DYNAMIC STRUCTURE AND TERNARY PHASE DIAGRAM OF DPPC-DLPC-CHOLESTEROL BY ESR

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。建立了一种在室温条件下通过研究水合层状液体混合物双棕榈酰- pc /双脲酰- pc /胆固醇（DPPC/DLPC/Chol）的w- esr光谱来测定复杂混合物中脂类双层相行为的方法。采用非线性最小二乘拟合方法对100多种不同组分的光谱进行了分析，得到了端链标记磷脂16-PC的旋转扩散速率和阶数参数。ESR光谱表现出相当大的变化，作为组成的函数，尽管各自的相通常相差不大。L α相和L β相有明显的区别，前者表现出较低的有序度和较高的运动速率，而定义明确的Lo相表现出最大的有序度和较快的运动速率。通常，在给定的阶段中会出现较小的变化。ESR光谱分析也产生相边界和共存区域，发现与以前的荧光方法的结果一致，尽管发现了新的特征。在某些情况下，通过观察来自相的吸收模式ESR光谱中等吸点的存在，可以证实相共存区。富dppc的L β相和富dppc的L α相在两相共存区内的动态结构性质不随组分的变化而沿系线变化，但两相的比值遵循热力学原理的杠杆规律。分析表明，16-PC自旋标签在L α相和L β相之间几乎相等地划分，使其成为研究这种共存相的有用探针。对两相共存区域的广泛研究需要确定联络线，这在本研究中是近似的。然而，本文提出了一种用ESR准确确定联络线的方法。

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 method has been developed for determining lipid bilayer phase behavior in complex mixtures by studying cw-ESR spectra for the hydrated lamellar liquid mixture Dipalmitoyl-PC/Dilauroyl-PC/Cholesterol (DPPC/DLPC/Chol) at room temperature. The spectra for more than 100 different compositions were analyzed by nonlinear least squares fitting to obtain the rotational diffusion rates and order parameters of the end-chain labeled phospholipid 16-PC. The ESR spectra exhibit substantial variation as a function of composition, even though the respective phases generally differ rather modestly from each other. The L alpha and L beta phases are clearly distinguished, with the former exhibiting substantially lower ordering and greater motional rates, whereas the well-defined Lo phase exhibits the greatest ordering and relatively fast motional rates. Typically, smaller variations occur within a given phase. The ESR spectral analysis also yields phase boundaries and coexistence regions which are found to be consistent with previous results from fluorescence methods, although new features are found. Phase coexistence regions were in some cases confirmed by observing the existence of isosbestic points in the absorption mode ESR spectra from the phases. The dynamic structural properties of the DPPC-rich L beta and DLPC-rich L alpha phases, within their 2-phase coexistence region do not change with composition along a tie-line, but the ratio of the two phases follows the lever rule in accordance with thermodynamic principles. The analysis shows that 16-PC spin label partitions nearly equally between the L alpha and L beta phases, making it a useful probe for studying such coexisting phases. Extensive study of 2-phase coexistence regions requires the determination of tie-lines, which were approximated in this study. However, a method is suggested to accurately determine the tie-lines by ESR.