Davis James H, Schmidt Miranda L
Department of Physics, University of Guelph, Guelph, Ontario, Canada.
Department of Physics, University of Guelph, Guelph, Ontario, Canada.
Biophys J. 2014 May 6;106(9):1970-8. doi: 10.1016/j.bpj.2014.03.037.
Static (2)H NMR spectroscopy is used to study the critical behavior of mixtures of 1,2-dioleoyl-phosphatidylcholine/1,2-dipalmitoyl-phosphatidylcholine (DPPC)/cholesterol in molar proportion 37.5:37.5:25 using either chain perdeuterated DPPC-d62 or chain methyl deuterated DPPC-d6. The temperature dependence of the first moment of the (2)H spectrum of the sample made with DPPC-d62 and of the quadrupolar splittings of the chain-methyl-labeled DPPC-d6 sample are directly related to the temperature dependence of the critical order parameter η, which scales as [Formula: see text] near the critical temperature. Analysis of the data reveals that for the chain perdeuterated sample, the value of Tc is 301.51 ± 0.1 K, and that of the critical exponent, βc = 0.391 ± 0.02. The line shape analysis of the methyl labeled (d6) sample gives Tc = 303.74 ± 0.07 K and βc = 0.338 ± 0.009. These values obtained for βc are in good agreement with the predictions of a three-dimensional Ising model. The difference in critical temperature between the two samples having nominally the same molar composition arises because of the lowering of the phase transition temperature that occurs due to the perdeuteration of the DPPC.
采用静态（2）H核磁共振光谱法研究摩尔比为37.5:37.5:25的1,2 - 二油酰基磷脂酰胆碱/1,2 - 二棕榈酰基磷脂酰胆碱（DPPC）/胆固醇混合物的临界行为，所用的DPPC分别为全氘代链的DPPC - d62或甲基氘代链的DPPC - d6。用DPPC - d62制备的样品的（2）H谱的一阶矩以及链甲基标记的DPPC - d6样品的四极分裂的温度依赖性与临界序参量η的温度依赖性直接相关，在临界温度附近，η的标度为[公式：见原文]。数据分析表明，对于全氘代链的样品，Tc值为301.51±0.1 K，临界指数βc = 0.391±0.02。甲基标记（d6）样品的线形分析给出Tc = 303.74±0.07 K和βc = 0.338±0.009。得到的这些βc值与三维伊辛模型的预测结果吻合良好。两种名义上具有相同摩尔组成的样品之间临界温度的差异是由于DPPC的全氘代导致相变温度降低而产生的。
