NMR study on microstructure of polymer produced by hydrosilation of styrene with poly(hydrogenmethylsiloxane)

The microstructure of the polymer formed by the hydrosilation of styrene with poly(hydrogenmethylsiloxane) was studied by ¹H- and ¹³C-NMR spectra. Two modes of addition in hydrosilation were found to occur randomly without the influence of the adjacent monomer unit by statistical analysis of sequence distribution of ²⁹Si-NMR spectrum.     

Frequency dependence of acoustic properties of aqueous glucose solutions in the VHF/UHF range

The bioultrasonic spectroscopy system was employed for measurements of velocity and attenuation coefficient of glucose solutions in the VHF/UHF range. The relation between the slope of the square of velocity and the relaxation parameters, and the relation between the frequency exponent on attenuation coefficient and the relaxation parameters are investigated. In order to carry out numerical calculations, a model for a single relaxation process is employed, wherein the attenuation coefficient is expressed as (A/( 1 + (f/falpha)2) + B)f2 where falpha is the attenuation relaxation frequency, and A and B are constants. The numerical calculations show that the slope of the square of the velocity is determined uniquely by the velocity relaxation frequency fv and v(infinity)2 - v(0)2 where v0 is the zero-frequency velocity and v(infinity) is the infinite-frequency velocity, and that the frequency exponent on the attenuation coefficient is determined uniquely by falpha and A/B. For experimental considerations, the velocities and the attenuation coefficients of 5, 15, and 25% concentration aqueous solutions of glucose were measured in the frequency range 20 to 700 MHz. The data for the 5 and 15% aqueous solutions can be explained using the single relaxation model. However, the data for the 25% aqueous solution suggest the existence of multirelaxation processes.     

Optical conductivity spectral anomalies in the off-center rattling system β-Ba8Ga16Sn30

We present optical conductivity studies of the type-I clathrate Ba8Ga16Sn30, using a terahertz time-domain spectrometer (0.3-3.0?THz). The lowest-lying spectral peak at 0.72?THz due to the Ba(2) ion's off-center vibration in the oversized cage shows a drastic and anomalous temperature dependence. Below about 100?K, the single broad peak splits into two subpeaks, and with further lowering of the temperature, the spectral shape of this so-called rattling phonon shows non-Boltzmann broadening to the point that the linewidth becomes comparable to the peak frequency. Whereas the initial splitting can be understood by assuming a multiwell anharmonic potential, the strong linewidth broadening toward low temperature cannot, since the Boltzmann factor generally sharpens the low-temperature spectra. The observed behavior suggests strong interaction between the local anharmonic phonons and other excitations.     

Numerical and experimental investigations of dependence of photoacoustic signals from gold nanoparticles on the optical properties

Gold nanoparticles (AuNPs) are used as a contrast agent of the photoacoustic (PA) imaging. The efficiency of AuNPs has been discussed with the absorption cross section. However, the effects of the scattering of the light by AuNPs and surrounding medium on the PA signal from AuNPs have not been discussed. The PA signals from the aqueous solution of AuNPs were examined in the numerical simulation and the experiment. In the numerical simulation, the absorption and scattering cross sections of spherical and polyhedral AuNPs were calculated by Mie theory and discrete dipole approximation. Monte Carlo simulation calculated the absorbed light energy in the aqueous solution of AuNPs. Based on the PA wave equation, the PA signals were simulated. In the experiment, the PA signal from the aqueous solution of AuNP was measured by use of a piezoelectric film and a Q-switched Nd:YAG laser operated at 532 nm. The results of the numerical simulation and the experiment agreed well. In the numerical simulation and the experiment, a single Au nanocube with 50-nm edge generated the peak value of the PA signal significantly. It was approximately 350 times and twice as large as the peak values of the spherical AuNPs with 10- and 50-nm diameters, respectively. The peak value of the PA signal depended on both the absorption and scattering coefficients of the AuNPs and the surrounding medium. The peak value increased with the scattering coefficient in a quadratic manner. The character of the temporal profile of the PA signal such as full width at half maximum depended on the scattering coefficient of the AuNPs.     

The charge-transfer polymerization of nitroethylene in electron-donating solvents

The anionic polymerization of nitroethylene was studied in N,N-dimethylformamide (DMF) and in dimethyl sulfoxide (DMSO) at 0–40°C. The polymerization proceeds spontaneously when monomer is mixed with solvent in the absence of light. From the observed results of the rate of polymerization, the molecular weight of polymer, the effects of additives and solvents, the copolymerization with acrylonitrile, and the optical absorption spectra it is concluded that the polymerization is initiated by the nitroethylene radical anion generated by the slow dissociation of the electron donor–acceptor (EDA) complexes between the solvent molecule and the monomer. The activation energy for the rate of polymerization was 50 and 29 kJ/mole in DMF and DMSO, respectively, which seems to be determined primarily by the dissociation of the EDA complexes. The significant features of this polymerization are that the initiation proceeds slowly and there is essentially no termination.     

Effect of laser-ablated copper nanoparticles on polymerization of 1,1,3,3-tetraphenyl-1,3-disilacyclobutane

We have studied the effect of copper nanoparticles produced by laser ablation on the ring-opening polymerization of 1,1,3,3-tetraphenyl-1,3-disilacyclobutane (TPDC). The particle size and distribution of laser-ablated, copper nanoparticles were controlled by laser-ablation conditions such as ambient pressure, laser fluence, and distance between target and substrate. Laser-ablated, copper nanoparticles induced polymerization of TPDC effectively, resulting in formation of poly(diphenylsilylenemethylene) (PDPhSM) thin films. The polymerization efficiency depended mainly on the particle size and the surface concentration of copper nanoparticles deposited on the TPDC films by laser ablation. No clear tendency was observed between oxidation of Cu nanoparticles and polymerization efficiency. This technique enables us to easily fabricate PDPhSM thin films and may become a new method for fabricating polymer–metal nanocomposites. PACS 81.05.Lg; 82.35.Np; 82.50.Hp     

Poly(diarylsilmethylene)s,I. Synthesis and characterization

Poly(diarylsilmethylene)s with phenyl or tolyl substituents on Si atoms were synthesized by ring-opening polymerization of corresponding 1,1,3,3-tetraaryl-1,3-disilacyclobutanes, and were characterized by means of DSC, x-ray diffraction and melt viscosity measurements. Three preparative routes including catalytic and noncatalytic polymerization methods were examined to see differences in properties of the resulting polymers. The polymers thus obtained were crystalline and soluble in limited solvents such as diphenyl sulfone at tem-peratures above 250°C. Poly(diphenylsilmethylene) exhibited a melting temperature of about 350°C, whereas those of polymers with tolyl groups were observed in a temperature range between 310 and 330°C. The melt viscosity of the poly(diarylsilmethylene)s was measured to obtain insight into the molecular weights of the polymers, and the results indicated that the molecular weights are modifiable by varying the monomer-to-catalyst ratio when solution polymerization is employed. The DSC and x-ray studies were also carried out with focusing on the melting and crystallization behavior of these polymers. © 1995 John Wiley & Sons, Inc.     

Silychristin derivatives conjugated with coniferylalcohols from silymarin and their pancreatic α-amylase inhibitory activity

Abstract

Silymarin is a mixture of flavonolignans extracted from the fruit of Silybum marianum (milk thistle). The latter is used as a medicinal plant to treat liver and gallbladder disorders. Recently, silymarin has been investigated for its effects against diabetes mellitus, and shown to reduce serum levels of glucose in model animals and in clinical trials. This effect can be explained mainly by the protective effect of silymarin against pancreatic beta-cells, but the involvement of other mechanisms is possible. We demonstrated the α-amylase inhibitory activity of silymarin and investigated the components responsible for this effect. Two major flavonolignans, silibinin and silychristin, did not show inhibition against α-amylase, but two novel silychristin derivatives conjugated with dehydrodiconiferyl alcohol were isolated as the mildly inhibiting components of silymarin. Further analyses indicated the presence of various silychristin derivatives in silymarin that may act synergistically to show α-amylase inhibitory activity.

     

Numerical evaluation of linearized image reconstruction based on finite element method for biomedical photoacoustic imaging

An image reconstruction algorithm for biomedical photoacoustic imaging is discussed. The algorithm solves the inverse problem of the photoacoustic phenomenon in biological media and images the distribution of large optical absorption coefficients, which can indicate diseased tissues such as cancers with angiogenesis and the tissues labeled by exogenous photon absorbers. The linearized forward problem, which relates the absorption coefficients to the detected photoacoustic signals, is formulated by using photon diffusion and photoacoustic wave equations. Both partial differential equations are solved by a finite element method. The inverse problem is solved by truncated singular value decomposition, which reduces the effects of the measurement noise and the errors between forward modeling and actual measurement systems. The spatial resolution and the robustness to various factors affecting the image reconstruction are evaluated by numerical experiments with 2D geometry.