| Summary: | 碩士 === 國立中山大學 === 化學系研究所 === 102 === The power of MRI is tremendously enhanced by the application of various types of MRI contrast agents which increase the relaxivity of water molecules close to them through strong dipolar interactions between water and the paramagnetic ions on the contrast agent. With about 30 years of advancement, MRI contrast agents with various functions, such as signal enhancement, target selection and molecular or event specificity, have been developed. More MRI contrast agents with different purposes are under development today. To better understand the mechanism of MRI contrast agents in various conditions and to develop new generation MRI contrast agents, it is desired that the interactions between the MRI contrast agents and other molecules in their proximity are better understood. We have found that macromolecular crowding effect is an important contributing factor that affects the performance of MRI contrast agents. Therefore, we have decided to carry out a full investigation of this phenomenon with different crowding molecules and MRI contrast agents. This work will report the results with sodium polyacrylate (NaPA) as crowder and Dotarem as MRI contrast agent and focus on the hydrophiliity of macromolecules. A linear relationship is found between the concentration of Dotarem and relaxation rates and chemical shift. A nonlinear relationship is found between the concentration of NaPA and relaxation rates and chemical shift. The hydrophilicity of macromolecular crowders has significant influence on overall crowding effect. The simple picture of volume exclusion must be updated and intermolecular interactions must be taken into account. Morevoer, the details of the crowding effect of NaPA and that of PEG are compared and discussed.
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