Short syntheses of (−)-clavaminol A and deacetyl (+)-clavaminol H

Concise stereoselective syntheses of (?)-clavaminol A and deacetyl (+)-clavaminol H have been achieved from simple starting materials. Highlights of the synthesis for (?)-clavaminol A include a highly diastereoselective chelation-controlled hydride reduction of an amino ketone to give the anti amino alcohol directly, and NaBH₄-mediated dehalogenation. The main synthetic approach for deacetyl (+)-clavaminol H features a highly diastereoselective chelation-controlled hydride reduction of the amino ketone to construct the anti amino alcohol and a palladium catalyzed hydrogenation reaction at the final step.     

超级微波消解-电感耦合等离子体发射光谱（ICP-OES）法测定土壤中18种元素

为提高土壤多元素同时检测的效率,采用超级微波消解-电感耦合等离子体发射光谱法测定土壤中钾、钠、钙、镁、铜、铁、锰、锌、磷、硫、硼、砷、镉、铬、铅、钴、镓、锂等18种元素含量。比较了超级微波消解、常规微波消解和电热板消解的处理效果,采用超级微波消解法对样品进行前处理,并优化了消解条件。在最优条件下,各元素的检出限在0.05~20 mg/kg,加标回收率在86.2%~107.5%,RSD在0.1%~3.0%,方法准确度及精密度可以满足多元素同时测定的需求,且该方法具有简单、快速、成本低、用酸量少、重现性好等特点。     

芫花有效成分的研究——Ⅲ.新的二萜原酸酯芫花酯丙的分离与结构

瑞香科植物芫花的花以乙醇提取,除分得芫花酯甲、酯乙外,尚分得新的二萜原酸酯芫花酯丙。根据光谱和化学反应确定其结构为1。从该植物根的石油醚提取物中分得已知二萜原酸酯-12-苯甲酰氧基瑞香毒素(2)。1和2均对皮肤有刺激作用,1对孕猴具有引产作用。     

Laser photolysis of zinc porphyrin dissolved in cyanohexylbiphenyl liquid crystal

A laser photolysis study of ZnTPP (P) oriented in nematic and isotropic cyanohexylbiphenyl (6CB) as a function of added 1.4-benzoquinone (Q) is reported. In the absence of Q, enhancement of triplet absorption below the clearing point (nematic phase) is observed. It is attributed to the improved alignment of the optical transition in the ordered matrix and also to the increase in the intersystem crossing efficiency. T−S₁. In the presence of Q in the nematic phase. An additional increase in triplet absorption is noticed. This result is interpreted in terms of a triplet radical pair [P^+√…Q^−√]^T,RP formation which is facilitated by the ordering in the liquid crystal, thus providing an additional channel for triplet formation. The triplet P^T in 6CB (nematic or isotropic) is quenched with a second-order rate of ≈10⁸ M⁻¹ s⁻¹ as compared to 2 × 10⁹ M⁻¹ s⁻¹ in toluene.     

三阶泛函微分方程的周期解的存在性

本文利用重合度理论研究了一类三阶泛函微分方程方程的2π-周期解的问题,获得了该方程存在2π-周期解的若干新结论,改进推广了有关文献中的已有结果．     

Axiomatisability and hardness for universal Horn classes of hypergraphs

We consider hypergraphs as symmetric relational structures. In this setting, we characterise finite axiomatisability for finitely generated universal Horn classes of loop-free hypergraphs. An Ehrenfeucht–Fraïssé game argument is employed to show that the results continue to hold when restricted to first order definability amongst finite structures. We are also able to show that every interval in the homomorphism order on hypergraphs contains a continuum of universal Horn classes and conclude the article by characterising the intractability of deciding membership in universal Horn classes generated by finite loop-free hypergraphs.     

Neutral Higgs bosons in the MNMSSM with explicit CP violation

Within the framework of the minimal non-minimal supersymmetric standard model (MNMSSM) with tadpole terms, CP violation effects in the Higgs sector are investigated at the one-loop level, where the radiative corrections from the loops of the quark and squarks of the third generation are taken into account. Assuming that the squark masses are not degenerate, the radiative corrections due to the stop and sbottom quarks give rise to CP phases which trigger the CP violation explicitly in the Higgs sector of the MNMSSM. The masses, the branching ratios for dominant decay channels, and the total decay widths of the five neutral Higgs bosons in the MNMSSM are calculated in the presence of explicit CP violation. The dependence of these quantities on the CP phases is quite recognizable, for given parameter values.