Antioxidant product analysis of Folium Hibisci Mutabilis

Folium Hibisci Mutabilis, a new member of Chinese Pharmacopoeia, can treat some diseases induced by reactive oxygen species. The study prepared a lyophilized aqueous extract of Folium Hibisci Mutabilis (LAFHM). LAFHM was found to enrich eight flavonoids (i.e., quercetin, luteolin, hyperoside, isoquercitrin, rutin, kaempferol, tiliroside, and vitexin) by HPLC analysis. These flavonoids were further compared using antioxidant assays, where triliroside and vitexin always exhibited higher IC₅₀ values than the others. In ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry analysis, these flavonoids could basically give two characteristic m/z values (226 and 196) and their corresponding double m/z values (i.e., 602, 570, 926, 926, 570, 1186, and 862), when treated by 1,1-diphenyl-2-picryl-hydrazl radical (DPPH^?). Finally, the coupling products of DPPH^?-treated triliroside were investigated using computational chemistry. It was found that the –OH in para-coumaroyl moiety to have the lowest bond disassociation energy among all phenolic -OHs in the triliroside. In conclusion, Folium Hibisci Mutabilis contains the above eight antioxidant flavonoids. Despite of the different antioxidant levels, they can generally produce flavonoid-radical coupling product and flavonoid-flavonoid homodimer during antioxidant process. Especially, tiliroside uses para-coumaroyl as linker to construct a tiliroside-radical coupling product at the meta-carbon atom.     

Evaluation of Bookkeeper mass deacidification based on historical book papers

Cellulose - Bookkeeper, the most widely used deacidification process based on MgO particles, was systematically evaluated on two sets of nonvaluable historical paper samples. Established analytical...     

Thermal electrocyclization reactions II: benzooctatetraenes and benzodecapentaenes

Thermal electrocyclization reactions of benzooctatetraenes and benzodecapentaenes substituted with R=H, Cl, and methyl were studied experimentally and computationally. Methyl and unsubstituted benzooctatetraenes and benzodecapentaenes give the [4.2.0]bicyclooctadiene products by 8π,6π-electrocyclization. Chlorine substitution led to thermal rearrangement of the initially formed 8π,6π-electrocyclization intermediates to give unprecedented products.     

Mechanical and anti‐stabbing properties of modified thermoplastic polymers impregnated multiaxial p‐aramid fabrics

New forms of hybrid multiaxial nanocomposites with enhanced mechanical and stab resisting properties are presented. This study is motivated by the lack of knowledge in the study of the multiaxial fabric nanocomposites with two modified thermoplastic matrices for antiballistic protection. Introduction of 5 wt.% silica nanoparticles in the composite of polyurethane/p‐aramid/poly (vinyl butyral) leads to significant improvement in mechanical properties, and the addition of silane as a coupling agents and glutaraldehyde as a crosslinking agents yielded maximal values of storage modulus, tensile modulus and anti‐stabbing properties for hybrid nanocomposites. Ballistic resistance testing and penetration depth of the hybrid nanocomposites were visualized using image analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Photophysics of Push–Pull Distyrylfurans,Thiophenes and Pyridines by Fast and Ultrafast Techniques

Time‐resolved transient absorption and fluorescence spectroscopy with nano‐ and femtosecond time resolution were used to investigate the deactivation pathways of the excited states of distyrylfuran, thiophene and pyridine derivatives in several organic solvents of different polarity in detail. The rate constant of the main decay processes (fluorescence, singlet–triplet intersystem crossing, isomerisation and internal conversion) are strongly affected by the nature [locally excited (LE) or charge transfer (CT)] and selective position of the lowest excited singlet states. In particular, the heteroaromatic central ring significantly enhances the intramolecular charge‐transfer process, which is operative even in a non‐polar solvent. Both the thiophene and pyridine moieties enhance the S₁→T₁ rate with respect to the furan one. This is due to the heavy‐atom effect (thiophene compounds) and to the ¹(π,π)*→³(n,π)* transition (pyridine compounds), which enhance the spin‐orbit coupling. Moreover, the solvent polarity also plays a significant role in the photophysical properties of these push–pull compounds: in fact, a particularly fast ¹LE*→¹CT* process was found for dimethylamino derivatives in the most polar solvents (time constant, τ≤400 fs), while it takes place in tens of picoseconds in non‐polar solvents. It was also shown that the CT character of the lowest excited singlet state decreased by replacing the dimethylamino side group with a methoxy one. The latter causes a decrease in the emissive decay and an enhancement of triplet‐state formation. The photoisomerisation mechanism (singlet/triplet) is also discussed.     

Deep extractive desulfurization of diesel fuels by FeCl3/ionic liquids

The extractive desulfurization of dibenzothiophene（DBT）,benzothiophene（BT）,and 4,6-dimethyldi-benzothiophene （4,6-DMDBT） in model oil was carried out using anhydrous FeCl₃ and 1-methyl-3-octylimidazolium chloride system（[Omim|Cl·2FeCl₃）.This new system exhibited high extractive efficiency and the sulfur removal of DBT in model oil(V_IL/V_oil=1/20) could reach 99.4%at room temperature for 30 min,which was obviously superior to single[Omim]Cl as extractant（22.9%）.When the[Omim|CI·2FeCl₃ was used,the S-removal of 4,6-DMDBT and BT could also be up to 99.3%and 96.2%, respectively.Moreover,the ionic liquid could be recycled five times without a significant decrease in extractive ability.     

Carprofen-imprinted monolith prepared by reversible addition–fragmentation chain transfer polymerization in room temperature ionic liquids

To obtain fast separation, ionic liquids were used as porogens first in combination with reversible addition–fragmentation chain transfer (RAFT) polymerization to prepare a new type of molecularly imprinted polymer (MIP) monolith. The imprinted monolithic column was synthesized using a mixture of carprofen (template), 4-vinylpyridine, ethylene glycol dimethacrylate, [BMIM]BF₄, and chain transfer agent (CTA). Some polymerization factors, such as template-monomer molar ratio, the degree of crosslinking, the composition of the porogen, and the content of CTA, on the column efficiency and imprinting effect of the resulting MIP monolith were systematically investigated. Affinity screening of structurally similar compounds with the template can be achieved in 200 s on the MIP monolith due to high column efficiency (up to 12,070 plates/m) and good column permeability. Recognition mechanism of the imprinted monolith was also investigated.     

Preparation and characterization of an imprinted monolith by atom transfer radical polymerization assisted by crowding agents

A method based on reverse atom transfer radical polymerization (R-ATRP) and molecular crowding has been used for design and synthesis of monolithic molecularly imprinted polymers (MIPs) capable of recognizing ibuprofen (IBU). 4-Vinylpyridine (4-VP) was used as the functional monomer, and ethylene glycol dimethacrylate (EDMA) was the crosslinking monomer. Azobisisobutyronitrile (AIBN)–CuCl₂–N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) was used as the initiating system. Compared with conventional radical polymerization-based IBU-MIPs, the imprinting effects of the obtained IBU-MIPs was enhanced, suggesting the merit of combination of reverse ATRP and molecular crowding. In addition, it was found that the polymerization time of the molecularly imprinted monolithic column, the amount of template, the degree of crosslinking, and the composition of mobile phase greatly affected retention of the template and the performance of molecular recognition .

Changes of organic acids and phenolic compounds contents in grapevine berries during their ripening

Changes of total content of phenolic substances, alteration in total titratable acidity and differences in tartaric acid content in grapes of four white (Müller-Thurgau — MT, Pinot Blanc — Rulandské bílé in Czech, RB, Sauvignon (Sg), and Muscat Ottonel — Mu?kát Ottonel in Czech, MO) and two blue (Dornfelder — Df and Blue Frankish — Frankovka in Czech, Fr) grapevine varieties throughout their growth, ripening and maturing (July–November). Potentiometric titration was applied for the determination of total titratable acids in grapes (expressed as tartaric acid equivalents in g L^?1). A spectrophotometric method according Rebelein based on the formation of a colored complex of ammonium metavanadate and tartaric acid was used for determination of tartaric acid in green juice made by pressing unripe grapes. A spectrophotometric method based on reduction of phosphomolybdato-tungsten complex in alkaline solution using Folin-Ciocalteau reagent was applied for determination of total content of phenolic substances (TCP).

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A Convenient Synthesis of Juglone Via Neutral Salcomine Oxidation

1,5-Dihydroxynaphthalene and its derivatives can be oxidized by molecular oxygen in the presence of catalytic amounts of salcomine under neutral conditions to afford the corresponding 1,4-naphthoquinones as the major products.