Effects of crosslinker density on the polymer network structure in poly‐N,N‐dimethylacrylamide hydrogels

To investigate the effects of crosslinker density on the properties of hydrogels, compression tests, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and Raman measurements were performed on poly‐N,N‐dimethylacrylamide hydrogels. The results of the compression tests showed that the Young's modulus increases as the crosslinker density increases. To understand the mechanism of the change in the mechanical properties, the structures of the polymer networks and water and the molecular vibrations were analyzed using SEM, DSC, and Raman methods. From the SEM images, it was found that the porosity estimated from the mesh size and cell density increases with increasing crosslinker density. In addition, the DSC and Raman results show that the thickness of the bound water increases as the porosity increases, although the density of the polymer chains in the porous wall remains nearly constant. The increase in the number density of polymer chains can be one of the mechanisms contributing to the increase in the mechanical strength of the hydrogels at lower crosslinker density below 5 mol %, as proposed by previous studies. At higher crosslinker density, however, the number density of polymer chains does not increase with increasing crosslinker density. The present results suggest that the bound water plays an important role in strengthening the hydrogel. The water structure may be one of the dominant factors governing the chemical and physical properties of hydrogels. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1017–1027     

Surface-initiated living radical polymerization from silica particles functionalized with poly(ethylene glycol)-carrying initiator

A novel yet versatile approach is described for surface-initiated living radical polymerization (SI-LRP) from silica particles (SiPs). Monodisperse SiPs were surface-modified with a newly designed surface-fixable initiator (BPEGE) having three components: a triethoxysilane moiety, a poly(ethylene glycol) (PEG) unit, and an initiation site for atom transfer radical polymerization (ATRP) in the form of a 2-bromoisobutyryl group. The surface-initiated ATRP of methyl methacrylate (MMA) mediated by a copper complex was carried out with the BPEGE-fixed SiPs. The polymerization proceeded in a living manner, producing SiPs coated with well-defined poly(MMA) of a target molecular weight with a graft density as high as 0.5 chains/nm². Thanks to the amphiphilic property of PEG, the system was successfully applied for SI-ATRP of PEG methacrylate and sodium p-styrenesulfonate in aqueous media in which the BPEGE-fixed SiPs were highly dispersed without causing any aggregations. The formation of colloidal crystals with the polymer brush-afforded SiPs demonstrated the high uniformity and perfect dispersibility of the hybrid particles.     

3-O-(E)-p-coumaroyl tormentic acid from Eriobotrya japonica leaves induces caspase-dependent apoptotic cell death in human leukemia cell line

Eleven triterpene acids, 1-11, isolated from the leaves of Eriobotrya japonica, were evaluated for inhibition of DNA topoisomerase (Topo) I and cytotoxicity against human leukemia (HL60) and melanoma cell lines (CRL1579). Among the compounds tested, four compounds, δ-oleanolic acid (4), ursolic acid (5), 3-O-(E)-p-coumaroyl tormentic acid (8), and betulinic acid (10), exhibited potent Topo I inhibitory activity (IC(50) 20.3-36.5 μM) and cytotoxicity against HL60 (EC(50) 5.0-8.1 μM). Upon assessing the apoptosis-inducing activity in HL60 cells, compound 8 exhibited induction of apoptosis detected by the observation of DNA fragmentation and membrane phospholipid exposure in flow cytometry. Western blot analysis showed that compound 8 markedly reduced the levels of procaspases-3 and 9, while being increased the levels of cleaved caspases-3 and 9. On the other hand, compound 8 exerted almost no influence on the expression of caspase-8. In addition, compound 8 increased significantly Bax/Bcl-2 ratio and activated caspase-2. These results suggested that compound 8 induced apoptotic cell death in HL60 via mainly mitochondrial pathway by, at least in part, Topo I inhibition. Therefore, compound 8 may be promising lead compound for developing an effective drug for treatment of leukemia.     

Radiation-Induced Polymerization of Styrene Oxide

Radiation-induced polymerization of styrene oxide in the liquid and solid states was carried out by initiating with γ-rays from ⁶⁰Co and electrons from a Van de Graaff accelerator.

Effects of dose rate, a radical inhibitor, and temperature on the polymerization were examined. Infrared spectra and viscosities of polymers obtained were measured.

From these experiments, the following results were obtained:

1. Apparent activation energies are 6.2 kcal/mole for the liquid-state polymerization and 0.17 kcal/mole for the solid-state polymerization, respectively.

2. The polymerization in liquid state is inhibited and retarded by p-ben-zoquinone.

3. The rate of polymerization is approximately proportional to the dose rate.

4. The viscosity of polymers obtained increases with irradiation dose.

5. Infrared spectrum of polymers obtained varies with the polymerization temperature.

It is emphasized in this paper that the chain-transfer and isomerization reactions are rapid and play an important role in the polymerization of styrene oxide, and that the polymer-forming process is not so rapid, owing to a step-by-step type of growing.     

Radiation-Induced Copolymerization of Chlorotrifluoroethylene with Olefins

The copolymerizations of chlorotrifluoroethylene with propylene and isobutylene were carried out at 0 ～ ?78°C by γ-ray irradiation. It was found that alternating copolymers are obtained over a wide range of monomer composition for both systems. The alternating copolymer of chlorotrifluoroethylene with isobutylene was found to be highly crystalline, but the copolymer of chlorotrifluoroethylene with propylene was found to be amorphous. The copolymerizations were considered to proceed via a radical mechanism, but in the case of the isobutylene-chlorotrifluoroethylene system a cationic polymerization also takes place simultaneously at ?78°C.     

A Redox‐Mediator‐Free Solar‐Driven Z‐Scheme Water‐Splitting System Consisting of Modified Ta3N5 as an Oxygen‐Evolution Photocatalyst

Tantalum nitride (Ta₃N₅) modified with various O₂‐evolution cocatalysts was employed as a photocatalyst for water oxidation under visible light (λ>420 nm) in an attempt to construct a redox‐mediator‐free Z‐scheme water‐splitting system. Ta₃N₅ was prepared by nitriding Ta₂O₅ powder under a flow of NH₃ at 1023–1223 K. The activity of Ta₃N₅ for water oxidation from an aqueous AgNO₃ solution as an electron acceptor without cocatalyst was dependent on the generation of a well‐crystallized Ta₃N₅ phase with a low density of anionic defects. Modification of Ta₃N₅ with nanoparticulate metal oxides as cocatalysts for O₂ evolution improved water‐oxidation activity. Of the cocatalysts examined, cobalt oxide (CoO_x) was found to be the most effective, improving the water‐oxidation efficiency of Ta₃N₅ by six to seven times. Further modification of CoO_x/Ta₃N₅ with metallic Ir as an electron sink allowed one to achieve Z‐scheme water splitting under simulated sunlight through interparticle electron transfer without the need for a shuttle redox mediator in combination with Ru‐loaded SrTiO₃ doped with Rh as a H₂‐evolution photocatalyst.     

Muon spin relaxation and positron annihilation in cyclohexane related to spur structures in radiation chemistry

Recent developments in the study of fast processes in radiation chemistry in our laboratory, the pico-second pulse radiolysis, single photon counting technique etc., are briefly mentioned with special emphasis on the study of hydrocarbon liquids. A very close correlation between positronium formation and spur reactions in radiation chemistry is also demonstrated with our recent study of the electron scavenger effects on Ps formation in cyclohexane as an example. Several problems in muonium chemistry are pointed out in the light of these investigations.     

Catalysis research at RITE

Catalysis research at the Research Institute of Innovative Technology for the Earth (RITE) is introduced. Catalysts for chemical fixation of CO2 , selective oxidation and photo reaction which are being developed to reduce the global environmental loads are described.     

Studies on Fe complexes produced by yeast. V. Role of the ligand in Fe absorption from an Fe(II)-oligosaccharide complex

The role of the ligand (oligosaccharide) of an Fe(II) complex (B1-c) produced in wine by Saccharomyces cerevisiae in gastrointestinal Fe absorption was examined. B1-c was found to consist of Fe(II) and an oligosaccharide having the composition of Ara: Xyl: Man: Glc: GalUA (1:1:1:5:1), and the sequence of these constituent monosaccharides was presumed by means of partial hydrolysis of B1-c with glycosidases and a diluted acid. The physicochemical comparison of the partially hydrolyzed, Fe(II)-containing products (Fe-containing fragments) obtained by glycosidase treatment indicated that the Man and GalUA residues of the ligand should be essential for stabilization of the complex form at the physiological pH in the digestive tract. The intestinal Fe absorption in vivo showed marked differences among the Fe-containing fragments having different ligands (sugar chains). Furthermore, the inhibitory effects of the Fe-containing fragments on B1-c uptake by brush border membrane vesicles of the small intestine varied with the ligand, probably being related to the composition of the sugar chain. These results suggest that the sugar chain of the ligand of B1-c may be involved, through its coordination with Fe(II), in (i) high stability and Fe solubility of B1-c at the physiological pH in the digestive tract and (ii) recognition of B1-c molecules in its transport system on the intestinal brush border membrane and, thereby, may contribute to excellent intestinal Fe absorption from B1-c.