Effects of various ester groups in γ-radiation degradation of syndiotactic poly(methacrylate)s

The γ irradiation of poly(methacrylate)s with various ester groups at room temperature was investigated by gel permeation chromatography and NMR techniques. The G values for scission and crosslinking for each of the polymers were estimated from the changes in the molecular weights and molecular weight distributions. The new structures formed during γ irradiation were examined by ¹H-NMR spectroscopy. All of the investigated poly(alkanemethacrylate)s were found to produce the alkane formates during γ irradiation, and for poly(2-methyl heptyl methacrylate) G(S) was less than 4G(X), indicating gel formation in this polymer. In the investigation of poly(benzyl methacrylate), no formate ester was found, but some small molecule compounds formed from the benzyl radical were detected. The benzyl group was also found to stabilize the polymer against radiation damage. © 1996 John Wiley & Sons, Inc.     

Gel permeation chromatography of polyoxymethylene

Gel permeation chromatography of polyoxymethylene has been studied using N,N-dimethylformamide as the solvent. Polyoxymethylene samples used here are a copolymer of tetraoxane with 1,3-dioxolane and a commercial polyoxymethylene whose molecular weight distributions are moderately broad. Their intrinsic viscosities [η] range from 1.4 to 2.8 dl/g. Factors affecting chromatograms are discussed, and the operating conditions were determined by using the analytical scale GPC. On the basis of these operating conditions, the molecular weight fractionation of polyoxymethylene was carried out by using the preparative scale GPC. It was found that polyoxymethylene can be effectively fractionated to give seven to ten fractions each of them containing the fractionated polymer ranging in weight from 0.2 to 8 mg when 40 mg polymer sample was used for a run of the measurement. The fractionated polymers were also found to have a narrow molecular weight distribution within a single peak, and their M_w/M_n values decrease with increasing molecular weight.     

Mechanism of elongation of gold or silver nanoparticles in silica by irradiation with swift heavy ions

It has been reported that elongated Au nanoparticles oriented parallel to one another can be synthesized in SiO₂ by ion irradiation. Our aim was to elucidate the mechanism of this elongation. We prepared Au and Ag nanoparticles with a diameter of 20 nm in an SiO₂ matrix. It was found that Au nanoparticles showed greater elongated with a higher flux of ion beam and with thicker SiO₂ films. In contrast, Ag nanoparticles split into two or more shorter nanorods aligned end to end in the direction parallel to the ion beam. These experimental results are discussed in the framework of a thermal spike model of Au and Ag nanorods embedded in SiO₂. The lattice temperature exceeds the melting temperatures of SiO₂, Au and Ag for 100 ns after one 110 MeV Br¹⁰⁺ ion has passed through the middle of an Au or Ag nanorod.     

Quantitative Visualization of the Interaction between Complement Component C1 and Immunoglobulin G: The Effect of CH1 Domain Deletion

Immunoglobulin G (IgG) adopts a modular multidomain structure that mediates antigen recognition and effector functions, such as complement-dependent cytotoxicity. IgG molecules are self-assembled into a hexameric ring on antigen-containing membranes, recruiting the complement component C1q. In order to provide deeper insights into the initial step of the complement pathway, we report a high-speed atomic force microscopy study for the quantitative visualization of the interaction between mouse IgG and the C1 complex composed of C1q, C1r, and C1s. The results showed that the C1q in the C1 complex is restricted regarding internal motion, and that it has a stronger binding affinity for on-membrane IgG2b assemblages than C1q alone, presumably because of the lower conformational entropy loss upon binding. Furthermore, we visualized a 1:1 stoichiometric interaction between C1/C1q and an IgG2a variant that lacks the entire C_H1 domain in the absence of an antigen. In addition to the canonical C1q-binding site on Fc, their interactions are mediated through a secondary site on the C_L domain that is cryptic in the presence of the C_H1 domain. Our findings offer clues for novel-modality therapeutic antibodies.     

High-throughput immunophenotyping by surface plasmon resonance imaging

Cell binding assays on antibody arrays permit the rapid immunophenotyping of living cells. The throughput of the analysis, however, is still limited due to our inability to perform parallel and quantitative detection of cells captured on the array. To address this limitation, we employed here an imaging technique based on surface plasmon resonance (SPR). SPR has been frequently used to monitor capture of proteins on antibody microarrays, while few cases were reported for capture of cells. Antibody arrays were prepared through the photopatterning of an alkanethiol monolayer on a gold-evaporated glass plate and the subsequent immobilization of various antibodies onto 4-9 separate spots created by photopatterning. A glass slip was mounted onto the array with a thin spacer to construct a parallel-plate chamber. Leukemia cells were injected into the chamber to conduct a binding assay, while refractive index changes at the vicinity of the array surface were monitored by SPR imaging. We observed that SPR signals were intensified on specific antibody spots but not on nonspecific spots. Confocal laser scanning microscopy revealed that the observed SPR signals were attributed to cell deformations caused by multivalent interactions with immobilized antibody, which effectively elevated the refractive index of a medium phase within an evanescent field. This effect could be suitably utilized to monitor quantitatively cell binding to multiple spots from a heterogeneous cell population.     

Oscillation of a tilted circular pad on a droplet for the self-alignment process

The seesaw-oscillation of a small circular pad on a single droplet was studied both numerically and experimentally. The circular pad with a diameter of 2.0–3.8 mm onto a water or glycerol droplet with a volume of 1–10 μL, and a bottom substrate with a smaller diameter than that of the pad were used in the experiment. The pad was then tilted and then the tilting fixture was quickly removed. The pad alternately oscillated and then finally stabilized in a horizontal position. The numerical model considering the surface tension and the viscous force of the droplet was developed and calculated using the same configurations as those in the experiment. The experimental and numerical data showed good agreement not only in terms of the oscillating frequency and damping ratio but the transient motion of the circular pad and instantaneous droplet surface shape.     

Preparation of TiO2 thin films using octadecylamine Langmuir-Blodgett films and evaluation of their photocatalytic activity

A study was conducted to demonstrate that nanometer-thick titanium dioxide (TiO(2)) thin films could be prepared by the hydrolysis of titanium potassium oxalate using octadecylamine (ODA) Langmuir-Blodgett (LB) films as templates. The amount of TiO(2) generated in the LB film was found to be proportional to the number of deposited ODA layers, which enables precise control of the TiO(2) film thickness. After heat treatment of the LB films at 300-600°C, the photocatalytic activities of the resulting TiO(2) films were determined from the decomposition of stearic acid cast films when irradiated with UV light for different time periods. Higher photocatalytic activity was observed in TiO(2) films heat treated at lower temperatures.     

Cancer chemopreventive ability of conjugated linolenic acids

Conjugated fatty acids (CFA) have received increased interest because of their beneficial effects on human health, including preventing cancer development. Conjugated linoleic acids (CLA) are such CFA, and have been reviewed extensively for their multiple biological activities. In contrast to other types of CFAs including CLA that are found at low concentrations (less than 1%) in natural products, conjugated linolenic acids (CLN) are the only CFAs that occur in higher quantities in natural products. Some plant seeds contain a considerably high concentration of CLN (30 to 70 wt% lipid). Our research group has screened CLN from different plant seed oils to determine their cancer chemopreventive ability. This review describes the physiological functions of CLN isomers that occur in certain plant seeds. CLN are able to induce apoptosis through decrease of Bcl-2 protein in certain human cancer cell lines, increase expression of peroxisome proliferator-activated receptor (PPAR)-γ, and up-regulate gene expression of p53. Findings in our preclinical animal studies have indicated that feeding with CLN resulted in inhibition of colorectal tumorigenesis through modulation of apoptosis and expression of PPARγ and p53. In this review, we summarize chemopreventive efficacy of CLN against cancer development, especially colorectal cancer.     

Transmission electron microscopic observations of nanobubbles and their capture of impurities in wastewater

Unique properties of micro- and nanobubbles (MNBs), such as a high adsorption of impurities on their surface, are difficult to verify because MNBs are too small to observe directly. We thus used a transmission electron microscope (TEM) with the freeze-fractured replica method to observe oxygen (O₂) MNBs in solutions. MNBs in pure water and in 1% NaCl solutions were spherical or oval. Their size distribution estimated from TEM images close to that of the original solution is measured by light-scattered methods. When we applied this technique to the observation of O₂ MNBs formed in the wastewater of a sewage plant, we found the characteristic features of spherical MNBs that adsorbed surrounding impurity particles on their surface.