A systematic infrared reflection-absorption spectroscopy and film balance study of the phase behavior of lipopolymer monolayers at the air-water interface
A systematic infrared reflection-absorption spectroscopy and film balance study of the phase behavior of lipopolymer monolayers at the air-water interface
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DOI：
10.1021/la981360r
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发表时间：
1999-05-11
期刊：
影响因子：
3.9
通讯作者：
Merkel, R
中科院分区：
文献类型：
--
作者：
Baekmark, TR;Wiesenthal, T;Merkel, R
脂聚合物是具有共价连接到脂质的聚合物链的脂质。我们利用红外反射吸收光谱系统地研究了一系列脂聚合物的单分子层行为。（IRRAS）和经典的朗缪尔膜平衡技术。脂聚合物在脂质链和聚合物中的化学组成不同。然而，在所有情况下，脂质链含有18个碳原子。我们发现脂聚合物在空气-水界面处表现出非常复杂的相行为，这取决于聚合物亲水性、聚合物长度和脂链饱和度等不同参数。我们能够测量到两个不同的平台制度在单层等温线。一个是观察到的脂聚合物的聚合物部分是只有轻微的水溶性和相关的：聚合物从水表面的解吸。这种脱附转变可以被称为煎饼-蘑菇转变。第二个高原政权的起源更不确定。Baekmark等人（Langmuir 1995，11，3975）将该平台解释为聚合物内的转变（蘑菇状至聚合物刷状构象），但在Goncalves da Silva等人（Langmuir 1996，12，6547）和Baekmark等人（Langmuir 1997，13，5521）的两个最近的出版物中，该解释受到质疑。在目前的工作中，我们表明，这第二个过渡是原生的lipopolymers的意义上说，它只能被观察到时，脂质和聚合物存在于同一个分子。在相同的基础上的电影平衡和IRRAS数据，我们能够表明，脂质烷基链必须参与的分子过程构成的“天然”过渡。为了解释“天然”转变的起源，我们认为烷基链缩合过程加上烷基链内笨拙异构体数量的大幅减少为“天然”转变提供了驱动力。
Lipopolymers are lipids with a polymer chain covalently attached to the lipid. We systematically studied the monolayer behavior of a series of lipopolymers by use of infrared reflection-absorption spectroscopy. (IRRAS) and classical Langmuir film balance techniques. The lipopolymers differed in chemical composition both in the lipid chains and in the polymers. However, the lipid chains contained 18 carbon atoms in all cases. We find the lipopolymers to show a very complex phase behavior at the air-water interface, depending on such diverse parameters as polymer hydrophilicity, length of polymer; and saturation of the lipid chains. We were able to measure up to two different plateau regimes in the monolayer isotherms. One is observed for lipopolymers where the polymer part is only slightly water-soluble and is correlated with the desorption of the: polymer from the water surface. This desorption transition can be termed a pancake-mushroom transition. The origin of the second plateau regime is more uncertain. Baekmark et al. (Langmuir 1995, 11, 3975) interpreted this plateau as a transition within the polymer (mushroom-to-polymer brush conformation), but in two recent publications, by Goncalves da Silva et al. (Langmuir 1996, 12, 6547) and Baekmark et al. (Langmuir 1997, 13, 5521) this interpretation has been questioned. In the present work we show that this second transition is native to lipopolymers in the sense that it can only be observed when a lipid and polymer are present in the same molecule. On the same basis of the film balance and the IRRAS data, we are able to show that the lipid alkyl chains must be involved in the molecular processes constituting the "native" transition. To account for the origin of the "native" transition, we suggest that a process of alkyl chain condensation coupled to a strong reduction in the number of gauche isomers within the alkyl chains supply the driving force for the "native" transition.