Solute molecules in the crystal growth process, the surface of the crystal by constant adsorption / desorption process to complete the process of immobilization of the crystal surface in order to achieve the gradual growth of the crystal. Therefore, the adsorption / desorption of solute molecules is a very important process in the crystal growth process, and its kinetic process has an important influence on the crystal growth kinetics. To learn more about the adsorption / desorption process on the surface of a crystal, you need to understand at least two processes. First, how does the molecule change from a solution state to a solid state? Second, the crystal surface molecules are adsorbed to a specific location? These two processes are still not very clear. In these two processes, the behavior of different molecules is not the same. The commonly used holistic approaches (eg, spectroscopy, quartz oscillator microbalance) are unable to investigate both processes because the average behavior of a large number of molecules does not reflect the behavior of a single molecule. Single-molecule technology can avoid the shortcomings of the above-mentioned overall research method and therefore is a powerful tool for carrying out relevant research.
Dai Guoliang, Associate Research Fellow, Key Laboratory of Microgravity, Institute of Mechanics, Chinese Academy of Sciences, and Professor Hsu Qi-yuan, a professor at Hokkaido University in Japan (2014), after years of cooperation, adopted a model system, monoclinic lysozyme crystal, Total internal reflection fluorescence microscope and confocal laser scanning microscope were used to observe the adsorption / desorption of fluorescently labeled lysozyme molecules on the lysozyme crystal surface.
The researchers first studied the growth of lysozyme crystals of lysozyme molecules fluorescent molecules stay in the crystal surface at different times the number density of lysozyme molecules with the adsorption time changes, the molecular adsorption rate obtained with the crystal surface The result of the change in residence time. The researchers found that there was an induction period (about 120 min) at the initial stage of the adsorption process. During the induction period, the number density of lysozyme molecules remains constant. After the induction period, the number density of lysozyme molecules increases linearly with growth time. Under the condition of crystal growth, the adsorption-desorption of lysozyme molecules (immobilized molecules) which stayed on the crystal surface for more than 20 min reached a steady state with a numerical density value greater than 0; while in the state of crystal dissolution-growth equilibrium , The number density is 0. This reflects the supersaturation of the solution has a significant influence on the molecular adsorption / desorption process. The above results help to understand more deeply the crystal growth kinetics and how the impurity molecules are distributed in the crystal.
The above research work is supported by the Chinese Academy of Sciences, Ministry of Science and Technology, Hokkaido University and other financial support.
Sectional view of the observation cell used in the experiment. The position indicated by the thick arrow is the observation surface of monoclinic lysozyme crystals in the experiment
Lysozyme molecules with different crystal surface residence time gradually change with the number of adsorption time on the crystal surface
The net adsorption rate of molecules under equilibrium and supersaturation varies with the residence time of molecules on the crystal surface
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