[The Configuration of Tadalafil and Tadalafil Analogues Found in Dietary Supplements].

This study determined the configuration of the isomers of tadalafil, nortadalafil, and homotadalafil in dietary supplements. The products purchased over the Internet studied included a honey product and a tablet, which contained tadalafil, and a candy, which contained nortadalafil and homotadalafil. Each of the pharmaceutical ingredients isolated from the products was measured with circular dichroism (CD).As a result, the CD spectrum of each isolated pharmaceutical ingredient was found to align with the standard CD spectrum of the 6R,12aR isomer, confirmed that each isolated tadalafil or tadalafil analogue included in a 6R,12aR isomer. According to a report, among the stereoisomers of tadalafil, the 6R,12aR isomers have the most potent inhibitory activities of phosphodiesterase-type-5. From the report, the potential strength of the inhibitory activity of the 6R,12aR isomers of nortadalafil and homotadalafil was suggested. Therefore, it seemed that the 6R,12aR isomer often used in the product.

Rapid Determination of Preservatives in Cosmetics Using a Core-Shell Column.

Preservatives are frequently added to cosmetics to maintain product quality. Our laboratory quantifies 11 preservatives in cosmetics each year for regulatory purposes. In laboratories, many manufactures also analyze the preservatives in their products for quality control. To analyze many cosmetic samples, a rapid analysis method is required for efficiency. In this study, we developed a rapid method for the simultaneous determination of 11 regulated preservatives in cosmetics using a core-shell column by high-performance liquid chromatography. In this method, the 11 preservatives were separated within 17 min, which was approximately half the time reported in the previous study. The peak resolution for each preservative was >2.6, the correlation coefficients of the calibration curves were >0.9988, the percent recoveries were 92.0-111.9% and the relative standard deviations were <3.5% (n = 3). The relative standard deviations among 6 researchers were <4.7%. Thus, it is an effective rapid determination method for the analysis of preservatives in cosmetics.

Surface dilatational moduli of poly(vinyl acetate) (PVAc) and PVAc-poly(n-hexyl isocyanate) (PHIC) blend films at the air-water interface.

Surface dilatational moduli of poly(vinyl acetate) (PVAc) film and blend films of PVAc and poly(n-hexyl isocyanate) (PHIC) were measured at the air-water interface. PVAc formed a film that was looser and also more stable against strain than the PHIC film. The apparent surface dilatational modulus and surface pressure of the blend films were superimposed on the lower concentration of PVAc, irrespective of the composition of PVAc. However, the additivity rule was not applicable to the apparent surface dilatational modulus and surface pressure. The scaling exponents of the apparent surface dilatational modulus against the added surface concentration decreased with an increase in the proportion of PVAc, suggesting that blend films gradually change from glass material to expanded films.

Stabilities and rheological properties of coagulated silica sols formed from fumed silica suspensions in the presence of hexadecyltrimethylammonium chloride.

The stability and rheological response of coagulated silica sols formed from fumed silica suspensions were investigated in aqueous KOH solution at pH 11 upon the addition of hexadecyltrimethylammonium chloride (C(16)TAC) as functions of silica and surfactant concentration. The coagulated silica sols with negative charges are stable at given concentration ranges of silica and C(16)TAC, and the C(16)TAC molecules are completely adsorbed on the silica surface in these ranges. The average hydrodynamic diameters of the coagulated silica colloidal sols at C(16)TAC concentrations from 1.0 x 10(-4) to 5.0 x 10(-4) M are almost twice the diameter observed in the absence of C(16)TAC, independent of silica concentration. At C(16)TAC concentrations below 4.0 x 10(-4) M, the resulting coagulated colloidal sols showed Newtonian responses under hysteresis loop measurements, whereas at above 5.0 x 10(-4) M, the flow curve changes from a positive hysteresis loop to a crossover hysteresis loop with increasing concentration. This change under shear flow is due to a partial breakdown of the coagulated structure of the fumed silica suspensions as a result of electrical neutralization. Finally, the coagulated colloidal sols which gave a crossover hysteresis loop present a shear-thinning behavior and their transit shear stresses exhibit overshoots whatever the shear rate used. Plots of the resulting steady-state viscosities against shear rate indicate shear-thinning behavior.

Molecular weight dependence of surface dilatational moduli of poly(n-hexyl isocyanate) films spread at the air-water interface.

The surface dilatational modulus of the monolayer of a well-known semiflexible polymer, poly(n-hexyl isocyanate) (PHIC), at the air-water interface was measured as a function of the molecular weight of PHIC. In the dilute regime, the surface dilatational modulus of PHIC showed a linear response over a measured strain range of 5%-20%. The modulus could be well-separated into the elastic component E' and the viscous component E'', irrespective of molecular weight of PHIC. The E' and E'' components, respectively, are mainly attributed to static compression modulus caused by a change in the area covered by the PHIC monolayer and the semiflexibility of the PHIC chain. In the semidilute regime, the surface dilatational modulus of PHIC showed a nonlinear response to even 1% of strain due to the semiflexibility of the PHIC chain. Moreover, the surface dilatational modulus of PHIC depended on its molecular weight: at the smaller strain, the surface dilatational modulus of the high molecular weight PHIC was larger than that of the low molecular weight PHIC. The surface dilatational modulus of the high molecular weight PHIC increased with the surface concentration, whereas that of the low molecular weight PHIC remained constant. The molecular weight dependence in the semidilute regime is caused by the difference in chain entanglement between the high and low molecular weight PHICs at the air-water interface.

Molecular weight dependence of LB morphology of poly(n-hexyl isocyanate) (PHIC).

The morphologies of Langmuir-Blodgett (LB) films of two fractionated poly(n-hexyl isocyanate) (PHIC) and those of their binary mixtures were observed by AFM, together with those of an unfractionated PHIC. The low molecular weight PHIC formed random packing of bundles consisting of rigid rods, while the high molecular weight PHIC formed random packing of bundles consisting of hairy rods. Bundle interpenetration was observed only for the latter in the semidilute regime. In the bilayer region, the area occupied by the PHIC bundles in the upper layer was obviously smaller for the high molecular weight PHIC than for the low molecular weight PHIC, suggesting that the bundles of high molecular weight PHIC more easily interpenetrate than those of low molecular weight PHIC. For the blended films composed of both low and high molecular weight PHICs, the characteristic morphologies of the respective PHIC samples were no longer present. Moreover, the morphologies of the blended films appeared to resemble each other at any molar fraction owing to the ideal miscibility of the low molecular weight and high molecular weight PHICs. The morphologies of the blended films were also similar to that of the unfractionated PHIC film in the dilute regime. In the semidilute regime, the blended films became rounded owing to an increase in bundles interpenetration between PHICs as compared to that in the dilute regime, whereas the morphology of unfractionated PHIC films remained unchanged as compared to that in the dilute regime.

Stability and rheological properties of silica suspensions in water- immiscible liquids.

This paper overviews silica suspensions in water-immiscible liquids, with an emphasis on their dispersion stability and rheological properties as a function of the surface characteristics of silica powders at lower silica volume fractions, ϕ, than 0.1. In addition, a critical review is presented the manufacturing process of silica powder by considering their microstructures. Hydrophilic fumed silica powders are in a gel state at lower ϕ than hydrophobic fumed silica powders in water-immiscible liquids. The interaction between the surface silanol groups is dominant in the former; whereas in the latter, the mutual interaction between the surface hydrophobic moieties and the dispersion media is favored. Moreover, the dynamic moduli of the hydrophobic fumed silica suspensions strongly depend on the mutual interaction between the hydrophobic moieties and the dispersion media. Their magnitudes become larger as mutual interactions increase. In addition, the effects of the adsorption of polymers and non-adsorbing polymers on the dispersion stability and rheological behavior of hydrophilic or hydrophobic fumed silica suspensions are discussed, by considering their small-angle neutron scattering (SANS) curves. The precipitated silica suspensions are more compact and form smaller microstructures than the fumed silica suspensions and their gels correspond to the weak-link gel.

Dispersion stability and rheological properties of silica suspensions in aqueous solutions.

This historical perspective overviews the dispersion stability and rheological properties of fumed and colloidal silica suspensions in aqueous solutions as a function of the volume fraction of silica (ϕ) (where ϕ is ≤0.1). The silica suspensions exist in a gel state at lower ϕ in acidic conditions than at alkaline pH. The steady-state shear viscosities of silica suspensions at acid conditions exhibit shear thinning behavior at lower ϕ than in alkaline conditions; the magnitudes of the dynamic moduli of the silica suspensions at acidic pH are larger than those at alkaline pH. Changes in the dispersion stability and rheological behavior of the silica suspensions may be attributable to the addition of salt, which decreases electrostatic repulsion. Furthermore, the effects of polymer adsorption on the dispersion stability and rheological behavior of hydrophilic or hydrophobic silica suspensions are discussed.

Effects of perfluorosulfonic acid adsorption on the stability of carbon black suspensions.

Carbon black particles were stabilized by the adsorption of perfluorosulfonic acid (PFSA) onto their surfaces in a mixture of water and isopropyl alcohol. The resulting carbon black suspensions were characterized by measurements of the adsorbed amounts of PFSA, the hydrodynamic diameter of carbon black particles with adsorbed PFSA, and by steady state shear viscosity measurements as functions of the PFSA and carbon black particle concentrations. An equilibrium adsorption of PFSA on carbon black particles was established within 1 day, and the resulting adsorption isotherm was dependent on the carbon black particle concentration; the amounts of adsorbed PFSA decreased with increased carbon black particle concentration. The hydrodynamic diameter of the carbon black particles in suspension increased with the amount of adsorbed PFSA, resulting in stabilization of the carbon black suspensions. Thus, the apparent steady-state shear viscosities of the carbon black suspensions at the first and second shear thinning regions decreased with an increase in the amount of adsorbed PFSA.

Structural control of peptide-coated gold nanoparticle assemblies by the conformational transition of surface peptides.

Gold nanoparticles having peptide chains on the surfaces have been prepared yb ring-opening polymerization of gamma-methyl L-glutamate N-carboxyanhydride with fixed amino groups on the nanoparticle surface as an initiator. The number of peptide chains on the surface was adjusted to ca. 2 molecules per gold nanoparticle by controlling the number of fixed amino groups on the surface. The peptide chains on the surface were partially saponified to obtain poly(gamma-methyl L-glutamate-co-L-glutamic acid) with 28 mol% of glutamic acid residues. The number-average molecular weight of the peptide was 73,000. We described structural control of the peptide-coated gold nanoparticle assembly by conformational transition of the surface peptides. In deionized water, the peptide chains on the nanoparticle took a random coil conformation, and the individual nanoparticles existed in dispersed globular species. On the other hand, the peptide chains on the nanoparticle took an alpha-helical conformation in trifluoroethanol. Under this condition, the alpha-helical peptide chains on distinct gold nanoparticles connected the nanoparticles to form a fibril assembly owing to the dipole-dipole interaction between the surface peptide chains. The morphology of the peptide-coated gold nanoparticle assembly could be controlled by the conformational transition of surface peptides, which was attended by solution composition changes.

Interfacial characteristics of binary polymer blend films spread at the air-water interface.

The interfacial characteristics of binary polymer blend films spread at the air-water interface are reviewed, focusing on their surface pressures, interfacial structures, and dilational moduli as a function of the miscibility. Miscible polymer blend films show thermodynamic, structural, and dynamic properties which are a combination of those from both components in the polymer blend present at the air-water interface. No preferential adsorption is observed and the behavior does not depend on the surface concentration regime. In contrast, for immiscible polymer blend films, preferential adsorption of one polymer phase occurs at the air-water interface and the interfacial characteristics in the semi-dilute and concentrated regimes are strongly controlled by one of the components of the adsorbed polymer.

Fumed and Precipitated Hydrophilic Silica Suspension Gels in Mineral Oil: Stability and Rheological Properties.

Hydrophilic fumed silica (FS) and precipitated silica (PS) powders were suspended in mineral oil; increasing the silica volume fraction (φ in the suspension led to the formation of sol, pre-gel, and gel states. Gelation took place at lower φ values in the FS than the PS suspension because of the lower silanol density on the FS surface. The shear stresses and dynamic moduli of the FS and PS suspensions were measured as a function of φ. Plots of the apparent shear viscosity against shear rate depended on φ and the silica powder. The FS suspensions in the gel state exhibited shear thinning, followed by a weak shear thickening or by constant viscosity with an increasing shear rate. In contrast, the PS suspensions in the gel state showed shear thinning, irrespective of φ. The dynamic moduli of the pre-gel and gel states were dependent on the surface silanol density: at a fixed φ, the storage modulus G' in the linear viscoelasticity region was larger for the FS than for the PS suspension. Beyond the linear region, the G' of the PS suspensions showed strain hardening and the loss modulus G″ of the FS and PS suspensions exhibited weak strain overshoot.

Silicone oil emulsions stabilized by polymers and solid particles.

Silicone oil emulsions stabilized by various emulsifiers such as polymers, solid particles alone, and solid particles with pre-adsorbed surfactants or polymers are reviewed, focusing on their emulsion stability and rheological properties as a function of the emulsifier concentration. An increase in the concentration of the emulsifier leads to a decrease in the droplet size and an increase in the emulsion stability, irrespective of the emulsifier. Moreover, the overlapping concentration of polymer can be regarded as a criterion for the preparation of emulsions using polymeric emulsifiers. Changes in the emulsion stability and rheological responses of the emulsions prepared by the solid particles with pre-adsorbed polymers are discussed in terms of the amounts of the emulsifiers adsorbed. For emulsions prepared from hydrophilic silica particles with pre-adsorbed polymers, a decrease in the droplet size of an order of magnitude can be controlled by an increase in the concentration of polymer, whereas hydrophilic silica particles alone cannot produce stable silicone oil emulsions.

Mixed films of poly(n-hexyl isocyanate) and poly(vinyl acetate) at the air-water interface.

We study interfacial properties of rigid-rod-like poly(n-hexyl isocyanate) (PHIC), flexible poly(vinyl acetate) (PVAc), and mixed films of PHIC and PVAc spread at the air-water interface as a function of the molar fraction of PHIC by surface pressure measurements and fluorescence microscopy. From the plots of the experimental mean area of the mixed polymer films at a constant surface pressure as a function of the molar fraction of PHIC in the mixed films, the binary mixtures of PHIC/PVAc were concluded to be compatible at the air-water interface. This means that the hydrophobic hexyl group of PHIC takes a horizontal orientation to the air-water interface rather than a perpendicular one, leading to PHIC and PVAc having the same interfacial orientation. Compatibility of the binary mixtures of PHIC/PVAc at the air-water interface is also confirmed by their fluorescence microscopic images, since PHIC proves to be inhomogeneous and PVAc is homogeneous with the aid of a fluorescence probe, respectively.

AFM studies on LB films of poly(n-hexyl isocyanate), poly(vinyl acetate), and their binary mixtures.

LB films of rigid-rod-like poly(n-hexyl isocyanate) (PHIC), flexible poly(vinyl acetate) (PVAc), and binary mixtures of PHIC as well as of PHIC and PVAc transferred on a mica surface from the air-water interface were observed by AFM. The grain structure of three individual PHIC samples in the AFM images changed shape from a rigid rod to a coiled rod with an increase in the molecular weight due to changes in the chain rigidity of PHIC. On the other hand, the AFM image of PVAc was similar to that of a mica surface, indicating that PVAc forms a uniform and homogeneous film. For the binary mixtures of PHIC, the grain structure in the AFM image of the highest molecular weight PHIC was expanded with a similar shape after the addition of the smallest one, whereas it lost its shape after the addition of the middle one. Their peak-to-valley values in the AMF images were similar to those of the individual PHIC samples. For the binary mixtures of PHIC with the highest mass and PVAc, the grain in the AFM image of the PHIC lost its shape after the addition of PVAc and it changed shape from a connected partial lost coil to an extended bundle rod with an increase in the PVAc component.

Polymer depletion-induced instability of silica suspensions in the presence of flexible and semiflexible polymers.

Polymer depletion-induced instability of silica suspensions in dilute toluene solutions of flexible polystyrene (PS) or semiflexible poly(hexyl isocyanate) (PHIC) was investigated by direct observation and oscillatory moduli measurements as functions of silica volume fraction and polymer molecular weight. Addition of the respective polymers to the gelled silica suspensions induces a gel settling. Below the silica volume fraction phi=4 vol%, PS chains compress the volume of the sediment silica phase, whereas PHIC chains expand it and play a role in swelling agents. Thus, PHIC chains lead to the formation of aggregates in the silica suspensions that are larger and less compact than those formed by the PS chains. On the other hand, above phi=4 vol% where the silica suspension occurs gelation, the effect of nonadsorbing polymers on changes in the volume of the silica phase is opposite. Moreover, polymer depletion interaction results in a mechanically stronger gelled phase, leading to the storage modulus G' values larger than those without polymer, but the effects of polymer concentration and polymer molecular weight on the G' values are not clear.

Effect of anisotropy on viscous fingering patterns of polymer solutions in linear Hele-Shaw cells.

Viscous fingering patterns of hydroxypropyl methyl cellulose (HPMC) solutions were investigated by forcing air in linear geometry isotropic and anisotropic Hele-Shaw cells as functions of HPMC concentration and injection pressure of air. The resulting patterns depended on the HPMC concentration and the cell anisotropy. The characteristic quantities of pattern growth, such as the finger velocity and the finger width, were evaluated. The finger velocity in the anisotropic linear cell was faster than that in the isotropic one, and the finger velocity and the finger width were well correlated with the pattern morphological changes. (c) 1999 American Institute of Physics.

Surface dilational moduli of polymer and blended polymer monolayers spread at air-water interfaces.

Surface dilational moduli of polymer monolayers, blended polymer monolayers, and polymer particle monolayers spread at air-water interfaces are reviewed, focusing on measurements using surface pressure isotherm, surface pressure relaxation, and oscillating barrier methods. Differences between the surface dilational moduli of condensed polymer monolayers and expanded polymer monolayers are explored. Moreover, the features of the surface dilational moduli in blended polymer monolayers are discussed in terms of their miscibility.

Dispersion method for safety research on manufactured nanomaterials.

Nanomaterials tend to agglomerate in aqueous media, resulting in inaccurate safety assessment of the biological response to these substances. The present study searched for suitable dispersion methods for the preparation of nanomaterial suspensions. Titanium dioxide (TiO2) and zinc oxide (ZnO) nanoparticles were dispersed in a biocompatible dispersion medium by direct probe-type sonicator and indirect cup-type sonicator. Size characterization was completed using dynamic light scattering and transmission electron microscopy. A series of dispersion time and output power, as well as two different particle concentrations were tested. Microscopic contamination of metal titanium that broke away from the tip of the probe into the suspension was found. Size of agglomerated nanoparticles decreased with increase in sonication time or output power. Particle concentration did not show obvious effect on size distribution of TiO2 nanoparticles, while significant reduction of secondary diameter of ZnO was observed at higher concentration. A practicable protocol was then adopted and sizes of well-dispersed nanoparticles increased by less than 10% at 7 d after sonication. Multi-walled carbon nanotubes were also well dispersed by the same protocol. The cup-type sonicator might be a useful alternative to the traditional bath-type sonicator or probe-type sonicator based on its effective energy delivery and assurance of suspension purity.

Surface dilational moduli of latex-particle monolayers spread at air-water interface.

Latex particles prepared by radical dispersion polymerization of styrene and diacetone acrylamide (DAAM) in the presence of potassium persulfate as an initiator were spread as particle monolayers at the air-water interface. The surface pressure isotherms of the latex-particle monolayers are almost reversible during the compression-expansion cycles. The surface dilational moduli of the latex-particle monolayers at a fixed surface pressure of 20 mN/m and a fixed frequency of 10 mHz are almost independent of the strain. Moreover, at a fixed strain of 10% and fixed surface pressures of 10 or 15 mN/m the surface dilational moduli of the latex particle monolayers were measured as a function of frequency. The Lissajous orbits of the latex-particle monolayers exhibit positive hysteresis loops for all surface pressure ranges examined. The crossover between the magnitude of the surface elastic modulus and the magnitude of the surface viscous modulus occurs between the frequencies of 10 and 12 mHz and beyond the frequency of 12 mHz the former is larger than the latter. Such crossover indicates that the strain response of the latex-particle monolayers behave changes from liquid-like viscoelastic behavior to solid-like behavior with increasing frequency.