甲基丙烯酸甲酯自由基聚合歧化终止机理

首先用过氧化二苯甲酰(BPO)引发甲基丙烯酸甲酯(MMA)自由基聚合合成聚甲基丙烯酸甲酯(PMMA),然后用偶氮二异丁腈(AIBN)为引发剂,研究PMMA中由歧化终止生成的末端双键与苯乙烯(St)的共聚合反应行为。采用体积排除色谱(SEC)、核磁共振波谱(NMR)对聚合物进行了分析表征。结果表明：与单体MMA相似,PMMA在化学位移δ=6.20和5.47处有对应于聚合物末端双键氢的NMR信号。远程异核和近程异核相关NMR,¹³C-NMR和DEPT-135 NMR分析和自由基共聚合实验确证：MMA自由基聚合的双基歧化终止为单一的链自由基末端β位甲基氢自由基转移机理,生成1,1-二取代甲基丙烯酸酯型双键。除双基歧化终止反应外,体系还明显地存在苯甲酰初级自由基和苯初级自由基与链自由基间的初级终止反应。     

对称中心相同的正交平衡多小波的存在性及参数化

1 引 言 多小波因为可同时满足对称性、紧支撑性、高阶消失矩和正交性,所以在信号处理等应用方面比单小波更有优势,但是,基于多小波的信号处理需进行预滤波[1,2],而预滤波又会破坏所设计的多小波的正交性、对称性等特性,这阻碍了多小波的应用.     

过氧化氢对烟草光合功能衰退的影响

采用不同浓度H2O2在离体、整株、亚细胞器水平上处理烟草(Nicotiana tabacumL.cv NC89),研究H2O2对烟草光合功能的影响.结果表明:0.1、1 mmol.L-1H2O2对烟草离体叶片的光合作用基本无影响,10、100mmol.L-1H2O2对烟草离体和连体叶片的光合作用有不同程度的抑制作用.H2O2处理离体叶片后,叶绿素含量的下降与内源H2O2水平上升显著相关.低浓度(0~20 mmol.L-1)和高浓度(20~200 mmol.L-1)H2O2处理类囊体膜和光系统Ⅱ(PSⅡ)复合体,结果显示:20 mmol.L-1H2O2对类囊体膜(主要是PSⅡ)多肽组分有所影响,表现为28~29、23、17 KD多肽的部分降解;高浓度H2O2处理,类囊体膜多肽组分,PSⅡ核心复合体28~29 KD,放氧复合体(OEC)33、23、17 KD,捕光色素蛋白CP43和CP47等多肽大幅度降解,光系统Ⅰ(PSⅠ)相对保守.这一结果首次说明了H2O2胁迫类囊体膜、PSⅡ颗粒后其多肽组分的变化.H2O2处理连体叶片时类囊体膜电子传递活性表现出相应的下降.     

两亲性单链蝌蚪状聚合物纳米粒子组装形成超级粒子及其超声响应性研究

Herein, we report self-assembly of tadpole-like single chain polymeric nanoparticles (TPPs) and the ultrasonic response of the resultant superparticles. The TPPs are with an intramolecularly crosslinked poly(2-(methacryloyloxy)ethyl pent-4-ynoate)-r-poly(hydroxyethyl methacrylate) (PMAEP-r-PHEMA) chain as the "head" and a poly(2-(dimethylamino)ethyl methacrylate (PDMAEMA) linear chain as the "tail", and are pre-pared simply and efficiently by Glaser-coupling of the pendant alkynes in the PMAEP-r-PHEMA block in the common solvent methanol. The formation of the TPPs was confirmed by gel permeation chromatograph, nuclear magnetic resonance spectroscopy, dynamic light scattering, static dynamic scattering, and transmission electron microscopy. In aqueous solution, the amphiphilic TPPs could self-assemble into regular superparticles, driven by ag-gregation of the hydrophobic "heads". Since in the structure there is no chain entanglement and the embedding of PDMAEMA chains disturb close-packing of the "heads", the superpar-ticles are responsive to a low-energy ultrasonic vibration, as evidenced by greatly enhanced release of the functional molecules from the superparticles by treatment of a low-energy ultrasound. Therefore, the superparticles should be very promising in the use as the drug carriers that can be manipulated from a long distance, considering that ultrasonic energy can be focused at a small area in a relatively long distance from the ultrasound-radiating source.