Polycontinuous geometries for inverse lipid phases with more than two aqueous network domains.
Polycontinuous geometries for inverse lipid phases with more than two aqueous network domains.
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DOI：
10.1039/c2fd20112g
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发表时间：
2013-01
影响因子：
3.4
通讯作者：
G. Schröder-Turk;L. de Campo;Myfanwy E. Evans;M. Saba;S. Kapfer;T. Varslot;Karsten Große-Brauckmann;S. Ramsden;S. Hyde
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文献类型：
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作者：
G. Schröder-Turk;L. de Campo;Myfanwy E. Evans;M. Saba;S. Kapfer;T. Varslot;Karsten Große-Brauckmann;S. Ramsden;S. Hyde
具有两个由光滑双层隔开的水网络域的反双连续立方相被牢固地确立为脂质/水体系中的平衡相。这篇文章的目的是突出概括这些双连续的几何形状，多连续的几何形状，这可以实现为脂质中间相与三个或更多个网络状的水域分开的一个分支双层。双层宽度变化方面的结构均匀性的分析表明，有序的多连续几何形状是脂质中间相结构的可能候选者，具有与反胶束相类似的链堆积特性（曾经被认为由于高堆积挫折而不存在）。所需的全球几何形状，以形成这些多网络相的平均分子形状是定量的表面活性剂的形状参数，v/（al），我们发现，它采用的值接近那些已知的脂质相。具体分析了具有三个水相结构的六方对称P6（3）/mcm的3etc（187 193）结构、由三个扭曲的金刚石网络组成的立方对称I43 d的3dia（24 220）结构、立方对称P4232的立方手性4srs（24 208）结构和对称P42/nbc的非手性4srs（5 133）结构。每一个由SRS网的四个共生的未失真的副本（与QII（G）螺旋相位中的网相同）组成。结构的均匀性进行了分析，假设头群接口是恒定的平均曲率表面的内侧表面的方法。为了便于将来的实验鉴定，我们提供了模拟的SAXS散射图案，对于4srs（24 208）和3dia（24 220）结构，与双连续QII（G）-螺旋和QII（D）-金刚石相具有显著的相似性，具有可比的晶格参数，并且只有一个峰，不能索引到已确立的结构。虽然迄今为止尚未报道多连续脂质相，但它们形成的可能性进一步由所报道的在表面活性剂存在下形成的固体三连续中孔硅酸盐结构（称为IBN-9）的观察结果表明[Han等人，Nat. Chem.，2009，1，123]。
Inverse bicontinuous cubic phases with two aqueous network domains separated by a smooth bilayer are firmly established as equilibrium phases in lipid/water systems. The purpose of this article is to highlight the generalisations of these bicontinuous geometries to polycontinuous geometries, which could be realised as lipid mesophases with three or more network-like aqueous domains separated by a branched bilayer. An analysis of structural homogeneity in terms of bilayer width variations reveals that ordered polycontinuous geometries are likely candidates for lipid mesophase structures, with similar chain packing characteristics to the inverse micellar phases (that once were believed not to exist due to high packing frustration). The average molecular shape required by global geometry to form these multi-network phases is quantified by the surfactant shape parameter, v/(al); we find that it adopts values close to those of the known lipid phases. We specifically analyse the 3etc(187 193) structure of hexagonal symmetry P6(3) /mcm with three aqueous domains, the 3dia(24 220) structure of cubic symmetry I43d composed of three distorted diamond networks, the cubic chiral 4srs(24 208) with cubic symmetry P4232 and the achiral 4srs(5 133) structure of symmetry P42/nbc, each consisting of four intergrown undistorted copies of the srs net (the same net as in the QII(G) gyroid phase). Structural homogeneity is analysed by a medial surface approach assuming that the headgroup interfaces are constant mean curvature surfaces. To facilitate future experimental identification, we provide simulated SAXS scattering patterns that, for the 4srs(24 208) and 3dia(24 220) structures, bear remarkable similarity to those of bicontinuous QII(G)-gyroid and QII(D)-diamond phases, with comparable lattice parameters and only a single peak that cannot be indexed to the well-established structures. While polycontinuous lipid phases have, to date, not been reported, the likelihood of their formation is further indicated by the reported observation of a solid tricontinuous mesoporous silicate structure, termed IBN-9, which formed in the presence of surfactants [Han et al., Nat. Chem., 2009, 1, 123].