Yamashita Jun, Shiono Manzo, Hato Masakatsu
Nanotechnology Research Institute, AIST, Tsukuba Central-5, Higashi 1-1-1, Tsukuba, Ibaraki, Japan.
J Phys Chem B. 2008 Oct 2;112(39):12286-96. doi: 10.1021/jp8029874. Epub 2008 Sep 6.
With a view to discovering a new family of lipids that form inverted cubic phases, the aqueous phase behavior of a series of lipids with isoprenoid-type hydrophobic chains has been examined over a temperature range from -40 to 65 degrees C by using optical microscopy, DSC (differential scanning calorimetry), and SAXS (small-angle X-ray scattering) techniques. The lipids examined are those with 5,9,13,17-tetramethyloctadecyl and 5,9,13,17-tetramethyloctadecanoyl chains linked to a series of headgroups, that is, erythritol, pentaerythritol, xylose, and glucose. All of the lipid/water systems displayed a "water + liquid crystalline phase" two-phase coexistence state when sufficiently diluted. The aqueous phase structures of the most diluted liquid crystalline phases in equilibrium with excess water depend both on the lipid molecular structure and on the temperature. Given an isoprenoid chain, the preferred phase consistently follows a phase sequence of an H II (an inverted hexagonal phase) to a Q II (an inverted bicontinuous cubic phase) to an L alpha (a lamellar phase) as A* (cross-section area of the headgroup) increases. For a given lipid/water system, the phase sequence observed as the temperature increases is L alpha to Q II to H II. The present study allowed us to find four cubic phase-forming lipid species, PEOC 18+4 [mono- O-(5,9,13,17-tetramethyloctadecyl)pentaerythritol], beta-XylOC 18+4 [1- O-(5,9,13,17-tetramethyloctadecyl)-beta- d-xylopyranoside], EROCOC 17+4 [1- O-(5,9,13,17-tetramethyloctadecanoyl)erythritol], and PEOCOC 17+4 [mono- O-(5,9,13,17-tetramethyloctadecanoyl)pentaerythritol]. The values of T K (hydrated solid-liquid crystalline phase transition temperature) of the cubic phase-forming lipids are all below 0 degrees C. Quantitative analyses of the lipid molecular structure-aqueous phase structure relationship in terms of the experimentally evaluated "surfactant parameter" allow us to rationally select an optimum combination of hydrophilic/hydrophobic part of a lipid molecule that will form a desired phase in a desired temperature range.
为了发现能形成反相立方相的新脂质家族，通过光学显微镜、差示扫描量热法（DSC）和小角X射线散射（SAXS）技术，在-40至65摄氏度的温度范围内研究了一系列具有类异戊二烯型疏水链的脂质的水相行为。所研究的脂质是那些具有与一系列头基相连的5,9,13,17-四甲基十八烷基和5,9,13,17-四甲基十八烷酰基链的脂质，即赤藓糖醇、季戊四醇、木糖和葡萄糖。所有脂质/水体系在充分稀释时均呈现“水 + 液晶相”的两相共存状态。与过量水处于平衡状态的最稀液晶相的水相结构既取决于脂质分子结构，也取决于温度。对于给定的类异戊二烯链，随着头基的A*（横截面面积）增加，优选相始终遵循从H II（反相六角相）到Q II（反相双连续立方相）再到Lα（层状相）的相序列。对于给定的脂质/水体系，随着温度升高观察到的相序列是Lα到Q II到H II。本研究使我们发现了四种形成立方相的脂质种类，即PEOC 18+4 [单 - O-(5,9,13,17-四甲基十八烷基)季戊四醇]、β-XylOC 18+4 [1 - O-(5,9,13,17-四甲基十八烷基)-β-D-吡喃木糖苷]、EROCOC 17+4 [1 - O-(5,9,13,17-四甲基十八烷酰基)赤藓糖醇]和PEOCOC 17+4 [单 - O-(5,9,13,17-四甲基十八烷酰基)季戊四醇]。形成立方相的脂质的T K（水合固 - 液晶相转变温度）值均低于0摄氏度。根据实验评估的“表面活性剂参数”对脂质分子结构 - 水相结构关系进行定量分析，使我们能够合理选择脂质分子亲水/疏水部分的最佳组合，从而在所需温度范围内形成所需相。
