Yasushige Mori

Determination of the metabolites of the new designer drugs bk-MBDB and bk-MDEA in human urine

This is the first report on identifying the specific metabolites of the new designer drugs 2-methylamino-1-(3,4-methylenedioxyphenyl)butan-1-one (bk-MBDB) and 2-ethylamino-1-(3,4-methylenedioxyphenyl)propan-1-one (bk-MDEA) in human urine using synthesized standards. Based on GC/MS and LC/MS, we identified N-dealkylation, demethylenation followed by O-methylation, and beta-ketone reduction as their major metabolic pathways. The quantitative analyses by LC/MS revealed that both demethylenation followed by O-methylation and beta-ketone reduction were superior to N-dealkylation and that both bk-MBDB and bk-MDEA were mainly metabolized into their corresponding 4-hydroxy-3-methoxy metabolites (4-OH-3MeO metabolites). After hydrolysis, the concentrations of 4-OH-3MeO metabolites and 3-hydroxy-4-methoxy metabolites of both bk-MBDB and bk-MDEA dramatically increased, suggesting that the metabolites mainly exist as their conjugates.

In-line aligned and bottom-up Ag nanorods for surface-enhanced Raman spectroscopy

We have demonstrated surface-enhanced Raman spectroscopy on arrays of Ag nanorods aligned in line by a dynamic oblique deposition technique. For the light polarized along the major axis of the nanorods, the plasma resonance of the Ag nanorods has been tuned to a wavelength suitable for Raman spectroscopy. The average width and the length-to-width ratio of the resulting nanorods are 56nm and 3.5, respectively, and the nanorods align in line with small gaps of a few 10nm. The Raman scattering for the polarized light along the nanorods is enhanced significantly as compared with that perpendicular to the nanorods. This polarization dependent Raman enhancement is attributed to the local field concentration at the ends of the nanorods. Since the preparation process is physical and completely bottom up, it is robust in its selection of the materials and is useful in providing the surface-enhanced Raman scattering sensors at low cost.

Size distribution analysis of colloidal gold by small angle X-ray scattering and light absorbance

Abstract The data measured by small angle X-ray scattering (SAXS) and the extinction spectra observed by spectroscopy were examined as the in situ measurements of the size distribution of gold nanoparticles and were compared with the results obtained from the photographs by a transmission electron microscope (TEM). The mean size can be estimated from the wavelength of the peak absorbance using Mie theory. However, the particle size distribution can only be estimated from fitting the calculated spectrum to the experimental one of the sample with above 30 nm diameter. On the other hand, the scattering data measured by a SAXS instrument can estimate the mean size from the slope of the Guinier plot, when the particle size distribution is narrow. In addition, the size distribution and mean size can be calculated by the experimental SAXS data when the log-normal or Schulz–Flory size distributions are assumed.

Titanium dioxide nanoparticles produced in water-in-oil emulsion

Titanium dioxide (titania) particles were prepared by a water-in-oil emulsion system, and studied for the photodecomposition property of methylene blue. Microemulsion (ME) consisted of water, cyclohexane or octane, and surfactant, such as polyoxyethylene (10) octylphenyl ether (TX-100), polyoxyethylene lauryl ether, or bis (2-ethylhexyl) sodium sulfosuccinate. Titanium tetraisopropoxide (TTIP) was dropped into the ME solution and then titania particles were formed by the hydrolysis reaction between TTIP in the organic solvent and the water in the core of ME. It was found that ME could be classified to the reversed micelle (RM) region and the swelling reversed micelle (SM) region according to the water content. The water droplets in RM were almost monodispersed, where the water content was small. On the other hand, the water droplets in SM had a size distribution, although most of the water molecules associated with surfactant molecules. The size of the particles prepared in the RM region was smaller than the ME size. In contrast, the size of the particles formed in the SM region was larger than the ME size, and coagulation of the particles was observed within a few hours. The smallest diameter of the particles was 2 nm in the system of cyclohexane with TX-100 surfactant when the molar ratio of water to surfactant was 2. Titania particles prepared in this condition were collected as amorphous powder, and converted to anatase phase at less than 500 K, which is lower than the ordinal phase transition temperature. These anatase phase titania particles only showed a significant photodecomposition of methylene blue by illumination with a Xenon lamp.

Adhesion force between particles and substrate in a humid atmosphere studied by atomic force microscopy

Abstract Using an atomic force microscope (AFM), adhesion forces between glass particles or AFM tips and hydrophilic or hydrophobic substrates were measured as a function of relative humidity (RH). The observed adhesion force between the glass particles and the hydrophilic substrate increased with RH due to strong capillary condensation. In contrast, the adhesion force between the glass particles and the hydrophobic substrate was found to be almost constant for all RHs, due to weak capillary condensation. The adhesion force between an AFM tip and a mica plate had a maximum value at a certain RH. This can be evaluated by calculating with consideration for the tip shape. On the other hand, the adhesion force for a silica plate increased drastically over a certain RH and could be explained due to the surface roughness of the silica plate. The presence of nanometer-scale roughness can play a critical role in the absolute value of the adhesion force between an AFM tip and the substrate in a humid atmosphere.

Colloidal properties of synthetic hectorite clay dispersion measured by dynamic light scattering and small angle X-ray scattering

Abstract Clay suspensions are composed of anisotropic disk-like charged particles and are of great importance in many industrial applications because of their gelation. However, the origin of the gelation is still under debate. The synthetic hectorite-type clays such as Laponite XLG form clear dispersions due to their high purity and very small crystallite size, so that they are particularly suited to light scattering studies. In the present work, we reported the structure of Laponite XLG clay suspension and the gelation process by using both dynamic light scattering (DLS) and small-angle X-ray scattering methods. The sol-gel transition (phase transition) was observed at a clay concentration of about 0.01 g/ml and the phase transition phenomena depends on neither the types nor the concentration of salt when below a certain salt concentration. Above a certain concentration of salt, flocculation (phase separation) was observed. The dependency of the value of this concentration on the salt type was the same as the empirical Schulze Hardy law for the critical coagulation concentration of isotropic colloidal suspensions. At low clay concentrations (below 0.01 g/ml), clay particles did not interact strongly; however, at higher concentrations (above 0.02 g/ml) where gelation and elasticity occurred, there were clear indications of inter particle interactions and random short-range ordering. DLS is thus one suitable method of analysis for the sol—gel transition without destroying the sample.

Tailoring coupling of light to local plasmons by using Ag nanorods/structured dielectric/mirror sandwiches

The optical properties of the sandwich of Ag nanorod array (NRA)/structured dielec- tric layer/Ag mirror have been investigated theoretically and experimentally, where the struc- tured dielectric layer has stacked sublayers of an anisotropic nanocolumnarlayer and a uniform layer. The functions of the nanocolumnar and the uniform sublayers are to control shape of the Ag nanorods and to tune optical path length inside the sandwich, respectively. Calculations based on a simple model by treating the NRAs as uniform effective media indicate that the antireflection condition is realized by changing the thickness of the dielectric layer and that the Ag nanorods absorb most of the incident light. The designed structures have been successfully fabricated by taking advantages of the dynamic oblique-angle deposition technique. Under the experimental antireflection condition, Raman scattering measured on the Ag NRA in the near infrared region exhibits significant enhancement. This indicates that the local electric field close to the Ag nanorods can be controlled by the interference of light in the nanostructured sandwiches.

Size Distribution of Gold Nanoparticles Used by Small Angle X-ray Scattering

ABSTRACT The size distribution of gold nanoparticles was estimated based on the scattering intensity data obtained from small angle X-ray scattering (SAXS) and compared with the result of micrographs by transmission electron microscopy. The slope of the Guinier plot was used to estimate the mean size assuming a narrow particle size distribution. When the size distribution is narrow, the mean size can be easily obtained from slope of a Guinier plot of scattering data within 10% error. Additionally, assuming a lognormal size distribution, the size distribution and the mean size can be calculated using the experimental SAXS data in the fitting analysis. The histogram method, which utilizes the coefficient matrix of scattering intensity, was also applied to the estimation of the size distribution, and this method could be useful for a rough estimate of the size distribution.

Effects of ionic strength of eluent on size analysis of submicrometre particles by sedimentation field-flow fractionation

Abstract Sedimentation field-flow fractionation (SdFFF) has a high resolution over a wide range of particle size compared with other methods of sub-micrometre particle size determinations, and has the grant advantage that the fractional collection is sorted by the particle mass. However, the retention behaviour in SdFFF depends strongly on the experimental parameters, especially the ionic strength of the eluent. The sizes calculated from the experimental results of SdFFF are underestimated if an eluent with low ionic strength is used, compared with those obtained by quasi-elastic light scattering spectroscopy, owing to the interparticle repulsion. There is a maximum value of the ionic strength of the eluent for particle size analysis, because rapid flocculation of particles occurs at high electrolyte concentrations. Further, hardly any difference in the retention times was found in SdFFF using different anionic surfactant solutions as the eluent.

Particle size analysis by sedimentation field flow fractionation. Performance and application

Recently commercial equipment using sedimentation field flow fractionation (SFFF) has become available for analysis of particulate materials in the sub-micron range. This paper describes the DuPont instrument and discusses its performance. A particular study is described on the comparison of the SFFF technique with that of quasi-elastic light scattering (QELS). The paper concludes that the instrument is capable of measuring particle size distributions with high resolution and precision, provided that no particles above the upper size limit — about 1 μm — are present.