Dave Paresh C, Inbaraj Johnson J, Lorigan Gary A
Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, USA.
Langmuir. 2004 Jul 6;20(14):5801-8. doi: 10.1021/la036377a.
X-band electron paramagnetic resonance (EPR) spectroscopy was used to study the structural and dynamic properties of magnetically aligned phospholipid bilayers utilizing a variety of phosphocholine spin labels (PCSL) as a function oftemperature. 1-Palmitoyl-2-[n-(4,4-dimethyloxazolidine-N-oxyl)stearoyl]-sn-glycero-3-phosphocholine (n-PCSL) in which a nitroxide group was attached to the different acyl chain positions of the phospholipid (n = 5, 7, 12, and 14) were used as an EPR spin probe to investigate magnetically aligned phospholipid bilayers from the plateau (near to the headgroup) region to the end of the acyl chain (center of the bilayers). The addition of certain types of paramagnetic lanthanide ions changes the overall magnetic susceptibility anisotropy tensor of the bicelles, such that the bicelles flip with their bilayer normal either parallel or perpendicular to the magnetic field. The present study reveals for the first time that, in the case of the n-PCSL, the bilayer normal is aligned parallel and perpendicular to the magnetic field in the presence of lanthanide ions having positive delta(chi) (e.g., Tm3+) and negative delta(chi) (e.g., Dy3+), respectively. The magnetic alignment of the bilayers and the corresponding segmental molecular order parameter, S(mol), were investigated as a function of the temperature. The S(mol) values decrease in the following order, 5-PCSL > 7-PCSL > 12-PCSL > 14-PCSL, for the magnetically aligned phospholipid bilayers. Also, the variable temperature study indicates that, by increasing the temperature, the order parameters S(mol) decreased for all the n-PCSLs. The results indicate that magnetically aligned phospholipid bilayers represent an excellent model membrane system for X-band EPR studies.
利用X波段电子顺磁共振（EPR）光谱，通过各种磷胆碱自旋标记（PCSL）研究了磁性排列的磷脂双层的结构和动力学性质，并将其作为温度的函数。1-棕榈酰-2-[n-（4,4-二甲基恶唑烷-N-氧基）硬脂酰]-sn-甘油-3-磷胆碱（n-PCSL，其中氮氧基团连接到磷脂的不同酰基链位置（n = 5、7、12和14））用作EPR自旋探针，以研究从高原（靠近头基团）区域到酰基链末端（双层中心）的磁性排列的磷脂双层。添加某些类型的顺磁性镧系离子会改变双分子层的整体磁化率各向异性张量，使得双分子层以其双层法线平行或垂直于磁场的方式翻转。本研究首次揭示，在n-PCSL的情况下，在分别具有正δ（χ）（例如，Tm3 +）和负δ（χ）（例如，Dy3 +）的镧系离子存在下，双层法线分别平行和垂直于磁场排列。研究了双层的磁性排列和相应的片段分子序参数S（mol）作为温度的函数。对于磁性排列的磷脂双层，S（mol）值按以下顺序降低：5-PCSL> 7-PCSL> 12-PCSL> 14-PCSL。此外，变温研究表明，通过升高温度，所有n-PCSL的序参数S（mol）均降低。结果表明，磁性排列的磷脂双层代表了用于X波段EPR研究的出色模型膜系统。
