Finding of remarkable synergistic effect on the aroxyl-radical-scavenging rates under the coexistence of α-tocopherol and catechins

Measurements of aroxyl radical (ArO^•)-scavenging rate constants () of antioxidants (AOHs) (α-tocopherol (α-TocH) and three catechins (CatHs) (ie, epicatechin (EC), epigallocatechin (EGC), and epigallocatechin gallate (EGCG)) were performed in ethanol solution, using stopped-flow spectrophotometry. values were measured not only for each AOH, but also for the mixtures of two AOHs (α-TocH and CatH). A notable synergistic effect that the value of α-TocH increases 1.29, 1.84, and 1.65 times under the coexistence of constant concentrations of EC, EGC, and EGCG, respectively, was observed for the solutions including α-TocH and CatH. Similarly, values of CatHs (EC, EGC, and EGCG) increased 1.72, 2.25, and 2.34 times under the coexistence of constant concentrations of α-TocH, respectively. UV-Vis absorption of α-tocopheroxyl radical (α-Toc^•) (λ_max = 428 nm), which had been produced by reaction of α-TocH with ArO^•, decreased remarkably under the coexistence of α-TocH and CatHs due to the fast α-TocH-regeneration reaction by CatHs. The result suggests that the prooxidant reaction due to α-Toc^• is suppressed by the coexistence of CatHs. By analyzing the formation and decay curves of α-Toc^•, it has been ascertained that one molecule of EGCG having three OH groups at B-ring may rapidly regenerate three molecules of α-Toc^• to α-TocH.     

Radiation-induced polymerization at high dose rate. II. α-Methylstyrene in bulk

Bulk polymerization of α-methylstyrene was carried out in a wide dose rate range, 7.6–256 rad/sec by γ rays and 8.5 × 10³–2.1 × 10⁵ rad/sec by electron beams. At high dose rate by electron beams, cationic polymerization took place along with formation of oligomeric product of DP _n = ～4. At low dose rate by γ rays, radical polymerization was found to occur in water-saturated monomer. The cationic polymerization at high dose rate proceeds with essentially the same mechanism as was already known in γ-ray polymerization of dry monomers. Relatively low reaction rate of the cationic polymerization compared with that of styrene is explained with the fact that the propagation of α-methylstyrene is much more easily inhibited by a slight amount of water.     

Novel lactonization of ethenetricarboxylate derivatives: intermolecular trapping of alkenes

A novel cyclization of 1,1-diethyl 2-tert-butyl ethenetricarboxylate (1a) in the presence of a Lewis acid afforded a 5,5-dimethyl-gamma-lactone derivative 2a. The reaction process has been shown to arise from formation by trapping of isobutylene generated in situ. Lewis acid-promoted intermolecular reactions of 1,1-diethyl 2-hydrogen ethenetricarboxylate (5) and various alkenes to afford highly functionalized gamma-lactones were also developed. [reaction: see text]     

Irreversible temperature‐responsive formation of high‐strength hydrogel from an enantiomeric mixture of starburst triblock copolymers consisting of 8‐arm PEG and PLLA or PDLA

Starburst triblock copolymers consisting of 8‐arm poly(ethylene glycol) (8‐arm PEG) and biodegradable poly(L ‐lactide) (PLLA) or its enantiomer poly(D ‐lactide) (PDLA), 8‐arm PEG‐b‐PLLA‐b‐PEG ( Stri‐L ), and 8‐arm PEG‐b‐PDLA‐b‐PEG ( Stri‐D ) were synthesized. An aqueous solution of a 1:1 mixture ( Stri‐Mix ) of Stri‐L and Stri‐D assumed a sol state at room temperature, but instantaneously formed a physically crosslinked hydrogel in response to increasing temperature. The resulting hydrogel exhibited a high‐storage modulus (9.8 kPa) at 37 °C. Interestingly, once formed at the transition temperature, the hydrogel was stable even after cooling below the transition temperature. The hydrogel formation process was irreversible because of the formation of stable stereocomplexes. In aqueous solution, gradual hydrolytic erosion was observed because of degradation of the hydrogel. The combination of rapid temperature‐triggered irreversible hydrogel formation, high‐mechanical strength, and degradation behavior render this polymer mixture system suitable for use in injectable biomedical materials, for example, as a drug delivery system for bioactive reagents or a biodegradable scaffold for tissue engineering. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6317–6332, 2008     

Chemo- and stereoselective six-membered oxonium ylide formation–[2,3]-sigmatropic rearrangement of 2-diazo-3-ketoesters with dirhodium(II) catalyst and its application to the synthesis of (+)-tanikolide

Dirhodium(II)-catalyzed oxonium ylide formation–[2,3]-sigmatropic rearrangement of 6-allyloxy-2-diazo-3-ketoesters possessing a C-6 substituent is described. The reaction of 6-alkyl- or 6-aryl-substituted 6-allyloxy-2-diazo-3-ketoesters with a catalytic amount of Rh₂(S-PTTL)₄ proceeded in a chemoselective and stereoselective manner to provide 6-substituted 2-allyl-3-oxotetrahydropyran-2-carboxylates in good yields and with high diastereoselectivities. To demonstrate the utility of this sequential reaction, we conducted the total synthesis of (+)-tanikolide, in which the construction of the δ-lactone skeleton was achieved by employing a 2-iodobenzamide-catalyzed oxidative cleavage of tetrahydropyran-2-methanol.     

Electrostatic self-assembly of neutral and polyelectrolyte block copolymers and oppositely charged surfactant

We investigated the phase behavior and the microscopic structure of the colloidal complexes constituted from neutral/polyelectrolyte diblock copolymers and oppositely charged surfactant by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The neutral block is poly(N-isopropylacrylamide) (PNIPAM), and the polyelectrolyte block is negatively charged poly(acrylic acid) (PAA). In aqueous solution with neutral pH, PAA behaves as a weak polyelectrolyte, whereas PNIPAM is neutral and in good-solvent condition at ambient temperature, but in poor-solvent condition above approximately 32 degrees C. This block copolymer, PNIPAM-b-PAA with a narrow polydispersity, is studied in aqueous solution with an anionic surfactant, dodecyltrimethylammonium bromide (DTAB). For a low surfactant-to-polymer charge ratio Z lower than the critical value ZC, the colloidal complexes are single DTAB micelles dressed by a few PNIPAM-b-PAA. Above ZC, the colloidal complexes form a core-shell microstructure. The core of the complex consists of densely packed DTA+ micelles, most likely connected between them by PAA blocks. The intermicellar distance of the DTA+ micelles is approximately 39 A, which is independent of the charge ratio Z as well as the temperature. The corona of the complex is constituted from the thermosensitive PNIPAM. At lower temperature the macroscopic phase separation is hindered by the swollen PNIPAM chains. Above the critical temperature TC, the PNIPAM corona collapses leading to hydrophobic aggregates of the colloidal complexes.     

Microcalorimetric study of protein adsorption onto calcium hydroxyapatites

To clarify the adsorption mechanism of proteins onto calcium hydroxyapatite (Hap), the present study measured adsorption (DeltaHads) and desorption (DeltaHdes) enthalpies of bovine serum albumin (BSA; isoelectric point (iep) 4.7, molecular mass (Ms) 67,200 Da, acidic protein), myoglobin (MGB; iep=7.0, Ms=17,800 Da, neutral protein), and lysozyme (LSZ; iep=11.1, Ms=14,600 Da, basic protein) onto Hap by a flow microcalorimeter (FMC). Five kinds of large platelike particles of CaHPO4.2H2O (DCPD) after hydrolyzing at room temperature with different concentrations of NaOH aqueous solution ([NaOH]) for 1 h were used. DCPD converted completely to Hap after treatment at [NaOH]>or=2%, and the crystallinity of Hap was increased with an increase in [NaOH] up to 10%. The amounts of protein adsorbed (Deltanads) and desorbed (Deltandes) were measured simultaneously by monitoring the protein concentration downstream from the FMC with a UV detector. The Deltanads values were also measured statically by a batch method in each system. The Deltanads values measured by the FMC and static measurements fairly agreed with each other. Results revealed that DeltaHBSAads was decreased with an increase in [NaOH]; in other words, DeltaHBSAads was decreased with the improvement of Hap's crystallinity, suggesting that the BSA adsorption readily proceeded onto Hap. This fact indicated a high affinity of Hap to protein. This affinity was further recognized by DeltaHBSAdes because its positive value was increased by increasing [NaOH]. These opposite tendencies in DeltaHBSAads and DeltaHBSAdes revealed that Hap possessed a high adsorption affinity to BSA (i.e., enthalpy facilitated protein adsorption but hindered its desorption). The fraction of BSA desorption was also decreased with an increase in [NaOH], confirming the high affinity of Hap to protein. Similar results were observed on the LSZ system, though the enthalpy values were smaller than those of BSA. In the case of neutral MGB, DeltaHBSAads also exhibited results similar to those of the BSA and LSZ systems. However, due to its weak adsorption by the van der Waals force, DeltaHBSAdes was small and almost zero at [NaOH]>or=2%. Hence, the fraction of MGB desorption was less dependent on [NaOH].     

Electrochromic hysteresis performance of a prussian blue film arising from electron-transfer control by a tris(2,2'-bipyridine)ruthenium(II)-doped WO(3) film as studied by a spectrocyclic voltammetry technique

A [Ru(bpy)(3)](2+) (bpy=2,2'-bipyridine)-doped WO(3) film was prepared as a base layer on a substrate by cathodic electrodeposition from a colloidal triad solution containing peroxotungstic acid (PTA), [Ru(bpy)(3)](2+), and poly(sodium 4-styrenesulfonate) (PSS). A Prussian blue (PB; Fe(II)-Fe(III)) film was cathodically electrodeposited on the [Ru(bpy)(3)](2+)-doped WO(3) film or neat WO(3) film from an aqueous Berlin brown (BB; Fe(III)-Fe(III)) colloid solution to yield a [Ru(bpy)(3)](2+)-doped WO(3)/PB bilayer film or WO(3)/PB bilayer film. For the spectrocyclic voltammogram (SCV) of the WO(3)/PB film, a redox response of Prussian white (PW; Fe(II)-Fe(II))/PB was observed at 0.11 V, however, further oxidation of PB to BB was not allowed by the interfacial n-type Schottky barrier between the WO(3) and PB layers. For the [Ru(bpy)(3)](2+)-doped WO(3)/PB film, any electrochemical response assigned to the redox of PB was not observed in the cyclic voltammogram, however, the in situ absorption spectral change recorded simultaneously showed the significant redox reactions based on PB. The SCV revealed that PW on the [Ru(bpy)(3)](2+)-doped WO(3) film is completely oxidized to PB by a geared reaction of Ru(II)/Ru(III) at 1.05 V, and that 32 % of PB formed is further oxidized to BB by the same geared reaction in the potential scan to 1.5 V. PB was completely re-reduced to PW by a geared reaction of H(x)WO(3)/WO(3) at -0.5 V in the reductive potential scan. These geared electrochemical reactions produced an electrochromic hysteresis performance of the PB film layered on the [Ru(bpy)(3)](2+)-doped WO(3) film.     

Enantioselective epoxidation by the chiral auxiliary approach: Asymmetric total synthesis of (+)-Ambrisentan

Enantioselective and a highly concise total synthesis of Ambrisentan are described. The chiral auxiliary controlled enantioselective epoxidation (Azerad protocol), photochemical regioselective epoxide opening, and base mediated ester hydrolysis reactions are the key reactions.