Development of a sensitive liquid chromatography/tandem mass spectrometry method for the determination of fenofibric acid in rat plasma

A rapid and sensitive LC‐MS/MS method for the quantification of fenofibric acid in rat plasma was developed and validated. Plasma samples were prepared by liquid–liquid extraction with a mixture of N‐hexane–dichloromethane–isopropanol (100:50:5, v/v/v). Isocratic chromatographic separation was performed on a reversed‐phase Discovery C₁₈ column (2.1 × 50 mm, 5 µm). The mobile phase was methanol–water–formic (75:25:0.25, v/v/v). Detection of fenofibric acid and the internal standard (IS) diclofenac acid was achieved by ESI MS/MS in the negative ion mode using m/z 317 → m/z 213 and m/z 294 → m/z 250 transitions, respectively. The method was linear from 0.005 to 1.250 µg/mL when 100 μL plasma was analyzed. The lower limit of quantification was 0.005 µg/mL. The intra‐ and inter‐day precision values were below 8.2%, and accuracy ranged from ?0.9 to 2.1% in all quality control samples. The recovery was 90.3–94.7% and 83.3% for fenofibric acid and IS, respectively. Total run time for each sample analysis was 2.5 min. The validated method was successfully applied to a pharmacokinetic study in six rats after oral administration of fenofibrate, the ester prodrug of fenofibric acid (equivalent to fenofibric acid 5 mg/kg). The method permits laboratory scientists with access to the appropriate instrumentation to perform rapid fenofibric acid determination. Copyright © 2011 John Wiley & Sons, Ltd.     

The water hexamer: cage, prism, or both. Full dimensional quantum simulations say both

State-of-the-art quantum simulations on a full-dimensional ab initio potential energy surface are used to characterize the properties of the water hexamer. The relative populations of the different isomers are determined over a wide range of temperatures. While the prism isomer is identified as the global minimum-energy structure, the quantum simulations, which explicitly include zero-point energy and quantum thermal motion, predict that both the cage and prism isomers are present at low temperature down to almost 0 K. This is largely consistent with the available experimental data and, in particular, with very recent measurements of broadband rotational spectra of the water hexamer recorded in supersonic expansions.     

Asymmetric total synthesis of (+)-monocerin

A concise asymmetric total synthesis of (+)-monocerin has been accomplished. The cis-fused furobenzopyranone of monocerin was efficiently constructed via a Lewis acid-mediated stereoselective cyclization of 1,2,4-triols intermediate.     

Stacking‐Induced Diamagnetic/Paramagnetic Conversion of Imidazo[1,2‐a]pyridin‐2(3 H)‐one Derivatives: Near‐Infrared Absorption and Magnetic Properties in the Solid State

Herein, we present three imidazo[1,2‐a]pyridin‐2(3 H)‐one derivatives that are diamagnetic in solution, but paramagnetic in the solid state, possibly owing to a stacking‐induced formation of phenoxide‐type radicals. Notably, a larger bathochromic shift of the absorption (even up to the near‐ infrared region) of these three compounds was observed in the solid state than in solution, which was attributable to the ordered columnar stacking arrangements or their single‐electron character as radicals in the solid state. Interestingly, compared to that in solution, (E)‐3‐(pyridin‐4′‐ylmethylene)imidazo[1,2‐a]pyridine 2(3 H)‐one displayed a largely red‐shifted emission (centered at 660 nm, with tailing above 800 nm) in the solid state. A larger bathochromic shift (260 nm) of the emission is an indication of better order and tight stacking in the solid state, which is brought about by the rigid and polar acceptor. These three compounds also reveal different magnetic susceptibilities at 300 K, thus implying that they possess various columnar stacking structures. Most interestingly, these three radicals exhibit unusual ferromagnetic‐to‐antiferromagnetic phase transitions, which can be attributed to anisotropic contraction and non‐uniform slippage of the columnar stacking chains.     

Synthesis and characterization of A2 + B3 type hyperbranched aromatic-aliphatic polyester with carboxyl end groups

New types of carboxyl-terminated hyperbranched polyesters (HBPEs) with aromatic-aliphatic structure were synthesized by single step-melt polycondensation of adipic acid (as A2 monomer) and phloroglucinol (as B3 monomer) as a core via A₂ + B₃ approach, at three different monomer mole ratios (A₂/B₃ = 1: 1, 1.5: 1, 2: 1, respectively). FTIR spectroscopy indicated that the polymers contained hydroxyl groups, ester bonds, benzene ring, methyl and methylene groups, which were in agreement with the expected HBPEs. The HBPEs have inherent viscosities about 0.24 to 0.27 dL/g. The degree of branching of the HBPEs was estimated to be 0.45–0.49% by ¹H-NMR and ¹³C-NMR measurements. The melting temperature of HBPE-1, HBPE-2 and HBPE-3 were 154, 155 and 160°C respectively measured by differential scanning calorimetry (DSC). The synthesized polymers were thermally stable; the thermogravimetric analysis (TGA) measurement revealed that HBPEs had 10% weight loss at 310°C in nitrogen.     

Clean,One‐Pot Synthesis of Naphthopyran Derivatives in Aqueous Media

A general and practical one‐pot synthesis of naphthopyran derivatives using hexadecyltrimethylammonium bromide (HTMAB) as catalyst (10 mol%) is described. This method provides several advantages such as neutral conditions, high yields and simple workup procedure. The catalyst is low cost, facile, active, environmentally friendly, and reusable. In addition, water is chosen as a green solvent.     

Synthesis and characterization of side chain cholesteric liquid crystalline elastomers derived from chiral bisolefinic crosslinking units

In this work we prepared a nematic monomer (4′‐allyloxybiphenyl 4′‐ethoxybenzoate, M₁ ), a chiral crosslinking agent (isosorbide 4‐allyloxybenzoyl bisate, M₂ ) and a series of new side chain cholesteric liquid crystalline elastomers derived from M₁ and M₂ . The chemical structures of the monomers and polymers were confirmed by FTIR and ¹H NMR spectroscopy. The mesomorphic properties were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy and X‐ray diffraction. The effect of the content of the crosslinking unit on phase behaviour of the elastomers is discussed. Polymer P₁ showed a nematic phase, P₂ –P₇ showed a cholesteric phase; P₆ formed a blue Grandjean texture over a broad temperature range 145–209.6°C, with no changed on the cooling. Polymers P₄ –P₇ , with more than 6?mol?% of chiral crosslinking agent, gave rise to selective reflection. Elastomers containing less than 15?mol?% of the crosslinking units displayed elasticity, reversible phase transition with wide mesophase temperature ranges, and high thermal stability. Experimental results demonstrated that, with increasing content of crosslinking agent, the glass transition temperatures first fell and then increased; the isotropization temperatures and mesophase temperature ranges decreased.     

微波辐照制备无皂阳离子PMMA胶乳粒子

在微波辐照条件下 ,用偶氮二异丁基脒盐酸盐 (AIBA)引发甲基丙烯酸甲酯的均聚 ,制得窄分散的无皂阳离子胶乳粒子 .讨论了引发剂的浓度、单体的浓度、离子强度等对粒子大小、分散性和乳液稳定性的影响 .对微波辐照和水浴加热进行比较 ,发现微波辐照反应速度快、反应无恒速阶段 ,所得粒子的粒径小 ,粒子数目多 ,这为通过改变反应条件制备适宜的窄分散的胶乳粒子提供了一条途径 .     

过渡金属配合物催化的二氧化碳的固定*

综述了利用过渡金属配合物和二氧化碳的配位及插入反应实现二氧化碳固定的基本方法、原理及其研究现状。