Sesquiterpenoids from the Rhizome of Ligularia virgaurea

Two novel sesquiterpene dimers, compounds 1 and 2 , were isolated from the rhizome of Ligularia virgaurea, together with the six known sesquiterpenoids 3 – 8 . Their structures were established by physico‐chemical and spectroscopic methods, especially by means of 1D‐ and 2D‐NMR as well as HR‐MS analyses. A mechanism based on a classical Diels–Alder cyclization is proposed for the formation of the dimer 1 from the precursors 8 and the quinone form of 6 (Scheme).     

高效液相色谱切换波长法测定多组分体系

1引言目前植物激素常采用反相高效液相色谱法检测,但植物中激素等多种组分同时存在,单一波长不能使每个组分都在最佳检测波长下检测。本实验采用切换波长法对植物样品进行多组分检测分析,提高了检测灵敏度。采用反相高效液相色谱法(HPLC)同时测定油菜中的内源激素赤霉素(GA3)、     

Hydrothermal synthesis and crystal structure of a layered vanadium oxide with an interlayer metal coordination complex: [Co(phen)3][V10O26]·H2O

A novel compound, [Co(phen)₃][V₁₀O₂₆]·H₂O, was hydrothermally synthesized and characterized by single-crystal X-ray diffraction. This compound crystallizes in the orthorhombic space group Ccca with a=13.447(3), b=29.936(6), c=23.252(5) Å, V=9360(3) Å³, Z=8 and R=0.0285. Data were collected on a Rigaku R-AXIS RAPID IP diffractometer at 293 K in the range of 1.36<θ<24.99°. The structure of the compound consists of vanadium oxide layers, which are built up from the infinite VO₄ chains by corners and edges sharing. The [Co(phen)₃]²⁺ complexes occupy the interlayer space and contact each other via π−π stacking interactions of the phen groups to form infinite one-dimensional chains.     

Emulsion polymerization of methyl methacrylate under pulsed microwave irradiation

Emulsion polymerization of methyl methacrylate (MMA) under pulsed microwave irradiation (PMI) with higher peak pulse power was studied. The effects of various parameters of PMI on the polymerization were analyzed and compared with that under conventional heating (CH) process. The results were summarized, as compared with that under CH, as follows. The amount of initiator used to reach constant conversion reduced by 50% at the same polymerization time; at the same initiator concentration 0.15 and 0.2 wt.%, the polymerization rate increased by 131% and 163%, respectively. The molecular weight of polymer obtained was 1.1-2.0 times larger than that under CH; at the same irradiation energy, the conversion achieved using a lower pulse power was greater than that using a higher pulse power. There seemed to be a factor of the irradiation energy efficiency; in other words, for the monomer conversion, the irradiation energy of low pulse power had a higher efficiency. The conversion achieved using a 3.5 μs pulse width was almost the same as that using a 1.5 μs pulse width. The results indicated that PMI had a significant non-thermal effect on the emulsion polymerization of MMA so as to effectively enhance the polymerization rate. The glass transition temperature (T_g), the polydispersity index (PDI) and the regularity of the polymer obtained using two processes were similar, indicating that the physical properties and microstructure of the polymer were not modified by the use of microwaves.     

exo- and enantioselective cycloaddition of azomethine ylides generated from N-alkylidene glycine esters using chiral phosphine-copper complexes

High diastereo- and enantioselectivities were obtained for the asymmetric 1,3-dipolar cycloaddition of azomethine ylides generated from N-alkylideneglycine esters with dipolarophiles using chiral phosphine-copper complexes as catalysts. Whereas the cycloaddition of azomethine ylides catalyzed by metal salts generally afforded endo-adducts as the predominant product, the present method is the first example of an exo-selective cycloaddition. [reaction: see text]     

马来酸酐封端聚碳酸亚丙酯的大分子偶联反应

自从 1 969年井上祥平[1] 发现二氧化碳 (CO2 )可以同环氧化合物直接共聚合成脂肪族聚碳酸酯(APC)以来 ,这一学科领域受到科学家的广泛关注[2～ 8] .这是因为CO2 所产生的温室效应 ,成为使全球变暖的主要因素[9,10 ] .已经确定CO2 使气侯变暖占诸多因素中的 66% .目前大气中CO2 的体积浓度为 345ppmv,由于人类的各类活动每年以 1ppmv的速度递增 .因此 ,降低CO2 排放量已成为全人类共同关注的热点之一 .另一方面 ,CO2 的固定化以及消耗、利用显然是一个应积极鼓励的研究课题 .目前人们已经将CO2 同环氧乙烷 (EO)、环氧丙烷 (PO)、环…     

Kinetic spectrophotometric determination of trace manganese (II) with dahlia violet in nonionic microemulsion medium

A new catalytic kinetic spectrophotometric method has been developed for the determination of trace amount of manganese (II) in nonionic microemulsion medium. The method is based on the catalytic effect of manganese (II) on the oxidation of dahlia violet by potassium periodate with nitrilotriacetic acid as an activitor in the presence of nonionic microemulsion. Under the optimum conditions, the calibration graph is linear in the range of 0.0004-0.0056 μg ml⁻¹ of manganese (II) at 580 nm. The detection limit achieved is 3.75×10⁻⁵ μg ml⁻¹. Manganese (II) in foodstuff samples was determined with satisfactory results.     

Thermodynamics and kinetics of the hydride-transfer cycles for 1-aryl-1,4-dihydronicotinamide and its 1,2-dihydroisomer

Five 1-(p-substituted phenyl)-1,4-dihydronicotinamides (GPNAH-1,4-H(2)) and five 1-(p-substituted phenyl)-1,2-dihydronicotinamides (GPNAH-1,2-H(2)) were synthesized, which were used to mimic NAD(P)H coenzyme and its 1,2-dihydroisomer reductions, respectively. When the 1,4-dihydropyridine (GPNAH-1,4-H(2)) and the 1,2-dihydroisomer (GPNAH-1,2-H(2)) were treated with p-trifluoromethylbenzylidenemalononitrile (S) as a hydride acceptor, both reactions gave the same products: pyridinium derivative (GPNA(+)) and carbanion SH(-) by a hydride one-step transfer. Thermodynamic analysis on the two reactions shows that the hydride transfer from the 1,2-dihydropyridine is much more favorable than the hydride transfer from the corresponding 1,4-dihydroisomer, but the kinetic examination displays that the former reaction is remarkably slower than the latter reaction, which is mainly due to much more negative activation entropy for the former reaction. When the formed pyridinium derivative (GPNA(+)) was treated with SH(-), the major reduced product was the corresponding 1,4-dihydropyridine along with a trace of the 1,2-dihydroisomer. Thermodynamic and kinetic analyses on the hydride transfer from SH(-) to GPNA(+) all suggest that the 4-position on the pyridinium ring in GPNA(+) is much easier to accept the hydride than the 2-position, which indicates that when the 1,4-dihydropyridine is used the hydride donor to react with S, the formed pyridinium derivative GPNA(+) may return to the 1,4-dihydropyridine by a hydride transfer cycle; but when the 1,2-dihydropyridine is used as the hydride donor, the formed pyridinium derivative can not return to the 1,2-dihydropyridine by the hydride reverse transfer from SH(-) to GPNA(+). These results clearly show that the hydride-transfer cycle is favorable for the 1,4-dihydronicotinamides, but unfavorable for the corresponding 1,2-dihydroisomers.     

Silica nanoparticles for separation of biologically active amines by capillary electrophoresis with laser-induced native fluorescence detection

This paper describes the analysis of biologically active amines by capillary electrophoresis (CE) in conjunction with laser-induced native fluorescence detection. In order to simultaneously analyze amines and acids as well as to achieve high sensitivity, 10 mM formic acid solutions (pH < 4.0) containing silica nanoparticles (SiNPs) were chosen as the background electrolytes. With increasing SiNP concentration, the migration times for seven analytes decrease as a result of increase in electroosmotic flow (EOF) and decrease in their electrophoretic mobilities against EOF. A small EOF generated at pH 3.0 reveals adsorption of SiNPs on the deactivated capillary wall. The decreases in electrophoretic mobilities with increasing SiNP concentration up to 0.3x indicate the interactions between the analytes and the SiNPs. Having a great sensitivity (the limits of detection at a signal-to-noise ratio (S/N) = 3 of 0.09 nM for tryptamine (TA)), high efficiency, and excellent reproducibility (less than 2.4% of the migration times), this developed method has been applied to the analysis of urinal samples with the concentrations of 0.50 +/- 0.02 microM, 0.49 +/- 0.04 microM, and 74 +/- 2 microM for TA, 5-hydroxytryptamine, and tryptophan, respectively. The successful examples demonstrated in this study open up a possibility of using functional nanoparticles for the separation of different analytes by CE.     

Conversion of phenyl-substituted cyclopentadienes to pyrylium cations

Phenyl-substituted cyclopentadienes are proved to form phenylated pyrylium cations in the presence of silver(I) perchlorate by insertion of an oxygen atom into the cyclopentadiene-ring. Three phenylated pyrylium compounds, [(Ph(5)C(5)O(+))(ClO(4)(-))](2)(CH(2)Cl(2)) (1), Ag(ClO(4))(H(2)O)(Ph(4)HC(5)O(+)) (ClO(4)(-)) (2), and (Ph(3)H(2)C(5)O(+))(ClO(4)(-)) (3) have been synthesized and characterized. A possible reaction pathway and formation mechanism of the pyrylium cation are proposed and discussed.