazolylazo)-2-naphthol (TAN) in mixtures of methanol-water at 25℃and an ionic strength of 0.1 mol/L are studied by a multi-wavelength spectrophotometric method.The acidity constants of all related equilibria are estimated using the whole spectral fitting of the collected data to an established factor analysis model DATAN program was used for determination of acidity constants.The corresponding pK_a values in methanol-water mixtures were determined.There is a linear relationship between acidity constants and the mole fraction of methanol in the solvent mixtures.