Phase behavior of monoglycerol fatty acid esters in nonpolar oils: reverse rodlike micelles at elevated temperatures

We have studied nonaqueous phase behavior and self-assemblies of monoglycerol fatty acid esters having different alkyl chain lengths in different nonpolar oils, namely, liquid paraffin (LP 70), squalane, and squalene. At lower temperatures, oil and solid surfactants do not mix at all compositions of mixing. Upon an increase in the temperature of the surfactant system, the solid melts to give isotropic single or two-liquid phases, depending on the nature of the oil and the surfactant. All monolaurin/oil systems form an isotropic single-phase liquid, but with a decreasing alkyl chain length of surfactant, they become less lipophilic and immiscible in oils. As a result, a two-phase domain is observed in the oil rich region of all monocaprylin/oil systems over a wide range of concentrations. Judging from the phase diagrams, the surfactants are the least miscible with squalane, and the order of miscibility tendency is squalene > LP 70 > squalane. With a further increase of temperature, the solubility of the surfactant in the oil increases, and the two-liquid phase transforms to an isotropic single phase. This phase transformation corresponds to the reverse of the cloud-point phenomenon observed in aqueous nonionic surfactant systems. Small-angle X-ray scattering (SAXS) measurements show the presence of reversed rodlike micelles in the isotropic single phase, and the length of the aggregates decreases with increasing temperature and increasing alkyl chain length of the surfactant. These results indicate a rod-sphere transformation with increasing lipophilicity of the surfactant and confirms the validity of Ninham's penetration model in the reversed system. An addition of a small amount of water dramatically enhances the elongation of the reverse micelles. Increasing the surfactant concentration or changing the oil from squalene to LP 70 also increases the length of the rodlike aggregates.     

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Spin-inversion dynamics in O₂ binding to a model heme complex, which consisted of Fe(II)-porphyrin and imidazole, were studied using nonadiabatic wave packet dynamics calculations. We considered three active nuclear degrees of freedom in the dynamics, including the motions along the Fe–O distance, Fe–O–O angle, and Fe out-of-plane distance. Spin-free potential energy surfaces for the singlet, triplet, quintet, and septet states were developed using density functional theory calculations, and spin–orbit coupling elements were obtained from CASSCF-level electronic structure calculations. The spin-inversion mainly occurred between the singlet state and one of the triplet states due to large spin–orbit couplings and the contributions of other states were extremely small. The present quantum dynamics calculations suggested that the narrow crossing region model plays a dominant role in the O₂ binding dynamics. In addition, the one-dimensional Landau–Zener model underestimated the nonadiabatic transition probability.     

Palladium(0)-catalyzed tandem cyclization of allenenes: direct construction of tricyclic heterocycles through aromatic C--H activation

Palladium(0)-catalyzed tandem cyclization of allenenes is described. Treatment of allenenes with an aryl halide, potassium carbonate, and catalytic [Pd(PPh(3))(4)] in dioxane afforded tri- or tetracyclic heterocycles in moderate to good yields through insertion of arylpalladium(II) halide into the allenic moiety, intramolecular carbopalladation, and aromatic C--H bond activation. The substituent on the olefin terminus has proven to be essential for the success of the tandem cyclization. The reaction with heterocyclic aryl halides such as iodopyrazine or 4-bromo-1-methylindole afforded tri- or tetracyclic heteroaromatic products in good yields.     

Poly(ethylene glycol)-conjugated phospholipids in aqueous micellar solutions: hydration, static structure, and interparticle interactions

By means of dielectric relaxation spectroscopy (DRS) and small-angle X-ray scattering (SAXS), we have investigated hydration behavior, solvent dynamics, and static structures of aqueous solutions of poly(ethylene glycol)-conjugated distearoyl phosphatidylethanolamine (DSPE-PEG) (molecular weight of PEG: M(PEG)= 2000, 5000, and 12,000 Da). A quantitative analysis of the bulk-water relaxation amplitude revealed the effective hydration number of a DSPE-PEG molecule per ethylene oxide monomer unit to be approximately 5.0-5.5, virtually independent of M(PEG). The overall hydration number of a DSPE-PEG molecule is ca. 20% higher than that of the corresponding normal PEG (without DSPE). This is attributed to both hydration of a charged head group of phosphoric acid in DSPE and a packing effect of PEG chains into micellar structures. The pair-distance distribution functions, p(r), extracted from the GIFT analysis of SAXS intensities show that the DSPE-PEGs form spherical-like micelles in water having the maximum diameter of approximately 16, 22, and 31 nm, respectively, for M(PEG) = 2000, 5000, and 12,000 Da and nearly identical aggregation numbers of 72 (+/-10%). The DSPE-PEG micelles behave as charged colloids whose interparticle interaction potential can be approximated by the screened Coulomb potential model. The extracted pair correlation function g(r) demonstrates that both electrostatic repulsion induced by the charged head group and excluded volume effects of the fully hydrated PEG layer contribute to repulsive interactions among the PEG-lipid micelles. This should be a key factor for the function of PEG lipids as a stabilizer of liposomes.     

Local structure at the air/liquid interface of room-temperature ionic liquids probed by infrared-visible sum frequency generation vibrational spectroscopy: 1-alkyl-3-methylimidazolium tetrafluoroborates

The air/liquid interface of 1-alkyl-3-methylimidazolium tetrafluoroborates with the general formula [C(n)mim]BF(4) (n = 4-11) was studied using infrared-visible sum frequency generation (SFG) vibrational spectroscopy. The probability of the gauche defect per CH2-CH2 bond in the alkyl chain decreases as the number of carbon atoms in the alkyl chain increases. This observation suggests that the interaction between the alkyl chains is enhanced as the alkyl chain length becomes longer. The frequencies of the C-H stretching vibrational modes observed in the SFG spectra are higher than those of the corresponding peak positions observed in the infrared spectra of the bulk liquids. This shift is consistent with a structure in which the alkyl chain protrudes from the bulk liquid into the air. A local structure, which originates from the intermolecular interaction between the ionic liquid molecules, is proposed to explain these observations.     

Small-angle X-ray scattering (SAXS) study on nonionic fluorinated micelles in aqueous system

We have investigated the self-organization structures of perfluoroalkyl sulfonamide ethoxylate, C(8)F(17)SO(2)N(C(3)H(7))(CH(2)CH(2)O)(10)H, a nonionic fluorinated surfactant in aqueous system by small-angle X-ray scattering (SAXS) technique. Structural modulation of the nonionic fluorinated micelle induced by temperature change, surfactant concentration, and the added fluorinated oils have been systematically studied. The SAXS data were analyzed by the indirect Fourier transformation (IFT), and the generalized indirect Fourier transformation (GIFT) depending on the volume fraction of the surfactant. Various plausible classical model calculations have been performed to confirm the consistency of the GIFT analysis of the SAXS data. Upon successive increase in temperature, the cylindrical micelles formed at lower temperatures undergo a continuous one-dimensional growth and ultimately near the cloud point an indication of flat planar like structural pattern is observed. The evolution in structure of particle near the demixing temperature may be due to onset of attractive interactions. The shape and size of the micelle is apparently unaffected by changing the surfactant concentration from 1 to 5 wt% at 25 degrees C. Nevertheless, addition of small amount of perfluoropolyether (PFPE) oil, of structure F(CF(2)CF(2)CF(2)O)(n)CF(2)CF(2)COOH (n approximately 21) modulate the micellar shape and size. Long cylindrical micelles eventually transform into globular like particles. The onset cylinder-to-sphere transition in the structure of micelles in the surfactant/water/oil system is probably due to amphiphilic nature of the oil, which tends to increase the spontaneous curvature. The lipophilic part of the oil tends to reside in the micellar core, whereas, the hydrophilic part goes close to the polar head group of the surfactant so that effective cross-sectional area per surfactant molecules increases and as a result spherical micelles tend to form. Perfluorodecalin (PFD) also decreases size of the micelles but its effect is poor compared to the PFPE oil.     

Determination of phosphate in seawater by CZE with on-line transient ITP

We developed CZE with indirect UV detection for the determination of phosphate in seawater using transient ITP as an on-line concentration procedure. The following optimum conditions were established: BGE, 5 mM 2,6-pyridinedicarboxylic acid (PDC) containing 0.01% hydroxypropylmethylcellulose (HPMC) adjusted to pH 3.5; detection wavelength, 200 nm; vacuum injection period of sample, 3 s (45 nL); terminating ion solution, 500 mM MES adjusted to pH 4.0; vacuum injection period of the terminating ion solution, 30 s (450 nL); applied voltage, 30 kV with the sample inlet side as the cathode. The LOD for phosphate was 16 microg/L (PO(3-)(4) -P) at S/N of 3. The respective values of the RSD of the peak area, peak height, and migration time for phosphate were 2.6, 2.3, and 0.34%. The proposed method was applied to the determination of phosphate in a seawater certified reference material for nutrients, MOOS-1, distributed by the National Research Council of Canada (NRC). The results were very similar to certified values. The method was also applied to the determination of phosphate in coastal seawaters. The results agreed with those obtained using a conventional spectrophotometric method.     

Notable effect of an electron-withdrawing group at C3 on the selective formation of alkylidenecyclobutanes in the thermal denitrogenation of 4-spirocyclopropane-1-pyrazolines. Nonstatistical dynamics effects in the denitrogenation reactions

A detailed study of the thermal denitrogenation of 3-carbomethoxy-substituted 4-spirocyclopropane-1-pyrazolines 6 was conducted. Alkylidenecyclobutane derivatives 7 were selectively formed in a stereospecific manner. Unrestricted density functional calculations for a 1-pyrazoline 10a indicated that the concerted cleavage of two C-N bonds is the energetically favored process for the denitrogenation reaction to give the 2-spirocyclopropyl 1,3-diyl, followed by a conrotatory ring-closure process, which was calculated to be the energy minimum pathway, to afford a spiropentane derivative. The calculated energy minimum pathway is largely inconsistent with the experimental results observed for the denitrogenation of 6 and 10a. The contradiction between the experimental and standard computational results was solved by considering nonstatistical dynamics effects in the concerted denitrogenation reactions. Although the energy minimum pathway from the transition states of the concerted denitrogenation of the 3-carboalkoxy-substituted 1-pyrazolines involves generation of the corresponding 1,3-diradicals, many trajectory calculations using the Bohn-Oppenheimer molecular dynamics model from the transition state for the concerted denitrogenation led directly to the formation of alkylidenecyclobutanes at the UB3LYP/6-31G(d) level of theory.     

Heat Transfer and Particle Behaviours in Dispersed Two-Phase Flow with Different Heat Conductivities for Liquid and Solid

Liquid-solid two-phase flow with heat transfer is directly simulated, to investigate the effects of the ratios of heat conductivities (solid to liquid) and bulk solid volume fraction from dense to dilute situations. The interaction between fluid and particles is solved by our original immersed solid approach on a rectangular grid system. A discrete element method with a soft-sphere collision model is applied for particle-particle and particle-wall interactions. Governing equation of temperature is time-updated with an implicit treatment for the diffusion term, which enables robust simulation with particles of very high/low ratios of heat conductivities (from 1/1000 to 1000) to the fluid. The local heat flux at the fluid-solid interface is modelled by a new flux decomposition technique, and incorporated into the implicit scheme of the temperature. The method is applied to a 2-D particulate flow in a natural convection in a square domain at a relatively low Rayleigh number. In the dense condition, for the cases with high ratios of heat conductivity, the heat transfer is promoted by strong convection, while the particles of low ratios of heat conductivity tend to hinder the development of the temperature rise in the flow field, causing a weak convection and low Nusselt number. Under a condition of relatively low solid volume fraction, fixed particles only depress the heat convection as the number of particles and heat conductivity ratio increase. For the cases with freely-moving particles, on the other hand, heat conductivity of particles has a stronger influence on the heat transfer of the system than the number of particles. The above simulation results highlight the effect of temperature distributions within the particles and liquid.