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美国斯坦福大学化学系教授Richard N.Zare于1997年提出[1]:“由化学家来构造生命”是21世纪最伟大的挑战之一,即“用化学的方法去得到能自我复制、自我组装,甚至有进化可能性的系统”是当今对化学家最严峻的挑战之一。为什么研究生命体系要寄希望于化学家呢?因为一则生命体系由 相似文献
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The persistence length and the overlap concentration(c~*) of poly(ethylene oxide)(PEO) and hydroxyethylcellulose(HEC) with similar molecular weight in 1×TBE buffer were studied by laser light scattering and viscometry.Their effect on DNA separation was investigated by capillary electrophoresis.It was determined that the persistence length of HEC was at least 5 times higher than that of PEO.Therefore,the c~* of HEC was smaller than that of PEO by a factor of ca.2.5.It was also found that the c~* values de... 相似文献
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在苯乙烯(St)-二乙烯苯(DVB)自由基聚合的凝胶化反应过程中,定时取样,得到凝胶化点前后及直至反应终点的一系列溶胶样品,利用光散射技术研究了溶胶相的重均分子量Mw、尺寸均方旋转半径Rg的变化过程,建立了Mw、Rg和反应时间t的标度关系,并在此基础上提出一神新的准确求取凝胶化时间tgel的方法. 相似文献
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<正>The effects of heating rate on the aggregate behavior of poly(ethylene oxide)-b-poly(N-isopropylacrylamide) in aqueous solutions were investigated in detail by laser light scattering and TEM.By employing two separate heating protocols,step-by-step heating at5 K/step and one-step jump,to heat the sample from 15℃to the selected temperature, we found that the heating rate only showed significant effect on the aggregates above the cloud point.The aggregate formed by step-by-step heating exhibited a much larger size and a broader size distribution than those formed by one-step jump heating.Moreover,neither of the aggregates were ideal micellar structures as indicated by the size and the R_g/R_h values.On the contrary,at temperatures below the cloud point where the block copolymer formed core-shelled micelles,the heating rate showed negligible effect on the size and size distribution of the micelles.Since the system underwent a phase separation above the cloud point,the heating rate effect could be reasonably explained by the phase separation mechanisms:the nucleation-and-growth mechanism in the metastable region and the spinodal decomposition mechanism in the unstable region. 相似文献
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The dependence of the scattered intensity on angles was measured by SAXS for a series of samples taken during the span process of the gelation of styrene with divinylbenzene. Based on these data. we obtained the fractal dimensions and their evolution for both sols and gels successfully. 相似文献
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Using three designed peptides with precisely-controlled charge density and three types of DNAs with different length and flexibility, the effect of charge density on the formation of PEC was studied. Highly charged(KKKK)5 interacts strongly with 21 bp ds DNA to form large complex, followed by precipitation; while the medium charged(KGKG)5 only form complex with 21 bp ds DNA at proper +/- charge ratios; and no prominent complex between weakly charged(KGGG)5 and 21 bp ds DNA is observed at the same conditions. Similar trend is observed when the peptides form complex with 2000 bp DNA or 21 nt ssD NA. It is also found that the complex formed by adding peptide to DNA is in random coil conformation, but the complex prepared by the inverse order is in molten globule state. Re-dissolution of the complex occurs only when DNA is added to peptides with similar or shorter length. 相似文献