Strength improvement and purification of Yb2Si2O7‐SiC nanocomposites by surface oxidation treatment

A two‐step processing was developed to prepare Yb₂Si₂O₇‐SiC nanocomposites. Yb₂Si₂O₇‐Yb₂SiO₅‐SiC composites were first fabricated by a solid‐state reaction/hot‐pressing method. The composites were then annealed at 1250°C in air for 2 hours to activate the oxidation of SiC, which effectively transformed the Yb₂SiO₅ into Yb₂Si₂O₇. The surface cracks purposely induced can be fully healed during the oxidation treatment. The treated composites have improved flexural strength compared to their pristine composites. The mechanism for crack healing and silicate transformation have been proposed and discussed in detail.     

Biocomposites Made from Short Abaca Fiber and Biodegradable Polyesters

Natural fiber‐reinforced biodegradable polyester composites were prepared from biodegradable polyesters and surface‐untreated or ‐treated abaca fibers (length ca. 5 mm) by melt mixing and subsequent injection molding. Poly(butylene succinate)(PBS), polyestercarbonate (PEC)/poly(lactic acid)(PLA) blend, and PLA were used as biodegradable polyesters. Esterifications using acetic anhydride and butyric anhydride, alkali treatment, and cyanoethylation were performed as surface treatments on the fiber. The flexural moduli of all the fiber‐reinforced composites increased with fiber content. The effect of the surface treatment on the flexural modulus of the fiber‐reinforced composites was not so pronounced. The flexural strength of PBS composites increased with fiber content, and esterification of the fiber by butyric anhydride gave the best result. For the PEC/PLA composites, flexural strength increased slightly with increased fiber content (0–20 wt.‐%) in the case of using untreated fiber, while it increased considerably in the case of using the fiber esterified by butyric anhydride. For the PLA composite, flexural strength did not increase with the fiber reinforcement. The result of soil‐burial tests showed that the composites using untreated fiber have a higher weight loss than both the neat resin and the composites made using acetylated fiber.

Flexural modulus of PBS composites as a function of fiber content.     

Hydrolytic degradation of poly[(R)-3-hydroxybutyric acid] in the melt

Poly[(R)-3-hydroxybutyric acid] [R-P(3HB)] was hydrolyzed in high-temperature and high-pressure water at the temperature range of 180-300 °C and for a period of 360 min. The formation, racemization, and decomposition of 3-hydroxybutyric acids (3HBs) and molecular weight change of R-P(3HB) were investigated. The highest yield of (R)-3-hydroxybutyric acid (R-3HB), ca. 80%, was obtained at 200 °C in the hydrolytic degradation periods of 240-360 min. Too-high hydrolytic degradation temperature such as 300 °C induced the decomposition and racemization of formed 3HBs, resulting in decreased yield of R-3HB. The hydrolytic degradation of R-P(3HB) proceeds homogeneously and randomly via a bulk erosion mechanism. The molecular weight of R-P(3HB) decreased exponentially without formation of low-molecular-weight specific peaks originating from crystalline residues. The hydrolytic degradation rates in the melt estimated from M_n changes were lower for R-P(3HB) than for poly(l-lactide) (PLLA) in the temperature range of 180-220 °C. The activation energy for the hydrolytic degradation (ΔE_h) of R-P(3HB) in the melt (180-250 °C) was 30.0 kcal mol⁻¹, which is higher than 12.2 kcal mol⁻¹ for PLLA in the melt in the temperature range (180-250 °C). This study reveals that hydrolytic degradation of PHB in the melt is an effective and simple method to obtain (R)-3HB and to prepare R-P(3HB) having different molecular weights without containing the specific low-molecular-weight chains, because of the removal of the effect caused by crystalline residues.     

Orientation and Grain Boundary Microstructure of Alumina in Al/Al2O3 Composites Produced by Reactive Metal Penetration

The orientation and grain boundary microstructure of alumina in reactive metal penetration Al/Al₂O₃ composites are studied using orientation imaging microscopy and the results are compared with those of sintered polycrystalline Al₂O₃. The interconnected Al₂O₃ in the composite material is separated by Σ3 boundaries (twins) with a 60° rotation around the [0001] direction. A high frequency (∼100%) of Σ3 coincidence boundaries in composite alumina is remarkable since only ∼12% of boundaries in a sintered polycrystalline Al₂O₃ are of special nature. The coincidence boundaries in the in situ alumina grow in a coherent and faceted manner.     

The physical character of coal char formed during rapid pyrolysis at high pressure

Rapid pyrolysis was conducted in a drop tube reactor using seven coals under various operating conditions. In addition to dense char, porous chars (network char and cenospheric char) were formed by the rapid pyrolysis under certain conditions. Porous char was mainly composed of film-like carbon and skeleton carbon. The pyrolyzed coal char particles were characterized in detail. Morphology and bulk density of porous char were quite different from the dense char formed under the same conditions, but elemental composition and BET surface area were similar to each other. CO₂ gasification reactivity of porous char was lower than dense char in the later gasification stage, and this was ascribed to the low reactivity of skeleton carbon.     

The Role of a Nonribosomal Peptide Synthetase in l‐Lysine Lactamization During Capuramycin Biosynthesis

Capuramycins are one of several known classes of natural products that contain an l ‐Lys‐derived l ‐α‐amino‐?‐caprolactam (l ‐ACL) unit. The α‐amino group of l ‐ACL in a capuramycin is linked to an unsaturated hexuronic acid component through an amide bond that was previously shown to originate by an ATP‐independent enzymatic route. With the aid of a combined in vivo and in vitro approach, a predicted tridomain nonribosomal peptide synthetase CapU is functionally characterized here as the ATP‐dependent amide‐bond‐forming catalyst responsible for the biosynthesis of the remaining amide bond present in l ‐ACL. The results are consistent with the adenylation domain of CapU as the essential catalytic component for l ‐Lys activation and thioesterification of the adjacent thiolation domain. However, in contrast to expectations, lactamization does not require any additional domains or proteins and is likely a nonenzymatic event. The results set the stage for examining whether a similar NRPS‐mediated mechanism is employed in the biosynthesis of other l ‐ACL‐containing natural products and, just as intriguingly, how spontaneous lactamization is avoided in the numerous NRPS‐derived peptides that contain an unmodified l ‐Lys residue.     

Discovery of a Novel Scaffold as an Indoleamine 2,3‐Dioxygenase 1 (IDO1) Inhibitor Based on the Pyrrolopiperazinone Alkaloid,Longamide B

Indoleamine 2,3‐dioxygenase 1 (IDO1) has emerged as a key target for cancer therapy, as IDO1 plays a critical role in the capacity of tumor cells to evade the immune system. The pyrrolopiperazinone alkaloid longamide B and its derivatives were identified as novel IDO1 inhibitors based on docking studies and small library synthesis. The thioamide derivative showed higher IDO1 inhibitory activity than longamide B, and displayed an activity similar to that of a representative IDO1 inhibitor, 1‐methyl‐tryptophan. These results suggest that the pyrrolopiperazinone scaffold of longamide B could be used in the development of IDO1 inhibitors.     

Development of anchored oligothiophenes on substrates for the application to the tunable transparent conductive films

Bis(triethoxysilyl)-substituted oligothiophene with a moderate π-conjugation length was newly synthesized and polymerized to give a polysilsesquioxane network having oligothiophene units dispersed homogeneously without phase separation. The polymer was fixed on glass or ITO substrate by spin-coating and annealing. The resulting film exhibited a high mechanical strength due to the covalent bonding with the substrates, and was electrochemically stable even after 300 redox cycles in electrolyte solution. Chemical oxidation of the polymer films yielded electrically conductive and almost transparent films.     

Mechanism‐Guided Library Design and Dual Genetic Selection of Synthetic OFF Riboswitches

After the recent discovery of bacterial riboswitches, synthetic riboswitches have been engineered by using natural and artificial RNA aptamers. In contrast to natural riboswitches, the majority of synthetic riboswitches in bacteria reported to date are ON switches that activate gene expression in response to the aptamer ligand. In this study, we adopted a mechanism‐guided approach to design libraries predisposed to contain OFF riboswitches that respond to thiamine pyrophosphate (TPP). The first library design exploited a pseudo‐Shine‐Dalgarno (SD) sequence located near the 3′‐end of the TPP aptamer, which would be less accessible to the ribosome when the aptamer is bound to TPP. In the second library, an SD sequence was strategically placed in the aptamer's P1 stem, which is stabilized upon ligand binding. OFF riboswitches were obtained by dual genetic selection of these libraries. The results underscore the importance of effective library design to achieve desired riboswitch functions.     

Separation selectivity of aqueous polyethylene glycol-based separation systems: DSC, LC and aqueous two-phase extraction studies

The distribution behavior of n-alcohols, ketones and nitroalkanes in aqueous liquid chromatography with a column packed with polyethylene glycol (PEG) gel, TSKgel Ether-250, was compared with that in aqueous two-phase systems (ATPSs) formed from PEG and Na₂SO₄ or (NH₄)₂SO₄. The plots of the distribution data obtained for the PEG gel system against those for the ATPS reveal that the separation selectivities exerted by the PEG gel system and the PEG-based ATPS are approximately the same. Differential scanning calorimetry studies on aqueous PEG solutions suggest that PEG polymer forms a hydration structure of which the composition is 50% (w/w) PEG or the hydration number per ethylene oxide is 2.4 and the separation selectivity of the PEG-water systems can be attributed to partition of solute compounds into the hydrated PEG polymer structure.