The origin of anomalous water diffusion in silica glasses at low temperatures

Anomalous water diffusion into SiO₂ glass was observed in a low temperature range, below ~850°C, under a constant water vapor pressure of 355 Torr (47.3 kPa). Both the effective water diffusion coefficient and water solubility exhibited an anomalous time dependence. For example, water solubility in the low temperature range increased initially, achieving much higher values than expected based on extrapolation from higher temperature data, and then decreased with time toward an equilibrium value. This phenomenon was reported earlier, but a complete explanation was not possible; a new model is presented based upon glass surface compressive stress generation and subsequent surface stress relaxation. Water diffusion can promote stress generation and stress relaxation, both of which affect the reaction between diffused molecular water and the glass structure. By considering these stress effects, the anomalous water diffusion behavior in silica glass is explained. Furthermore, the same model can account for the reversal of external tensile and compressive stress effects on water solubility and diffusivity in silica glass observed after a few hours of heat treatment at 650°C in 355 Torr water vapor pressure.     

Development of Novel Inhibitors for Histone Methyltransferase SET7/9 based on Cyproheptadine

The histone methyltransferase SET7/9 methylates not only histone but also non‐histone proteins as substrates, and therefore, SET7/9 inhibitors are considered candidates for the treatment of diseases. Previously, our group identified cyproheptadine, used clinically as a serotonin receptor antagonist and histamine receptor (H1) antagonist, as a novel scaffold of the SET7/9 inhibitor. In this work, we focused on dibenzosuberene as a substructure of cyproheptadine and synthesized derivatives with various functional groups. Among them, the compound bearing a 2‐hydroxy group showed the most potent activity. On the other hand, a 3‐hydroxy group or another hydrophilic functional group such as acetamide decreased the activity. Structural analysis clarified a rationale for the improved potency only by tightly restricted location and type of the hydrophilic group. In addition, a SET7/9 loop, which was only partially visible in the complex with cyproheptadine, became more clearly visible in the complex with 2‐hydroxycyproheptadine. These results are expected to be helpful for further structure‐based development of SET7/9 inhibitors.     

The formation of graphene–titania hybrid films and their resistance change under ultraviolet irradiation

We report the fabrication of hybrid films of graphene and monolayer titania using a simple electrostatic self-assembly method. Ultraviolet (UV) responses of the hybrid films based on the graphene–titania structure were investigated. We observed that the resistance of the graphene–titania hybrid increased exponentially with UV irradiation time and decreased exponentially when UV was turned off. Time constants of the order of hundreds of seconds were identified and found to be sensitive to the gas environment of graphene. The UV response as well as the time constant is tunable by varying the number of titania layers. Our results confirmed that UV irradiation played a significant role in the resistance modulation of graphene as well as graphene–titania hybrid films.     

Fine structure of tooth enamel in the yellowing human teeth: SEM and HRTEM studies

Objective : The aim of this study was to clarify an influence of the fine structure of human tooth enamel to the yellowing teeth. Materials and methods : Sound maxillary first premolars of 15–50‐year‐old females that were extracted for the orthodontic treatment were used as the test samples. The tooth enamel sections of these teeth that prepared by ion polishing were observed by scanning electron microscopy (SEM). Furthermore, the fine structure of substance filling the inter‐rod spaces was analyzed by high resolution transmission electron microscopy (HRTEM). Results : In white tooth, the inter‐rod spaces were observed at the width of about 0.1 μm, while in yellow tooth, the inter‐rod spaces were not clearly observed by SEM. HRTEM observations revealed for the first time that the inter‐rod spaces were filled with fine particles of poorly crystallized hydroxyapatite in the yellow tooth. In yellow tooth, it was considered that the color of the inner dentin was recognized due to the decrease of light scattering by filling the tooth enamel inter‐rod spaces. The generation of particles in the tooth enamel inter‐rod spaces was considered to be caused by the long‐time progression of calcification. Conclusions : These results suggested that the change in fine structure, filling in inter‐rod spaces of tooth enamel, was related to progression of calcification in the inter‐rod spaces with advancing age and one of the factors of yellowness of human tooth. Microsc. Res. Tech. 79:14–22, 2016. © 2015 Wiley Periodicals, Inc.     

Mechanism of Mechanical Strength Increase of Soda–Lime Glass by Aging

Two models have been proposed to explain the mechanical strength increase of abraded or indented soda–lime glasses upon aging, namely, crack tip blunting and the release of residual tensile stress near the crack tip. To clarify the mechanism, the time dependence of the strengthening of an abraded soda–lime glass was investigated. Effects of aging media, such as moist air, distilled water, 1 N HCI and 1 N NaOH solutions, as well as the abrasion flaw depth, were determined. The strength increase rate in water of abraded soda–lime glass was compared with those of borosilicate and high-silica glasses. The effect of stressing during aging was also investigated. It was found that the rate of strength increase was faster with decreasing abrasion flaw depth and with decreasing chemical durability. For a given flaw depth, an acidic solution produced the fastest strengthening. The strengthening rate was found to accelerate because of the "coaxing'effect of stressing during aging. From these observations, it was concluded that the strengthening rates relate to the diffusion process and chemical reactions, especially the alkali–hydrogen (or hydronium) ion-exchange reaction, near the crack tip. The role of the residual tensile stress appears to be similar to that of the applied tensile stress, helping the diffusion process near the crack tip. The observed strength increase of soda–lime glass by aging was thus attributed to the effective blunting of the crack tip geometry by the glass–water reaction.     

Oxidation Resistance Evaluation of Silicon Carbide Ceramics with Various Additives

Five silicon carbide ceramics with various additives were evaluated for oxidation resistance at 1300°C in flowing dry and wet air. In the dry atmosphere, the oxidation of the five samples was diffusion-controlled, and in wet atmosphere they exhibited a linear relation beween weight gain by oxidation and water vapor content. Water vapor in the atmosphere strongly accelerated oxidation. The influence of oxidation on room-temperature strength was complex, but the samples were not as affected by oxidation.     

Properties of networks obtained by internal plasticization of epoxy resin with aromatic and aliphatic glycidyl compounds

In order to improve the fracture properties of p, p′-diaminodiphenylmethane-cured epoxy resin, various kinds of aromatic and aliphatic glycidyl compounds were investigated as a modifier at an amount of 30 wt %. Several compounds promoted the fracture toughness. In any glycidyl compounds, however, heat resistance was decreased by the modification. The dynamic mechanical properties of the modified epoxy resins were measured. The crosslinking density ρ was calculated from the theory of rubber elasticity, and the mechanical properties of the resins were discussed in regard to the crosslinking density. Tensile strength was scarcely affected by the crosslinking density. Elongation at break and Izod impact strength increased remarkably with decrease in crosslinking density. The fracture toughness K_Ic- increased with decrease in crosslinking density except at small ρ.     

Conformational analysis of ethylene oxide and ethylene imine oligomers by quantum chemical calculations: solvent effects

Summary  Conformational analyses using quantum chemical calculations were carried out for 1- to 4-mers of ethylene oxide (EO) and ethylene imine (EI) oligomer models (EO-x and EI-x, x = 1 - 4) in the liquid phase using four solvents (permittivity: ε = 2.0 ~80.1). The results were compared against those obtained in the gaseous phase. The calculations involved either RHF/6-31+G(d,p) or B3LYP/6-31G(d) // SCRF/IPCM, based on the observed and calculated results for the energy difference between trans- and cis-dichloroethane. The conformations repeated for a unit of X-C, C-C and C-X bonds (X: O or N) were examined. For both oligomers, the energies of every conformer decreased with increasing ε values, and were linear against the Kirkwood function (K_f = (ε-1)/(2ε+1)). For the EO oligomers, the (ttt)_x conformer was most stable in the gaseous phase. In liquid phases, however, the preference for the gauche-conformation (gauche preference) of the C-C bonds increased with higher values of ε. In the case of EO-3, the (tg⁺t)_x conformer was most stable above an ε value of 8.9, which were in good agreement with those observed for triglyme solutions using NMR analysis. For the EI oligomers, the (tg⁺t)_x conformer was most stable in either gaseous or liquid phase, and the gauche preference of the C-C bonds in both phases were comparable. These results were in good agreement with those observed for di-MEDA solutions using NMR analysis. It was estimated that such small solvent effects on gauche preferences of the EI oligomers result in weakening for hydrogen bonds (NH-N) of neighboring imino groups by solvents.     

Kinetic parameters for anodic oxidation of hypochlorite ion on Pt and Pt oxide electrodes in alkaline solution

Kinetic parameters for the anodic oxidation of hypochlorite ion have been determined by means of normal pulse voltammetry by using a platinum disk as the working electrode. By using the working electrode that formed an oxide film by electrochemical pretreatment, the effect of the lattice oxygen of the surface oxide on the reaction was also examined. The measurement results were analyzed by the classical method, and then the analytical results were evaluated by digital simulation. The normal pulse voltammogram of the hypochlorite ion showed quasi-reversible oxidation waves. The apparent rate constant was calculated to be 5.0-8.1 × 10⁻⁴ cm s⁻¹, depending on the electrode surface state. At the low-concentration range of <4.0 mg Cl dm⁻³, the oxidation current was concentration dependent at the cathodically polarized electrode, while it became independent after the anodic polarization.     

Preparation and properties of biodegradable network poly(ester-carbonate) elastomers

Biodegradable elastomeric network poly(ester-carbonate)s were prepared from multifunctional aliphatic carboxylic acids such as tricarballylic acid (Y_t) or trimesic acid (Y) and polycarbonate diols (PCD) with molecular weights of 1000 and 2000 g/mol. Prepolymers prepared by a melt polycondensation were cast from dimethylformamide solution and postpolymerized at 270 °C for 40-80 min to form a network. The resultant films were transparent, flexible and insoluble in organic solvents. WAXS exhibited the crystalline peaks due to polycarbonate segments for the network films from PCD₂₀₀₀, while those from PCD₁₀₀₀ were amorphous. The tensile properties were determined for these network films at the temperatures 22, 30, 40 and 50 °C. These films showed elastomeric properties at all temperatures measured. The elongation at break was much higher for the films from PCD₂₀₀₀ (208-434%) than those from PCD₁₀₀₀ (40-120%), and decreased with increasing temperatures. The weight losses of the network films degraded in the buffer solution of Rhizopus delemar lipase at 37 °C increased with time, suggesting that these network films are biodegradable. The degradation rate of the network films from Y_t is faster than that from Y. The GPC curves showed that the lipase hydrolyzed both the ester linkages between Y or Y_t and PCD as well as polycarbonate moiety in the network polymer.