Division for Organic Chemistry and Biochemistry, Ruđer Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia.
Division of Analytical Chemistry, Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, 10000 Zagreb, Croatia.
Biochim Biophys Acta Biomembr. 2023 Jan 1;1865(1):184072. doi: 10.1016/j.bbamem.2022.184072. Epub 2022 Oct 8.
One of the most distinguished quantities that describes lipid main phase transition, i.e. the transition from the gel (L) to the fluid (L) phase, is its melting temperature (T). Because melting is accompanied by a large change in enthalpy the, L → L transition can be monitored by various calorimetric, structural and spectroscopic techniques and T should be the same regardless of the metric monitored or the technique employed. However, in the case of DPPE multilamellar aggregates there is a small but systematic deviation of T values determined by DSC and FTIR spectroscopy. The aim of this paper is to explain this discrepancy by combined UV/Vis spectroscopic and MD computational approach. Multivariate analysis performed on temperature-dependent UV/Vis spectra of DPPE suspensions demonstrated that at 55 ± 1 °C certain phenomenon causes a small but detectable change in suspension turbidity, whereas a dominant change in the latter is registered at 63.2 ± 0.4 °C that coincides with T value determined from DSC curve. If this effect should be ignored, the overall data give T value the same as FTIR spectra data (61.0 ± 0.4 °C). As the classical MD simulations suggest that about 10° below T certain undulations appear at the surface of DPPE bilayers, we concluded that certain discontinuities in curvature fluctuations arise at reported temperature which are to some extent coupled with lipid melting. Ultimately, such events and the associated changes in curvature affect T value measured by different techniques.
描述脂质主相变的一个最显著的量是其熔融温度 (T)，即从凝胶 (L) 相到流体 (L) 相的转变。由于熔融伴随着焓的巨大变化，因此可以通过各种量热法、结构和光谱技术来监测 L→L 相变，并且 T 应该是相同的，无论监测的度量单位或采用的技术如何。然而，在 DPPE 多层聚集物的情况下，通过 DSC 和 FTIR 光谱法确定的 T 值存在微小但系统的偏差。本文的目的是通过联合 UV/Vis 光谱和 MD 计算方法来解释这种差异。对 DPPE 悬浮液的温度依赖性 UV/Vis 光谱进行的多元分析表明，在 55±1°C 时，某些现象会导致悬浮液浊度发生微小但可检测的变化，而后者的主要变化发生在 63.2±0.4°C，与从 DSC 曲线确定的 T 值一致。如果忽略此效果，则总体数据给出的 T 值与 FTIR 光谱数据相同（61.0±0.4°C）。由于经典 MD 模拟表明在 T 以下约 10°时 DPPE 双层膜的表面会出现某些波动，我们得出结论，在报告的温度下会出现某些曲率波动的不连续性，这些波动在某种程度上与脂质熔融相关。最终，这些事件和相关的曲率变化会影响不同技术测量的 T 值。
