ATRP-ARGET of a Styrene Monomer onto Modified Natural Rubber Latex as an Initiator.

Atom transfer radical polymerization with an activator regenerated by electron transfer (ATRP-ARGET) was performed for graft copolymerization of styrene onto natural rubber in the latex stage as a heterogeneous system. Deproteinized and subsequently brominated natural rubber particles in the latex stage were subjected to graft copolymerization of styrene on their surfaces in the presence of an activated ATRP catalyst. 1H NMR spectroscopy and size exclusion chromatography (SEC) characterized the particles. Ozonolysis was performed to deduct the polyisoprene contribution to SEC. Graft copolymerization in heterogeneous media by extraction with an acetone/2-butanone solution. Both the linear evolution of the molecular weight versus monomer conversion and the high grafting efficiency associated with a narrow molecular weight distribution of the resulting grafted polystyrene confirm a living radical behavior.

Entropic and Energetic Elasticities of Natural Rubber with a Nanomatrix Structure.

The entropic and energetic elasticities of natural rubber with a nanomatrix structure are investigated by measuring the viscoelastic properties of deproteinized natural rubber (DPNR)-graft-polystyrene (PS). A nanomatrix structure is formed by graft copolymerization of styrene onto the surface of natural rubber particles, followed by coagulation. The morphology of the nanomatrix structure is observed with transmission electron microscopy. Natural rubber particles with about 1 µm diameter are well dispersed in a nanomatrix of PS. The horizontal shift factor (aT) and vertical shift factor (bT) are determined by superposition to create a master curve according to the time-temperature superposition principle. The positive slope of DPNR appears in the plot of bT versus temperature, suggesting that entropic elasticity occurs. In contrast, the slopes of DPNR-graft-PS are negative at lower temperatures but positive at higher temperatures. The negative slope, which suggests entropic elasticity, may be attributed to the formation of a nanomatrix structure. Natural rubber with a nanomatrix structure realizes both energetic elasticity and entropic elasticity.

Distribution of Nanodiamond Inside the Nanomatrix in Natural Rubber.

The distribution of nanodiamond inside a nanomatrix, which is related to the mechanical and viscoelastic properties, is investigated for a natural rubber-nanodiamond composite. The composite is prepared by reacting nanodiamond with deproteinized natural rubber (NR-ND) in the presence of a tert-butylhydroperoxide (TBHPO)/tetraethylenepentamine (TEPA) radical initiator at 30 °C in the latex stage and subsequent drying. The morphology of the composite is observed by three-dimensional transmission electron microscopy. NR-ND prepared with an initiator exhibits a nanomatrix structure, whereas NR-ND prepared without an initiator displays an island matrix structure. The nanomatrix is densely loaded with 15 nm or smaller-sized nanodiamond. Both the mechanical and viscoelastic properties of NR-ND depend upon the morphology. The stress at break and the plateau modulus are 12 MPa and 1.19 × 106 Pa, respectively, when NR-ND is prepared with a TBHPO/TEPA initiator and contains 25 w/w % nanodiamond, which are 4 and 8 times higher than those of deproteinized natural rubber, respectively.

Modification of graphene oxide and its effect on properties of natural rubber/graphene oxide nanocomposites.

Modification of graphene oxide (GO) by vinyltriethoxysilane (VTES) was investigated to study the effect of silanized GO on radical graft copolymerization of GO onto deproteinized natural rubber (DPNR). The modified GO, GO-VTES (a and b), was characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy, contact angle, thermal gravimetric analysis, and scanning electron microscopy. The XRD results showed the appearance of an amorphous region of silica particles at a diffraction angle of 22°. The formation of silica was investigated by 29Si NMR, and it was found that the hydrolysis and condensation of VTES proceed more completely in basic conditions than in acidic conditions. The silica content of GO-VTES(b) was 43%, which is higher than that of GO-VTES(a) (8%). Morphology of silica was observed by SEM. The DPNR/GO-VTES nanocomposites prepared with the same amount of GO, GO-VTES(a), and GO-VTES(b) were characterized with tensile tests and dynamic mechanical tests. The stress at break of DPNR/GO-VTES(a) and DPNR/GO-VTES(b) was 5.2 MPa and 4.3 MPa, respectively, which were lower than that of DPNR/GO. However, it exhibited higher stress at small strains and higher storage modulus than DPNR/GO.

Syntheses of procyanidin B2 and B3 gallate derivatives using equimolar condensation mediated by Yb(OTf)3 and their antitumor activities.

Synthesis of procyanidin B2 and B3 gallate derivatives, 3-O-gallate, 3"-O-gallate, and 3,3"-di-O-gallate, were synthesized using equimolar condensation mediated by Yb(OTf)3. Synthesized compounds showed significant antitumor effects against human prostate PC-3 cell lines. Their activities were weaker than well-known EGCG and prodelphinidin B3.

Adzuki bean (Vigna angularis) extract reduces amyloid-ß aggregation and delays cognitive impairment in Drosophila models of Alzheimer's disease.

BACKGROUND/OBJECTIVES: Alzheimer's disease is a neurodegenerative disease that induces symptoms such as a decrease in motor function and cognitive impairment. Increases in the aggregation and deposition of amyloid beta protein (Aß) in the brain may be closely correlated with the development of Alzheimer's disease. In this study, the effects of an adzuki bean extract on the aggregation of Aß were examined; moreover, the anti-Alzheimer's activity of the adzuki extract was examined. MATERIALS/METHODS: First, we undertook thioflavin T (ThT) fluorescence analysis and transmission electron microscopy (TEM) to evaluate the effect of an adzuki bean extract on Aß42 aggregation. To evaluate the effects of the adzuki extract on the symptoms of Alzheimer's disease in vivo, Aß42-overexpressing Drosophila were used. In these flies, overexpression of Aß42 induced the formation of Aß42 aggregates in the brain, decreased motor function, and resulted in cognitive impairment. RESULTS: Based on the results obtained by ThT fluorescence assays and TEM, the adzuki bean extract inhibited the formation of Aß42 aggregates in a concentration-dependent manner. When Aß42-overexpressing flies were fed regular medium containing adzuki extract, the Aß42 level in the brain was significantly lower than that in the group fed regular medium only. Furthermore, suppression of the decrease in motor function, suppression of cognitive impairment, and improvement in lifespan were observed in Aß42-overexpressing flies fed regular medium with adzuki extract. CONCLUSIONS: The results reveal the delaying effects of an adzuki bean extract on the progression of Alzheimer's disease and provide useful information for identifying novel prevention treatments for Alzheimer's disease.

Identification and characterization of oligomeric proanthocyanidins with significant anti-cancer activity in adzuki beans (Vigna angularis).

The aim of the present study was to characterize and evaluate the anti-cancer activity of proanthocyanidin-enriched fractions from adzuki beans. For this purpose, we concentrated proanthocyanidins from adzuki beans (Vigna angularis) into five fractions using Amberlite XAD-1180N, Toyopearl HW40F, and Sepacore C-18 reverse-phase flash column chromatography. Proanthocyanidin-enriched fractions were characterized as (epi)catechin hexamer, heptamer, and octamer, epigallocatechin-(epi)catechin pentamer, and epigallocatechin-(epi)catechin hexamer using electrospray ionization time-of-flight mass spectrometry and thiolytic degradation. These fractions showed significant anti-cancer activity against the human PC-3 prostate cancer cell line. They also significantly suppressed the expression of the fatty acid-binding protein 5 gene, which plays critical roles in cell growth and metastasis in prostate cancer.

Epicatechin oligomers longer than trimers have anti-cancer activities, but not the catechin counterparts.

Since procyanidins (oligomeric catechin or epicatechin) were reported to exhibit health benefits, much attention has been paid to the synthesis of these compounds, especially those that are longer than trimers. In the present study, syntheses of cinnamtannin A3 (epicatechin pentamer), A4 (epicatechin hexamer), catechin tetramer, pentamer, arecatannin A2 (epicatechin-epicatechin-epicatechin-catechin) and A3 (epicatechin-epicatechin-epicatechin-epicatechin-catechin) were achieved. The key reaction was a Lewis acid mediated equimolar condensation. The antitumor effects of these synthesized compounds against a human prostate cancer cell line (PC-3) were investigated. Among the tested compounds, cinnamtannin A3, A4 and arecatannin A3, which possess epicatechin oligomers longer than tetramers as the basic scaffold, showed significant activities for suppression of cell growth, invasion and FABP5 (fatty acid-binding protein 5) gene expression. Effects on cell cycle distribution showed that cell cycle arrest in the G2 phase was induced. Furthermore, these epicatechin oligomers suppressed significantly the expression of the cancer-promoting gene, FABP5, which is related to cell proliferation and metastasis in various cancer cells. Interestingly, the suppressive activities were associated with the degree of oligomerization of epicatechin. Thus, synthetic studies clearly demonstrate that epicatechin oligomers longer than trimers have significant anti-tumorigenic activities, but not the catechin counterparts.

Synthesis of Arecatannin A1 from Dimeric Epicatechin Electrophile.

Synthesis of arrecatannin A1 (1) was accomplished from dimeric epicatechin electrophile, which was prepared by Zn(OTf)2 mediated self-condensation, and monomeric catechin nucleophile. The condensation was successfully worked using Yb(OTf)3 as a Lewis acid in good yield.

[Studies on analysis of terpene resin in imported chewing gums].

We have developed an analytical method for terpene resins in chewing gum. The fraction including terpene resins was prepared by means of hexane extraction and two silica gel column chromatography treatments (hexane and ethyl acetate) from chewing gum. The terpene resin fraction was analyzed with LC/MS and IR. The terpene resins are mixtures of polymeric pinene and/or limonene, which have a monomer molecular weight of 136. The MS spectrum of the terpene resin peak on the LC/MS total ion chromatogram showed protonated molecular ion (M + H)+ peaks at intervals of m/z 136, characteristic of a complex mixture of polyterpenes. IR spectroscopy is a suitable technique to identify the terpene resin type, ie., pinene or limonene. When the method was applied to imported chewing gum sold in Japan, terpene resins were clearly detected.