Concentration-dependent aggregation of CHAPS investigated by NMR spectroscopy.
Concentration-dependent aggregation of CHAPS investigated by NMR spectroscopy.
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DOI：
10.1021/jp911720w
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发表时间：
2010-03
期刊：
影响因子：
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通讯作者：
Xianguo Qin;Maili Liu;Daiwen Yang;Xu Zhang
中科院分区：
文献类型：
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作者：
Xianguo Qin;Maili Liu;Daiwen Yang;Xu Zhang
CHAPS（3-[（3-胆酰胺丙基）二甲酰胺]-1-丙磺酸盐）是一种两性离子表面活性剂，广泛应用于各种生物领域。本文采用核磁共振波谱法研究了表面活性剂在氧化氘溶液中随浓度的聚集。根据化学位移差（Delta Delta）、自扩散系数(D)和弛豫速率(R（1)、R(2)）等核磁共振参数，我们发现存在两个断点。第一个断点对应于广泛接受的正常临界胶束浓度（cmc）。第二种是意料之外的，归因于第二种cmc，表明存在另一种更高浓度的胶束。进一步利用自旋扩散淬灭的1D选择性NOESY分析表明，在第二cmc以上的浓度下，CHAPS分子可能形成两层球形胶束结构，其内层分子的脂肪族基团与外层的类固醇基团相互作用。我们的TEM实验也证实了两种胶束的存在。CHAPS胶束大小对浓度的依赖性解释了为什么某些蛋白质只有在高于第二个cmc的浓度时才可溶解和稳定。因此，我们的发现为膜蛋白功能和结构研究中CHAPS浓度的优化提供了依据。
CHAPS (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate) is a zwitterionic surfactant, which has been extensively used in various biological fields. In the present work, the concentration-dependent aggregation of the surfactant in deuterium oxide solution was investigated by NMR spectroscopy. We have found that two break points exist on the basis of the NMR parameters such as chemical shift difference (Delta delta), self-diffusion coefficient (D), and relaxation rates (R(1), R(2)). The first break point corresponds to the widely accepted normal critical micelle concentration (cmc). The second one is unexpected and ascribed to the second cmc, indicating that there is another type of micelle at higher concentrations. Further analysis using 1D selective NOESY with spin-diffusion quenching reveals that at the concentration above the second cmc CHAPS may form a two-layer spherical structure of micelles, with the aliphatic groups of CHAPS molecules in the inner layer interact with the steroid groups in the outer layer. The existence of two types of micelles has also been supported by our TEM experiment. The dependence of CHAPS micelle size on concentration explains why some proteins are soluble and stable only at concentrations above the second cmc. Therefore, our finding provides a basis for optimizing CHAPS concentration in functional and structural studies of membrane proteins.