Hypothesis

Molecular dynamics simulation can be used to differentiate between the adsorption properties of rhamnolipid congeners at a vacuum-water interface.

Experiments

Adsorption of five congeners with differing alkyl chains (two C10 chains, two C14 chains or mixed C14C10 and C10C14), number of rhamnose rings (mono- or di-) and carboxyl group charge (non-ionic or anionic) are simulated at the vacuum-water interface.

Findings

All rhamnolipids adsorb in the interfacial region with rhamnose and carboxyl groups closer to the water phase, and alkyl chains closer to the vacuum phase, but with differing adsorbed conformations. Headgroups of uncharged congeners show two preferred conformations, closed and partially open. Di-rhamnolipid has a low proportion of closed conformation, due to the steric constraints of the second pyranose ring. Charged congeners show strong preference for closed headgroup conformations. For rhamnolipids with equal alkyl chains lengths (C10C10, C14C14) the distribution of alkyl chain tilt angles is similar for both. Where chain lengths are unequal (C14C10, C10C14) one chain has a greater tendency to tilt towards the water phase (>90°). The order parameter of the alkyl chains shows they are disordered at the interface. Together, these results show congener-dependent adsorbed conformation differences suggesting they will have differing surface-active properties at vacuum-water and oil-water interfaces.

中文翻译：

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真空-水界面处鼠李糖脂的同族依赖构象：分子动力学模拟

假设：

分子动力学模拟可用于区分鼠李糖脂同类物在真空-水界面的吸附性能。

实验：

在真空下模拟五个具有不同烷基链的同系物（两个C10链，两个C14链或混合的C14C10和C10C14），鼠李糖环数（单或双）和羧基电荷（非离子或阴离子）的吸附-水界面。

发现：

所有鼠李糖脂都在界面区域吸附，其中鼠李糖和羧基更接近水相，烷基链更接近真空相，但是具有不同的吸附构象。不带电同类物的头基显示出两个优选的构象，即封闭的和部分开放的。由于第二吡喃糖环的空间约束，二鼠李糖脂具有低比例的闭合构象。带电同类物显示出对封闭的头基构象的强烈偏好。对于具有相同烷基链长度的鼠李糖脂（C10C10，C14C14），烷基链倾斜角的分布对于这两种都相似。在链长不相等的情况下（C14C10，C10C14），一条链更倾向于向水相倾斜（> 90 ^o）。烷基链的有序参数表明它们在界面处无序。总之，这些结果显示了同类物相关的吸附构象差异，表明它们在真空-水和油-水界面处将具有不同的表面活性。