Determination of tie-line fields for coexisting lipid phases: an ESR study.
Determination of tie-line fields for coexisting lipid phases: an ESR study.
复制标题
共存脂质相的联络线场的确定：ESR 研究。
DOI：
10.1021/jp808412x
复制
发表时间：
2009
期刊：
影响因子：
--
通讯作者：
Freed,JackH
中科院分区：
文献类型：
--
作者：
Smith,AndrewK;Freed,JackH
本文提出了一种新的方法——系线场（TLF）法，通过拟合从共存曲线上和共存区域内的成分中获得的电子自旋共振（ESR）谱，来全局确定任何三组分两相共存区域的系线。将TLF方法应用于脂质系统脑鞘磷脂/二油基磷脂酰胆碱/胆固醇（SPM/DOPC/chol）的液序相（Lo）和液序相（Ld）共存区，说明了TLF方法的有效性，该方法先前也使用ESR光谱通过较早的方法获得了其结合线的估计。TLF方法的关键是对称为“直纹曲面”的共存区域的唯一参数化。直纹表面的使用使人们能够保证连接线不会交叉，这是相位规则所要求的，而以前的方法缺乏这个重要的约束。它还可以同时使用完整的数据集来确定TLF，并导致比以前使用的更有效的实验设计。该方法首先在合成数据集上进行了测试，然后用参数化模型对ESR光谱进行了最小二乘拟合，得到了与该脂质体系其他已知信息一致的系线场。最佳拟合系线场由一组不完全平行的系线组成；它们的斜率逐渐变化，最大的斜率在共存曲线组成与最高和最低胆固醇浓度相连的共存区域内。将结果与更约束的系线场表示方法的结果以及SPM/DOPC/chol体系系线确定方法的结果进行了比较。准确测定脂质系统相共存区域的系线场是确定共存脂质组分作为细胞膜模型的必要步骤。
A novel method we refer to as the tie-line field (TLF) method has been developed to globally determine the tie lines of any three-component two-phase coexistence region by fitting electron-spin resonance (ESR) spectra obtained from compositions on the coexistence curve and within the coexistence region. The TLF method is illustrated by applying it to the liquid-ordered (Lo) and liquid-disordered (Ld) phase coexistence region of the lipid system brain-sphingomyelin/dioleoylphosphatidylcholine/cholesterol (SPM/DOPC/chol), for which an estimate of a tie-line was previously obtained by an earlier method also using ESR spectra. The essential aspect of the TLF method is the unique parametrization of the coexistence region called a “ruled surface”. The use of the ruled surface enables one to guarantee that tie lines do not cross, as required by the phase rule, whereas previous methods lack this important constraint. It also makes simultaneous use of the full data set in determining the TLF and leads to a more efficient experimental design than previously used. The method is first tested out on synthetic data sets, then least-squares fitting of the ESR spectra with the parametrized model results in a tie-line field consistent with other known information on this lipid system. The best-fit tie-line field consists of the set of tie lines which are not exactly parallel; they exhibit a gradual change in slope with the largest slope within the coexistence region connecting the coexistence curve compositions with the highest and lowest cholesterol concentrations. The results are compared with those from more constrained methods of representing the tie-line fields as well as with the previous tie-line determination for the SPM/DOPC/chol system. An accurate determination of the tie-line field of phase coexistence regions in lipid systems is a necessary step in determining coexisting lipid compositions to serve as models of cell plasma membranes.