DETERMINATION OF TIE-LINE FIELDS FOR COEXISTING LIPID PHASES

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 发展了一种新的方法来确定任意三组分两相共存区域的连接线，方法是将从共存曲线上和共存区域内的组成得到的电子自旋共振(ESR)谱进行拟合。将该方法应用于脂类体系brain-sphingomyelin/dioleoylphosphatidylcholine/cholesterol(SPM/DOPC/胆固醇)的液-有序(LO)和液-无序(LD)共存区域。该方法的基本方面是对共存区域进行唯一的参数化处理，称为“直纹面”，以及对共存曲线的了解。用参数化模型对ESR谱进行最小二乘拟合，得到了与该脂质体系的其他已知信息一致的联络线场。直纹曲面的使用使人们能够保证联络线不会相交。最适合的连接线区域由一组不完全平行的连接线组成；它们的斜率逐渐变化，在连接胆固醇浓度最高和最低的共存曲线成分的共存区域内斜率最大。将结果与用更多约束方法表示联络线场的结果进行了比较。准确测定脂类体系中相共存区域的连线区域是确定共存类脂成分作为细胞膜模型的必要步骤。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. A novel method has been developed to 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 method was applied to the liquid-ordered (Lo) and liquid-disordered (Ld) phase coexistence region of the lipid system brain-sphingomyelin/dioleoylphosphatidylcholine/cholesterol (SPM/DOPC/cholesterol). The essential aspects of the method were a unique parameterization of the coexistence region called a "ruled surface" and knowledge of the coexistence curve. Least-squares fitting of the ESR spectra with the parameterized model resulted in a tie-line field consistent with other known information on this lipid system. The use of the ruled surface allows one to guarantee that tie lines do not cross. The best-fit tie-line field consisted of the set of tie lines which were not exactly parallel; they exhibited 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 were compared with those from more constrained methods of representing the tie-line fields. 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.