The Experts below are selected from a list of 111 Experts worldwide ranked by ideXlab platform
Kouichi Nakagawa - One of the best experts on this subject based on the ideXlab platform.
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EPR Investigations of Spin-Probe Dynamics in Aqueous Dispersions of a Nonionic Amphiphilic Compound
Journal of the American Oil Chemists' Society, 2008Co-Authors: Kouichi NakagawaAbstract:Dynamics of various spin probes in aqueous dispersions of nonionic Amphiphilic Compound, [poly(oxyethylene) hydrogenated castor oil, HCO], were investigated by EPR (electron paramagnetic resonance) and saturation recovery (SR) spectroscopies. Partitioning, rotational correlation time (τ_R), rotational diffusion coefficient, and electron spin-lattice relaxation time ( T _1e) in dispersions of the HCO membrane were obtained. The partitioning of water soluble spin probes, DTBN and TEMPO, in the aqueous and vesicle phases was determined by an EPR linewidth simulation as a function of temperature. The results suggest that DTBN and TEMPO have a similar partitioning in the vesicle phase throughout the temperatures studied. The longer τ_R and shorter T _1e (~0.33 μs) values of DTBN in the vesicle phase were obtained, and could be attributed to the probe environment in the membrane. The simulation results for fast tumbling probes were quite different from those of conventional intensity analysis (spectral parameter, f ). Thus, the simulation and T _1e analyses have provided a quantitative understanding of the probe dynamics in both phases. Aliphatic spin probes, doxylstearic acids (DSAs) and 3β-doxyl-5α-cholestane (CHL), were used for monitor of various membrane motions. The EPR spectra were quantitatively analyzed by a slow tumbling simulation. The rotational diffusion coefficients and order parameter were obtained by the simulation. In addition, the direct observations of the behavior of the probes were measured by SR method. The results were consistent with T _1e obtained for spin probes. Thus, the quantitative results regarding EPR, SR method, various simulation analyses have provided detailed information regarding physicochemical properties of the various moieties of the probe region in the Amphiphilic Compound.
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electron spin lattice relaxation times of spin probes in aqueous dispersions of a unique Amphiphilic Compound obtained by a saturation recovery method
Bulletin of the Chemical Society of Japan, 2008Co-Authors: Kouichi NakagawaAbstract:Electron spin-lattice relaxation times (Tie) of a unique nonionic Amphiphilic Compound, (poly(oxyethylene) hydrogenated castor oil, HCO) in aqueous dispersions, were investigated by electron paramagnetic resonance (EPR) and saturation recovery (SR) spectroscopies. The spin probes, 5-doxylstearic acid (5-DSA) and 3β -doxyl-5α -cholestane (CHL), were used to obtain Tie values for the head group region in the HCO membrane. Analysis of SR signals from both probes showed that the Tie value (≈5 μs at 20°C) indicates relatively faster relaxation behavior in the region than that of 12-DSA. No abrupt change (such as phase transition) of the relaxation time was observed in the temperature region studied. Thus, the present Tie results indicate relative flexibility for both probe moieties in the membrane throughout the temperatures studied.
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spin probe investigations of head group behavior in aqueous dispersions of a nonionic Amphiphilic Compound
Lipids, 2007Co-Authors: Kouichi NakagawaAbstract:Head group behavior of nonionic Amphiphilic Compound, (poly(oxyethylene) hydrogenated castor oil, HCO), in aqueous dispersions were investigated by EPR (electron paramagnetic resonance) in conjunction with a modern slow-tumbling simulation. The aliphatic spin probes, 5-doxylstearic acid (5-DSA) and 3β-doxyl-5α-cholestane (CHL), were used to obtain fluidity of the surface region of the membrane. The order parameter (S 0) using the simulation for 5-DSA and CHL in the region were approximately 0.4 and 0.2, respectively. The ordering results suggest that the head group region of the membrane is somewhat fluid. The rotational diffusion coefficients (R ⊥ ≈ 1/(6τR)) for the probes were 3.4 × 107 and 7.1 × 107 s−1, respectively. Activation energies, calculated using the temperature dependence of diffusion coefficients, were 18 and 17 kJ/mol for the probes. The EPR results imply that the CHL probe in the HCO membrane has quite different behavior in comparison with that of PC (phosphatidylcholine) from egg. Thus, the present EPR analyses have provided quantitative insight into the surface region of the Amphiphilic membrane.
D Vollhardt - One of the best experts on this subject based on the ideXlab platform.
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Theoretical description of 2D-cluster formation of nonionic surfactants at the air/water interface
Colloid and Polymer Science, 2015Co-Authors: Yu. B. Vysotsky, E. S. Kartashynska, D VollhardtAbstract:Recent progress in modeling of the surfactant behavior from atomistic to continuous at the air/water interface across different space-time scales is reviewed. Advantages and disadvantages of modern quantum mechanical, molecular dynamical, and mesoscale methods are discussed for description of interactions between Amphiphilic molecules leading to formation of 2D films. The use of nonempirical and semiempirical methods for assessment of the thermodynamic and structural parameters of large van der Waals complexes is of particular interest. An approach for calculation of the thermodynamic and structural parameters of clusterization for nonionic surfactants at the air/water interface is proposed on the basis of the quantum chemical semiempirical PM3 method. This approach implicitly takes into account the influence of the interface on the surfactant molecules via stretching and orienting effect. The calculations are carried out in the supermolecule approximation for a limited number of small Amphiphilic aggregates with different alkyl chain. The correlation analysis of the calculated data array provides the increments contributing by the intermolecular CH · · · HC interactions and interactions between hydrophilic parts into the thermodynamic parameters of formation and clusterization. Obtained increments are further used for constructing the dependencies of the thermodynamic clusterization parameters per one monomer on the alkyl chain length for large clusters up to 2D films. In the framework of the proposed theoretical approach, the next parameters are calculated as follows: enthalpy, entropy, and Gibbs’ energy of clusterization for 11 homologous series of nonionic surfactants, threshold chain length enabling the process of monolayer formation at standard conditions, the “temperature effect” of clusterization, and the structural parameters of the monolayer unit cell (particularly the tilt angle) depending on the size of the hydrophilic headgroup of the Amphiphilic Compound.
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n n alkyl n n dimethylammonioacetic acid bromides the first complete series of crystal and molecular structure determinations of an Amphiphilic Compound with alkyl chain lengths n 1 16
Acta Crystallographica Section B-structural Science, 2000Co-Authors: R Rudert, Burkhard Schulz, Gunter Reck, D Vollhardt, Jorg KriwanekAbstract:The molecular and crystal structures of 16 N-n-alkyl N,N-dimethylammonioacetic acid bromides with chain lengths between n = 1 and n = 16 have been determined. All Compounds from n = 5 to n = 16 form bilayers with interdigitated chains. The even-numbered chains display the chain packing type M2II. The chain packing of the odd-numbered chain Compounds is less regular. The head groups of all Compounds are connected via electrostatic N+⋯Br− interactions, and by OH⋯Br− hydrogen bonds. The Compounds with short chains are packed in different ways. Their molecular conformation depends on the crystal packing.
Jorg Kriwanek - One of the best experts on this subject based on the ideXlab platform.
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n n alkyl n n dimethylammonioacetic acid bromides the first complete series of crystal and molecular structure determinations of an Amphiphilic Compound with alkyl chain lengths n 1 16
Acta Crystallographica Section B-structural Science, 2000Co-Authors: R Rudert, Burkhard Schulz, Gunter Reck, D Vollhardt, Jorg KriwanekAbstract:The molecular and crystal structures of 16 N-n-alkyl N,N-dimethylammonioacetic acid bromides with chain lengths between n = 1 and n = 16 have been determined. All Compounds from n = 5 to n = 16 form bilayers with interdigitated chains. The even-numbered chains display the chain packing type M2II. The chain packing of the odd-numbered chain Compounds is less regular. The head groups of all Compounds are connected via electrostatic N+⋯Br− interactions, and by OH⋯Br− hydrogen bonds. The Compounds with short chains are packed in different ways. Their molecular conformation depends on the crystal packing.
Nelson Marquez - One of the best experts on this subject based on the ideXlab platform.
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thermodynamic parameters of the chromatographic equilibrium distribution process of Amphiphilic Compound by hplc part i fatty acid
Ciencia, 2004Co-Authors: Belgica Bravo, Gerson Chavez, Fredy Ysambertt, Alain Graciaa, J Lachaise, R E Anton, Jeanlouis Salager, Nelson MarquezAbstract:The retention behaviour of fatty acids on a reverse phase HPLC column is reported. Retention increases as the acetonitrile/methanol mobile phase becomes richer in acetonitrile. For a given solvent mixture, retention increases (linearly) with the acid chain length. Retention factor (k) is dimensionless and independent on any geometrical parameters of the column or HPLC system. It could be considered to be a thermodynamic characteristic of the adsorbent-Compound-eluent system. HPLC experiments carried out at different temperatures allow to plot the variation of the ln k vs. 1/T, and to calculate the DG°, DH° and DS° of transfer of one molecule from the mobile phase to the stationary phase. According to a Van’t Hoff expression, the retention decreases as temperature increases. Both DH° and DS° are negative, a result that corroborates that the adsorption of the n-alkyl chains onto the stationary phase is favourable from the energetic point of view, and that it increases the molecular order.
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thermodynamic parameters of the chromatographic equilibrium distribution process of Amphiphilic Compound by hplc part ii nonylphenol polyethoxylated
Ciencia, 2004Co-Authors: Belgica Bravo, Gerson Chavez, Fredy Ysambertt, Ana Caceres, Nelson MarquezAbstract:The oligomer distribution of polyethoxylated surfactants was determined by isocratic normal-phase HPLC on amino column at variable column temperature. As temperature increases, both the absolute retention and selectivity decrease, with a resulting decrease in the separation of the individual oligomers. The effect is correlated with the rising lipophilic character of surfactant species as temperature increases, hence decreasing the interaction with the polar stationary phase. Therefore, the resolution and elution time of the surfactant oligomers can be adjusted by simply changing the temperature. HPLC experiments carried out at different temperatures allow to obtained Van’t Hoff plot, and to calculate the free energy (DG°), enthalpy (DH°) and entropy (DS°) of transfer of one oligomer molecule from the mobile phase to the stationary phase.
Atsushi Yoshizawa - One of the best experts on this subject based on the ideXlab platform.
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liquid crystallinity and biological activity of a novel Amphiphilic Compound
Chemistry Letters, 2009Co-Authors: Atsushi Yoshizawa, Yuuka Takahashi, Rie Terasawa, Shota Chiba, Kenji Takahashi, Masaharu Hazawa, Ikuo KashiwakuraAbstract:We have designed an Amphiphilic Compound in which phenylpyrimidine and D-glucamine are connected via a flexible spacer. The Compound shows two thermotropic lamellar bilayer mesophases with differen...
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Phase Transition Behaviour of Amphiphilic Supermolecules Possessing a Semiperfluorinated Alkyl Chain
Molecular Crystals and Liquid Crystals, 2007Co-Authors: Akihisa Yamaguchi, Atsushi YoshizawaAbstract:Recently we have found that a novel Amphiphilic Compound, 1H, 1H, 2H, 2H-heptadecafluoro-1-decyl 3, 4, 5- tris[6-(4′-cyanobiphenyl-4-yloxy)hexyloxy]benzoate, exhibited the phase sequence of isotropic liquid -smectic A-bicontinuous cubic-crystal. In this study, we have prepared Compounds possessing biphenyl groups or alkyl chains instead of the cyanobiphenyl groups of the Amphiphilic Compound and investigated their liquid-crystalline properties using optical microscopy and differential scanning calorimetry. The Compound possessing the biphenyl groups was found to exhibit a columnar phase, however, the Compound possessing the alkyl chains did not show any liquid-crystalline phase. We discuss the structure-property relationship in the Amphiphilic oligomers.
