Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122, United States.
J Phys Chem B. 2011 Nov 17;115(45):13181-90. doi: 10.1021/jp205999p. Epub 2011 Oct 26.
The packing of lipids on silica (SiO(2)) nanoparticles (NPs) was investigated by Raman spectroscopy for 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) as a function of their size, for SiO(2) NPs of 5, 15, 25, 45, and 100 nm nominal diameter. Raman spectral indicators in the C-C and C-H stretching regions were used to determine conformational order and alkyl chain packing for these systems. As the ratio of NP to lipid size decreases, packing in a normal bilayer configuration increases free volume and decreases hydrophobic interaction between the chains. For the 15, 25, 45, and 100 nm SiO(2), for which single supported lipid bilayers (SLBs) are formed around the NPs, the Raman data indicate that there is increased interdigitation and increased lateral packing order between the chains with decreasing NP size, which improves hydrophobic association and decreases the voids that would occur for normal bilayers. For the same size NP, there is increased interdigitation and lateral packing for the DSPC compared with DPPC lipids, as expected based on the greater void volume that would be created for the longer alkyl chain lengths. Another mechanism for filling this void space is the formation of gauche kinks for the terminal methyl groups at the center of the bilayer, which can be monitored by a Raman band at 1122 cm(-1). These gauche defects are most prevalent for the largest size (100 nm) NPs but are observed for all NP sizes. For the 5 nm SLBs, which form aggregates, we hypothesize that bilayer bridging can occur between the NPs. Compared with the 15 nm NPs, the order parameter increases but there are fewer trans conformers, possibly due to chains that are loosely packed or isolated in the interstitial regions.
采用拉曼光谱研究了脂质在二氧化硅（SiO2）纳米粒子（NPs）上的包裹情况，所用脂质为 1,2-二棕榈酰-sn-甘油-3-磷酸胆碱（DPPC）和 1,2-二硬脂酰-sn-甘油-3-磷酸胆碱（DSPC），研究了它们的尺寸对 SiO2 NPs（标称直径为 5、15、25、45 和 100nm）的影响。在 C-C 和 C-H 伸缩区域使用拉曼光谱指标来确定这些体系的构象有序性和烷基链堆积情况。随着 NP 与脂质尺寸比的减小，正常双层结构中的堆积会增加自由体积并减少链间的疏水相互作用。对于 15、25、45 和 100nm 的 SiO2，由于在 NPs 周围形成了单支持的脂质双层（SLB），拉曼数据表明，随着 NP 尺寸的减小，链间的交错和横向堆积有序性增加，这改善了疏水性缔合并减少了正常双层中可能出现的空隙。对于相同尺寸的 NP，DSPC 脂质的交错和横向堆积比 DPPC 脂质更多，这与长烷基链长度会产生更大的空隙体积的预期相符。另一种填充这些空隙的机制是双层中心的末端甲基形成 gauche 弯曲，通过拉曼光谱在 1122cm-1 处的带可以监测到这种 gauche 缺陷。这些 gauche 缺陷在最大尺寸（100nm）的 NPs 中最为普遍，但在所有 NP 尺寸中都观察到。对于形成聚集体的 5nm SLB，我们假设 NPs 之间可能会发生双层桥接。与 15nm NPs 相比，有序参数增加，但 trans 构象体减少，这可能是由于链松散堆积或在间隙区域中隔离所致。
