THE EFFECT OF BENZYL ALCOHOL ON THE MICELLAR PROPERTIES OF CTAB IN KBr SOLUTION

ABSTRACT

The effect of benzyl alcohol on the micellar size and shape of CTAB in KBr solution has been investigated by means of viscosity, LLS (laser light scattering), and NMR measurements. The surfactant CTAB (cetyltrimethylammonium bromide) and KBr content are kept constant at 0.01 mol.L^?1 and O.l^?1 mol.. The data from the various techniques are quantitatively in agreement. The viscosity of 0.01 mol.L^?1 CTAB/ 0.01mol.L^?1 KBr micellar system has a marked maximum at benzyl alcohol content 0.6%(v/v), where the size of rod micelles are largest. The results from 'H-NMR spectra of CTAB molecules show that before the maximum viscosity, benzyl alcohol is located in the interfacial region of CTAB micelles in the presence of KBr salt. If more benzyl alcohol is added, it starts solubilizing in the palisades of the micelles.     

TIME-RESOLVED SPECTROSCOPIC STUDIES ON PHOTOPHYSICAL PROPERTIES OF BENOXAPROFEN IN MICELLAR SOLUTIONS: AN INTRAMICELLAR FLUORESCENCE QUENCHING

The micellar dependencies of the photophysical properties of benoxaprofen (BXP), a 2-phenyl benzoxazole derivative, have been investigated using fluorescence spectroscopy and laser flash photolysis techniques. The fluorescence of BXP in aqueous solution has been observed to be remarkably quenched upon addition of a surfactant, cetyltrimethyl ammonium bromide (CTAB) or Triton X-100, in contrast to its enhancement in sodium dodecyl sulfate (SDS) micellar solution. Time-resolved fluorescence measurements show that the fluorescence decays biexponentially in the micellar solution, indicating the relaxation of micellar environments surrounding the excited BXP. The major component of fluorescence lifetimes in CTAB or Triton X-100 micellar phase is even shorter (330–427ps) than in SDS micellar phase (731 ps). The nonradiative decay constants are significantly larger (ca 3.0 times 10⁹ s^?1) in the CTAB or Triton X-100 micellar phase than in SDS micelles by a factor of ca 10. The major nonradiative decay is interpreted to be the internal conversion due to nuclear geometric change of BXP in the first excited singlet state. This is consistent with the observation that the quantum yields of intersystem crossing are very low (less than 0.01) in the micellar solutions as determined by the laser flash photolysis technique. The laser-induced transient absorption spectrum of BXP in CTAB or Triton X-100 micellar solution shows that the decay kinetics of the transients in CTAB or Triton X-100 are significantly different from first order kinetics in SDS.     

Micellar Catalysis of Composite Reactions II. The Effect of CTAB Micelles on the Alkaline Fading of Malachite Green

The alkaline fading of malachite green, which is interpreted as parallel first order and second order reactions, has been studied in cetyltrimethylammonium bromide (CTAB) micellar solution at 25°C using spectrophotometry. A micellar catalytic model is proposed in this paper for constant concentration of hydroxideion. For this model, the first order and the second order rate constants in CTAB micellar phase,k_1m and k_2m have been obtained.

The experimental results indicate that the first order reaction of malachite green cation with water is catalysed by CTAB micelles while the second order reaction of malachite green cation with hydroxide ion is inhibited by CTAB micelles. The first order rate constant in CTAB micellar phase, k_1m , is 210 times of that in the bulk phase, but the second order rate constant in CTAB micellar phase, k_2m , is 0. 166 time of that in the bulk phase. The results are interpreted mostly in relation to the micellar micropolarity and electrostatic interaction. @Keywords: Micelle, Micellar catalysis, Parallel first order and seond order reactions, Malachite green     

分数级反应热动力学研究—丙烯酰胺聚合反应动力学

应用n级等摩尔浓度反应的热动力学理论,在30℃和40℃下研究了丙烯酰胺在水溶液中和CTAB胶束溶液中由亚硫酸钠引发的聚合反应动力学.讨论了引发剂和CTAB的浓度对聚丙烯酰胺分子量的影响。     

An inimitable and ecological pleasant technique for the assessment of trace amount of copper (II) in tangible samples with new complexing reagent

A simple and rapid spectrophotometric technique has been designed for the trace copper analysis employing 1-(2-Thiazolylazo)-2-naphthol (TAN) reagent in aqueous micellar solution of cetyl trimethylammonium bromide (CTAB) as a surfactant. Copper complexed with 1-(2-Thiazolylazo)-2-naphthol to form bis[1-(2-Thiazolylazo)-2-naphthol]copper. The present spectrophotometric technique was very important since the micellar system was used in place of the toxic, high cost and time-consuming solvent extraction steps. The technique showed an enhanced detection efficiency, specificity, and molar absorptivity. It was found that the molar absorption coefficient and sensitivity of Sandel were ε 2.45 × 10⁴ L mol^?1cm^?1 and 2.6 ngcm^?2 at λ_max 578.4 nm. A linear calibration plot in the range 0.12–5.0 μg mL^?1 was obtained; a stoichiometric metal ligand ratio [M:L] of 1:2 was found for the formation of Cu-[TAN]₂. The complex was formed at pH 9.5 and was stable up to 24 h. The proposed technique has been employed to study copper from different alloys, biological, environmental and pharmaceutical samples.     

THE EFFECT OF SINGLE MICELLES OF SURFACTANTS ON POLYMERIZATION OF ACRYLAMIDE

The polymerization of acrylamide in micellar solutions of cationic, anionic, zwitterionic and nonionic surfactants, initiated by NaHSO₃, has been studied at 20 and 30° C with time variable method of thermokinetics for the 1. 5-order reaction in this paper. Reaction mechanism has been suggested and rate equations have been derived. The results indicate that ionic (CTAB, TTABDTAB, SDS) and zwitterionic (SLS) surfactants catalyze the polymerization in the order SDS>SLS>DTAB ≈ TTA≈ CTAB, and nonionic surfactant (Brij35) has slight inhibition effect. These effects are mainly caused by the effect of the formation of micelle- HSO₃ complex on the step of initiator to form free radical.     

THE EFFECTS OF MIXED MICELLES OF SURFACTANTS ON POLYMERIZATION OF ACRYLAMIDE

The polymerization of acrylamide in mixed micellar solutions of surfactants, initiated by NaHSO₃ has been studied at 20 and 3Q° C with time variable method of thermokinetics for 1. 5-order reaction. The results indicate that the mixed micellar systems of cationic or anionic with zwitterionic surfactants (SLS/ CTAB, SLS/ TTAB, SLS/ SDS) and cationic with nonionic surfactants (Brij 357sol; CTAB, Bri-J35/TTAB, Brij35/ DTAB) have catalytic effect on the polymerization in the order, at 20° C. SLS/ SDS SLS/ TTAB SLS/ CTAB Brij35/ CTAB at 30° C SLS/ SDS SLS/ TTAB≈ / CTAB Bri-j35/ DTAB= sBrij35/ TTAB as Brij35/ CTAB, while Brij35/ SDS mixed micellar system has inhibition. These effects are attributed to the effect of the Stern layer of mixed micelles on the step of initiator (HSOT) to form free radical.     

Kinetics and mechanism of interaction of dipeptide (glycyl–glycine) with ninhydrin in aqueous micellar media

The rates of reaction between ninhydrin and dipeptide glycyl–glycine (Gly–Gly) have been determined by studying the reaction spectrophotometrically at 70°C and pH 5.0 in aqueous and in aqueous cationic micelles of cetyltrimethylammonium bromide (CTAB). The reaction follows first‐ and fractional‐order kinetics, respectively, in [Gly–Gly] and [ninhydrin]. The observed rate constant is affected by [CTAB] changes and the maximum rate enhancement is ca. three‐fold. As the k_ψ ? [CTAB] profile shape is characteristic of bimolecular reactions catalyzed by micelles, the catalysis is explained in terms of the pseudo‐phase model of the micelles (proposed by Menger and Portnoy and developed by Bunton and Romsted). The presence of inorganic salts (NaCl, NaBr, Na₂SO₄) does not reveal any regular effect but the data with organic salts (NaBenz, NaSal) show an increase in the rate followed by a decrease. The kinetic data have been used to calculate the micellar binding constants K_S for Gly–Gly and K_N for ninhydrin and the respective values are 317 and 69 mol^?1 dm³. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 643–650, 2006     

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.     

MICELLAR CATALYSIS OF COMPOSITE REACTIONS I MICELLAR EFFECT ON THE CONSECUTIVE FIRST ORDER REACTION

The micellar catalytic model (or the consecutive first order reaction has been proposed in this paper. It was applied to the alkaline hydrolysis of dimethyl phthalate in micellar solutions of surfactants (CTAB, SDS and Triton X-100), and the alkaline hydrolysis of bis (2,4-dinitrophenyl) posphate in CTAB micellar solution. Rate constants obtained in micellar phase indicate that the two steps of alkaline hydrolysis of dimethyl phthalate are both inhibited by all of the surfactants investigated. CTAB micelle exhibits a greater catalytic effect on the alkaline hydrolysis of bis (2, 4-dinitrophenyl) phosphate. this may be arised from the local concentration effect of hydroxide ion in CTAB micellar phase. Nevertheless. the second order rate constant of bis-(2, 4-dinitrophenyl) phosphate in the micellar phase is smaller than that in the bulk phase.     

Cleavage of phosphate diesters mediated by Zn(II) complex in Gemini surfactant micelles

The cleavage of 2-hydroxypropyl p-nitrophenyl phosphate (HPNP) catalyzed by the Zn(II)-biap (biap: N,N-bis(2-ethyl-5-methylimidazole-4-ylmethyl)aminopropane) complex has been investigated spectrophotometrically in a micellar solution of cationic Gemini surfactant 16-2-16 [bis(hexadecyldimethylammonium)ethane bromide] and CTAB (hexadecyltrimethylammonium bromide) at 25+/-0.1 degrees C. The experimental results reveal that a higher rate of acceleration (about 2016-fold) of HPNP cleavage promoted by the Zn(II)-biap complex has been observed in the 16-2-16 micellar solution in comparison with the background rate (k(0)) of HPNP spontaneous cleavage at 25 degrees C. Reaction rates of HPNP cleavage in CTAB micellar solutions are only about 40% of that in Gemini 16-2-16 micelles under comparable conditions. In addition, the cleavage rates of HPNP in Gemini micelles and in CTAB micelles are respectively 29.5 times and 12 times faster than that in aqueous buffer. Especially, a "sandwich absorptive mode" has been proposed to explain the acceleration of HPNP cleavage in a cationic micellar solution.     

PNPP Cleavage Catalyzed by Schiff Base Mn(III) Complexes Containing Polyether Side Chains in CTAB Micellar Solutions

Two Schiff base Mn(III) complexes containing polyether side chain were synthesized and characterized. The catalytic hydrolysis of p‐nitrophenyl picolinate (PNPP) by the two complexes in the buffered CTAB micellar solution in the pH range of 6.60–8.20 was investigated kinetically in this study. The influences of acidity, temperature, and structure of complex on the catalytic cleavage of PNPP were also studied. The mechanism of PNPP hydrolysis catalyzed by Schiff base manganese(III) complexes in CTAB micellar solution was proposed. The relative kinetic and thermodynamic parameters were determined. Comparied with the pseudo‐first‐order rate constant (k ₀) of PNPP spontaneous hydrolysis in water, the pseudo‐first‐order rate constants (k _obsd) of PNPP catalytic hydrolysis are 1.93×10³ fold for MnL¹ ₂Cl and 1.06×10³ fold for MnL² ₂Cl in CTAB micellar solution at pH=7.00, T=25°C, and [S]=2.0×10^?4mol · dm^?3, respectively. Furthermore, comparing the k _obsd of PNPP catalytic hydrolysis by metallomicelles with that of PNPP hydrolysis catalyzed only by metal complexes or CTAB micelle at the above‐mentioned condition, metallomicelles of MnL₂(L=L¹, L²) Cl/CTAB exhibit notable catalytic activities for promoting PNPP hydrolysis, and MnL¹ ₂Cl/CTAB system is superior in promoting cleavage of PNPP relative to MnL² ₂Cl/CTAB system under the same experimental conditions. The results indicate that the rate of PNPP catalytic cleavage is influenced by the structures of the two complexes, the acidity of reaction systems, and the solubilization of PNPP in CTAB micelles.     

Kinetics of the alkaline hydrolysis of fenuron in aqueous and micellar media

The kinetics of the hydrolysis of fenuron in sodium hydroxide has been investigated spectrometrically in an aqueous medium and in cationic micelles of cetyltrimethylammonium bromide (CTAB) medium. The reaction follows first‐order kinetics with respect to [fenuron] in both the aqueous and micellar media. The rate of hydrolysis increases with the increase in [NaOH] in the lower concentration range but shows a leveling behavior at higher concentrations. The reaction followed the rate equation, 1/k_obs = 1/k + 1/(kK[OH^?]), where k_obs is the observed rate constant, k is rate constant in aqueous medium, and k is the equilibrium constant for the formation of hydroxide addition product. The cationic CTAB micelles enhanced the rate of hydrolytic reaction. In both aqueous and micellar pseudophases, the hydrolysis of fenuron presumably occurs via an addition–elimination mechanism in which an intermediate hydroxide addition complex is formed. The added salts decrease the rate of reaction. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 638–644, 2007     

Influences of Micelle Formation and Added Salts on the Hydrolysis Reaction Rate of p‐Nitrophenyl Benzoate in Aqueous Buffered Media

The hydrolysis reaction rate of p‐nitrophenyl benzoate (p‐NPB) has been examined in aqueous buffer media of pH 9.18, containing surfactants, cetyltrimethylammonium bromide (CTAB) and chloride (CTAC), or sodium dodecyl sulfate (SDS) at 35°C. Although the rate constant [log (k /s⁻¹)] of p‐NPB hydrolysis has once decreased slightly below the critical micelle concentration (CMC) value for CTAB and CTAC, it has begun to increase drastically with micellar formation. With increasing concentrations larger than the CMC value, the log (k /s⁻¹) value has reached the optimal value, i.e., a 140‐ and 200‐fold rate acceleration for CTAB and CTAC, respectively, compared to that without a surfactant. Whereas the anionic surfactant, SDS, has caused only a gradual rate deceleration in the whole concentration range (up to 0.03 mol dm⁻³). Increases in pH of the buffer have resulted in increases of the hydrolysis rate. In the CTAB micellar solution, the remarkably enhanced rate has been retarded significantly by the addition of only 0.10 mol dm⁻³ bromide salts. The effects of rate retardation caused by the added salts follows in the order of NaBr > Me₄NBr > Et₄NBr > Pr₄NBr > n‐Bu₄NBr. In the absence of surfactant, however, the addition of the bromide salts has accelerated the hydrolysis rate, except for the metallic salt of NaBr, with the order of Me₄NBr < Et₄NBr < Pr₄NBr < n‐Bu₄NBr. In the CTAC micellar solution, similar rate retardation effects have been observed in the presence of chloride salts (NaCl, Et₄NCl, and n‐Bu₄NCl). The effects of added salts have been interpreted from the viewpoints of the changes in activity of the OH⁻ ion and/or the nucleophilicities of the anions from the added salts.     

Solubilization of caffeic acid into the cationic micelles and biogenic synthesis of silver nanoparticles for the degradation of dye

Solubilization of caffeic acid into the aqueous solution of cationic cetyltrimethlyammonium bromide (CTAB) has been studied by using differential spectroscopic and conductivity methods. The solubility of caffeic acid increases with increasing the CTAB concentrations. The solubilization constant of caffeic acid into CTAB (K_X = 1.8 × 10⁵), standard free energy (ΔG⁰_P = ?30.0 kJ/mol), and relative solubility (S_t/S₀ = 53.5) were estimated at room temperature from UV–visible data. The critical micellar concentration (CMC) of CTAB decreases linearly with caffeic acid concentration due to the presence of hydrophobic benzene moiety. The interaction of caffeic acid with CTAB has also been discussed. The solubilized caffeic acid was used as a reducing agent for the preparation of silver nanoparticles (AgNPs). The as-prepared AgNPs were used as an activator of persulphate. The generated reactive oxygen species (OH^?) and reactive sulphur species SO₄^-?) were responsible for the degradation of xylenol orange dye in water.     

The reduction of hexanitrocobaltate(III) ion in the presence of hexadecyltrimethylammonium bromide

The influence of cationic surfactant hexadecyltrimethylammonium bromide (CTAB) on the kinetics of the spontaneous reduction of the analytically important compound, sodium hexanitrocobaltate(III), was studied. The spontaneous reduction was monitored spectrophotometrically at pH 2 and 5 and at concentrations of CTAB from 1 × 10⁻⁵ to 5 × 10⁻⁴ M. The mechanism of this process was described using two consecutive first-order reactions. A decrease in the rate constant for reduction at pH 5 in solutions containing CTAB in concentrations of 5.6 × 10⁻⁵ M (critical micelle concentration) compared with its rate in an aqueous solution was observed. These effects could be explained by electrostatic and hydrophobic/hydrophilic interactions between the micellar pseudophase and the hexanitrocobaltate(III) ion. The article is published in the original.     

THE EFFECT OF SURFACTANT MICELLES ON THE ALKALINE HYDROLYSIS OF DIMETHYLFORMAMIDE

The alkaline hydrolysis of dimethylformamide has been studied at 40'C in micellar solutions of single surfactant (CTAB. SDS. Brij 35) with the analog thermoanalytical curve method of thermokinetics. A kinetic equation of micellar catalysis under the condition of highter reactant concentration than micellar concentration ([S]>[M]) has been derived from the pseudophase model of micellar catalysis and some relative assumptions, The kinetic parameters. k_m, k_2mand the association constant of reactant with micelle K₁, have been calculated in this way. the results indicate that these surfactant micelles exhibit catalytic effect on the reaction. This is attributed to the micropolarity and local concentration effect of micelles.     

Kinetics of basic hydrolysis of tris(1,10‐phenanthroline)iron(II) in macromolecular assemblies of CTAB

The kinetics of basic hydrolysis of tris(1,10‐phenanthroline)iron(II) has been carried out in aqueous, N‐cetyl‐N,N,N‐trimethyl ammonium bromide (CTAB) micellar, and CTAB reverse micellar media by UV–visible spectroscopy system. The reaction follows the overall second‐order kinetics; first order in each Fe(II) complex and the base (^?OH). CTAB micelles catalyze the reaction rate through the adsorption of the Fe(II) complex and the hydroxyl ions on the micellar surface. In the reverse micellar medium, interesting physicochemical features are observed. Being ionic nature of reactants, both the reactants prefer to stay and react inside the water pool in place of the hydrophobic environment. The rate increases with w, that is, the size of the water pool, attains a maximum value at w = 8.33, and then decreases. But the rate increases as the concentration of surfactant increases at fixed w values. For a better explanation of the kinetic data, the activation parameters, standard enthalpy of activation (Δ^?H°), standard entropy of activation (Δ^?S°), and energy of activation (E_a) were determined. All kinetic data corroborate the proposed mechanism. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 579–589, 2011     

Micelle-Catalyzed Interaction Between [Ni(II)-Gly-Gly]+ and Ninhydrin

The effect of cationic micelles of cetyltrimethyl ammonium bromide (CTAB) on the observed pseudo-first-order rate constant for the interaction of nickel dipeptide complex [Ni(II)-Gly-Gly]⁺ with ninhydrin has been studied spectrophotometrically. At constant temperature and pH, increase in the [CTAB] from 0.0 to 60.0 × 10^?3 mol dm^?3 caused nearly three-fold increase of the rate constant. The micellar catalysis is explained in terms of the pseudophase model. From the observed kinetic data, binding constants of micelle–[Ni(II)-Gly-Gly]⁺ (K _S), and micelle–ninhydrin (K _N) are evaluated, respectively, to be 5.3 mol^?1 dm³ and 84.0 mol^?1 dm³. The role of added inorganic (NaCl, NaBr, Na₂SO₄) and organic salts (NaBenz, NaSal) on the reaction rate has also been examined.     

Oxidation of 2,6-Di-tert-butylphenol by dioxygen catalyzed by tetrasodium phthalocyaninatocobalt(II) tetrasulfonate in aqueous micellar media

The oxidation of 2,6-di-tert-butylphenol by dioxygen has been investigated in aqueous micellar aggregates of cetyltrimethylammonium bromide (CTAB) using tetrasodium phthalocyaninatocobalt(II) tetrasulfonate (CoPcTsNa₄) as catalyst. The CTAB/CoPcTsNa4 system showed enhanced catalytic activity in the oxidation of 2,6-di-tert-butylphenol compared to that observed in the oxidation reaction in the absence of CTAB. 2,6-Di-tert-butyl-1,4-benzoquinone and 3,5,3′,5′-tetra-tert-butyl-4,4-diphenoquinone were identified as reaction products. The initial rate constants of auto-oxidation reaction was found to increase with increasing the pH range from 7.0 to 13.0. The rate constants k_obs of auto-oxidation reaction showed linear dependence on catalyst concentration. The rate of auto-oxidation reaction was found to fit a Michealis-Menten kinetic model for the saturation of catalyst sites with increasing 2,6-di-tert-butylphenol concentration and dioxygen pressure. Tetrasodium phthalocyaninatocobalt(II) tetrasulfonate in aqueous micellar solution of CTAB was found to be mainly monomeric.