Effect of Ultrasonic Irradiation on the Probability of Primary Nucleation of L-Arginine Hydrochloride

Most of the amino acids that are utilized as medical raw materials and food additives show polymorphism. To improve the functionality of amino acid crystals, an effective method of polymorph control is required in the crystallization process. Here, primary nucleation of L-arginine hydrochloride by ultrasonication was investigated. L-Arginine hydrochloride exhibits polymorphism, and it crystallizes into three distinct crystal forms. A cooling crystallization experiment was performed, and nucleation of each polymorph upon ultrasonication was observed. In addition, the nucleation was analyzed using the nucleation probability theory. The results indicate that ultrasonic irradiation would significantly induce the nucleation of a particular polymorph.     

Synthetic Peroxides Promote Apoptosis of Cancer Cells by Inhibiting P-Glycoprotein ABCB5

This article discloses a new horizon for the application of peroxides in medical chemistry. Stable cyclic peroxides are demonstrated to have cytotoxic activity against cancer cells; in addition a mechanism of cytotoxic action is proposed. Synthetic bridged 1,2,4,5-tetraoxanes and ozonides were effective against HepG2 cancer cells and some ozonides selectively targeted liver cancer cells (the selectivity indexes for compounds 11 b and 12 a are 8 and 5, respectively). In some cases, tetraoxanes and ozonides were more selective than paclitaxel, artemisinin, and artesunic acid. Annexin V flow-cytometry analysis revealed that the active ozonides 22 a and 23 a induced cell death of HepG2 by apoptosis. Further study showed that compounds 22 a and 23 a exhibited a strong inhibitory effect on P-glycoprotein (P-gp/ABCB5)-overexpressing HepG2 cancer cells. ABCB5 is a key player in the multidrug-resistant phenotype of liver cancer. Peroxides failed to demonstrate a direct correlation between oxidative potential and their biological activity. To our knowledge this is the first time that peroxide diastereoisomers have been found to show stereospecific antimalarial action against the chloroquine-sensitive 3D7 strain of Plasmodium falciparum. Stereoisomeric ozonide 12 b is 11 times more active than stereoisomeric ozonide 12 a (IC₅₀=5.81 vs 65.18 μm ). Current findings mean that ozonides merit further investigation as potential therapeutic agents for drug-resistant hepatocellular carcinoma.     

Effect of microstructures on dielectric breakdown strength of sintered reaction-bonded silicon nitride ceramics

Silicon nitride (Si₃N₄) was prepared from silicon by a sintered reaction-bonded silicon nitride method using yttria and magnesia as sintering additives. Post-sintering (PS) of nitrided compacts was carried out at 1850°C under a nitrogen pressure of 1 MPa. Effect of PS time on microstructure and dielectric breakdown strength (DBS) of the prepared Si₃N₄ ceramics was evaluated. The DBS was measured using specimens with four different thicknesses (0.30, 0.20, 0.10, and 0.05 mm) in order to examine the thickness dependence. The porosity of the sintered Si₃N₄ decreased by prolonging the PS time, and the full density could be achieved at the PS time of over 6 h. After full densification, rod-like β-Si₃N₄ grains grew up, and their maximum grain size increased from 45.1 to 154.7 μm by prolonging the PS time from 6 to 48 h. The DBS of the thick Si₃N₄ substrates (0.30 mm) showed little variation from 35.4 to 47.0 kV/mm, regardless of the PS time. On the other hand, that of the thin ones (0.05 mm) dramatically decreased from 99.5 to 9.8 kV/mm with increased the PS time from 6 to 48 h. Because the DBS sharply decreased at the thin substrate sintered for longer time in which some large-elongated grains might span the substrate thickness-wise throughout, it was inferred that the interface between β-Si₃N₄ grains and grain boundary phase/intergranular glassy films might be a path of the dielectric breakdown.     

Effect of wet-jet milling on the c-axis orientation of hydroxyapatite ceramics fabricated using a strong magnetic field

Controlling the crystal orientation of hydroxyapatite, an inorganic material that is a major component of human hard tissues is important to fabricate better artificial bones and artificial tooth roots. To obtain highly oriented hydroxyapatite ceramics under a strong magnetic field, a good dispersion of the raw materials in the slurry must be obtained. This study investigates the effect of wet-jet milling of a slurry on the orientation of hydroxyapatite ceramics fabricated using a strong magnetic field. Although the prolonged ball milling with ZrO₂ balls of the raw powder fractures the primary particles of hydroxyapatite, wet-jet milling is used to successfully pulverize agglomerated hydroxyapatite raw powder without changing the morphology of the primary particles. Evidently, ceramics with a highly oriented c-axis of hydroxyapatite are obtained by molding the wet-jet milled slurry in a strong rotating magnetic field. They exhibit anisotropy in fracture toughness, and the fracture toughness calculated from the crack length perpendicular to the rotating axis is higher than that calculated from the crack length parallel to it. Furthermore, these values are higher than those of randomly oriented hydroxyapatite ceramics, which may be owing to the crystal orientation dependence of the fracture toughness of the hydroxyapatite grains and grain boundaries.     

Structurally Diverse Polyamines: Solid‐Phase Synthesis and Interaction with DNA

A versatile solid‐phase approach based on peptide chemistry was used to construct four classes of structurally diverse polyamines with modified backbones: linear, partially constrained, branched, and cyclic. Their effects on DNA duplex stability and structure were examined. The polyamines showed distinct activities, thus highlighting the importance of polyamine backbone structure. Interestingly, the rank order of polyamine ability for DNA compaction was different to that for their effects on circular dichroism and melting temperature, thus indicating that these polyamines have distinct effects on secondary and higher‐order structures of DNA.     

deNOx Performance and Reaction Mechanism of the Di-Air System

The detailed reaction mechanism of Di-Air, which showed the unprecedented high deNO_x performance at high temperature conditions, was studied in this work. Since the Di-Air phenomenon occurs with continuous short pulse injections of hydrocarbons over NSR (NO_x storage and reduction) catalyst, this study focused on the specific function of HC as an effective reductant for NO_x reduction reaction. As a first step, the deNO_x performance was compared with three different reductant gases including CO, H₂ and C₃H₆ in a modified synthetic gas bench equipped with a gas injector which enables continuous small amount of injections. At inlet gas temperature of 450 °C C₃H₆ showed the best deNO_x performance whereas H₂ was the best at 150 °C. Moreover the result of temperature programmed desorption showed that intermediate species represented by –NCO (isocyanates) produced from C₃H₆ was thermally more stable than that produced from CO. These results confirmed that the injected HC reacts with adsorbed NO_x on NSR catalyst generating thermally stable intermediates, which could contribute the high deNO_x performance at high temperature conditions.     

The content of tocopherols and oxidative quality of oils prepared from sunflower (Helianthus annuus L.) seeds roasted in a microwave oven

Sunflower seeds ((Helianthus annuus were roasted for 6, 12, 20 or 30 min at a frequency of 2450 MHz using a domestic microwave oven. After the kernels were separated from the sunflower seeds, the quality characteristics and the compositions of the oils were investigated in relation to their tocopherol distributions, and they were further evaluated as compared with an unroasted oil sample. Only minor increases (p < 0.05) in chemical and physical changes of the oils, such as the carbonyl value, the p‐anisidine value and the color development, occurred at a prolonged roasting period. Significant decrease (p < 0.05) was observed in the amounts of phospholipids in the oils after microwave roasting. Nevertheless, compared to the original level, more than 92 wt‐% tocopherols still remained after 30 min of roasting. With a few exceptions, these results indicate that the exposure of sunflower seeds to microwaves for 12 min caused no significant (p < 0.05) loss or change in the content of tocopherols and polyunsaturated fatty acids in the kernels.     

Synthesis of polychloroprene–silica composites by sol‐gel method in the presence of modified polychloroprene containing triethoxysilyl group

Triethoxysilyl‐modified polychloroprene (CR) latex was synthesized by the emulsion copolymerization of 2‐(3‐triethoxysilylpropyl)‐1,3‐butadiene with chloroprene. This latex was mixed with unmodified CR latex and tetraethoxysilane to obtain CR–silica composites by sol‐gel reaction in the latex. SEM observation showed that the silica particles in unvulcanized composites have various diameters ranging from 0.1 to 0.6 μ m, and their size became larger with the decrease of the silica content. Vulcanized CR–silica composites showed that the tensile modulus and tear strength improved with an increase of the amount of modified CR. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1545–1552, 2005     

Enhanced Immunostimulatory Activity of Covalent DNA Dendrons

The present study focused on the design and synthesis of covalent DNA dendrons bearing multivalent cytosine-phosphate-guanine oligodeoxynucleotides (CpG ODNs) that can stimulate the immune system through the activation of TLR9. These dendrons were synthesized using branching trebler phosphoramidite containing three identical protecting groups that enabled the simultaneous synthesis of multiple strands on a single molecule. Compared with linear ODNs, covalent DNA dendrons were found to be more resistant to nuclease degradation and were more efficiently taken up by macrophage-like RAW264.7 cells. Cellular uptake was suggested to be mediated by macrophage scavenger receptors. The covalent DNA dendrons composed of multivalent immunostimulatory branches enhanced the secretion of proinflammatory cytokines TNF-α and IL-6 from RAW264.7 cells, and 9-branched DNA dendrons showed the highest enhancement. Given their enhanced efficacy, we expect covalent DNA dendrons to be useful structures of oligonucleotide medicines.     

Decomposition and regeneration of methane in the absence and the presence of a hydrogen-absorbing alloy CaNi5

Suitable catalysts for the decomposition of methane into carbon and hydrogen and for the regeneration of methane by hydrogenation of the carbon have been looked for in a series of transition metals and precious metals supported on various carriers. The most active catalyst for both reactions was Ni/SiO₂. The carbon formed on this catalyst was thermodynamically less stable than graphite. The different rate equations for the decomposition of methane obtained for the fresh and carbon deposited Ni/SiO₂ suggest that the rate-determining steps are different for the two catalysts. The highest number of carbon atoms deposited per one Ni atom was 31 at 773 K. However, the number of methane molecules recovered easily at 773 K was limited to 1.5 per Ni atom.

A physical mixture of Ni/SiO₂ and CaNi₅, a hydrogen-absorbing alloy, enhanced the decomposition rate of methane, enabling the complete conversion of methane at 773 K beyond the thermodynamic limitation. The presence of CaNi₅ at 273 K separated from the catalyst in a reaction system further enhanced the decomposition of methane due to an increased hydrogen-absorbing capacity of the CaNi₅ at low temperatures. The carbon deposited on Ni/SiO₂ in this case was reactive to be hydrogenated back to methane at 773 K, giving an average 7.5 CH₄ molecules per one Ni atom.