The polymorphism of lipid aggregates has long attracted detailed study due to the myriad factors that determine the final mesophase observed. This study is driven by the need to understand mesophase behaviour for a number of applications, such as drug delivery and membrane protein crystallography. In the case of the latter, the role of the so-called 'sponge' (L₃) mesophase has been often noted, but not extensively studied by itself. The L₃ mesophase can be formed in monoolein/water systems on the addition of butanediol to water, which partitions the headgroup region of the membrane, and decreases its elastic moduli. Like cubic mesophases, it is bicontinuous, but unlike them, has no long-range translational symmetry. In our present study, we show that the formation of the L₃ phase can delicately depend on the addition of dopant lipids to the mesophase. While electrostatically neutral molecules similar in shape to monoolein (DOPE, cholesterol) have little effect on the general mesophase behaviour, others (DOPC, DDM) significantly reduce the region in which it can form. Additionally, we show that by combining cholesterol with the anionic lipid DOPG, it is possible to form the largest stable L₃ mesophases observed to date, with correlation lengths over 220 Å.

中文翻译：

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海绵（L3）中间相的脂质型掺杂

由于决定最终观察到的中间相的因素众多，脂质聚集体的多态性一直吸引着详细的研究。这项研究是由对许多应用（例如药物递送和膜蛋白晶体学）的理解中间相行为的需求驱动的。在后者的情况下，通常已经注意到所谓的“海绵”（L ₃）中间相的作用，但其本身并未得到广泛研究。L ₃中间相可在单丁烯醇/水体系中通过向水中添加丁二醇而形成，这可分隔膜的头基区域并降低其弹性模量。像立方中间相一样，它是双连续的，但与它们不同，它没有长距离的平移对称性。在我们目前的研究中，我们表明L的形成₃相可以微妙地依赖于添加掺杂脂质与中间相。形状类似于单油精的静电中性分子（DOPE，胆固醇）对一般的中间相行为影响很小，而其他分子（DOPC，DDM）则显着减少了其形成的区域。此外，我们表明，通过将胆固醇与阴离子脂质DOPG结合，可以形成迄今为止观察到的最大的稳定L ₃中间相，相关长度超过220。