Arleth Lise, Ashok Beena, Onyuksel Hayat, Thiyagarajan Pappannan, Jacob Jaby, Hjelm Rex P
Manuel Lujan Jr. Neutron Scattering Center, MS H805, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
Langmuir. 2005 Apr 12;21(8):3279-90. doi: 10.1021/la047588y.
Aqueous dispersions of mixed egg yolk phosphatidylcholine (PC) and poly(ethylene glycol) (PEG) modified distearoyl phosphatidylethanolamine (DSPE) were investigated with the purpose of determining shape, size, and conformation of the formed mixed micelles. The samples were prepared at a range of DSPEPEG to PC molar ratios ([DSPEPEG/PC] from 100:0 to 30:70) and with, respectively, DSPEPEG2000 and DSPEPEG5000, where 2000 and 5000 refer to the molar masses of the PEG chains. Particle shape and internal structure were studied using small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS). The contrast of the micelles is different for X-rays and neutrons, and by combining SANS and SAXS, complementary information about the micelle structure was obtained. The detailed structure of the micelles was determined in a self-consistent way by fitting a model for the micelles to SANS and SAXS data simultaneously. In general, a model for the micelles with a hydrophobic core, surrounded by a dense hydrophilic layer that is again surrounded by a corona of PEG chains in the form of Gaussian random coils attached to the outer surface, is in good agreement with the scattering data. At high DSPEPEG contents, nearly spherical micelles are formed. As the PC content increases the micelles elongate, and at a DSPEPEG/PC ratio of 30:70, rodlike micelles longer than 1000 angstroms are formed. We demonstrate that by mixing DSPEPEG and PC a considerable latitude in controlling the particle shape is obtained. Our results indicate that the PEG chains in the corona are in a relatively unperturbed Gaussian random coil conformation even though the chains are far above the coil-coil overlap concentration and, therefore, interpenetrating. This observation in combination with the observed growth behavior questions that the "mushroom-brush"transition is the single dominating factor for determining the particle shape as assumed in previous theoretical work (Hristova, K.; Needham, D. Macromolecules 1995, 28, 991-1002).
研究了混合蛋黄磷脂酰胆碱（PC）与聚乙二醇（PEG）修饰的二硬脂酰磷脂酰乙醇胺（DSPE）的水分散体，目的是确定所形成混合胶束的形状、大小和构象。样品在一系列DSPEPEG与PC的摩尔比（[DSPEPEG/PC]从100:0到30:70）下制备，分别使用DSPEPEG2000和DSPEPEG5000，其中2000和5000指PEG链的摩尔质量。使用小角X射线散射（SAXS）和小角中子散射（SANS）研究颗粒形状和内部结构。胶束对X射线和中子的对比度不同，通过结合SANS和SAXS，获得了关于胶束结构的互补信息。通过将胶束模型同时拟合到SANS和SAXS数据，以自洽的方式确定了胶束的详细结构。一般来说，具有疏水核心的胶束模型与散射数据吻合良好，该疏水核心被致密的亲水层包围，亲水层又被以高斯无规线团形式附着在外表面的PEG链冠层包围。在高DSPEPEG含量下，形成近球形胶束。随着PC含量增加，胶束伸长，在DSPEPEG/PC比为30:70时，形成长度超过1000埃的棒状胶束。我们证明，通过混合DSPEPEG和PC，可以在控制颗粒形状方面获得相当大的自由度。我们的结果表明，冠层中的PEG链处于相对未受干扰的高斯无规线团构象，尽管链远高于线团-线团重叠浓度，因此相互渗透。这一观察结果与观察到的生长行为相结合，对“蘑菇-刷”转变是否是先前理论工作（Hristova，K.；Needham，D.Macromolecules 1995，28，991 - 1002）中假设的决定颗粒形状的单一主导因素提出了质疑。
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