Micro construction of poly(epsilon-caprolactone)/poly(L-lactic acid) blend film by solution casting under microwave irradiation

The micro construction of poly(epsilon-caprolactone) (PCL) and poly(L-lactic acid) (PLLA) blend films fabricated by solution casting under microwave irradiation was investigated by selective enzymatic degradation and scanning electron microscopy (SEM). The results were totally different from the blends obtained by conventional methods. The blend was more homogeneous and the PCL continuous phase more compact as no spherulites and tiny zone separation were observed from the film surface and no PCL network was observed inside the film, and the degradation of a PCL plank by Pseudomonas lipase was significantly retarded. The distributed PLLA micro spheres were enlarged and amorphous. The thermal behavior of the blend by microwave heating revealed that PCL and PLLA underwent a melting process, which induced the variations of the PCL phase and PLLA spheres. The weight loss caused by degradation of the PCL/PLLA blend obtained by conventional methods (B50c) is greater than that of the blend obtained by microwave methods (B50m), which reflects the change in morphology from a loose PCL network (B50c) to a dense PCL plank (B50m).     

Phase Selectively Soluble Dendritic Derivative of 4-(Dimethylamino)- pyridine: An Easily Recyclable Catalyst for Baylis-Hillman Reactions

Among the reactions in which C-C bonds are formed, the Baylis-Hillman coupling of aldehydes with α, β-unsaturated carbonylic compounds is currently attracting much interest due to the atom economy, the mild conditions and the generation of functional groups1,2. Furthermore, compared to the Heck, Suzuki and other palladium catalyzed C-C bond forming reaction3, the Baylis-Hillman reaction can be promoted by using organic bases in the complete absence of any metal4. However, almost all the …     

The Adsorption and Thermal Decomposition of CH2CO (CD2CO) on Si(111)-7 × 7

The adsorption and thermal decomposition of ketene on Si(l 11)-7 × 7 were investigated using various surface analysis techniques. When the surface was exposed to ketene at 120 K, two CO stretching modes at 220 and 273 meV appeared in HREELS, corresponding to two adsorbed ketene states. After the sample was annealed at ?250 K, the 273 and the 80 meV peaks vanished, indicating the disappearance of one of the adsorption states by partial desorption of the adsorbate. In a corresponding TPD measurement, a desorption peak for ketene species was noted at 220 K. Annealing the sample at 450 K caused the decomposition of the adsorbate, producing CH_x and O adspecies. Further annealing of the surface at higher temperatures resulted in the breaking of the CH bond, the desorption of H and O species and the formation of Si carbide. The desorption of H at 800 K was confirmed by the appearance of the D₂ (m/e = 4) TPD peak at that temperature when CD₂CO was used instead of CH₂CO.     

用红外光谱研究苯乙烯-4(甲基丙烯酸)2,2,6,6-四甲基哌啶醇酯共聚物的序列结构

<正> 苯乙烯(简称St)-4(甲基丙烯酸)2,2,6,6-四甲基哌啶醇酯(简称MTMP)共聚物(简称PDS)是七十年代发展起来的一种新型高效光稳剂。本文用IR研究了一系列自由基聚合的PDS共聚物,找出了MTMP对序列结构敏感的吸收峰,发现MTMP的1152.5厘米~(-1)峰位置与三单元序列分布F_(SMS)值有一定线性关系,还对通过测量MTMP羰基伸缩振动ν_(C=O)峰位置来计算二单元序列分布P_(mm)的关系进行了讨论。     

Norvancomycin-capped silver nanoparticles: Synthesis and antibacterial activities against E. coli

The synthesis of norvancomycin (NVan)-capped silver nanoparticles (Ag@NVan) and their notable in vitro antibacterial activities against E. coli, a Gram-negative bacterial strain (GNB), are reported here. Mercaptoacetic acid-stabilized spherical silver nanoparticles with a diameter of 16±4 nm are prepared by a simple chemical reaction. The formation process of the silver nanoparticles is investigated by UV-visible (UV-vis) spectroscopy and transmission electron microscopy (TEM). NVan is then grafted to the terminal carboxyl of the mercaptoacetic acid in the presence of N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDAC). The TEM images of single bacteria treated with Ag@NVan show that plenty of Ag@NVan aggregate in the cell wall of E. coli. A possible antibacterial mechanism is proposed that silver nanoparticles may help destroy the stability of the outer membrane of E. coli, which makes NVan easier to bind to the nether part of the peptidoglycan structure. The antibacterial activities of silver nanoparticles on their own, together with the rigid polyvalent interaction between Ag@NVan and cell wall, enables Ag@NVan to be an effective inhibitor of GNB. This kind of bionanocomposites might be used as novel bactericidal materials and we also provide an effective synthesis method for preparing functional bioconjugated nanoparticles here. Supported by the National Natural Science Foundation of China (Grant No. 50373036) and Fok Ying Tung Education Foundation (Grant No. J20040212)     

Estrogen receptor ligands. 12. Synthesis of the major metabolites of an ERalpha-selective, dihydrobenzoxathiin antagonist for osteoporosis

[reaction: see text] During the course of drug metabolism studies, a major metabolite of compound 1 was detected in rhesus monkeys and assigned structure 4. The intriguing biotransformation of 1 leading to 4 was confirmed by a 19-step total synthesis starting from resorcinol (11), the key feature of which was the construction of the oxygen bridge utilizing a phenolic oxidation and trapping sequence. In addition, the synthesis of a related metabolite (5) is described.     

Large-scale synthesis and microstructure of SnO2 nanowires coated with quantum-sized ZnO nanocrystals on a mesh substrate

Large-quantity single-crystal SnO(2) nanowires coated with quantum-sized ZnO nanocrystals (nc-ZnO/SnO(2) nanowires) were directly synthesized by thermal evaporation of SnO powder and a mixture of basic ZnCO(3) and graphite powders. A common stainless steel mesh was used to collect the products. The microstructure and possible growth mechanism of the nc-ZnO/SnO(2) nanowires were investigated. Results showed that tetragonal structured SnO(2) nanowires were obtained, whose surfaces were coated with single-layer ZnO nanocrystals with an average diameter of less than 5 nm. The nanowires had cross-rectangle section with width-to-thickness aspect ratio ranging from 2:1 to 5:1. The lengths of the nanowires were several tens of micrometers. ZnO nanocrystals were single crystalline wurtzite structures, which coated the whole nanowires and distributed uniformly. The possible growth mechanism of the composite nanowires may be enucleated that Zn atoms in the source vapor will replace the Sn atoms on the surface of the formed SnO(2) nanowires due to the higher reducibility of Zn than Sn. Two strong Raman scattering peaks at 626 and 656 cm(-1) appeared in the micro-Raman spectrum of nc-ZnO/SnO(2) nanowires. The origins of the peaks were discussed. Most importantly, the method can be extended to other composite oxide nanowires that are synthesized by oxidizing two kinds of metals, such as high reducibility elements Mg, Al, Zn, and Ti, and low reducibility elements In, Ge, Ga, etc.     

Rigid rod anchored to infinite membrane

We investigate the shape deformation of an infinite membrane anchored by a rigid rod. The density profile of the rod is calculated by the self-consistent-field theory and the shape of the membrane is predicted by the Helfrich membrane elasticity theory [W. Helfrich, Z. Naturforsch. 28c, 693 (1973)]. It is found that the membrane bends away from the rigid rod when the interaction between the rod and the membrane is repulsive or weakly attractive (adsorption). However, the pulled height of the membrane at first increases and then decreases with the increase of the adsorption strength. Compared to a Gaussian chain with the same length, the rigid rod covers much larger area of the membrane, whereas exerts less local entropic pressure on the membrane. An evident gap is found between the membrane and the rigid rod because the membrane's curvature has to be continuous. These behaviors are compared with that of the flexible-polymer-anchored membranes studied by previous Monte Carlo simulations and theoretical analysis. It is straightforward to extend this method to more complicated and real biological systems, such as infinite membrane/multiple chains, protein inclusion, or systems with phase separation.     

聚苯醚砜在二甲基甲酰胺中稀溶液性质的研究(Ⅱ)

本文用广角及准弹性光散射法测定了聚苯醚砜各级分在DMF中和在θ溶剂中25℃时的均才半径R_G,第二维利系数A_2,流体力学半经R_H,扩散系数D_O,扩散系数的浓度依赖性k_F以及这些参数与分子量M的关系。它们的结果如下R_G=0.031MO~(0.55) D_O(θ)=0.906×10~(-4)M~(0.5) D_0=1.445×10~(-4)M~(0.55)A_2=0.033M~(-0.35) k_D(θ)=0.5M~(0.34) k_D=2.3×10~(-6)M~(1.36)α_H=R_H/R_H(θ)=0.63M~(0.05)R_H(θ)=0.0299M~(0.5)R_H=0.0188M~(0.55) 作者讨论了静态与动态两种高分子尺寸之间的关系;三种溶胀因子α_η和、α_H、α_G之间的关系;以及摩擦系数的浓度系数k_F与流体力学体积V_H之间的关系。它们的结果满足下面各关系式: R_H/R_G=[π(v+1)(2v+1)/3]~(1/2)(2-v)(1-v)/2, α_η~3=α_(G)~2α_H, k_F=1.2A_2M+N_AV_H/M,K_F(θ)=N_AV_H/M     

Dioxygen Affinities and Catalytic Oxidation Performance of Cobalt (II)Complexes with N-Aryl Hydroxamic Acid

It is well known that the study on biomimetic oxygen carriers not only has important theoretic significance to discover the mechanism of reversible bonding, activating oxygen as well as the oxidation reaction in organism, but also has potential application in separating oxygen from air and realizing the high efficiency and selectivity of catalytic oxidation reaction under a mild condition1. Metal- porphyrin and metal- phthalol- gaunine have been extensively used as biomimetic oxygen carriers u…