目的:采用超高效液相色谱—四极杆飞行时间质谱(UPLC-Q-TOF/MS)联用技术,对1、2、3年生防风样本进行分析,确定不同生长年限防风中香豆素类成分的含量变化。方法:使用超高效液相BEH C_(18)色谱柱(2.1 mm×100 mm, 1.7μm),以0.1%甲酸...目的:采用超高效液相色谱—四极杆飞行时间质谱(UPLC-Q-TOF/MS)联用技术,对1、2、3年生防风样本进行分析,确定不同生长年限防风中香豆素类成分的含量变化。方法:使用超高效液相BEH C_(18)色谱柱(2.1 mm×100 mm, 1.7μm),以0.1%甲酸水(A)-0.1%甲酸乙腈(B)为流动相梯度进行洗脱;使用高分辨飞行质谱仪,配置ESI离子源,在正、负离子模式下采集质谱数据,使用Markerview数据处理软件对高维质谱数据进行PCA处理,初步筛选目标化合物为香豆素类成分,根据高分辨质谱采集到的精准质量数及同位素等信息进一步确定质谱碎片的分子式,利用精确分子质量等信息与对照品及高分辨质谱自备数据库谱图进行比对从而得到鉴定结果,利用此结果进一步分析其含量变化规律。结果:鉴定或推断出不同生长年限防风中含量差异较大的13种香豆素类成分,其中补骨脂素等5个成分的含量逐年增加,而8-羟基补骨脂素等7个化合物含量以2年生最高,3年生略有下降,仅2-[(8-Methoxy-4-methyl-6-oxo-6H-benzo[c]chromen-3-yl)oxy]propanoic acid的含量以1年生最高。结论:该方法快速、准确,为不同生长年限防风中香豆素成分分析提供一种新的研究方法。展开更多
The site order parameter (SOP) has been adopted to analyze various orders of structure formation and distribution during the crystallization of a polyethylene globule simulated by molecular dynamics. The SOP not only ...The site order parameter (SOP) has been adopted to analyze various orders of structure formation and distribution during the crystallization of a polyethylene globule simulated by molecular dynamics. The SOP not only identifies different orders among the structures but also different phases. The results showed that intermediate structures with medium order exist unevenly in the early stage of nucleation, which differs from traditional models. We found that the nucleation relies on crystallinity fluctuations with increasing amplitude, and a baby nucleus with different shape and increasing size suddenly appears in the fluctuations. Once its size is large enough, the baby nucleus becomes the nucleus. In the growth stage, a number of lamellar mergences were observed and their selective behaviors were related to the orientation differences between the lamellae to be merged. The SOP distribution of all atoms in the system during crystallization had two peaks: one for the amorphous phase and the other for the crystalline phase. The intermediate structures with medium orders are located between the two peaks as an order promotion pathway. The data show that the medium order structure fluctuates at the growth front and is not always available, and that the medium order structure existing at the front is not always good for development. It is possibly caused by chain entanglement. Structure fluctuation at the growth front enables the system showing thousands of the most probable configurations to approach the precursor. The growth front is thus active for a while and inactive at other times.展开更多
Rubber elasticity theory is of fundamental importance in polymer science. The traditional theory is athermal, describing rubber deformation behavior as entropy elasticity without an internal energy contribution. It ha...Rubber elasticity theory is of fundamental importance in polymer science. The traditional theory is athermal, describing rubber deformation behavior as entropy elasticity without an internal energy contribution. It has been found experimentally, however, that the internal energy contribution is not zero. In the present study we have used conformational elasticity theory to calculate the internal energy contribution of polydimethylsiloxane (PDMS) and results obtained are consistent with a number of experimental observations.展开更多
文摘The site order parameter (SOP) has been adopted to analyze various orders of structure formation and distribution during the crystallization of a polyethylene globule simulated by molecular dynamics. The SOP not only identifies different orders among the structures but also different phases. The results showed that intermediate structures with medium order exist unevenly in the early stage of nucleation, which differs from traditional models. We found that the nucleation relies on crystallinity fluctuations with increasing amplitude, and a baby nucleus with different shape and increasing size suddenly appears in the fluctuations. Once its size is large enough, the baby nucleus becomes the nucleus. In the growth stage, a number of lamellar mergences were observed and their selective behaviors were related to the orientation differences between the lamellae to be merged. The SOP distribution of all atoms in the system during crystallization had two peaks: one for the amorphous phase and the other for the crystalline phase. The intermediate structures with medium orders are located between the two peaks as an order promotion pathway. The data show that the medium order structure fluctuates at the growth front and is not always available, and that the medium order structure existing at the front is not always good for development. It is possibly caused by chain entanglement. Structure fluctuation at the growth front enables the system showing thousands of the most probable configurations to approach the precursor. The growth front is thus active for a while and inactive at other times.
基金supported by the National Natural Science Foundation of China (29874035)
文摘Rubber elasticity theory is of fundamental importance in polymer science. The traditional theory is athermal, describing rubber deformation behavior as entropy elasticity without an internal energy contribution. It has been found experimentally, however, that the internal energy contribution is not zero. In the present study we have used conformational elasticity theory to calculate the internal energy contribution of polydimethylsiloxane (PDMS) and results obtained are consistent with a number of experimental observations.
