Halladay H N, Stark R E, Ali S, Bittman R
Department of Chemistry, College of Staten Island, City University of New York, Staten Island 10301.
Biophys J. 1990 Dec;58(6):1449-61. doi: 10.1016/S0006-3495(90)82490-5.
Magic-angle spinning 1H and 13C nuclear magnetic resonance (NMR) have been employed to study 50%-by-weight aqueous dispersions of 1-octadecanoyl-2-decanoyl-sn-glycero-3-phosphocholine (C[18]:C[10]PC) and 1-octadecanoyl-2-d19-decanoyl-PC (C[18]:C[10]PC-d19), mixed-chain phospholipids which can form interdigitated multibilayers. The 1H NMR linewidth for methyl protons of the choline headgroup has been used to monitor the liquid crystalline-to-gel (LC-to-G) phase transition and confirm variations between freezing and melting temperatures. Both 1H and 13C spin-lattice relaxation times indicate unusual restrictions on segmental reorientation at megahertz frequencies for C(18):C(10)PC as compared with symmetric-chain species in the LC state; nevertheless each chemical moiety of the mixed-chain phospholipid exhibits motional behavior that may be classified as liquidlike. Two-dimensional nuclear Overhauser spectroscopy (NOESY) on C(18):C(10)PC and C(18):C(10)PC-d19 reveals cross-peaks between the omega-methyl protons of the C18 chain and the N-methyl protons of the phosphocholine headgroup, and several experimental and theoretical considerations argue against an interpretation based on spin diffusion. Using NMR relaxation times and NOESY connectivities along with a computational formalism for four-spin systems (Keepers, J. W., and T. L. James. 1984. J. Magn. Reson. 57:404-426), an estimate of 3.5 A is obtained for the average distance between the omega-methyl protons of the C18 chain and the N-methyl protons of the phosphocholine headgroup. This finding is consistent with a degree of interdigitation similar to that proposed for organized assemblies of gel-state phosphatidylcholine molecules with widely disparate acyl-chain lengths (Hui, S. W., and C.-H. Huang. 1986. Biochemistry. 25:1330-1335); however, acyl-chain bendback or other intermolecular interactions may also contribute to the NOESY results. For multibilayers of C(18):C(10)PC in the gel phase, 13C chemical-shift measurements indicate that trans conformers predominate along both acyl chains. 13C Spin-lattice relaxation times confirm the unusual motional restrictions noted in the LC state; nevertheless, 13C and 1H rotating-frame relaxation times indicate that the interdigitated arrangement enhances chain or bilayer motions which occur at mid-kilohertz frequencies.
魔角旋转1H和13C核磁共振（NMR）已被用于研究1-十八烷酰基-2-癸酰基-sn-甘油-3-磷酸胆碱（C[18]:C[10]PC）和1-十八烷酰基-2-d19-癸酰基-PC（C[18]:C[10]PC-d19）的50%（重量）水分散体，这两种混合链磷脂可形成相互交错的多层膜。胆碱头部基团甲基质子的1H NMR线宽已被用于监测液晶到凝胶（LC-to-G）相变，并确认冻结和熔化温度之间的变化。1H和13C自旋晶格弛豫时间均表明，与LC状态下的对称链物种相比，C(18):C(10)PC在兆赫兹频率下链段重排存在异常限制；然而，混合链磷脂的每个化学部分都表现出可归类为类似液体的运动行为。对C(18):C(10)PC和C(18):C(10)PC-d19进行的二维核Overhauser光谱（NOESY）显示，C18链的ω-甲基质子与磷酸胆碱头部基团的N-甲基质子之间存在交叉峰，并且一些实验和理论考虑因素反对基于自旋扩散的解释。利用NMR弛豫时间和NOESY连接性以及针对四自旋系统的计算形式（Keepers, J. W., and T. L. James. 1984. J. Magn. Reson. 57:404 - 426），得出C18链的ω-甲基质子与磷酸胆碱头部基团的N-甲基质子之间的平均距离估计为3.5 Å。这一发现与具有广泛不同酰基链长度的凝胶态磷脂酰胆碱分子有序组装体所提出的相互交错程度一致（Hui, S. W., and C.-H. Huang. 1986. Biochemistry. 25:1330 - 1335）；然而，酰基链回折或其他分子间相互作用也可能对NOESY结果有贡献。对于凝胶相中的C(18):C(10)PC多层膜，13C化学位移测量表明反式构象在两条酰基链上均占主导。13C自旋晶格弛豫时间证实了在LC状态下所观察到的异常运动限制；然而，13C和1H旋转框架弛豫时间表明，相互交错的排列增强了在中千赫兹频率下发生的链或双层运动。
