X-rays are electromagnetic waves that can travel straight to the ship and make the film sensitive. The X-rays applied in crystal structure analysis are electromagnetic waves with a long wave of about 0.1 nm. Since this wavelength has the same order of magnitude as the distance between atoms in the crystal and the regularity of the arrangement of molecules in the crystal structure, when X-rays are incident on the crystal. Each atom in the crystal emits secondary X-rays and interferes with each other to form a diffraction pattern. If you compare this process with optical microscopy imaging, the two have similarities. Under the microscope, a bundle of parallel visible light is incident on an object, which scatters the incident light, and the objective lens converges the scattered light to form an image.
For X-rays, since there is no material that can be used as a focusing mirror, it is impossible to directly condense the scattered light to form an object image, and the structure inside the crystal is seen. However, the diffraction pattern of the crystal has a certain relationship with the structure inside the crystal, that is, the arrangement of the diffraction points in the diffraction pattern and the distance between the points are related to the arrangement of the biomolecules in the crystal and the repeating period, and the intensity of the diffraction point. The distribution is related to the characteristics of the biomacromolecular structure itself.
Therefore, we can estimate the arrangement of molecules in the crystal structure and the size of the repetition period by analyzing the arrangement of the diffraction points and the distance between the measurement points, and by measuring the intensity of the diffraction points, applying a series of mathematical methods, with the aid of electrons. The computer measures the coordinates of each atom in the molecule in space to determine the structure and crystal structure of the entire molecule.
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