Hollinshead Clare M, Harvey Richard D, Barlow David J, Webster John R P, Hughes Arwel V, Weston Anne, Lawrence M Jayne
Pharmaceutical Science Division, King's College London, The Franklin Wilkins Building, 150 Stamford Street, London SE1 9NH, UK.
Langmuir. 2009 Apr 7;25(7):4070-7. doi: 10.1021/la8028319.
The structure of the monolayer formed at an air/water interface by the phospholipid distearoylphosphatidylcholine (DSPC) has been determined as a function of the monolayer surface pressure (pi) using Brewster angle microscopy and neutron reflectivity. The microscopy studies demonstrate that the DSPC molecules form an extremely homogeneous monolayer on the water surface with no evidence of any domain formation. The neutron reflectivity measurements provide information on the thickness of the DSPC alkyl chains, head groups, and associated solvent distributions, along with the separations between these distributions and the interfacial area per molecule. Partial structure factor analyses of the reflectivity data show that the area occupied by each DSPC molecule decreases from 49 A2 at pi = 20 mN/m to 44 A2 at pi = 50 mN/m. There are concomitant increases in the widths of the lipids' alkyl chains and headgroup distributions (modeled as Gaussians), with the former rising from 18 A (at pi = 20 mN/m) to 20 A (at pi = 50 mN/m) and the latter rising from 14 A (at pi = 20 mN/m) to 18 A (at pi = 50 mN/m). The compression of the monolayer is also shown to give rise to an increased surface roughness, the principal component of which is found to be the thermal roughness caused by capillary waves. At all surface pressures studied (covering the range from 20 to 50 mN/m), the alkyl chains and head groups of the DSPC are found to have roughly the same orientations, with the alkyl chains tilted with respect to the surface normal by about 34 degrees and the head groups lying parallel to the interface normal, projecting vertically down into the aqueous subphase. Given the various trends noted on how the structure of the DSPC monolayer changes as a function of pi, we extrapolate to consider the structure of the monolayer immediately before its collapse.
利用布鲁斯特角显微镜和中子反射率,已确定了磷脂二硬脂酰磷脂酰胆碱(DSPC)在空气/水界面形成的单层结构与单层表面压力(π)的函数关系。显微镜研究表明,DSPC分子在水面上形成了极其均匀的单层,没有任何域形成的迹象。中子反射率测量提供了有关DSPC烷基链、头部基团和相关溶剂分布的厚度信息,以及这些分布之间的间距和每个分子的界面面积。对反射率数据的部分结构因子分析表明,每个DSPC分子占据的面积从π = 20 mN/m时的49 Ų减小到π = 50 mN/m时的44 Ų。脂质的烷基链和头部基团分布(建模为高斯分布)的宽度随之增加,前者从18 Å(在π = 20 mN/m时)增加到20 Å(在π = 50 mN/m时),后者从14 Å(在π = 20 mN/m时)增加到18 Å(在π = 50 mN/m时)。还表明单层的压缩会导致表面粗糙度增加,其主要成分是由毛细波引起的热粗糙度。在所有研究的表面压力下(覆盖20至50 mN/m的范围),发现DSPC的烷基链和头部基团具有大致相同的取向,烷基链相对于表面法线倾斜约34度,头部基团与界面法线平行,垂直向下伸入水相下层。鉴于注意到的DSPC单层结构随π变化的各种趋势,我们进行外推以考虑单层在坍塌前的结构。