Abstract: Self-assembled pseudopolyrotaxane hydrogel formed by polyethylene glycol (PEG) and cyclodextrin (CD) can be used as a slow-release carrier for proteins. In this ternary system, there may be certain interactions between PEG, CD and proteins. With bovine serum albumin (BSA) as the model protein, the structure changes of BSA in the PEG/a-CD pseudopolyrotaxane hydrogel was studied by ultraviolet-visible absorption spectrum, fluorescence spectrum, powder X-ray diffraction (XRD) techniques, and NOESY spectra. The results showed that BSA had a significant effect on the formation rate of the hydrogel. The fluorescence and synchronous fluorescence spectrum analysis showed that the ternary structure of BSA had minor changes in the hydrogel, which led to red-shift of the maximum fluorescence emission wavelength, and the microenvironment of Trp and Tyr residues also changed slightly in the hydrogel. These changes became more significant with the increasing of BSA concentration. Moreover, when BSA was added, the diffraction angles in XRD spectra at 2q = 6.56°, 11.54°, 12.06°, 20.56°, 22.04°and 26.04°showed remarkable changes compared with those of the pure pseudopolyrotaxane, demonstrating that the crystalline pattern of PEG/a-CD pseudopolyrotaxane was changed in the presence of BSA. The results reflected that BSA was not simply physically mixed with the PEG/a-CD pseudopolyrotaxane hydrogel, but that it might prefer to form complexes with the hydrogel. 2D NOESY spectra also showed that the presence of mutual coupling of hydrogen atoms between BSA and PEG/a-CD, demonstrated the interaction between them.

Key words: pseudopolyrotaxane hydrogel, bovine serum albumin, cyclodextrin, polyethylene glycol, spectroscopy, powder X-ray diffraction

摘要： 聚乙二醇（PEG）与环糊精（CD）自组装形成的准聚轮烷水凝胶可作为蛋白缓释载体。在此三元体系中，PEG、CD和蛋白质之间可能存在一定的相互作用。本文以牛血清白蛋白（BSA）为模型蛋白，通过紫外-可见吸收光谱，荧光光谱，X射线粉末衍射（XRD）和NOESY谱分析等技术，研究BSA在PEG/a-CD准聚轮烷水凝胶中结构的变化。结果表明BSA对水凝胶的生成速率具有显著的影响。通过荧光光谱和同步荧光光谱分析可知，BSA在水凝胶中其三级结构发生轻微变化，致使最大荧光发射波长发生红移，而Trp和Tyr残基在水凝胶中其微环境发生了微小变化。这些变化随着BSA浓度的提高而趋于显著。对比XRD谱图发现，水凝胶在加入BSA前后，2q = 6.56°、11.54°、12.06°、20.56°、22.04°、26.04°这些衍射角位置的谱峰发生明显变化，说明BSA对PEG/a-CD准聚轮烷的晶型有一定的改变，反映了BSA与水凝胶不只是单纯的混合，而且存在形成复合物而改变蛋白质结构的可能性。2D NOESY谱图也表明BSA与PEG/a-CD准聚轮烷之间存在氢原子的相互耦合作用，证明了两者之间的相互作用。

关键词: 准聚轮烷水凝胶, 牛血清白蛋白, 环糊精, 聚乙二醇, 光谱, X射线粉末衍射