Novel taxoids from the Chinese yew Taxus yunnanensis

Six new taxoids, taxuyunnanines W (1), X (2), Y (3), Z (5), 10-deacetyl-10-(β-glucopyranosyl)-yunnanxane (8), and 7-(β-xylosyl)-N-methyl-taxol C (10), as well as taxuchin B (4) and yunnanxane (7), have been isolated from the bark of Taxus yunnanensis. Compounds 1 and 2 were characterized as 11(15→1)-abeo taxoids containing an orthoester group, which have not been reported from any Taxus plants to date; isolates 3 and 5 are the examples of taxanes having a tetrahydronfuran ring, being reported only for the second time; and 8 is the first natural 6/8/6 skeletal type taxane glucosidic form. This is also the first report of a co-occurrence of xylosidation and N-methylation in a taxane (10). Compound 4 is the only known chlorine-containing taxane found in nature thus far, and is being reported from this plant for the first time. The structures were determined by spectroscopic and chemical means including 1D and 2D NMR spectra.     

Using fluorene to lock electronically active moieties in thermally activated delayed fluorescence emitters for high-performance non-doped organic light-emitting diodes with suppressed roll-off

Thermally activated delayed fluorescence (TADF) emitters with aggregation-induced emission (AIE) features are hot candidates for non-doped organic light-emitting diodes (OLEDs), as they are highly emissive in solid states upon photoexcitation. Nevertheless, not every AIE-TADF emitter in the past had guaranteed decent efficiencies in non-doped devices, indicating that the AIE character alone does not necessarily afford ideal non-doped TADF emitters. As intermolecular electron-exchange interaction that involves long-lived triplet excitons plays a dominant role in the whole quenching process of TADF, we anticipate that it is the main reason for the different electroluminescence performances of AIE-TADF emitters. Therefore, in this work, we designed two TADF emitters SPBP-DPAC and SPBP-SPAC by modifying a reported less successful emitter BP-DPAC with extra fluorenes to increase intermolecular distances and attenuate this electron-exchange interaction. With the fluorene lock as steric hindrance, SPBP-DPAC and SPBP-SPAC exhibit significantly higher exciton utilization in non-doped films due to the suppressed concentration quenching. The non-doped OLEDs based on SPBP-DPAC and SPBP-SPAC show an excellent maximum external quantum efficiency (EQE) of 22.8% and 21.3% respectively, and what''s even more promising is that ignorable roll-offs at practical brightness (e.g., 1000 and 5000 cd m⁻²) were realized. These results reveal that locking the phenyl rings as steric hindrance can not only enhance the molecular rigidity, but also cause immediate relief of concentration quenching, and result in significant performance improvement under non-doped conditions. Our approach proposes a feasible molecular modification strategy for AIE-TADF emitters, potentially increasing their applicability in OLEDs.

Two TADF emitters were developed by modifying a reported less successful emitter BP-DPAC with fluorene to suppress concentration quenching. Their non-doped OLEDs displayed excellent EQEs of 22.8% and 21.3% with well-suppressed roll-off.     

Particle Transport with Asymmetric Unbiased Forces and Entropic Barrier

Transport of a Brownian particle moving along the axis of a three-dimensional （313） symmetric and periodic tube is investigated in the presence of asymmetric unbiased forces. It is found that in the presence of entropic barrier, the asymmetry of the unbiased forces is a way of inducing a net particle current. The particle current is a peaked function of temperature, which indicates that the thermal noise may facilitate the transport even in the presence of entropic barrier. There exists an optimized radius at the bottleneck at which the particle current takes its maximum value. The current can be influenced by the slope of tube walls and there exists an optimized slope for which the particle current takes its maximum value.     

Noise-Induced Transition in a Voltage-Controlled Oscillator Neuron Model

In the presence of Gaussian white noise, we study the properties of voltage-controlled oscillator neuron model and discuss the effects of the additive and multiplicative noise. It is found that the additive noise can accelerate and counterwork the firing of neuron, which depends on the value of central frequency of neuron itself, while multiplicative noise can induce the continuous change or mutation of membrane potential.     

溶剂热法制备硫化镍空心微球

以醋酸镍和硫代乙酰胺为原料, 乙醇为溶剂, 在150 ℃的溶剂热条件下制备了硫化镍空心微球, 并用XRD, TEM, SAED和SEM对产物进行了表征. 结果显示, 这些空心微球由β-NiS和α-NiS组成, 从反应开始得到的α-NiS实心球通过内核的消溶演变而成.     

铋对铅铋合金表面氧化膜生成的影响

铋对铅铋合金表面氧化膜生成的影响;铋;PbO;PbO+PbO·PbSO4;PbO2;蓄电池     

Dispersive Properties of tunnelling—induced transparency in an asymmetric double quantum well

We have investigated the dispersive properties of tunnelling-induced transparency in asymmetric double quantum well structures where two excited states are coupled by resonant tunnelling through a thin barrier in a three-level system of electronic subbands. The intersubband transitions exhibit high dispersion at zero absorption, which leads to the slow light velocity in this medium as compared with that in vacuum (c=3×10⁸). The group velocity in a specific GaAs/AlGaAs sample is calculated to be v_g=c/4.30. This structure can be used to compensate for the dispersion and energy loss in fibre optical communications.     

Metal compound-mediated hydrolytic cleavage of oxidized insulin B chain:Regioselectivity and influence of peptide secondary structure

The interaction of oxidized insulin B chain(B)with cis-[Pd-(en)Cl2](en=ethylenediamine),cis-[Pd-(dtco-3-OH)Cl2](dtco-3-OH=dithiacyclooctan-3-ol)and CuCl2 was studied by electrospray inass spectrometry.It is discovered that the binding of Pd(Ⅱ)complexes and the sites of cleavage are highly dependent on the secondary structure and local environment of B.The hydrolytic cleavage of denatured B by Pd(Ⅱ)complexes was monitored by HPLC.The reaction is regioselective and follows first order kinetics with half-life of 4.8 days at 40℃.Two amide bonds,i.e.at Leu6-Cys7 and at Gly8-Ser9,which are close to the two potential Pd(Ⅱ)binding sites His5 and His10,are selectively cleaved.In the case of Cu(Ⅱ)ion as promoter,only one cleavage site was observed which is located at Gly8-Ser9 bond.These results provide improved understanding on the design of artificial metallopeptidase.     

Structure and electrospray mass spectrometry studies on dithiacyclooctan-3-ol-containing palladium (II) complex of trans -[Pd(dtco-3-OH)_2](ClO_4)_2·2DMSO

The structure of trans-[Pd(dtco-3-OH)2] (ClO4)2·2DMSO, in which dtco-3-OH is dithiacyclooctan-3-ol and DMSO is dimethyl sulfoxide, was determined by X-ray crystallographic analysis. The crystal data: space group pi, a = 0.7077(2) nm, b = 1.0788(1) nm, c = 1.1111(1) nm, α=67.710(8)°, β = 73. 59(2)°, γ = 85. 39(2)°,R1 = 0 . 0368 and Rw = 0.0998. The palladium (II) is coordinated by four sulfur atoms with a regular square planar configuration. The Pd-S distances are 0.2314(1) and 0.2317(1) nm, respectively. Both dtco-3-OH ligands are in the boat-chair configuration and two hydroxyl groups are on the opposite sites of the PdS4 coordination plane and are towards Pd(II). The Pd-O distance is 0. 285 nm, indicating a weak interaction between them. A typical hydrogen bond between the hydroxyl group of dtco-3-OH ligand and DMSO was observed in the crystal structure. An aqueous solution prepared with the crystals of the complex was used for the investigation of electrospray mass spectrometry ( ESMS ). Besid     

低钠条件下MCM-22分子筛的动态合成及其在甲烷无氧芳构化中的催化性能

由于 MCM- 2 2分子筛 [1] 具有独特的结构性质 ,故在许多烃类转化反应中已表现出突出的催化特性 [2～ 4 ] .我们在甲烷无氧芳构化的前期工作中发现 [5] ,酸性适当 ,具有交叉孔道且孔径与苯的动力学直径 (～ 0 .6nm)相当的分子筛载体活性较高 .MCM- 2 2的酸性与 ZSM- 5相当 [6 ,7] ,且拥有两套互不相通的多维孔道体系 [8] ,一套为二维正弦孔道 ,有效孔径为十元环 ( 0 .4nm× 0 .59nm) ;另一套亦为十元环孔道体系 ( 0 .4nm× 0 .54nm) ,但含有内径为十二元环的超笼 ( 0 .71 nm× 0 .71 nm× 1 .82 nm) .因此 ,以 MCM- 2 2为载体的催化剂…