Effect of pH on kinetics of the decay of the radicals formed during photolysis of 2,2,4,6-tetramethyl-1,2-dihydroquinoline in aqueous and micellar solutions

Kinetics of the decay of the transient radicals formed from 2,2,4,6-tetramethyl-1,2-dihydroquinoline (TMQ) in aqueous and micellar solutions of sodium dodecyl sulfate were studied by flash photolysis as a function of pH. In aqueous and micellar solutions of TMQ the mechanism of the decay of the transient species and the reaction products are different from those in homogeneous organic solutions. The decay of the transient radicals follows first-order kinetics in the entire range of pH under consideration in both aqueous and micellar solutions. In aqueous solutions at pH 9–12, the decay rate constant decreases from 25.3 to 3.7 s⁻¹. In micellar solutions at different pH, different types of micellar catalysis were observed. At pH 1, the rate constant in a micellar solution is slightly lower than that in an aqueous solution. At pH 3–11, the decay rate constant increases (positive micellar catalysis). The apparent rate constant depends linearly on the concentration of TMQ in micelles. The rate constant for the reaction of the transient radical cation with TMQ was determined (200 L mol⁻¹ s⁻¹). At pH>13, the decay rate constant in micelar solutions is lower than that in aqueous solutions (negative micellar catalysis). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 703–708, April, 1997.     

Phase behavior and solution properties of sodium (3-dodecanoyloxy-2-hydroxy-propyl) succinate in water

Sodium (3-dodecanoyloxy-2-hydroxy-propyl) succinate (SLGMS) is a conjugated anionic surfactant in which a glycerol residue connects with a hydrophilic sodium succinate and dodecanoate. Aqueous micellar phase (W_m), hexagonal (H₁), bicontinuous cubic (V₁), and lamellar (L_α) phases are successively formed with increasing the surfactant concentration in a binary SLGMS-water system. The Krafft point is below 0 °C. The effective cross sectional area per surfactant molecule, a _s, in the H₁ phase is almost constant, 0.5 nm², and the shape of cylindrical micelle is almost unchanged with surfactant concentration. The cmc value of SLGMS measured by means of surface tension, electrical conductivity, and fluorescence probe methods is in the range of 4∼9 × 10⁻⁵ mol/l that is much lower than that of sodium dodecanoate, 2 × 10⁻² mol/l, or SDS, 8 × 10⁻³ mol/l. Hence, it is considered that the polar glycerol part in the SLGMS acts as a hydrophobic part. The solubilization of oil in the SLGMS solution is much higher than that in the SDS solution and this also suggests that the glycerol and succinic units act as lipophilic moieties. Received: 15 June 2000/Accepted: 27 July 2000     

Solubilization of Aliphatic Carboxylic Acids (C3-C6) by Sodium Dodecyl Sulfate and Brij 35 Micellar Pseudophases

The apparent dissociation constants of 1-propanoic, 1-butanoic, 1-pentanoic and 1-hexanoic acids were obtained for the first time in Brij 35 micellar solutions with concentration from 0.03 to 0.20 mol⋅L⁻¹ and sodium dodecyl sulfate (SDS) micellar solutions with concentrations from 0.01 to 0.30 mol⋅L⁻¹. A pronounced effect of Brij 35 micelles on the acid-base properties of aliphatic acids was observed. The binding constants, K _b, of carboxylic acids to micellar pseudophases of SDS and Brij 35 were estimated within the framework of the pseudophase model. The dependences of Gibbs energies of transfer from water to the micellar pseudophases were constructed, and Gibbs energies were evaluated for methylene and carboxylic group transfers into Brij 35 and SDS micelles. Comparison of the Gibbs energies of methylene group transfer from water to Brij 35 and SDS suggests that the mechanisms of hydrocarbon group transfer into the core of nonionic and anionic micelles involving the same monomer hydrophobic tail length are similar.     

Effect of electron-withdrawing power of the substituted group on?OH radical reaction with substituted aryl sulphides: A pulse radiolysis study

In neutral aqueous solution of (phenylthio)acetic acid, hydroxyl radical is observed to react with a bimolecular rate constant of 7.2 × 10^-1 dm³ mol⁻s⁻ and the transient absorption bands are assigned to^•OH radical addition to benzene and sulphur with a rough estimated values of 50 and 40% respectively. The reaction of the^•OH radical with diphenyl sulphide (k = 4.3 × 10⁸ dm³ mol⁻¹ s⁻¹) is observed to take place with formation of solute radical cation, OH-adduct at sulphur and benzene with estimated values of about 12, 28 and 60% respectively. The transient absorption bands observed on reaction of^•OH radical, in neutral aqueous solution of 4-(methylthio)phenyl acetic acid, are assigned to solute radical cation (λ_max = 550 and 730 nm), OH-adduct at sulphur (λ_max = 360 nm) and addition at benzene ring (λ_max = 320 nm). The fraction of^•OH radical reacting to form solute radical cation is observed to depend on the electron-withdrawing power of substituted group. In acidic solutions, depending on the concentration of acid and electron-withdrawing power, solute radical cation is the only transient species formed on reaction of^•OH radical with the sulphides studied.     

Receptor properties of calix[4]resorcinarenes toward tetramethylammonium and choline cations in micellar solutions of sodium dodecyl sulfate

Concentration range of solubilization of calix[4]resorcinarene (H₈L) in sodium dodecyl sulfate (SDS) micelles was found. The interaction of the deprotonated form of H8L (tetraanions [H₄L]⁴⁻) with tetramethylammonium (TMA) and choline cations in micellar solutions of SDS was studied by pH-metry and NMR spectroscopy. The concentration dependences of the change in the cloud point in a multicomponent system TMA (choline)-[H₄L]⁴-SDS-tetrabutylammonium bromide were determined. A correlation of these dependences with host-guest binding processes was found. The sharp change in the cloud points of the corresponding micellar solutions in concentration regions of TMA (0-5·10⁻⁴ mol L⁻¹) and choline (0–1.1· 10⁻³ mol L⁻¹) is caused by the formation of inclusion complexes TMA (choline)-[H₄L]⁴⁻ at the interface of the aqueous and micellar pseudophases. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1366–1371, August, 2006.     

Studies of the reaction of the hydroxyl radical with the oxalate ion in an acidic aqueous solution by pulse radiolysis

The reaction of the · OH radical with the oxalate ion in an acidic aqueous solution was studied by pulse radiolysis. The rate constant for the reaction of formation of the radical HOOC-COO·(λ_max = 250 nm, ɛ = 1800 L mol⁻¹ cm⁻¹) is (5.0±0.5)·107 L mol⁻¹ s⁻¹. In the reaction with the hydrogen ion (k = 1.1·10⁷ L mol⁻¹ s⁻¹), the radical HOOC-COO· is transformed into a nonidentified radical designated arbitrarily as H⁺(HOOC-COO)· (λ_max = 260 nm, ɛ = 4000 L mol⁻¹ cm⁻¹). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1165–1167, June, 2008.     

Neutral thallium clusters in aqueous solutions. Pulse radiolysis study

The formation of neutral Tl₂ (λ_max = 390 nm) and Tl₄ (λ_max = 360 nm) clusters in dilute aqueous solutions of Tl₂SO₄ containing formate ions was found by pulse radiolysis. The rate constants for the recombination of Tl⁰ atoms and Tl₂ clusters are equal to 1.5·10¹⁰ L mol⁻¹ s⁻¹ and 1.0·10¹⁰Lmol⁻¹ s⁻¹ (±30%), respectively, and the extinction coefficient of Tl₂ at 390 nm is −6.0·10³ L mol⁻¹ cm⁻¹ Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2367–2369, December, 1999.     

Effect of dioctyl sulfide on the kinetics of oxidative dissolution of gold nanoparticles in triton N-42 reverse micelles

The effect of additions of hydrophobic dioctyl sulfide (L) on the kinetics of dissolution of gold nanoparticles in the interaction with a dispersed aqueous hydrochloric solution of H₂O₂ in Triton N-42 reverse micelles (decane was the dispersion medium) was studied spectrophotometrically. The process consists of a two-stage oxidation Au⁰ → AuCl₂⁻ → AuCl₄⁻ at the surface of gold particles; the first stage occurs in two ways: a spontaneous reaction and an autocatalytic reaction involving AuCl₄⁻ ions. With small additions of L (c _L < c _Au), only spontaneous oxidation of Au(0) to Au(I) takes place because Au(I) is completely bound in an inert complex AuLCl. When unbound L is exhausted, the newly formed AuLCl is accumulated in micellar shells, changes the properties of the medium inside the micelles, and affects the rate constant of the autocatalytic reaction, which increases with increasing c _L. At high concentrations of L, the coagulation of particles occurs instead of their dissolution, because of the deterioration of the protective properties of micellar shells as a result of the ingression and accumulation of dioctyl sulfide molecules on account of selective adsorption on gold particles. The rate constants of all stages of dissolution and coagulation are determined.     

Small-angle neutron-scattering study of bis(quaternaryammonium bromide) surfactant micelles in water. Effect of the long spacer chain on micellar structure

The microstructure of the normal micelles formed by dimeric surfactants with long spacers, [Br⁻(CH₃)₂N⁺(C _m H_{2 m +1})-(CH₂) _S  -(C _m H_{2 m +1})N⁺(CH₃)₂Br⁻, m = 10 and s = 8, 10 and 12], has been investigated by small-angle neutron scattering and compared with previously reported results for micelles of the same dimeric surfactants with shorter spacers (m = 10 and s = 2, 3, 4 and 6). It was found that for dimeric surfactants with long spacers (s = 8 and 10), both micellar growth and variation in shape occur to only a small extent, if at all, compared with dimeric surfactants with short spacers. However, for the dimeric surfactant with the longest spacer, s = 12, the extent of micellar growth and shape variation is also large. These results are due to the differences in conformation of dimeric surfactants with short spacers (s = 2–6) compared with that of the surfactants with long spacers (s = 8–12). Received: 15 June 1998 Accepted: 22 July 1998     

Kinetic, spectral and redox properties of the transients formed on one-electron reduction of 3, 3, 6, 6-tetramethyl-3, 4, 6, 7, 9-pentahydro-10-phenyl (1, 8) (2H, 5H) acridinedione in aqueous-organic mixed solvent system: A pulse radiolysis study

The phenyl substituted acridine-1,8-dione (AD) dye reacts with (CH₃)₂*COH radicals with a bimolecular rate constant of 0.6 × 10⁸ dm³ mol⁻¹ s⁻¹ in acidic aqueous-organic mixed solvent system. The transient optical absorption band (λ_max = 465 nm, ɛ = 6.8 × 10² dm³ mol⁻¹ cm⁻¹) is assigned to ADH* formed on protonation of the radical anion. In basic solutions, (CH₃)₂*COH radicals react with a bimolecular rate constant of 4.6 × 10⁸ dm³ mol⁻¹ s⁻¹ and the transient optical absorption band (λ_max = 490 nm, ɛ = 10.4 × 10³ dm³ mol⁻¹ cm⁻¹) is assigned to radical anion, AD*⁻, which has a pK_a value of 8.0. The reduction potential value of the AD/AD*⁻ couple is estimated to be between −0.99 and −1.15 V vs NHE by pulse radiolysis studies. The cyclic voltammetric studies showed the peak potential close to −1.2 V vs Ag/AgCl.     

A 1H NMR study of 1,4-bis(N-hexadecyl-N, N-dimethylammonium)butane dibromide/sodium anthranilate system: spherical to rod-shaped transition

The effect of addition of sodium anthranilate to 5 mM micellar solutions of gemini surfactant 1,4-bis(N-hexadecyl-N,N-dimethylammonium)butane dibromide is investigated by ¹H NMR. The solubilization site of anthranilate anion near the micellar surface is inferred. In the micelles, the An⁻ ions intercalate among the surfactant headgroups producing morphological changes.     

Micellar behavior of acrylamide– octylphenylpoly(oxyethylene) acrylate copolymer in aqueous solution

The copolymer of acrylamide and octylphenylpoly(oxyethylene) acrylate macromonomer (AM-C₈PhEO₇Ac) was synthesized and characterized by IR and NMR spectroscopy. The molecular weight of the copolymer was determined to be 1.21 × 10⁵ by static light scattering. The weight contents of AM and macromonomer were determined to be 67.8 and 32.2%, respectively, by elemental analysis. The micellar behavior of the copolymer in aqueous solution was studied by UV spectroscopy and atomic force microscopy (AFM). The molecules of AM-C₈PhEO₇Ac copolymer form monomolecular micelles in the concentration range 4 × 10⁻⁶ – 3 × 10⁻⁵ g/ml and polymolecular micelles at concentrations above 3 × 10⁻⁵ g/ml according to the UV analysis. The AFM images indicate that the monomolecular micelles are globular with diameters of 70 nm and have a narrow size distribution. The polymolecular micelles can be globular or cylindrical depending on the concentration, and have a wide size distribution. Received: 10 February 1999 Accepted in revised form: 28 June 1999     

Effect of chain aggregation on the conductivity and ESR spectra of polyaniline

Solutions of polyaniline in m-cresol with and without camphorsulfonic acid (CSA), as well as films cast from these solutions were studied by ESR spectroscopy at 133–423 K and by optical spectroscopy in the range λ = 350–1100 nm. An analysis of the optical and ESR spectra shows that in the solutions and films without CSA polyaniline is fully doped but the conductivity of these films is low (∼10⁻⁸ S cm⁻¹; cf. 100 S cm⁻¹ for the films with CSA). Compared with the CSA-containing samples, the samples without CSA are characterized by broader ESR lines and higher contribution of the Curie spins to the magnetic susceptibility. These facts indicate a weak aggregation of polyaniline chains without CSA, which leads to low conductivity. A formula was proposed, which describes the temperature dependence of the polyaniline ESR linewidth and allows the interchain distance and the mobility of electrons moving along polymer chains to be determined. The conductivity of polyaniline films is affected by moderate heating (363–388 K) of the films and solutions from which the films were cast. It was found that the interchain distances correlate with the conductivity of the films and with the broadening of their ESR lines caused by the effect of O₂. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2701–2711, December, 2005.     

Positronium formation in aqueous Triton X-100 solution

The influence of micelles, formed by the aggregation of nonionic surfactant molecules, on positronium formation (combination of e⁻ and e⁺) probability is discussed in the light of radiation chemical phenomenon at the end part of the radiation track. The contribution due to the parapositronium/narrow-component intensity in the presence of micellar aggregation and further structural reorganization constitutes important aspects of the ortho-para conversion process.     

Pulse radiolysis study of redox reactions of safranine T in sodium dodecylsulphate (SDS) micellar medium

Reaction of hydrated electrons with safranine T (SF⁺), a phenazine dye useful as sensitizer in photogalvanic cell and the transient semireduced species formed by this reaction have been studied in SDS micellar medium using the technique of pulse radiolysis. Thee _aq ⁻ reaction with SF⁺ in the micellar environment was only marginally slower (5.1 × 10⁹ dm³ mol⁻¹ s⁻¹) as compared to that in homogeneous aqueous medium (2.2 × 10¹⁰ dm³ mol⁻¹ s⁻¹) explicable on the basis of our finding that although a large fraction of the dye gets localized near the micelle Stern layer where the molecule experiences a dielectric.constant of ≈40, a small but significant concentration of the dye exists in the aqueous bulk as charge pair complex with the anionic surfactant monomer (association constant for the formation of the complex being 2.8 × 10⁴ dm³ mol⁻¹). The transient semireduced absorption band observed in the micellar medium showed a red shift of ≈ 50 nm and also the decay of the transient, which was very fast with 2k = 1 × 10⁹ dm³ mol⁻¹ s⁻¹ in aqueous medium, was stable in the SDS micellar medium over a few tens of milliseconds suggesting that the radical is incorporated deeper than the parent molecule in the SDS micelle. The effect of this stability on the photogalvanic conversion needs to be examined.     

Comparison of aggregation behaviors between branched and linear block polyethers: MesoDyn simulation study

The comparison of aggregation behaviors between the branched block polyether T1107 (polyether A) and linear polyether (EO)₆₀(PO)₄₀(EO)₆₀ (polyether B) in aqueous solution are investigated by the MesoDyn simulation. Polyether A forms micelles at lower concentration and has a smaller aggregation number than B. Both the polyethers show the time-dependent micellar growth behaviors. The spherical micelles appear and then change to rod-like micelles with time evolution in the 10 vol% solution of polyether A. The micellar cluster appears and changes to pseudo-spherical micelles with time evolution in the 20 vol% solution of polyether A. However, the spherical micelles appear and change to micellar cluster with time evolution in the 20 vol% polyether B solution. The shear can induce the micellar transition of both block polyethers. When the shear rate is 1?×?10⁵ s^?1, the shear can induce the sphere-to-rod transition of both polyethers at the concentration of 10 and 20 vol%. When the shear rate is lower than 1?×?10⁵ s^?1, the huge micelles and micellar clusters can be formed in the 10 and 20 vol% polyether A systems under the shear, while the huge micelles are formed and then disaggregated with the time evolution in the 20 vol% polyether B system.     

Electrical Conductance Studies in Aqueous Solutions of Glutaric Acid,Disodium Glutarate and Sodium Hydrogen Glutarate

Conductivity measurements of glutaric acid and disodium glutarate in dilute aqueous solutions were performed in the 288.15 to 323.15 K temperature range. The limiting equivalent conductances of glutarate anions, λ ^o(HGlut⁻,T) and λ ^o(1/2Glut²⁻,T), and the dissociation constants of glutaric acid, K ₁(T) and K ₂(T), were derived by the use of the Onsager and the Quint and Viallard conductivity equations. The applied molecular model was successfully confirmed by analyzing the conductivities of sodium hydrogen glutarate at 298.15 K.     

Studies of Monolayer and Mixed Micelle Formation of Anionic and Nonionic Surfactants in the Presence of Adenosine-5-monophosphate

The interactions between the anionic surfactant di-(2-ethylhexyl) phosphate sodium salt (DEP) and two nonionic surfactants, dimethyldecyl phosphineoxide (DDPO) and dimethyltetradecyl phosphineoxide (DTPO), at the interface and in the micellar phases were investigated in the absence and presence of adenosine-5-monophosphoric acid disodium salt (AMP). The mixed systems were DEP–DDPO, DEP–DDPO/AMP (0.001 mol⋅L⁻¹), DEP–DTPO, and DEP–DTPO/AMP (0.001 mol⋅L⁻¹) at different bulk mole fractions of the anionic component (α ₁=0.9,0.8,0.6,0.4,0.2). The mixed systems studied were investigated based on the theoretical models of Rubingh and Clint. The results showed surface tension reduction efficiency. The adsorbed mixed monolayer demonstrated stronger interactions than the mixed micelles, whereas AMP increased the interfacial interactions more than those in the micellar phase. The Gibbs energy of mixing suggests that the stability of the mixed micellar phase is greater than that of the micellar phases of the individual components. The synergism that occurred in the different mixed phases is discussed.     

Photostimulated changes in WO3 nanosized films

During the irradiation of WO₃ films d = 7–160 nm thick by light at λ = 320 nm (I = (1.5–7) × 10¹⁵ quantum cm⁻² s⁻¹), absorption band at λ = 850 nm appeared along with absorption band edge shift to shorter waves. The subsequent irradiation of samples at λ = 850 nm caused the disappearance of the longwave absorption band. The intrinsic absorption edge of WO₃ films was determined (λ = 320 nm). The degree of transformations of WO₃ films increased under atmospheric conditions as the intensity of incident light and the time of irradiation (1–140 min) grew and as film thickness decreased. A mechanism of photochemical transformations of WO₃ films was suggested. This mechanism included the generation of electron-hole pairs, the recombination of part of nonequilibrium charge carriers, the formation of [eV_a²⁺e] centers, and the isolation of photolysis products.     

Kinetic regularities of micellar catalysis in the dephosphorylation with peroxide anion

The acid-base equilibrium of hydrogen peroxide in water solutions of cetyltrimethylammonium bromideand the reactivity of hydroxide and peroxide anions with respect to 4-nitrophenyl diethyl phosphate were investigated. In the micelles the acid ionization constant of the hydrogen peroxide increased three-fold. The application of the pseudophase distribution model under the conditions of competitive sorption of HO⁻ and HOO⁻ anions with the micelles of cetyltrimethylammonium bromide to the estimation of the main kinetic parameters of the micellar process was tested.