Heptaethylene Glycol Research Articles

Phase Behavior of Heptaethylene Glycol Dodecyl Ether and Its Aqueous Mixture Revealed by DSC and FT-IR Spectroscopy

The phase behavior of heptaethylene glycol dodecyl ether (C12E7) and its aqueous mixture was investigated by means of differential scanning calorimetry (DSC) and Fourier transform infrared (FT-IR) spectroscopy in the temperature range from −20 to 70 °C. Phase boundaries among various phases including mesomorphic phases were determined on the basis of DSC thermograms, from which the binary phase diagram of this mixture system was constructed. According to the phase diagram, the mixture with the composition of 31 wt % H2O exhibits the following phase sequence with increasing temperature: solid → H1 (normal hexagonal) → V1 (normal bicontinuous-type cubic) → Lα (lamellar) → liquid. FT-IR measurements for the mixture with this composition revealed the following features concerning the conformational structure of the C12E7 molecule and the interaction between the surfactant and D2O in each phase. In the solid phase, the polyoxyethylene (POE) chain of the surfactant molecule has a rather extended structure with a trans-rich conformation, in contrast to the case of pure C12E7, in which a helical structure is dominant. When the solid phase transforms to the H1 phase, the hydrogen-bond interaction between C12E7 molecules and between C12E7 and water are both weakened, and the fraction of gauche-conformer in the POE chain increases, whereas the alkyl chain adjacent to the POE chain remains, taking a rather trans-zigzag conformation. The enhanced fraction of gauche-conformer in the POE chain suggests that the POE chain has a helical structure in this phase. The increase in temperature within the H1 region causes a conformational change in both the POE chain and the alkyl chain of the surfactant to a more disordered structure. Among the phases of V1, Lα, and liquid, no significant difference is seen in the conformational structure and interaction with water molecules of the surfactant.

Inclusion of Poly(ethylene glycol)s by Crystalline (R)-(1-Naphthyl)glycyl-(R)-phenylglycine

Crystallization of (R)-(1-naphthyl)glycyl-(R)-phenyl-glycine [(R,R)-1] in the presence of oligo(ethylene glycol) dimethyl ethers 2(n) or poly(ethylene glycol)s (PEGs, 3(Mn )) afforded inclusion compounds. The ratio of (R,R)-1/the guest polymer (2 or 3) was proportional to the length of the polymer chain. The crystal structure of a hepta(ethylene glycol) dimethyl ether-included compound was disclosed by X-ray crystallography which showed that (R,R)-1 molecules form a sheet and the guest molecule penetrates the crystal lattice of (R,R)-1 through a one-dimensional channel on the sheet. Powder X-ray analysis revealed that, regardless of the length of the guest polymer, the distance between the neighboring sheets remains unchanged (12.0–12.3 Å) in these inclusion crystals. By thermal analysis, it was shown that the decomposition points of these inclusion compounds became higher with the longer PEG included. The inclusion phenomenon enabled the fractionation of PEGs with various molecular weights, among which longer PEG was preferably included.

Correlation of Membrane/Water Partition Coefficients of Detergents with the Critical Micelle Concentration

The membrane/water partition coefficients, K, of 15 electrically neutral (non-charged or zwitterionic) detergents were measured with phospholipid vesicles by using isothermal titration calorimetry, and were compared to the corresponding critical micellar concentrations, cmc. The detergents measured were oligo(ethylene oxide) alkyl ethers (C mEO n with m = 10/ n = 3, 7 and m = 12/ n = 3…8); alkylglucosides (octyl, decyl); alkylmaltosides (octyl, decyl, dodecyl); diheptanoylphosphatidylcholine; Tritons (X-100, X-114) and CHAPS. A linear relation between the free energies of partitioning into the membrane and micelle formation was found such that K · CMC ∼ 1. The identity K · CMC = 1 was used to classify detergents with respect to their membrane disruption potency. “Strong” detergents are characterized by K · CMC < 1 and solubilize lipid membranes at detergent-to-lipid ratios X b < 1 (alkylmaltosides, tritons, heptaethylene glycol alkyl ethers). “Weak” detergents are characterized by K · CMC > 1 and accumulate in the membrane- to detergent-to-lipid ratios X b > 1 before the bilayer disintegrates (alkylglucosides, pentaethylene glycol dodecyl ether).

Evolutionary behaviour of miniemulsion phases: II. Growth mechanism of miniemulsion droplets

The growth mechanism of droplets of hexadecane-in-water emulsions stabilized by heptaethylene glycol mono-n-dodecyl ether was studied by means of photon correlation spectroscopy. When the water-to-oil ratio (WOR) was varied from 4 to 10, a translucent oil in water emulsion (a so-called `miniemulsion') was obtained, while an opaque oil in water emulsion (O/W emulsion) was prepared when WOR was equal to 3. The z-average hydrodynamic radius of droplets, rz, was measured over the 24 days after preparation. Plotting the cube of the z-average radius as a function of time, we found that r 3z varies linearly with time in the system of the O/W emulsion (WOR = 3). This suggests that the process by which the droplets grow is that of Ostwald ripening. On the other hand, the same plot for the system of miniemulsions (4 < WOR < 10) shows two regimes in the process. In both regimes, r 3z varies linearly with time. The rate obtained for the earlier stage is smaller than that of the latter stage. The droplet size distribution became too broad compared with the prediction of Lifshitz-Slezov-Wagner theory for Ostwald ripening ~10 days after preparation. Then it approached the predicted distribution again ~20 days after preparation.

Evolutionary behaviour of miniemulsion phases: I. Hard sphere interaction and bound water on miniemulsion droplets

The interaction between nano sphere droplets in translucent oil in water (O/W) emulsion phases, so-called miniemulsion phases, was investigated by using light scattering measurement techniques. We choose the ternary system of water/hexadecane/Mergital LT7 (the main component is heptaethylene glycol mono-n-dodecyl ether). Rayleigh ratio measurement was performed with changing dispersed phase volume fraction ´, and it revealed the fact that the osmotic compressibility is in good agreement with that of a hard sphere fluid. The dependence of the collective diffusion coefficients, measured by dynamic light scattering experiments, is similar to those observed in colloidal hard sphere suspensions. We found out that the ratio of the hydrodynamic diameter to the hard sphere diameter is 1.19 and the volume fraction of dispersed droplets is given by = 1.35´. Preparing miniemulsions with various water to oil ratios, it was revealed that the ratio /´ was varied from 1.01 to 1.33. This indicates that the underestimation of the total volume of droplets calculated by the sum of surfactant and oil volume was not negligible. It is therefore considered that the volume fraction of bound water on miniemulsion droplets should be taken into account. We briefly discuss the idea that bound water plays an important role in obtaining a homogeneous miniemulsion phase.

Structural analysis of metal-surface protect surfactants by tandem mass spectrometry.

The applicability of tandem mass spectrometry to the quality analysis of metal-surface protect surfactants without any pretreatment or purification of the sample solution was investigated. Three typical spectra were constructed and verified by FAB CID-MS/MS using sodium n-dodecylsulfate (anionic surfactant), tetradecyl dimethylbenzylammonium chloride (cationic surfactant) and heptaethylene glycol mono-n-dodecyl ether (nonionic surfactant) as a model. The FAB CID-MS/MS spectra of metal-surface protect surfactants provided useful structural information that analyte surfactants have a polyoxyethylene structure, which has been identified as a nonionic surfactant. The authors concluded that FAB CID-MS/MS will be a good analytical method for direct quality analysis without any pretreatment or purification of the metal-surface protect surfactant for industrial use.

Surface Potentials of Mixed Micelles Composed of Arachidonic Acid and Heptaethylene Glycol Dodecyl Ether

The surface potentials (Δψ) of the mixed micelles composed of arachidonic acid (AA) and nonionic heptaethylene glycol dodecyl ether (HED) were estimated at 25 and 60°C by measuring the fluorescence intensity of 8-anilino-1-naphthalenesulfonate (ANS) as a fluorescent probe. The surface potentials of AA-HED mixed micelles, |-Δψ|, increased with increasing mole fraction of AA (XAA), and decreased with increasing ionic strength (I). These changes are due to the effects of the negative charge of AA and of the ionic atmosphere of Na+, respectively. The surface charge density (σ) was nearly independent of I and proportional to XAA, indicating that the surface state of AA-HED mixed micelles is represented by the Gouy-Chapman theory. The absolute value of σ for AA-HED mixed micelles at 60°C was slightly decreased as compared with that at 25°C.

Tuning micelles of a bioactive heptapeptide biosurfactant via extrinsically induced conformational transition of surfactin assembly.

We have studied the effects of extrinsic environmental conditions on the conformation of surfactin, a heptapeptide biosurfactant from Bacillus subtilis, in aqueous solutions. It has been made clear that temperature, pH, Ca2+ ions and the synthetic nonionic surfactant hepta-ethylene glycol (C12E7) affect the conformation of surfactin in aqueous solutions. The beta-sheet formation reached a maximum at 40 degrees C both in presence and absence of (C12E7) and the nonionic surfactant enhances the beta-sheet formation even at 25 degrees C. Ca2 + induced the formation of alpha-helices and caused this transition at 0.3 mM with surfactin monomers or at 0.5 mM with surfactin micelles, but above these transition concentrations of Ca2+ beta-sheets were observed. In micellar solution the beta-sheet structure was stabilized at pH values below 7 or upon addition of Ca2+ in concentrations above 0.5 mM. Our results indicated that the bioactive conformation of surfactin is most likely the beta-sheets when the molecules are assembled in micelles. The beta-sheet structure in micelles could be retained by tuning the micelles. Surfactin micelles could be tuned in the bioactive conformation by manipulating pH, temperature, Ca2+ or (C12E7) concentrations in surfactin solutions. Our results strongly indicated that Ca2+ and other molecules (such as C12E7) may function as directing templates in the assembly and conformation of surfactin in micelles. Thus, we suggest environmental manipulation and template-aided micellation (TAM) as a new approach for preparing predesigned micelles, microemulsions or micro-spheres for specific application purposes.

Tuning micelles of a bioactive heptapeptide biosurfactant via extrinsically induced conformational transition of surfactin assembly.

We have studied the effects of extrinsic environmental conditions on the conformation of surfactin, a heptapeptide biosurfactant from Bacillus subtilis, in aqueous solutions. It has been made clear that temperature, pH, Ca2+ ions and the synthetic nonionic surfactant hepta-ethylene glycol (C12E7) affect the conformation of surfactin in aqueous solutions. The beta-sheet formation reached a maximum at 40 degrees C both in presence and absence of (C12E7) and the nonionic surfactant enhances the beta-sheet formation even at 25 degrees C. Ca2 + induced the formation of alpha-helices and caused this transition at 0.3 mM with surfactin monomers or at 0.5 mM with surfactin micelles, but above these transition concentrations of Ca2+ beta-sheets were observed. In micellar solution the beta-sheet structure was stabilized at pH values below 7 or upon addition of Ca2+ in concentrations above 0.5 mM. Our results indicated that the bioactive conformation of surfactin is most likely the beta-sheets when the molecules are assembled in micelles. The beta-sheet structure in micelles could be retained by tuning the micelles. Surfactin micelles could be tuned in the bioactive conformation by manipulating pH, temperature, Ca2+ or (C12E7) concentrations in surfactin solutions. Our results strongly indicated that Ca2+ and other molecules (such as C12E7) may function as directing templates in the assembly and conformation of surfactin in micelles. Thus, we suggest environmental manipulation and template-aided micellation (TAM) as a new approach for preparing predesigned micelles, microemulsions or micro-spheres for specific application purposes.

Phase Behavior of Binary Mixture of Heptaethylene Glycol Decyl Ether and Water: Formation of Phase Compound in Solid Phase

Differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR) were used to construct and characterize the phase diagram for a binary mixture of heptaethylene glycol decyl ether (C10E7) and water in the temperature range from −60 to 80°C. Plots of the endothermic peak temperatures obtained by DSC measurements against compositions provided eutectic solid–liquid phase boundaries with a eutectic composition of 34 wt% of H2O. On the other hand, heat of fusion per unit weight of the mixture changed discretely at the composition corresponding to the “eutectic” composition. Furthermore, the IR spectra obtained for the mixture in the solid phase were well reproduced as a superposition of those for the mixture of 34 wt% H2O and pure components but were not reproduced by superimposing the spectra obtained for the solid surfactant and ice. These observations indicate that a solid phase compound is formed between C10E7and water with a stoichiometry of 1:14 and that the compound and pure components exist as separate phases, rather than the phases separating into surfactant and ice, which would be expected if the C10E7/water mixture formed a true eutectic mixture system. It is estimated from the composition corresponding to the phase compounds that two molecules of water per oxyethylene unit are bound to hydrophilic polyoxyethylene chain of C10E7to form a hydrated compound.

Effects of Surfactants on Solvolysis of p-Nitrophenyl Alkanoates Catalyzed by 4-(Dialkylamino)pyridine-Functionalized Polymer in Aqueous Methanol Solution

Catalysis of the solvolysis of p-nitrophenyl alkanoates 2 (n = 2-18) by 4-(dialkylamino)pyridine-functionalized polymer 1 in the presence of sodium n-dodecyl sulfate (SDS), n-dodecyltrimethylammonium bromide (DTAB), and heptaethylene glycol n-dodecyl ether (HEGDE) was investigated in 50:50 (v/v) methanol-water buffer (0.05 M H 2 PO 4 - /HP0 4 2- , pH 8.0) solution. Strikingly, a large rate enhancement is observed in the presence of anionic surfactant SDS for the solvolysis of 2 (n = 10-18) as compared with the corresponding reaction catalyzed by 1 or SDS alone. SDS is believed to bind both substrate and catalyst within micellar aggregates and influence reactivity by a combination of catalyst-substrate proximity and micellar microenvironment. In the presence of HEGDE, no significant effects on the 1-catalyzed solvolysis of 2 (n < 8) were observed. At (2.5-7.5) x 10 -5 unit mol L -l 1, the solvolysis rate exhibits a modest decrease for 2 (n = 10 and 12) and a modest increase for 2 (n = 14, 16, and 18) with added nonionic surfactant HEGDE. The solvolysis rate for 1-catalyzed solvolysis of 2 (n = 2 -18) was found to be unchanged by cationic surfactant DTAB in aqueous methanol solution.

Surface Potential of Mixed Micelles Composed of Dibucaine Hydrochloride and Heptaethylene Glycol Dodecyl Ether.

The surface potential (Δψ) of the mixed micelles composed of dibucaine hydrochloride (DC) and nonionic heptaethylene glycol dodecyl ether (HED) has been estimated by measuring the fluorescence intensity of ammonium 8-anilino-1-naphthalenesulfonate (ANS) as a fluorescent probe. The value of +Δψ increases with an increasing mole fraction of DC (XDC) and decreases with increasing ionic strength (I). These changes are due to the effects of the ositive charge of DC and of the ionic atmosphere of Cl-, respectively. Surface charge density (σ) was, therefore, determined from Δψ according to the Gouy-Chapman theory, with a results that σ is nearly independent of I and proportional to XDC. These results have led to a conclusion that the state of the diffuse layer surrounding the Stern layer at the micelle surface is represented well by the Gouy-Chapman theory.

Structural Chemistry of Poly(ethylene glycol) Complexes of Lead(II) Nitrate and Lead(II) Bromide.

The reaction of 1:1 stoichiometries (1:1.5 for the nitrate/tetraethylene glycol (EO4) and pentaethylene glycol (EO5) complexes) of PbX(2) (X = NO(3), Br) with five- to eight-donor poly(ethylene glycols) (PEGs) in 3:1 CH(3)CN/CH(3)OH (CH(3)CN only for the nitrate/EO5 complex) followed by solvent evaporation resulted in six crystalline materials upon which X-ray structural analyses were carried out: [Pb(NO(3))(2)(EO4)](n)(), [Pb(NO(3))(2)(EO5)], [Pb(NO(3))(2)(EO6)], [PbBr(EO5)(&mgr;-Br)PbBr(2)].H(2)O, [PbBr(NCMe)(EO6)](2)[PbBr(2)(EO6)][PbBr(3)](2), and [PbBr(EO7)][PbBr(3)]. The nitrates crystallize as tight ion pairs with the PEG ligands coordinating in an equatorial plane around the Pb(2+) ions. Because EO4 has only five oxygen donors, this complex exhibits steric unsaturation which is overcome by a monodentate interaction with a third nitrate anion that is also coordinated to a neighboring Pb(2+) ion. The six donors of EO5 coordinate in an equatorial plane resulting in a 10-coordinate complex with trans, twisted, bidentate nitrate anions. The seven-donor hexaethylene glycol (EO6) only uses six of its oxygen donors to coordinate Pb(2+). [Pb(NO(3))(2)(EO4)](n)() is monoclinic, P2(1)/c, with a = 7.902(3) Å, b = 22.136(6) Å, c = 8.910(2) Å, beta = 90.96(3) degrees, and Z = 4. [Pb(NO(3))(2)(EO5)] is triclinic P&onemacr;, with a = 9.332(3) Å, b = 10.025(3) Å, c = 11.688(4) Å, alpha = 68.41(3) degrees, beta = 68.39(3) degrees, gamma = 68.58(3) degrees, and Z = 2. [Pb(NO(3))(2)(EO6)] is monoclinic P2(1)/c, with a = 16.289(4) Å, b = 10.773(4) Å, c = 12.329(4) Å, beta = 106.77(2) degrees, and Z = 4. Lead(II) bromide complexes with PEGs tend to crystallize as PEG complexed cations with polymeric lead(II) bromide anions. In the EO5 complex, bromide anions in the polymer also coordinate to the PEG-wrapped Pb(2+) cations. The hexa- and heptaethylene glycol (EO6 and EO7, respectively) complexes contain discreet ions. In these halide complexes, EO7 is the only PEG to expand the Pb(2+) coordination number from eight to nine. [PbBr(EO5)(&mgr;-Br)PbBr(2)].H(2)O is triclinic P&onemacr;, with a = 7.922(6) Å,b = 15.802(9) Å, c = 19.001(9) Å, alpha = 73.19(8) degrees, beta = 88.91(9) degrees, gamma = 87.22(9) degrees, and Z = 4. [PbBr(NCMe)(EO6)](2)[PbBr(2)(EO6)][PbBr(3)](2) is monoclinic P2(1)/c, with a = 14.389(4) Å, b = 31.931(9) Å, c = 8.029(2) Å, beta = 97.76(3) degrees, and Z = 2. [PbBr(EO7)][PbBr(3)] is monoclinic Cc, with a = 13.165(3) Å, b = 24.732(5) Å, c = 8.007(1) Å, beta = 94.58(2) degrees, and Z = 4.

Effects of ?-tocopherol and its acetate on the hydrolytic activity of phospholipase D in egg yolk phosphatidylcholine bilayers

Effects of α-tocopherol (Toc) and α-tocopherol acetate (TocA) on the hydrolysis activity of phospholipase D (fromStreptomyces chromofuscus) were studied in small unilamellar vesicles (SUV) of egg yolk phosphatidylcholine (PC). Choline produced in the reaction was monitored by use of a choline oxidase — oxygen electrode. Addition of 18 mol% Toc into SUV (2 mM PC) brought about a twofold rate of choline production. On the other hand, the effect of 18 mol% TocA in SUV was very small. The apparent maximum velocity,Vmax(app), increased by addition of Toc in SUV. The apparent Michaelis constant,Km(app), was unchanged by addition of Toc and TocA in SUV. The Toc and TocA molecules did not have significant effects when PC was solubilized in the micelles of heptaethylene glycol dodecyl ether. The effects of Toc and TocA are, therefore, not due to specific ones on the enzyme itself, but rather upon the bilayer-organization of the substrate. Measurements of spreading pressure showed complete miscibility of PC and Toc, and limited mutual solubility of PC and TocA, suggesting stronger attractive interactions between Toc and PC than those between TocA and PC in the bilayers.

Effects of 1,2-diacylglycerol and cholesterol on the hydrolysis activity of phospholipase D in egg-yolk phosphatidylcholine bilayers

Effects of cholesterol (Chol) and 1,2-diacylglycerol (DAG) on the hydrolysis activity of phospholipase D (from Streptomyces chromofuscus) were studied in small unilamellar vesicles (SUV) of egg-yolk phosphatidylcholine (PC). 1,2-Diacylglycerol used here is derived from PC. Choline produced in the reaction was monitored by using a choline oxidase-oxygen electrode. Addition of 18.3 mol% Chol into SUV (2 mM PC) led to a small increase in the reaction rate. On the other hand, 18.3 mol% DAG in SUV brought about at 5–6-fold rate of choline production. The apparent maximum velocity, V max(app), increased by addition of DAG and Chol in SUV. In PC/Chol-SUV, the effect of increase in V max(app) was largely compensated by the increase in the apparent Michaelis constant, K m(app). The Chol and DAG molecules did not have significant effects on the kinetic parameters, when PC was solubilized in the micelles of heptaethylene glycol dodecyl ether. The effects of Chol and DAG are, therefore, not due to specific ones on the enzyme itself, but rather upon the bilayer-organization of the substrate. We discuss the activation of phospholipase D in terms of the influences of DAG and Chol on the structure of hydrophilic region and fluidity of the bilayers.

Ionic features in free liquid films of non-ionics

The thickness of thin liquid films stabilized by heptaethylene glycol mono n-dodecyl ether (C 12E 7) is measured as a function of NaCl concentration. This thickness passes through a maximum at around 1 M, similar to what has been found with other non-ionic surfactants. In films stabilized by a mixture of C 12E 7 and sodium dodecyl sulfate (SDS) or cetyl trimethyl ammonium chloride (CTAC), the maximum is much less pronounced, and there appears an enhanced thickness at lower NaCl concentration. We have extended the self-consistent field lattice theory of Böhmer, Evers and Scheutjens for the adsorption of polyelectrolytes to liquid films stabilized by a mixture of non-ionic and ionic surfactants. This theory accounts for the presence of electric fields and for the excluded volumes of surfactant segments and ions. In this way, the thickness of the double layer is increased and, therefore, the enhanced thickness at low salt concentration can be explained by electrostatic repulsion. When the thickness of the mixed film is corrected for this repulsion, the result of pure C 12E 7 films is retrieved, re-establishing the effect of electrolytes on non-ionic surfactants. The maximum at high salt concentration for non-ionic films in the absence of ionic additives cannot be explained in this way. We suggest an explanation for this maximum in terms of contributions of monolayer fluctuations leading to an additional repulsion that is dependent on the salt concentration.

Surface Potential of Mixed Micelles Composed of Prostaglandin B2 and Heptaethylene Glycol Dodecyl Ether by the Fluorescence Method

Abstract The surface state of negatively charged mixed micelles prepared by addition of prostaglandin B2 (PGB2) to nonionic heptaethylene glycol dodecyl ether (HED) has been investigated and the surface potential (Δψ) of the micelles has been estimated by measuring the fluorescence intensity of ammonium 8-anilino-1-naphthalenesulfonate (ANS) as a fluorescent probe. Since the binding constant of ANS, k, is dependent on the surface potential of the micelle, the value of Δψ was determined according to the equation Δψ=−59.16log(k0⁄k) at 25°C, where k0 is the k of HED micelle. The value of |−Δψ| increases with increasing mole fraction of PGB2 (XPGB2) and decreases with increasing ionic strength (J). These changes are due to the effects of the negative charge of PGB2 and of ionic atmosphere of Na+, respectively. Surface charge density (σ) was, therefore, determined from Δψ according to the Gouy-Chapman theory, with a result that σ is nearly independent of J and proportional to XPGB2. These results have led to a conclusion that the state of the diffuse layer surrounding the Stern layer on the micelle surface is represented well by the Gouy-Chapman theory as well as a previous result for the system of sodium dodecyl sulfate (SDS) and HED. The value of |−σ| for PGB2 micelle is less than that for SDS micelle, which suggests that PGB2 forms a loosely packed micelle.

Effects of surfactants on the rate of thinning of the dimple between a horizontal glass plate and an air bubble in water

We in investigated the effects of sodium dodecyl sulfate (SDS) on the rate of thinning of the dimple formed between an air bubble and a glass plate horizontally immersed in water. The activation energy of thinning of the dimple increases with increasing concentration of SDS and flattens in the saturated adsorption region. The increment may be regarded as the activation energy of the surface flow. Addition of dodecanol to the saturated adsorption surface of SDS results in further increase in activation energy. The Arrhenius equation does not hold for these cases but should be transformed to k = A′ exp(−ΔH ‡/RT + ΔS ‡/R , where ΔH ‡ and ΔS ‡ are the activation enthalpy and entropy of thinning of the dimple, respectively, and the latter was estimated from the data for dodecanol. The electrical force acting between glass and bubble surfaces is rather smaller in SDS solutions in potassium chloride solutions because of the compensation of the ionic strength effect by the surface charge effect. It may be conclude that ΔH ‡ would be contributed by the surface shear viscosity but not by the surface area viscosity, because a nonionic surfactant, heptaethylene glycol dodecyl, has no effect on ΔH ‡ .

Measurement of the critical micelle concentration of nonionic surfactants by the first derivative absorption spectrum method.

The absorption maximum of a drug in surfactant solution often shifts at surfactant concentrations above the critical micelle concentration (cmc). The first derivative absorption spectrum (FDAS) was used to evaluate the wavelength shift and to measure the cmc of surfactants.The cmc's of heptaethylene glycol dodecyl ether (HED), octaethylene glycol dodecyl ether (OED) and sodium dodecyl sulfate (SDS) obtained by the FDAS method were 1.2×10-4, 1.4×10-4 and 7.6×10-3 M, respectively. These cmc values were higher than those obtained by the surface tension method (the Wilhelmy plate method) because of the difference of the positions where the values were estimated on the curve (see text). In the measurement of cmc by the FDAS method, less sample and a shorter time are needed, and the reproducibility of this method is satisfactorily high. Though the FDAS method can be utilized for ionic and nonionic surfactants, it is particularly effective for nonionic surfactants, while the previous methods for cmc measurement of nonionic surfactant are generally cumbersome and time-consuming.It was found that the degree of shift-length increased with increasing alkyl chain length of alkylparabens (or alkyl gallates). Therefore, it seems that the use of alkylparabens (or alkyl gallates) of greater alkyl chain length is most convenient in the determination of cmc values by the FDAS method.

Effects of EDTA Derivatives on the Photoreduction of Methyl Viologen by a Thiacarbocyanine Sensitizer in a Micellar Solution

Abstract The photoinduced reduction of Methyl Viologen (MV2+) by ethylenediaminetetraacetate (EDTA), 1,2-propanediamine-N,N,N′,N′-tetraacetate (MeEDTA), and trans-1,2-cyclohexanediamine-N,N,N′,N′-tetraacetate (CyDTA) was investigated by using 3,3′-dioctadecylthiacarbocyanine (C18–18+) as a sensitizer in a micellar solution of a nonionic surfactant, heptaethylene glycol monododecyl ether. The production rate of reduced Methyl Viologen (MV+·) decreased with the light-irradiation time, while the deceleration increased in the order of: CyDTA&amp;lt;MeEDTA&amp;lt;EDTA. The concentration of the EDTA derivatives at the micellar surface was estimated to be in the order of EDTA&amp;lt;MeEDTA&amp;lt;CyDTA, this difference in the concentration being attributed to such hydrophobic groups as methyl group and cyclohexane ring in the EDTA-derivative molecules. The high concentration of the EDTA derivatives at the surface accelerated the reaction of the sensitizer divalent cation radical (C18–182+·) with the EDTA derivatives, prevented the consumption of MV+· through the back reaction of C18–182+· with MV+·, and facilitated the efficient photoproduction of MV+·. It was demonstrated that the hydrophobic interaction between the EDTA-derivative molecules and the micellar surface is an important factor in determining the efficiency of the photoinduced MV+· production.