Micellar catalysis in flow injection systems: the nitrosation reaction.

The use of aqueous micellar carrier streams in flow injection is shown to catalyse on-line reactions and thereby improve the sensitivity relative to non-micellar systems. The effect of several different micellar systems on the nitrosation reaction of N,N-diethylaniline in acidic solution was investigated. The mechanism of the micellar enhancement is discussed and the sensitivities of the method in both aqueous and micellar media are compared. The presence of the cationic surfactant, cetyltrimethylammonium bromide, is shown to improve the sensitivity of the analysis. The effect of the micellar solution on the dispersion characteristics of the system was also studied. The greater viscosity of the micellar phase increases dispersion for non-reacting systems, but when monitoring a reaction product the increased reaction rate can counteract this and the micellar carrier can show less over-all dispersion than the aqueous carrier.     

Fluorescence investigation of affinity interaction between bovine serum albumin and triazine dye in reversed micelles

The effect of Cibacron Blue 3GA (CB) on the fluorescence emission spectra of bovine serum albumin (BSA) was investigated in cationic reversed micelles formed with cetyltrimethylammonium bromide (CTAB) compared with that in aqueous phase. The anionic CB had electrostatic interactions with cationic CTAB and affinity interactions with BSA in the reversed micelles. The addition of CB in the reversed micellar phase led to a great decrease in the fluorescence intensity of BSA and a remarkable red shift of the wavelength of emission maximum (λ_max). The fluorescence intensity of BSA decreased and the λ_max decreased 5 nm (blue shift) without the addition of CB in the reversed micellar phase. The fluorescence intensity of BSA with the addition of CB had the strongest value in the aqueous phase with the presence of CTAB, a less strong value in the reversed micellar phase, and a weak value in the aqueous phase without the presence of CTAB. The increase in λ_max of BSA with the addition of CB in the reversed micellar phase might indicate the decrease in the hydrophobic microenvironment of the Trp residue of BSA, contrary to those microenvironments in the absence of CB.     

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.     

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.     

Comparison of Aqueous,Micellar and Microemulsion Carriers in Flow Injection Analysis. The Base Hydrolysis of Acetylsalicylic Acid

Abstract

The potential applicability of surfactant solutions as carrier streams in flow injection analysis is examined. The reaction rates determined for the base catalyzed hydrolysis of acetylsalicylic acid in aqueous, micellar and microemulsion solutions show a rate enhancement of 40% for the static microemulsion system when compared to the aqueous solution. However, when the identical microemulsion solution is employed as a carrier stream in flow injection analysis with ultraviolet detection, this enhancement in rate is not observed. To our knowledge, all previous work employing microemulsions in FIA has been concerned only with detection enhancement, here we present direct comparisons between aqueous and microemulsion carriers concerning rates of reaction, peak dispersion and analytical figures of merit. The loss in relative sensitivity can be traced to the increased dispersion in the microemulsion system (D = 14.36) when compared to the aqueous carrier (D = 12.52). Additionally, an increased skewness was observed in the peaks obtained with a microemulsion carrier, yielding further information about the physical dispersion process occuring in the sample plug.     

Exploitation of reversed micelles as a medium in mimetic peroxidase-catalyzed fluorogenic reaction between hydrogen peroxide and l-tyrosine

The peroxidase activity of mimetic enzyme, iron tetrasulfonatophthalocyanine (FeTSPc), was characterized in reversed micelles of hexadecyltrimethylammonium bromide (CTAB) formed in n-heptane-n-pentanol solution (2:1, V:V). The assay is based on its catalytic effect on the oxidation reaction of l-tyrosine (l-tyr) by hydrogen peroxide. The influences of environmental factors, such as the water content, CTAB concentration and pH, on the peroxidase activity of FeTSPc were investigated. It was observed that the reaction rate was distinctly enhanced in CTAB reversed micelles as compared with the rate in aqueous solution. Under optimum conditions, application of the FeTSPc-catalyzed fluorescence system in reversed micelles to the determination of H(2)O(2) and FeTSPc led to a highly sensitive system compared with that in aqueous solution, permitting detection limits of 5x10(-9) mol l(-1) H(2)O(2) and 2.3x10(-9) mol l(-1) FeTSPc. The advantages and limitations of employing the reversed micellar media in such mimetic peroxidase-catalyzed fluorescent detection schemes were discussed.     

Electrochemical reduction of p-nitrosodiphenylamine in, a cationic micellar system

The electroreduction of p-nitrosodiphenylamine (p-NDPA) in an alkaline aqueous solution containing cetyltrimethylammonium bromide (CTAB) as a cationic surfactant was investigated by polarography, cyclic and rotating disc voltammetry. It was found that the reduction of p-NDPA in cationic micellar systems takes place by the ECE mechanism, and, compared to the reduction of the same compound in a homogeneous water solution, has a somewhat lower rate of the overall electrode reaction. The lower reaction rate of p-NDPA reduction in micellar medium is probably due to three main factors: solubilization of p-NDPA in CTAB micelles, adsorption of monomeric surfactant species at the electrode surface and a lower rate of the base catalyzed dehydration reaction (C-step) in the micellar system.     

STUDIES ON THERMOKINETICS(XVI) THE KINETICS OF THE POLYMERIZATION OF ACRYLAMIDE IN MICELLAR SOLUTION

The kinetics of the polymerization of acrylamide in aqueous solution and CTAB micellar solution initiated by sodium sulfite has been investigated with the theory and method of thermokinetics for n order reactions with equal concentration in this paper. The influence of initiator and CTAB concetrations on molecular weight of polyacrylamide has been discussed.The second—order rate constants of this reaction at 30 and 40°C in aqueous solution are 0. 112and 0. 0262dm³ mol^-1s^_1, respectively. The activation energy,based on measurements at these two temperatures,is 66. -4kJ mol^-1. The ratio k2√n in CTAB micellar solution is smaller than that in aqueous solution. The rate of forming radical in micellar solution has been decreased.     

Micellar catalysis of oxidation of glycolic acid by N-bromophthalimide

Catalysis of oxidation of glycolic acid by N-bromophthalimide by micelles of cetyltrimethylammonium bromide (CTAB) at 318 K was investigated. The observed value of critical micelle concentration of CTAB in the presence of other components was lower than those reported in the literature. The oxidation reaction was strongly catalyzed by cationic micelles of CTAB. The reaction rate increased with CTAB concentration until the steady state was achieved. The reaction kinetics corresponded to first, fractional and inverse fiactional orders with respect to changes of concentration of reaction components. Effects of solvent, phthalimide, mercuric acetate, and potassium chloride on the reaction kinetics were also studied. The micelle-catalyzed oxidation reaction was shown to fit Arrhenius equation. The experimental data were rationalized in terms of Menger-Portnoy model considering a distribution of the reactants between the micellar and aqueous phases.     

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     

正戊醇对CTAB/KBr胶束体系流变性的影响

报道了正戊醇对CTAB/KBr胶束体系流变性的影响。结果表明：在0.01mol.dm^-^3CTAB(十六烷基三甲基溴化铵)溶液中,正戊醇促使CTAB/KBr胶束体系的粘度增大至一最大值,然后降低在0.08mol.dm^-^3CTAB/KBr的溶液中,正戊醇能促使该胶束体系呈现粘弹性。根据动态荧光法测定的胶束聚集对以上结果进行了解释。     

Interaction between biosurfactant surfactin and cationic surfactant cetyl trimethyl ammonium bromide in mixed micelle

An anionic/cationic mixed surfactant aqueous system of surfactin and cetyl trimethyl ammonium bromide (CTAB) at different molar ratios was studied by surface tension and fluorescence methods (pH 8.0). Various parameters that included critical micelle concentration (cmc), micellar composition (X ₁), and interaction parameter (β ^m) as well as thermodynamic properties of mixed micelles were determined. The β ^m was found to be negative and the mixed system was found to have much lower cmc than pure surfactant systems. There exits synergism between anionic surfactin and cationic CTAB surfactants. The degree of participation of surfactin in the formation of mixed micelle changes with mixing ratio of the two surfactants. The results of aggregation number, fluorescence anisotropy, and viscosity indicate that more packed and larger aggregates were formed from mixed surfactants than unmixed, and the mixed system may be able to form vesicle spontaneously at high molar fraction of surfactin.     

Experimental studies on the effect of temperature on dispersion in a flow-injection system

The effect of temperature on dispersion in a flow-injection system is described. Systems both with and without chemical reaction were investigated. The reaction studied was that of p-nitrophenol with sodium hydroxide. The results indicate that temperature does indeed have a significant and predictable effect on the dispersion of a sample plug. Findings agree with the random walk model for flow-injection systems.     

Micelle-sensitized constant-energy synchronous fluorescence spectrometry for the simultaneous determination of pyrene, benzo[a]pyrene and perylene.

The use of micellar media in constant-energy synchronous fluorescence spectrometry has been proposed. The influence of some aqueous micellar systems on the determination of pyrene, perylene and benzo[a]pyrene has been investigated. The presence of these micellar systems allows their determination in aqueous media, thus avoiding the use of an organic solvent, and greatly enhances the fluorescence signals. The combination of a constant-energy synchronous scanning technique and a micellar system provided a single spectrum for the simultaneous identification and quantitative determination of the three polycyclic aromatic hydrocarbons (PAHs). Further there was no energy transfer among them, making the measurement simple and fast. A constant-energy difference of 2800 cm(-1) was selected. The analytical characteristics of the proposed method in the presence of anionic micelles of sodium dodecylsulfate (SDS) were studied. The detection limits were at a level of ng ml(-1). Analysis of water samples from two different origins spiked with known amount of pyrene, perylene and benzo[a]pyrene also gave satisfactory results, and total average recoveries were greater than 97.1%.     

A surfactant type fluorescence probe for detecting micellar growth

We report on the detection of micellar growth in anionic, cationic, and catanionic surfactant systems using a novel surfactant type fluorescence probe, sodium 12-(N-dansyl)amino-dodecanate (12-DAN-ADA). The fluorescent group was incorporated in the tail of the surfactant which tethers the fluorescent group deep inside the apolar micellar cores. The fluorescence anisotropy of 12-DAN-ADA was found to be very sensitive for directly detecting the micellar growth in micelles containing oppositely charged surfactants, including cationic CTAB systems and mixed systems of oppositely charged surfactants (DEAB/SDS); in regard to the like charged SDS micellar systems, the sensitivity can be greatly enhanced by addition of a water soluble quencher which quenches the background fluorescence from the equilibrium population of free 12-DAN-ADA.     

On the Kinetics of Heterogeneous Free Radical Crosslinking Polymerization1)

Abstract

In this paper, two oximato complexes, mononuclear [Cu(Hdmg)₂] and binuclear [Cu₂(Hdmg)₂(H₂dmg)]ClO₄ · H₂O (H₂dmg: dimethylglyoxime), were synthesized and characterized. Hydrolyses of carboxyl acid esters, p‐nitrophenyl picolinate (PNPP) and p‐nitrophenyl acetate (PNPA), catalyzed by these two complexes were investigated in different micellar systems in the pH range from 6.58–8.65 at 25°C. The results obtained indicate that these two complexes exhibit good catalytic function. It also appears that both complexes accelerate the hydrolytic cleavage of PNPP and PNPA in cationic CTAB micellar solution faster than that in nonionic Brij35 micellar solution, which may be due to the different coordinating ability of substrates to complexes and electrostatic interaction between micelles and complexes. For binuclear Cu(II), the rate constant (k _N) for the hydrolysis of PNPA is about two times larger than that for PNPP in CTAB micellar solution, while in Brij35 micellar solution, the k _N values for PNPA and PNPP are roughly the same. This small difference may be ascribed to the configurations of intermediates formed during the reaction and electrostatic interaction between micelles and reactants.     

Micellization and mixed micellization of cationic gemini (dimeric) surfactants and cationic conventional (monomeric) surfactants: Conductometric,dye solubilization,and surface tension studies

In the present study, we have investigated the self-association, mixed micellization, and thermodynamic studies of a cationic gemini (dimeric) surfactant, hexanediyl-1,6-bis(dimethylcetylammonium bromide (16-6-16)) and a cationic conventional (monomeric) surfactant, cetyltrimethylammonium bromide (CTAB). The critical micelle concentration (CMC) of pure (16-6-16 and CTAB) and mixed (16-6-16+CTAB) surfactants was measured by electrical conductivity, dye solubilization, and surface tension measurements. The surface properties (viz., C₂₀ (the surfactant concentration required to reduce the surface tension by 20 mN/m), Π_CMC (the surface pressure at the CMC), Γ_max (maximum surface excess concentration at the air/water interface), A_min (the minimum area per surfactant molecule at the air/water interface), etc.) of micellar (16-6-16 or CTAB) and mixed micellar (16-6-16+CTAB) surfactant systems were evaluated. The thermodynamic parameters of the micellar (16-6-16 and CTAB) and mixed micellar (16-6-16+CTAB) surfactant systems were also evaluated.     

Flow-injection spectrophotometric determination of molybdenum and vanadium with carminic acid in the presence of cetyltrimethylammonium bromide

The color-forming reactions of molybdenum(VI) and vanadium(IV) with carminic acid (CA) in the presence of cetyltrimethylammonium bromide (CTAB) were used in the flow-injection determination of these metals. The micellar medium enhances the spectrophotometric features of the Mo(VI)-CA and V(IV)-CA binary complexes, and the higher solubility of these complexes when the CTAB concentration is above critical micelle concentration permits the easy application of flow-injection systems. Under the optimum conditions, linear calibration graphs were obtained from 0.76 to 28.8 g/ml for molybdenum and from 0.30 to 9.1 g/ml for vanadium. The detection limits were 0.33 and 0.16 g/ml for molybdenum and vanadium, respectively. The selectivity of the method was investigated and the procedure was successfully applied to the determination of molybdenum in steels and pharmaceuticals and of vanadium in petroleum products.     

Determination of vitamins A and E in milk samples by fluorescence in micellar media

The fat-soluble vitamins A and E in milk samples were determined by fluorescence at room temperature in an aqueous media of micellar solutions. Different types of surfactants were studied; the cationic hexadecyltrimethylammonium bromide (CTAB), the anionic sodium dodecylsulfate (SDS) and the non-ionic polyoxyethylene(23)laurylether (Brij 35). The detection limits ranged between 50 and 90 ng.L-1 for both vitamins in CTAB and Brij 35. The method has been applied to the determination of vitamins A and E in milk samples.     

Micellar and Solvent Effects on the Rate of Reaction Between L-Tyrosine and Ninhydrin

Kinetics of the reaction of L-tyrosine and ninhydrin has been studied spectrophotometrically at pH = 5.0 and temperature 80°C in aqueous, aqueous-organic and aqueous cationic micelles of cetyltrimethylammonium bromide (CTAB). The product formed in all the media remains the same. Also, the reaction is catalyzed in both organic solvent and CTAB micellar media. The results obtained in micellar media are treated quantitatively in terms of pseudo-phase model. The rate constants and binding constants with the micelles have been evaluated.