不同嵌段比的PEG-b-PDMAEMA共聚物在水溶液中的自聚集行为

采用氢核磁共振(¹H-NMR)、动态光散射(DLS)及透射电子显微镜(TEM)对聚乙二醇-嵌段-聚甲基丙烯酸N,N-二甲氨基乙酯(PEG-b-PDMAEMA)三种具有不同PEG/PDMAEMA嵌段比的PEG-b-PDMAEMA共聚物在水溶液中的自聚集行为进行了研究. 研究表明, 两嵌段比例是影响聚合物胶束化过程的关键因素: 只有当其中聚乙二醇含量较低(质量分数低于33%)时, 聚合物才具有其pH/温度敏感胶束化特性. 此外, 共聚物溶液随温度胶束化过程与共聚物嵌段比大小密切相关. PEG-b-PDMAEMA这种不同于传统双亲性嵌段共聚物(DHBCs)在选择性溶剂中独特的胶束化行为, 是由聚合物溶液体系中各种基团之间的氢键作用决定的.     

Regioselective syntheses of 7-nitro-7-deazapurine nucleosides and nucleotides for efficient PCR incorporation

Substitution at the C(7) position of purine nucleotides by a potent electron-withdrawing nitro group facilitates the cleavage of glycosidic bonds under alkaline conditions. This property is useful for sequence-specific cleavage of DNA containing these analogues. Here we describe the preparation of 7-deaza-7-NO(2)-dA and 7-deaza-7-NO(2)-dG using two different approaches, starting from 2'-deoxy-adenosine and 6-chloro-7-deaza-guanine, respectively. These modified nucleosides were converted to nucleotide triphosphates, each of which can replace the corresponding, naturally occurring triphosphate to support PCR amplification. [structure: see text]     

Two New Cyclopeptides from Arenaria oreophila (Caryophyllaceae)

Two new cyclopeptides, named arenariphilin A ( 1 ) and arenariphilin B ( 2 ), were isolated from the whole plants of Arenaria oreophila. Their structures were determined as cyclo‐(Thr‐Gly) ( 1 ) and cyclo‐(Ser₁‐Gly ‐Ser₂‐Ile ‐Phe₁‐Phe₂) ( 2 ) on the basis of spectral data, especially by 2D‐NMR.     

A cytotoxic compound from the leaves of Juglans mandshurica

From Juglans mandshurica leaves, a new quinone compound was isolated through bioassay-guided fractionation. The structure elucidation of the compound was established based on spectroscopic studies, notably of the 2D NMR spectra. The compound exhibited moderate cytotoxic activities against Hela, MCF-7, BGC823 and 3T3-Llcell lines with IC50 ranges from 7.5 to 26.8 μmol/L.     

Boomerang‐Type Substitution Reaction: Reactivity of Fullerene Epoxides and a Halofullerenol

The C_s‐symmetric fullerene chlorohydrin C₆₀(Cl)(OH)(OOtBu)₄ reacts with 4‐dimethylaminopyridine (DMAP) and 1,4‐diazabicyclo[2.2.2]octane (DABCO) to yield two isomers with the formula C₆₀(O)(OOtBu)₄ in good yields. These isomers differ with respect to the location of the epoxy functionality. The one from DMAP is C_s symmetric, whereas that from DABCO is C₁ symmetric with the epoxy group on the central pentagon. Two different mechanisms are proposed to explain the chemoselectivity of these reactions. The reaction with DMAP involves single‐electron transfer as the key step; DMAP acts as the electron donor. A combination of an oxygen‐atom shift and S_N2′′ processes (boomerang substitution) are responsible for the formation of isomer with DACBO. Various related reactions support the proposed mechanisms. The structures of new fullerene derivatives were determined by spectroscopy, single‐crystal X‐ray analysis, and chemical correlation experiments.     

Sesquiterpenoids and Phenylpropane Derivatives from Sonchus uliginosus

Six new compounds were isolated from the whole plant of Sonchus uliginosus, including three eudesmane‐type sesquiterpenoids (1β,6α)‐1,6,14‐trihydroxyeudesm‐3‐en‐12‐oic acid γ‐lactone ( 1 ), (1β,6α)‐1,6,14‐trihydroxyeudesma‐3,11(13)‐dien‐12‐oic acid γ‐lactone ( 2 ), and (1β,6α)‐1,6‐dihydroxy‐14‐O‐[(4‐hydroxyphenyl)acetyl]eudesma‐3,11(13)‐dien‐12‐oic acid γ‐lactone ( 3 ), and three phenylpropane derivatives, 4‐hydroxy‐γ,3,5‐trimethoxybenzenepropanol ( 6 ), γ,3,4,5‐tetramethoxybenzenepropanol ( 7 ), and γ,3,4,5‐tetramethoxybenzenepropanol acetate ( 8 ), together with the two known compounds 4 and 5 . The new structures were elucidated by means of spectroscopic methods, such as IR, EI‐MS, HR‐ESI‐MS, 1D‐ and 2D‐NMR, and by comparison of the spectroscopic data with those reported for structurally related compounds.     

Copper‐Bismuth Bimetallic Microspheres for Selective Electrocatalytic Reduction of CO2 to Formate

Electrocatalytic carbon dioxide reduction holds great promise for reducing the atmospheric CO₂ level and alleviating the energy crisis. High‐performance electrocatalysts are often required in order to lower the high overpotential and expedite the sluggish reaction kinetics of CO₂ electroreduction. Copper is a promising candidate metal. However, it usually suffers from the issues of poor stability and low product selectivity. In this work, bimetallic Cu‐Bi is obtained by reducing the microspherical copper bismuthate (CuBi₂O₄) for selectively catalyzing the CO₂ reduction to formate (HCOO^–). The bimetallic Cu‐Bi electrocatalyst exhibits high activity and selectivity with the Faradic efficiency over 90% in a wide potential window. A maximum Faradaic efficiency of ~95% is obtained at –0.93 V versus reversible hydrogen electrode. Furthermore, the catalyst shows high stability over 6 h with Faradaic efficiency of ~95%. This study provides an important clue in designing new functional materials for CO₂ electroreduction with high activity and selectivity.     

A New Synthetic Route to 12-Oxo-1, 15-pentadecanlactam

12-Oxo-1,15-pentadecanlactam 7 was synthesized from cyclododecanone with a totalyield of 36% in a seven-step reaction. The azide 5 to 12-nitro-1,15-pentadecanlactam 6 is the key step featured by direct ring expansion.     

Evidence for orbital-specific electron transfer to oriented haloform molecules

Beams of hyperthermal K atoms cross beams of the oriented haloforms CF(3)H, CCl(3)H, and CBr(3)H, and transfer of an electron mainly produces K(+) and the X(-) halide ion which are detected in coincidence. As expected, the steric asymmetry of CCl(3)H and CBr(3)H is very small and the halogen end is more reactive. However, even though there are three potentially reactive centers on each molecule, the F(-) ion yield in CF(3)H is strongly dependent on orientation. At energies close to the threshold for ion-pair formation ( approximately 5.5 eV), H-end attack is more reactive to form F(-). As the energy is increased, the more productive end switches, and F-end attack dominates the reactivity. In CF(3)H near threshold the electron is apparently transferred to the sigma(CH) antibonding orbital, and small signals are observed from electrons and CF(3)(-) ions, indicating "activation" of this orbital. In CCl(3)H and CBr(3)H the steric asymmetry is very small, and signals from free electrons and CX(3)(-) ions are barely detectable, indicating that the sigma(CH) antibonding orbital is not activated. The electron is apparently transferred to the sigma(CX) orbital which is believed to be the LUMO. At very low energies the proximity of the incipient ions probably determines whether salt molecules or ions are formed.     

STM study on quinacridone derivative assemblies: modulation of the two-dimensional structure by coadsorption with dicarboxylic acids

We describe the two-dimensional (2D) assemblies of N,N'-dialkyl-substituted quinacridone derivatives on highly orientated pyrolytic graphite observed by scanning tunneling microscopy, and focus our discussion on whether the supramolecular organization can be modulated by the coadsorption of dicarboxylic acids. Our experiments have demonstrated that the quinacridone derivatives can form different 2D nanostructures when coadsorbed with dicarboxylic acids of different length at the liquid/graphite interface. Interestingly, N,N'-dihexadecyl-substituted quinacridone derivative alternately takes two different conformations in two columns for its coadsorption with pentadecanedioic acid and form a gridlike structure. It is shown that a cooperative effect of different interactions can be modulated by introducing guest molecule, leading to formation of different self-assembled nanostructures.