Preparation and separation of all possible rotamers of a stereochemical analog of meso-tartaric acid: optically inactive and optically active isomers of (R,S)-2,2′-bis(methoxycarbonyl)-6,6′-dimethyl-9,9′-bitriptycyl

All the three possible rotamers of the title compound were separated by chromatography, and unambiguously identified by NMR and X-ray analysis. One of the isomers was optically inactive C_i conformation. The other optical active forms were resolved to give a pair of enantiomers, which were characterized by optical rotation and CD spectra. Thus the optical inactivity of a compound such as meso-tartaric acid that can take C_i conformation in solution, is now ascribed to that the molecule has an optically inactive C_i conformer and equal amounts of optically active conformers, that are enantiomers, in solution.     

Cloning and characterization of an active fragment of luciferase from a luminescent marine alga, Pyrocystis lunula

Two marine dinoflagellates, Lingulodinium polyedrum and Pyrocystis lunula, emit light in a reaction involving the enzymatic oxidation of its tetrapyrrole luciferin by molecular oxygen. The characteristic properties of P. lunula luciferase have not been clarified, whereas L. polyedrum luciferase, which has three active domains, has been characterized. A cloned partial cDNA of the P. lunula luciferase encodes an active fragment corresponding to part of domain 2 and all of domain 3 of L. polyedrum luciferase. The homology of the amino acid sequence between the two luciferases in domain 3 is about 84.3%. A recombinant His-tagged luciferase fragment containing domain 3 (Mr = 46 kDa) catalyzed the light-emitting oxidation of luciferin (lambdamax = 474 nm). This protein was purified by a single affinity-chromatography procedure. The pH-activity profile and the bioluminescence spectrum of the recombinant enzyme having a third domain are almost identical to those of an extract from P. lunula cultured in vitro. The recombinant enzyme is active at pH 8.0, although the recombinant enzyme derived from the second domain of L. polyedrum luciferase is inactive at pH 8.0. Substitution of Glu-201 by histidine in the third domain of P. lunula luciferase showed a decrease of activity above pH 7.0, suggesting that histidine residues could be responsible for pH-sensitivity in dinoflagellate luciferase.     

Temperature dependence of free volume of polyacrylamide gels studied by positron lifetime measurements

Changes of positronium (Ps) cavity radii in polyacrylamide and poly(N-isopropylacrylamide) gels were studied from 120 to 300 K by positron lifetime technique and it has been shown that the Ps cavity radius in the hydrogels changes by three or four stages. Temperature dependence of the Ps cavity radius exhibits variations similar to common polymers around the glass transition temperature. Hydrophilicity of the polymer chains significantly affects the Ps cavity radius just below 273 K. These results suggest an important role of free volume on the state of water in hydrogels.     

Formation and Crystallization Behavior of Gels in the Na2O-SiO2-TiO2-ZrO2 System

SiO₂-TiO₂-ZrO₂ and 5Na₂O·95(SiO₂ + TiO₂ + ZrO₂) gels were synthesized and role of Na₂O in gel formation and crystallization behavior of gels were studied. From Si(OC₂H₅)₄, Ti(iso-OC₃H₇)₄, Zr(n-OC₃H₇)₄ and NaOCH₃ solutions in EtOH without H₂O, transparent and opaque gels were obtained. Opaque bulk gels, rich in TiO₂ or ZrO₂ composition in Na₂O containing SiO₂-TiO₂-ZrO₂ system, contain agglomerated spherical particles of diameter small <10 m, in contrast with opaque gels having large particles <30 m in alkali-free SiO₂-TiO₂-ZrO₂ system. Crystallization temperature (Tc) was measured by DTA on dried gels. Compared with the alkali-free SiO₂-TiO₂-ZrO₂ gels, 5 mol% Na₂O containing gels gave lower Tc in SiO₂ rich compositions and higher in TiO₂ rich or ZrO₂ rich compositions.     

Ellagitannin Digestion in Moth Larvae and a New Dimeric Ellagitannin from the Leaves of Platycarya strobilacea

Ellagitannins (ETs) are plant polyphenols with various health benefits. Recent studies have indicated that the biological activities of ETs are attributable to their degradation products, including ellagic acid and its gut microflora metabolites, such as urolithins. Insect tea produced in the Guangxi region, China, is made from the frass of moth larvae that feed on the ET-rich leaves of Platycarya strobilacea. Chromatographic separation of the Guangxi insect tea showed that the major phenolic constituents are ellagic acid, brevifolin carboxylic acid, gallic acid, brevifolin, and polymeric polyphenols. Chemical investigation of the feed of the larvae, the fresh leaves of P. strobilacea, showed that the major polyphenols are ETs including pedunculagin, casuarictin, strictinin, and a new ET named platycaryanin E. The new ET was confirmed as a dimer of strictinin having a tergalloyl group. The insect tea and the leaves of P. strobilacea contained polymeric polyphenols, both of which were shown to be composed of ETs and proanthocyanidins by acid hydrolysis and thiol degradation. This study clarified that Guangxi insect tea contains ET metabolites produced in the digestive tract of moth larvae, and the metabolites probably have higher bioavailabilities than the original large-molecular ETs of the leaves of P. strobilacea.     

Photocycloaddition reaction of methyl 2- and 3-chromonecarboxylates with various alkenes

The irradiation of methyl 2- and 3-chromonecarboxylate in the presence of various alkenes afforded cyclobutane type adducts, whose structures were established by X-ray structural analysis. Methyl 2-chromonecarboxylate showed higher photochemical reactivity than methyl 3-chromonecarboxylate, in which endo adducts were yielded as major products.     

Cyclic sample pooling using two‐dimensional liquid chromatography system enhances coverage in shotgun proteomics

We report a cyclic sample pooling technique devised in two‐dimensional liquid chromatography–electrospray ionization mass spectrometry (LC‐ESI‐MS) shotgun proteomics that renders deeper proteome coverage; we combined low pH reversed‐phase (RP) LC in trifluoroacetic acid in the first dimension, followed by cyclic sample pooling of the eluate and low‐pH RP‐LC in formic acid in the second dimension. The new protocol has a significantly higher resolving power suitable for LC‐ESI‐MS/MS shotgun proteomics. Copyright © 2013 John Wiley & Sons, Ltd.     

Polymerization and photoinitiation behavior in the light-cured dental composite resins

The polymerization behavior and photoinitiation process in the visible light-cured dental composite resins were studied using ESR and IR spectroscopies. The concentration of methacryl propagating radical corresponded to the transmittance of irradiated light. While the radical was stable and long-lived in the cured resin, its concentration quickly decreased in the oral cavity due to the ventilation of atmospheric oxygen accompanied by respiration. Camphorquinone radical in the presence of tertiary amine easily initiated the radical polymerization. A decrease in monomer consumption was explained by the inhibition effect of oxygen in the photoinitiation process. Post-curing by the residual radical proceeded effectively in the deeper part of the resin.     

Pi-face-selective Diels-Alder reactions of 3,4-di-tert-butylthiophene 1-oxide and 1-imide and formation of 1,2-thiazetidines

3,4-Di-tert-butylthiophene 1-oxide (1a) reacted with a series of electron-deficient alkenic dienophiles at its syn-pi-face relating to the S=O bond to give [4+2] adducts in excellent yields. The 1-oxide 1a also reacted even with angle-strained dienophiles acenaphthylene and norbornene at its syn-pi-face to afford [4+2] adducts; in the latter case, norbornene reacted exclusively at its exo-pi-face. The oxide 1a reacted with dimethyl acetylenedicarboxylate to produce dimethyl 4,5-di-tert-butylphthalate in high yield with spontaneous extrusion of SO from the initial adduct even at room temperature. Similarly, 3,4-di-tert-butylthiophene 1-(p-toluenesulfonyl)imide (3a) reacted with alkenic dienophiles at its syn-pi-face relating to the S=N bond to give [4+2] adducts in good yields. The reaction of 3a with 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) afforded a 1,2-thiazetidine 12a, the first example of S-unoxidized 1,2-thiazetidine, in good yield, through rearrangement of the initial [4+2] adduct. The molecular structure of 12a is discussed on the basis of the X-ray crystallographic analysis. Comparison of the foregoing reactions leads to the conclusion that the 1-oxide 1a is more reactive as a diene than the 1-imide 3a, which is more reactive than 3,4-di-tert-butylthiophene 1,1-dioxide. The origin of the syn-pi-face selectivities of 1a and 3a in Diels-Alder reactions is discussed in terms of the orbital mixing rule and steric effect and also based on B3LYP/6-31G(d) calculations.