Laboratorio de Biomembranas, Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes, Bernal (B1876BXD), Buenos Aires, Argentina.
Langmuir. 2010 Jun 15;26(12):10084-92. doi: 10.1021/la100214v.
The use of liposomes to encapsulate materials has received widespread attention for drug delivery, transfection, diagnostic reagent, and as immunoadjuvants. Phospholipid polymers form a new class of biomaterials with many potential applications in medicine and research. Of interest are polymeric phospholipids containing a diacetylene moiety along their acyl chain since these kinds of lipids can be polymerized by Ultra-Violet (UV) irradiation to form chains of covalently linked lipids in the bilayer. In particular the diacetylenic phosphatidylcholine 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DC8,9PC) can form intermolecular cross-linking through the diacetylenic group to produce a conjugated polymer within the hydrocarbon region of the bilayer. As knowledge of liposome structures is certainly fundamental for system design improvement for new and better applications, this work focuses on the structural properties of polymerized DC8,9PC:1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes. Liposomes containing mixtures of DC8,9PC and DMPC, at different molar ratios, and exposed to different polymerization cycles, were studied through the analysis of the electron spin resonance (ESR) spectra of a spin label incorporated into the bilayer, and the calorimetric data obtained from differential scanning calorimetry (DSC) studies. Upon irradiation, if all lipids had been polymerized, no gel-fluid transition would be expected. However, even samples that went through 20 cycles of UV irradiation presented a DSC band, showing that around 80% of the DC8,9PC molecules were not polymerized. Both DSC and ESR indicated that the two different lipids scarcely mix at low temperatures, however few molecules of DMPC are present in DC8,9PC rich domains and vice versa. UV irradiation was found to affect the gel-fluid transition of both DMPC and DC8,9PC rich regions, indicating the presence of polymeric units of DC8,9PC in both areas. A model explaining lipids rearrangement is proposed for this partially polymerized system.
脂质体用于包裹材料的应用在药物传递、转染、诊断试剂和免疫佐剂方面受到了广泛关注。磷脂聚合物形成了一类新的生物材料，在医学和研究中有许多潜在的应用。人们感兴趣的是含有二乙炔基部分的聚合磷脂，因为这些脂质可以通过紫外（UV）辐射聚合形成双层中共价连接的脂质链。特别是二乙酰基磷脂酰胆碱 1,2-双（10,12-二十三酰基）-sn-甘油-3-磷酸胆碱（DC8,9PC）可以通过二乙炔基形成分子间交联，在双层的烃区域内形成共轭聚合物。由于了解脂质体结构对于新的和更好的应用系统设计的改进肯定是基础，因此这项工作集中在聚合 DC8,9PC：1,2-二肉豆蔻酰-sn-甘油-3-磷酸胆碱（DMPC）脂质体的结构特性上。通过分析掺入双层的自旋标记的电子自旋共振（ESR）谱，以及从差示扫描量热法（DSC）研究中获得的量热数据，研究了含有不同摩尔比的 DC8,9PC 和 DMPC 混合物的脂质体，以及暴露于不同聚合循环的脂质体。如果所有脂质都聚合了，那么在辐照后就不会预期到凝胶-流动转变。然而，即使经过 20 个 UV 辐照循环的样品也出现了 DSC 带，表明大约 80%的 DC8,9PC 分子没有聚合。DSC 和 ESR 都表明，在低温下，两种不同的脂质几乎不混合，然而在 DC8,9PC 丰富的区域中存在少量的 DMPC 分子，反之亦然。发现 UV 辐射会影响富含 DMPC 和 DC8,9PC 的区域的凝胶-流动转变，表明在这两个区域都存在 DC8,9PC 的聚合单元。对于这个部分聚合的系统，提出了一个解释脂质重排的模型。
