Guo W, Hamilton J A
Department of Biophysics, Boston University School of Medicine, Massachusetts 02118, USA.
Biochemistry. 1995 Oct 31;34(43):14174-84. doi: 10.1021/bi00043a023.
Multinuclear (1H, 13C, 31P) MASNMR and static solid-state 31P NMR were used to study the molecular interactions between dipalmitoylphosphatidylcholine (DPPC) and free cholesterol (CHOL) in multilayers of DPPC containing 0-65 mol % CHOL with respect to total lipid at temperatures between 25 and 55 degrees C. 13C chemical shifts and line shapes for DPPC and CHOL resonances were measured in 13C MASNMR spectra. The apparent chemical shift anisotropy (CSA) of the DPPC acyl methylene resonances [(CH2)n] was calculated from the 1H MASNMR spectra. CSA and line shape changes were recorded as a function of CHOL content by 31P static solids and MASNMR. The presence of CHOL significantly changed the 13C chemical shifts and line shapes of DPPC carbonyl carbons below or above the main transition temperature of pure DPPC. Chemical shift changes were also observed for CHOL carbons as a function of the mixing ratio, signifying a changing local environment of CHOL. For mixtures with CHOL > 50 mol %, 13C MASNMR detected crystalline CHOL in the monohydrate form. When the excess CHOL was in a submicroscopic crystalline form that was not readily detected by differential scanning calorimetry, or optical microscopy (but readily observed by 13C MASNMR), the 31P powder pattern was affected, suggesting interaction of the excess CHOL with the aqueous interface of the bilayer. These results suggest the potential of 13C MASNMR for detection of crystalline CHOL in biological samples.
利用多核（1H、13C、31P）魔角旋转核磁共振（MAS NMR）和静态固态31P NMR，在25至55摄氏度的温度范围内，研究了二棕榈酰磷脂酰胆碱（DPPC）与游离胆固醇（CHOL）在含有0 - 65摩尔％CHOL（相对于总脂质）的DPPC多层膜中的分子相互作用。在13C MAS NMR光谱中测量了DPPC和CHOL共振的13C化学位移和线形。从1H MAS NMR光谱计算DPPC酰基亚甲基共振[（CH2）n]的表观化学位移各向异性（CSA）。通过31P静态固体和MAS NMR记录CSA和线形变化作为CHOL含量的函数。CHOL的存在显著改变了纯DPPC主转变温度以下或以上的DPPC羰基碳的13C化学位移和线形。还观察到CHOL碳的化学位移变化作为混合比的函数，表明CHOL的局部环境在变化。对于CHOL> 50摩尔％的混合物，13C MAS NMR检测到一水合物形式的结晶CHOL。当过量的CHOL呈亚微观结晶形式，差示扫描量热法或光学显微镜不易检测到（但13C MAS NMR很容易观察到）时，31P粉末图谱会受到影响，表明过量的CHOL与双层的水界面相互作用。这些结果表明13C MAS NMR在检测生物样品中结晶CHOL方面的潜力。
