| Summary: | 博士 === 國立清華大學 === 化學系 === 98 === This study is focus on using atomic force microscope (AFM) as the tool to scan the biomolecular surface morphology and measure molecular interactions. For the biomolecules, we use tapping mode AFM to scan the surface morphology of liposome, salmonella, and peptide segment of prion. According to the surface morphology experiment of prion, the prion will form a large domain fibril, and its length is greater than 400 nm, its width is 11.2 ± 1.3 nm, and its height is 0.9 ± 0.1 nm. The experiment also shows that the probe as the applied force increasing, the height of the prion will decrease. Therefore the experiment will be based on using the force that can not cause the change of prion height to perform the scan of surface morphology. Accroding with the data of the solid-state NMR can conduct that fibril is arranged in the anti-parallel order and and form by two parallel fibrils.
The surface morphology scans of the Semonella and liposome shows that salmonella is with a stick-like structure and its dimension are 2.37 (± 0.44) ?慆 x 1.29 (± 0.20) ?慆 x 0.74 (± 0.22) ?慆. The average diameter and height of liposome is 299 ± 70 nm and 52.9 ± 17.1 nm. The experiment also shows that there are several humps about the size of liposome on the surface of the salmonella, and it is conjecture to be the wrinkles of the cell membrane.In the other hand, the observing of liposome shows that liposome will collapse into lipid bilayer and monolayer due to its instability on mica and HOPG surface. According to the phenomenon, we put the Salmonella antibody functionalized liposome on HOPG. We successfully fix the salmonella on the surface by using antigen–antibody interactions.
For the molecular interactions measurement, we use AFM to measure the unbinding forces of 15-crown-5 ether (15c5) to alkali metal ion, alkaline earth metal ion, and Pb2+. On the other side, we observe the effects of solvent polarity and neighboring molecules of the unbinding force and binding probability. The result shows that 15c5 will form the 2:1 complexation to the larger ion, such as, K+ and Pb2+. The smaller ions will not form the complex, such as Na+ and Mg2+. Under the temperature experiment and loading rate experiment, we find that the unbinding force is independent to the loading rate when it probes under room temperature. This means that the unbinding process is under thermodynamic equilibrium state. Neverless, the tempeture decrease to 262 K, the unbinding force is dependent to the loading rate. This means that under the lower temperature the molecular dynamics decrease.
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