Neal Sharon L
Department of Chemistry and Biochemistry, University of Delaware, Newark, DE, USA.
Appl Spectrosc. 2018 Jan;72(1):102-113. doi: 10.1177/0003702817729347. Epub 2017 Sep 15.
The phase behavior of aqueous 1,2-dimyristoyl-sn-glycero-3-phosphorylcholine (DMPC)/1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC) mixtures between 8.0 ℃ and 41.0 ℃ were monitored using Raman spectroscopy. Temperature-dependent Raman matrices were assembled from series of spectra and subjected to multivariate analysis. The consensus of pseudo-rank estimation results is that seven to eight components account for the temperature-dependent changes observed in the spectra. The spectra and temperature response profiles of the mixture components were resolved by applying a variant of the non-negative matrix factorization (NMF) algorithm described by Lee and Seung (1999). The rotational ambiguity of the data matrix was reduced by augmenting the original temperature-dependent spectral matrix with its cumulative counterpart, i.e., the matrix formed by successive integration of the spectra across the temperature index (columns). Successive rounds of constrained NMF were used to isolate component spectra from a significant fluorescence background. Five major components exhibiting varying degrees of gel and liquid crystalline lipid character were resolved. Hydrogen-bonded water networks exhibiting varying degrees of organization are associated with the lipid components. Spectral parameters were computed to compare the chain conformation, packing, and hydration indicated by the resolved spectra. Based on spectral features and relative amounts of the components observed, four components reflect long chain lipid response. The fifth component could reflect the response of the short chain lipid, DHPC, but there were no definitive spectral features confirming this assignment. A minor component of uncertain assignment that exhibits a striking response to the DMPC pre-transition and chain melting transition also was recovered. While none of the spectra resolved exhibit features unequivocally attributable to a specific aggregate morphology or step in the gelation process, the results are consistent with the evolution of mixed phase bicelles (nanodisks) and small amounts of worm-like DMPC/DHPC aggregates, and perhaps DHPC micelles, at low temperature to suspensions of branched and entangled worm-like aggregates above the DMPC gel phase transition and perforated multi-lamellar aggregates at high temperature.
利用拉曼光谱监测了8.0℃至41.0℃之间的1,2 - 二肉豆蔻酰 - sn - 甘油 - 3 - 磷酸胆碱（DMPC）/1,2 - 二己酰 - sn - 甘油 - 3 - 磷酸胆碱（DHPC）水混合物的相行为。从一系列光谱中组装出温度依赖性拉曼矩阵，并对其进行多变量分析。伪秩估计结果的共识是，七到八个成分解释了光谱中观察到的温度依赖性变化。通过应用Lee和Seung（1999）描述的非负矩阵分解（NMF）算法的一个变体，解析了混合物成分的光谱和温度响应曲线。通过用其累积对应物（即通过跨温度指数（列）对光谱进行连续积分形成的矩阵）扩充原始温度依赖性光谱矩阵，减少了数据矩阵的旋转模糊性。使用连续几轮的约束NMF从显著的荧光背景中分离出成分光谱。解析出了五个表现出不同程度凝胶和液晶脂质特征的主要成分。具有不同程度组织化的氢键水网络与脂质成分相关。计算了光谱参数以比较解析光谱所表明的链构象、堆积和水合作用。基于观察到的光谱特征和成分的相对含量，四个成分反映了长链脂质的响应。第五个成分可能反映了短链脂质DHPC的响应，但没有明确的光谱特征证实这一归属。还回收了一个归属不确定的次要成分，它对DMPC预转变和链熔化转变表现出显著响应。虽然解析出的光谱中没有一个明确显示出可归因于特定聚集体形态或凝胶化过程中某一步骤的特征，但结果与混合相双分子层（纳米盘）以及少量蠕虫状DMPC/DHPC聚集体，或许还有DHPC胶束在低温下向高于DMPC凝胶相转变时的分支和缠结蠕虫状聚集体悬浮液以及高温下的穿孔多层聚集体的演变是一致的。
